IperionX continues to advance domestic titanium manufacturing and thermal processing capabilities in a recent commitment to reduce long lead times for critical pump components used for naval shipbuilding. This addresses supply chain constraints that have slowed ship construction and maintenance. By shortening production timelines, the initiative supports improved fleet readiness while reinforcing domestic manufacturing capacity for mission-critical naval systems.
The effort is being demonstrated through a project with Carver Pump Company, a U.S.-based manufacturer of mission-critical pumps for naval applications. Carver Pump has placed an initial purchase order with IperionX for prototype titanium components. Leveraging domestically produced titanium metal powder and integrated in-house manufacturing, the project will focus on producing and testing cost-competitive replacements for traditionally cast pump components.
Titanium components are essential in naval pump systems due to their high strength-to-weight ratio, corrosion resistance, and ability to withstand extreme marine environments. However, traditionally cast titanium parts often face supply chain bottlenecks, with lead times exceeding 12 months, contributing to equipment and vessel downtime.
Anastasios (Taso) Arima CEO IperionX Source: IperionX
IperionX’s approach is designed to deliver step-change improvements in production efficiency. Each titanium component is expected to be produced in less than one week using the company’s low-cost domestically produced titanium metal powder and advanced manufacturing capabilities, significantly reducing reliance on conventional casting routes.
“Transitioning from lead times measured in years to timelines measured in days allows us to better support on-time naval shipbuilding and sustainment, directly enhancing fleet readiness,” said Anastasios (Taso) Arima, CEO of IperionX.
The purchase order covers the development of four prototype pump impellers, with manufacturing anticipated to be complete in May 2026. Successful completion of the prototyping and testing phase could lead to larger-scale production agreements supporting additional naval components.
Press release is available in its original form here.
In this Technical Tuesday installment, Dr. Edward Rolinski and Dan Herring, respectively known as “Doctor Glow” and The Heat Treat Doctor®, explore how anodic plasma nitriding for titanium alloys avoids the damaging effects of conventional cathodic nitriding while improving wear resistance, corrosion resistance, and component reliability for aerospace and medical applications.
This informative piece was first released inHeat Treat Today’sNovember 2025 Annual Vacuum Heat Treating print edition.
Traditional plasma/ion nitriding is a well-established technology. However, it has issues that can be overcome by the newer anodic plasma nitriding method. This article introduces the idea of using anodic plasma nitriding for titanium and titanium alloys to avoid the damaging effect of conventional (cathodic) plasma nitriding. Read how this approach could provide harder, defect-free layers that improve wear, corrosion resistance, and overall component reliability for aerospace and medical critical parts.
What Is Anodic Nitriding?
Anodic nitriding is a type of plasma nitriding process in which the component parts being treated are placed at an anodic (positive) potential instead of the usual cathodic (negative) potential. Unlike conventional plasma (cathodic glow discharge) nitriding, where the component is bombarded by high-energy positive ions, anodic nitriding involves low-energy electron bombardment of the component’s surface.
Anodic nitriding is particularly effective for materials with very high negative Standard Free Energy of nitride formation (e.g., titanium, zirconium) as it helps avoid or reduce the edge effect, a well-known problem in cathodic nitriding that leads to uneven ion bombardment and hardening on corners and edges.
Background: Plasma Nitriding Complexities
Glow-discharge plasma nitriding is applied to a wide range of materials, including cast irons, carbon steels, stainless steels, nickel, titanium alloys, and powder metal (Roliński 2014). The plasma nitriding and nitrocarburizing processes allow for the formation of surface layers known to have superior tribological properties (Roliński 2014). However, coverage of the parts with the glow discharge is not always uniform, especially when complex geometry loads are processed (see Figure 1).
Figure 1. Small dark spots (see circled area) indicate CDS during pulse plasma nitriding. Note: Non-uniform glow discharge at the top of the part. Source: Roliński and HerringFigure 2. Load of stainless-steel parts after pulse plasma nitriding. Note: Edge effect (EE) around the part. Source: Roliński and Herring
Glow-discharge plasma nitriding is a thermochemical treatment involving high-energy particles. Ions of nitrogen or other gas species accelerate and gain energy in the cathodic dark space (CDS) around the workpiece — which is the cathode in a direct current electrode setup. They activate the surface first by sputtering to remove any native oxides present. The sputtering treatment also results in the generation of a substantial quantity of solid particles, generated from the part itself, including metal atoms that levitate near the surface of the part (Merlino and Goree 2004; Roliński 2005). In processing titanium, for example, this affects both adsorption and diffusion at the surface creating conditions that degrade layer quality (Hubbard, et al. 2010). A negative impact of this “dusty” plasma on the uniformity of the nitrided layer in complex-geometry workpieces has been reported (Ossowski, et al. 2016).
In addition, it is well known that there is a so-called corner/edge effect (EE) observed during plasma nitriding related to uneven circulation of these dust particles around the cathode (see Figure 2). In extreme situations, especially when complex geometry parts are treated, the EE caused by a non-uniform distribution of the electric field on corners, cavities, etc., results in excessive and non-uniform distribution of these plasma deposits (PD). In this way, the EE amplifies the already-present problem of redeposition, leading to the formation of various microdefects and uneven nitrided layer thickness (Merlino and Goree 2004; Roliński 2005, 2024; Ossowski, et al. 2016).
Figure 3. Titanium component after gas nitriding in ammonia | Source: Roliński and Herring
Plasma nitriding of titanium is usually performed at 680–1100°C (1256–2012°F). Negative aspects of using cathodic polarization on titanium include plasma/ion bombardment resulting in surface damage due primarily to micro arcing and contamination of the surface with the deposited compounds and their uneven distribution due to EE (Merlino and Goree 2004; Roliński 2005, 2014, 2024; Ossowski, et al. 2016). Although arcing has been eliminated by applying pulse plasma techniques, sputtering can only be controlled in a limited way, especially when complex geometry parts are nitrided. Therefore, gas nitriding in ammonia has been used occasionally for hardening titanium parts. A resulting golden appearance representing the presence of TiN nitride is produced on the surface (see Figure 3).
Anodic Nitriding of Titanium Alloys
Research has been conducted on anodic plasma nitriding of steels (Zlatanovic 1986; Michalski 1993; Kenĕz 2018). Ammonia or active nitrogen species generated in the plasma can nitride the anode just as they do the cathode. The active species causing nitriding are active nitrogen atoms and highly reactive NH radicals (NH*) formed in near plasma. NH radicals (aka imidogen radicals) are chemical species with a nitrogen-hydrogen bond along with an unpaired electron. For titanium, hydrogen must be excluded in many situations because it reacts with titanium to form stable hydrides that embrittle the product (Roliński 2015).
The standard free enthalpy of formation of titanium nitrides has an exceptionally large negative value, which means that titanium nitride will form in a spontaneous way when the titanium anode reacts with excited nitrogen nearby (Roliński 2015). Switching the treated components from cathodic to anodic polarization offers several notable advantages. A glow discharge in pure nitrogen or argon generates only positive ions that are accelerated toward the cathode/workpiece. Because these gas mixtures lack negative ions, only electrons from the anodic glow strike the anode/workpiece. This results in activation of the surface without negative aspects of the collisions of the heavier particles, such as N2+ (i.e., a nitrogen molecular ion with a +1 charge), causing excessive sputtering. At the same time, charge-free particles of nitrogen, such as N2* and N*, react with the anode and are chemisorbed at the surface at sufficiently high temperature, leading eventually to formation of the diffusion layer.
It is believed that the anodic-nitriding process may have positive effects in treating precision parts made of titanium and other alloys for use in both the aerospace and medical industries. This method will allow treatment at the lowest possible temperature due to activation of the surface with the electrons from anodic polarization. The texture, appearance, and defect-free surface will produce a superior part and will enhance the performance of many of those components. This will be important when corrosion or optical properties of the surface play a significant role.
Anodic nitriding of titanium can be accomplished within a conventional plasma nitriding system, provided that the central anode is appropriately designed and positioned. This anode or portion of it must be made of titanium to prevent evaporation and transfer of any impurities to the parts.
Applications
Figure 4. Schematic representation of the anodic plasma nitriding apparatus. Note the gold color characteristic for titanium nitride TiN present on the titanium fixturing and parts, all being identified as “anode.” | Source: Roliński and Herring
Titanium alloys are popular in orthopedics due to their bone-like elasticity, strength, and biocompatibility (Roliński 2015; Froes 2015). Surface engineering processes like anodic nitriding can play a significant role in extending the performance of orthopedic devices several times beyond their normal life expectancy.
Super elastic intermetallic materials, such as 60NiTi, are used in rolling element bearings due to their resistance to corrosion and shock (Pohrelyuk, et al. 2015; Corte, et al. 2015). They are typically prone to rolling contact fatigue (RCF) degradation. Any surface defects present in those components, such as local concentration of impurities or micro-cracks, will result in premature failure. Anodic plasma nitriding can be potentially used to harden the surfaces of bearing components made from these alloys by forming a hard, defect-free layer, which may improve their RCF properties.
It is expected that parts made of titanium or other alloys with the smooth surface subjected to the anodic nitriding will be microdefects-free, enabling their broad applications in medical field, aerospace industry, and optical and semiconductor devices.
References
Corte, Ch. Della, M. K. Stanford, and T. R. Jett. 2015. “Rolling Contact Fatigue of Superelastic Intermetallic Materials (SIM) for Use as Resilient Corrosion Resistant Bearings.” Tribology Letters 26: 1–10.
Froes, F. H., ed. 2015. Titanium: Physical Metallurgy, Processing and Applications. Materials Park, OH: ASM International.
Hubbard, P., J. G. Partridge, E. D. Doyle, D. G. McCulloch, M. B. Taylor, and S. J. Dowey. 2010. “Investigation of Mass Transfer within an Industrial Plasma Nitriding System I: The Role of Surface Deposits.” Surface and Coatings Technology 204: 1145–50.
Kenĕz, L., N. Kutasi, E. Filep, L. Jakab-Furkas, and L. Ferencz. 2018. “Anodic Plasma Nitriding in Hollow Cathode (HCAPN).” HTM Journal of Heat Treatment and Materials 73 (2): 96–105.
Merlino, R. L., and J. A. Goree. 2004. “Dusty Plasmas in the Laboratory, Industry, and Space.” Physics Today, July, 32–38.
Michalski, J. 1993. “Ion Nitriding of Armco Iron in Various Glow Discharge Regions.” Surface and Coatings Technology 59 (1–3): 321–24. https://doi.org/10.1016/0257-8972(93)90105-W.
Ossowski, Maciej, Tomasz Borowski, Michal Tarnowski, and Tadeusz Wierzon. 2016. “Cathodic Cage Plasma Nitriding of Ti6Al4V.” Materials Science (Medžiagotyra) 22 (1).
Pohrelyuk, I., V. Fedirko, O. Tkachuk, and R. Poskurnyak. 2015. “Corrosion Resistance of Ti-6Al-4V Alloy with Oxidized Nitride Coatings in Ringer’s Solution.” Inzynieria Powierzchni (Surface Engineering) 1: 38–46.
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, 413–57. Woodhead Publishing Series in Metals and Surface Engineering 62. Cambridge, UK; Waltham, MA; and Kidlington, UK: Woodhead Publishing.
Roliński, E. 2015. “Nitriding of Titanium Alloys.” In ASM Handbook, Volume 4E: Heat Treating of Nonferrous Alloys, edited by G. E. Totten and D. S. McKenzie, 604–21. Materials Park, OH: ASM International.
Roliński, Edward. 2024. “Practical Aspects of Sputtering and Its Role in Industrial Plasma Nitriding.” In ASM Handbook Online, Volume 5: Surface Engineering. Materials Park, OH: ASM International. https://doi.org/10.31399/asm.hb.v5.a0007039.
Roliński, E., J. Arner, and G. Sharp. 2005. “Negative Effects of Reactive Sputtering in an Industrial Plasma Nitriding.” Journal of Materials Engineering and Performance 14 (3): 343–50.
Zlatanovic, M., A. Kunosic, and B. Tomčik. 1986. “New Development in Anode Plasma Nitriding.” In Proceedings of the International Conference on Ion Nitriding, Cleveland, OH, September 15–17, edited by T. Spalvins, 47–51. Cleveland, OH: NASA Lewis Research Center.
About The Authors:
Dr. Edward Rolinski “Doctor Glow”
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.
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 700 technical articles.
For more information: Contact Dan at dherring@heat-treat-doctor.com.
En esta entrega de Martes Técnico, el Dr. Edward Rolinski y Dan Herring, conocidos respectivamente como “Doctor Glow” y The Heat Treat Doctor®, exploran cómo el nitrurado por plasma anódico para aleaciones de titanio evita los efectos dañinos del nitrurado catódico convencional mientras mejora la resistencia al desgaste, la resistencia a la corrosión y la confiabilidad de los componentes para aplicaciones aeroespaciales y médicas.
Este artículo informativo se publicó por primera vez en Heat Treat Today’sNovember 2025 Annual Vacuum Heat Treating print edition.
La nitruración tradicional por plasma/iónica es una tecnología consolidada. Sin embargo, presenta problemas que pueden solucionarse con el nuevo método de nitruración anódica por plasma. Este artículo presenta la idea de utilizar la nitruración anódica por plasma para titanio y aleaciones de titanio, evitando así los efectos perjudiciales de la nitruración catódica por plasma convencional. Descubra cómo este enfoque podría proporcionar capas más duras y sin defectos que mejoran el desgaste, la resistencia a la corrosión y la fiabilidad general de los componentes para piezas críticas de la industria aeroespacial y médica.
Qué es la nitruración anódica?
La nitruración anódica es un tipo de proceso de nitruración por plasma en el que las piezas tratadas se ubican en un potencial anódico (positivo) en lugar del potencial catódico (negativo) habitual. A diferencia de la nitruración por plasma convencional (descarga catódica), donde el componente se bombardea con iones positivos de alta energía, la nitruración anódica implica el bombardeo de electrones de baja energía sobre la superficie del componente.
La nitruración anódica es particularmente efectiva para materiales con una alta energía libre estándar negativa de formación de nitruros (p. ej., titanio, circonio), ya que ayuda a evitar o reducir el efecto de borde, un problema bien conocido en la nitruración catódica que provoca un bombardeo iónico desigual y endurecimiento en esquinas y bordes.
Antecedentes: Complejidades de la nitruración por plasma
La nitruración por plasma con descarga luminiscente se aplica a una amplia gama de materiales, como fundiciones, aceros al carbono, aceros inoxidables, níquel, aleaciones de titanio y pulvimetalurgia (Roliński, 2014). Los procesos de nitruración por plasma y nitrocarburación permiten la formación de capas superficiales con propiedades tribológicas superiores (Roliński, 2014). Sin embargo, la cobertura de las piezas con la descarga luminosa no siempre es uniforme, especialmente cuando se procesan cargas de geometría compleja (véase la Figura 1).
Figura 1. Pequeñas manchas oscuras (ver el área rodeada por el círculo) indican CDS durante la nitruración por plasma pulsado. Nota: Descarga luminiscente no uniforme en la parte superior de la pieza. Source: Roliński and HerringFigura 2. Carga de piezas de acero inoxidable tras la nitruración por plasma pulsado. Nota: Efecto de borde (EE) alrededor de la pieza. Source: Roliński and Herring
La nitruración por plasma de baja descarga es un tratamiento termoquímico que utiliza partículas de alta energía. Los iones de nitrógeno u otras especies gaseosas se aceleran y ganan energía en el espacio oscuro de Crookes (CDS) alrededor de la pieza, que es el cátodo en una configuración de electrodos de corriente directa. Primero activan la superficie mediante pulverización catódica (sputtering) para eliminar cualquier óxido nativo presente. El tratamiento de pulverización catódica también genera una cantidad sustancial de partículas sólidas, generadas por la propia pieza, incluyendo átomos metálicos que flotan cerca de la superficie (Merlino y Goree, 2004; Roliński, 2005). En el procesamiento del titanio, por ejemplo, esto afecta tanto la adsorción como la difusión en la superficie, creando condiciones que degradan la calidad de la capa (Hubbard, et al., 2010). Se ha descrito un impacto negativo de este plasma “polvoriento” en la uniformidad de la capa nitrurada en piezas de geometría compleja (Ossowski et al., 2016).
Además, es bien sabido que durante la nitruración por plasma se observa el denominado efecto esquina/borde (EE), relacionado con la circulación desigual de estas partículas de polvo alrededor del cátodo (véase la Figura 2). En situaciones extremas, especialmente al tratar piezas de geometría compleja, el EE, causado por una distribución desigual del campo eléctrico en esquinas, cavidades, etc., da lugar a una distribución excesiva y desigual de estos depósitos de plasma (PD). De esta manera, el EE agrava el problema ya existente de la redeposición, lo que provoca la formación de diversos microdefectos y un espesor desigual de la capa nitrurada (Merlino y Goree, 2004; Roliński, 2005, 2024; Ossowski et al., 2016).
Figura 3. Componente de titanio después de nitruración gaseosa en amoníaco. Source: Roliński and Herring
La nitruración por plasma del titanio se realiza habitualmente a 680–1100 °C (1256–2012 °F). Entre los aspectos negativos del uso de la polarización catódica en titanio se incluyen el bombardeo de plasma/iónico, que provoca daños superficiales debido principalmente a micro-arcos y la contaminación de la superficie con los compuestos depositados, así como su distribución desigual debido al EE (Merlino y Goree, 2004; Roliński, 2005, 2014, 2024; Ossowski et al., 2016). Aunque el arco eléctrico se ha eliminado mediante la aplicación de técnicas de plasma pulsado, la pulverización catódica solo se puede controlar de forma limitada, especialmente cuando se nitruran piezas de geometría compleja. Por lo tanto, la nitruración gaseosa en amoníaco se ha utilizado ocasionalmente para endurecer piezas de titanio. Se produce un aspecto dorado resultante en la superficie que indica la presencia del nitruro TiN (véase la Figura 3).
Nitruración anódica de aleaciones de titanio
Se han realizado investigaciones sobre la nitruración anódica de aceros por plasma (Zlatanovic 1986; Michalski 1993; Kenĕz 2018). El amoníaco o las especies de nitrógeno activo generadas en el plasma pueden nitrurar el ánodo al igual que al cátodo. Las especies activas que causan la nitruración son átomos de nitrógeno activo y radicales NH altamente reactivos (NH*) formados en el plasma cercano. Los radicales NH (también conocidos como radicales imidógenos) son especies químicas con un enlace nitrógeno-hidrógeno junto con un electrón desapareado. En el caso del titanio, el hidrógeno debe excluirse en muchas situaciones, ya que reacciona con el titanio para formar hidruros estables que fragilizan el producto (Roliński, 2015).
La entalpía libre estándar de formación de nitruros de titanio tiene un valor negativo excepcionalmente alto, lo que significa que el nitruro de titanio se formará espontáneamente cuando el ánodo de titanio reaccione con nitrógeno excitado cercano (Roliński, 2015). Cambiar de polarización catódica a anódica de los componentes tratados ofrece varias ventajas notables. Una descarga luminosa en nitrógeno puro o argón genera únicamente iones positivos que se aceleran hacia el cátodo/pieza de trabajo. Dado que estas mezclas de gases carecen de iones negativos, solo los electrones de la luminiscencia anódica inciden en el ánodo/pieza de trabajo. Esto produce la activación de la superficie sin los efectos negativos de las colisiones de partículas más pesadas, como N₂+ (es decir, un ion molecular de nitrógeno con carga +1), lo que provoca una pulverización catódica excesiva. Al mismo tiempo, partículas de nitrógeno sin carga, como N₂* y N*, reaccionan con el ánodo por quimisorción en la superficie a una temperatura suficientemente alta, lo que finalmente conduce a la formación de la capa de difusión.
Se cree que el proceso de nitruración anódica puede tener efectos positivos en el tratamiento de piezas de precisión de titanio y otras aleaciones para su uso en las industrias aeroespacial y médica. Este método permitirá el tratamiento a la temperatura más baja posible gracias a la activación de la superficie con los electrones de la polarización anódica. La textura, la apariencia y una superficie sin defectos producirán una pieza superior y mejorarán el rendimiento de muchos de esos componentes. Esto será importante cuando la corrosión o las propiedades ópticas de la superficie sean importantes.
La nitruración anódica del titanio puede lograrse mediante un sistema convencional de nitruración por plasma, siempre que el ánodo central esté diseñado y ubicado adecuadamente. Este ánodo, o parte del mismo, debe estar hecho de titanio para evitar la evaporación y la transferencia de impurezas a las piezas.
Aplicaciones
Figura 4. Representación esquemática del aparato de nitruración por plasma anódico. Observe el color dorado característico del nitruro de titanio (TiN) presente en los accesorios y piezas de titanio, todos identificados como “ánodo”. Source: Roliński and Herring
Las aleaciones de titanio son populares en ortopedia debido a su elasticidad, resistencia y biocompatibilidad similares a las del hueso (Roliński 2015; Froes 2015). Los procesos de ingeniería de superficies, como la nitruración anódica, pueden desempeñar un papel importante a la hora de prolongar el rendimiento de los dispositivos ortopédicos varias veces más allá de su vida útil normal.
Los materiales intermetálicos superelásticos, como el 60NiTi, se utilizan en elementos de rodamientos debido a su resistencia a la corrosión y al impacto (Pohrelyuk et al., 2015; Corte et al., 2015). Suelen ser propensos a la degradación por fatiga de contacto rodante (RCF). Cualquier defecto superficial presente en estos componentes, como la concentración local de impurezas o microfisuras, provocará un fallo prematuro. La nitruración por plasma anódico puede utilizarse para endurecer las superficies de los componentes de rodamientos fabricados con estas aleaciones, formando una capa dura y sin defectos, lo que puede mejorar sus propiedades ante el RCF.
Se espera que las piezas de titanio u otras aleaciones con la superficie sometida a nitruración anódica estén libres de micro-defectos, lo que permite su amplia aplicación en el campo médico, la industria aeroespacial y los dispositivos ópticos y semiconductores.
Referencias
Corte, Ch. Della, M. K. Stanford, and T. R. Jett. 2015. “Rolling Contact Fatigue of Superelastic Intermetallic Materials (SIM) for Use as Resilient Corrosion Resistant Bearings.” Tribology Letters 26: 1–10.
Froes, F. H., ed. 2015. Titanium: Physical Metallurgy, Processing and Applications. Materials Park, OH: ASM International.
Hubbard, P., J. G. Partridge, E. D. Doyle, D. G. McCulloch, M. B. Taylor, and S. J. Dowey. 2010. “Investigation of Mass Transfer within an Industrial Plasma Nitriding System I: The Role of Surface Deposits.” Surface and Coatings Technology 204: 1145–50.
Kenĕz, L., N. Kutasi, E. Filep, L. Jakab-Furkas, and L. Ferencz. 2018. “Anodic Plasma Nitriding in Hollow Cathode (HCAPN).” HTM Journal of Heat Treatment and Materials 73 (2): 96–105.
Merlino, R. L., and J. A. Goree. 2004. “Dusty Plasmas in the Laboratory, Industry, and Space.” Physics Today, July, 32–38.
Michalski, J. 1993. “Ion Nitriding of Armco Iron in Various Glow Discharge Regions.” Surface and Coatings Technology 59 (1–3): 321–24. https://doi.org/10.1016/0257-8972(93)90105-W.
Ossowski, Maciej, Tomasz Borowski, Michal Tarnowski, and Tadeusz Wierzon. 2016. “Cathodic Cage Plasma Nitriding of Ti6Al4V.” Materials Science (Medžiagotyra) 22 (1).
Pohrelyuk, I., V. Fedirko, O. Tkachuk, and R. Poskurnyak. 2015. “Corrosion Resistance of Ti-6Al-4V Alloy with Oxidized Nitride Coatings in Ringer’s Solution.” Inzynieria Powierzchni (Surface Engineering) 1: 38–46.
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, 413–57. Woodhead Publishing Series in Metals and Surface Engineering 62. Cambridge, UK; Waltham, MA; and Kidlington, UK: Woodhead Publishing.
Roliński, E. 2015. “Nitriding of Titanium Alloys.” In ASM Handbook, Volume 4E: Heat Treating of Nonferrous Alloys, edited by G. E. Totten and D. S. McKenzie, 604–21. Materials Park, OH: ASM International.
Roliński, Edward. 2024. “Practical Aspects of Sputtering and Its Role in Industrial Plasma Nitriding.” In ASM Handbook Online, Volume 5: Surface Engineering. Materials Park, OH: ASM International. https://doi.org/10.31399/asm.hb.v5.a0007039.
Roliński, E., J. Arner, and G. Sharp. 2005. “Negative Effects of Reactive Sputtering in an Industrial Plasma Nitriding.” Journal of Materials Engineering and Performance 14 (3): 343–50.
Zlatanovic, M., A. Kunosic, and B. Tomčik. 1986. “New Development in Anode Plasma Nitriding.” In Proceedings of the International Conference on Ion Nitriding, Cleveland, OH, September 15–17, edited by T. Spalvins, 47–51. Cleveland, OH: NASA Lewis Research Center.
About The Authors:
Dr. Edward Rolinski “Doctor Glow”
El Dr. Edward Rolinski, conocido afectuosamente como “Doctor Glow”, es un distinguido científico sénior que ha liderado la investigación sobre nitruración por plasma/iones desde la década de 1970. Posee títulos avanzados en tecnología de fabricación y metalurgia, incluyendo un doctorado en Ciencias. Se ha centrado en los procesos de nitruración por plasma, especialmente en aleaciones de titanio y pulvimetalurgia. A lo largo de su carrera, el Dr. Rolinski ha sido autor de numerosos capítulos y artículos técnicos influyentes, incluyendo para ASTM International y el Manual ASM, y es un prolífico colaborador en publicaciones del sector. Tras décadas de liderazgo e innovación en ingeniería de superficies y tratamiento térmico, ahora es un consultor en la industria del tratamiento térmico.
Dan Herring (The Heat Treat Doctor®) The HERRING GROUP, Inc.
Dan Herring, conocido como The Heat Treat Doctor®, lleva más de 50 años en la industria. Dedicó sus primeros 25 años al tratamiento térmico antes de fundar su empresa de consultoría, The HERRING GROUP, en 1995. Su amplia experiencia en el campo abarca la ciencia de los materiales, la ingeniería, la metalurgia, el diseño de equipos, la especialización en procesos y aplicaciones, y la investigación de nuevos productos. Es autor de seis libros y más de 700 artículos técnicos.
Para más información: Contacte con Dan en dherring@heat-treat-doctor.com.
In this Technical Tuesday installment, Neil Owen, general manager at Stresstech Inc., examines how BNA is redefining process verification across multiple industries by making quality control both traceable and measurable.
Heat treatment plays a crucial role in achieving the mechanical strength, fatigue resistance, and dimensional stability demanded of ferromagnetic steel components used in automotive, aerospace, energy, and heavy manufacturing sectors. From furnace batch carburizing to localized induction hardening, these processes are designed to produce precise microstructural transformations and stress distributions. Barkhausen Noise Analysis (BNA) has emerged as an effective method to confirm that these transformations have occurred uniformly across all parts and also detect subtle localized deviations.
Introduction
Verifying uniform microstructural transformations and stress distributions during critical heat treatment processes remains a challenge for quality control teams. Traditional verification methods, such as hardness testing, microstructural sectioning, and metallographic examination, are accurate but slow, invasive, and limited to a small area. Non-destructive alternatives, like eddy current or ultrasonic testing, provide some insight but often lack the sensitivity to microstructural and stress variations that accompany phase transformations. As manufacturers seek faster, data-driven approaches to verify furnace and surface heat treatment quality, Barkhausen Noise Analysis (BNA) has emerged as a highly sensitive and efficient solution.
BNA offers a non-destructive, microstructure-responsive means of assessing heat treatment performance, directly reflecting the metallurgical state of ferromagnetic materials. Its unique advantage lies in its sensitivity to both magnetic domain behavior and residual stress, which are influenced by the phase composition, hardness, and internal stress of the steel. This makes it an ideal verification tool for confirming that intended transformations — particularly the shift from softer ferritic or pearlitic microstructures to harder martensitic or bainitic phases — have occurred fully and uniformly.
The Barkhausen Noise Phenomenon
When a ferromagnetic material is subjected to a varying magnetic field, its magnetic domains (i.e., regions within the crystal lattice where magnetic moments are aligned) reorient in discrete jumps rather than continuously. Each jump releases a small electromagnetic pulse known as Barkhausen noise. The cumulative signal, measured as a function of applied field strength, provides a distinct magnetic “fingerprint” of the material’s condition.
Figure 1. Visual comparison of how the magnetic domain reorients in discrete jumps within hard vs. soft ferromagnetic material Source: Stresstech Inc.
Hardness is related to the number of pinning sites (e.g., dislocations, precipitations, or other irregularities) in a material. When a magnetic field is applied to a ferromagnetic material, magnetic domain walls start to move. Domain walls collide with pinning sites in the material structure which impedes the domain wall movement. Magnetic domain walls move more easily in soft materials than in hard materials. Since hard materials contain numerous pinning sites, domain wall movements are more restricted. In soft materials, domain walls can make bigger jumps.
Because these parameters directly reflect the results of heat treatment, BNA provides a sensitive, immediate, and quantifiable indicator of metallurgical condition. When steel transforms from a soft ferritic–pearlitic structure to a hard martensitic one, the Barkhausen signal typically decreases by a factor of four to five, providing a clear signature of successful transformation.
Responsiveness to Microstructural Transformation
BNA is especially valuable because it responds directly to the magnetic consequences of metallurgical change. In untransformed ferritic–pearlitic steel, magnetic domains move freely, generating strong Barkhausen activity. As the microstructure transforms to martensite or bainite during quenching, domain wall motion becomes constrained by high dislocation density and lattice distortion, resulting in a lower, sharper Barkhausen response.
This distinct contrast enables this analysis to serve as both a quick verification tool and a diagnostic method. A simple contact check using a handheld probe can confirm within seconds whether a part or batch has achieved the target hardness and transformation state. Alternatively, an automated scanning or mapping inspection can reveal subtle variations caused by uneven heating, quenching, or post-process re-tempering and grinding.
Unlike many other non-destructive techniques, it requires no special surface preparation or coupling media. Measurements can be made directly on machined or ground surfaces, provided they are ferromagnetic and accessible. In some cases, BNA can also operate through coatings, such as HVOF chromium coatings on structural steel, and provide accurate insights. This makes it ideal for in-process verification, final inspection, and field assessments, supporting real-time process control and fast decision-making.
Comparison with Adjacent Verification Methods
While no single inspection method captures every variable, BNA occupies a distinctive position in the non-destructive testing landscape. Hardness testing provides a direct mechanical measure of strength but is destructive and slow. Eddy current techniques are fast but primarily respond to surface conductivity and hardness, not underlying microstructure. Ultrasonic methods are excellent for detecting internal flaws but less effective in distinguishing between tempered and hardened phases. X-ray diffraction remains the reference standard for residual stress measurement but is stationary, slower, and typically limited to laboratory use.
BNA bridges these gaps by offering metallurgical sensitivity, speed, and portability, making it an ideal complement to conventional hardness and microstructure testing and providing immediate feedback without sectioning or preparation. Several defining attributes are as follows:
Fast — each measurement takes only seconds
Non-destructive — contact-based, leaving no surface mark
Microstructure-sensitive — reflects both phase transformation and stress state
Portable and adaptable — usable in-line or in the field with handheld or robotic probes
Case Example 1: Induction-Hardened Camshaft Inspection for Heat Treatment Defects
Camshafts undergo highly localized induction hardening to create a wear-resistant surface layer while maintaining ductility in the core. Variations in induction power, cleanliness from machining waste, coil positioning, or quench delay can lead to soft spots or over-tempered areas, which reduce fatigue life. Similarly, aggressive post-hardening grinding can cause thermal rehardening or burn damage, both of which affect local stress and hardness.
Figure 2. Sensor on camshaft Source: Stresstech Inc.
BNA provides a fast, non-destructive way to detect these variations. In one case, a powertrain manufacturer applied a line scan across each cam lobe using an automated BNA system. The resulting Barkhausen map revealed both high-signal areas (softer, grinding burned, re-tempered zones) and low-signal regions (hardened/normal zones).
Subsequent correlation with microhardness profiles confirmed that regions with elevated Barkhausen activity corresponded to localized softening due to heat treatment defects or rehardening from grinding burn damage, while areas with reduced response aligned to the master part readings that verify successful production of parts. This dual sensitivity allowed engineers to distinguish between heat treatment and surface finishing issues using a single technique.
Figure 3. Graphical Barkausen response showing heat treatment defect (soft spot) on cam lobe (etched lobe shown) Source: Stresstech Inc.
After integrating BNA into the inspection cell, the manufacturer reduced scrap and rework rates by over 25% through optimizing their production process based on resulting data, while gaining digital traceability for each camshaft. Automated result logging allowed process engineers to correlate defects with specific machine parameters, improving control and accountability across both induction and grinding stages.
Case Example 2: Detecting Manufacturing Defects in Heat Treated Wind Turbine Gearbox components
Moventas (now operating as Flender Finland Oy), an expert in wind turbine gearbox manufacturing, has been in the industry for 40 years and is passionate about innovating gearbox solutions that enable cost-savings & trouble-free operation. Over the past 30 years, starting from the very first Barkhausen system to the latest robotized system, Moventas has trusted their grinding inspection to Barkhausen noise measurement systems.
Figure 4. Moventas Exceed Evo+ Source: Flender Finland Oy
Nowadays, wind turbine manufacturers require that surfaces of heat treated gears are also tested for the possibility of grinding burn. Grinding burn is a common name for thermal damages that occur on the surface during grinding processes following heat treatment. These burns cause local discolorations on the surface, and they can soften or harden surface layers and cause unwanted residual stress.
Nowadays, wind turbine manufacturers require that surfaces of heat treated gears are also tested for the possibility of grinding burn. Grinding burn is a common name for thermal damages that occur on the surface during grinding processes following heat treatment. These burns cause local discolorations on the surface, and they can soften or harden surface layers and cause unwanted residual stress.
Figure 5. RoboScan XL measuring a sun pinion Source: Stresstech Inc.
Moventas is an advanced BNA user and uses it beyond just sorting good samples to burnt ones.
Taisto Kymäläinen, quality manager at Moventas, explains that Barkhausen’s method allows for the early detection of damage, as BNA reacts in the smallest changes in a microstructure. As a result, it can be used to optimize a grinding process to find correct grinding parameters. For example, BNA can reveal flaws in cooling or grinding stone wear before actual burn appears.
This means that with critical energy applications, BNA can be relied upon as a complete non-destructive testing technique when looking at microstructure consistency and integrity.
As BNA can identify consistent and accurate heat treatment characteristics of components, as well as additional damage caused during the manufacturing process, it is often relied upon as a crucial quality control check to verify each component in critical applications. Since BNA is a comparative method, users need to determine acceptable levels for their products with the master sample procedure. The master sample procedure can be validated with X-ray diffraction measurements or nital etching, for example. When the master sample procedure is set, BNA is an accurate method to detect microstructure changes.
This method has now become widely utilized by the energy sector as an established testing method, which is gaining widespread adoption by OEMs and operators as the gold standard of quality control inspections of critical components across their technologies.
Integration into Quality Systems
Modern Barkhausen measurement platforms combine precise sensing with digital analysis, providing traceable, repeatable, and operator-independent quality data. Results can be stored locally or integrated into manufacturing execution systems (MES) and quality management systems (QMS) for statistical process control and long-term trending.
Because of its portability and speed, BNA supports a range of industrial inspection strategies:
In-process verification of heat treated batches or ground components
Incoming inspection of hardened parts from suppliers
Failure analysis and field verification during maintenance and overhaul
When used alongside hardness or residual stress testing, this inspection technique enriches process understanding by revealing how microstructure, hardness, and stress interact. It transforms heat treatment verification from a subjective evaluation into a quantitative, magnetic-domain-based diagnostic of material integrity.
Conclusion
BNA provides a unique combination of speed, non-destructiveness, and metallurgical sensitivity for verifying heat treatment performance in ferromagnetic steels. Its fundamental sensitivity to magnetic domain wall mobility allows it to distinguish between soft, untransformed ferritic–pearlitic structures (high signal) and hard, fully transformed martensitic or bainitic phases (low signal).
For furnace batch processes, this technique delivers rapid confirmation that complete transformation has occurred and that quenching uniformity has been achieved. For localized induction-hardened or ground components, it identifies heat treatment defects, soft spots, and grinding-related damage in a single inspection.
As manufacturers pursue smarter, faster, and more traceable quality control systems, BNA is a practical bridge between metallurgical science and modern production efficiency, providing a magnetic fingerprint that reveals the true structural and stress condition of steel components.
About The Author:
Neil Owen, General Manager, Stresstech Inc.
Neil Owen serves as the general manager of Stresstech Inc. (Americas), based in Pittsburgh, PA. He helps manufacturers and researchers apply Barkhausen Noise Analysis and X-ray diffraction for heat treatment verification and quality control. With hands-on and leadership experience, he bridges advanced NDT with production needs in aerospace, automotive, and related critical sectors across the Americas.
For more information: Contact Neil at Neil.Owen@stresstech.com or LinkedIn.
A United States military base will receive an electrically heated draw batch oven for use in heat treating aerospace components. The industrial oven was engineered to meet critical safety requirements and the stringent demands of aerospace heat treating.
Electrically heated draw batch oven to heat various steel parts for aerospace components. Source: Wisconsin Oven CorporationDoug Christiansen, Senior Application Engineer of Wisconsin Oven Corporation
Manufactured by Wisconsin Oven Corporation, the system features combination-style airflow that delivers both horizontal and vertical upward heat flow to ensure optimal heating rates and consistent temperature distribution across the product. Temperature uniformity has been verified through a Class 1 Temperature Uniformity Survey (TUS) conducted in accordance with pyrometry specification AMS 2750H, with achieved uniformity of ±5°F at 200°F, 700°F, and 1200°F.
“This draw batch oven was designed with additional safety features for operators, tight uniformity, and compliance standards required by the U.S. Military. The temperature uniformity survey was performed prior to shipment to verify compliance with AMS 2750H Class 1 requirements,” said Doug Christiansen, senior application engineer.
The oven features “can” style construction with a heavy plate exterior and six inches of high-temperature insulation for durability and thermal efficiency. A custom portable load/unload cart allows operators to stage the load before heating and remove it for cooling.
The UL508A-certified control panel includes a Eurotherm 3504 programmable temperature controller with advanced auto-tune and Ethernet communication. It also features a high-limit instrument to prevent over-temperature conditions, along with low-voltage calibration TC jack plugs and a variable frequency drive for the recirculation blower.
Press release is available in its original form here.
Heat Treat Todaypublishes twelve print magazines a year and included in each is a letter from the editor. This letter is from the October 2025 Ferrous & Nonferrous Heat Treatments/Mill Processingprint edition. In today’s letter,Bethany Leone, managing editor at Heat Treat Today, shares her insights on where artificial intelligence stands in the heat treating industry nine months into 2025.
In January 2025, the heat treat industry was envisioning operational improvements thanks to leaps in artificial intelligence (AI) developments. Now, nine months later, are we still searching for AI?
Managed by AI
Daniel Llaguno, President of NUTEC Bickley
For many industry players, AI has started in the office before the furnace. This can look like creating manuals, writing emails, and reading contracts to interpret legal language.
Daniel Llaguno, president of NUTEC Bickley, calls this the early stages of AI adoption. His company has leveraged AI for onboarding and training new employees — a low-risk, high-value application.
Like many suppliers, they are exploring how AI could eventually reshape furnace development, likely on an open-loop system first (versus a closed-loop where AI receives furnace information and immediately sends back direction to the furnace controls on how to respond).
The Furnace Floor
Jason Orosz, President of Global Heat Treating Services
The next step is already visible: integrate AI into existing IIoT platforms that manage floor operations. Platforms that you may already have considered are QMULUS by NITREX, PdMetrics by Ipsen, and Edge Process Management (EPM Data) by Eurotherm, a Watlow company. These are just a sampling of advanced management systems on the marketplace, and ones that are at different stages of incorporating AI and machine learning for process optimization.
QMULUS has already deployed across all North American Heat Treating Services locations, according to Jason Orosz, president of Global Heat Treating Services. He says AI has been useful in “helping with analysis, troubleshooting, and quality control” — themes you will hear repeatedly in early AI applications.
Evolving To Meet Expectations
Michael Mouilleseaux, General Manager of Erie Steel, Ltd
What should AI integration into furnace operations look like? Michael Mouilleseaux, general manager at Erie Steel, has commented that heat treat AI should help the industry shed its “black magic” reputation. He envisions advanced analysis that could, for example, “correlate intergranular oxidation (IGO) results with furnace integrity checks (i.e., leaks), eventually establishing hard limits for allowable leak rates.”
Still, obstacles remain. “I think it’s going to be a while before commercial heat treaters can relinquish furnace control over to an AI,” Orosz added, specifically commenting on maintaining furnace parameters. This makes sense due to the need for commercial heat treaters to conform to client specifications. Rather, he says in-house heat treat operations “are likely going to be the first movers in that area since they can make their own rules.” For readers of this publication — who primarily are coming from these types of operations — that should be an encouragement: you have a key role to innovate.
Lee Rothleutner, Manager of Materials R&D, The Timken Company
One other key factor for this integration to occur within operations comes with acknowledging the heavy digital capacity that AI requires. Lee Rothleutner, manager of Materials R&D at The Timken Company, commented on this very point, writing to me that for high-quality digital data, the heat treat industry needs to commit not just to the investment but to maintaining a robust data collection and storage infrastructure. He also foresees one pathway of AI integration beyond preventative maintenance, noting, “AI applications can extend to process optimization, quality control, and energy efficiency improvements.”
What To Do Now
For successful integration of AI technology, the common denominator is that management teams are being encouraged to constantly try new ways to innovate with AI.
The first thing you need to do is open an email and send me your AI integration story. Just kidding. (Not really.)
Finally, if you are attending ASM Heat Treat 2025 this month, bring your AI to the table … literally, if you have a booth. Showcase what you’ve been doing at your location or become a part of the conversation. Lee Rothleutner, quoted above, will be participating in a panel discussion on this very topic in the afternoon of Tuesday, October 21.
The Heat TreatToday booth is #944. Not everyone is accustomed to the rapid pace of tech adoption; we want to help one another understand the risks and potential that AI brings, and your stories are critical. I look forward to talking with you.
References
Glenn, Doug, and Llaguno, Daniel. 2025. Interview by Heat Treat Today. Private recording, February.
Loepke, Mike. 2025. “Digitalization Propels Heat Treating to Industry of the Future.” Heat Treat Today 7 (8).
We’re celebrating getting to the “fringe” of the weekend with a Heat TreatFringe Fridayinstallment: Global System, a manufacturer specializing in the production of fire-resistant doors, shutters, and smoke curtains, is adding a furnace from a well-known heat treat solutions manufacturer. The device will be used to carry out fire resistance tests for building products in accordance with the standard temperature curve. Critically, it has the ability to test solutions intended for both industrial and private use, enabling them to significantly increase competitiveness and productivity.
While not exactly heat treat, “Fringe Friday” deals with interesting developments in one of our key markets: aerospace, automotive, medical, energy, or general manufacturing.
The contract covers the delivery of a vertical fire test furnace. This includes a flue gas purification system, a complete set of equipment, installation, commissioning, and staff training.
The furnace, supplied by SECO/WARWICK, enables advanced testing at temperatures reaching up to 1200°C (2192°F), in accordance with current fire resistance standards, which are applicable in both commercial building and maritime construction.
“The device may, in the future, support certification processes which the Partner is considering as their next development step,” says Mariusz Raszewski, Deputy Director of the Aluminum and Atmospheric Solutions Sales Division at SECO/WARWICK. He continues, “Laboratory furnaces for fire resistance testing in various configurations are intended for testing the fire resistance of suspended ceilings, vision panels, walls, columns and other structural elements. These tests are crucial for delivering safe construction solutions to the market.”
Mariusz Raszewski, Deputy Director of the Aluminum and Atmospheric Solutions Sales Division at SECO/WARWICK (Source: LinkedIn)Łukasz Jeleński, Technical Director of Global System sp. z o.o. (Source: LinkedIn)
“Safety and property protection are priorities in every facility. Global System provides fire protection solutions for various types of buildings — from residential and public utility structures to production halls and warehouses…. The device will allow us to conduct advanced product development research, including analysis of resistance to high temperatures and the impact of various fire conditions. Thanks to this, Global System will be able to further improve its products, increasing their safety and durability,” emphasized Łukasz Jeleński, Technical Director of Global System sp. z o.o.
He continued, “The furnace from SECO/WARWICK will allow us to test the properties of our products, and in the future, to apply for their certification. This is a big step in the company’s development. Additionally, having our own research facilities will enable us to carry out fire tests much faster and shorten the time to market for new solutions.”
The technology of fire testing furnaces is gaining popularity among building material manufacturers, as evidenced by SECO/WARWICK’s supply of a similar device to the French building materials giant KNAUF SAS. Several years ago, the company also supplied ALUPROF with a fire resistance test furnace. The SECO/WARWICK system allows the Partner to test new products, such as windows, doors, and façade systems before they are introduced to the market.
According to the State Fire Service, the highest number of fires in recent years was recorded in 2022 (93,453 incidents), which was an increase of more than 44% compared to 2021 (64,730). In the public utility buildings segment, the number of fires remained around 1,200–1,300 cases per year. Encouragingly, there has been a clear downward trend in fires in residential buildings from 2021 (20,633) to 2024 (16,656). The level for production and warehouse buildings has been relatively stable. In both cases, the number of fires did not exceed 1,500 per year. This shows just how important it is to raise public awareness of the crucial role fire protection systems play in buildings; implementation can contribute to improving safety.
Press release is available in its original form here.
ArcelorMittal is advancing a major expansion in electrical steel production that includes a preparation line, a continuous annealing and varnishing line, and a slitting line — developments that reflect ongoing job growth and investment in industrial heat treating processes worldwide. The project has already mobilized more than 300 external contractors, with 175 employees now dedicated to the new lines and staffing expected to reach approximately 200 as the next phase of work progresses. Phase 2, currently underway, includes construction of an annealing-pickling line and a reversible rolling mill, with all five planned production lines scheduled to be operational by 2027.
Entry zone of the continuous annealing and varnishing line Source: ArcelorMittal FranceBruno Ribo Managing Director ArcelorMittal France
ArcelorMittal France announced that the first three lines of its new electrical steel production unit at the Mardyck industrial site will enter into operation by the end of 2025. The project, representing a €500 million investment and described as the largest undertaken by the Group in Europe over the past decade, marks a significant expansion in the production of electrical steels, complementing the company’s existing output at Saint-Chély-d’Apcher and bringing the company’s total European output to approximately 295,000 metric tons annually.
Bruno Ribo, managing director of ArcelorMittal France, emphasized the significance of the development for both the site’s workforce and the broader market. “Creating new production lines is an exceptional experience in the life of an industrial site. It is just as exceptional for our employees who have been involved in the development of the lines, from the project phase to the operational phase. I, like them, will be very moved to see the first of the 155,000 tons of electrical steel that we will eventually deliver annually roll off the lines,” he said.
Annealing and varnishing line control cabin Source: ArcelorMittal France
The electrical steels produced at Mardyck — ultra-thin rolled steels engineered for specific magnetic and mechanical properties — are used in all types of electric motors. ArcelorMittal notes that the new unit will support the electrification of applications in both industrial and automotive sectors. As global demand grows for these specialty steels, capacity developments of this scale create benchmarks for manufacturers across regions, including North America, as companies assess long-term sourcing strategies and material availability for high-efficiency motor components and transformer systems.
The project is supported in part by a €25 million contribution from the French State under the France 2030 program.
Press release is available in its original form here.
Heat Treat Today has gathered the four heat treat industry-specific economic indicators for December 2025. The December results suggest more limited growth than what was predicted in November of 2025.
December’s indices showed modest expansion with mixed momentum across different indicators. The Inquiries stayed moderately positive at 51.3 (from 56.5 in November). Bookings are encouraging at 56.3 (up from 55 in November). The Backlog index is in contraction territory at 46.3 (from 55 in November). Finally, the Health of the Manufacturing Economy index showed moderate growth at 53.8 (from 56.5 in November).
The data suggests cautious optimism but warrants close monitoring of inquiry trends and backlog levels in coming months.
The results from this month’s survey (December) are as follows: numbers above 50 indicate growth, numbers below 50 indicate contraction, and the number 50 indicates no change:
Anticipated change in Number of Inquiries from November to December:51.3
Anticipated change in Value of Bookings from November to December: 56.3
Anticipated change in Size of Backlog from November to December: 46.3
Anticipated change in Health of the Manufacturing Economy from November to December: 53.8
Data for December 2025
The four index numbers are reported monthly by Heat Treat Today and made available on the website.
Heat TreatToday’sEconomic Indicatorsmeasure and report on four heat treat industry indices. Each month, approximately 800 individuals who classify themselves as suppliers to the North American heat treat industry receive the survey. Above are the results. Data started being collected in June 2023. If you would like to participate in the monthly survey, please click here to subscribe.
Producing durable, wear-resistant gears for the wind turbine industry requires exacting control of carbon diffusion. Modern low pressure carburizing (LPC) is pushing the boundaries of control and consistency. This technology fine tunes carbon diffusion into the surface of components, and applied in a new pit-style vacuum furnace, it also delivers temperature uniformity, stronger gears, and shorter cycle times for large, complex components, all while eliminating oxidation and direct CO₂ emissions. In this Technical Tuesday installment, Tom Hart, director of sales for North America at SECO/WARWICK Corporation, examines how modern LPC technology in a pit-style vacuum furnace is reshaping high-volume carburizing for today’s in-house heat treaters.
This informative piece was first released inHeat Treat Today’sNovember 2025 Annual Vacuum Heat Treating print edition.
The Need To Carburize
Carburizing is a thermochemical treatment that finds applications across the automotive, aviation, and energy industries, particularly in power transmission systems. The widespread use of this process across many industries stems from its ability to improve mechanical properties by enriching the surface of steel with carbon.
Consider the wind turbine industry, growing with a CAGR (compound annual growth rate) of 6.2% from 2024 to 2033 (GlobeNewswire 2024). Carburizing plays a key role in the production of gears and pinions. These components, often made of alloy steels, such as 18CrNiMo7-6, 4320, 4820, and 9310 (GearSolutions 2009, Jantara 2019), must meet high strength and quality requirements. Carburized layers, often over 4 mm thick, provide resistance to wear and dynamic loads, which is important given the turbine’s expected service life of at least twenty years.
In practice, however, gears often require servicing after five to seven years (Jantara 2019), with their failures generating long downtimes and high costs (Perumal and Rajamani 2014).
Figure 1a: Pit-LPC in a hardening cell (model)Figure 1b: The view from the operator platform
The carburizing process, combined with hardening (usually in oil) and tempering, increases:
Surface hardness: improving abrasian resistance
Core ductility: protecting against cracks
Fatigue strength: extending the life of the part, which translates into lower operating costs
Alternative technologies, such as nitriding or surface hardening, offer other benefits (e.g., reduced deformation), but have limitations, such as thinner hardened layers, relatively long nitriding process times, or difficulties with complex geometry for surface hardening.
Pit Meets Vacuum LPC
Traditional atmospheric carburizing, despite its established position, has reached its limits in process performance expectations. In response to market needs, LPC (low pressure carburizing) technology is being increasingly implemented to enable precise process control, reduced emissions, and improved energy efficiency. More specifically, a pit furnace with vacuum heat treatment capabilities, aka the Pit-LPC, has been designed and developed to carburize thick layers on very large and/or long parts. This furnace combines the advantages of LPC technology with the ability to integrate existing hardening cells, facilitating the modernization of older installations.
While a vacuum furnace opening to an air atmosphere is a feature previously reserved for atmospheric furnaces, this innovative pit furnace has ceramic insulation and a dedicated heating system to leverage this capability. The chamber door can therefore be opened at process temperature in an air atmosphere for the direct transfer of the charge to the hardening tank. Additionally, the furnace is equipped with a closed circuit forced cooling system, which significantly shortens the charge cooling time from the carburizing temperature to the hardening temperature, increasing efficiency and shortening the production cycle.
Furthermore, the furnace allows for the process to be carried out at temperatures of 1925°F (1050°C) and higher, significantly shortening carburizing time and reducing production costs, even while maintaining a safe level of grain growth (e.g., 1800°F (980°C)).
Benefits of LPC technology designed in a pit furnace include:
Reduced process time due to higher operating temperatures
Elimination of internal oxidation (IGO) in the carburizing process
Highly uniform carburized layer
Low process gas consumption
No direct CO₂ emissions and fire risk
Ready for operation without lengthy conditioning
Computer-aided process support
Additionally, the furnace design increases work safety and comfort in its elimination of open flames, risks of explosion, and the need for constant atmospheric monitoring.
Figure 2. SimVac program window with an example LPC process simulation
This new pit furnace is compatible with SimVac software, developed by Lodz University of Technology and SECO/WARWICK, which enables the simulation and optimization of LPC parameters, reducing the need for process tests. SimVac Plus is a simulation software that includes a vacuum carburizing module (Figure 2). The program can be used either as a standalone tool for designing processes based on the desired carburized layer requirements or to visualize the effect of a given boost/diffusion sequence in the form of a carbon profile.
Testing the Furnace Characteristics and Technical Parameters
The furnace was designed to meet the highest requirements for heat treatment equipment. The basic technical parameters are as follows:
Working space / charge weight: 71″ diameter x 118″ deep / 17,600 lb (1,800 mm x 3,000mm deep / 8,000 kg)
Operating temperature: up to 2010°F (1100°C)
Heating power: 360 kW, three independent zones
Vacuum level: 10⁻² torr
Carburizing gas: acetylene
Temperature Uniformity
Temperature distribution tests were conducted in the furnace, with 12 load thermocouples arranged according to the diagram shown in Figure 2. Measurements were taken at several temperatures under vacuum conditions. The purpose of the tests was to confirm compliance with the Class 1 ±5°F (3°C) requirements of the AMS2750 standard.
Figures 3a-d. Location of the TUS load thermocouples and the results in vacuum at temperatures of 1550°F (840°C), 1800 °F (980°C), and 1925°F (1050°C)
The results presented in Figure 3 indicate that the furnace provides above-average temperature uniformity, which is particularly important for a large workspace with 71″ diameter x 118″ deep (1,800 mm diameter × 3,000 mm deep) and the processing of large-sized components with thick layers. The temperature difference (ΔT) between the extreme thermocouples, measured at 1550°F (840°C), 1800 °F (980°C), and 1925°F (1050°C), did not exceed 3.5°F (2°C). This means that the furnace meets the Class 1 requirements of the AMS2750 standard by a wide margin.
Operational Dynamics
Additionally, to evaluate the furnace’s operational dynamics, heating and cooling tests were performed on an empty device with samples. Figure 4a shows the heating curve; the furnace reaches a temperature of 1800°F (980°C) in 60 minutes. The furnace’s high energy efficiency has a heat loss of just 32 kW under these circumstances.
Figure 4a. Heating RateFigure 4b. Cooling Rate
Figure 4b shows teh curve of cooling forced by nitrogen at atmospheric pressure, measured in three zones and on samples with diameters of 1″ (25 mm) and 4″ (100 mm). The temperature drops from 1800°F (980°C) to 575°F (300°C) in 60 minutes; reaching 210°F (100°C) takes only two hours, whereas natural cooling would take several days.
Vacuum tests show that the furnace reaches operating vacuum of 10⁻¹ hPa in under 30 minutes and has a leakage rate of 10⁻³ mbar·l/s, which meets the industry standard for vacuum furnaces.
Test of Atmosphere vs. Vacuum Carburizing Processes
To obtain a carburized layer 0.145–0.160″ (3.7–4.0 mm) thick for 52.3 HRC (550HV1), two tests were compared: one in the PEGAT atmosphere furnace (Figure 5a) and another in the Pit-LPC vacuum furnace (Figure 5b). In both cases, the charge consisted of seven gears made of 18CrNiMo7-6 material, with a total weight of approximately 6.5 tons and a surface area of 280 ft² (26 m²). The process consisted of three stages:
Stage I: heating to the carburizing temperature and soaking
Stage II: actual carburizing with cooling to the hardening temperature and holding
Stage III: hardening in an external quenching tank — identical in both processes
Table A. Atmosphere vs. Vacuum Carburizing Process ComparisonFigure 5a. Essential process data and schematic flow of the carburizing process in a PEGAT atmosphere furnaceFigure 5b. Essential process data and schematic flow of the carburizing process in the Pit-LPC vacuum furnace
The LPC process, which consists of saturation and diffusion segments (Figure 6) allows for the precise control of carbon distribution. As the process progresses, the duration of the diffusion segments is extended, ensuring uniform saturation of the material.
Figure 6. Vacuum carburizing process trends in the Pit-LPC
After carburizing and hardening, all components were tempered at 355°F (180°C) for three hours.
Table B. Chemical Composition of 18CrNiMo7-6 (according to EN10084)
Gears and samples made of 18CrNiMo7-6 steel were used for destructive testing, in accordance with the EN 10084 standard. Six cylindrical samples were placed throughout the workspace — inside and outside the part — to assess carburization uniformity.
Tests conducted:
Vickers microhardness (HV1): performed on a Struers Durascan 70 device, allowing for the determination of hardness profiles and carburized layer depth (ECD) — a load of 9.81 N (HV1).
Surface and core hardness (Rockwell): measurements were performed on a Wilson Wolpert TESTOR tester with a load of 1470.1 N. At least five measurements were taken for each sample.
Microstructure: assessed on a Nikon LV150 optical microscope after nital etching.
Internal oxidation (IGO): analyzed on the unetched surface of the microsection.
Figures 7a-f. Microhardness profiles after the full process (carburizing, hardening, and tempering)
Figure 7 shows the microhardness profiles for the tested samples. For each sample, microhardness paths were inspected in three cross-sections. Based on this, the effective ECD layer thickness obtained on each sample was determined, as presented in Table C.
Table C. Thickness of the Carburized Layer Read from the Microhardness Charts (effective case depth average is 0.145–0.160″ (3.7–4.0 mm) at 52.3 HRC (550 HV1))
Average ECD values obtained for the samples ranged from 0.148 to 0.154″ (3.77 to 3.91 mm).
Surface and core hardness values for all samples were consistent and typical of carburized layers (Table D). Surface hardness ranged from 61.0 to 63.2 HRC and core hardness from 39.9 to 40.7 HRC. Interestingly, samples located on the inner side of the wheel achieved slightly higher surface hardness values (caused by retained austenite and cooling intensity).
Table D. Measured values of surface hardness and core hardness
Microstructure images of low-tempered martensite, along with retained austenite, were identified, ranging from 17 to 20% (Figure 8). The amount of retained austenite was determined using NIS-Elements software. No variation in structure was observed depending on sample location.
Figure 8a. Exemplary post-processing microstructure pictures of sample 1 surface. Magnifications x100 (left) and x500 (right). Nital etching 2%. Martensite with residual austenite (approx. 18%).Figure 8b. Exemplary post-processing microstructure pictures of sample 4 surface. Magnifications x100 (left) and x500 (right). Nital etching 2%. Martensite with residual austenite (approx. 20%).
The presence of intergranular oxidation (IGO) was also inspected, averaging 5.5 μm throughout the tested samples. For comparison, intergranular oxidation in the atmospheric process averages above 15 μm. In the new LPC pit furnace, internal oxidation only occurs during unloading and transfer of the charge to the hardening tank, whereas in the atmospheric furnace, the presence of oxygen in the carburizing atmosphere is also significant, significantly increasing the IGO value.
The level of hardening deformation after the process conducted in the new LPC pit furnace and the atmosphere furnace is comparable due to the use of the same hardening tank in both devices and the absence of the carburizing process.
Comparison of Process Economics
Economic aspects play a key role in modern heat and thermochemical processing. Therefore, the consumption of basic utilities was compared for the reference processes (described in Chapter 5), resulting in a 0.152″ (3.8 mm) thick hardened layer. The analysis included a Pit-LPC and a PEGAT-type atmospheric furnace, both with identical workspace and the same charge. In addition, the LPC process was simulated at 1900°F (1040°C). The results are summarized in Table E.
Table E. Comparison of utility consumption and costs
The results show that the new LPC furnace model consumes significantly less electricity by approximately 57%, which translates into a lower carbon footprint, especially when energy is derived from fossil fuels. Nitrogen consumption is comparable, with a slight advantage for the Pit-LPC (savings of up to 10%).
The largest differences are found in carburizing gases. The atmospheric furnace consumes 9,900 ft³ (280 m³) of methane — approximately 440 lb (200 kg) and an additional 4.4–13.2 lb (2–6 kg) of propane per process. In the LPC furnace, acetylene consumption is reduced to 39.2 lb (17.8 kg) because carburizing gas only flows during the boost phase.
Importantly, the LPC process does not generate direct CO₂ emissions, unlike an atmospheric furnace, which emits approximately 1325 lb (600 kg) of CO₂ per cycle. Cooling water consumption in the new LPC furnace is also reduced by over 45%.
The presented comparison of utility consumption in the two types of furnaces directly translates into the economic aspects of using these devices and conducting production processes. For cost comparison purposes, the following unit utility costs were assumed, as presented in Table F:
Table F. Unit costs of energy factors and technological gases according to European averages
In summary, the total utility costs for the process conducted in the Pit-LPC at 1800°F (980°C) are 53% lower compared to an atmospheric furnace conducted at 1700°F (925°C). At a temperature of 1925°F (1040°C), savings reach 60%. These savings are primarily due to lower energy and process gas consumption. Furthermore, the lack of CO₂ emissions eliminates the need to pay emission fees.
The efficiency of this furnace is almost twice as much at 1795°F (980°C) and three times as much at 1925°F (1040°C) compared to an atmospheric furnace.
Summary
The new Pit-LPC vacuum furnace combines the design features of a top-loaded pit and performs carburizing using vacuum technology instead of atmospheric technology. Bringing higher processing temperatures than traditional atmospheric furnaces to the market, as well as the ability to open hot in an air atmosphere, this technology proves that direct transfer of the charge to the hardening tank is possible in vacuum furnaces.
Another key development, this design significantly shortens carburizing time compared to atmosphere furnaces since the furnace can operate under vacuum, inert gas (nitrogen, argon), air, and carburizing gases, at temperatures up to 2010°F (1100°C).
Since this new pit furnace design does not require the use a retort or atmosphere mixer, which are the most vulnerable components inside a traditional atmospheric furnace, the furnace operates with greater reliability and lower costs. Furthermore, an efficient and robust vacuum pumping system provides the vacuum environment and operational readiness in less than 30 minutes. Time is also saved by the integrated closed-loop gas cooling system that shortens cooling time: dropping temperatures from 1800°F (980°C) to 1545°F (840°C) in 30 minutes for a full charge and to 210°F (100°C) in two hours for an empty furnace, operations which would take several hours and days respectively in atmosphere furnaces.
The advanced thermal insulation and a uniform heating element layout ensure high energy efficiency and precise temperature uniformity in the working space, yielding additional cost and energy savings.
This carburizing process is based on FineCarb LPC technology and supported by the SimVac simulator, enabling precise carbon profile shaping and achieving layers 0.148–0.154″ (3.77–3.91 mm) thick with high repeatability.
With the ability to operate at temperatures up to 1925°F (1050°C), the new LPC pit-styled furnace significantly shortens process time, reduces utility consumption, and lowers operating costs by up to 50%, while increasing productivity by a factor of x2 to x3. One of these furnaces can replace two to three atmosphere furnaces of the same size.
Finally, the furnace operates in a safe and non-flammable atmosphere, emits no direct CO₂, and reduces energy consumption, making it an environmentally friendly solution.
Conclusions
The Pit-LPC furnace is a modern alternative to the traditional atmosphere furnace and offers a number of advantages in terms of quality, efficiency, safety, economy, and ecology. Providing an innovative solution for vacuum carburizing and meeting stringent carburization layer thickness guidelines, this design is a viable option to fully replace traditional atmospheric pit furnaces operating in a carburizing atmosphere.
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Perumal, S., and G. P. Rajamani. 2014. “Improving the Hardness of a Wind Turbine Gear Surface by Nitriding Process.” Applied Mechanics and Materials 591: 19–22.
Tom Hart Director of Sales for North America SECO/WARWICK Corporation
Tom Hart joined SECO/WARWICK in 2011 as a sales engineer and has been in the precision manufacturing industry for over 16 years. His responsibilities have him caring for SECO/WARWICK’s clients and their various process and heat treatment equipment needs. Tom received his manufacturing engineering degree from Edinboro University of Pennsylvania, has authored numerous white papers, and is recognized throughout the heat treatment industry as a go-to-guy for thermal processing.
