QUENCHING TECHNICAL CONTENT

The Jominy Rapid Quench, Part 2: Automotive Applications

/ AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, QUENCHING TECHNICAL CONTENT

In the second of the two-part series, the Advanced Rapid Quench Jominy Tester application for automotive underbody parts is examined. In this article, Dr. Gopal Nadkarni, an associate professor of mechanical engineering at the University of Akron, explains how automotive manufacturers can integrate this little-used test methodology following existing industry practices. It also makes the case for updating the ASTM A255 Jominy test method to measure enhanced hardenability under modern industrial quenching conditions.

This informative piece was first released in Heat Treat Today’s August 2026 Annual Automotive Heat Treating print edition.

Introduction

In “The Jominy and Rapid Quench, Part 1: An American Story” (see Heat Treat Today: Induction Heat Treating, April 2026), the Jominy test adopted in the 1940s was shown to revolutionize how complex metallurgical phenomena in most steels during cooling could be understood using a simplified method of cooling a 4-inch bar of steel from one end. Since then, the ASTM A255: Standard Test Method for Determining Hardenability of Steel (Jominy test) has become the dominant form of characterizing steel behavior under multiple cooling conditions (ASTM International 2020).

Figure 1. Grossman H values for quenching in water shows the gap between ASTM A255 and current industrial quench practices (modified from Liscic 2010) | Image Credit: Gopal Nadkarni

When the Jominy test was developed, quenching technology relied primarily on relatively mild water agitation (Figure 1). Industrial heat treatment has evolved dramatically since then. These advances raise an important question: Does the traditional Jominy test still represent the cooling conditions experienced by modern industrial components?

The answer is both yes and no. The conventional Jominy test remains an outstanding comparative tool because of its simplicity, reproducibility, and enormous historical database (Chandler 1994). However, improved understanding of quench heat transfer — specifically, the laminar umbrella flow underneath rapidly quenched Jominy test ends hides a “film boiling layer” that impedes heat transfer in the first critical seconds of quenching — suggests that the standard unintentionally limits the maximum cooling rate during the first critical seconds of quenching. Consequently, the hardenability curves engineers have relied upon for decades may not fully represent the hardening potential of steels subjected to today’s rapid or intensive quenching processes.

This article proposes extending the Jominy test’s usefulness through a modified methodology that better reproduces modern industrial quenching conditions while preserving the standardization that has made ASTM A255 indispensable.

Intensive Quenching for Industrial/Automotive Parts

Figure 2. Schematic of heat transfer experienced by quenched parts during cooling with and without the vapor barrier (i.e., Leidenfrost layer) (Modified from Kobasko, et al. 2010)

If methods existed to consistently remove the vapor barrier during the first few seconds of quenching, engineers could increase heat transfer substantially (Figure 2) to maximize hardenability. Dr. Nikolai Kobasko and Dr. Michael Aronov have worked at this theory for the last three decades, demonstrating significant material processing benefits with intensive (or rapid) quench practices. Other scientists have also teamed up with heat treaters in the U.S. to demonstrate commercial adoption of industrial parts (Totten, et al. 2024).

Today, intensive quench practices are being seriously assessed by several automotive manufacturers as a way to not only maximize hardenability, but also to control distortion after quenching, impart beneficial compressive stresses below the surface, and reduce spotty hardness, as well as lower cost and improve sustainability practices by employing lower alloy steels.

Automotive Designs Require Updated Tests

Figure 3. The part production cycle requires a deep understanding of the supply chain variables. 

The automotive part production cycle is complex and requires close coordination across multiple stakeholders to achieve desired property outcomes (Figure 3). Designers often rely on “real test” data as input to finite element models to predict critical mechanical properties that correlate with structural life for fatigue, wear, or fracture resistance, with most of these parts being heat treated. They also lean on the correlating structure properties for required parts using the universal ASTM A255 Jominy test as a reference. While this serves as a unique fingerprint for the alloy used, it is by no means an ideal representation of hardenability because chemistry variations that result in a large H-band (Figure 4a).

This approach also falls short because Jominy cooling rates do not reflect real-world quenching, which can be seen as enhanced hardenability under industrial conditions (Figure 4b). Heat treaters use high-velocity forced convective flow to create violent agitation, improve quench consistency, increase hardness, and break up the film boiling layer. However, complex parts like gears pose an issue: it is difficult to guarantee uniformity of instantaneous cooling rates and may only break up parts of the persistent vapor layer (Figure 4b). The result is uneven heat transfer and spotty hardness across the part.

Figure 4. Hardenability is dependent on steel chemistry and microstructure management for the same heat of alloy (a) and uniform quench processing management between batch to batch (b) | Image Credit: Gopal Nadkarni

Automotive part designers need consistent hardness to ensure reliable service and accurate life predictions, but industrial quench conditions do not ensure 100% removal of the vapor barrier. To ensure performance, automotive designers specify higher alloy steels than necessary. In addition, engineering drawings often specify suboptimal surface hardness (suboptimal hardenability) to stay within hardenability realities of accepted heat treatments. Increased costs are often necessary if parts do not hit design targets and require secondary processing (e.g., tempering, carburizing, carbonitriding).

Overcoming Slow Automotive Adoption

Despite excellent data over the past two decades (Kobasko, et al. 2010; Totten, et al. 2024) showing the usefulness of rapid quench technology in maximizing hardenability for bar/plate steels, the paradox is that the technology has been slow to be adopted. We can learn lessons on adopting new steel/processing technologies from the flat steel side used for body-in-white/chassis, where the entire supply chain came together (Auto/Steel Partnership) in 1987 and produced significant lightweighting programs like the 1994 ULSAB (UltraLight Steel Autobody).

If automotive OEMs desire to use the benefits of enhanced hardenability, they must work with the supply chain and standardization bodies (ASTM) to promote widespread adoption. This would allow performance and productivity gains to be adopted at scale quickly.

Intensive quenching has seen limited adoption in mass-produced automotive parts because engineers lack standardized material data that comes after industrial adoption. Therefore, their confidence in process repeatability at scale is not in place. Past experience with promising technologies like austempered ductile iron (ADI) reinforced caution around safety-critical components, especially when processing risks remain difficult to validate. As a result, rapid quenching faces less of a technology adoption challenge than a technology translation challenge: the industry must reduce perceived risk through shared standards, comparable data, and coordinated supply chain validation.

Figure 5. The standard Jominy test is universally used across the supplychain because of its usefulness in specification, standardization, andease of use. The proposed rapid Jominy test could be easily adapted toextend the overall usefulness to measure enhanced hardenability anddevelop new alloy chemistries.​ | Image Credit: Gopal Nadkarni

The good news is that we have standard methods characterizing hardenability that are well-established and reliable for thousands of grades of steel. For rapid quenching to be acceptable, we need to reduce risk and increase accountability across the supply chain. One way is to extend the current ASTM A225 standard Jominy test used by all (Figure 5) and use proven strategies that flat steel producers used to implement ultrahigh strength designs in steel.

From Theory to Practice: Removing the Vapor Blanket in the ASTM Jominy Test

In short, rapid quenching uses high-pressure, high-velocity water impingement to disrupt the vapor film almost immediately. This allows the surface to transition quickly into nucleate boiling and forced convection, dramatically increasing heat transfer.

The Jominy test can track the improved hardenability results, if we can make a slight modification to the ASTM 255 test bar design. The modified Jominy test’s critical feature is a flat, tapered configuration versus the traditional flat end face (Figure 6a), and it ensures that the standard uniaxial quench condition is imposed when the bar is sealed in an enclosed chamber. This refinement improves flow control for consistent and repeatable results, therefore providing better alignment with standardized quench conditions used in industry. Another test bar version with a bar end was developed through a university-industry collaborative venture that is useful to measure enhanced compressive stresses (Funk 2021).

The modified bar has been proven to be a close twin of the standard 1-inch diameter bar. The current setup uses a high-pressure nozzle to break up the vapor layer similar to industrial quench conditions and is noticeably different from the laminar flow (H < 1.4) used in the ASTM A225 test. The flow conditions (velocities > 40 m/s, pressures > 120 kPa) have been optimized to ensure that the persistent vapor barrier never forms, achieving high heat transfer rates (H > 5) from the start of quenching till the end of the cooling period.

Figure 6. (a) Schematic of modified Jominy bar to achieve rapid quenching; (b) example AISI 1045 data developed with new tester; and (c) enhanced hardenability due to rapid quenching is estimated to produce ~50% martensite (45 HRC) deeper in a 3-inch diameter bar ​| Image Credit: Gopal Nadkarni

As a result, current low alloy automotive grades can be quickly analyzed and compared for properties as well as depth of hardening to published hardenability curves, allowing a useful screening tool for adoption.

If heat treaters and steelmakers want to cater to automotive clients who want to reap the benefits of rapid quenching, they need to understand whether their grades are suitable. The simplest approach is to use the rapid quench methodology that has been described here for low alloy steels of interest. This will ensure that true and maximized hardenability data can be used by design engineers to optimize automotive steel parts.

In a recent research study (Nadkarni, et al. 2025), both standard hardenability and true (enhanced) hardenability curves were developed for a benchmark AISI 1045 grade (Figure 6b). The 50% martensite line (45 HRC) is clearly deeper, indicating a significant increase in hardenability, with corresponding Jominy (J in 1/16″) distances moving from J2 to J3.5 (from 3.2 mm to 5.5 mm). An example of how the data can be used practically for a sample 3-inch bar shows that depth of hardening to HRC45 is likely to be significantly higher in rapidly quenched steels (Figure 6c).

The increased hardenability results shown for the benchmark AISI 1045 have been replicated for a wide variety of steels including AISI 1020, AISI 8620, AISI 6150, M50, and tool steels like H13. However, we need to be cautious about extrapolating the results to steels where significant retained austenite can form under enhanced quench conditions.

The significance of adopting such a practice into a new or modified ASTM standard will have global implications. Standardized adoption of advancing technology will support automotive manufacturers in optimizing the performance of their current steel compositions through more controlled distortion and reduced variability in material properties.

Acknowledgements

Figure 7. The integrated Jominy Rapid Quench Tester developed at Induction Tooling Inc. for student training and research (Funk 2021). Students at the University of Akron standing with research leadership: Dr. Gopal Nadkarni, University of Akron (second from the left); Bill Stuehr, Induction Tooling, Inc. (third from left); and Joe Powell, Integrated Heat Treating Solutions, Inc. (fourth from left).​

The author is grateful for support provided by Bill Stuehr (Induction Tooling Inc.) and Joe Powell (Akron Steel Treating), along with research funding for graduate and undergraduate students from the University of Akron Center for Precision Manufacturing and Forging Industry Education and Research Foundation (FIERF).

References

ASTM International. 2020. Standard Test Methods for Determining Hardenability of Steel. ASTM A255-20a. West Conshohocken, PA: ASTM International. https://doi.org/10.1520/A0255-20A.

Chandler, Harry, ed. 1994. Heat Treater’s Guide: Practices and Procedures for Irons and Steels. Materials Park, OH: ASM International.

Kobasko, N. I., M. A. Aronov, J. A. Powell, and G. E. Totten. 2010. Intensive Quenching Systems: Engineering and Design. West Conshohocken, PA: ASTM International.

Funk, Bethany. 2021. “Industry-Academia Partnership Developing New Jominy End-Quench Test.” Heat Treat Today 4, no. 6 (September): 56–61.

Nadkarni, Gopal. 2026. “The Jominy and Rapid Quench Part 1: An American Story.” Heat Treat Today 9, no. 4 (April): 25–27.

Nadkarni, Gopal, Nafi Bhuiyan, Saikishan Suryanarayanan, and Ryan Souders. 2025. “The Relevance of the Standard Jominy Test for Rapid/Intensive Quenching.” Paper presented at the Heat Treat 2025 Conference & Exposition, Huntington Place, Detroit, MI, October 21–23.

Totten, George E., Rosa Simencio Otero, Xinmin Luo, and Lauralice C. F. Canale, eds. 2024. ASM Handbook, Volume 4F: Quenchants and Quenching Technology. Materials Park, OH: ASM International. https://doi.org/10.31399/asm.hb.v04F.9781627084505.

About The Author:

Dr. Gopal Nadkarni
Associate Professor of Mechanical Engineering
University of Akron

Dr. Gopal Nadkarni is an Associate Professor of Mechanical Engineering at the University of Akron and manages its Manufacturing Graduate Certificate Program. He brings extensive industry and innovation experience, having held previous leadership roles at industry and in technology ventures, with research and teaching focused on manufacturing, materials, and product design.

To contribute to ongoing industry-academia research regarding this topic, please contact Professor Gopal Nadkarni.

For more information: Contact Gopal Nadkarni at gnadkarni1@uakron.edu.

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Ask the Heat Treat Doctor®: What is pH Really?

/ MANUFACTURING HEAT TREAT TECH, PARTS CLEANING TECHNICAL-CONTENT, QUENCHING TECHNICAL CONTENT

Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues. In this installment, Dan Herring discusses the science behind pH — what it really measures, and why it matters — and offers practical guidance on monitoring water quality in open and closed systems found throughout the heat treat shop.

This informative piece was first released in Heat Treat Today’s May 2026 Sustainable Heat Treat Technologies print edition.

Introduction to pH

The term “pH” is used to describe a unit of measure that indicates the degree of acidity or alkalinity of a solution. It is measured on a scale of 0 to 14 (Table A). pH is an abbreviation that stands for the “potential of hydrogen”; the “p” being the symbol for potential (or power) and “H” the symbol for hydrogen.

Table A. pH Chart (Herring 2015b)

A Slightly Deeper Dive

What most people don’t realize is that pH is a complex concept rooted in chemical equilibrium, thermodynamics, and electrochemistry. The formal definition of pH is “the negative logarithm of the hydrogen ion activity” and can be expressed mathematically by the following formula where au+ is the activity of hydrogen ions, a dimensionless quantity (Rumble 2024):

In this form, pH provides a way of expressing the degree of the activity of an acid or base in terms of its hydrogen ion activity. Acids and bases have, respectively, free hydrogen [H+] and free hydroxyl [OH−] ions. Since the relationship between hydrogen ions and hydroxyl ions in a given solution is constant for a given set of conditions, either one can determine the other. In other words, pH is really a measurement of both acidity and alkalinity, even though by definition it is a selective measurement of hydrogen ion activity.

Since pH is a logarithmic function, a change of one pH unit represents a tenfold change in hydrogen ion concentration, that is, of both the hydrogen ion and the hydroxyl ion at different pH values (Table A). Note that each decrease in pH by one pH unit means a tenfold increase in the concentration of hydrogen ions.

A Little Chemistry

In school, we learned that all substances are made up of millions of tiny atoms. These atoms combine to form molecules. In water, for example, each molecule is made up of two hydrogen (H) atoms and one oxygen (O) atom. The formula for a molecule of water is expressed by the familiar symbol H2O. That is, there are two hydrogen atoms needed for each oxygen atom to form a stable compound.

Now, the behavior of pH in aqueous systems is governed by the equilibrium of water to form positive and negative ions (so-called self-ionization), which can be expressed as:

or in the following form we more commonly think of:

Hency, at 25°C (Kw = 1.0 x 10-14), the equilibrium constant for this process is:

Then for pure water, where aH+ = a0H-, we have that aH+ = 10-7 hence pH = -log10 (10-7) = 7.00 which is neutrality at 25°C (77°F).

Finally, it is important to note that Kw is temperature-dependent: it increases with temperature, meaning neutral pH decreases slightly as temperature rises (e.g., ~6.14 at 100°C). Therefore, “neutral pH” is not always 7 — it depends on thermal conditions.

A Practical Application — Water Quality in the Heat Treat Shop

Water is used in most of our heat treat shops for a variety of purposes, perhaps less than before but still vitally important. Examples include parts washers, heat exchangers, water cooled bearings on fans and rolls, seals on pit furnace covers, water cooled jackets on continuous furnaces, water cooled jackets for quench tanks, top or side cooling chambers, inner doors and plate coils, and make up water for water systems, to name a few.

Table B. Typical Water Requirements for Open Systems (Decelles 2002)
Table C. Water Requirements for Closed Hydronic Systems (Heatlink Group 2006)

Water quality requirements are often defined differently for open systems (Table B) and closed (recirculated) systems (Table C). Open systems are typically more problematic as the issue of water quality varies. Water is often classified as “soft” or “hard” depending on its mineral content (i.e., the amount of calcium and magnesium dissolved in the water). Soft water has an ideal hardness of approximately 120 ppm (7 grains/gallon). Hard water often results in the formation of mineral deposits, which can lead to blockages in water systems (Figure 1).

Figure 1. Sludge buildup and flow blockage in the top cool of an integral quench furnace | Image Credit: The HERRING GROUP, Inc.

Furthermore, we must ensure that the water being discharged from our heat treatment operations is clean and meets EPA standards. Finally, we must be especially careful to avoid cross-contamination from other sources in the shop (e.g., polymers, quench oils, chemicals).

In Summary

Two little consonants, pH, are deceptively simple yet so profoundly important. They represent the thermodynamic state of solutions, but in reality, link microscopic interactions with real world issues. As heat treaters, our focus is to not take our water supply and water systems for granted since unexpected surprises, unwanted downtime, and expensive repairs can result. When is the last time you tested your water?

References

Herring, Daniel H. 2015a. Atmosphere Heat Treatment. Vol. 2. Southfield, MI: BNP Media.

Herring, Daniel H. 2015b. “The Importance of pH.” Industrial Heating, January.

Heatlink Group. 2006. Water Quality in Hydronic Systems. June 21, 2006. https://www.heatlink.com/sites/default/files/Info%20Sheet/L2329-Water-Quality-in-Hydronic-Systems-2006-06-21.pdf.

Decelles, P. 2002. The pH Scale. Johnson County Community College. Archived webpage. http://staff.jccc.net/pdecell/chemistry/phscale.html.

Rumble, John R., ed. 2024. CRC Handbook of Chemistry and Physics. 105th ed. Boca Raton, FL: CRC Press.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.

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The Jominy and Rapid Quench, Part 1: An American Story

/ HARDNESS TESTERS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

In this two-part series, Dr. Gopal Nadkarni, an associate professor of mechanical engineering at the University of Akron, revisits the American origins and impacts of the Jominy test while exploring how rapid quenching technologies are exposing its limitations. Discover how a new approach builds on ASTM foundations to better reflect today’s high-performance cooling methods.

This informative piece was first released in Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition.

Introduction

For nearly a century, the Jominy End-Quench Test has shaped how North American engineers design alloys, specify steels, and heat treat critical components across automotive, oil and gas, heavy machinery, and aerospace industries. It involves one small piece of steel and a stream of water. Simple, repeatable, and powerful, it was revolutionary for its time. But it derived from a different world of manufacturing. Furnaces were batch loaded. Parts required hand transfer. Quenching utilized tanks with modest agitation — not high-pressure sprays, induction-to-quench lines, or high-performance water systems.

Today’s rapid quench technologies reveal a key limitation: the classic Jominy test can systematically underestimate what many steels are capable of under aggressive convective cooling. Why? Because film boiling — a vapor layer at the steel surface — chokes heat transfer right where it matters most.

In order to take advantage of a wider range of materials and processing methods, a shift in how to leverage this test is necessary. The discussion that follows elaborates on this American origin story of the Jominy’s test and what challenge the film boiling layer posed 75 years ago versus today.

Pursuing Performance: The Origins of the Jominy Test

In 1947, Fred P. Peters wrote in Scientific American that hardenability was no longer just a technical trend; it was a revolution changing how the steel industry did business. He was describing a shift in which clients wanted to move away from buying a grade based on chemistry specs alone to buying a product that would guarantee performance.

*Hardenability: the ability of a steel to harden to a certain depth. Hardness, by comparison, is the measurement of how hard a material is at a given location. High hardenability ensures desired properties and microstructure at a given depth for critical components; this leads to more efficient optimized part designs.

But there was a problem: Steelmaking was, and still is, a complex science with unavoidable variability arising from chemical, thermal, and metallurgical processes involved. From batch-to-batch, a single supplier could achieve different hardenability results. That variability caused headaches for manufacturers.

Two metallurgists working with General Motors, Walter Jominy and A.L. Boegehold, proposed an elegant solution: standardize the cooling conditions instead of chasing exact chemistry. Pinpointing the “maximum hardness at center” had been an estimate derived from submerging several steel bars of various diameters in a quench tank. Speaking to the Detroit Chapter of American Society of Metals, the metallurgists pushed for an end-quench test using a standardized one-inch round bar, heated uniformly, and quenched at one end with a water jet. Their practical solution replicated the range of cooling rates from the maximum cooling rate (water) at the quench face to the slowest cooling rate (air) at the other end of the bar. The resulting hardness profile became a “fingerprint” of that alloy’s hardenability.

That fingerprint changed everything.

Figure 1. Diagram of the Jominy End-Quench Test | Reference: ASTM A255-02

Metallurgists could now rapidly compare alloys from different suppliers or with minor chemistry differences. Additionally, design engineers could specify hardenability bands rather than tight chemistry limits. Steelmakers could adjust compositions and quickly verify performance. Scrap heats dropped. Costs fell. Customers gained predictable, repeatable results. ASTM A255 formalized the method, and the Jominy test became the global language of hardenability (Figure 1).

Known Limitations and Rapid Quench

Heat treaters know the Jominy test is a simplification. The specimen is a straight bar, not a gear or forging. Only one end is quenched. The cooling method represents one type of quench: water, not oil, polymer, or gas.

There’s also a compositional limitation; highly alloyed steels often show little variation along the four-inch test length.

But one limitation has taken on new importance in modern heat treatment: the vapor blanket.

The Vapor Blanket Problem

When red-hot steel hits water, a vapor layer instantly forms on the surface. This “Leidenfrost layer” acts like insulation. Heat transfer drops until the vapor film collapses and nucleate boiling begins.

That means the cooling severity at the Jominy face is not just “water quench.” It is water quench through a steam barrier.

So, the hardenability curve we measure reflects steel transformation behavior plus a boiling-limited surface condition. If that vapor layer is removed or shortened, the cooling rate at the surface rises, and the steel may harden deeper than the standard Jominy curve suggests.

Heat treaters know this problem firsthand. Agitated water tanks try to break up the vapor film, but removal is inconsistent. The result can be uneven hardening — the “spotty” surfaces everyone has seen. And the usual workarounds are to add alloy, carburize deeper, or accept extra process time and cost. In other words, the industry learned to design around the vapor blanket instead of eliminating it. The “Leidenfrost Layer” describes this insulating vapor blanket phenomenon that occurs when liquid meets a hot surface significantly hotter than its boiling point.

A Different Philosophy: Rapid Quenching

Over the past two decades, a new approach has gained traction: do not accept film boiling — remove it.

Researchers, such as Dr. Kobasko and Dr. Aronov, showed through modeling and experiments that high-velocity, high-pressure water flow can consistently suppress the vapor layer, a method known as Intensive Quenching™. This approach pushes the hot surface quickly into high heat transfer by removing the vapor film and has been referred to as High Convective Quenching, High-Pressure Convective Quenching, and Rapid Quenching.

The result is more than faster cooling.

Figure 2. Quench rate and surface reactions

Early formation of a martensitic surface shell creates compressive stresses that enhance fatigue and wear resistance. Parts can show deeper effective hardening and improved surface performance without increasing alloy content (Figure 2). Some studies even suggest differences in martensite morphology (twinned morphology) compared to conventional quenching (lath morphology). This is not just “harder steel.” It is a different thermal-mechanical response at the surface.

Rethinking the Jominy Test

If quenching technology has changed, should the hardenability test evolve too?

Research at the University of Akron has shown that the standard Jominy setup itself forms a vapor layer. Raising the jet height does not eliminate it. That means the test measures hardenability under a boiling-limited condition, not under maximum achievable heat transfer.

Figure 3. Standard vs. Rapid Quench Hardenability | Image Credit: Gopal Nadkarni

Working with industry partners, the university researchers developed a modified end-quench configuration that uses high-convective water impingement to strip the vapor barrier. The measurement philosophy remains Jominy-based i.e. measure hardness along the length of the bar. What changes is that the end of the flat bar is given a slight taper to allow it tightly seal into a chamber where a water jet is sprayed on the surface, much like a jet pressure washer. Modeling this scenario allows us to predict that the new pressure and flow conditions are sufficient to strip the vapor and keep it from reforming, thus creating conditions of maximum heat transfer without the continuous formation of the film. The old “umbrella” method of cooling does not ensure the removal of the vapor or film on surface. The result is a new method that reveals how steels behave under rapid quench — conditions increasingly used in advanced heat treat operations (Figure 3).

Why This Matters to Industry Now

For 75 years, engineers have relied on handbooks filled with Jominy curve diagrams. Those curves remain valuable, but they reflect a quenching severity rooted in mid-20th-century practice.

Today, heat treaters, steelmakers, and designers have a chance to expand that framework. A rapid-quench Jominy approach could help:

  • Optimize alloy design for modern quench systems
  • Improve simulation accuracy in digital twins
  • Reduce over-alloying and cost
  • Increase part performance and consistency

This is not about redefining hardenability. It is about recognizing that hardenability is expressed under a defined cooling boundary. As quenching technology advances, our standardized ways of describing steel response should advance with it.

In Part 2, we’ll look at how this modified Jominy approach aligns with ASTM philosophy, what simulation reveals, and how rapid quenching translates into real improvements for gears, heavy components, and other critical parts.

About The Author:

Dr. Gopal Nadkarni
Associate Professor of Mechanical Engineering
University of Akron

Dr. Gopal Nadkarni is an Associate Professor of Mechanical Engineering at the University of Akron and manages its Manufacturing Graduate Certificate Program. He brings extensive industry and innovation experience, having held previous leadership roles at industry and in technology ventures, with research and teaching focused on manufacturing, materials, and product design.

To contribute to ongoing industry-academia research regarding this topic, please contact Professor Gopal Nadkarni.

For more information: Contact Gopal Nadkarni at gnadkarni1@uakron.edu.

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Cómo domar a tu dragón

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

Cuando una carga se atasca durante el temple, cada segundo cuenta y las decisiones improvisadas pueden aumentar el riesgo. En esta entrega de “Martes Técnico“, Bruno Scomazzon, gerente general de Precision Heat Treat Ltd., describe un procedimiento de respuesta de emergencia paso a paso para este escenario, uno de los más peligrosos en el tratamiento térmico con atmósfera. Basándose en la experiencia real, esta guía tiene como objetivo ayudar a las empresas a desarrollar sus propios procedimientos eficaces para mantener la seguridad, controlar las condiciones del horno y coordinarse con los servicios de emergencia en situaciones de alto riesgo.

Este artículo informativo se publicó por primera vez en Ingles en Heat Treat Today’s February 2026 Annual Air & Atmosphere Heat Treating print edition.

Si tiene comentarios o preguntas sobre este artículo, háganoslo saber en: editor@heattreattoday.com.

Traducido por Víctor Zacarías. To read this article in English, click here.

Descripción del escenario

Se ha transferido una carga a la cámara de temple y el elevador está descendiendo al aceite, pero la carga se atasca y no se sumerge por completo. La puerta interior se cierra correctamente, y la puerta exterior (frontal) permanece cerrada.

Esta es una situación de altísimo riesgo que requiere el estricto cumplimiento de los procedimientos de emergencia. El objetivo es proteger: primero al personal (minimizar la posibilidad de lesiones o que la situación empeore), luego las instalaciones y, finalmente, el equipo.

1. Medidas inmediatas

NO abra la puerta exterior

Es posible que sienta la tentación de evaluar la situación, pero resista la tentación. NO se coloque frente a la puerta exterior ni justo al lado de ella, y nunca la abra mientras la carga esté “colgada”. Abrir esta puerta puede introducir oxígeno en una cámara caliente, lo que provocaría:

  • Explosiones o incendios repentinos (flash fire).
  • Pérdida de contención debido a deformación de la puerta o falla mecánica.

En casos extremos, la puerta exterior puede resultar dañada (arrancada, atascada o parcialmente abierta) y presentar llamas visibles. Esto requiere alertar inmediatamente a los bomberos.

Si la puerta exterior no se puede cerrar

En este caso, notifique inmediatamente a los bomberos e indíqueles que se preparen para una respuesta con espuma. NO permita el uso de agua. ¡Esto podría provocar reacciones violentas con el aceite o la atmósfera y propagar el fuego!

El personal de respuesta capacitado debe:

  • Colocarse el equipo de protección personal (EPP).
  • Preparar el equipo de extinción de incendios.
  • Estar listos para proteger los sistemas críticos hasta que lleguen los bomberos.

NO apague el horno.

Figura 1. Horno de atmósfera durante su operación normal. | Image Credit: Precision Heat Treat Ltd.
Figura 2. Puerta del vestíbulo parcialmente abierta durante una simulación controlada para | Image Credit: Precision Heat Treat Ltd.

2. Mantener el suministro eléctrico

Para garantizar que los sistemas esenciales permanezcan activos, debe mantener el suministro eléctrico. Asegúrese de que los siguientes sistemas permanezcan activos:

  • Cambie el modo del horno de automático a manual. Esto evitará cualquier secuenciación del PLC que active automáticamente las puertas, los elevadores y los manipuladores.
  • Mantenga las llamas piloto encendidas.
  • Mantenga el enfriamiento del aceite en funcionamiento para evitar el sobrecalentamiento del tanque.
  • Apague los calentadores de aceite para evitar una carga térmica adicional en el tanque de temple.
  • Mantenga la agitación del temple a baja velocidad durante todo el proceso para ayudar a disminuir la temperatura en la superficie de interfaz entre la carga y el aceite. Esto evita la estratificación y disipa el calor por radiación en el aceite.
  • Mantenga el recirculador en funcionamiento.
  • Mantenga la instrumentación en funcionamiento para el monitoreo.

NOTA: La pérdida de estos sistemas elimina la visibilidad, el control de la atmósfera y las opciones de respuesta seguras.

3. Gestión de la atmósfera

Mantenga una atmósfera protectora y una presión positiva en el horno para evitar la entrada de oxígeno y la combustión incontrolada:

  • Ajuste el control del potencial de carbono a “0”.
  • Cierre el suministro de gas de enriquecimiento.
  • Cierre el suministro de amoníaco.
  • Cierre el suministro de aire de dilución.

Purga de nitrógeno

Estos pasos dependen de si se dispone de una purga de nitrógeno; se recomienda encarecidamente que esté disponible para todas las unidades con temple integral o de paso directo. Asegúrese de comprender cuánto tiempo tarda su horno en purgar completamente el gas endotérmico. Si bien la norma NFPA 86 recomienda cinco ciclos de purga, algunos expertos aconsejan prever hasta diez por hora en caso de emergencia. Cada horno debe contar con datos de purga establecidos en condiciones normales para que los operadores puedan actuar con confianza cuando el tiempo es crucial.

Figura 3. Suministro de nitrógeno utilizado para purga de emergencia y control de la atmósfera. | Image Credit: Precision Heat Treat Ltd.
  • Inicie inmediatamente una purga de nitrógeno (si está disponible) y manténgala durante todo el evento.
  • Utilice al menos el flujo mínimo especificado en su documentación. Si es seguro, se puede utilizar un flujo mayor para ayudar a desplazar los gases inflamables de las cámaras de calentamiento y temple.
  • Mantenga la temperatura del horno a 815°C (1500°F) durante la purga.

Pueden quedar espacios residuales de gas Endo atrapados en zonas con poca ventilación. Si la temperatura de la cámara desciende por debajo del punto de ignición antes de que se haya desplazado todo el gas inflamable, la entrada de oxígeno podría provocar una explosión. En algunos casos, el Endo atrapado y los desequilibrios de presión pueden causar fugas repentinas, en las que se expulsa aceite o gas debido a la acumulación de presión interna.

Después de la purga

El objetivo de la purga con nitrógeno es desplazar el gas endotérmico con una atmósfera inerte, manteniendo una temperatura elevada para facilitar la combustión de los gases inflamables residuales y prevenir la formación de mezclas peligrosas. Este proceso debe garantizar una presión positiva en todo el horno.

  • Una purga seguida de enfriamiento por inmersión de nitrógeno es un método válido si la purga se ha completado de forma verificable.
  • Según el tamaño del horno y la velocidad de enfriamiento:
  • Los hornos más grandes pueden enfriarse lo suficientemente lento como para completar la purga.
  • Las unidades más pequeñas o de enfriamiento más rápido pueden requerir un breve mantenimiento de la temperatura antes del enfriamiento controlado o el enfriamiento por inmersión.

NOTA: Una vez que la carga suspendida se enfríe a una temperatura segura (aproximadamente 65°C), realice el apagado estándar del equipo.

Sin nitrógeno (en Endo)

Si no hay purga de nitrógeno, o esta es insuficiente, la única opción es dejar que la carga acumulada se enfríe en el vestíbulo mientras se continúa quemando Endo y se mantiene la temperatura del horno a 1500°F. Una vez que el vestíbulo/tanque de aceite se enfríe por debajo de 150°F y haya pasado el peligro, inicie el apagado estándar del horno.

4. Gestión de la seguridad

  • Alerte inmediatamente al cuerpo de bomberos local. Si la situación se vuelve incontrolable o si existe alguna duda sobre la capacidad de mantener el control, evacúe las instalaciones y espere a que lleguen profesionales capacitados. La seguridad del personal de la planta es primordial.
  • Notifique al departamento de seguridad de la planta y a la administración del sitio.
  • Evacúe a todo el personal no esencial del área de tratamiento térmico.
  • Informe a todos los departamentos que se está produciendo un incidente de alto riesgo.

Los bomberos son más eficaces cuando conocen sus instalaciones antes de que ocurra una emergencia. Asegúrese de que conozcan la distribución de sus operaciones, incluyendo:

  • Ubicación y tamaño de los tanques de aceite
  • Paneles eléctricos
  • Válvulas de cierre de gas
  • Zonas calientes

5. Periodo de enfriamiento controlado

  • Mantenga la protección con atmósfera durante todo el evento.
  • NO abra las puertas hasta que la temperatura del vestíbulo sea baja y estable.
  • El tiempo de enfriamiento dependerá de la masa de la carga y la retención de calor. Prevea cinco horas o más.
  • Utilice la estabilidad de la presión del horno, las observaciones de los efluentes y el comportamiento de los gases como indicadores indirectos de la temperatura.

6. Procedimiento de recuperación de la carga

  • Una vez enfriado y estabilizado, realice el apagado estándar, comenzando con la eliminación del gas endotérmico, si corresponde.
  • NO intente retirar la carga manualmente hasta que el sistema esté verificado como seguro.
  • Solo el personal de mantenimiento puede recuperar la carga, utilizando equipo de protección personal (EPP) y las herramientas adecuadas.

7. Familiarización con el cuerpo de bomberos

Toda instalación debe establecer una buena relación con el cuerpo de bomberos local antes de que ocurra una emergencia. Procure revisiones anuales e identifique lo siguiente:

  • Número de hornos
  • Volumen de los tanques de aceite de temple para extinción de incendios
  • Ubicación de las zonas calientes y los paneles de control
  • Puntos de parada de emergencia

Las puertas atascadas suelen deberse a fallos en las válvulas neumáticas. Cerrar el suministro de aire comprimido y purgarlo puede permitir que el mecanismo se reinicie. Consulte siempre el manual del equipo o al fabricante antes de intentar cualquier solución.

Considere que el inspector de bomberos que realice las revisiones no es necesariamente quien acudirá a combatir los incendios; capacite a quienes sí lo harán.

Protocolo posterior al incidente

Antes de volver a poner en funcionamiento el horno, asegúrese de:

  • Realizar una investigación formal.
  • Identificar y corregir la(s) causa(s) raíz.
  • Documentar todos los parámetros clave y las acciones tomadas.
  • Capacitar nuevamente a los operadores según sea necesario.

Señalización del horno

Es probable que un operador lea el plan de seguridad, pero podría olvidar un protocolo vital durante una emergencia. Contar con advertencias claras y llamativas, impresas y colocadas en el panel, que el operador pueda retirar y utilizar en caso de emergencia, puede ser de gran utilidad.

Reflexiones finales

No podemos predecir todas las consecuencias. Ningún procedimiento puede contemplar todas las variables posibles en una emergencia real. Una vez que un evento se pone en marcha, lo único que podemos hacer es responder con el mejor criterio, capacitación e intenciones, priorizando siempre la seguridad de las personas.

Este documento pretende ser una referencia práctica: una guía estructurada elaborada con esmero, experiencia real y buenas prácticas. No es una solución universal, sino una herramienta para ayudar a los equipos a crear o mejorar sus propios procedimientos eficaces y a responder de forma adaptativa en situaciones de alto riesgo.

La preparación contra incendios es esencial en toda planta de tratamiento térmico. Los incendios ocurren, y no siempre son pequeños. Es fundamental saber cuándo actuar, cuándo evacuar y cuándo pedir ayuda. Los manuales de equipos proporcionan una base, pero la preparación mediante capacitación y planificación es la mejor defensa.

Agradecimientos: El autor agradecer a Daniel H. Herring, “The Heat Treat Doctor,” a The HERRING GROUP, Inc., y a Avery Bell de Service Heat Treat en Milwaukee por sus valiosas contribuciones.

Acerca del autor:

Bruno Scomazzon
Gerente General
Precision Heat Treat Ltd.

Bruno Scomazzon es el gerente general de Precision Heat Treat Ltd. en Surrey, Columbia Británica, Canadá, y cuenta con más de 40 años de experiencia en procesos metalúrgicos y operaciones de tratamiento térmico.

Para más información: Contacte a Bruno en bruno@precisionheattreat.com.

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Ask The Heat Treat Doctor®: What Oil Quenching “Tricks” Help Manage Distortion?

/ MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues. In this installment, Dan Herring discusses practical strategies for managing distortion through oil quenching, focusing on how subtle adjustments — such as delaying agitation to extend the vapor blanket phase — can influence heat transfer behavior and improve dimensional stability in challenging geometries like thin-walled, large-diameter gears.

This informative piece was first released in Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition.

The Question

A reader’s question caught the Doctor’s eye and will provide some valuable information we all can benefit from. Let’s learn more:

“I have a question about a technique we used sometimes in my factory for distortion reduction. As you know, in the oil quench cooling there are 3 steps:
1. Vapor Blanket Phase (≈ 840–700°C)
2. Boiling Phase (≈ 700–400°C)
3. Convection (≈ 400–40°C)
In addition to [running] a martempering oil (Houghton M240) and a high oil temperature of 80–100°C, a technique we used successfully to reduce the distortion in thin wall large (> 1m) gears was to wait 1 minute without agitation just after placing the parts in the oil tank. Once the minute has passed, we start with the agitator speed at 1,700 rpm.
The technical reason for this improvement is to extend the vapor blanket step and hence reduce the distortion created by the boiling step. My questions are: What effect does the vapor blanket step have on thermal uniformity, and is it possible to get a similar result in the agitator speed, for instance, start with a low rotating speed and finishing with a high speed?”

The Three Phases of Quenching

As a brief reminder, let’s revisit the three distinct stages of cooling (Figure 1). The first stage, the “vapor blanket” (or “film boiling”) stage, is characterized by the Leidenfrost phenomenon, which is the formation of an unbroken vapor blanket that surrounds and insulates the work piece. It forms when the supply of heat from the surface of the part exceeds the amount of heat that can be carried away by the cooling medium.

The stability of the vapor layer, and thus the ability of the oil to harden steel, is dependent on: the metal’s surface irregularities; oxides present; surface-wetting additives, which accelerate the breakdown and destabilize the vapor blanket; and the quench oil’s molecular composition, including the presence of more volatile oil degradation by-products (Herring 2015). In this stage, the cooling rate is relatively slow in that the vapor envelope acts as an insulator, and cooling is a function of conduction through the vapor envelope.

The second stage, the “vapor transport” (or “nucleate boiling” or “bubble boiling”) stage, is where the highest heat transfer rates are produced — and where the greatest amount of distortion occurs. The point at which this transition occurs and the rate of heat transfer in this region depend on the oil’s overall composition (base oil, speed accelerators, and antioxidant package). It begins when the surface temperature of the part has cooled enough so that the vapor envelope formed in the first stage collapses. Violent boiling of the quenching liquid results, and heat is removed from the metal at a very rapid rate, largely due to heat of vaporization. The boiling point of the quenchant determines the conclusion of this stage. Size and shape of the vapor (bubbles) are important in controlling the duration of this stage.

Figure 1. The three stages of liquid quenching | Image Credit: The Heat Treat Doctor®

The third stage of cooling is called the “convection” (or “liquid”) cooling stage. The cooling rate during this stage is slower than that developed in the second stage and is exponentially dependent on the oil’s viscosity, which will vary with the degree of oil decomposition. Heat transfer rates increase with lower viscosities and decrease with increasing viscosity. This final stage begins when the temperature of the metal surface is reduced to the boiling point (or boiling range) of the quenching liquid.

The Answer

A sage veteran once reminded the Doctor that we cannot control distortion, only manage it.

As we know, if we were able to control the heat transfer during the nucleate boiling phase, the result would be less gear distortion, especially when the geometry (in this case thin wall, large diameter gears) makes it even more challenging.

What many people do not realize is that in addition to the correct choice of oil, oil temperature, the proper size and design of the quench system (which is fixed for all part or load configurations), and the uniform removal of the vapor blanket in the first stage of quenching influences the development and type of heat transfer that will occur in the nucleate boiling phase — yes, it is uncontrolled, but it can be influenced.

A delay in the start of agitation ensures the vapor blanket phase is extended and (in a sense) more uniformly conforms to the part geometry than it would otherwise. The result is that it is easier to be uniformly swept away once the agitation begins. Interestingly, the vapor blanket begins to form within the first few seconds of quenching and begins to collapse (often in a nonuniform way) as the surface temperature drops. Agitation delay times ranging from 1 to 2 minutes have been used in industry, which are primarily a function of material, (gear) geometry, and tooth profile/thickness.

As to the other question, some manufacturers recommend quenching into slowly agitated oil (100–125 rpm) — the slower agitation only intended to push any moisture molecules around, then increasing the speed to normal agitation rates once the load is fully submerged. Appropriate safety precautions must be followed with either method. A great deal of success has been reported using this method for many of the same reasons as above.

On another note, there is some merit in vacuum oil quenching to vary the pressure over the oil. Interestingly, the characteristics (i.e., size and distribution) of the “bubbles” formed in the nucleate boiling phase changes and the end result is that they can be more easily and more uniformly swept away.

In Summary

A word or two is in order about measuring and maintaining the quench oil. Measuring the efficiency (i.e., speed) of an oil can be done in one of two ways. The first method is by measuring the oil’s cooling ability (i.e., hardening power). Since cooling ability is independent of steel selection (composition and grain size) this method is popular since it provides information about the oil itself independent of its end use application (Figure 2).

Figure 2. Typical cooling curves and cooling-rate curves for new oils | Image Credit: The Heat Treat Doctor®
Table A. Classification of Quench Oils

The older GM Quench-O-Meter method (Table A) can be used as well.

Variables Affecting Dimensional Change

A number of factors influence post-heat treat distortion, including those related to material, manufacturing, and heat treating (Figure 3).

Figure 3. Distortion (Ishikawa) diagram | Image Credit: The Heat Treat Doctor®

When selecting an oil quench process, some of the many factors to consider include:

  • Material — form, chemistry, hardenability, grain size, homogeneity, cleanliness, microstructure
  • Heat treatments performed at the mill
  • Starting microstructure — mill or third-party heat treating prior to manufacturing
  • Manufacturing process — sequence of operations, tooling, speeds & feeds
  • Part orientation during manufacturing, as opposed to grain orientation
  • Grids, baskets, and fixtures — both material & design
  • Load configuration — part spacing, orientation, arrangement (load density)
  • Load weight (gross or net)
  • Maximum quench fixture size, weight, shape
  • Part geometry and mass — maximum/minimum part section thickness, consideration for whether the component part is uniform in thickness or has thin and thick sections next to one another
  • Residual stress state before heat treatment
  • Targeted hardness range (initial or final)
  • Type of process being run (e.g., hardening, case hardening)
  • Free quenching or restricted (press or roll) quenching
  • Oil type — quenching characteristics, cooling curve data
  • Oil speed, condition, viscosity (fast, 7–9 second oil; medium, 10–14 second oil; slow, 15–18 second oil; or marquench, >20 second oil)
  • Oil temperature (initial, instantaneous rate of rise, recovery time to initial temperature)
  • (Effective) quench tank volume
  • Height of oil above the load
  • Agitation — agitators or pumps
  • Quench tank design factors
    • Agitation method and number of agitators or pumps
    • Type of quench tank baffling
    • Location/size of agitators or pumps
    • Type of agitators (e.g., fixed, two speed, variable)
    • Propeller size (e.g., diameter, clearance in draft tube)
    • Internal tank baffling (e.g., draft tubes, directional flow vanes)
    • Flow direction
    • Flow restrictions (quench elevator and baffling design)
    • Volume of oil
    • Maximum (design) temperature rise
    • Heat exchanger-type, size, heat removal rate (instantaneous and total demand)
    • Quench elevator design (e.g., hearth type, sidewalls, flow restrictions)
  • Flow velocity (with and without a load present)
  • Number of furnaces to be served by the quench system
  • Duty cycle (i.e., the frequency of quenching or time between quenches)
  • Post heat treatment operations, if applicable
  • Furnace temperature uniformity
  • Furnace repeatability
  • Type of furnace atmosphere
  • Post processing (e.g., washing, deep freeze or cryogenic treatment, number of tempers)
  • Time delay between heat treat operations (especially important for high hardenability materials to avoid cracking)

References

Herring, Daniel H. 2015. Atmosphere Heat Treatment. Volume 2, BNP Media II.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.

Ask The Heat Treat Doctor®: What Oil Quenching “Tricks” Help Manage Distortion? Read More »

Improve Vacuum Quench, Maximize Tool Life

/ HARDENING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT, VACUUM FURNACES TECHNICAL CONTENT

Vacuum furnaces performing hardening have been in use for over 50 years, yet many heat treaters may not be taking full advantage of newer, more advanced analysis tools and methods. Controlling the cooling pressure can dramatically improve toughness and tool life, but only if applied with precision. In this Technical Tuesday installment, Paulo Duarte, technical director at Treatnorte, explores the science behind gas quenching, the role of step cooling, and why measuring and adjusting cooling curves is critical for consistent, high-performance results.

This informative piece was first released in Heat Treat Today’s March 2026 Annual Aerospace Heat Treating print edition.

Introduction

It has been a long time since the invention of the vacuum hardening process, yet innovation in this field continues. In recent years, industrial furnaces capable of operating with higher cooling gas pressures — up to 15 bar now commonly offered on the market — have become standard. But do we truly know how to make the best use of such high pressures?

Pressures up to 10 bar were first applied to cool small parts made from cold-work tool steels, such as sheet metal stamping tools. However, such high pressures can lead to cracking in larger hot-work steel dies when cooled directly. Step cooling was introduced as a solution: start with a fast initial cooling at higher temperatures to avoid carbide formation, then gradually lower pressure stages during the final cooling phase to reduce distortion and minimize the risk of crack appearance.

Despite this empirical knowledge, the question remains: do we really understand what we are doing? Are we routinely measuring cooling rates to determine where they stand on the CCT diagram, predicting microstructure and properties, and adjusting quenching parameters accordingly? And are we certain about which pressures to use for producing high-performance, demanding tools?

Cooling in Vacuum Furnaces

Quenching is one of the most critical steps in the hardening cycle. It transforms austenite into the optimal final microstructure, avoiding the formation of coarse carbides and pearlitic constituents during cooling. This ensures the finest possible microstructure.

Figure 1. Gas quenching in a vacuum hardening furnace | Image Credit: SECO/WARWICK
Figure 2. Surface cooling rates region on systematic analysis of parts quenching in a 600 mm x 600 mm x 900 mm furnace. Parts comprising weights from 500 up to 1,000 kg. Cooling pressures varies from 4 to 5 bar. Hot work tool steel. | Image Credit: Metaltec Solutions

In vacuum furnaces, this is typically achieved by injecting cooling gas through nozzles directed at the surface of the parts located in the furnace hot zone. During cooling, the gas circulates through the chamber, being drawn through furnace ports into contact with the heat exchanger tubes. A turbine then blows the cooled gas back into the hot zone where the load is located (Figure 1).

The higher the programmed cooling pressure, the greater the volume of gas passing through the nozzles over the same period of time. This increases the heat transfer from the parts to the cooling gas, resulting in a faster cooling rate.

By measuring successive cooling curves for different loads, specifically for single hot-work steel tools weighing over 500 kg, surface cooling rates pass through the bainitic–martensitic domain (the green area of the CCT diagram shown in Figure 2). Thinner parts tend to cool closer to the martensitic end at the Ms-Bs intersection, while larger tools tend to approach the pearlitic nose.

These observations highlight the importance of adjusting cooling pressure to produce the desired microstructure and account for the different cooling behaviors of large, medium, and small parts.

Investigative Approach: Testing Furnace Data Against CCT Diagrams

Measuring part temperatures during cooling began over 20 years ago, using thermocouples and data loggers, and comparing the results to steel continuous cooling transformation (CCT) diagrams. Most vacuum furnaces do not include this capability as standard, and when available as optional software, many companies choose not to invest in it. In 2005, it was discovered what few in the industry knew at the time: hardening hot-work tool steels in industrial vacuum furnaces often results in a bainitic–martensitic microstructure. This phenomenon is now more widely recognized, with published cooling curves overlaid on CCT diagrams for larger tools becoming more available.

Even so, open discussion remains rare, partly because many heat treaters are reluctant to present this evidence to academia, fearing criticism that their results do not match the fully martensitic microstructure taught at universities. This is not a debate about right or wrong, but rather an opportunity for research and improvement in heat treatment practices worldwide.

After initial testing with a 600 mm × 600 mm × 900 mm French-made single-chamber furnace, trials continued with a larger 900 mm × 900 mm × 1,800 mm German-made vacuum furnace. These tests began by measuring both surface and core temperatures for repeated cycles with small and large charges ranging from small cold-work tools to hot-work tool steel parts weighing 500–1,500 kg. Leading vacuum furnace manufacturers in North America and Europe have developed technologies capable of successfully heat treating small, medium, and large tools, resulting in microstructures that often contain both bainite and martensite. This is, in fact, an inherent characteristic of the technology. Such tools have performed well in service for decades. That said, heat treaters using higher cooling pressures have seen improved tool life significantly, while also increasing the risk of treatment failures if the pressure is too high.

In the last 10 years, properties and microstructure analyses have shown that variations in cooling rate can significantly change the microstructure and toughness of the part even within the same bainitic–martensitic domain of the CCT diagram.

With the emergence of Industry 4.0 and 5.0, along with digitalization and AI, systematic research into heat treatment processes combined with quenching deformation simulation can lead to better selection of cooling pressures. This is a critical parameter in controlling the hardening process, and it has a direct impact on part toughness and service performance. Metaltec Solutions introduced one of the first software tools aimed at improving vacuum heat treatment through Industry 4.0 concepts in 2017. This technology represents a step toward greater awareness and precision in tool steel hardening, helping heat treaters program their cycles for optimal performance in demanding applications.

Regulating Pressure in Vacuum Hardening Furnaces

To obtain the best possible microstructures, gas quenching must be programmed in the furnace so that the cooling rate is kept as close as possible to the martensitic end, i.e., at the Ms-Bs intersection, of the CCT diagram, avoiding the formation of coarse and undesirable microconstituents in the steel. This is achieved by selecting the highest permissible cooling pressure that still prevents cracking or excessive deformation. While small parts can withstand direct high-pressure cooling, larger tools require a reduction in cooling pressure.

Preliminary Pressure Comparison

For optimal quenching of large parts, the cooling pressure should not remain constant throughout the entire cooling cycle. Instead, high pressure should be applied during the initial cooling stage to prevent coarse carbides and pearlite formation and then reduced when the surface temperature reaches approximately 550°C (1022°F). This creates a martempering stage at lower pressures, reducing the risk of distortion and cracking.

Figure 3a. Cooling pressure effect on Vidar Superior (an H11 steel grade
variation) part surface toughness | Image Credit: Metaltec Solutions
Figure 3b. Cooling pressure effect on 400 mm x 400 mm x 400 mm
block surface toughness | Image Credit: Metaltec Solutions

If we measure the toughness of steel pieces quenched at different cooling pressures, then tempered together to achieve a typical 46–48 HRC hardness (in hot work tool steel), we find that higher cooling pressures result in greater toughness. Using older furnace pressures (around 3 bar) yields lower toughness, whereas increasing cooling pressure can improve toughness by approximately 60% (Figure 3a). This translates into longer tool life, since high-pressure-quenched tools better absorb stress, delaying the initiation and propagation of cracks. These benefits result from higher cooling rates (Figure 3b) and the corresponding finer microstructures achieved.

Although quenching at 3, 6, and 9 bar passes through the same transformation domain on the CCT curve, differences in the resulting internal steel structure, whether coarser or finer, are clearly observable.

True Toughness and Speed

Looking in more detail at the above findings, we can observe that when parts are cooled in a 900 mm × 900 mm × 1,800 mm vacuum furnace, the gas temperature drops below the Ms temperature (for typical hot work tool steels) in less than one minute. The gas temperature then remains near room temperature during the subsequent cooling of the parts (Figure 4a).

Figure 4a. Cooling NADCA block in a large vacuum hardening furnace; gas cooling rate according to gas pressure used | Image Credit: Metaltec Solutions
Figure 4b. Cooling NADCA block in a large vacuum hardening furnace; surface cooling curves and its respective toughness after tempering, with the alteration of the cooling curve behavior provided by the martempering (final hardness level 46–48HRC hot work tool steel | Image Credit: Metaltec Solutions

The parts, however, take considerably longer to cool down to the furnace unloading temperature, depending on the cooling pressure applied. When analyzing the cooling of large dies using the NADCA block as the standard size for comparison, the surface cooling curves vary according to the applied pressure, falling into the bainitic–martensitic domain for 3, 6, and 9 bar cooling pressures.

From this data, it can be seen that hardness is not significantly affected by using 3, 6, or 9 bar cooling pressures, even though the higher pressures produce cooling rates up to twice as fast as the slower ones. Toughness, however, is largely influenced by the way the cooling curves pass through the bainitic–martensitic domain, whether crossing the Bs and Ms intersection closer to the martensitic end (9 bar), near the center (6 bar), or closer to the pearlitic nose (3 bar).

Tuning Pressure and Time

These results show that, within the typical cooling rates of vacuum hardening (Figure 2), toughness varies significantly with cooling pressure, corresponding to finely tuned cooling speeds ranging from approximately 9 to 16°C/min (48 to 61°F/min) between 800°C and 500°C (932°F and 1472°F). This highlights the need to use the highest possible cooling pressures to achieve excellent properties while avoiding direct high-pressure cooling of large parts by applying step cooling with an initial fast cooling phase, followed by reduced pressure.

How Microstructure Drives Toughness

The reason for achieving better properties at higher cooling pressures lies in the resulting microstructure, as shown in Figure 5. Fine bainite and martensitic needles, formed through faster cooling rates, are responsible for the higher toughness observed. When lower cooling pressures are used, the cooling rate decreases, leading to coarser needle sizes (Figres 5a–c) and, consequently, lower toughness values.


Figure 5a-c. Microstructures obtained after quenching Orvar Supreme (premium H13 steel): a) 100°C/min; b) 12°C/min; c) 3°C/min (or, a) 180°F/min; b) 22°F/min; c) 5°F/min) | Image Credit: Metaltec Solutions
Figure 6. Toughness model | Image Credit: Metaltec Solutions

This can be explained by Figure 6. In a coarser microstructure, cracks can propagate more easily because there are fewer obstacles to their advance. In finer microstructures, the higher density of needles forces cracks to deviate repeatedly from their path due to the branching effect, altering the directions of crack propagation. This “shock absorber” effect — caused by the frequent detours a crack experiences when traveling through a greater number of fine needles — is the reason for the toughness improvement observed when higher cooling pressures are used to achieve faster cooling rates.


Figure 7. Convection coefficients for a 900 mm × 900 mm × 1,800 mm vacuum hardening furnace according to the pressure being used | Image Credit: Metaltec Solutions

Each furnace behaves differently, from one furnace builder to another and also depending on the level of maintenance of a furnace. So a similar furnace to the one used for obtaining cooling curves and corresponding toughness values (Figure 4b) was used to obtain the convection coefficients (Figure 7). We can see a strong correlation between convection coefficient, pressure, and final toughness obtained, indicating that these features must be carefully adjusted to reach optimal part properties and longer service life.

Conclusion

Properly applying cooling pressures, through direct high-pressure cooling for small loads or step cooling for larger tools, can significantly increase part toughness and extend tool life. The key lies in understanding how cooling curves interact with the bainitic–martensitic microstructure and adjusting pressure according to part size, geometry, and furnace characteristics.

By measuring temperatures, analyzing microstructures, and fine-tuning cooling cycles, heat treat operators can achieve consistent, high-performance results, as demonstrated with the above studies on tool steels. Faster, well-controlled cooling typically produces finer bainitic–martensitic microstructures which results in a part with “shock absorber” qualities.

Ultimately, maximizing cooling pressure, not just for minimal distortion, creates more durable tools, reduces downtime, and strengthens competitiveness through part performance.

About The Author:

Paulo Duarte
Technical Director
Treatnorte

Paulo Duarte is an independent researcher and consultant on heat treat technologies, also working as technical director at Treatnorte. His education and expertise in metallurgy have culminated in several articles and patents. Previously, he was the project manager at Metalsolvus and also had been the technical manager and heat treatment manager within bohler-uddeholm group for the Portuguese market. Currently, Paulo focuses on helping heat treaters by providing innovative, more efficient, and profitable heat treatment services to companies.

For more information: Contact Paulo Duarte at pauloduarte@treatnote.pt.

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Ask The Heat Treat Doctor®: Why and How Do We Heat Treat Gears? Part Two

/ AEROSPACE HEAT TREAT TECHNICAL CONTENT, CARBURIZING TECHNICAL CONTENT, HARDENING TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, OP-ED, QUENCHING TECHNICAL CONTENT, VACUUM FURNACES TECHNICAL CONTENT

Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues. In this installment, Dan Herring continues his discussion on gear heat treatment, exploring vacuum and induction hardening methods for gears — from low-pressure carburizing for advanced materials to single shot and tooth-by-tooth induction techniques — and how each can be matched to the specific demands of any gear application.

This informative piece was first released in Heat Treat Today’s March 2026 Annual Aerospace Heat Treating print edition.

In Part One of this discussion (Air & Atmospheres Heat Treating, February 2026), we discussed various gear types, materials, and how they can be atmosphere heat treated. This month, we are focusing on vacuum and induction heat treating methods. Let’s learn more.

Vacuum Heat Treatment Processing Methods

Table A. Advanced Materials Processed by LPC

Vacuum processing can be used for most of the atmosphere treatments mentioned in Part One including carburizing (Figure 1). Low pressure carburizing (LPC) is a proven technology and the choice for many advanced applications in aerospace, automotive, off-highway, and motorsports markets, as well as the development of carburizing cycles for high-performance materials (Table A).

Figure 1. Typical commercial heat treat load of gears for vacuum carburizing (Otto and Herring 2007) | Image Credit: Photo courtesy of Midwest Thermal-Vac
Figure 2. Pyrowear 675 – LPC – anneal – double normalize – harden – anneal – deep freeze – double temper | Image Credit: The HERRING GROUP, Inc.

The range of effective case depths for most of these grades can range up to 2.0–3.0 mm (0.080–0.120 inches) without significant sacrifice of microstructure (Figure 2). Furnace variables, such as temperature uniformity (± 3°C or ± 5°F), control of cycle parameters (boost/diffuse times, gas flow rate, pressure, hydrocarbon type) and surface carbon optimize the microstructure, producing case uniformities of ± 0.05 mm (± 0.002 inches). Where permitted, the range of carburizing temperatures now includes the use of high temperature (> 980°C, or 1800°F) techniques.

All these advanced materials required extensive development testing to produce custom designed recipes to optimize cycle parameters. Also, quenching methods (Otto and Herring 2002) have improved, allowing us to achieve desired core properties with quenching parameter selection (high-pressure gas or oil) for distortion-sensitive and distortion-prone part geometries (Otto and Herring 2005, 2008).

Induction Hardening Methods

Various methods of hardening via applied energy are used in manufacturing gears, including flame hardening, laser surface hardening, and induction hardening.

Of the various types of applied energy processing, induction hardening is the most common. Induction heating is a process that uses alternating electrical current that induces a magnetic field, causing the surface of the gear teeth to heat. The area is then quenched resulting in an increase in hardness within the heated area. This process is typically accomplished in a relatively short time. The final desired gear performance characteristics are determined not only by the hardness profile and stresses but also by the steel composition and prior microstructure. External spur and helical gears, bevel and worm gears, racks, and sprockets are commonly induction hardened. Typical gear steels include AISI/SAE grades 1050, 1060, 1144, 4140, 4150, 4350, 5150, and 8650.

Figure 3. Patterns produced by induction hardening (Rudnev 2000)

The hardness pattern produced by induction heating (Figure 3) is a function of the type and shape of inductor used, as well as the heating method. Quenching or rapidly cooling the workpiece can be accomplished by spray or submerged quench. The media typically used for the quench is a water-based polymer. The severity of this quenchant can be controlled by the polymer’s concentration. Cooling rates are usually somewhere in between what would be obtained from pure water and oil. In some unusual situations compressed air or nitrogen is used to quench the part.

The most common methods for hardening gears and sprockets are by single shot (Figure 4) or the tooth-by-tooth method (Figure 5). Single shot often requires large kW power supplies but results in short heat/quench times and higher production rates. This technique uses a circumferential copper inductor, which will harden the teeth from the tips downward.

Figure 4. Typical single shot induction hardening operation | Image Credit: Photo courtesy of Ajax-Tocco-Magnethermic
Figure 5. Tooth-by-tooth induction hardening of a helical gear | Image Credit: Photo courtesy of Ajax-Tocco-Magnethermic

The larger and heavier loaded gears (where pitting, spalling, tooth fatigue, and endurance are issues) need a hardness pattern that is more profiled like those produced by carburizing, which can be obtained by tooth-by-tooth hardening. This method is limited to gear tooth sizes with modulus 4.23–5.08 (6 or 5 DP) using frequencies from 2 to 10 kHz and about 2.54 (10 DP) using a range of 25 to 50 kHz.

The lower the frequency, the deeper the case depth. Tooth-by-tooth hardening is a slow process and usually reserved for gears and sprockets that are too large to single shot due to power constraints. The process involves heating the root area and side flanks simultaneously, while cooling each side of the adjacent tooth to prevent temper-back on the backside of each tooth. The induction system moves the coil at a pre-programmed rate along the length of the gear. The coil progressively heats the entire length of the gear segment while a quench follower immediately cools the previously heated area. The distance from the coil to the tooth is known as coupling or air gap. Any changes in this distance can yield variation in case depth, hardness, and tooth distortion. The gear is indexed after each tooth has been hardened, often skipping a tooth. This requires at least two full revolutions in the process to complete the hardening of all teeth. Straight, spur, and helical gears up to 5.5 m (210 inches) weighing 6,800 kg (15,000 lb) have been processed with this method. The entire process yields a repeatable soft tip of the tooth with hard root and flank. In other applications, the tip and both flanks can be hardened simultaneously and yield a soft root.

In Summary

Today’s design engineer has the good fortune of being able to choose from a number of heat treatment technologies for any given type of gear material and design. When selecting a gear hardening method, it is essential to specify not only the desired mechanical and metallurgical properties, but the critical dimensions that must be held and even the desired stress state of the gears themselves. The secret to success is understanding the advantages and limitations of each technology and taking these into consideration when determining the overall cost of gear manufacturing.

References

Herring, Daniel H. 2004a. “Gear Heat Treatment: The Influence of Materials and Geometry.” Gear Technology, March/April.

Herring, Daniel H. 2004b. “Reducing Distortion in Heat-Treated Gears.” Gear Solutions, June.

Herring, Daniel H. 2007a. “Oil Quenching Technologies for Gears.” With Steven D. Balme. Gear Solutions, July.

Herring, Daniel H. 2007b. “Heat Treating Heavy Duty Gears.” With Gerald D. Lindell. Gear Solutions, October.

Herring, Daniel H. 2012–2016. Vacuum Heat Treatment. Vols. 1–2. BNP Media Group.

Herring, Daniel H. 2014–2015. Atmosphere Heat Treatment. Vols. 1–2. BNP Media Group.

Herring, Daniel H., Gerald D. Lindell, D. J. Breuer, and B. Matlock. 2001. “Atmosphere vs. Vacuum Carburizing.” Heat Treating Progress, November.

Herring, Daniel H., Gerald D. Lindell, D. J. Breuer, and B. Matlock. 2002. “An Evaluation of Atmosphere and Vacuum Carburizing Methods for the Heat Treatment of Gears.” In Off-Highway Conference Proceedings. SAE International.

Otto, Frederick J., and Daniel H. Herring. 2002a. “Gear Heat Treatment: Today and Tomorrow, Part 1.” Heat Treating Progress, June.

Otto, Frederick J., and Daniel H. Herring. 2002b. “Gear Heat Treatment: Today and Tomorrow, Part 2.” Heat Treating Progress, July/August.

Otto, Frederick J., and Daniel H. Herring. 2005. “Vacuum Carburizing of Aerospace and Automotive Materials.” Heat Treating Progress, January/February.

Otto, Frederick J., and Daniel H. Herring. 2007. “Advancements in Precision Carburizing of Aerospace and Motorsports Materials.” Heat Treating Progress, May/June.

Otto, Frederick J., and Daniel H. Herring. 2008. “Improvements in Dimensional Control of Heat Treated Gears.” Gear Solutions, June.

Rudnev, V. 2000. “Gear Heat Treating by Induction.” Gear Technology, March/April.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.

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How To Tame Your Dragon

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

When a load hangs up during quenching, seconds matter and improvised decisions can escalate risk. In this Technical Tuesday installment, Bruno Scomazzon, general manager of Precision Heat Treat Ltd., outlines a step-by-step emergency response procedure for exactly this scenario, which is one of the most dangerous in atmosphere heat treating. Drawing on real-world experience, this guide is intended to help companies develop their own effective procedures for maintaining safety, controlling furnace conditions, and coordinating with emergency responders in high-risk situations.

This informative piece was first released in Heat Treat Today’s February 2026 Annual Air & Atmosphere Heat Treating print edition.

If you have comments or questions about this article, please let us know at: editor@heattreattoday.com

Para leer el artículo en español, haga clic aquí.

Scenario Overview

A load has been transferred to the quench and the elevator is lowering into the oil, but the load becomes hung up and fails to fully submerge. The inner door successfully closes, and the outer (front) door remains closed.

This is an extremely high-risk situation requiring strict adherence to emergency procedures. The goal is to protect: first the personnel (minimize the chance of injury or escalation of the situation), then the facility, and finally the equipment.

1. Immediate Actions

DO NOT Open Outer Door

There may be a natural urge to assess the situation but resist temptation. DO NOT stand in front of or directly beside the outer door and never open it during an active hang-up. Opening this door can introduce oxygen to a hot chamber, causing:

  • Explosions or flash fires.
  • Loss of containment due to door warping or mechanical failure.

In extreme cases, the outer door may be compromised (blown off, stuck open, or partially open) with visible flames. This warrants immediate escalation to the fire department.

If Outer Door Cannot Be Closed

In this scenario, immediately notify the fire department and advise them to prepare for a foam response. DO NOT allow the use of water. This may trigger violent reactions with oil or atmosphere and spread the fire!

Internal trained responders should:

  • Don PPE.
  • Retrieve fire suppression gear.
  • Be ready to protect critical systems until responders arrive.

DO NOT shut down the furnace.

Figure 1. Atmosphere furnace during normal
operation | Image Credit: Precision Heat Treat
Ltd.
Figure 2. Vestibule door partially opened during a
controlled simulation to illustrate gas release
behavior — not an actual incident | Image Credit:
Precision Heat Treat Ltd.

2. Maintain Electrical Power

To ensure essential systems stay active, you must maintain electrical power. Ensure these systems stay active:

  • Set the furnace cycle to manual mode from auto mode. This will bypass any PLC sequencing from auto cycling doors, elevators, and handlers.
  • Keep the pilots lit.
  • Keep the oil cooler running to prevent tank overheating.
  • Shut off oil heaters to prevent additional heat loading in the quench tank.
  • Keep quench agitation on low during the entire period to assist in lowering the temperature at the interface surface area between the hot load and the oil. This prevents stratification and dissipates radiant heat into the oil.
  • Keep the recirculating fan running.
  • Keep the instrumentation functioning for monitoring.

NOTE: Loss of these systems eliminates visibility, atmosphere control, and safe response options.

3. Atmosphere Management

Maintain a protective atmosphere and positive furnace pressure to prevent oxygen ingress and uncontrolled combustion:

  • Set the carbon control to “0”.
  • Shut off the enriching gas.
  • Shut off the ammonia.
  • Shut off the dilution air.

Nitrogen Purge

These steps depend on whether a nitrogen purge is available; it is highly advised that nitrogen purge be available for all IQ or straight through units. Be sure you understand how long it takes for your specific furnace to fully purge endothermic gas. While NFPA 86 recommends five volume turnovers, some experts advise planning for up to ten per hour in an emergency. Each furnace should have established purge data under normal conditions so operators can act with confidence when time is critical.

Figure 3. Bulk nitrogen supply used for emergency purging and atmosphere control | Image Credit: Precision Heat Treat Ltd.
  • Begin a nitrogen purge immediately (if available) and maintain it throughout the event.
  • Use at least the minimum flow rate specified in your documentation. If safe, higher flow may be used to help displace flammable gases from the heating and quench chambers.
  • Maintain furnace temperature at 1500°F during the purge.

Residual pockets of Endo gas may remain trapped in less ventilated areas. If the chamber temperature drops below the ignition point before all flammable gas has been displaced, the introduction of oxygen could trigger an explosion. In some cases, trapped Endo and pressure imbalances can lead to sudden releases (“furnace burp”), where oil or gas is expelled due to internal pressure buildup.

After the Purge

The goal of the nitrogen purge is to displace Endothermic gas with an inert atmosphere while maintaining elevated temperature to assist in burning off residual flammable gases and preventing dangerous mixtures. This process must ensure positive pressure throughout the furnace.

  • A purge followed by plunge cooling in nitrogen is a valid approach if the purge is verifiably complete.
  • Depending on furnace size and cooling rate:
  • Larger furnaces may cool slowly enough for a complete purge.
  • Smaller or faster-cooling units may require a brief temperature hold before controlled cooling or plunge cooling.

NOTE: Once the hung-up load cools to a safe temperature (~150°F), perform a standard shutdown.

Without Nitrogen (in Endo)

If there is no nitrogen purge, or it is insufficient, the only option is to let the hung-up load cool in the vestibule while continuing to burn Endo and maintain the furnace temperature at 1500°F. Once the vestibule/oil tank cools below 150°F and the danger has passed, initiate a standard furnace shutdown.

4. Safety Management

  • Alert the local fire department immediately. If the situation becomes unmanageable, or if there is any doubt about the ability to maintain control, evacuate the facility and wait for trained professionals. The safety of plant personnel is paramount.
  • Notify plant safety and site management.
  • Evacuate all non-essential personnel from the heat treat area.
  • Inform all departments that a high-risk incident is in progress.

Fire departments are most effective when they are familiar with your facility before an emergency occurs. Make sure they know the layout of your operation, including:

  • Oil tank locations and sizes
  • Electrical panels
  • Gas shutoffs
  • Hot zones

5. Controlled Cooling Period

  • Maintain atmosphere protection throughout the event.
  • DO NOT open doors until the vestibule’s temperature is low and stable.
  • Cooling time will depend on load mass and heat retention. Expect five or more hours.
  • Use furnace pressure stability, effluent observations, and gas behavior as indirect temperature indicators.

6. Load Recovery Procedure

  • Once cooled and stabilized, perform a standard shutdown, starting with the removal of endothermic gas if applicable.
  • DO NOT attempt manual load removal until the system is verified safe.
  • Only maintenance personnel may retrieve the load, using PPE and appropriate tools.

7. Fire Department Familiarization

Every facility should build rapport with the local fire department before an emergency ever happens. Schedule annual walkthroughs and identify the following:

  • Number of furnaces
  • Quench oil tank volumes
  • Hot zone and live panel locations
  • Emergency shutoff points

Stuck doors are commonly caused by failed pneumatic valves. Shutting off and bleeding compressed air may allow the mechanism to reset. Always consult your equipment manual or the manufacturer before attempting corrective action.

The fire inspector conducting walkthroughs is not the one coming to fight your fires — train the ones who are.

8. Post-Incident Protocol

Before returning the furnace to service:

  • Conduct a formal investigation.
  • Identify and correct root cause(s).
  • Document all key parameters and actions taken.
  • Re-train operators as needed.

Furnace Signage

An operator is likely to read your safety plan but may forget a vital protocol during an emergency. Having bold, brightly colored warnings printed and posted at the panel that the operator can remove and use in an emergency can be invaluable.

Final Reflections

We cannot predict every consequence. No procedure can account for every possible variable in a live emergency. Once an event is in motion, all we can do is respond with the best judgment, training, and intentions — always with the safety of people as the highest priority.

This document is intended as a working reference: a structured reference developed with care, real-world experience, and best practices. It is not a one-size-fits-all solution, but a tool to help teams create or enhance their own effective procedures and respond adaptively in high-risk situations.

Fire preparedness is essential in every heat treating facility. Fires happen, and they are not always small. It is critical to know when to act, when to evacuate, and when to call for help. Equipment manuals provide a foundation, but preparedness through training and planning is the best defense.

Acknowledgments: The author would like to thank Daniel H. Herring, “The Heat Treat Doctor,” The HERRING GROUP, Inc., and Avery Bell with Service Heat Treat in Milwaukee for their valuable input.

About The Author:

Bruno Scomazzon
General Manager
Precision Heat Treat Ltd.

Bruno Scomazzon is the general manager of Precision Heat Treat Ltd. in Surrey, British Columbia, Canada, with over 40 years of experience in metallurgical processes and heat treating operations.

For more information: Contact Bruno at bruno@precisionheattreat.com.

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Insufficient Austenitizing in Steel Heat Treatment: Causes, Effects, and How to Prevent It

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, HARDENING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

Insufficient austenitizing affects far more than final hardness. It disrupts phase transformation, weakens mechanical performance, and increases the risk of distortion or failure in demanding service conditions. In this Technical Tuesday installment, Ana Laura Hernández Sustaita, founder of Consultoría Carnegie, explains the metallurgical origins of incomplete austenite formation, how furnace uniformity, heating rate, steel chemistry, and part geometry contribute to the problem, and modern process-control and simulation strategies that ensure full transformation and repeatable, high-quality results.

This informative piece was first released in Heat Treat Today’s January 2026 Annual Technologies To Watch print edition.

Para leer el artículo en español, haga clic aquí.

Introduction

When a steel part is insufficiently austenitized, it is commonly referred to as underhardening, the resulting loss of hardness after quenching. However, in this article, we will extend the discussion beyond hardness alone, exploring the phenomenon of insufficient austenitizing, analyzing its causes and direct influence on microstructure and mechanical properties, and discussing modern strategies to prevent it.

The Role of Austenitizing in Heat Treatment

The main purpose of heat treatment is to produce a homogeneous or a desired mixed microstructure that ensures the required mechanical properties for the intended service conditions: tensile strength, impact resistance, yield strength, etc. Austenitizing is the first critical step for many processes. It involves heating the steel above the A3 temperature (typically 30–50°C or 85–120°F higher) to transform its microstructure into a face-centered cubic (FCC) lattice for a certain period of time. This step resets the steel’s structural history, particularly after casting, forging, or rolling, and defines the baseline for subsequent quenching and tempering operations.

What Is Insufficient Austenitizing?

Figure 1. Time-temperature-austenitization diagram for Ck 45 (SAE/AISI 1045) steel. | Image Credit: Figure 7, ASM International 2013

Austenite formation involves structural and compositional changes influenced by the initial microstructure and the steel’s chemical composition. When austenitizing parameters are not properly established, such as insufficient temperature, inadequate soaking time, or poor furnace performance (e.g., lack of thermal uniformity), the transformation remains incomplete. The result is a microstructure containing undesired residual phases that compromise hardness, dimensional stability, and mechanical strength. Therefore, any microstructure that fails to fully transform to austenite due to these factors can be directly associated with insufficient austenitizing.

Common causes of insufficient austentizing include:

  • Inadequate austenitizing temperature: Ferrite and carbides do not fully dissolve if the temperature is too low.
  • Insufficient holding time: A short soak time prevents uniform carbon diffusion throughout the austenite.
  • Thermal non-uniformity in the furnace (cold zones): This leads to regions with different degrees of transformations.
  • Chemical composition of the steel: Alloying elements modify diffusion kinetics and impact the critical transformation temperatures.
  • Geometry and dimensions of the part: Larger cross-sections require longer soak times for full heat diffusivity.
  • Rapid heating rates: Excessive heating, especially during induction hardening, can result in structural inhomogeneity and incomplete transformation.

Effects of Insufficient Austentizing

Heterogeneous Microstructure

As illustrated in the ASM Handbook, Volume 4A: Steel Heat Treating Fundamentals and Processes (2013), the kinetics of austenite formation depend strongly on the heating rate. At lower heating rates, diffusion-driven homogenization occurs at relatively lower temperatures, whereas rapid heating produces microstructural heterogeneity, an effect that is especially critical in induction or direct-flame heating. In other words, insufficient austenitizing is more likely to occur when high heating rates are used.

Consequently, a microstructure with heterogeneous composition leads to variations in the martensite transformation temperatures (Ms and Mf) throughout the part. During quenching, regions with lower carbon content transform earlier, producing softer martensite, while areas with higher carbon content transform at lower temperatures, resulting in internal stresses and an overall inconsistent microstructure.

Risk of Distortion and Premature Failure

The transformation from BCC or BCT to FCC (Defined: BCC: body-centered cubic; BCT: body-centered tetragonal; FCC: face-centered cubic) lattice during austenitizing involves a specific volume change. If this transformation occurs unevenly, differential expansion generates internal stresses, distortion, and in severe cases, microcracks. Rapid heating or poor furnace convection exacerbates these effects by producing steep temperature gradients across the part.

Reduced Hardness and Mechanical Strength

Incomplete transformation leaves undissolved carbides and residual ferrite, reducing hardenability and the amount of carbon in solid solution. This limits the formation of martensite during quenching and lowers final hardness and strength.

Increased Brittleness and Lower Toughness

A mixed structure of ferrite, pearlite, partial martensite, and retained austenite results in mechanical anisotropy and reduced energy absorption under impact loading. This condition increases the risk of brittle fracture, particularly in high-stress or cyclic applications.

How to Prevent Insufficient Austenitizing

Accurate Furnace Control

Figure 2. Example of loading analysis | Image Credit:
Consultoría Carnegie

To ensure proper process control during the soaking stage, it is essential to use calibrated thermocouples strategically positioned inside the furnace to obtain accurate temperature measurements. Regular calibration prevents temperature reading errors and directly contributes to heat treatment quality. It is also important to get advice from an expert to determine the recommended service life of the thermocouples. Maintaining proper traceability and replacing them at the appropriate intervals ensures optimal system performance.

Additionally, the use of internal circulation fans in convection furnaces helps maintain thermal uniformity, preventing the formation of hot or cold zones.

Another method to monitor and control process temperature is using temperature data loggers. These devices, which are connected to contact thermocouples and placed directly on the parts, are especially recommended for components with complex geometries or large cross-sections. They record real-time temperature data throughout the process, allowing verification that no transient fluctuations occur during the soaking period.

Accurate Loading Distribution

For loads where heat treatment must be applied to a significant number of parts, it is recommended that a study be conducted to determine the maximum stacking height that will ensure proper heat flow and uniform heating. A preliminary assessment can be performed by strategically placing thermocouples in different locations and on different parts, for example, on the first part in the load, one in the middle section, and another at the bottom of the stacking tower.

Once the parts enter the process, their heating behavior can be monitored to verify that the soaking time is sufficient for all pieces in the stack to complete their transformation upon reaching the target temperature or to determine whether adjustments to the loading configuration are necessary.

Use of Thermodynamic Simulation to Optimize Process Parameters

Each steel grade has an optimum austenitizing temperature in function of its chemical composition. For carbon steels (10XX series), these temperatures can be estimated using the Fe–C diagram; however, once alloying elements are added, this diagram is no longer sufficient. In such cases, it becomes necessary to rely on critical temperature calculations or on more advanced tools such as thermodynamic simulations using specialized software, like Thermo-Calc®.

Although the ideal scenario would be to heat treat each material at its specific optimum temperature, this approach is impractical in industrial production; the required processing of each part individually would slow the manufacturing line and increasing resource consumption, including time and fuel.

Thermodynamic tools such as Thermo-Calc allow engineers to evaluate how variations in chemical composition (arising from casting tolerances or adjustments in alloying elements) affect transformation temperatures. This enables the selection of an optimum processing temperature that ensures complete austenitization for all possible compositional variations within the specification. As a result, the heat treatment operation becomes more robust, more reproducible, and more energy efficient.

For example, in Figure 3, if a 4140 steel is heated only to 750°C (1380°F) instead of 850°C (1560°F), the ferrite will not fully dissolve. As a result, the microstructure will consist of soft martensite and residual ferrite after quenching, rather than a fully homogeneous and hard martensitic structure. This significantly reduces the material’s hardness and mechanical strength.

Figure 3. Equilibrium diagram, AISI 4140 0.38C, 0.78Mn, 0.85Cr, 0.22Mo (%wt.) | Image Credit: Consultoría Carnegie
Figure 4. Histogram of Ac3 transformation temperature for AISI 4140 steel within the specification range. | Image Credit: Consultoría Carnegie

We can observe in the histogram (Figure 4) that even within the same steel grade, the A3 temperature can vary from approximately 760−776°C (1400−1429°F) solely due to the composition tolerances specified for the alloy. If we also consider the presence of residual or microalloying elements, it becomes clear that we cannot expect identical behavior during heat treatment or identical mechanical properties across all heats.

In such cases, thermodynamic tools allow us to evaluate a batch of possible chemistries and determine an optimal austenitizing temperature that is suitable for all compositional variations.

Heating Curve Design

To ensure that transformation temperatures are reached uniformly (whether in processes involving large loads or parts with variable geometries), it is advisable to implement controlled heating rates. Although this approach may increase processing time, the benefits include reduced distortion risk and assurance of complete austenitic transformation.

The key is to design an appropriate time–temperature profile, which depends on factors such as part dimensions and material properties, including thermal diffusivity, heat capacity, density, and thermal conductivity.

Conclusion

Insufficient austenitizing, also known as underhardening, represents far more than a loss of hardness. It is a metallurgical deficiency that affects microstructural homogeneity, dimensional stability, and mechanical performance. Through rigorous control of temperature, time, and furnace uniformity combined with modern simulation tools, engineers can ensure reliable transformations, minimize distortion, and achieve consistent high-quality results in steel heat treatment.

References

ASM International. 2013. ASM Handbook. Vol. 4A: Steel Heat Treating Fundamentals and Processes.

Callister, W. D. 2019. Materials Science and Engineering: An Introduction. Hoboken, NJ: Wiley.

Herring, Dan. Metallurgical Fundamentals of Heat Treatment. Industrial Heating.

Krauss, G. 1980. Principles of Heat Treatment of Steel. ASM International.

Nuñez González, G. 1990. Fallas en los Tratamientos Térmicos para Aceros Herramienta.

Thomas, L. 2018. “Austenitizing Part 2: Effects on Properties.” Knife Steel Nerds. https://knifesteelnerds.com/2018/03/01/austenitizing-part-2-effects-on-properties/.

Totten, G. E. 2007. Steel Heat Treatment: Metallurgy and Technologies. Boca Raton, FL: CRC Press.

About The Author:

Ana Laura Hernández Sustaita
Founder
Consultoría Carnegie

Ana Laura Hernández Sustaita holds a Master’s degree in Materials Science and engineering. She is the founder of Consultoría Carnegie, a technical consulting and training firm specializing in steel heat treatment in Mexico. Additionally, she works as a technical support engineer at Thermo-Calc Software, providing assistance to clients across México, Canada, and United States of America. Ana actively promotes metallurgical education throughout Latin America and advocates for the integration of computational tools into industrial heat treatment practice.

For more information: Contact Ana Hernández at anahdz@consultoriacarnegie.com.

Insufficient Austenitizing in Steel Heat Treatment: Causes, Effects, and How to Prevent It Read More »

Austenización Insuficiente en el Tratamiento Térmico: Causas, Efectos y Cómo evitarla

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, HARDENING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, QUENCHING TECHNICAL CONTENT

Un austenizado insuficiente afecta mucho más que la dureza final. Interrumpe la transformación de fase, debilita el rendimiento mecánico y aumenta el riesgo de deformación o fallo en condiciones de servicio exigentes. En esta entrega de Technical Tuesday, Ana Laura Hernández Sustaita, fundadora de Consultoría Carnegie, explica los orígenes metalúrgicos de la formación incompleta de la austenita; como la uniformidad del horno, la velocidad calentamiento, la composición química del acero y la geometría de la pieza, contribuyen a ese problema; y las estrategias modernas de control de procesos y simulación que garantizan una transformación completa y resultados repetibles de alta calidad.

Este artículo informativo se publicó por primera vez en Heat Treat Today’s January 2026 Annual Technologies To Watch print edition.

To read this article in English, click here.

Introducción

En inglés, el término underhardening se utiliza para describir aceros que no alcanzan una austenización completa, lo que se traduce en una pérdida de dureza después del temple. Sin embargo, en este artículo ampliaremos el análisis más allá de la dureza, centrándonos en el fenómeno de la austenización insuficiente, analizando sus causas, su influencia directa en la microestructura y en las propiedades mecánicas, así como las acciones que podemos implementar en el proceso para prevenirla.

El rol del proceso de austenización

El objetivo principal del tratamiento térmico es obtener una microestructura homogénea o mixta que garantice las propiedades mecánicas requeridas para las condiciones de servicio establecidas: resistencia a la tracción, resistencia al impacto, límite elástico, entre otras.

El proceso de austenización es el primer paso crítico para muchos procesos. Consiste en calentar el acero por encima de la temperatura A3 (normalmente entre 30 y 50°C/85 y 120°F adicionales) para obtener una microestructura con red cúbica centrada en las caras (FCC) durante un tiempo determinado. Este paso es fundamental después de procesos como solidificación, forja o laminado, ya que “reinicia” la historia microestructural del acero.

¿Qué es la austenización insuficiente?


Figura 1. Diagrama tiempo-temperatura de austenización para acero Ck 45 (SAE/AISI 1045). | Image Credit: Figure 7, ASM International 2013

La formación de austenita implica cambios estructurales y composicionales influenciados tanto por la microestructura inicial como por la composición química del acero. Cuando los parámetros de austenización no se establecen adecuadamente: temperatura insuficiente, tiempo de permanencia corto o problemas de desempeño del equipo, como la falta de uniformidad térmica del horno, la transformación no se completa. El resultado es una microestructura que conserva fases no deseadas, lo que afecta la dureza, la estabilidad dimensional y la resistencia mecánica. Por lo tanto, cualquier microestructura que no logre transformarse completamente a austenita debido a los factores mencionados puede considerarse un caso de austenización insuficiente.

Causas de la Austenización Insuficiente:

  • Temperatura de austenización inadecuada: si la temperatura es demasiado baja, no se logra la disolución completa de ferrita o carburos.
  • Tiempo de empape insuficiente: un tiempo de empape (permanencia) demasiado corto impide la difusión homogénea del carbono en la austenita.
  • Distribución térmica no uniforme en el horno: produce zonas con distintos grados de transformación.
  • Composición química del acero: los elementos de aleación modifican la cinética de difusión y desplazan las temperaturas críticas de transformación.
  • Geometría y dimensiones de la pieza: las secciones más grandes demandan mayor tiempo de empape, para alcanzar el calentamiento completo.
  • Velocidades de calentamiento rápidas: pueden impedir la homogeneización de la microestructura y generar una transformación incompleta, especialmente en procesos por inducción.

Efectos de una austenización insuficiente

Microestructura heterogénea

Tal como se ilustra en el ASM Handbook, Volume 4A: Steel Heat Treating Fundamentals and Processes, la cinética de formación de la austenita depende fuertemente de la velocidad de calentamiento. A bajas velocidades, la homogeneización por difusión ocurre a temperaturas relativamente menores; en contraste, los calentamientos rápidos generan heterogeneidad microestructural, un efecto especialmente crítico en procesos como el endurecimiento por inducción o el calentamiento directo por flama. En otras palabras, la austenización insuficiente se presenta con mayor frecuencia cuando se emplean altas velocidades de calentamiento.

En consecuencia, una microestructura con composición heterogénea provoca variaciones en las temperaturas de transformación martensítica (Ms y Mf) a lo largo de la pieza. Durante el temple, las regiones con menor contenido de carbono transforman primero, originando una martensita más suave, mientras que las zonas más ricas en carbono transforman a menores temperaturas, generando tensiones internas y una microestructura inconsistente.

Mayor riesgo de deformaciones y fallas prematuras en servicio

Anteriormente se mencionó que el proceso de austenización implica un cambio en la estructura cristalina del material. Si este cambio no es homogéneo a lo largo de la pieza, se presentarán diferentes fases, resultando en un arreglo cristalográfico variado y, por ende, un cambio volumétrico. Por otra parte, calentar una pieza muy rápidamente provoca que el calor no se distribuya ni penetre de manera uniforme, causando transformaciones heterogéneas y, por lo tanto, tensiones debido a los cambios volumétricos en la estructura cristalina.

Reducción en la dureza y resistencia mecánica

Una austenización incompleta deja restos de ferrita o carburos no disueltos en la microestructura, que impide la transformación completa a martensita durante el temple, reduciendo la dureza final. Además, una menor cantidad de carbono en solución afecta negativamente la resistencia mecánica.

Aumento de la fragilidad y menor tenacidad

Una microestructura heterogénea (ferrita y perlita con martensita parcial y austenita retenida) disminuye la resistencia mecánica. Esto se traduce en menor capacidad para soportar cargas sin fracturarse.

Como prevenir la austenización ineficiente

Control preciso de temperatura y tiempo del horno

Figura 2. Ejemplo de un análisis de carga | Image Credit: Consultoría Carnegie

Para garantizar un control adecuado durante el mantenimiento, es fundamental utilizar termopares calibrados y ubicarlos estratégicamente dentro del horno para asegurar mediciones precisas. La calibración periódica previene errores en la lectura de temperatura, lo que contribuye directamente a la calidad del proceso. Además, es indispensable contar con la asesoría de un experto para determinar la vida útil recomendada de los termopares. Mantener una trazabilidad adecuada y realizar los reemplazos en tiempo y forma asegurará un funcionamiento óptimo del sistema.

Por otra parte, el uso de ventiladores internos en hornos de convecciones nos ayudara a mantener una uniformidad térmica dentro del horno, evitando zonas frías o calientes.

Otra forma de poder controlar la temperatura del proceso es el uso de registradores de temperatura o graficadores de temperatura. Estos dispositivos, conectados a termopares de contacto instalados directamente en las piezas, son especialmente recomendables para componentes con geometrías complejas con grandes espesores. Su función es registrar la temperatura en tiempo real y verificar que no existan fluctuaciones durante el tiempo de mantenimiento.

Distribución adecuada de la carga

En cargas donde es necesario realizar el tratamiento térmico de una cantidad considerable de piezas, es recomendable llevar a cabo un estudio para determinar la altura máxima de apilamiento que permita un flujo de calor adecuado y un calentamiento homogéneo. Un análisis preliminar puede realizarse colocando termopares estratégicamente en diferentes ubicaciones y en distintas piezas: por ejemplo, en la primera pieza de la carga, otra en la parte media y una más en la parte inferior de la torre de apilamiento.

Una vez que las piezas ingresan al proceso, es posible monitorear el comportamiento térmico de cada una de ellas, verificando que el tiempo de empape sea suficiente para que todas alcancen la transformación requerida al llegar a la temperatura objetivo, o bien, determinar si es necesario realizar ajustes en la configuración de la carga.

Uso simulación termodinámica para optimizar los parámetros del proceso

Cada grado de acero tiene una temperatura óptima de austenización determinada por su composición química. En los aceros al carbono (serie 10xx), estas temperaturas pueden estimarse mediante el diagrama Fe–C; sin embargo, cuando se incorporan elementos de aleación, dicho diagrama deja de ser suficiente. En esos casos, es necesario recurrir al cálculo de temperaturas críticas o al uso de herramientas más precisas, como simulaciones termodinámicas mediante software especializado, por ejemplo, Thermo-Calc®.

Aunque lo ideal sería tratar cada material a su temperatura específica, en la producción industrial esto no es eficiente, ya que implicaría procesar cada pieza de manera individual, lo cual ralentizaría la línea de fabricación y aumentaría el consumo de recursos, como tiempo y gas.

El uso de herramientas termodinámicas como ThermoCalc software ® permite evaluar cómo las variaciones en la composición química (debidas a tolerancias de colada o ajustes en elementos de aleación) afectan las temperaturas de transformación. Esto facilita la selección de una temperatura óptima de proceso que garantice que, para cada composición posible dentro de las especificaciones, las temperaturas de austenización sean las adecuadas. Con ello se optimiza el rendimiento del tratamiento térmico y se mejora la reproducibilidad del proceso.

Por ejemplo, en la figura 3, si un acero 4140 se calienta únicamente a 750°C (1380°F) en lugar de 850°C (1560°F), la ferrita no se disolverá por completo. Como resultado, después del temple se obtendrá una microestructura compuesta por martensita blanda y ferrita residual, en lugar de una martensita homogénea y dura. Esto reduce significativamente la dureza y la resistencia mecánica del material.


Figura 3. Diagrama de un eje para un acero 4140, (Fe, 0.4C, 0.8Mn, 0.2Si, 0.8Cr, 0.2Mo, 0.02Ni) | Image Credit: Consultoría Carnegie

Figura 4. Histograma de la temperatura de transformación Ac3 para un acero AISI 4140 dentro del rango
de especificación. | Image Credit: Consultoría Carnegie

En el histograma (figura 4) podemos observar que, incluso tratándose del mismo grado de acero, la temperatura A₃ puede variar aproximadamente 760−776°C (1400−1429°F) únicamente debido a las tolerancias químicas establecidas en la especificación. Si además consideramos la presencia de elementos residuales o microaleantes, es evidente que no podemos esperar el mismo comportamiento durante el tratamiento térmico ni las mismas propiedades mecánicas en todas las coladas.

En estos casos, herramientas termodinámicas como ThermoCalc software® permiten evaluar un conjunto amplio de posibles composiciones químicas y determinar una temperatura de austenización óptima que sea adecuada para todas las variaciones permitidas dentro de la especificación.

Diseño de curvas/rampas de calentamiento

Para asegurar que las temperaturas de transformación se alcancen de manera homogénea (tanto en procesos con cargas de alto volumen, como en piezas con geometrías variables) es recomendable implementar un calentamiento controlado. Aunque esto puede aumentar el tiempo de procesamiento, los beneficios incluyen una menor probabilidad de distorsión y la garantía de lograr una transformación austenítica completa.

La clave radica en diseñar un perfil adecuado de tiempo–temperatura, el cual dependerá de factores como las dimensiones de la pieza y las propiedades del material, entre ellas: difusividad térmica, capacidad calorífica, densidad y conductividad térmica.

Conclusión

La austenización insuficiente, conocida como underhardening, representa mucho más que una simple pérdida de dureza. Es una deficiencia metalúrgica que afecta la homogeneidad microestructural, la estabilidad dimensional y el desempeño mecánico.

Mediante un control riguroso de la temperatura, el tiempo y la uniformidad del horno, combinado con herramientas modernas de simulación, los ingenieros pueden asegurar transformaciones confiables, minimizar la distorsión y lograr resultados constantes y de alta calidad en el tratamiento térmico de los aceros.

Referencias

ASM International. 2013. ASM Handbook. Vol. 4A: Steel Heat Treating Fundamentals and Processes.

Callister, W. D. 2019. Materials Science and Engineering: An Introduction. Hoboken, NJ: Wiley.

Herring, Dan. Metallurgical Fundamentals of Heat Treatment. Industrial Heating.

Krauss, G. 1980. Principles of Heat Treatment of Steel. ASM International.

Nuñez González, G. 1990. Fallas en los Tratamientos Térmicos para Aceros Herramienta.

Thomas, L. 2018. “Austenitizing Part 2: Effects on Properties.” Knife Steel Nerds. https://knifesteelnerds.com/2018/03/01/austenitizing-part-2-effects-on-properties/.

Totten, G. E. 2007. Steel Heat Treatment: Metallurgy and Technologies. Boca Raton, FL: CRC Press.

Acerca de la autora:

Ana Laura Hernández Sustaita
Fundadora
Consultoría Carnegie

Ana Laura Hernández Sustaita cuenta con Maestría en Ciencia e Ingeniería de los Materiales, Es fundadora de Consultoría Carnegie, una firma de consultoría y capacitación técnica especializada en el tratamiento térmico de aceros en México. Asimismo, se desempeña como Ingeniera de Soporte Técnico en Thermo-Calc Software, brindando asistencia a clientes en México, Canada y Estados Unidos de América. Ana promueve activamente la educación metalúrgica en Latinoamérica y fomenta la integración de herramientas computacionales en la práctica industrial del tratamiento térmico.

Para más información: Contacte con Ana Hernández en anahdz@consultoriacarnegie.com.

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