Newton Heat Treating has completed a major equipment upgrade, replacing steam accumulators that had been in service for 20 years in its uphill quenching/cold stabilization operation. The upgrade directly impacts the company’s aerospace processing capabilities, with many parts destined for optical components in space applications undergoing this critical heat treatment process.

According to the company, the new steam accumulators have delivered immediate operational improvements. The heat treat transfer time from the steam accumulators to the steam chambers (where parts are inserted) is faster, providing better tensile stress reduction. Energy efficiency has also improved, with steam blasting time cut by about 10%.

John Avalos, quality engineer at Newton Heat Treating, reported, “primary operator who runs this process, Alfred Ojeda, said that the new steam accumulators don’t take as long to pressurize.” This will cut down on processing time, he explains.

Newton Heat Treating partnered with McKenna Boiler Works, Inc. for the installation project, which was completed on time and to specifications.

The uphill quenching/cold stabilization process is essential for aerospace components, particularly those requiring precise dimensional stability and stress relief for mission-critical optical systems used in space.

Want to learn more about uphill quenching? Check out the Heat Treat Radio episode where Newton Heat Treating CEO Greg Newton and John Avalos discuss this little-known but highly effective process for controlling residual stress in aluminum alloys.

Press release is available in its original form here. Additional details provided by the company.

Ask The Heat Treat Doctor® has returned to bring sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.

This informative piece was first released in Heat Treat Today’s November 2025 Annual Vacuum Heat Treating print edition.

Case depth, case uniformity, and final mechanical (as well as other) properties rely not only on controlling both equipment and process variability during heat treatment, but on having clean, properly prepared part surfaces prior to and during heat treating. Expert Dan Herring encourages to learn more below.

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Case hardening is a thermochemical surface treatment process designed to add a particular element or combination of elements to a material such as steel. Familiar examples include carbon (carburizing); carbon and nitrogen (carbonitriding); boron (boriding); nitrogen (nitriding); and nitrogen and carbon (nitrocarburizing — ferritic or austenitic). These processes are typically designed to increase the near surface hardness of steel after quenching.

However, various problems can arise due to either the materials or the manufacturing methods employed prior to or during heat treating that will retard or prevent absorption and/or diffusion of the desired element(s) during heat treating. Some of the metallurgical consequences can include:

• Shallow or uneven case depths
• Surface oxidation
• Intergranular oxidation or decarburization
• High levels of retained austenite
• Soft spots due to incomplete hardening

Machine-Induced Surface Conditions

Improper machining prior to case hardening can compromise surface integrity. Tooling choices, improperly maintained equipment, inadequate operator training, and even environmental factors can contribute to a variety of issues.

While machining problems occur frequently, they are mostly preventable. Attention to part surface condition, cleanliness, and mechanical integrity is essential before heat treating. Training, standardizing machining protocols, planned preventative maintenance programs, and part inspection prior to heat treating will help avoid these issues. Consult Table A for further details on how the causes and effects of undesirable machine-induced surface conditions can be solved.

Splatter of Stop-off Paints on Unintended Areas

A material that masks the surface of steel and delays or prevents case hardening is called a stop-off or maskant. These materials are applied to specific areas of a steel part to prevent the diffusion of hardening elements (like carbon or nitrogen) into the surface during case hardening processes, such as carburizing, nitriding, or carbonitriding. (See Table B.)

Enriching Gas Additions (Sooting)

During the carburizing or carbonitriding process, it is not uncommon to develop a layer of soot on the surface of the parts, especially if the enriching gas additions begin before the entire load is uniformly up to temperature. In some instances, the amount of soot formation is such that the case depth or uniformity is affected. This is often difficult to diagnose, as the soot layer “washes off” during quenching in a liquid, and the part surfaces come out of the furnace looking reasonably clean.

Material-Related Issues

The use of scrap in steelmaking, especially for low alloy case hardening steels can lead to a relatively high level of impurities and tramp elements. At high temperatures these impurities tend to segregate at grain boundaries and migrate toward the surface. This type of segregation can retard case hardening by impeding element (e.g., carbon) transfer. For example, the effects of tin (Sn) and antimony (Sb) on the kinetics of carburization are particularly problematic (Figure 1).

The effect of tramp elements on retardation of carburization can be expressed in the following order (Andreas, et al. 1996), namely Sb > Sn > P > Cu > Pb. To see the effect of one such element, the carbon transfer coefficient (ß) for typical commercial steels is shown as a function of antimony (Sb) content (Figure 2).

In Summary

These are a few of the many causes delaying or preventing case hardening from being effective. There are many others, including alkaline cleaning compounds (in too high a concentration) and even phosphate and other drawing lubricants used in the manufacture of fasteners. Inspection and cleaning of the part surface prior to case hardening will avoid many of these issues. Reviewing material certification sheets for elements known to interfere with case hardening is also an effective way to anticipate problems with case hardening.

References

Herring, Daniel H. 2014. Atmosphere Heat Treatment, Volume 1. Troy, MI: BNP Media.

Herring, Daniel H. 2015. Atmosphere Heat Treatment, Volume 2. Troy, MI: BNP Media.

Ruck, Andreas, Monceau, Daniel, and Grabke, Hans Jürgen. 1996. “Effects of Tramp Elements Cu, P, Pb, Sb, and Sn on the Kinetics of Carburization of Case Hardened Steels.” Steel Research 67 (6): 242–48.

About the Author

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

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

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

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Over the past year, Heat Treat Today has experienced many transitions: sending off several amazing editors into the next, family-focused stage of life and integrating the gifts of several outstanding editors and operations individuals. As we’ve dedicated time to focus on making what we do more compelling and helpful to you, we come to the last month of the year grateful for the opportunities we’ve had to take a call from an industry colleague, receive an editorial email from a reader, and bump shoulders at your heat treat operations and various industry events.

This Thanksgiving, we are thankful for how our team and the industry transforms. This is a particularly acute blessing as we see the final leaves descend this fall. God bless you and keep you and yours through all the changes of life.

For housekeeping purposes: our offices will be closed on November 27 and 28. Happy Thanksgiving!

An international, multi-billion-dollar corporation at the forefront of drivetrain technologies has commissioned a complete isothermal annealing line, due to be delivered in Q1 2026. The furnaces are designed to be in compliance with CQI-9, the comprehensive audit covering the most common heat treat processes employed by the automotive industry. This investment underscores the automotive industry’s commitment to delivering higher-quality components while meeting stringent manufacturing standards.

The system has been designed in close collaboration with NUTEC Bickley to ensure everything meets the company’s specific operational needs. The contract comprises both high-temperature and low-temperature furnaces, as well as an isothermal cooling chamber and blast cooling tunnel, together with all the ancillary equipment and full material handling and conveying system.

Arturo Arechavaleta, VP Metal Furnaces at NUTEC Bickley, said: “Our client for this multifaceted project is an auto component world leader that supplies nearly every major vehicle manufacturer. It has an established reputation in delivering high quality parts and promoting sustainability in the supply chain. I am delighted the NUTEC Bickley was chosen to partner in the design and manufacture of this isothermal annealing line.”

At the heart of the new facility will be a double pusher tray high-temperature furnace (HTF) designed specifically for processing carbon steel automotive parts. The system incorporates a fully automatic electrical double pusher system with steel trays sliding over rails with idle rolls. Processing two trays across the width helps reduce the line’s footprint while maximizing throughput.

The natural gas unit features four automatic temperature zones, each with two high-velocity nozzle-mix burners that provide excellent turbulence and outstanding recirculation within the furnace chamber. Operating temperatures range between 850°C and 950°C (1560°F-1740°F), with temperature uniformity targets of ±5°C (±40°F) for processes below 680°C (1260°F) and ±10°C (±18°F) at or above 680°C (1260°F).

The isothermal annealing process involves multiple stages that work in seamless coordination.

First, forged carbon steel parts move into an isothermal cooling chamber (ICC) after initial heat treating where the load temperature is rapidly reduced from 950°C (1740°F) to 660°C (1220°F) within five to 10 minutes, bringing parts to their transformation point. This rapid cooling uses ambient air supplied from an external cooling fan.

Then, parts proceed to a low-temperature furnace (LTF) operating at between 630°C and 700°C (1170°F-1290°F), which uses a fuel-only control system for enhanced temperature uniformity. The furnace relies on three automatic temperature control zones and six burners.

Finally, tray loads pass through a blast cooling tunnel (BCT) where forced convection cooling with ambient air brings parts down to approximately 400°C (750°F) before exit.

The complete line includes comprehensive material handling and conveying systems that operate fully automatically. It features entrance and transfer cars with movement systems, transfer car tracks, exit transfer cars with tray dumper units, integrated air cooling units, return conveyors with electrical dolly systems, and automated loading stations. The entire parts handling system is linked to the process via Master PLC and HMI for seamless operation.

Press release is available in its original form here.

In this Technical Tuesday installment, Nick Hicks, metallurgical services manager at Rolled Alloys, emphasizes the importance of mastering the basics of sigma phase metallography in stainless steels. Understanding these fundamentals helps you know when to consult a metallurgist and guarantee top performance of heat treated parts.

This informative piece was first released in Heat Treat Today’s November 2025 Annual Vacuum Heat Treating print edition.

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Heat treaters are always seeking new methods of heat treat and new alloys to improve performance at a lower cost. In the world of stainless steel, there are well-known choices like 310 and newer options like RA 253 MA®. These alloys have exceptional qualities, especially RA 253 MA, which has creep strength up to 2000°F and oxidation resistance up to 2000°F. However, heat treaters should be aware of a potential issue when using such alloys: the formation of sigma phase over time.

In some cases, premature wear in nickel alloys was attributed to sigma phase embrittlement, but it’s important to note that sigma phase does not actually precipitate in nickel alloys. Instead, the actual microstructure may exhibit grain boundary oxidation or carbides. This article seeks to provide a clearer understanding of sigma phase metallography and its impact on stainless steels.

Definition of Sigma Phase

Sigma phase is an intermetallic compound made up of chromium and iron. It is hard, brittle, and non-magnetic. At room temperature, the presence of sigma phase can make the material so brittle that a sudden, hard impact can shatter a piece of metal that contains it, similar to a piece of glass. Pure sigma phase forms when the chromium content is between 42% and 50%, and it is one of the equilibrium phases in the iron-chromium phase diagram as seen in Figure 1.

The peak temperature for sigma phase formation in a 46% Cr alloy is 1510°F. A literature review reveals that different sources cite varying temperature ranges for sigma phase formation. This variation is due to each alloy having its own unique sigma formation range. According to one expert (Kelly 2005), sigma phase can form in the temperature range of 1100°F–1600°F (590°C–870°C).

Metallurgy of Sigma Phase

Many engineers require assistance in distinguishing between sigma phase and the formation of grain boundary oxides and carbides. Otherwise, they might reach incorrect conclusions. Sigma phase is a precipitation product that can manifest in both individual grains and along grain boundaries. Examples of sigma phase formation can be observed in Figures 2–4.

When observing nickel and certain nickel alloys like RA330®, confusion can arise due to the presence of grain boundary oxidation or carbide formation. These occurrences are often mistaken for sigma phase formation by engineers, but it’s important to note that a nominal nickel content of at least 35% is sufficient to prevent sigma phase formation.

Figure 5 depicts RA330 after a 3,000-hour duration at 1900°F. Despite 1900°F being significantly higher than the sigma formation range, some engineers determined that the grain boundary oxides were sigma phase. When there is any uncertainty, it is advisable to consult with a metallurgist who is knowledgeable about the metallography of these alloys.

Physical Properties of Material with and without Sigma Phase

Table A displays the results of impact testing for six different alloys aged at three different temperatures for varying durations. All the alloys experienced some degree of deterioration over time, with certain alloys showing significant losses and reduced ductility. Further analysis revealed that each alloy has its own specific temperature at which sigma phase formation occurs most rapidly. In fact, the formation of sigma phase is dependent on the time at temperature, which makes a C-type curve.

Figure 6 depicts the time temperature transformation curves for sigma phase formation for a few different stainless steels. Any point past a specific alloy’s curve results in the formation of sigma phase.

The results of elevated temperature impact testing for six alloys are presented in Table B. Many of the values in the table indicate that these alloys generally show either no loss of ductility or significantly less loss of ductility when the testing is carried out at elevated temperatures. In most cases, the materials still exhibit sufficient ductility to be safely used at these temperatures.

When these alloys have formed sigma phase and then cooled to room temperature, it’s important to prevent any kind of impact. At operating or heat treating temperatures, these alloys generally maintain enough ductility to be safely used.

Table D displays the results of Charpy testing conducted on RA330 after aging. Although there is a slight decrease in ductility, the material still exhibits sufficient energy absorption to be considered quite ductile and safe for use at room temperature.

Conclusion

Sigma phase precipitation is a phenomenon that occurs in stainless steels and alloys containing less than 35% nominal nickel content. This does not occur in nickel alloys with 35% nickel or more. Sigma phase can make materials very brittle at room temperature. However, at elevated temperatures within typical heat treating ranges, most materials retain sufficient toughness to be used without any concern. It’s important to note that even at high temperatures, toughness is lost. More caution should be exercised in choosing alloys for vibrating systems, as constant vibration can cause premature failure if sigma phase has formed.

Engineers may mistakenly identify grain boundary oxidation or carbides as sigma phase formation in alloys that do not actually form sigma phase. To ensure accurate conclusions, it is important to have interpretations verified by experienced metallurgists who are familiar with the metallography of stainless steels and nickel alloys.

An understanding of the basics of sigma phase metallurgy in stainless steels will help the heat treater, manufacturer, and end user avoid failures associated with sigma phase embrittlement.

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References

Andersson, Thomas, and Thomas Odelstam. 1984. Sandvik 253MA (UNS S30815) – The Problem Solver for High Temperature Applications. Sandviken, Sweden: R&D Centre AB Sandvik Steel Bulletin, October.

ASM International. 1986. Binary Phase Diagrams. Metals Park, OH: ASM International.

Crucible Inc., Materials Research Center. 1972. Private Communications, January 10 and June 22.

Herring, Daniel H. 2012. “Sigma Phase Embrittlement.” Industrial Heating. Troy, MI: BNP Media, March.

Kelly, James. 2005. Heat Resistant Alloys. Rolled Alloys. https://www.scribd.com/document/90619472/HeatResistantAlloys-RolledAlloys.

Lien, George E. 1968. Behavior of Superheater Alloys in High Temperature, High Pressure Steam. New York, NY: The American Society of Mechanical Engineers.

Rolled Alloys. n.d. Internal Reports. Temperance, MI.

Rolled Alloys. n.d. Rolled Alloys Bulletin 1353: RA 353 MA® Alloy. Temperance, MI.

About The Author:

Nick Hicks is the metallurgical services manager at Rolled Alloys. He holds a bachelor’s degree in mechanical engineering from the University of Toledo and a master’s degree in materials science from Worcester Polytechnic Institute. Nick represents Rolled Alloys at organizations such as the Materials Technology Institute (MTI) and the American Society for Testing and Materials (ASTM). He is also a former Emerging Professional on the ASM Heat Treat Board. Nick specializes in stainless steel and nickel alloy metallurgy for high-temperature and corrosion-resistant applications.

For more information: Contact Nick at nhicks@rolledalloys.com.

This article was initially published in Industrial Heating. All content here presented is original from the author.

From its roots in Seattle to its facilities across the western United States, Stack Metallurgical Group has built a legacy defined by precision, quality, and innovation. Founded in 1946, the company began with a few repurposed World War II furnaces and a small team dedicated to serving local foundries. Over time, it expanded its capabilities, added new furnace technologies, and became a trusted partner to some of the leading manufacturers in the Northwest.

As the business evolved over the decades, acquisitions and expansions shaped it into the organization known today. In 1982, the Stack Metallurgical Group consolidated in Portland and added multiple vacuum furnaces to increase capacity. A full-service facility followed in Spokane in 1984, and a new site, Aerospace Aluminum Processing, was established in Salt Lake City in 2015. These additions created a broad network capable of meeting the demanding needs of aerospace, defense, and advanced manufacturing industries.

At its core, the company remains focused on delivering heat treating excellence backed by decades of experience and technological investment. With over 75 years of service, it supports clients producing everything from rocket engines to precision cutlery, maintaining approvals across a comprehensive list of industry standards.

Among its many capabilities, vacuum heat treating stands as the cornerstone of the heat treater’s expertise. This process, essential for alloys such as nickel and titanium, provides unmatched control and consistency — critical qualities for aerospace, power generation, and high-performance tool applications. Complementing vacuum processing are extensive Endothermic heat treating operations for ferrous alloys, enhancing hardness, wear resistance, and toughness, along with aluminum heat treating and anodizing services that strengthen components and improve corrosion resistance.

The company’s facilities house six internal-quench Endothermic furnaces, more than two dozen air furnaces, and over fifteen vacuum furnaces across its Portland and Spokane locations. In Portland and Salt Lake City, aluminum quench and aging furnaces support aerospace and precision manufacturing work, while the Salt Lake site also features an advanced anodizing line and multiple paint booths for finishing applications.

Beyond equipment and technology, the company’s greatest strength lies in its relationships. The organization has long operated with a client-first philosophy, one that views every heat treat job as a collaboration. Every employee takes personal ownership of each component that passes through their care. This approach, built on partnership and dedication, has earned the trust of manufacturers across the industry.

Partnership has long been a defining value, especially with regional tool and knife manufacturers. Working closely with these partners, the team develops specialized processes that enhance product performance, helping create some of the toughest, sharpest, and most consistent tools available today.

Equally vital to the company’s legacy of enduring quality are its people. Many employees have been part of the organization for more than a decade, with several bringing multiple decades of experience. This continuity has fostered a culture of craftsmanship, accountability, and deep technical knowledge, qualities that customers recognize and trust.

Future growth will follow the same guiding principles that have carried the company for generations: hiring exceptional people, investing in new equipment, and expanding capabilities to serve a growing manufacturing base. As U.S. production advances, Stack Metallurgical Group remains committed to helping clients achieve superior results through dependable heat treating and metal processing solutions.

With more than seven decades of proven performance, the company continues to set the standard for precision, quality, and care, proving that craftsmanship, which built on consistency and innovation, never goes out of style.

For more information:

Stack Metallurgical Group

5938 N Basin Ave
Portland, OR 97217

sales@stackmet.com
www.stackmet.com

Main image: Stack Metallurgical Group’s largest vacuum furnaces at Stack Portland’s Vacuum Department, shortly after commissioning in 2015

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