Nitriding Selection Guide: Gas, Plasma, or Salt Bath?

/ MANUFACTURING HEAT TREAT TECH, NITRIDING TECHNICAL CONTENT

Nitriding offers a unique combination of surface hardness, wear resistance, fatigue performance, and dimensional stability, making it a preferred thermochemical treatment for a wide range of industrial components. Readers will learn about the key benefits of nitriding, as well as the strengths and limitations of gas, plasma, and salt bath processes. In this Technical Tuesday installment, the aim of this guide by Daniel H. Herring, aka The Heat Treat Doctor®, and Dr. Edward Roliński, a senior scientist and recognized authority on plasma and ion nitriding, is to help engineers and heat treaters evaluate which nitriding technology best aligns with material requirements, case depth targets, and performance objectives.

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

Why Choose Nitriding?

Nitriding is a unique process that offers design engineers the ability to both predict and control the outcome of the heat treating process. The key advantage is that it significantly increases surface hardness, wear resistance, and fatigue life of component parts while minimizing dimensional change due to the low temperature nature of the process.

#1 Minimal Post-Processing

Nitriding can be used on a variety of component parts and metal forming tools made of steel or cast irons for applications in which wear, fatigue, or corrosion resistance is an important consideration. Steels, stainless steels, tool steels, powder metallurgy parts, and many other materials can be nitrided.

Table A. Recommended Ranges of Nitriding Potential (SAE International Aerospace Material Standard AMS 2759/10), latest revision
Notes:
1. Class 0: No white layer permitted on the surface of a nitrided part.
2. Class 1: 0.0127 mm (0.0005 inches) maximum white layer, 15% porosity or less.
3. Class 2: 0.0254 mm (0.001 inches) maximum white layer, 10%–50% porosity of the thickness of the white layer.

Dimensional change in nitriding is primarily governed by composition, tempering temperatures, time/temperature of nitriding, relative thickness of case/core, shape of the part, and areas masked off to prevent nitriding. The amount of growth is typically constant for identical parts nitrided in different batches by a fixed processing cycle. Most parts are nitrided in a two- or three-stage process and not ground after nitriding (Table A). This affords them excellent dimensional stability (Herring 2011). Once the amount of growth for a particular part has been established, allowances can be made during final machining (prior to nitriding) to ensure repeatable results.

By contrast, heat treating processes such as hardening or carburizing are performed at higher temperatures and result in dimensional and/or shape changes often requiring post-heat treat manufacturing steps (Roliński 2014). As such, the nitriding process has become an ever more popular choice.

#2 Case Depth Control

Nitriding as a thermochemical process is capable of producing a variety of case depths, an attribute affected by temperature, time, and nitriding potential (if there is not a compound zone formed). Caution should be used when stating a required case depth since a number of definitions for total case depth are in use. For this article, authors will use Table B to show how case depths are typically total case depths (core hardness + 50 HV0.5) that vary by material.

Table B. Typical Case Depths and Case Depth Ranges for Steels

For example, on an M2 tool steel, the case depth might vary between 25–100 µm (0.001”–0.004”). By contrast, 4140 or Nitralloy® can produce case depths in ranging from 100–500 µm (0.004–0.020”), with 305–380 µm (0.012–0.015”) being typical. For low/medium carbon steels and powder metal, white layer thickness may vary from 5µm–25 µm (0.0002”–0.001”) and is the overriding consideration.

#3 Enhancing Tribological Properties

Nitriding enhances various key tribological properties related to friction, wear resistance, lubrication interaction, and texture. These include improvement in sliding motion and reduced energy losses; wear characteristics involving resistance to adhesion, abrasion, fatigue, and corrosion; and lubrication, especially as it relates to load-carrying capacity, surface roughness, and surface texture/hardness.

#4 Nitriding Applications

The nitriding process can be used for surface hardening of both very small and very large parts (see lead image above and Figure 1). Typical examples are gears and shafts, stamping dies, piston rods, springs, pump housings, and welding tables. Dies are typically made of cast iron or tool steels, while gears and other powertrain components are made of alloy steels. All applications require precise control of the compound zone (i.e., white layer) thickness. If selective nitriding is required, areas are masked using a stop-off paint, or in plasma processes, mechanical masking is an option.

Figure 1. (a) A Bluco DD2040 modular welding table (double density hole pattern, 2m x 4m x 0.2m) after completion of gas nitriding heat treat cycle and post-processing; (b) A Bluco HD2040 modular welding table (high density hole pattern, 2m x 4m x 0.2m) being removed fro ma pit furnace following a gas nitriding heat treat cycle | Image Credit: Bluco
Figure 2. Typical nitrided surface appearance | Image Credit: Heat Treat Doctor®

Once finished, nitrided surfaces are typically smooth and grayish in appearance (Figure 2). If a “shiny” or “bright” surface or one of extremely low roughness is required, polishing methods can be used (e.g., superfinishing). The surface has high hardness, and is under residual compressive stress, which is critical in increasing bending fatigue and rolling contact fatigue (RCF) properties.

Gas, Plasma, Salt Bath

Table C. Comparison of Gas, Plasma/Ion, and Salt Bath Processes (Hemsath 2019)

There are three types of nitriding, each with their own strengths and limitations: gas, plasma/ion, and salt bath. Table C highlights these differences for immediate comparison. For a further breakdown of each process’s strengths, the authors have written unique articles exploring the three processes in greater depth, available on www.heattreattoday.com under each of the names:

Conclusion

Nitriding is a key technology to achieve heat treated results that modern manufacturing expects. But between gas, plasma, and salt bath, there are pros and cons to whichever method is chosen. Engineers need to assess what material needs and process outcomes are most significant to the outcome in order to select the right technology.

References

Boßlet, Jochim. n.d. Melonite®/QPQ Process Brochure. HEF Durferrit.

Hemsath, Mark K., and Daniel H. Herring. 2019. “Nitriding—Growth and Tribological Benefits for Surface Engineering.” In Heat Treating Progress 2019 Conference Proceedings. Materials Park, OH: ASM International.

Herring, Daniel H. 2011. “Principles of Gas Nitriding, Parts 1–4.” Industrial Heating, April–May.

Herring, Daniel H. 2013. “Masking Techniques, Part One.” Industrial Heating, April.

Herring, Daniel H. 2020. “An Overview of Nitriding—Technology and Tribological Benefits.” Industrial Heating, March.

Mittemeijer, Eric J., and Marcel A. J. Somers, eds. 2026. Thermochemical Surface Engineering of Steels. Elsevier.

Pye, David. 2003. Practical Nitriding and Ferritic Nitrocarburizing. Materials Park, OH: ASM International.

Resnick, Michael. n.d. “Private Correspondence.” HEF Durferrit USA. https://www.hefusa.net/salt_bath_nitriding_liquid_nitriding/overview.html

Roliński, E. 1987. “Effect of Plasma Nitriding Temperature on Surface Properties of Stainless Steel.” Surface Engineering 3: 35–40.

Roliński, E. 2004. “Ion Nitriding and Nitrocarburizing of Sintered PM Parts.” Industrial Heating, October: 33–35.

Roliński, E. 2005. “When and Why Ion Nitriding/Nitrocarburizing Makes Good Sense.” Industrial Heating, August: 67–72.

Roliński, E. 2005. “Negative Effects of Reactive Sputtering in Industrial Plasma Nitriding.” Journal of Materials Engineering and Performance 14 (3): 343–350.

Roliński, E. 2006. “Plasma Nitriding Automotive Stamping Dies.” Heat Treating Progress 6 (5): 19–23.

Roliński, E. 2014. “Plasma Assisted Nitriding and Nitrocarburizing of Steel and Other Ferrous Alloys.” In Thermochemical Surface Engineering of Steels, chap. 11, edited by E. J. Mittemeijer and M. A. J. Somers, 413–449. Cambridge, UK: Woodhead Publishing.

Roliński, Edward. 2024. “Practical Aspects of Sputtering and Its Role in Industrial Plasma Nitriding.” ASM Handbook Online Update, Vol. 5: Surface Engineering. Materials Park, OH: ASM International.

Roliński, E., J. Arner, and G. Sharp. 2005. “Negative Effects of Reactive Sputtering in Industrial Plasma Nitriding.” Journal of Materials Engineering and Performance 14 (3): 343–350.

Roliński, E., G. Sharp, and A. Konieczny. 2006. “Plasma Nitriding Automotive Stamping Dies.” Heat Treating Progress 6 (5): 19–23.

Roliński, E., and G. Sharp. 2004. “Ion Nitriding and Nitrocarburizing of Sintered PM Parts.” Industrial Heating, October: 33–35.

Roliński, E., and G. Sharp. 2005. “When and Why Ion Nitriding/Nitrocarburizing Makes Good Sense.” Industrial Heating, August: 67–72.

Roliński, E., and G. Sharp. 2017. “Controlling Plasma Nitriding.” Materials Performance and Characterization 6 (4): 698–716.

Roliński, E., J. Ludeman, J. McCain, V. Popovski, and M. Woods. 2021. “Nitriding Mechanisms of Ferrous Powder Metal Products in Gas, Salt, and Plasma Methods.” In Proceedings of PowderMet2021/AMPM2021/Tungsten2021, 330–337.

SAE International. n.d. AMS 2759/10 Aerospace Material Standard (latest revision).

Senatorski, J., J. Tacikowski, E. Roliński, and S. Lampman. 2017. “Tribology of Nitrided and Nitrocarburized Steels.” In ASM Handbook, Vol. 18: Friction, Lubrication, and Wear Technology, edited by George E. Totten, 638–652. Materials Park, OH: ASM International.

Spies, H. J., and A. Dalke. 2014. “Case Structure and Properties of Nitrided Steels.” In Comprehensive Materials Processing, edited by G. Krauss, Vol. 12, 439–488. Oxford, UK: Elsevier.

Winter, K. M., and J. Kalucki. 2013. “Gas Nitriding and Gas Nitrocarburizing of Steels.” In ASM Handbook, Vol. 4A: Steel Treating—Fundamentals and Processes, edited by Jon I. Dossett and George E. Totten, 647–679. Materials Park, OH: ASM International.

About The Authors

Dan Herring
(The Heat Treat Doctor®)
The HERRING GROUP, Inc.

Dan Herring, who is most well known as The Heat Treat Doctor®, has been in the industry for over 50 years. He spent the first 25 years in heat treating prior to launching his consulting business, The HERRING GROUP in 1995. His vast experience in the field includes materials science, engineering, metallurgy, equipment design, process and application specialist, and new product research. He is the author of six books and over 1000 technical articles.

Dr. Edward Rolinski, affectionately known as “Doctor Glow,” is a distinguished senior scientist having spearheaded research on plasma/ion nitriding since the 1970s. He holds advanced degrees in manufacturing technology and metallurgy, including a PhD and Doctor of Science. His focus has been on plasma nitriding processes, especially involving titanium alloys and powder metallurgy. Over his career, Dr. Rolinski authored numerous influential technical chapters and articles, including for ASTM International and the ASM Handbook, and is a prolific contributor to industry publications. After decades of leadership and innovation in surface engineering and heat treating, he is now a consultant in the heat treating industry. 

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

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The Jominy Rapid Quench, Part 2: Automotive Applications

/ AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, QUENCHING TECHNICAL CONTENT

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

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

Introduction

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

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

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

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

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

Intensive Quenching for Industrial/Automotive Parts

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

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

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

Automotive Designs Require Updated Tests

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

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

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

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

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

Overcoming Slow Automotive Adoption

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Acknowledgements

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

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

References

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

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

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

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

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

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

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

About The Author:

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

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

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

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

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Why Choose Salt Bath Nitriding?

/ MANUFACTURING HEAT TREAT TECH, NITRIDING TECHNICAL CONTENT

For applications requiring exceptional wear resistance, corrosion protection, and rapid processing, salt bath nitriding continues to be a reliable surface engineering solution. In this article, Daniel H. Herring, aka “The Heat Treat Doctor,” and Dr. Edward Rolinski, a senior scientist and recognized authority on plasma and ion nitriding, explain how salt bath nitriding can create a durable compound layer that helps parts last longer and perform better across a wide range of industrial applications.

If you’re looking for a broader introduction, watch for the upcoming print feature, “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” for an overview of nitriding, its key benefits, and a side-by-side of the three primary nitriding processes.

Salt bath nitriding, like gas nitriding, has been around for a very long time and is still in active use today. This method introduces nitrogen, and sometimes carbon, into the surface layer of steels, cast iron, and sintered powder metal by immersing the part in a molten salt bath containing nitrogen-bearing salts at elevated temperatures. The process enhances wear resistance, fatigue strength, corrosion resistance, and surface hardness without significantly affecting the core mechanical properties of the base material.

Salt bath nitriding has ability to form a thick compound zone up to 0.025 mm (0.001 inches). The process can enhance the corrosion resistance of steels, particularly when combined with post-oxidation. Also, salt bath nitriding is an excellent way to improve tribological properties of the treated components (“Melonite®/QPQ Process,” HEF USA).

A diverse range of industries and products leverage this process (e.g., automotive, aerospace, oil & gas; hydraulic and pneumatic machinery, firearms, metal forming and forging tools, material handling equipment, and tooling). Components like camshafts, gears, piston pins, hydraulic systems, and cutting tools benefit from the enhanced surface properties imparted by this process.

Salt bath nitriding is performed at temperatures typically ranging from 500°C to 630°C (930°F to 1165°F) to produce a controlled and highly uniform release of nitrogen at the surface of the workpiece (Figure 1). Nitrogen diffuses into, and chemically combines with, nitride-forming elements in the metal, producing a tough, ductile compound layer with exceptional mechanical properties through a catalytic reaction. This hard compound layer has wear properties that are reportedly 200% to 1000% greater than the original material, and greatly enhanced resistance to corrosion, galling, and scuffing (Pye, 2003).

Figure 1. Salt bath nitriding modifies the surface metallurgy and properties (“Salt Bath Nitriding, Controlled Liquid Nitriding (Overview),” HEF USA)

The salt reacts with the metal surface to form a hardened compound layer (primarily composed of ε-iron nitride and γ’-iron nitride) and a diffusion zone beneath it where nitrogen atoms diffuse into the metal matrix (Figure 2).

Figure 2. Microstructure of a sale bath nitrided component (“Salt Bath Nitriding, Controlled Liquid Nitriding (Overview),” HEF USA)

Case depth is a function of both treatment time and material. The final surface hardness is a function of the material composition. Higher percentages of nitride forming elements (Cr, Mo, Al, V, Mn, Ti, W) produce higher surface hardnesses (Table A).

Table A. Surface Hardness as a Function of Material (“Melonite®/QPQ Process,” HEF USA)

Salt bath nitriding remains a valuable surface engineering technique due to its effectiveness in enhancing durability, wear resistance, and corrosion performance. While environmental and safety concerns exist, advancements in salt chemistry and waste management continue to make this process viable for modern industrial applications.

References

Boßlet, Jochim. n.d. Melonite®/QPQ Process Brochure. HEF Durferrit. 

Herring, Daniel H. and Edward Roliński. 2026. “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” Heat Teat Today, August.

Pye, David. 2003. Practical Nitriding and Ferritic Nitrocarburizing. Materials Park, OH: ASM International. 

About The Authors

Dan Herring
(The Heat Treat Doctor®)
The HERRING GROUP, Inc.

Dan Herring, who is most well known as The Heat Treat Doctor®, has been in the industry for over 50 years. He spent the first 25 years in heat treating prior to launching his consulting business, The HERRING GROUP in 1995. His vast experience in the field includes materials science, engineering, metallurgy, equipment design, process and application specialist, and new product research. He is the author of six books and over 1000 technical articles.

Dr. Edward Rolinski, affectionately known as “Doctor Glow,” is a distinguished senior scientist having spearheaded research on plasma/ion nitriding since the 1970s. He holds advanced degrees in manufacturing technology and metallurgy, including a PhD and Doctor of Science. His focus has been on plasma nitriding processes, especially involving titanium alloys and powder metallurgy. Over his career, Dr. Rolinski authored numerous influential technical chapters and articles, including for ASTM International and the ASM Handbook, and is a prolific contributor to industry publications. After decades of leadership and innovation in surface engineering and heat treating, he is now a consultant in the heat treating industry. 

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

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Why Choose Plasma Nitriding?

/ MANUFACTURING HEAT TREAT TECH, NITRIDING TECHNICAL CONTENT

As manufacturers look for greater control, precision, and flexibility in surface hardening, plasma nitriding has emerged as a versatile alternative to traditional nitriding methods. In this article, Daniel H. Herring, aka “The Heat Treat Doctor,” and Dr. Edward Rolinski, a senior scientist and recognized authority on plasma and ion nitriding, examine the advantages of plasma nitriding, including its ability to treat stainless steels, selectively harden complex geometries, and process powder metallurgy components.

If you’re looking for a broader introduction, watch for the upcoming print feature, “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” for an overview of nitriding, its key benefits, and a side-by-side of the three primary nitriding processes.

Plasma nitriding can be used over a broad range of heat treating temperatures and is used for all types of ferrous alloys (Figures 1 and 2). Additionally, it has the ability to activate the surfaces of oxidized stainless steels to allow them to be nitrided (Winter and Kalucki 2013; Roliński 1987).

Figure 1. Plasma nitrided A-286 Alloy Marble’s Etchant | Image Credit: The Herring Group, Inc.
Figure 2. Plasma nitrided duplex stainless steel 2205 Marble’s Etchant | Image Credit: The Herring Group, Inc.

Activation of the surface involves both ion bombardment and sputtering of the surface/cathode in the areas where the glow discharge covers the surface (Figure 3). The actual contact area of the part with the cathodic base plate or fixture does not nitride. The problem of edge effect, which is related to uneven distribution of sputtered atoms at corners and edges of a component (Roliński et al. 2005; Roliński 2024), is addressed primarily by proper adjustment of the processing gas pressure, which changes the thickness of the cathodic glow, making it more uniform around contour of the part. Masking areas that do not need to be hardened is simple. For example, a nut on a thread or a steel plate on a section with small holes is sufficient to protect those surfaces from the glow discharge and prevent nitriding.

Figure 3. Typical “glow” around component parts during plasma nitriding | Image Credit: The Herring Group, Inc.
Figure 4. Plasma/Ion nitrided powder metal component run at 565°C (1050°F) in a mixture of nitrogen/hydrogen at a ratio of 1:3 and pressure 3.5 mbar. 3% Nital. (Roliński et al, 2021)

Plasma nitriding is a unique process capable of surface hardening low-density sinter/powder metal (PM) products, even those less than 7.3 g/cm3 (Figure 4) and PM stainless steels (Roliński 2004). This is especially true when a portion of the treated component requires masking (Roliński and Sharp 2005, 2004). Active nitrogen species generated by the glow discharge penetrate only near-surface cavities/porosities, forming a nitrided layer. By contrast, ammonia in gas nitriding penetrates throughout the entire thickness of the component increasing the brittleness of the nitrided part.

Plasma nitriding is a low-nitriding potential process because the compound zone/white layer is typically very thin without extreme control accuracy of the nitriding parameters. This is a result of sputtering and a low partial pressure of nitrogen during processing (Roliński 2014). Plasma nitriding requires much less processing gases, such as nitrogen and hydrogen, than gas nitriding with ammonia. In addition, only small quantities of hydrocarbon gases are needed to dope the atmosphere and form epsilon-type compound zones at the surface (Roliński and Sharp, 2004).

Long parts, such as extruder screws and shafts, can be plasma nitrided even in “cold-wall vessels,” which do not have external heaters (Hemsath and Herring 2019).

References

Hemsath, Mark K., and Daniel H. Herring. 2019. “Nitriding—Growth and Tribological Benefits for Surface Engineering.” In Heat Treating Progress 2019 Conference Proceedings. Materials Park, OH: ASM International. 

Herring, Daniel H. and Edward Roliński. 2026. “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” Heat Teat Today, August.

Roliński, E. 1987. “Effect of Plasma Nitriding Temperature on Surface Properties of Stainless Steel.” Surface Engineering 3: 35–40. 

Roliński, E., J. Arner, and G. Sharp. 2005. “Negative Effects of Reactive Sputtering in Industrial Plasma Nitriding.” Journal of Materials Engineering and Performance 14 (3): 343–350. 

Roliński, E., and G. Sharp. 2004. “Ion Nitriding and Nitrocarburizing of Sintered PM Parts.” Industrial Heating, October: 33–35. 

Roliński, E., and G. Sharp. 2005. “When and Why Ion Nitriding/Nitrocarburizing Makes Good Sense.” Industrial Heating, August: 67–72.

Roliński, E. 2014. “Plasma Assisted Nitriding and Nitrocarburizing of Steel and Other Ferrous Alloys.” In Thermochemical Surface Engineering of Steels, edited by E. J. Mittemeijer and M. A. J. Somers, 413–449. Cambridge, UK: Woodhead Publishing.

Winter, K. M., and J. Kalucki. 2013. “Gas Nitriding and Gas Nitrocarburizing of Steels.” In ASM Handbook, Vol. 4A: Steel Treating—Fundamentals and Processes, edited by Jon I. Dossett and George E. Totten, 647–679. Materials Park, OH: ASM International. 

About The Authors

Dan Herring
(The Heat Treat Doctor®)
The HERRING GROUP, Inc.

Dan Herring, who is most well known as The Heat Treat Doctor®, has been in the industry for over 50 years. He spent the first 25 years in heat treating prior to launching his consulting business, The HERRING GROUP in 1995. His vast experience in the field includes materials science, engineering, metallurgy, equipment design, process and application specialist, and new product research. He is the author of six books and over 1000 technical articles.

Dr. Edward Rolinski, affectionately known as “Doctor Glow,” is a distinguished senior scientist having spearheaded research on plasma/ion nitriding since the 1970s. He holds advanced degrees in manufacturing technology and metallurgy, including a PhD and Doctor of Science. His focus has been on plasma nitriding processes, especially involving titanium alloys and powder metallurgy. Over his career, Dr. Rolinski authored numerous influential technical chapters and articles, including for ASTM International and the ASM Handbook, and is a prolific contributor to industry publications. After decades of leadership and innovation in surface engineering and heat treating, he is now a consultant in the heat treating industry. 

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

Why Choose Plasma Nitriding? Read More »

Why Choose Gas Nitriding?

/ MANUFACTURING HEAT TREAT TECH, NITRIDING TECHNICAL CONTENT

Among today’s nitriding technologies, gas nitriding remains the most widely used process for enhancing surface hardness, wear resistance, and fatigue performance while preserving dimensional stability. In this Technical Tuesday installment, Daniel H. Herring, aka “The Heat Treat Doctor®,” and Dr. Edward Rolinski, a senior scientist and recognized authority on plasma and ion nitriding, explain where gas nitriding excels, its process advantages and limitations, and the applications best suited for the technology.

If you’re looking for a broader introduction, watch for the upcoming print feature, “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” for an overview of nitriding, its key benefits, and a side-by-side of the three primary nitriding processes.

Gas nitriding represents 60–70% of all nitriding processes. The main benefit of gas nitriding, specifically when compared to plasma nitriding, is its ability to harden the entire surface of the component. Masking can be done by copper plating or painting with a nitriding-specific stop-off paint (Figure 1). Modern gas nitriding processes also allow treating of stainless steel, where PVC and other chemicals are used for surface pre-activation. Maintenance increases when these activating agents are used.

Figure 1. Large steel pinions being prepared for nitriding | Image Credit: Nitrex
Figure 2. Typical small parts and loading arrangements for gas nitriding (Herring 2011)

Case depths are typically total case depths (core hardness + 50 HV0.5) and vary by material (see Table B in Herring et al. 2026). Caution should be used when stating a required case depth as a number of definitions for total case depth are in use.

Another benefit of using gas nitriding is its ability to form a thick compound zone up to 0.025 mm (0.001 inches). The process can enhance the corrosion resistance of steels, particularly combined with post-oxidation. Also, gas nitriding is an excellent way to improve tribological properties of the treated components (Senatorski et al. 2017). Modern controls allow for automatic process adjustment over the length of the cycle and control of the nitriding atmosphere based on nitriding potential (Kn value) or ammonia dissociation rate (Herring 2020; Winter and Kalucki 2013). This allows for precise growth of the compound zone type and thickness, tight case depth ranges, and repeatability.

Dimensional change in nitrided parts, typically very small, is governed largely by composition, tempering temperatures, time/temperature of nitriding, relative thickness of case/core, shape of the part, and areas masked off to prevent nitriding. The amount of growth is usually constant for identical parts nitrided in different batches by a fixed processing cycle. After the amount of growth for a particular part has been determined experimentally, allowance for it can be made prior to nitriding during final machining prior to nitriding.

Table A. Single Stage Gas Nitriding Case Depth Time at 525°C (975°F) (Herring 2011)

Sharp corners or edges should be avoided on parts to be nitrided, because the projections formed at sharp corners receive higher nitrogen concentration and are susceptible to brittleness and chipping. These sharp edges nitride through the section and are without support from a soft ductile core.

In the single stage process, a temperature range of 500°C–540°C (925°F–1005°F) is typical, and process times range from 1 to 100 hours (Table A). The dissociation rate of ammonia is held in the range of 15% to 30%. The process produces a brittle, nitrogen-rich white layer at the surface comprised of various iron nitrides (Fe2-3N, Fe4N). One advantage of this thick white layer is that it will provide longer component service life in abrasive and adhesive wear applications.

Most parts, however, are nitrided in a two- or even three-stage process and not ground after nitriding (Table C). This affords them excellent dimensional stability (Herring 2011). Case depth is affected by temperature (Figure 3), time (Figure 4), nitriding potential (if there is not a compound zone formed), and how the total case depth is defined.

Table B. Recommended Ranges of Nitriding Potential (SAE International Aerospace Material Standard AMS 2759/10)
Figure 3. Gas nitriding case depth versus time for 4140 steels at 538ºC (1000ºF) (Adapted from Stange Electronik GmbH Data) 
Figure 4. Effect of temperature on formation of 0.51 mm (0.020 inches) case depth during nitriding 4140 steel (Adapted from Stange Electronik GmbH Data) 

References

Herring, Daniel H. 2011. “Principles of Gas Nitriding, Parts 1–4.” Industrial Heating, April–May. 

Herring, Daniel H. 2020. “An Overview of Nitriding—Technology and Tribological Benefits.” Industrial Heating, March. 

Herring, Daniel H. and Edward Roliński. 2026. “Nitriding Selection Guide: Gas, Plasma, or Salt Bath?” Heat Teat Today, August.

SAE International. n.d. AMS 2759/10 Aerospace Material Standard (latest revision). 

Senatorski, J., J. Tacikowski, E. Roliński, and S. Lampman. 2017. “Tribology of Nitrided and Nitrocarburized Steels.” In ASM Handbook, Vol. 18: Friction, Lubrication, and Wear Technology, edited by George E. Totten, 638–652. Materials Park, OH: ASM International. 

Winter, K. M., and J. Kalucki. 2013. “Gas Nitriding and Gas Nitrocarburizing of Steels.” In ASM Handbook, Vol. 4A: Steel Treating—Fundamentals and Processes, edited by Jon I. Dossett and George E. Totten, 647–679. Materials Park, OH: ASM International. 

About The Authors

Dan Herring
(The Heat Treat Doctor®)
The HERRING GROUP, Inc.

Dan Herring, who is most well known as The Heat Treat Doctor®, has been in the industry for over 50 years. He spent the first 25 years in heat treating prior to launching his consulting business, The HERRING GROUP in 1995. His vast experience in the field includes materials science, engineering, metallurgy, equipment design, process and application specialist, and new product research. He is the author of six books and over 1000 technical articles.

Dr. Edward Rolinski, affectionately known as “Doctor Glow,” is a distinguished senior scientist having spearheaded research on plasma/ion nitriding since the 1970s. He holds advanced degrees in manufacturing technology and metallurgy, including a PhD and Doctor of Science. His focus has been on plasma nitriding processes, especially involving titanium alloys and powder metallurgy. Over his career, Dr. Rolinski authored numerous influential technical chapters and articles, including for ASTM International and the ASM Handbook, and is a prolific contributor to industry publications. After decades of leadership and innovation in surface engineering and heat treating, he is now a consultant in the heat treating industry. 

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

Why Choose Gas Nitriding? Read More »

Message from the Editor: The Greatest Engineering Skill

/ EDITOR

Heat Treat Today publishes twelve print magazines a year and included in each is a letter from the editor. This letter is from the July 2026 Annual Super Brands Issue print edition. In today’s letter, Bethany Leone, managing editor at Heat Treat Today, shares her insights on why interpreting client needs, not technical know-how, is often the real challenge engineers face — and how deliberately practicing creative thinking, the willingness to ask “what if…?”, is the skill that builds resilience in the face of change.

I had the pleasure of attending an award ceremony for a local metallurgy chapter filled with academia and industry players in metals processing. As we chatted around the table exchanging first-hand stories about aerospace engineering industry feats and reflecting on materials capabilities, the conversation took a turn. What was their biggest challenge of their careers? The unanimous, almost immediate consensus came down to interpreting client needs.

One gentleman with a full career and retirement worth of experience commented first. A lot of confusion came from the misuse of or difference in terms. For example, use of the term “sheet” versus the desired “foil” outcome in rolling operations. This reminded me of a maxim my colleague and managing editor predecessor likes to quote: “The beginning of wisdom is the definition of terms.” Until you understand what the terms of the discussion are, neither you nor your listener can make much of it.

Another expert chimed in and shared that clients often brought their own expectations of what made for a sufficient thermal processing outcome. But with testing, though the specs were met, the part failed. Finding the words to bridge the gap between the expectations of clients and the world of testing that he lived in was a regular feat of strength. Or perhaps a feat of the mind through creative thinking.

In both cases, technical expertise was not the limiting factor. The challenge was finding a new way to understand and communicate a problem.

Exercising Creativity

Today’s world of advanced technology does not necessarily undervalue creative thinking, but it is a metric that is often misidentified. What is often thought of as creative thinking is often another skill: problem solving, logical reasoning, savvy use of tools.

These are all excellent abilities to have. But I fear for myself and especially for the engineers navigating the new manufacturing world that we are not flexing the creative thinking muscle purposefully. There are increasing defaults in our lives that minimize effort while maintaining quality outcomes (note the key word: maintain). With technology’s rapid advances, practicing creative thought increasingly requires a deliberate choice to break through what is normal or assumed to be “right” answers in search of new solutions.

This skill is built by repeated efforts to challenge accepted norms — think, perhaps, heat treat process recipes — and invites “what if…?” to solve new problems. This is not a necessary tool to apply to every instance of challenge, but the effort to break mental rules is a scientific superpower that makes us and our operations resilient in the face of change.

Research suggests that mentally stimulating activities like crosswords and sudoku may support cognitive health and delay cognitive decline. And while logical thinking and memory skills play a foundational role in problem solving, the magic moments often come with a forced “what if…?” Whether in a scribbled newspaper game or on the plant floor, this daring thought comes after you have done your due diligence, executed the research, laid the logical framework, and tested for solutions systematically.

What If…?

Decide to practice and not offload this ability. You are among many who finesse every tuning, manage every hot zone refabrication, or confront each production issue. Therefore, the greatest engineering skill will be to let curiosity prevail and slowly, painstakingly find the words to ask the right questions.

Bethany Leone
Managing Editor
Heat Treat Today
Contact: Bethany Leone at bethany@heattreattoday.com

Message from the Editor: The Greatest Engineering Skill Read More »

New DRI Plant Planned for US Pig Iron Production

/ FOUNDRY CASTING NEWS, MANUFACTURING HEAT TREAT NEWS

NEMO Industries is planning a new direct reduction iron (DRI) plant in Louisiana to strengthen domestic pig iron production by supplying high-carbon DRI for electric smelting. The project will support both U.S. and international markets while incorporating technologies designed to improve process efficiency and provide flexibility for future lower-carbon ironmaking.

NEMO Industries has selected Tenova, a global metals technology company with North American operations, to provide the ENERGIRON direct reduction technology for its proposed Ironworks I facility. Located in Louisiana, the plant will produce up to 2.5 million metric tons per year of hot and cold DRI. Tenova will begin front-end engineering design (FEED) as the project advances toward a final investment decision, currently expected in December 2027.

The facility will use the ENERGIRON Zero Reformer configuration, a direct reduction technology jointly developed by Tenova and Danieli. The plant will also incorporate the HYTEMP hot DRI transport system and be designed to accommodate future carbon caption integration. In addition, the facility includes provisions for future hydrogen use as Gulf Coast hydrogen infrastructure develops, providing flexibility for evolving feedstock and decarbonization strategies.

Michael DuBose
Co-Founder and President
NEMO Industries
Stefano Maggiolino
President and CEO
Tenova HYL

Michael DuBose, co-founder and president of NEMO Industries said recent market disruptions have underscored the need for a more resilient domestic pig iron supply chain. “Recent market disruptions including war, tariffs, and weather have reinforced the national security case for a resilient American pig iron supply,” DuBose said. “ENERGIRON DRI technology positions us to develop a pig iron facility that will strengthen the American steel supply chain and reduce our reliance on imported steel inputs.”

Stefano Maggiolino, president and CEO of Tenova HYL, said the project highlights how direct reduction technology can help manufacturers balance operational efficiency and sustainability goals. “It gives NEMO Industries the technical foundation in terms of capital and operating expenditures, carbon content, and sustainability to prove its DRI-based pig iron model,” he said.

Press release is available in its original form here.

New DRI Plant Planned for US Pig Iron Production Read More »

News from Abroad: Electrification and Steel Processing Advances

/ HEAT TREAT NEWS

In today’s News from Abroad installment, we highlight several major global developments — from electrified furnace technology and low-carbon steelmaking to advanced casting and electrical steel production — demonstrating how manufacturers are modernizing thermal operations to boost efficiency, improve product quality, and support the growing demand for sustainable metals production.

Heat Treat Today partners with two international publications to deliver the latest news, tech tips, and cutting-edge articles that will serve our audience — manufacturers with in-house heat treat. Furnaces International, a Quartz Business Media publication, primarily serves the English-speaking globe, and heat processing, a Vulkan-Verlag GmbH publication, serves mostly the European and Asian heat treat markets.

Electric Pusher Furnace Improves Aluminum Heating Efficiency

Novelis expects to cut emissions by approximately 4,500 tons CO2eq per year. | Image Credit: Novelis

“Novelis has started operating its first electric pusher furnace at its Sierre plant, Switzerland. The pusher furnace is used to heat aluminum ingots prior to rolling.”

“As part of the Net Zero Lab Valais roadmap, Novelis plans to continue to scale electrification and low-carbon energy integration at its Sierre plant, while also exploring decarbonization solutions across the company’s global production network.”

Read more: “Novelis commissions electric pusher furnace” at furnaces-international.com.

Electric Arc Furnace Advances Green Steel Production

Henan Jiyuan Iron and Steel Group orders electric arc furnace from Danieli. | Image Credit: Alcoa Norway

“Danieli has signed a contract with Henan Jiyuan Iron and Steel Group for the supply of a new 55t ECS Zerobucket electric arc furnace (EAF). The order marks the first EAF for Henan Jiyuan and aids in the company’s transition from blast furnace steelmaking to green steel production.”

“The new EAF will allow Henan Jiyuan to establish a more efficient and environmentally friendly special steel production process.”

Read more: “Danieli to supply first EAF to Henan Jiyuan” at furnaces-international.com.

Continuous Casting Raises Rail Steel Standards

Primetals Technologies will supply a 6-strand bloom caster as part of WISCO’s plans to improve its production line layout. | Image Credit: Primetals Technologies

“Wuhan Iron and Steel Co., Ltd. (WISCO) and Primetals Technologies recently signed a contract for a 6-strand bloom caster project.”

“The new caster will further strengthen the company’s manufacturing capabilities in high-end areas such as rail steel, automotive, and photovoltaic applications, and marks another milestone in the partnership between the two companies.”

Read more: “Primetals Technologies and WISCO to Set New Benchmark in Zero-Defect Rail Steel Casting” at heat-processing.com.

Electrical Steel Project Adds Thermal Processing Capacity

Fives signs contract with Sanbao Group for new electrical steel lines. | Image Credit: Fives

“Fives, an international engineering group, has signed a contract with Fujian Kunbao New Materials, part of Sanbao Group, to design and supply two high-performance strip processing lines for electrical steel production in Zhangzhou, China.”

“The project includes the delivery of two complete decarburizing and coating lines (DCL) dedicated to producing grain-oriented (GO) electrical steel, a critical material used in power transmission and distribution systems.”

Read more: “Fives to supply full electrical steel lines to Sanbao Group” at heat-processing.com.

News from Abroad: Electrification and Steel Processing Advances Read More »

Major Steel Plant Shifts to Electric Steelmaking

/ AUTOMOTIVE HEAT TREAT NEWS

A major steel plant is replacing its existing blast furnace route with electric steelmaking as part of a transition to lower-emission steel production. The project will convert the facility into an electric arc furnace-based operation while supporting continued production of high-quality flat steel products, including grades used in the automotive industry.

Tenova, a global industrial furnace and metals technology supplier with North American operations, will supply the electric arc furnace for the transformation of Hüttenwerke Krupp Mannesmann (HKM) in Duisburg, Germany. The furnace, designed with a production capacity of 2.5 million tons per year, will be Germany’s largest electric arc furnace and will become the technological center of the plant’s transition under its new owner, Salzgitter AG.

The investment marks the beginning of a new phase for the Duisburg-Huckingen steelworks. By replacing the existing blast furnace route with electric steelmaking, HKM expects to reduce the carbon footprint of its operations while maintaining the plant’s competitiveness. The project reflects continued investment in electric steelmaking technologies as steel producers pursue lower-emission manufacturing.

Tenova’s scope of supply includes a 285-ton Consteel® EAF, complete with auxiliary plants on a turnkey basis. The furnace will incorporate Tenova’s Consteel® continuous scrap charging technology and an Electro Magnetic Stirring (EMS) System developed in partnership with ABB. It is designed to deliver a continuous production rate of 380 tons per hour to the existing secondary metallurgy line and slab caster, enabling production of high-quality flat steel products, including grades that meet automotive industry standards. The new facility will be installed in a dedicated building within the HKM production site.

Paolo Stagnoli
Sales and Marketing Director for EAF & LF
Tenova

According to Paolo Stagnoli, sales and marketing director for EAF & LF at Tenova, the project followed an extensive period of collaboration between HKM and Tenova to develop a solution tailored to the operational requirements of the Duisburg steelworks. “It took almost two years of joint studies and intensive discussion between HKM and Tenova to define this ambitious project and fine-tune the technological solution to the unique constraints and needs of the productive site,” he said.

The project expands Tenova’s portfolio of electric arc furnace installations and reflects continued adoption of electric steelmaking technologies designed to improve process efficiency, reduce energy consumption, minimize environmental impact, and support lower-carbon steel production.

Press release is available in its original form here.

Major Steel Plant Shifts to Electric Steelmaking Read More »