MANUFACTURING HEAT TREAT TECH

Acero Descarburizado: Crítico para el Endurecimiento por inducción de Cuchillas Rotativas

/ ANNEALING TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

Para las operaciones de tratamiento térmico internas (in house), el objetivo principal es producir un producto confiable con un desempeño consistente en servicio. Sin embargo, la cadena de suministro y los procesos especializados pueden generar factores que comprometen la consistencia. En este artículo, Heat Treat Today destaca la importancia de contar con material base consistente para el tratamiento térmico por inducción interno de National Steel Rule, y cómo se puede implementar el proceso esencial de descarburización controlada en la planta proveedora de acero.

Este artículo informativo se publicó por primera vez en Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition. Traducido por Ana Laura Hernández Sustaita.

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

To read this article in English, click here.

Introducción: Regla de Acero que se Dobla

La empresa National Steel Rule produce reglas de corte rotativas para la industria del cartón corrugado. Ubicada en Linden, Nueva Jersey, la empresa suministra productos a las industrias de troquelado a nivel mundial. La compañía ha establecido altos estándares de abastecimiento, investigación y pruebas de material para sus reglas de corte, además de contar con un completo laboratorio con equipos de troquelado rotativo y plano.

Su regla de acero se adquiere de una planta proveedora de acero que realiza una descarburización controlada en todo el material. Cuando National recibe el material, procesa el acero para generar los dientes, empleando endurecimiento por inducción como parte del proceso (ver la imagen principal al inicio de este artículo). La regla de corte terminada se vende posteriormente a fabricantes de troqueles de regla de acero, quienes montan estas cuchillas junto con una goma de expulsión sobre tableros de madera cortados con láser. El fabricante debe asegurarse de que las cuchillas de las reglas estén libres de defectos, ya que incluso grietas microscópicas se abrirán durante el troquelado.


Figura 1. Regla de acero doblada de diámetro pequeño | Crédito de la imagen: National Steel Rule

Las cuchillas rotativas y otros productos de National dependen de la compra de acero descarburizado. “La flexibilidad y la conformabilidad son fundamentales”, afirma Ed Mucci, presidente de la empresa, y Alexander Heucke, ingeniero en jefe. La regla de corte debe doblarse para formar una cuchilla circular; durante el servicio, la cuchilla rota para cortar el material corrugado. La geometría de la curvatura puede ser extrema, llegando a doblarse hasta un diámetro interior de 7 pulgadas. Por lo tanto, la compra de acero descarburizado es crítica para el negocio del fabricante. Actualmente, National obtiene el material a nivel internacional. Mucci explica: “Los fabricantes no utilizan grandes cantidades de acero descarburizado, lo que dificulta su abastecimiento, al menos a nivel nacional”.

El material para las reglas rotativas suele ser acero al carbono C36 (SAE 1036) a C50 (SAE 1050) con un rango de dureza de 32–34 HRC. Mucci y Heucke señalan que el acero que utilizan presenta una capa de descarburización total de 0.0005” de profundidad, con una descarburización parcial adicional de al menos 0.0005”–0.00075”. Esto garantiza que cuando una regla se dobla, la superficie se elongue en lugar de agrietarse. Doblar la regla es, en sí mismo, una prueba para comprobar si se ha descarburado correctamente, y las pruebas metalúrgicas sirven como verificación de control de calidad para garantizar que los proveedores estén produciendo los niveles adecuados de descarburización.

Endurecimiento Preciso por Inducción de los Dientes

Si bien el doblado es esencial para formar la curvatura apropiada, los dientes deben ser resistentes al desgaste y la rotura. La regla de corte rotativa de National tiene una expectativa de desempeño de al menos 750,000 impresiones en papel, que es en sí mismo un material altamente abrasivo. Para lograrlo, las operaciones de tratamiento térmico internas endurecen por inducción el borde de la regla, garantizando una larga vida útil del troquel.

Existen dos métodos usados para endurecer los dientes. El método principal es maquinar el perfil de la tira de acero y posteriormente endurecer por inducción el borde. Posteriormente los dientes son rectificados. “Esto nos da un mejor control sobre la profundidad de endurecimiento”, comenta Mucci y Heuke. El segundo método consiste en endurecer por inducción después de rectificar los dientes. “Debemos asegurarnos de que el endurecimiento de los dientes no sea muy profundo, ya que esto puede afectar la capacidad de doblado”. El endurecimiento por inducción implica ciclos muy cortos, y por lo tanto requiere un control minucioso del proceso para garantizar resultados consistentes. Entre los métodos de control del proceso se utilizan crayones indicadores de temperatura, que se funden a una temperatura específica. También se realizan pruebas de dureza.


Figura 2. Detalle de la capa descarburizada | Crédito de la imagen: National Steel Rule

Revisitando la Descarburización

“Generalmente se intenta prevenir la descarburización o incluso agregar carbono a la superficie”, comenta Mark Hemsath, consultor ejecutivo en WINGENS CONSULTANTS y reconocido experto e innovador en la industria del tratamiento térmico. “La descarburización a menudo ocurre accidentalmente en sistemas de recocido mal diseñados, especialmente en hornos de tratamiento continuo.”


Figura 3. Diagrama de Ellingham que muestra la relación hidrógeno-vapor de agua, clave para una descarburización controlada exitosa.

Figura 4. Horno típico de recocido tipo campana. | Crédito de la imagen: RAD-CON

El oxígeno en forma de aire o de vapor es la clave del proceso de descarburización. Menor porcentaje de carbono en la superficie indica un acero más blando y maleable, y si bien el arte de un proceso de descarburización controlada es bien conocido, puede resultar un desafío. El proceso de descarburización suele realizarse por debajo de 1500°F (815°C). “El método preferido es usar vapor de agua o vapor como fuente de oxígeno”, señala Hemsath. Esto se basa en la estabilidad de la relación hidrógeno-vapor de agua (H2/H2O) derivada del diagrama de Ellingham. Estas relaciones H2/H2O indican las propiedades no oxidantes de la mezcla gaseosa, lo que permite que actúe como agente reductor de carbono en la atmósfera del horno. La mayoría de las empresas fabricantes de hornos pueden proporcionar el equipo necesario y personalizar las dimensiones para hacerlos adecuados para este proceso especial. Estos hornos suelen ser de tipo campana o tipo foso con retorta.

Dos Métodos para Controlar la Descarburización

Existen dos formas de realizar intencionalmente un proceso de descarburización. La primera consiste en descarburar todo el producto. En este método, la descarburización se aplica de manera uniforme en toda la superficie de la lámina o bobina. “Este acero laminado en frío generalmente con menor contenido de carbono, se utiliza en electrodomésticos que requieren una buena adherencia del esmalte”, explica Hemsath. Empresas como U.S. Steel y AK Steel (ahora parte de Cleveland-Cliffs) han utilizado esta forma de descarburización controlada.

Otra forma es la descarburización selectiva en la superficie. Hemsath explica: “Si la descarburización solo se requiere en los bordes, se podrían mantener las bobinas enrolladas firmemente, por lo tanto, la descarburización afectaría principalmente a los bordes. Se produciría una pérdida de carbono que disminuiría hacia el centro de las superficies enrolladas”.

Conclusión

“El acero descarburizado tiene mucha demanda, ya que la mayoría de las industrias buscan endurecer y templar los aceros que utilizan”, indica Mucci. De hecho, la prevención de la descarburización del acero es más común y suele destacar en ferias industriales, presentaciones técnicas y publicaciones de procesamiento térmico. Sin embargo, existen productos que dependen de la descarburización intencional para funcionar correctamente.

La descarburización controlada en la planta proveedora de acero presenta desafíos, en parte porque lograr una descarburización exitosa y consistente no suele ser económicamente viable para el mercado norteamericano de tratamiento térmico. Estos desafíos abarcan problemas de acceso regional, acceso a nichos de mercado, necesidades de selección de equipos y ejecución de procesos técnicos.

La experiencia de National destaca los desafíos que enfrentan las plantas proveedoras de acero de América del Norte para proveer a las empresas de tratamiento térmico interno, acero descarburizado de forma fiable y bien controlada que mantenga su vida útil.


Agradecimientos: Heat Treat Today agradece a Dan Herring, The Heat Treat Doctor®, The HERRING GROUP, Inc., quien fue fundamental en el desarrollo de este artículo.


Para más información: Contacte con Heat Treat Today’s Editorial Team en editor@heattreattoday.com.

La imagen principal: Regla rotativa RP8 con borde endurecido | Crédito de la imagen: National Steel Rule

Acero Descarburizado: Crítico para el Endurecimiento por inducción de Cuchillas Rotativas Read More »

Decarburized Steel Critical for Induction Hardening Rotary Blades

/ ANNEALING TECHNICAL CONTENT, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

For in-house heat treat operations, the number one goal is to produce a reliable product with consistent in-service performance. Yet supply chain and specialized processes can cause consistency stressors. In this article, Heat Treat Today underlines the importance of consistent feedstock for in-house induction heat treater, National Steel Rule, and how the essential mill process of controlled decarburization can be actualized.

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

If you have any comments or queries, on this article, let us know at editor@heattreattoday.com.

Para leer el artículo en español, haga clic aquí.

Introduction: Steel Rule that Bends

National Steel Rule manufactures rotary cutting rule for the corrugated box industry. Located in Linden, New Jersey, the company supplies products to the die making and die cutting industries globally. They have established a high standard of sourcing, researching, and testing material for their rule, in addition to a complete testing laboratory with both rotary and flat die cutting equipment.

Their steel rule is purchased from a mill that performs a controlled decarburization on the entire feedstock. When National receives the steel feedstock, they work the steel to create teeth, employing induction hardening as part of the process. The finished cutting rule is then sold to steel rule die makers who mount these blades and an ejection rubber on laser cut wooden boards. The manufacturer must ensure their rule blades are sound, as even microscopic cracks will open during the die cutting process.

Figure 1. Small diameter bent rule | Image Credit: National Steel Rule

National’s rotary blades and other products rely on purchasing decarburized steel. “Flexibility and formability are paramount,” states Ed Mucci, president of the company, and Alexander Heucke, chief engineer. Cutting rule must be bent to form a circular blade; in service, that blade rotates to cut into the corrugated material. The curve geometry can be extreme, often bending up to a 7-inch interior diameter. As such, the purchase of decarburized steel is critical for the manufacturer’s business. At present, National sources the material internationally. Mucci explains, “Manufacturers aren’t using large quantities of decarburized steel, making it challenging to source, at least domestically.”

Rotary rule feedstock typically involves C36 (SAE 1036) to C50 (SAE 1050) carbon steel with a hardness range of 32–34 HRC. Mucci and Heucke note that their steel of choice has a total decarburization layer to a depth of 0.0005” depth, with partial decarburization of at least another 0.0005–0.00075”. This ensures that when the rule is bent, the surface stretches versus cracks. Bending the rule is itself a test of whether it has been properly decarburized, with metallurgical testing serving as a quality control verification that suppliers are producing the appropriate decarburization levels.

Precise Induction Hardening Teeth

While bending is essential to forming the appropriate curve, the teeth must be resistant to wear and breakage. National’s rotary cutting rule has performance expectations of at least 750,000 impressions on paper, itself a highly abrasive material. To do this, their in-house heat treat operations induction harden the edge of the rule to ensure a long die life.

There are two methods used to harden the teeth. The primary method is to shave a profile into the strip steel and then induction harden this edge. Serrated teeth are then ground in. “This gives us better control of hardening depth,” according to Mucci and Heuke. The second method is to induction harden after the serrated teeth are ground in. “We have to make sure we don’t harden the teeth too deeply, or we can affect the bendability.”

Induction hardening involves short cycles, and as such requires careful process control to guarantee consistent results; temperature-indicating crayons that melt at a specific temperature are used as one of the process control methods. Hardness testing is performed as well.

Screenshot

Decarburization Revisited

“Usually, one tries to prevent decarburization or even add carbon,” states Mark Hemsath, executive consultant at WINGENS CONSULTANTS and longtime expert and innovator in the thermal processing industry. “Decarb often occurs by accident in poorly designed annealing systems, especially in continuous-type furnaces.”

Figure 3. Ellingham Diagram depicting that hydrogen-to-water vapor relationship, the key to a successful, controlled decarburization.
Figure 4. Typical bell-annealing furnace | Image Credit: RAD-CON

Oxygen, in the form of air or water vapor, is key to the decarburizing process. Less carbon on the surface means a softer, more malleable steel, and while the art of a controlled decarburization process is well known, it can be challenging. Decarburization is a process usually performed below 1500°F. “The preferred method is to use water vapor or steam as a source of the oxygen,” notes Hemsath, pointing to the stability of hydrogen-to-water vapor (H₂/H₂O ratio) derived from the Ellingham diagram. These H₂/H₂O ratios indicate the non-oxidizing qualities of the gaseous mixture, which will allow it to be the carbon reducing agent in the atmosphere. Most furnace companies can provide the necessary equipment and customize size specifications to make it suitable for this special process, and these furnaces are typically retort-based bell or pit type.

Two Methods to Control the Decarb

There are two ways that a decarburization process can be intentionally completed. The first is decarburizing the entire product. In this method, even decarburization is applied to the entire coil sheet surface. “This cold rolled steel, typically with lower carbon, is used for appliances that need enamel adhesion,” Hemsath explained, noting U.S. Steel and AK Steel, now a part of Cleveland-Cliffs, have used this form of controlled decarburization.

Another form of decarburization is selective surface decarburization. Hemsath shared, “If selective decarburizing is required only on the edges, then you could keep the coils tightly wound and the decarburization would affect mainly the coil edges. There would be ingress of carbon loss, reducing towards the center of the wound coil surfaces.”

Conclusion

“Decarburized steel just isn’t in high demand,” according to Mucci, as “most industries are looking to harden and temper the steels they use.” In fact, preventative steel decarburization is more typical and often emphasized in trade shows, technical presentations, and in thermal processing publications. Yet there are products that rely on intentional decarburization to be successful.

Controlled decarburization at the mill brings challenges, in part because successful, consistent decarburization is not often cost effective for the North American thermal processing market. These challenges encompass regional access issues, niche market access, equipment selection needs, and technical process execution.

National’s experience underlines the challenges North American mills face in providing local, in-house heat treaters with reliably, well-controlled decarburized steel that will maintain service life.

Acknowledgements: Heat Treat Todayextends thanks to Dan Herring, The Heat Treat Doctor® at The HERRING GROUP, Inc., who was instrumental in the development of this article.

For more information: Contact Heat Treat Today’s Editorial Team at editor@heattreattoday.com.

Main image: RP8 rotary rule edge hardened | Image Credit: National Steel Rule

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Consider Carbon Footprint in Material Selection Strategy

/ CONTROLS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

When carbon-footprint assessment happens during material selection for CAE simulations and product design, the result is more informed and sustainable decisions. In this Technical Tuesday installment, Mariagrazia Vottari, chief technical officer at Total Materia AG, shows how informed material choices can identify lower-impact alternatives without compromising structural, mechanical, or physical requirements.

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

Introduction

Governments and industries worldwide are setting increasingly ambitious targets to reduce greenhouse gas (GHG) emissions and strengthen environmental responsibility across supply chains. New sustainability frameworks, mandatory reporting requirements, and carbon-pricing mechanisms are accelerating the shift toward low-carbon production, including stricter expectations for transparent environmental data and lifecycle assessments.

Consequently, global supply chains must adapt quickly, integrating sustainability considerations from the earliest stages of product design through manufacturing, distribution, and end-of-life management. Environmental performance, traceability, and responsible material selection are becoming essential elements of modern engineering and product-development strategies.

Materials themselves represent a major share of global GHG emissions, increasing from 5 to 11 global net anthropogenic GHG emissions (GtCO₂-eq) between 1995 and 2015, and rising from 15% to 23% of global totals. For most products, materials dominate the carbon footprint until manufacturing is complete.

Accurate material selection in early product design and CAE (computer aided engineering) simulations is critical. Beyond traditional factors, such as mechanical performance and cost, engineers must now consider carbon footprint, environmental impact, lightweighting, regulatory compliance, and supply chain optimization to reduce overall emissions.

Therefore, sustainable product design will incorporate Life Cycle Assessment (LCA) of materials using selected indicator(s) providing environmental impact to materials selection. For example, in the automotive industry, ranking (c) is often calculated as c = 0.4 × mass + 0.2 × cost + 0.4 × CF.

Other more complex decision-making models for materials selection have been proposed. This exemplifies the need for reliable and simplified calculation of carbon footprint (CF) value for thousands of diversified structural materials, from carbon and stainless steel to special alloys, nonferrous metals, and polymers, considering their manufacturing routes, processing, finish, and transport. A full LCA study is demanding in terms of both data collection efforts and user expertise requirements, while streamlined LCA often uses generic data related to the materials production, energy used for their processing, and transportation. Typically, streamlined LCA uses only a fraction of the inputs to estimate carbon footprint compared to the full LCA inventory. This article presents recent developments designed to help engineers in the CAE simulation field to cope with these challenges.

Streamlined LCA Methodology

Figure 1. LCIA assessment approach | Image Credit: Total Materia

There are numerous simplification approaches in LCA; the following describes the approach that combines the composition of alloys with carbon footprint values of base metal and alloying elements production. The LCA tool described in the current study (Figure 1) can cover a variety of ferrous and non-ferrous alloys due to the use of:

  • Chemical compositions from a large database containing structural material properties, which comprises more than 500,000 materials; and
  • Country, manufacturing route, processing, and transport-specific life cycle inventory (LCI) collected from Ecoinvent v3.10, along with relevant data from scientific articles.

Goal, Scope, Functional Unit and System Boundaries

The aim of this LCA is to quantify the impact of steel and various non-ferrous alloys (Al, Cu, Mg, Ni, and Ti based) according to ISO 14040 standards, analyzing the influence of the composition on the carbon footprint.

The functional unit has been defined as 1 kg of produced material, considering the country of manufacturing and processing as well as transport to the buyer’s gate.

The scope of this study is to estimate the environmental impact of the production and the transport of materials (cradle to gate), accounting for raw materials extraction, manufacturing, and processing.

Inventory Data and Impact Category

Ecoinvent’s Life Cycle Inventory Assessment (LCIA) datasets were used where possible, including:

  • Base metals
  • Alloying elements, utilized in the manufacturing calculation through chemical composition weighting
  • Processing, quantified in kg CO₂-eq per kg of material, per kg of removed material, or per m², varying with the type of processing
  • The energy mix, allowing country-specific calculation
  • Transport, covering a wide range of routes

Calculations are based on the cut-off system model, the IPCC 2021 no LT LCIA method, and the climate change Global Warming Potential (GWP100) indicator.

Additional sources were used from scientific literature for data not available in Ecoinvent. The calculation scope expanded with:

  • Scrap content adjustment manufacturing contributions from various countries/regions
  • Contributions from different manufacturing routes
  • Various processes in different countries/regions

For intensive electricity-consuming processes, such as hot rolling, cold rolling, and stamping, electricity consumption data (measured in MJ/kg or kWh/kg) has been collected. This data, combined with the energy mix information from Ecoinvent, contributes to the final calculation.

Figure 2. System boundaries | Image Credit: Total Materia

The final CO₂-eq score is the cumulative sum of contributions from material production (manufacturing), processing, and transport as shown in Figure 2, illustrating the system boundaries considered in the study.

Analysis CF Results

In this work, six different alloys that are commonly used have been selected for the carbon footprint analysis. The chemical composition of alloys is defined by specific standard, while details on studied alloys production are presented in Figure 3.

Figure 3. Result of CF calculation for selected alloys | Image Credit: Total Materia

After specifying details on manufacturing (country, method, and recycled content), processing (country and processing applied), and transport (type and distance), the values of carbon footprint are determined for each alloy (Figure 3), providing the contribution of each stage of analysis.

The lowest environmental impact of all studied alloys was steel 1.4301 with a value of 2.5 kg CO₂-eq/kg. This is because a manufacturing route for the 1.4301 alloy was EAF (electric arc furnace) with 100% recycled content, where electricity is used to melt scrap steel and produce new steel, in contrast to BF-BOF (blast furnace-basic oxygen furnace) where extraction of iron ore is needed and relies heavily on coal or coke as a fuel source for the blast furnace, which emits significant amounts of CO₂ during combustion. Although numerous factors or variables play a role in determining the environmental impacts of metal production, one of the most significant parameters is recycled content.

Titanium alloy has the highest environmental impact of all studied alloys, emitting up to 47.3 kg CO₂-eq/kg of material. Ti-6Al-4V alloy was selected for this study even though it is very expensive and has a high energy consumption of production in the long and demanding Kroll process, because it is one of the most popular joint implant materials due to its biocompatibility, low density, and strength.

Although Al, Cu, and Fe-Ni-based alloys have similar CF values (4.7 to 8 kg CO₂-eq/kg), in the case of aluminum and copper alloys, the most significant contribution comes from the processing of those alloys (52 to 68%), unlike Incoloy in which processing contributes a modest 0.72%. The CF value for Incoloy 800 is three times greater than 1.4301 alloy. The high environmental impact of Incoloy 800 is mainly caused by nickel content (max. 10% in 1.4301 alloy, while max. 35% in Incoloy 800) and very high carbon footprint values for nickel itself. This is proof of why chemical composition cannot be neglected.

The effect of transportation is very small, only contributing up to 3.6% for selected transport parameters. However, it can have much higher relative contribution for low-impact alloys, especially over long distances. In Figure 4, the effect of different transport types shows that the selection of air transport can double the carbon footprint value of the material compared to sea transport (for the same manufacturing and processing parameters).

Figure 4. Effect of different transport types | Image Credit: Total Materia
Figure 5. Detailed contribution analysis for 1.4301 steel | Image Credit: Total Materia

Further contribution analysis can be made for each alloy given the detailed contribution for manufacturing and each processing step, as well as transportation type, as shown in Figure 5 for the 1.4301 steel. Results show that deep drawing increases carbon footprint with a factor of 5 in comparison with hot rolling. This suggests that such processes should be performed on locations having energy supplied from renewable sources.

Material Selection, Looking for a Greener Alternative

Besides identifying more environmentally sustainable manufacturing processes such as alternative production routes, higher scrap content, different locations, processing with lower energy demand, and greener transportation options, another approach to reducing the carbon footprint is to identify alternative materials with different chemical compositions but similar mechanical and physical properties.

Although the selection of alternative materials must consider various factors related to the availability, supply chain, etc., from the environmental point of view, the decision can be facilitated by using a proper cross-reference system that simultaneously suggests alternatives based on various criteria. There are two scenarios for material selection:

  1. In the early design phase when the material is still not selected and when certain mechanical, physical, compliance and sustainability requirements should be fulfilled.
  2. When a certain material already in use should be replaced with a greener alternative but maintain the same characteristics.

In the first case, material-selection tools like the Total Materia Optimizer can be used to support engineers in comparing and ranking materials based on multiple technical and regulatory criteria. This tool can evaluate thousands of potential candidates simultaneously and filter them according to user-defined parameters, such as mechanical performance, chemical composition, cost, regulatory status, or regional availability as shown in Figure 6.

Figure 6. Results of multicriteria search | Image Credit: Total Materia
Figure 7. Alternatives to 1.4301 steel based on cross references | Image Credit: Total Materia

In the second case, when the material is already in use, finding an alternative material with a lower CF value is possible in a material-selection tool’s carbon footprint module through the cross-reference option. The system offers alternatives based on various criteria. As an example for this case, 1.4301 alloy is used with all set-up parameters from Figures 4 and 6 (with CF value of 2.528 kg CO₂-eq/kg). The analysis shown in Figure 7 suggests 921 alternative materials ordered by CF value in ascending order. In this view, a user can add additional columns with mechanical and physical properties to ensure that the material also fulfills the required characteristics. In this example, material NSSC 2120 meets the required mechanical and physical criteria, and the CF value is reduced from 2.5 to 2.2 kg CO₂-eq/kg (which is a reduction of 12%) compared to the initially selected material 1.4301.

Conclusions

This approach for assessing the environmental impact of ferrous and non-ferrous alloys based on material composition and processing routes has been illustrated through a carbon footprint evaluation. It enables engineers to compare materials not only by cost and performance but also by their carbon intensity, supporting more informed and sustainable selection decisions. The method also helps identify greener manufacturing options, such as alternative routes, higher recycled content, lower-energy processing, or reduced-impact transport, early in product design while maintaining quality and performance.

Future improvements include expanding datasets to cover additional processing steps, incorporating more specific manufacturing routes — especially for non-ferrous alloys — and increasing regional coverage to reflect local energy mixes. These enhancements will further refine emission factors and improve the accuracy of carbon-footprint assessments.

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Nilsson, A. E., M. M. Aragonés, F. A. Torralvo, V. Dunon, H. Angel, K. Komnitsas, and K. Willquist. 2017. “A Review of the Carbon Footprint of Cu and Zn Production from Primary and Secondary Sources.” Minerals 7: 168.

About The Author:

Mariagrazia Vottari
Chief Technical Officer
Total Materia AG

Mariagrazia Vottari is the chief technical officer at Total Materia AG, leading the Engineering Department and overseeing data content development and material intelligence initiatives. She has a background in mechanical engineering and nearly 20 years of experience in the industry, with a strong focus on materials engineering, data processing, and digital solutions for the manufacturing industry.

For more information: Contact Mariagrazia Vottari at m.vottari@totalmateria.com.

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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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Answers in the Atmosphere: Hydrogen Part 1 — Powerful Reducing Properties, High Thermal Conductivity

/ ATMOSPHERE GENERATORS TECHNICAL CONTENT, BULK GASES & SYSTEMS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, OP-ED, SINTERING POWDER/METAL TECHNICAL CONTENT

In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, examines the powerful reducing properties and high thermal conductivity that make hydrogen a critical atmosphere in metal thermal processing.

This informative piece on hydrogen’s role in sintering, annealing, and surface protection — including how it is sourced, how it behaves inside the furnace, and how operations can safely manage this flammable atmosphere under NFPA 86 — was first released in Heat Treat Today’s April 2026 Annual Induction Heating & Melting print edition.

Hydrogen is widely used in metal thermal processing for sintering of powdered metal fabrication technologies and for heat treatment (e.g., annealing, brazing) of bulk metal manufactured components. This column draws heavily from an interview the author had with Stephen Feldbauer Ph.D., director of Research & Development at Abbott Furnace. Abbott Furnace is a leading furnace manufacturer for continuous furnaces and furnace controls. As R&D Director, Steve leads Abbott’s work in pioneering furnace advances with a special focus on debinding and sintering.

Why Hydrogen?

Stephen Feldbauer, PhD
Director of Research & Development
Abbott Furnace

Hydrogen provides two desirable characteristics to heat treaters: very high chemical reducing potential and the highest thermal conductivity of any gas. The high reducing potential enables hydrogen to convert heated metal oxide coatings to pure metals. This is extremely helpful for successful sintering of powder metallurgical parts. Superior thermal conductivity enables rapid part heat up and cool down. Compared with either vacuum or inert gas atmospheres, hydrogen enables much faster throughput and achieves shorter furnace cycles.

Hydrogen-containing atmospheres are required to successfully sinter most iron-based metal parts, whether manufactured by powder metallurgy (PM), metal injection molding (MIM), or binder-jet metal additive manufacturing techniques. As-received, the iron-containing metal powders used for these advanced fabrication techniques are covered with an iron-oxide coating, making it virtually impossible to successfully sinter the particles together under reasonable temperature conditions. Reducing the oxide coating enables successful sintering.

Hydrogen-based atmospheres used with a tube or strand furnace are the primary surface protective technology used for drawn components (e.g., wire, tubing, and profiles). Hydrogen simultaneously protects the part surface from oxidation and allows metal to anneal, which softens it and restores toughness after it has been hardened by the drawing process.

Sourcing Hydrogen

Because of its high reactivity, hydrogen is almost never found in nature as a pure gas (H2). Instead, it is generally found as a component in a compound like water (H2O) or a hydrocarbon gas or liquid, such as methane (CH4), propane (C3H8), or longer hydrocarbon. In order to be used as a thermal processing atmosphere, hydrogen is liberated from these hydrogen-containing compounds to exist as a pure gas while in use in the hot furnace.

The liberation of elemental hydrogen from its compound carrier can happen at a remote plant operated by an industrial gas company provider, in which case the hydrogen would be compressed or liquified for delivery to the thermal treatment client, or may be conducted at the site of the thermal processor themselves through use of on-site generation equipment. User choices of approaches to pure hydrogen supply will be covered in future columns.

Inside the Furnace

Inside the hot furnace, hydrogen changes metal oxide coatings to pure metals by preferentially reacting with the metal oxides to produce pure metal and water vapor. Thus, the furnace atmosphere dewpoint (a measure of gaseous water content) will increase as the hydrogen simultaneously creates pure metal surfaces and produces water vapor as a byproduct. The water vapor is swept out of the furnace and replaced by the clean furnace atmosphere that flows counter current to the heated metal product. Furnace atmosphere controls for hydrogen-based atmospheres use dewpoint as a key operating parameter.

Hydrogen’s ability to protect the part surface from oxidation is critical in the annealing process. | Image Credit: Abbott Furnace

Since furnaces must open to admit parts for thermal processing, the furnace, the atmosphere system, and the procedures must all be designed to prevent unsafe conditions caused by hydrogen leaking out of the furnace, or air leaking in. Furnaces intended for a flammable gas atmosphere use doors, curtains, and pilot lights (i.e., flame curtains) to prevent hydrogen or other flammable gas from leaving the furnace without being combusted. These precautions avoid explosions inside or outside the furnace.

Furnaces for hydrogen-containing atmospheres utilize unique design and construction approaches to safely use this flammable atmosphere. In the U.S., furnace design and operation is guided by NFPA 86, the furnace code. NFPA 86 defines certain furnace design features and also defines standard operating techniques for safe operation with a combustible atmosphere, such as a hydrogen-containing atmosphere. Similar codes and standards are used in other countries.

Next month, this column will pick up the question of cost by looking at options for generation of hydrogen atmosphere blends. Generation of pure hydrogen will be a future topic.

About The Author:

David (Dave) Wolff
Industrial Gas Professional
Wolff Engineering

Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.

For more information: Contact Dave Wolff at Wolff-eng@icloud.com.

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Robotic Material Handling in Heat Treatment

/ CARBURIZING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, VACUUM FURNACES TECHNICAL CONTENT

Manual loading and batch transfers are giving way to robotic material handling in modern heat treat operations. In this Technical Tuesday installment, Dennis Beauchesne, general manager of ECM USA, examines how automation improves repeatability, boosts productivity, and reduces operator exposure to hazardous conditions near furnace hot zones — and how robotics, vision systems, and mobile transport technologies are helping heat treat facilities build safer and more efficient production environments.

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

Robotic material handling is rapidly transforming modern heat treat operations traditionally dependent on manual loading and batch transfer. As heat treaters face increased pressure to improve throughput and working conditions while maintaining strict quality standards, automation has become a strategic investment.

Figure 1. SEW-EURODRIVE (Lyman, SC) robotic integration by ECM Robotics features a rear robot and pallets on the left and open area on the right for dunnage storage and management | Image Credit: ECM USA

Heat treat material handling is more than simple part movement. Parts must first be positioned onto fixtures or loaded into bins which are transferred, placed into the furnace, and then moved again for quenching and/or tempering — sometimes under undesirable conditions depending on the installed technology. Additionally, a robot needs to store dunnage in the designated robot area during the processing of the parts in the furnace and then reuse it when the parts are unloaded from the furnace. Dunnage can also be stored in the heat treat area and handled by automation (Figure 1). Robotics and automation promote efficiency and repeatability in this process, which is difficult to achieve with manual operations.

Robotic Advantages

The most significant advantages of robotic material handling are repeatability, consistency, and reduction of work force. Robots execute the same motions cycle after cycle, which ensures uniform loading and proper spacing between parts within fixtures or baskets. For example, in vacuum furnaces, correct part placement is essential to achieving even heat distribution and minimizing distortion. Automated loading eliminates error caused by human fatigue or procedure changes, leading to more consistent and desirable metallurgical results and reduced scrap/re-work.

Improved throughput and increased productivity are other major justifications for robotic integration. Heat treatment can hold-up manufacturing due to cycle times and variable material flow. Robotic systems streamline loading and unloading, reduce wait time between cycles, and allow furnaces to operate at optimal capacity. In high-volume environments, robotics can be managed with upstream machining and downstream finishing processes to create a continuous, automated production line. This level of integration shortens lead times and supports just-in-time manufacturing.

Safety is equally if not more important, as handling baskets or fixtures near hot zones increases operator risk of burns and injuries. Integrating robotics improves workplace safety by removing operators from direct exposure to these hazards. This solution also addresses labor shortages by allowing skilled personnel to focus more on process optimization and quality control rather than repetitive physical tasks.

Specifically in vacuum heat treatment, robotic systems are particularly beneficial. Vacuum furnaces require precise loading to maintain thermal uniformity and protect sensitive components. Automated loaders can transfer loads between heating chambers, quench cells, and temper furnaces in a continuous process flow that minimizes temperature loss and handling delays. Metallurgical results (e.g., hardness, case depth, distortion) are also directly influenced. This is especially helpful for critical and sensitive applications, such as aerospace components and medical devices.

Robotic Components Explained

For manufacturers with in-house heat treat or commercial shops processing multiple part types, the flexibility to program and handle a wide range of part geometries, weights, and batch sizes is vital for efficient operations. Quick-change grippers, adaptive tooling, mobile transport, and vision systems are key robotic components to achieve this goal (Figure 2). Vision systems of today are far more advanced in assisting with the programming phase than those from just a few years ago.

Figure 2. ECM Robotics manipulating parts | Image Credit: ECM USA
Figure 3. AGV (automated guided vehicle), a portable robot that follows a path, delineated physically (e.g. lines on the floor) or through other guide posts (e.g. radio waves, magnets, lasers) | Image Credit: ECM USA

After the load building, automated mobile robots (AMR) or automated guided vehicles (AGV) can also be used to transport loads to and from the furnace. These mobile robots are integrated into factories to automate the transport of loads between different areas without requiring fixed infrastructure (rails or magnetic strips). This system coexists easily with operators and other equipment and adapts well to production floor changes. Integration of AMRs and AGVs frees up operators for more value-added tasks and reduces manual labor time (Figure 3).

Quick-change grippers or end effectors are tailored to the specific application and conditions when in use. Their design focuses on optimizing part clamping, friction, and contact while considering part geometry, cycle constraints, and precision requirements. Gripping technologies are available as pneumatic, electric, magnetic, or vacuum and can handle even the most delicate or fragile components in soft (flimsy) or hard state. Heat treat specific robotics companies, like ECM Robotics, also provide robotic machine vision systems. Integration of these vision systems improves precision and handling to optimize pick & place, palletizing, bulk unloading, and assembly.

For example, by identifying parts based on the diameter or number of teeth on the gear, these systems can then sort and track them within a heat treatment cell through part marking, tray/fixture encoding (QR codes), and weight scenarios or simply virtually through software, which removes the need to use any hardware tracking. Vision systems go beyond the physical movement of parts; by checking for surface imperfections and integrity, they are advantageous for quality assurance purposes.

The most common issue in the heat treating industry when integrating with robots has been fixture warpage. Modern 3D cameras can detect bent or warped pins and alloy trays to allow for movement to a new position. This capability allows for much more robust loading and unloading using moderately warped fixturing, which is common in heat treat operations. While the best consistency typically comes with the use of carbon fiber composite (CFC) trays, it is not necessary to upgrade to all CFC fixtures to get consistent loading and unloading as the system can be designed to handle either alloy trays or CFC as well as some systems with both.

In a recent vacuum furnace installation, a heat treater automated their gear cutting operation to prepare the dunnage before low pressure carburizing. The robotics integration simplified part storage by specific location to allow the robot to “see” with its vision system. Parts were then scanned using QR coding by laser marking and automatically connected to the part’s recipe as stored in the system. Typically, in a modular system using low pressure carburizing, individual cells are utilized and production is recipe driven. In this case, after a part was scanned, the recipe was uploaded into the next available cell, and the scanned parts and heat treat fixture were moved to the cell.

Capital Investment

While the initial capital investment in robotics can be significant, long-term returns are quickly realized through process optimization, better working conditions, reduced re-work, higher up-time, improved quality, and reduced labor hours. Predictive maintenance features and diagnostic monitoring further reduce unscheduled downtime. As manufacturers evaluate total cost of ownership, robotic material handling often proves to be a strategic solution that supports both operational efficiency and competitive positioning.

Future Impact on the Industry

In an industry where precision, repeatability, and reliability are essential, robotic material handling is increasingly valuable for modernizing heat treatment operations. By combining automation with advanced furnace technology or upgrading material handling of older furnace equipment, manufacturers can achieve safer workplace conditions, higher metallurgical quality, and greater overall process efficiency.

Looking ahead, the role of robotics in heat treatment will continue to expand alongside industry trends. Data-driven automation, AI-assisted scheduling, and collaborative robots are opening new possibilities for smarter, more connected facilities. Rather than replacing human expertise, robotics complement it by providing process precision and efficiency to allow heat treat professionals to focus on process innovation and more value-added responsibilities.

References

International Federation of Robotics. 2023. World Robotics Report.

Beauchesne, D. 2025. Heat Treat Robotic Paradigm Shift. Heat Treat Today, January.

About The Author:

Dennis Beauchesne
General Manager
ECM USA

Dennis Beauchesne brings experience of over 200 vacuum carburizing cells installed on high pressure gas quenching and oil quenching installations. He has worked in the thermal transfer equipment supply industry for over 30 years, 24 of which have been with ECM USA where he is the General Manager.

For more information: Contact Dennis Beauchesne at DB@ECM-USA.com.

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Keeping the Burners in Tune

/ BURNERS & COMBUSTION SYSTEMS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH, OP-ED

Jim Roberts of U.S. Ignition engages readers in a Combustion Corner editorial about keeping industrial burners in tune — examining how everything from simple orifice plates to sophisticated burner control units (BCUs) and P-type radiant tubes drive efficiency and temperature uniformity in modern heat treating furnaces.

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

In part 2 of this series (Aerospace Heat Treating, March 2026), we talked about how balancing the pressure can save gas and reduce emissions. So, how do they do it?

Figure 1. ECOMAX® with eductor and burner control unit BCU | Image Credit: Honeywell

There are some fairly sophisticated and exacting control systems that can use flow meters that compensate and monitor pressure fluctuations. The air and gas valving will then react to inputs from the orifice meters and pressure monitors. Some systems may even extract a sample of the flue gas at the exhaust, much like the sensors on your automobile catalytic converter. The use of these burner control units (BCUs) keeps burners tuned to exacting performance. A lab setup example of that technique is shown in Figure 1.

Other setups are quite simple and perform at their best on the normal setting. In other words, if the process temperature is 1850°F, engineers design burners to perform optimally at that temperature and for thermal input to be achieved 90% of the time. In this scenario, orifice plates and control valves set for that optimum performance hold the combustion system steady at that input; variations are minimal.

The burners may not run perfectly when coming up to heat, but that is hopefully a short-term situation, and as the furnace comes up to heat the burner, systems settle into a desired tune range. Think of these as the dragsters at a racetrack. We’ve all seen how they shudder and quake while waiting to go flat out down the racetrack. But when gas is pushed into them, they blow fire, smooth out, and go to unbelievable performance levels. Only we furnace guys would make that comparison… or maybe just this guy.

It bears noting that recirculation patterns can take on many variations depending on the type of heat treating you may be doing. Direct fired systems for stress relieving and straight up hardening operations use a high velocity direct fired system (Figure 2). That is where the aforementioned eductor pulls the flue gases out of the furnace and over the heat exchanger. Recirculation takes place in front of the burner in a high velocity stream exiting the nozzle. A percentage of the chamber gases gets pulled into that flue stream.

Figure 2. ECOMAX® in direct heating
systems | Image Credit: Honeywell
Figure 3. Examples of the design and the flue gas flow pattern | Image Credit: Honeywell
Figure 4. Schematics of P-type and double P-types tubes | Image Credit: Honeywell

In the case of controlled atmosphere furnaces, where radiant tubes are utilized for the heating system, all sorts of different techniques exist. In the designs of recuperative recirculating style burners (i.e., FGR burners, flue gas recirculation), the tube designs are diverse and varied. Early designs of single ended tubes (SER) were the first to utilize recirculation designs (Figure 3).

Later, steel mills began to experiment and use P-type and double P-type tubes for strip annealing lines and galvanizing lines (Figure 4). You can see in these figures that the flue gases get pulled around, and we get the benefit of heat we have already generated and gas we have already burned. This creates a very good improvement in tube temperature uniformity and heat delivery. The arrows on the figures show the flow pattern of the gases.

So, in conclusion, there is no conclusion. Design improvements will continue to be made as long as we have requirements for efficient and emission-responsible operations in our heat treating plants and furnaces. Understanding that the world requires heat treating to be available for just about everything, and that we need to address those needs with ever-improving technologies… now THAT is pressure.

Till next time.

About The Author:

Jim Roberts
President
US Ignition

Jim Roberts president at U.S. Ignition, began his 45-year career in the burner and heat recovery industry focused on heat treating specifically in 1979. He worked for and helped start up WB Combustion in Hales Corners, Wisconsin. In 1985 he joined Eclipse Engineering in Rockford, IL, specializing in heat treating-related combustion equipment/burners. Inducted into the American Gas Association’s Hall of Flame for service in training gas company field managers, Jim is a former president of MTI and has contributed to countless seminars on fuel reduction and combustion-related practices.

For more information: Contact Jim Roberts at jim@usignition.com.

Keeping the Burners in Tune Read More »

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.

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

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.

Cómo domar a tu dragón Read More »

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 »