voestalpine Fastening Systems, a supplier to the railway industry, is bolstering its hardening processes of steel parts with a technological line consisting of multiple furnaces and washers. The process will be carried out in a protected nitrogen atmosphere with temperatures up to 1742°F (950°C) on parts to be used in railway rolling stock.
Mariusz Raszewski Deputy Director of Aluminum Process and CAB Furnaces SECO/WARWICK
The technological line on order from SECO/WARWICK consists of two CaseMaster furnaces, three tempering furnaces, and two washers. In addition, the railway supplier will have an electric chamber, a cooling station, and an endothermic atmosphere generator delivered.
“[T]he result of technological tests carried out in a service hardening plant that the customer was acquainted with … convinced voestalpine Fastening Systems that we would meet the high requirements of the contract. The line is configured in such a way that if the volume of the company products decreases, the customer can also offer commercial processing due to the wide technological spectrum of this main furnace unit,” said Mariusz Raszewski, deputy director of the Aluminum Process and CAB Furnaces Team at SECO/WARWICK.
The technological line will include a loader operating in automatic mode, a set of roller tables, and a closed-loop water system. The number of the supplied technological line units is selected to ensure the quality of manufactured components. The whole process will be supervised by a master system, which is used to continuously monitor the heat treatment equipment operation and provides advanced data analysis for the production processes.
Mariusz Fogtman Chief Operating Officer voestalpine Fastening Systems
“The universal furnace solution will allow [the client] to process various parts in various configurations. Apart from technological parameters, it is important for us to limit processed part deformations, which is possible with the solution on order,” said Mariusz Fogtman, chief operating officer, voestalpine Fastening Systems Sp. z o. o.
This is the first cooperation between both partners in this product area. SECO/WARWICK has previously delivered vacuum furnaces to the voestalpine Group.
Press release is available in its original from here.
Digital tools lead the way in vacuum hardening operations to ensure energy efficiency and processing repeatability. In this Technical Tuesday installment, Paulo Duarte, project manager at Metalsolvus, examines various advantages of wrought versus cast alloys in heat treat operations.
This informative piece was first released in Heat Treat Today'sMarch 2025 Aerospace print edition.
Vacuum hardening has been the chosen process for hardening tools used in plastic injection, die casting, and metal sheet stamping over the past few decades. Although widely used and accepted, there is still room for improvement in tool performance through quality driven procedures. By employing easy methods of measurement, study, and testing, it is possible to enhance part integrity and mechanical properties, while simultaneously reducing heat treatment time and energy consumption. Advanced metallurgical analyses of heat treatment cycles and equipment can introduce better tools on the market, as well as provide time and cost saving heat treatments.
Basics of Vacuum Hardening
Figure 1. Cooling parts in vacuum hardening furnaces — inert gas injection on the hot chamber during cooling
In vacuum hardening furnaces, temperature and time are carefully controlled at specific load locations to ensure optimal hardening. Optimal practices focus on heating and soaking the metal parts during heat treatment. The controlled introduction of vacuum and inert gases during the process ensures the right protective atmosphere for treatment, resulting in steel that is mainly free from oxidation and decarburization. This preserves the surface integrity of the tools.
Cooling is achieved through the injection of an inert gas into the heating chamber, with controlled pressure and adequate recirculation between the heat exchanger and the hot zone (Figure 1). Different gas injection directions are utilized depending on the load being treated, ensuring optimal cooling.
Hardening of Large Tools
Figure 2. Large molds positioned inside the vacuum hardening furnace, two parallel cavities
Heating and quenching large tools is one of the most challenging situations for vacuum hardening, as temperature control and part microstructure integrity are more difficult to obtain, which affects part quality. Large tools, typically made of hot work tool steels, are hardened in large furnaces. To minimize deformation, parts are preferably positioned vertically inside the furnace (Figure 2).
Surface soaking times for big tools can significantly exceed
standard austenitization and tempering times due to thermal gradients existing within the parts. Mold cores usually achieve the right soaking and tempering recommendation through accurate temperature control, monitored by well-positioned core thermocouples. A tool’s microstructure and performance will depend heavily on geometry, size, and temperature uniformity achieved during treatment. See Figure 3 for the core and surface typical hardening cycles for large tools.
Figure 3. Heating and soaking cycle for the hardening of large tools (“Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel”)
The cooling phase is crucial in determining the final properties of both the surface and core of the tool. Higher gas injection pressures result in faster cooling and increased toughness, but this also introduces greater deformation risks, when directly cooled from austenitization temperature, so martempering done at low pressures is usually required.
Balancing cooling pressure is one of the most secret topics in vacuum hardening. With a variety of parameters and procedures used among heat treaters, measuring and testing is essential for achieving consistent quality for better controlling the hardening process and attaining the best part quality.
Figure 4. Microstructure and toughness obtained after the use of different hardening cooling rates (image from Transactions of the 15th NADCA Congress, 1989)Figure 5. Microstructure of Uddeholm Orvar Supreme steel after quenching using different cooling rates
The use of higher or lower inert gas pressures directly affects the cooling rate, making it faster or slower, respectively. Regulating the gas injection pressure during the cooling phase significantly impacts the material’s toughness, even when cooling occurs within the bainitic-martensitic domain commonly observed in vacuum hardening practices. Faster cooling leads to finer microstructures, which in turn results in tougher materials. However, fully martensitic microstructures are rarely achieved in industrial vacuum hardening furnaces and are typically limited to smaller loads composed of small parts. In larger parts, the risk of pearlite formation increases, especially when cooling rates fall around 3°C/min (5°F/min) at the core, as illustrated in Figures 4 and 5.
In industrial heat treatments of large tools, accurately monitoring core temperature is challenging, as it is difficult to position a thermocouple hole exactly at the innermost location or a nearby region. This makes it harder to control the hardening process and prevent pearlite formation. Therefore, studying the process to establish effective control measures is essential for achieving the highest possible
quality.
Figure 6. Mold temperature gradients during vacuum hardening: a) FEM mesh, b) gradients during heating at lower temperatures, c) gradients at the last pre-heating steps, and d) gradients during austenitization from Maia et al. “Study of Heating Stage of Big Dimension Steel Parts Hardening”; e) gradients during mold cooling from Pinho et al. “Modelling and Simulation of Vacuum Hardening of Tool Steels”
Heat treatment simulation simplifies this task by allowing the hardening process to be predicted, with thermal gradients estimated and compensated through furnace control parameter adjustments. Figure 6 presents a real case study, where the temperature distribution inside a large mold was fully characterized during the entire heat treatment cycle using FEM (finite element method) simulation and validated through actual thermocouple measurements. FEM simulation, as a proven and highly effective technique for predicting heat treatment cycles, enables heat treaters to implement optimized, computer-supported heat treatment practices.
Vacuum Hardening Standard Block Size and Cycle Forecast
When working with loads composed of small to medium-sized parts, the core temperature of the load can be monitored using dummy standard blocks. These blocks have a central hole to accommodate the thermocouple used to control the heat treatment cycle. The dummy block should be selected to closely match the size of the largest part in the load. However, in commercial heat treatment settings, part sizes can vary widely, making it difficult to maintain a comprehensive set of dummy blocks that represents all possible heat treatment scenarios.
Once again, simulation proves valuable in helping heat treaters gather useful data to anticipate the heat treatment cycle and determine the appropriate range of dummy blocks to have available on the shop floor. The procedure for selecting the dummy block range and forecasting the corresponding heat treatment times is outlined in the following equations. Ideally, the standard block should be made from the same material as the largest part in the load. If the materials differ, the characteristic length of the block can be calculated using the first of the equations to the right.
Table 1 lists a range of proposed dummy block sizes to be used for monitoring the load temperature during heat treatment. The time to end of soaking at higher temperature is also given by Table 1 for a typical 600 x 600 x 900 mm hardening furnace. Times were obtained by FEM simulation and can be used to forecast the end of austenitization in a hardening process of each dummy block.
Table 1. Proposed dimensional distribution range for cubic and cylindrical standard blocks and expected cycle times in a typical 600 x 600 x 900 mm hardening furnace (data from Figueiredo et al., “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments”)
The simulated times were validated by using real parts temperature measurement by thermocouples. These were the calculated errors based on simulation and heat treat validation trial:
Optimizing the Vacuum Hardening of Tools
Figure 7. Effect of selecting different temperature (ΔT) range for starting to control the isothermal stage time. a) ΔT criteria and respective cycle time reduction; b) surface mechanical properties obtained by using different ΔT; and c) core properties after tempering at different ΔT range (Miranda et al., “Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel,” MSC)
FEM simulation can also be used to optimize the heat treatment process, but metallurgical testing remains crucial for providing reliable insights into safely reducing cycle time and energy consumption. Typically, for setting the isothermal stage time, a tolerance of -5°C relative to the temperature setpoint is used, leading to savings in both heat treatment duration and power consumption, as shown in Figure 7a. However, Figure 7b demonstrates that higher tolerance values (ΔT) can be considered. Tolerances of up to -10°C or even -20°C can be applied for controlling the soaking time without significantly affecting the hardness and toughness of the parts. Naturally, these results depend on the desired setpoints for the isothermal stages, but Figure 7c reflects the worst-case scenario for ΔT, referring to the use of lower austenitizing and tempering temperatures commonly applied in the hardening of hot-work tool steels.
Future Trends of Vacuum Hardening
Innovations like digitalization, automation, and resource reduction, as part of Industry 5.0 initiatives, are expected to drive advancements in heat treatment processes. Long martempering, a heat treatment under development for hardening hot-work tool steels, shows promise as an alternative to traditional quenching and tempering. This process offers a balance of high hardness and toughness in significantly less time, providing energy savings and faster turnaround.
New Vacuum Hardening Process — Long Martempering
Figure 8. New long martempering heat treatment cycle: AISI H13 premium toughness for two different long martempering temperatures (“Study of The Bainitic Transformation of H13 Premium Steel”)
Long martempering is a heat treatment under development that can be used to harden hot-work tool steels. Long martempering is a process somewhat similar to austempering but is applied to steels rather than cast irons. Performed at temperatures within the martempering range, long martempering corresponds to an interrupted bainitic heat treatment with a specific process window (Figure 8) where high toughness is achieved at hardness levels exceeding those obtained through traditional quenching and tempering. Table 2 lists the mechanical properties attained for 5Cr hot-work premium tool steels.
Table 2. Mechanical properties of the new hardening process — long martempering
The transformation during long martempering is not yet fully characterized in terms of microstructure, however, curved needles of bainitic ferrite are observed without carbide precipitation. This phenomenon is generally not associated with steel but rather with ausferrite in cast irons. Nonetheless, it is evident in at least H11 and H13 premium steel grades. This one day martempering treatment could potentially replace the traditional two- to three-day heat treatment cycle for large tools, offering significantly faster lead times and reduced energy consumption. Moreover, the mechanical properties achieved through long martempering are notable, as high levels of both hardness and toughness are obtained simultaneously, as demonstrated in Table 2.
The integration of heat treatment equipment with management software enhances furnace utilization, quality control systems, and maintenance practices. Industry 5.0 can be implemented in heat treatment plants through the connection of databases that collect inputs from furnaces (e.g., temperature, time, pressure, heating elements, and auxiliary equipment performance) and production data (e.g., batch numbers, order details, operator information, cycle setup, and load weight). This data is analyzed by software to generate valuable insights for plant management, process optimization, predictive maintenance, and quality control.
A supervision interface for a 5.0 solution can monitor furnaces and control them remotely in real time (Figure 9). Operators receive updates on tasks, alerts, and production schedules. Additionally, plant productivity, efficiency, and maintenance can be tracked through the same supervision software, whether on site or remote. Automatic reporting is also possible, enabling the approval or rejection of cycles based on criteria that are not typically used in heat treatment plants. This not only improves quality but also facilitates process optimization and cost reduction.
Conclusion
Acquiring a full understanding of furnaces in operation through data measurement and analysis allows full control over the heat treatment process. This facilitates process development, enabling cycle optimization and improvement in part quality. Additionally, testing and simulation practices can lead to cost reduction and shorter lead times.
The introduction of long martempering and Industry 5.0 will significantly enhance heat treatment processes, leading to improved delivery times and reduced operational risks. Automation and digitalization bring more data to the shop floor, improving plant management and resulting in greater efficiency, higher quality parts, and simplified task execution.
Finally, current personnel are busy with routine operations that are based on long established practices and may be limiting opportunities for innovation. Therefore, new teams or external consultants can be leveraged to focus on designing, studying, testing, and implementing each new heat treatment solution.
References
Fernandes, José, Laura Ribeiro, and Paulo Duarte. “Study of the Bainitic Transformation of H13 Premium Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2021.
Figueiredo, Ana, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments.” MSC thesis, Faculty of Engineering of Oporto University, 2022.
Kind & Co. “Vacuum Hardening with Highest Levels of Precision.” Accessed January 30, 2025. https://www.kind-co.de/en/company/technologies/vacuum-hardening.html.
Maia, Pedro, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of Heating Stage of Big Dimensions Steel Parts Hardening.” MSC thesis, Faculty of Engineering of Oporto University, 2013.
Metaltec Solutions. “Brochure Presentation.” Accessed January 30, 2025. https://www.metalsolvus.pt/en/wp-content/uploads/2019/01/plant-supervision-brochure-V3.pdf.
Miranda, Isabel, Laura Ribeiro, and Paulo Duarte. “Heat Treatment of AISI H11 Premium Hot-Work Tool Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2024.
Pinho, José Eduardo, Gil Andrade Campos, and Paulo Duarte. “Modelling and Simulation of Vacuum Hardening of Tool Steels.” MSC thesis, Aveiro University, 2017.
Ramada. “New Hardening Furnace up to 4 Tons.” Accessed January 30, 2025. https://www.ramada.pt/pt/media/noticias/novo-forno-de-tempera-vacuo---ate-4-tons-.html.
Schmetz. “Schmetz Heat Treatment Furnaces.” Accessed January 30, 2025. https://edelmetal.com.tr/en/heat-treatment-furnaces.
Schmetz. Sketch of the Cooling Process in the Vacuum Hardening Furnace: Schmetz Commercial Proposals Drawing – Metalsolvus Training Courses Documentation.
Seco/Warwick. Vector 3D Hardening Furnace Commercial Brochure.
Solar Manufacturing. “Solar Vacuum Hardening Furnace.” Accessed January 30, https://solarmfg.com/vacuum-furnaces-horizontal-iq-vacuum-furnaces.
Wallace, J.F., W. Roberts, and E. Hakulinen. “Influence of Cooling Rate on the Microstructure and Toughness of Premium Grade H13 Die Steels.” Transactions of the 15th NADCA Congress (1989).
About The Author:
Paulo Duarte, project manager at Metalsolvus, is a researcher and consultant on heat treat technologies. His education and expertise in metallurgy has culminated in several articles and patents. He was a former technical manager within bohler-uddeholm group for the Portuguese market and heat treatment manager with the same group. Currently, Paulo focus on helping heat treaters by providing innovative, more efficient, and profitable heat treatment services to companies.
For more information: Contact Paulo Duarte at paulo.duarte@metalsolvus.pt.
Chiz Bros., which provides solutions for refractory and high temperature applications in the metals industries, recently completed the acquisition of Advanced Material Science, a thermal and electrical insulation material distributor and a long-term vendor of the company.
Mark Rhoa, Jr. Vice President of Sales Chiz Bros
In addition to distributing insulation material out of its southwestern Pennsylvania location, Advanced Material Science focuses on custom CNC machining. Chiz Bros. plans to invest in improvements to machinery, inventory, and safety practices relating to its refractory applications which also serve the power, glass, and ceramics industries.
“The acquisition of Advanced Material Science will help us expand our offerings in regard to induction insulation and utilize their quick turnaround and precise machine services,” said Mark Rhoa, Jr., vice president of Chiz Bros. “We are excited to welcome them into the Chiz Bros. family. We pride ourselves on supplying high quality materials and AMS certainly fits that mold.”
“Advanced Material Science has always enjoyed working with Chiz Bros. as a customer, and now we can take a step further and work together as one company,” said John Pertinaci, who has been plant manager of AMS for more than seven years and will remain in that role. “I look forward to this new relationship and the mutual benefits it will bring to the industry.”
The Cybersecurity Maturity Model Certification (CMMC) 2.0 compliance process is detailed and complicated, and businesses in the defense industrial base (DIB) may be tempted to delay this regulatory hurdle. In this Cybersecurity Desk column, which was first released inHeat Treat Today’sMarch 2025 Aerospace print editionJoe Coleman, cybersecurity officer at Bluestreak Compliance, a division of Bluestreak | Bright AM™, explains why companies putting off CMMC 2.0 compliance may end up scrambling to meet deadlines, incurring costly delays, and even facing potential disqualification from future DoD contracts.
Introduction
The Cybersecurity Maturity Model Certification (CMMC) 2.0 is not only a regulatory hurdle, it represents a fundamental shift in the cybersecurity landscape for the Defense Industrial Base (DIB). Ignoring this critical initiative can have severe and potentially irreversible consequences for your company’s future.
Many companies mistakenly believe they can afford to delay their CMMC 2.0 compliance efforts, assuming they have plenty of time to prepare. This is a dangerous assumption. Achieving CMMC 2.0 compliance is a detailed and complicated process that typically takes 12–18 months. Delaying implementation can leave your company scrambling to meet deadlines and increase the risk of costly delays, missed opportunities, and even potential disqualification from future DoD contracts.
The High Cost of Inaction
The consequences of failing to prioritize CMMC 2.0 compliance are significant:
Loss of revenue and market share: Non-compliance directly impacts your ability to bid on and win DoD contracts. This translates to lost revenue, limiting growth and a significant competitive disadvantage against companies that have already achieved compliance
Erosion of trust and reputation: Failing to meet cybersecurity standards can damage your company’s reputation within the DIB. This loss of trust can impact not only your relationship with the DoD, but also with other key stakeholders, including clients, contractors, partners and investors. Some of your clients may have already asked if you are compliant.
Increased vulnerability to cyberattacks: A weak cybersecurity posture leaves your company highly susceptible to cyberattacks. These attacks can have devastating consequences, including data breaches, system disruptions, and significant financial losses. The key cybersecurity component of CMMC is NIST Special Publication 800-171.
Significant financial penalties: Non-compliance can result in substantial financial penalties, including fines and contract termination. These penalties can severely impact your company’s bottom line and long-term growth.
Operational disruption: The process of implementing and maintaining CMMC 2.0 controls can require significant amounts of time and resources. Delaying these efforts can disrupt your company’s operations, impacting productivity and potentially hindering critical projects.
The Benefits of Proactive Action
By proactively addressing CMMC 2.0 compliance, your company can gain a significant competitive advantage to win more business:
Competitive head start: Companies that prioritize CMMC 2.0 compliance gain a significant first-mover advantage. They can demonstrate their commitment to enhanced cybersecurity to the DoD, build stronger relationships with government agencies, and position themselves as preferred partners for future contracts.
Reduced stress and increased efficiency: Starting early allows for a more gradual and less stressful implementation process. This reduces the risk of last-minute scrambling and allows for a more efficient and effective integration of cybersecurity measures into your existing workflows.
Enhanced cybersecurity posture: The CMMC 2.0 framework provides a structured approach to enhancing your overall cybersecurity posture. By implementing these controls, you not only improve your compliance but also strengthen your defenses against a wide range of cyber threats.
Improved operational resilience: A robust cybersecurity program enhances your company’s operational resilience. By minimizing the risk of cyberattacks and their potential disruptions, you can ensure business continuity and maintain a competitive edge in the market.
Building a culture of security: CMMC 2.0 implementation encourages a shift towards a culture of security within your company. This includes raising awareness among employees about cybersecurity risks, fostering a sense of shared responsibility, and promoting best practices at all levels.
Conclusion
Click image to download a list of cybersecurity acronyms and definitions.
CMMC 2.0 is not an option; it is a critical requirement for any company seeking to do business with the DoD, its prime contractors, and/or downstream service providers. Procrastination is not an option. By taking proactive steps to understand and address CMMC 2.0 requirements, your company can mitigate risks, enhance its cybersecurity posture, and gain a significant competitive advantage in the evolving defense landscape.
For an up-to-date resource list of common cybersecurity acronyms, click the image to the right.
About the Author:
Joe Coleman Cyber Security Officer Bluestreak Consulting Source: Bluestreak Consulting
Joe Coleman is the cybersecurity officer at Bluestreak Compliance, which is a division of Bluestreak | Bright AM™. Joe has over 35 years of diverse manufacturing and engineering experience. His background includes extensive training in cybersecurity, a career as a machinist, machining manager, and an early additive manufacturing (AM) pioneer. Joe presented at the Furnaces North America (FNA 2024) convention on DFARS, NIST 800-171, and CMMC 2.0.
In this Heat TreatRadioepisode, host Doug Glennsits down with Fernando Carminholi, the business development manager at Hubbard-Hall, to discuss solvent and aqueous cleaners and why cleaning is a crucial step in both pre and post thermal processing to ensure quality part outcomes. Fernando offers practical guidance, discusses solvent vs. aqueous cleaning methods, common pitfalls, and upcoming EPA regulations that could impact the industry.
From production to engineering to quality, there are valuable insights for everyone on optimizing cleaning process for better part quality, longer furnace life, and maintaining compliance in the latest regulatory environment.
Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.
The following transcript has been edited for your reading enjoyment.
Doug Glenn:Welcome toHeat TreatRadio.I would like to start off with some parts cleaning basics. Do all parts need to be heat treated? Why do we do cleaning? And what are the risks of not cleaning?
General Parts Cleaning (01:40)
Fernando Carminholi: Thank you for this opportunity to talk about cleaners and the importance of cleaning. We’re going to focus on the cleaning before the heat treat, but there is also a cleaner after the heat treat when you remove quenching agents.
You asked how to know if parts need to be cleaned. And my answer to that is “yes,” and it could be “maybe” as well. The “maybe” is because some really light oily parts with light oil go to the furnace and there is not a problem. I would say that maybe 10% of all the parts heat treated do not need cleaned in any kind of operation. They go from stamping or deep drawing straight to the furnace.
But the rest — the 90% — will require cleaning. And that’s exactly what we’re going to talk about today.
Approximately 30%–35% will pass through a solvent cleaning. When we’re talking about solvent cleaning, there are two different ways to clean parts. One is the well-known technology of open-top degreasers. You have your solvent in a proper tank, and then you have some chillers on top to hold the vapor; this is called a “vapor degreaser.” You see a lot of these machines on the market from the 80s and 90s.
Another way to use solvents is in a closed vacuum machine, which is a more technologically updated machine.
And the rest of parts, I would say more than 50%, are cleaned in water-based cleaners, which could be in a spray application, a spiral tunnel, or immersion.
And normally, what kind of oils do we clean? As the years go on, there are new regulations for the oils with all the modernization. Every year the R&Ds work with new kinds of oils — cooling fluids, rust inhibitors, forming lubricants, and deep drawing compounds. Plus, they could be synthetic, and every year the oils become more difficult to remove. That’s the big challenge for the cleaning operation.
Doug Glenn: I assume the solvents must keep up with the changes in the chemistry of the cleaners?
Fernando Carminholi: Sure. Both of the systems have to keep up: the solvents and the aqueous.
Doug Glenn: If I’m hearing you right, Fernando, you’re saying that probably 90% of parts in in the heat treat process are cleaned. Maybe 35% of those get solvent-based cleaning and the rest aqueous-based.
I’ve heard that there are various reasons why we clean. Obviously if you’re going into a vacuum furnace, there are different reasons for why you clean than if you’re going into an air and atmosphere furnace. You’re wanting to make sure you don’t drag all those contaminants into a vacuum furnace. That’s one reason why you clean, right?
Fernando Carminholi: Exactly. But most will be more atmospheric furnaces. And then what do you drag in? Most of the clients we’re talking about move high volumes inside the furnace.
Let’s think about it in two different ways. If you don’t clean at all, or you have a bad cleaning, what is the problem? If you don’t have a cleaner at all because it’s a really light, clean oil and part that doesn’t drag that much oil, it could be fine.
But let’s think about a big operation with lots of oil, maybe fasteners or a kind of part that carries more oil to the furnace; it will produce a lot of drag and it will burn. You will have furnace contamination that will contaminate the oxygen and the carbon — it can cause decarbonization which can affect the hardness and the mechanical properties of the parts. The easiest way to see that this is happening is if there is a lot of smoke, which is common.
Fasteners that may carry more oil to the furnace
Doug Glenn: It is common. And one thought I had is not only will it potentially affect the parts, but it can impact the life of your furnace because you’re getting a lot of contamination, it’s going to need more maintenance, and you can damage your furnace.
Fernando Carminholi: Definitely. It will need more maintenance and shorten the life of the furnace. The smoke can also cause an uneven heat distribution inside the furnace and can lead to warping, cracks, and inconsistent hardness on the part. And that’s the result of no cleaning at all.
Now look at it another way. If you have the cleaner, machine-cleaning solvents or water based, and somehow you’re not cleaning the parts well, you can drag more than oil to the furnace. You can drag other compounds. With water-based cleaners in particular, you can drag the rinses together with all the chemicals.
And you have a different areas, like in nitriding or FNC operations, where the area with the oil that was not cleaned well will suffer some soft spots and unformed hardness — like the opposite of using sunscreen on the beach. You can cause surface defects like heating stains and areas that are well heat treated as well as areas where the structure is not as expected.
Doug Glenn: It’s almost like unintentionally using a stop-off paint on your part.
I want people who may not have dealt with parts cleaning in the past to hear some of these things: Not all parts need cleaned. A good number of parts do. If oil on the surface, or contamination, or spottiness on the finish of the part is not an issue, then you may not need to wash. But a very large percentage of parts that are heat treated do get washed in either solvents or aqueous-based, water-based solvents. And it’s good for the life of your furnace, the interior furnace, the maintenance of your furnace, and the properties of the parts.
Legislation (11:40)
I want to move on to a second topic that I thought would be very enlightening to some of our more experienced parts cleaning people. That is the area of legislation that Hubbard-Hall is aware of that’s going to be coming down the pike that we need to be aware of. Can you talk a little bit about the legislation regarding parts cleaning?
Fernando Carminholi: When we’re talking about legislation, everything that the EPA stated, let’s separate again into two different topics: water based and solvent based. When we’re talking about water-based cleaners, you have to watch out for what kind of raw materials you’re using.
What is the cleaner formulation? Because if you don’t rinse well, that’s something that you need to control in your process. If you don’t rinse well, you’re going to be dragging a lot of those materials. That can cause all the problems that we’ve already talked about. But legislation for water-based cleaners is less problematic.
I would like to wave a red flag right now because if you’re working with some product that will be restricted, you need to change.
And then, for example, you have some restrictions with some surfactants. And it’s based, but, for example, none of the latest. All those new formulations, I would say that they’re already free of.
Another big topic to discuss, and something that everyone is talking about now, is products containing PFAS. It could be in both a water-based cleaner and in the solvent.
Doug Glenn: What are those two things that you mentioned?
Fernando Carminholi: PFAS are fluorinated compounds. You see a lot of these in Teflon based, fire extinguisher foam, and in a lot of different things in the industry. These are forever chemicals. So far there is not a good, stable way to treat and eliminate these chemicals from the drinking water. This is something that the industry is regulating: how to treat and how to waste those chemicals because some of those compounds.
We’re talking about PPT (part per trillion); it’s a really low amount in the drinking water. But this is something to watch out for on the chemicals. This is something that is already suffering restriction, and it’s a hot topic.
Doug Glenn: Are these rules that are coming down federally based or are they state based?
Fernando Carminholi: These are federal. If you look up PFAS, all the surface finishing world and the wastewater world is talking about them. If you look at Congress, a lot of regulations from the government are talking about maybe having different states with different numbers. This is something that is already defining the rules and defining how to analyze and how to treat it.
Hubbard-Hall already does PFAS-free manufacturing. We decided not to work in this way.
I would like to switch gears a little bit here. With regulations, normally we talk more about the solvents. The solvents we’re talking about — methylene chloride, TCE (trichloroethylene), perchloroethylene, propyl mide — are the halogenated solvents that are already on the list. The EPA is working on this already.
I have a cheat sheet with some numbers I would like to bring up. If you go on the Hubbard-Hall website, you can find this table. To create this chart, we took all the regulations and put them in one table for different solvents. When the EPA rule was stated, for example, methylene chloride is already finishing. The rule was dated March 2024. All companies have until March 2026 to stop using this solvent as a cleaner.
Click the image for more information
There are exceptions. For example, if you use them for NASA or federal use, you have a little bit more time. For TCE, you have less than one year; by January 2026th, you’re not going to be able to use TCE as a vapor degreaser.
There are some alternatives for that. If you’re using an open-top machine, fluorinated solvents are an alternative; they have low global warming potential and are non-flammable, stable products. Those are available on the market.
Another alternative is modified alcohol, which is the best choice. This is a formulated alcohol. It’s not a book solvent. It’s a formulated product. It has a good cleaning ability and a good permeability because that’s the beauty of the solvent. It can go between the parts or inside the holes to clean everything. And modified alcohols can be used in the vacuum cleaning machine. It will work almost the same as the vacuum furnace. But on the cleaning side you have all the equipment running in a vacuum and you have a distillation process that will remove oil and the water from the part.
Doug Glenn: I’m curious about that chart that we were looking at. As you know, most of our readers and listeners are manufacturers who have their own in-house heat treating and we get a lot of commercial heat treaters, too. But our core audience are those manufacturers who have their own in-house heat treat. How many of them do you think are using either solvent or water-based solutions that are going to be ruled out by these regulations?
Fernando Carminholi: I would say that today 20% use halogenated solvents that need to be ruled out and switched for another technology. In some states, such as New York and Minnesota, this is already in place. They cannot use them. But the final date rule to be enacted, for example, for TCE would be January of 2026.
The unique one that is just proposed but is not finalized yet is the NPB. I think that will take between 3–5 years to be fully restricted.
Doug Glenn: It seems safe to say that there’s a significant number of people out there currently using cleaning solvents that will be outlawed over the next 3–5 years, so they need to start looking for another technology?
Fernando Carminholi: I would like to wave a red flag right now because if you’re working with some product that will be restricted, you need to change. Or use the same equipment. But as I told you, the fluorinated solvent would be 3–4 times more expensive.
On the other hand, if you’re going to buy equipment to use modified alcohol, there are not that many equipment manufacturers and that’s the limit. If 20% of this market needs to change, they will expect to change six months before. I would say that today you have equipment manufacturing expecting to deliver equipment in six months.
Doug Glenn: People need to keep in mind the lead time that they’re not going to get that equipment that quickly.
Aqueous Based vs. Solvent Cleaners (25:07)
Doug Glenn: Let’s jump in and talk about the pros and cons of using aqueous (or water-based) versus solvent cleaners. What’s the difference and why would we choose one over the other?
Fernando Carminholi: This is a really extensive debate. You can see some videos at the Hubbard-Hall website talking about this. What I see in the market is that companies selling only solvent will always talk poorly about the water-based. Companies that sell only water-based products are talking bad about the solvents and regulations.
I would say that Hubbard-Hall plays on both sides. We understand the best usage for different applications. I would try to go on the really high level. “Hey, I am the solvent side; I need to keep on the solvent side.” Or, “I need to go for a water based.”
First of all, you need to understand the contamination. What kind of oil? We’re talking about the cooling fluid, rust inhibitor, dip drawing, a lot of heavy, chlorinated oil, whether it contains sulfur, or whether it is a polar or nonpolar-based — that would decide what kind of solvent or water-based product you’re going to use. Normally, when you have an oil-based hydrocarbon, it tends to be easier to remove with solvents. When you have a water-based cooling agent or rust inhibitor, that’s easier to remove with a water base. This is one thing to consider, but it doesn’t mean that if you have a hydrocarbon you cannot remove it with water.
A discussion about waste and cost of parts cleaning
Another thing that you need to take a look at is the part geometry. If it is a flat part, it’s easy to remove oils with a spray. Or you may need ultrasonics to remove oils if there are a lot of blind holes and parts really close to each other. That’s an advantage of going to the solvents here because even if you use a really good surfactant, which will change the surface tension, the solvent tends to have a much better permeability — that’s the term for cleaning the really deep holes and the parts really close to each other.
Another thing to consider is I would call overall the EHS. That means what is the company? Is it okay to use inside the factory? Do I need VOCs? Do I need aqueous to be VOC free? For solvents you need to check how flammable they are.
Waste in Cleaning (29:07)
When we’re talking about waste and footprint — what is the difference between the systems? The footprint for solvent is smaller because all you need is the degreaser machine, open top or vacuum cleaner. You clean and you dry. Normally, the drying process is way easier with the solvent.
Plus, you don’t have all the other processes needed for the water based. All the waste generated from the solvent that you have is possibly some water that came from the water-based rust inhibitor or even the oil or some cleaner that is already gone. You have this weighed and then you send for a partner that will pick it up and take care of the waste.
For aqueous, this is different. You will need rinses. You will need a temperature to dry. You need blowers; you need heaters. The o-rings [ET1] may be needed to dry the parts, and that’s a problem. If you leave the water behind, it can lead to corrosion, for example. So that’s a big difference between solvent and water-based.
Doug Glenn: The reason the solvent is not an issue so much with the drag out, where you keep part of the cleaning solution on the products, is because of evaporation? Solvents evaporate much quicker than water.
Fernando Carminholi: Yes, that’s right. That’s why old open-top vapor machines could be a problem because the EPA [MS2][JM3] tightens limits every year. When you have an old machine with chillers on the top, you have the vapor phase, which is when you heat up your solvent. And then you have the chillers, which is the coil to condensate back. If the chiller is not working well, the solvency will go to the atmosphere. At the end, when you take out your part, it will dry up really easily. When you go for the closed system, you don’t have this emission.
That is another big difference between solvent and water-based. When you have a machine based on the solvent, you feel the machine. Normally, we’re talking about five to ten drums of product, and the consumption is really low. Clients spend one drum every 2 or 3 months for solvent depending on the system. For aqueous, you need all the rinses. So every time that you run a load, you go through the rinse, and you drag solution out of your tank, so the consumption will be higher for water based.
The Cost Debate (33:07)
Doug Glenn: So as far as variable cost, your aqueous system might have a higher operational cost?
Fernando Carminholi: That’s another good debate. The operational costs need to include the equipment as well.
Doug Glenn: I was going to ask about the difference between capital equipment costs. You said the solvent is a smaller footprint, does that mean it is a lower price?
Fernando Carminholi: Yes, I would say for the aqueous, if you need to include ultrasonic, for example, because you need an invasive way to use the waves to clean the parts, it will increase the cost. However, normally the cycles for the water based are lower. You can produce more parts.
No clear winner here when talking about cost
For example, if you were cleaning parts in a plant that already has a wastewater system, you will need to treat the water (possibly 1 to 2 gallons per minute depending on the flow rate on the rinses). This water needs to be treated before it is dumped into the sewage. You also need to follow the regulations and the limits.
But the cost overall depends on the parts. If we start to talk about cost, there’s a big difference now. Not that long ago, before Covid, water used to be cheap. But now water is very expensive. Energy is very expensive. Waste is very, very, very expensive. Then if you take all this rework, it is unacceptable. We like to say, cleaners can be cheap, but poor cleaning is always expensive.
The cleaning process will be cheaper than the heat treated part or even the steel or grinding or blasting. If you take the overall cost, cleaning is nothing. But if you don’t do the best that you can do, it can cause a huge problem, and that’s one thing to keep in mind.
Doug Glenn: Product failure, most notably. The more critical the part, the more important to make sure it’s cleaned.
Is it safe to say there’s no clear winner here when we talk about cost of equipment versus cost of operation for aqueous or solvent?
Fernando Carminholi: It really depends on the parts, the level of cleanliness that you want, and the kind of oil you’re using.
If you have a part that cannot be cleaned with aqueous because there’s a lot of holes and you need to clean inside the holes or the parts are close together, then there is no comparison. But you can bring up a lot of factors and put them side-by-side.
Solvent could be more expensive because of the chemical consumption, but for aqueous you need more equipment. When you’re talking about a vacuum cleaning machine, it will be a substantial capital expense for the equipment — over $1 million.
I’m seeing equipment manufacturers for the vacuum washing machine. They’re looking at the market and they see the problem of the mix of oils and cooling and you can use what they call a hybrid system. On the same machine you can use water-based fluid and then go to the solvent fluid. That’s a new feature in the market.
Doug Glenn: That’s very interesting. It’s a hybrid piece of equipment that starts with an aqueous wash and then finishes up maybe with a solvent washer?
Fernando Carminholi: Exactly.
Cleaning and the Environment (39:03)
Doug Glenn: Let’s move on to the fourth and final topic. I want to wrap up this third thing that we’re talking about as far as the pros and cons of aqueous versus solvent. If a listener has questions about which system makes the most sense for them, I’m sure your team at Hubbard-Hall can help them answer that question.
Fernando Carminholi: The best way to evaluate is to get a picture of your situation. We look at your costs, the pros and cons that you have today, your timeline for changing, whether you’re solvent regulated, for example.
We can do a scenario on how much you’re going to spend on the new line if you need a new line. We do have a prototype line where we can run some tests, different cleaners or solvent, or open-top machine. We can run different scenarios, evaluate the costs, and find a more environmentally friendly solution.
Doug Glenn: The last question I do want to ask you is about the cleaning process. How do we make it more efficient, profitable, and environmentally friendly?
Fernando Carminholi: The chemical manufacturers look it up in different ways. Let’s start with the solvent. Like I told you, there are a few. It’s a really low drag out. But it is dependent on the solvent, especially talking about modified alcohol. All the oil that you bring on the part could contain product that would change the pH of the chemical, and it could go really acidic or it could go really alkaline. That will screw up your machine; that will attack your parts. So, you lost the solution. You can have problems with the seal casket. You can attack the parts if you go acidic.
There are some ways to extend the life, and then you can analyze the solvent. You can add some stabilizers to continuously use the same solution because this is a fairly new technology. About ten years ago, the chemical manufacturers developed way better stabilizers to handle these new kinds of oil that we mentioned to extend the shelf life or the life of the solvent as much as we can. That’s a big savings.
On the aqueous side, what can be done? The problem here is why you dump your process. It’s because oil as well. Hubbard-Hall does work with a feature that’s a piece of equipment that is a membrane filtration. We built this equipment internally. We have sold it to many clients already. This technology has been on the market for 40 years; it’s well tested. This technology filters the oil out of the cleaner to extend the life of the cleaner.
I will give one example. We have a client with parts that are brake calipers. They need to dump the cleaners every 2–3 weeks. That’s a cost to put chemicals is a cost to treat. With the membrane filtration, it’s been more than five years without dumping the solution.
We understand that it recovers like 98% of the cleaner in the future oil that you don’t need. This changes the cost a lot. That’s why there are a lot of variables that we can put on the equation. That’s why I ask listeners with this problem that if you’re looking for the solution, we’re more than happy to jump in and evaluate one system or another and compare costs for what you have.
Doug Glenn: Does that membrane filtration system you’re talking about work on both solvent and water based?
Fernando Carminholi: No, normally the solvent has the distillation process to separate the solvent, the water, and the oil.
The main drain will work only on the water based and when you use product that will emulsify the oil. And emulsifying means the cleaner is able to mix the oil and the water like you see in milk when you have 2% of fat.
Doug Glenn: All right. Well, Fernando, I really appreciate your time and your being here.
Fernando Carminholi: Thank you for this opportunity. I hope that all the subscribers understand a little bit more clearly how important the cleaning process is before the heat treat.
About The Guest
Fernando Carminholi Business Development Manager Hubbard-Hall
Fernando Carminholi is the business development manager at Hubbard-Hall, a six-generation family business that develops, services, and supplies specialty chemicals for ferrous and non-ferrous metals. A chemical engineer graduate from E.S.P.M. in Sao Paulo, Brazil, he oversees the company’s distribution channels and business development team. Fernando has extensive experience in the chemical specialty products industry for surface finishing, focusing on industrial parts cleaning, metal pre-treatment, and functional electroplating.
A continuous line for protective atmosphere brazing has been contracted by a company involved in the research, development, and production of precision metal parts for the automotive industry. The EV/CAB line is intended for the production of large-sized electric vehicle battery coolers.
Piotr Skarbiński Vice President of Aluminum and CAB Products Segment SECO/WARWICK
The EV/CAB line, manufactured and delivered by SECO/WARWICK, will help the company in their manufacture of automotive heat exchangers and is the first for the company, which has production plants in the US as well as Singapore, Malaysia, Thailand, Germany, and China.
“CAB continuous furnaces use a variable speed drive (to transport products) with a stainless-steel mesh conveyor belt. The controlled atmosphere brazing process heats the product to the brazing temperature, while maintaining a uniform product temperature in a protective nitrogen atmosphere devoid of oxygen,” said Piotr Skarbiński, vice president of the Aluminum Process and CAB Business Segment at SECO/WARWICK. “Societal awareness related to the need to care for the natural environment is growing globally, and consistent legal changes in this direction are causing the electromobility sector to grow.”
The CAB line ordered involves a hybrid gas-electric heating method and consists of a 1.6 m wide furnace TTBB chamber, radiation preheating chamber, radiation brazing furnace, cooling chamber with air jacket, final cooling chamber and control system. The furnace is fully electric; however, at the client’s request, space was provided for the installation of gas-powered heating, which provides the flexibility for future savings. Radiation CAB furnaces provide continuous brazing of products with similar dimensions and features. The temperature is distributed evenly over the entire length of the belt due to several independent heating zones.
In addition to manufacturing electric vehicle battery coolers, the company produces precision metal parts for the computer and telecommunications industries.
Press release is available in its original from here.
La mayoría de quienes aplican el tratamiento térmico reconocen la importancia de medir la austenita retenida (RA, por sus siglas en inglés); no obstante, muchos optan por no realizar estas mediciones por razones de tiempo y/o de los costos asociados. Este artículo explica los motivos por los cuales se deben practicar las mediciones RA, los factores a favor y en contra de las tecnologías de medición tradicionales y los beneficios de realizar la medición en la planta misma, utilizando tecnologías más avanzadas.
This informative piece was first released inHeat Treat Today’sMarch 2025 Aerospace Heat Treating print edition. To read the article in English, click here.
La importancia del porcentaje de austenita retenida
Antes de entrar a examinar algunas metodologías de medición, es necesario entender lo básico en relación a la austenita retenida, al igual que la importancia que reviste el porcentaje de la misma (%RA).
Austenita retenida (RA) es el nombre que se le da a la austenita que durante el proceso de templado no se transforma en martensita. En términos sencillos, la austenita retenida (figura 1) ocurre cuando el acero se ha templado sin llegar de manera contundente a la temperatura de acabado de la martensita (Mf); es decir, la temperatura ha estado por encima de lo requerido para permitir la formación de martensita al 100%. Debido a que la Mf está por debajo de la temperatura ambiente en la mayoría de las aleaciones que contienen más del 0.30% de carbón, se pueden presentar cantidades significativas de austenita retenida en la martensita a temperatura ambiente. (Herring, Atmosphere Heat Treatment).
Al tratarse del %RA, con frecuencia existe un equilibrio muy sensible entre sus efectos benéficos (el aumento en la durabilidad de ciertos componentes manufacturados) y sus atributos negativos (la creación de piezas susceptibles de fracturas y averías). Por tal motivo es de crítica importancia que los tratadores térmicos logren el %RA óptimo para la aplicación deseada.
Por ejemplo, en las industrias de la aeronáutica y la astronáutica, con frecuencia se especifica que los niveles de RA sean inferiores al 8%, y para piezas como los cojinetes y los actuadores lineales, se requiere un RA por debajo del 3%, lo más cercano posible a cero. No obstante, en otras aplicaciones, como por ejemplo los engranajes grandes para generadores de energía, energía eólica y plataformas de rendimiento, se ha identificado que un RA en el rango del 15-30% reviste mayores beneficios. (Errichello et al., “Investigations of Bearing Failures”). De igual manera, un alto % RA es una ventaja en el caso de cojinetes que vayan a entrar en contacto con lubricantes contaminados.
Figura 1. Microestructura en la superficie de la trayectoria de un cojinete de rodamiento 12CrNi3 (o SAE/AISI 9310) compuesto por martensita templada en la que se evidencia austenita retenida (áreas blancas)
Marco DeGasperi, gerente técnico de Verichek, se pronunció al respecto señalando que el %RA es de crítica importancia para los inyectores de combustible, para piezas pequeñas en aplicaciones médicas y para aplicaciones de alto nivel y alto volumen tales como las placas de desgaste en la industria minera. Lo resumió afirmando: –Cuando tu ejercicio se trate de someter a presión y movimiento cualquier dispositivo de calibración fina…si utilizas la palabra “precisión” para darte a conocer, vas a querer hacerte a una [herramienta de medición del %RA].
Las mismas características que le dan a la austenita retenida muchas de sus propiedades particulares, son a la vez las respons ables de significativos problemas de funcionamiento. Sabemos que la austenita es la fase normal del acero a altas temperaturas, mas no a temperatura ambiente. Debido a que la austenita retenida existe por fuera del rango normal de su temperatura, es metaestable, lo que quiere decir que, cuando entre en funcionamiento, los factores como la temperatura, el estrés, y aún el tiempo, harán que se transforme en martensita no revenida. Es más, junto con dicha transformación se dará un cambio en el volumen (aumentará) generando un alto grado de estrés interno en el componente y provocando muchas veces la formación de grietas lo que podrá llevar a que las piezas fallen en el campo.
El % RA también es importante, no solo por el impacto sobre la estabilidad dimensional, sino además por las propiedades mecánicas tales como el límite elástico, la resistencia a la fatiga, la tenacidad, y la manejabilidad. (Herring, Atmosphere Heat Treatment). A manera de ejemplo, DeGasperi identifica en la industria automotriz las consecuencias de un %RA demasiado alto o demasiado bajo: –Hablemos de las piezas en una transmisión o en una caja de transferencia; aquí es donde se dan los casos en los que se empiezan a romper los cojinetes, o terminas viéndote en la obligación del retiro masivo del producto del mercado. Y por lo general toda la cadena de suministro identifica al anterior como el culpable cuando ninguno en toda la cadena se ha tomado la molestia de probar las piezas por sí mismo.
Por el contrario, en algunos casos, la RA diseminada en pequeñas cantidades aporta para que el material resista la propagación de fracturas por fatiga y disminuye el estrés por fatiga en el contacto de rodamiento, así que lograr el correcto equilibrio en la cantidad de RA es importante en muchas aplicaciones. Además, el % justo de RA es esencial para el control de calidad, al igual que para evitar problemas de seguridad y retiros masivos del mercado. El debido control y la medición precisa del % RA en las aleaciones de acero es un punto crítico para garantizar la calidad y la seguridad de los componentes terminados, salvaguardando así la reputación y el margen de ganancia tanto de los tratadores térmicos como de los fabricantes.
Métodos de medición de RA
El medir con precisión la RA es de vital importancia para establecer si existe el balance correcto entre la austenita retenida y la martensita en determinado componente. Los tratadores térmicos tienen a su disposición varias metodologías para esta medición, cada una con sus respectivas ventajas y desventajas. Para el tratador térmico entender la importancia de medir el % RA representa tan solo una parte de la batalla ganada, mientras que la otra parte se gana cuando se logra identificar un método de medición que sea rápido, preciso y rentable.
La difracción de rayos-X: el mejor y más preciso de los métodos
Figura 2a. Una unidad de sobremesa ArexD de GNR
La difracción de rayos-X, utilizada para identificar y cuantificar las fases en un material, se considera el método más preciso de medición de RA en acero ya que logra establecer los niveles de RA hasta el rango aproximado de 0.5-1% (GNR, “AreX Diffractometer,” 3). En la difracción de rayos-X, las diferentes fases cristalinas demuestran diferentes patrones de difracción, lo que permite que sean identificadas y medidas. Además del análisis de fases, la difracción de rayos-X se puede utilizar para analizar car acterísticas microestructurales tales como la textura, el esfuerzo residual y el tamaño del grano.
Hoy en día, la difracción de rayos-X es una solución segura y no-destructiva que permite valorar una región mucho más amplia que la de varios de los otros métodos disponibles, sin necesidad de gran preparación ni análisis de la muestra, haciendo de ésta una solución más eficiente y efectiva. Es la tecnología más opcionada para una empresa que requiera valorar la RA con un resultado esperado inferior al 10%,
La actual generación de difractómetros de rayos-X ostenta un diseño de sobremesa con un peso aproximado de 25 libras. Existen modelos con costos inferiores a los USD $100.000, lo que los hace rentables frente al costo de un difractómetro tradicional (USD $200.000) que tenía además la desventaja de presentar dificultades cuando la muestra tuviera fases y reflexiones adicionales, ya fuera por el tamaño del grano, por los carburos o por las texturas que pudieran provocar disturbios y variaciones en la medición. La nueva generación de equipos de rayos-X logra superar estos obstáculos utilizando múltiples picos de difracción para minimizar los efectos de la orientación preferida y detectar la interferencia de los carburos.
Figura 2b. Una unidad de sobremesa ArexD de GNR
Las máquinas modernas de difracción de rayos-X tienen la capacidad de recoger hasta siete picos de difracción (tres para la fase ferrítica/martensítica y cuatro para la fase austenítica) para luego establecer la concentración de porcentaje por volumen de RA en la muestra al comparar las intensidades de los picos y analizar las relaciones entre éstos de acuerdo con el ASTM E975-22 (práctica estándar para la determinación por rayos-X de austenita retenida en acero con orientación cristalográfica cercana a la aleatoria).
No es complicado usar los equipos modernos de difracción de rayos-X. En menos de tres minutos se logra la medición con tan solo ubicar la muestra en la máquina y oprimir el botón de inicio. Estos difractómetros realizan mediciones en muestras de diferentes tamaños y se valen de software intuitivo, dando lugar a que cualquier técnico, tenga o no experiencia previa en metalurgia o difracción, efectúe la medición de manera rápida, precisa y eficiente.
La microscopía óptica: un método a prueba del tiempo
La RA se puede medir de manera metalográfica con un microscopio óptico. En la mayoría de los casos, un metalúrgico con experiencia puede establecer el %RA en el rango hasta del 10-15%, lo cual es más que suficiente para muchas aplicaciones, con el beneficio adicional de que también caracteriza la microestructura.
Este método, que implica establecer la fracción de austenita mediante el contraste derivado del comportamiento de grabado o morfología, es de bajo costo; sin embargo, puede ser demorado. En libros de referencia existen tablas y diagramas que ayudan a determinar el porcentaje de austenita retenida utilizando métodos comparativos. La microscopía óptica es subjetiva ya que depende del individuo y la interpretación que haga de la muestra bajo el microscopio.
Figura 3. Ejemplo de la técnica para medir los picos de %RA
Métodos alternos
Los tratadores térmicos también disponen de otros varios métodos de medición de la RA. Entre los más comunes se encuentran:
La inducción magnética: Aquí se magnetiza una muestra al punto de saturación y se mide la polarización de saturación. Con esto, se calcula la diferencia entre la saturación medida y la saturación teórica de la RA utilizando la ecuación.
La inducción magnética no es destructiva y ofrece un rango más alto y amplio que el de la microscopía óptica (1-30%). Sin embargo, al ser una medición de volumen, es necesario que el instrumento sea calibrado a los materiales específicos, junto con sus tratamientos térmicos y geometrías, lo cual exige mucho tiempo y depende en un alto grado de la habilidad del técnico.
Difracción de electrones por retrodispersión (EBSD, por sus siglas en inglés): Utilizar este método de medición de RA implica ubicar la muestra en un microscopio electrónico de barrido (SEM, por sus siglas en inglés) para caracterizar la estructura cristalográfica al igual que la microestructura. Las mediciones de RA con base en esta técnica no suelen ser muy precisas y dependen de la correcta preparación de la muestra. Adicionalmente, es un método destructivo y arroja una medida sobre un volumen muy pequeño.
En conclusión
El medir acertadamente el nivel de austenita retenida permite que tanto el ingeniero de diseño como el metalúrgico maximicen los efectos benéficos que ofrece, al mismo tiempo evitando sus consecuencias negativas. El tratador térmico, por su parte, deberá tener en cuenta la química del material y las variables del proceso de tratamiento térmico tales como la temperatura de austenización, la rapidez de enfriamiento, los tratamientos criogénicos o de congelación profunda y las temperaturas de templado.
Referencias
Errichello, Robert, Robert Budny, and Rainer Eckert. “Investigations of Bearing Failures Associated with White Etching Areas (WEAs) in Wind Turbine Gearboxes.” Tribology Transactions 56, no. 6 (2013): 1069–1076.
GNR, Analytical Instruments Group. “AreX Diffractometer: GNR Proposal for measuring Retained Austenite in the industrial domain and in laboratory.”
Herring, Daniel H., Atmosphere Heat Treatment. Volume I. Chicago: BNP Media, 2014.
Agradecimientos
Queremos agradecer a los siguientes contribuyentes por su aporte en el desarrollo de este artículo: Thomas Wingens, presidente y especialista en Heat Treat, WINGENS CONSULTANTS; Dennis Beauchesne, gerente general, ECM USA; Tim Moury, presidente & CEO, Marco DeGasperi, gerente técnico, Jeff Froetschel, vicepresidente y director financiero, Verichek Technical Services, Inc.; y Dan Herring, The Heat Treat Doctor®, The HERRING GROUP, Inc.
Most heat treaters recognize the importance of measuring retained austenite (RA), yet many opt not to perform these measurements due to time and/or cost constraints. This Technical Tuesday installment explains why performing RA measurements is necessary, the pros and cons of traditional measurement techniques, and the benefits of using more current and in plant technologies.
This informative piece was first released inHeat Treat Today’sMarch 2025 Aerospace Heat Treating print edition. To read the article in Spanish, click here.
Why Retained Austenite Percentage Matters
Before examining measurement methodologies, it is important to understand the fundamentals of retained austenite and why the percentage of retained austenite (RA%) matters.
Austenite that does not transform to martensite upon quenching is called retained austenite (RA). In simple terms, retained austenite (Figure 1) occurs when steel is not fully quenched to the martensite finish (Mf) temperature; that is, low enough to form 100% martensite. Because the Mf is below room temperature in most alloys containing more than 0.30% carbon, significant amounts of retained austenite may be present within the martensite at room temperature (Herring, Atmosphere Heat Treatment).
When it comes to RA%, there is often a delicate balance between its beneficial effects (an increase in the life of certain manufactured components) and its negative attributes (the creation of parts that are prone to cracking and failure). For this reason, it is crucial that heat treaters achieve the optimal RA% for the intended application.
For example, in the aeronautics and astronautics industries, RA levels are often specified to be under 8% and, for devices such as bearings and linear actuators, RA under 3% and as close to zero as possible is required. In other applications, however, such as large gearing for power generation, wind energy, and performance platforms, in the range of 15–30% or more RA has been found beneficial (Errichello et al., “Investigations of Bearing Failures”). Also, high RA% has been found beneficial for bearings that will be subjected to contaminated lubricants.
Figure 1. 12CrNi3 (similar to SAE/AISI 9310) bearing roller path surface microstructure consisting of
tempered martensite with evidence of retained austenite (white areas)
Marco DeGasperi, technical manager at Verichek, weighed in on this, noting that for fuel injectors, small pieces in medical applications, and high-level, high-volume applications like wear plates in the mining industry, RA% is critical. He summarized with the statement, “When you’re applying pressure and motion to anything that’s fine-tuned … If you have ‘precision’ in your name, you probably want [an RA% measurement device].”
The very characteristics that give retained austenite many of its unique properties are those responsible for significant problems in service. We know that austenite is the normal phase of steel at high temperatures, but not at room temperature. Because retained austenite exists outside of its normal temperature range, it is metastable. This means that in service, factors such as temperature, stress, and even time will see it transform into untempered martensite. In addition, a volume change (increase) accompanies this transformation and induces a great deal of internal stress in a component, often manifesting itself as cracks, which leads to parts failing in the field.
RA% is also important not only because of its influence on dimensional stability but on mechanical properties such as yield strength, fatigue strength, toughness, and machinability (Herring, Atmosphere Heat Treatment). For example, looking in the automotive industry, DeGasperi gives an example of the consequences of having too high or too low RA%: “Let’s say pieces in a transmission or a transfer case; this is when gears start breaking or you get issued wide-end recalls. And then usually the supply chain all starts blaming the guy before them when nobody throughout the supply chain has actually tested the parts themselves.”
Alternatively, in some cases, finely dispersed RA helps the material resist the propagation of fatigue cracks and improves rolling contact fatigue stress, so balancing the amount of RA is important in many applications. Also, the correct RA% is essential for quality control, and proper control and accurate measurement of RA% in steel alloys is crucial to guaranteeing the quality and safety of finished components, as well as protecting the reputation and profitability of heat treaters and manufacturers.
RA Measurement Methods
Accurate RA measurements are critical to determine whether the correct balance of retained austenite and martensite exists within a given part. Several RA measurement methodologies are available to heat treaters, each having their own unique set of advantages and disadvantages. For heat treaters, understanding why it is crucial to measure the percentage of RA is only half the battle. Finding a cost-effective, fast, and accurate measurement method is the other half.
X-Ray Diffraction: The Best and Most Accurate Method
Figure 2a. An ArexD table-top unit from GNR
X-ray diffraction, which is used to identify and quantify phases in a material, is considered the most accurate method of RA measurement in steels as it can precisely determine RA levels down to the range of approximately 0.5–1% (GNR, “AreX Diffractometer,” 3). In X-ray diffraction, different crystalline phases have different diffraction patterns, allowing them to be identified and measured. In addition to phase analysis, X-ray diffraction can be used to analyze microstructural features such as texture, residual stress, and grain size.
Today, X-ray diffraction is a non-destructive, safe solution that can sample a much larger region than many other available methods and does not involve much sample preparation and analysis, making it a more efficient and effective solution. This is the option of choice for a company that needs to test RA with expected readings under 10%.
The current generation of X-ray diffractometers are tabletop sized, weighing about 25 lbs. With models under $100,000, they are also cost-effective when compared to traditional X-ray diffractometers ($200,000), which were sometimes problematic in the presence of additional phases and reflections due to grain size, carbides, or textures that could cause disturbances and variances in measurement. The new generation of X-ray equipment compensates for these obstacles via the use of multiple diffraction peaks to minimize the effects of preferred orientation and detect interference from carbides.
2b. An ArexD table-top unit from GNR
Modern X-ray diffraction machines can collect up to seven diffraction peaks (three for ferrite/martensite phase and four for austenite phase) and then determine the volume percent concentration of RA in the sample by comparing the intensities of the peaks and analyzing the peak ratios in accordance with the ASTM E975-22 (standard practice for X-ray determination of retained austenite in steel with near random crystallographic orientation).
The use of today’s X-ray diffraction equipment is not complicated. It can be measured in under three minutes by simply placing the sample in the machine and pressing the start button. These X-ray diffractometers measure various-sized samples and use intuitive software so the measurement can be performed quickly, accurately, and efficiently by any technician — with or without prior metallurgical or diffraction experience.
Optical Microscopy — A Time-Proven Method
RA can be measured metallographically with an optical microscope. An experienced metallurgist can usually determine RA% down to approximately 10–15% RA. For many applications, this is more than adequate and has the added benefit of characterizing the microstructure as well.
This method, which involves determining the austenite fraction using contrast from etching behavior or morphology, is low cost, however, it can be somewhat time consuming. Charts and diagrams in reference books are available to help determine the percentage of retained austenite by comparative methods. Optical microscopy is subjective as it is dependent upon the individual and their interpretation of the sample under the microscope.
Figure 3. Example of how RA% peaks are measured
Alternative Methods
Several other methods for measuring RA are available to heat treaters. The most common of these methods includes:
Magnetic Induction: Here, a sample is magnetized to saturation and the saturation polarization is measured. The difference between measured and theoretical saturation of the RA can then be calculated using this equation:
Magnetic induction is non-destructive and offers a higher, broader range than optical microscopy (1–30%). However, because it is a volume measurement, the instrument needs to be calibrated to the specific materials, heat treatment, and geometries, which is time consuming and highly dependent on the skill of the technician.
Electron Backscatter Diffraction (EBSD): Using this RA measurement method involves placing a sample in a Scanning Electron Microscope (SEM) to characterize the crystallographic structure as well as the microstructure. RA measurements using this technique are not particularly accurate and are reliant upon proper sample preparation. Additionally, it provides a very small measure volume and is a destructive test method.
Conclusion
Accurate measurement of the level of retained austenite allows both the design engineer and metallurgist to maximize its beneficial effects without suffering from its negative consequences. On the part of the heat treater this means taking into account the material chemistry and the heat treat process variables such as austenitizing temperature, quench rate, deep freeze or cryogenic treatments, and tempering temperatures.
References
Errichello, Robert, Robert Budny, and Rainer Eckert. “Investigations of Bearing Failures Associated with White Etching Areas (WEAs) in Wind Turbine Gearboxes.” Tribology Transactions 56, no. 6 (2013): 1069–1076.
GNR, Analytical Instruments Group. “AreX Diffractometer: GNR Proposal for measuring Retained Austenite in the industrial domain and in laboratory.”
Herring, Daniel H., Atmosphere Heat Treatment. Volume I. Chicago: BNP Media, 2014.
Acknowledgments
We’d like to thank the following contributors for the support of this article: Thomas Wingens, President & Heat Treat Specialist, WINGENS CONSULTANTS; Dennis Beauchesne, General Manager, ECM USA; Tim Moury, President & CEO, Marco DeGasperi, Technical Manager, Jeff Froetschel, VP & CFO, Verichek Technical Services, Inc.; and Dan Herring, The Heat Treat Doctor®, The HERRING GROUP, Inc.
Conticon, a steel-wire manufacturer, is expanding production capabilities at its North American plant by installing a CONTIROD® CR3700 line to address the growing demand for high-quality copper rod for the automotive and telecommunications industries. The line, which includes a furnace plant, casting machine, rolling plant, and cooling line, is a fully integrated casting and rolling process that turns copper cathodes and clean copper scrap into material for conductors, boosts the capacity of the existing plant.
The company, a joint venture between Grupo Condumex and Xignux, a manufacturer of electrolytic tough pitch (ETP) copper rod, commissioned SMS group to provide and complete the installation of the CONTIROD® line at its plant in Celaya-Villagrán, Mexico, boosting the current line, which has an annual capacity of approximately 230,000 tons. With an additional 320,000 tons from the new line, the total theoretical capacity is approximately 550,000 tons per year. The line is the only manufacturing process for cast wire rod that utilizes a Hazelett twin-belt casting machine, which physically precludes porosity in the casting bar’s core.
Impression of a comparable CONTIROD® CR3700 line with a capacity of 60 tons per hour
SMS, which has a long-standing relationship Condumex, Inc, dating back to the installation of the first line in 1984, is providing the company with a complete CONTIROD® line, encompassing both process and electrical equipment to enhance production at the Conticon facility. The new line covers every stage of production, including the charging device, furnace plant, casting machine, rolling plant, and cooling line, as well as the coil forming and handling systems. This comprehensive solution not only increases productivity thanks to its ease of maintenance and operation but also enhances process control and operator safety. The new CONTIROD® CR3700 line has a capacity of 48 tons per hour.
The new line offers sustainability benefits, including reductions of 55 percent for electrical energy consumption and 30 percent for natural gas. These efficiencies are achieved through advanced design and process integration and optimized thermal heat utilization, thus minimizing energy waste and enhancing the system’s overall efficiency. The technology package also features process control systems that ensure precise operation, further contributing to energy savings.
Press release is available in its original form here.
