hardening

Improving Hardening and Introducing Innovation for In-House Heat Treat

/ AEROSPACE HEAT TREAT, HARDENING TECHNICAL CONTENT

In this Technical Tuesday by Paulo Duarte, project manager, Metalsolvus, explores how digital tools lead the way in vacuum hardening operations to ensure energy efficiency and processing repeatability.

This piece was originally published in Heat Treat Today’s March 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

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.

Figure 1. Cooling parts in vacuum hardening furnaces — inert gas injection on the hot chamber during cooling

Hardening of Large Tools

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).

Figure 2. Large molds positioned inside the vacuum hardening furnace, two parallel cavities

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)

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.

Figure 5. Microstructure of Uddeholm Orvar Supreme steel after quenching using different cooling rates

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.

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.

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”

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 di cult 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 following equations.

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”)

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.

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:

  • Plate Example: 20 x 300 x 200 mm
  • Ideal standard block: diameter or edge: 51 mm
  • Maximum Error — same material block:
    • Cylindrical: -0.2% (-0.7 min)
    • Cubic: -0.1% (-0.4 min)
  • Maximum Error — block — Stainless steel 304:
    • Cylindrical: +2.2% (+9.2 min)
    • Cubic: +1.65% (+6.9 min)
  • EDM Block Example: 200 x 200 x 200 mm
  • Ideal standard block: diameter or edge: 200 mm
  • Maximum Error — same material block:
    • Cylindrical: -3.9% (-22.6 min)
    • Cubic: 0% (0 min)
  • Maximum Error — block — stainless steel 304:
    • Cylindrical: +17.3% (+100.3 min)
    • Cubic: +12.2% (+70.8 min)

Optimizing the Vacuum Hardening of Tools

Figure 7. Effect of selecting different temperature (T) range for starting to control the isothermal stage time. a) T criteria and respective cycle time reduction; b) surface mechanical properties obtained by using different T; and c) core properties after tempering at different T 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.

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”)

New Vacuum Hardening Process — Long Martempering

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.

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.

Table 2. Mechanical properties of the new hardening process — long martempering

Industry 5.0

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.

Figure 9. Heat treatment plant supervision solution

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

Figure 10. Heat treatment quality automatic report including automatic approval

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 longestablished 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-supervisionbrochure-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/novoforno-de-tempera-vacuo—ate-4-tons-.html.

Schmetz. “Schmetz Heat Treatment Furnaces.” Accessed January 30, 2025. https://edelmetal.com.tr/en/heat-treatmentfurnaces.

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, 2025. https://solarmfg.com/vacuum-furnaces/horizontal-iq-vacuumfurnaces.

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 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 bohleruddeholm group for the Portuguese market and heat treatment manager with the same group. Currently, Paulo efforts 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.

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    Tool & Die Capabilities Increase with Heat Treat Box Furnace

    / ALUMINUM PROCESSING NEWS, FEATURED NEWS, HARDENING NEWS, MANUFACTURING HEAT TREAT, OVENS-HIGH-TEMPERATURE, TEMPERING NEWS

    An electric box furnace, currently headed to a Midwest equipment provider, will ultimately be installed at a Snap-on production facility that services tool and die support within the company’s production line.

    The model QDD29 economical dual-chamber heat treating and tempering oven from L&L Special Furnace has a compact over/under design that saves floor space and provides reliable heat treating in-house.

    QDD29 economical dual-chamber furnace (Source: L&L Special Furnace)

    The top chamber is primarily deployed for heat treating tool steels at temperatures up to 2200°F; the tempering chamber is suited to temperatures up to 1250°F and has a recirculation baffle that makes it suitable for small aluminum work as well. The hardening and tempering chambers have interior dimensions of 12” wide by 8” high by 24” deep, with total external dimensions of 55” wide by 70” tall by 56” deep.

    The QDD29 is controlled with digital single setpoint controls along with overtemperature protection. Solid-state relays drive the heating elements in a control circuit.

    This press release is available in its original form upon request.

    Find Heat Treating Products and Services When You Search on Heat Treat Buyers Guide.com

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    Induction Through Heating + Intensive Quenching: A “Green Ticket” for Steel Parts

    / CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, QUENCHING TECHNICAL CONTENT

    OCOn site at heat treat operations, gas-fired furnaces can be a significant source of carbon emissions. But depending on the desired heat treatment, an alternative approach that combines induction through heating and intensive quenching could be the “green ticket.” Learn about the ITH + IQ technique and discover how certain steels may benefit from this approach.

    This Technical Tuesday article was composed by Edward Rylicki, Vice President Technology, and Chris Pedder, Technical Manager Heat Treat Products and Services, at Ajax TOCCO Magnethermic Corp., and Michael Aronov, CEO, IQ Technologies, Inc. It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologies print edition.

    Introduction

    Chris Pedder,
    Technical Manager Heat Treat Products and Services, Ajax TOCCO Magnethermic Corp.
    Source: Ajax TOCCO Magnethermic Corp.

    Induction heating is a green, environmentally friendly technology providing energy savings and much greater heating rates compared to other furnace heating methods. Other advantages of induction heating include improved automation and control, reduced floor space, and cleaner working conditions. Induction heating is widely used in the forging industry for heating billets prior to plastic deformation. Induction heating is also used for different heat treatment operations such as surface and through hardening, tempering, stress relieving, normalizing, and annealing. However, the amount of steel products subjected to induction heating in the heat treating industry is much less compared to that processed in gas-fired furnaces.

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    Gas-fired heat treating equipment is a major source of carbon emissions in the industry. As shown in Reference 1, induction through heating (ITH) followed by intensive quenching (IQ) (an “ITH + IQ” technique) eliminates, in many cases, the need for a gas-fired furnace when conducting through hardening and carburizing processes — the two most widely used heat treating operations for certain steel parts. Eliminating gas-fired furnaces will result in significant reduction of carbon emissions at on-site heat treat operations.

    Dr. Michael Aronov,
    CEO, IQ Technologies, Inc.
    Source: Ajax TOCCO Magnethermic Corp.

    The goal of this article is twofold: 1) to evaluate carbon emissions generated during through hardening of steel parts and carburizing processes when conducted in gas-fired furnaces, and 2) to discuss how these emissions can be reduced to zero using the ITH + IQ process.

    Evaluation of Carbon Emissions for Through Hardening and Carburizing Processes

    Ed Rylicki,
    Vice President Technology, Ajax TOCCO Detroit Development & Support Center
    Source: Ajax TOCCO Magnethermic Corp.

    Most through hardening and carburizing operations for steel parts are conducted in batch and continuous integral quench gas-fired furnaces. Assumptions made for evaluating CO2 emissions produced by a typical integral quench furnace are presented in Table 1. Note: The values of carbon emissions presented Table 1 are conservative since they don’t consider the amount of CO2 produced by furnace flame screens and endothermic gas generators used to provide a controlled carburizing atmosphere in the furnace. Also, it’s assumed that the furnace walls are already heated through when loading the parts, so there are no heat losses associated with the thermal energy accumulated by the furnace walls.

    Table 1. Assumptions for calculating of carbon emissions by integral quench furnace
    Source: Ajax TOCCO Magnethermic Corp.

    Emissions Generated During the Through Hardening Process

    A furnace time/temperature diagram for the through hardening process considered is presented in Figure 1. Carbon emissions Ehard produced by the furnace considered during heating of the load to the austenitizing temperature prior to quenching are calculated by using the following equation,

     

    (Equation 1)
    Ehard = k • Qhard

    where:

    ■ k = the emission coefficient (equal to 0.050 • 10-3 kg per 1 kJ of released energy when burning natural gas (see Reference 2)
    ■ Qhard = thermal energy required for heating up the above load from ambient to the austenitizing temperature

    A value of Qhard is calculated by the equation below,

    (Equation 2)

    Qhard = M • C • (Ta -To) / Eff = 1,135 • 0.56 • (843 - 20) / 0.65 = 0.805 • 106kJ

    where:

    ■ M = load weight, kg
    ■ C = steel specific heat capacity (kJ/kg°C)
    ■ Ta = part austenitizing temperature (°C)
    ■ To = part initial temperature (°C)
    ■ Eff = furnace thermal efficiency (a ratio of the furnace thermal losses to the gross heat input)

    From equations (1) and (2), the amount of carbon emissions produced by the above furnace during one hardening operation is 40.2 kg. To determine an annual amount of carbon emissions, calculate the number of hardening cycles per year (Nhard) run in the furnace. From Figure 1, a duration of one hardening cycle is 4 hours (3 hours for austenitizing of the parts plus 1 hour for quenching the parts in oil and unloading/loading the furnace). Thus, Nhard is equal to:

    Nhard = 360 day • 24 hour • 0.85 / 4 hour = 1826

    Figure 1
    Source: Ajax TOCCO Magnethermic Corp.

    Annual CO2 emissions from one integral quench batch gas-fired furnace are 40.2 • 1836 = 73,807 kg, or more than 73 t

    Emissions Generated During Carburizing Process

    A simplified furnace time/temperature diagram for the carburizing process considered is presented in Figure 2. Carbon emissions (Ecarb) produced by the above furnace during the carburizing process are calculated by the following equation,

    (Equation 3)

    Ecarb = k • Qcarb

    where:

    ■ Qcarb = a thermal energy expended by the furnace during the carburizing process. A value of Qcarb amounts to two components: 

    (Equation 4)

    Qcarb = Qcarb1 + Qcarb2

    Qcarb in the following equation is:

    ■ Qcarb1 = energy required for heating up the load to the carburizing temperature
    ■ Qcarb2 = energy needed for maintaining the furnace temperature during the remaining duration of the carburization process (for compensation of the furnace thermal losses since the parts are already heated up to the carburizing temperature)

    A value of Qcarb1 is calculated using equation (2) where the part carburizing temperature Tc is used instead of part austenitizing temperature Ta (see Table 1):

    Qcarb1 = 1,135 • 0.56 • (927 – 20) / 0.65 = 0.887 • 106 kJ

    A value of Qcarb2 is a sum of the flue gas losses and losses of the thermal energy through the furnace walls by heat conduction. Qcarb2 is evaluated from the following considerations. Since the assumed furnace thermal efficiency is 65%, the furnace heat losses are equal to 35% of the gross heat input to the furnace. Hence, the furnace heat losses Qloss1 during the load heat up period (the first 3 hours of the carburizing cycle, see Figure 2) are the following:

    Qloss1 = Qcarb1 • 0.35 = 0.887 • 106 • 0.35 = 0.31 • 106 kJ.

    The furnace heat losses during the remaining 8 hours of the carburizing cycle Qloss2 are proportionally greater and are equal to:

    Qloss2 = Qloss1 • 8 hr /3 hr = 031 • 106 • 8 /3 = 0.827 • 106 kJ

    Thus, the total amount of the thermal energy expended by the furnace during the carburizing cycle is Qcarb = 0.887 • 106 + 0.827 • 106 = 1.71 • 106 kJ. The total amount of the CO2 emissions from carburizing of the load in the furnace considered according to equation (3) is: Ecarb = 0.050 • 10-3 • 1.71 • 106 = 85.7 kg. To determine an annual amount of carbon emissions from one carburizing furnace, calculate the number of carburizing cycles run in the furnace per year. Per Figure 2, a duration of one carburizing cycle is 12 hour (1 hour for the furnace recovery plus 10 hour for carburizing of parts at 927°C plus 1 hour for quenching parts in oil and for unloading and loading the furnace). Thus, the number of carburizing cycles per year Ncarb is:

    Ncarb = 360 day • 24 hr • 0.85 / 12 hr = 612

    Figure 2
    Source: Ajax TOCCO Magnethermic Corp.

    Annual CO2 emissions from one integral quench batch carburizing furnace is about 85.7 • 612 = 52,448 kg, or more than 52 t.

    Reducing Carbon Emissions Using the ITH + IQ Process

    Reference 1 presents results of two case studies of the ITH + IQ process on automotive input shafts and drive pinions. The study was conducted with a major U.S. automotive part supplier. A two-step heat treating process was used for the input shafts, consisting of batch quenching parts in oil or polymer using an integral quench gas-fired furnace for core hardening followed by induction hardening. This two-step method of heat treatment is widely used in the industry for many steel products. It provides parts with a hard case and tough, ductile core.

    Substituting the “ITH + IQ” method for the two-step heat treating process not only eliminates the batch hardening process, but also requires less alloy steel for the shafts that don’t require annealing after forging. Thus, in this case, applying the ITH + IQ technique eliminates two furnace heating processes for the input shafts, resulting in the reduction of the CO2 emissions to zero for the shafts’ heat treatment. Per client evaluation, as mentioned in Reference 1, the hardness profile in the intensively quenched input shafts was similar to that of the standard shafts. Residual surface compressive stresses in the intensively quenched shafts were greater in most cases compared to that of the standard input shafts, resulting in a longer part fatigue life of up to 300%.

    Per Reference 1, the environmentally unfriendly  carburizing process can be fully eliminated in most cases for automotive pinions when applying the ITH + IQ method and using limited hardenability (LH) steels that have a very low amount of alloy elements. A case study conducted for drive pinions with one of the major U.S. automotive parts suppliers demonstrates the intensively quenched drive pinions met all client’s metallurgical specifications and passed both the ultimate strength test and the fatigue test. It was shown that the part’s fatigue resistance improved by about 150% compared to that of standard carburized and quenched in oil drive pinions. In addition, distortion of the intensively quenched drive pinions is so low that no part straitening operations were required.

    Conclusion

    Coupling Ajax TOCCO’s induction through heating method with the intensive quenching process creates a significant reduction of CO2 emissions produced during heat treatment operations for steel parts. For the through hardening process, eliminating just one batch integral quench gas-fi red furnace will reduce carbon emissions by more than 73 ton per year. For the carburizing process, eliminating just one batch carburizing furnace will reduce carbon emissions by more than 52 ton per year. Note that for continuous gas-fired furnaces, the carbon emission reduction will be much greater due to higher continuous furnaces production rates (hence a much higher fuel consumption).

    Per our experience, the ITH + IQ process can be applied to at least 20% of the currently through-hardened and carburized steel parts. Per two major heat treating furnace manufacturers in the U.S., there are thousands of atmosphere integral quench batch and continuous furnaces in operation in the U.S. That means hundreds of gas-fired heat treating furnaces can be potentially eliminated, drastically reducing carbon emissions in the U.S., supporting a lean and green economy.

     

    References

    [1] Michael Aronov, Edward Rylicki, and Chris Pedder, “Two Cost-Effective Applications of Intensive Quenching Process for Steel Parts,”Heat Treat Today, October 2021, https://www.heattreattoday.com/processes/quenching/quenching-technical-content/two-cost-effective-applications-for-intensive-quenching-of-steel-parts/.

    [2] U.S. Energy Information Administration.

    About the Authors:

    Ed Rylicki has been in the induction heating industry for over 50 years. He is currently Vice President Technology at Ajax TOCCO Detroit Development & Support Center in Madison Heights, Michigan.

    Mr. Chris Pedder has over 34 years of experience at Ajax Tocco Magnethermic involving the development of induction processes in the heat treating industry from tooling concept and process development to production implementation.

    Dr. Michael Aronov has over 50 years’ experience in design and development of heating and cooling equipment and processes for heat treating applications. He is CEO of IQ Technologies, Inc. and a consultant to the parent company Ajax TOCCO Magnethermic.

    For more information: Contact info@ajaxtocco.com or 800.547.1527

     

     

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    Michelin Acquires New Vacuum Furnace

    / AUTOMOTIVE HEAT TREAT, FEATURED NEWS, VACUUM FURNACES NEWS

    HTD Size-PR LogoMichelin, a European tire manufacturer with technology centers in the U.S., will receive a new vacuum furnace from a global supplier with locations in North America. Tire manufacturing requires specialized tools; tools and dies used in production are heat treated in vacuum furnaces. The furnace, with a 16" x 16" x 24" heating chamber, will be used for gas hardening and will remove the need for third-party hardening.

    Maciej Korecki
    Vice President of Business of the Vacuum Furnace Segment
    SECO/WARWICK

    Michelin will receive a SECO/WARWICK Vector® vacuum furnace, enabling efficient hardening processes with the use of high pressure and cooling gas. “With a relatively low expenditure," explains Maciej Korecki, vice president of Business, Vacuum Furnace Segment at SECO/WARWICK, "the compact Vector vacuum furnace makes it possible to become independent from third parties. It also provides better control over the quality of heat-treated components and reduces the risk of delays which, as a result of lack of deliveries, slow down or obstruct manufacturing processes (tire manufacturing in this case)."

    Michelin Acquires New Vacuum Furnace Read More »

    Induction Hardening: Understanding the Basics

    / FEATURED NEWS, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, MANUFACTURING HEAT TREAT

    OCInduction is a curious member in the family of heat treating. Its presence is valuable, yet there’s a mystery surrounding it that has even veteran heat treaters exploring it to gain understanding. Journey through this induction hardening primer to learn about this important misfit of the heat treating world.

    This Heat Treat Today Technical Tuesday original content feature, written by Kyle Hummel, P.E., COO at Contour Hardening, first appeared in Heat Treat Today's May 2021 Induction print edition. Feel free to contact Karen Gantzer at karen@heattreattoday.com if you have a question, comment, or any editorial contribution you’d like to submit.

    Kyle Hummel, P.E..
    Chief Operations Officer
    Contour Hardening

    In the world of heat treat, induction hardening just doesn’t fit in. There is no big furnace, cycle times are a matter seconds, and the entire process takes place right before your eyes rather than behind the walls of a furnace chamber. Many heat treaters have one old induction machine sitting in the corner of the shop floor, with one remaining employee who knows how to operate it.

    Induction is different than all other types of heat treatment, and even many metallurgists shy away from the "black magic" that occurs during the process. When I ask customers how familiar they are with induction hardening, they usually state that they have seen it before, mention something about a coil, but that’s about the extent of their knowledge.

    The purpose of this article is to give readers, who are not familiar with the induction hardening process, some background on the fundamental aspects and terminology of the process. The information encompasses the most common questions I am asked by new customers as well as information I would provide in training new employees. My hope is that it will give you enough familiarity with the process to become more comfortable engaging in a conversation about induction hardening.

    Why Use Induction?

    Selective hardening – Induction allows you to harden only the desired portion of a part, whereas most furnace-based heat treat processes treat the entire component. This means you can harden the particular area that you want to harden, while leaving the rest of the component soft enough to machine further.

    Strength – Not only does the part become harder, but the stress (called residual compressive stress) that is induced into the part will make it stronger. Other processes can meet the improved wear resistance of the added hardness but fail to strengthen the part at all, or not as much as induction hardening.

    Single piece flow – Because induction hardening is not a batch process (typically one part is hardened at a time), induction machines can be placed in a manufacturing cell, allowing the process flow to be uninterrupted.

    Induction hardening in action

    Equipment and Tooling

    Induction Hardening Machine – Systems will vary significantly in size and complexity depending on the components they are hardening. The primary components of the machine consist of a power supply, heat station (transformer), workstation, and HMI. The fluids system is composed of quenchant to cool the part being hardened and distilled water to cool the internal components of the machine. Heat time, power supply output, part rotation, and quenchant parameters should be controlled, monitored, and logged for each part.

    Power Supplies – Power supplies are the most important component of the induction hardener. For the purpose of this article, we will discuss the two most important outputs of the power supply, frequency and power.

    Frequency is important because it will help determine the depth of heating. Lower frequencies heat deeper into the part, and higher frequencies heat closer to the surface. To remember this, I like to use the analogy of whales using very low frequency calls to communicate over miles and miles of ocean, whereas the high-pitched squeak of a mouse can only be heard several feet away. For induction hardening, frequencies are split into two groups: medium frequency (MF) and radio frequency (RF). The MF range is typically from 3-50kHz, and RF is from 100-400kHz.

    Power is important because it will determine how large of a part you can harden, and how long the heat time will need to be. The more power that a machine can output, the larger the part it can harden and the faster it can harden to a specified case depth. Typical power supply outputs for induction hardening range from 25kW to 1MW.

    Coils – The induction coil is a copper conductor that is shaped in order to harden the specified area of the part. The current that flows through the coil is what produces the magnetic field, which in turn heats the part. Coils are typically part specific, since they need to be precisely constructed to heat a particular portion of the part.

    Modern induction coils are water cooled and can be made of tubing or machined copper pieces that are brazed together to make a particular shape to fit the part. They are frequently equipped with sections of a material called flux intensifier, which helps to drive the magnetic field in a certain direction in order to intensify heating in that area and make the coil more efficient.

    It is also common to have the quenching designed into the coil (machine integral quench, or MIQ) so that quenchant can be applied immediately after heating without the need to move the part to an auxiliary quench mechanism.

    Process Basics

    Single Shot – Single shot hardening is the most common method of induction hardening where the part and coil remain in the same spot during the heating process. Typically, the part is brought into proximity of the coil, the heating and quenching processes are applied to the part, and then the part is removed from the coil.

    Scanning – Scanning involves heating and quenching a small portion of the part while moving either the coil or the part until the desired area is hardened. Quench is directionally applied to the part so that as a new portion of the part is heated, the previously heated section is being quenched appropriately. Scanning is frequently used to harden shafts because heating the entire shaft at once would require too much power.

    Dual Frequency – Dual frequency hardening combines the benefits of the deeper heating of the lower MFs with the surface heating capabilities of higher RFs. By utilizing two different frequencies, it is possible to contour the hardening pattern more effectively on gear-like components, which further improves the strength of the part. The frequencies can either be applied consecutively (low frequency preheat followed by a high frequency final heat) or simultaneously.

    Induction Tempering – Induction can also be used to complete the temper process in a few seconds rather than furnace tempering which could take hours. Induction tempering takes place after the hardening process and involves heating the part to a much lower temperature than is required during hardening. The targeted temperature for induction temper is higher than that of furnace tempering due to the decreased temper time. This softens the hardened area slightly in order to increase the toughness of the part and improve crack susceptibility.

    Quenching – The quench process is just as important as the heating process with induction hardening. Almost all modern systems use a water/polymer quenchant mixture in the range of 5-20% polymer instead of using oils. The quench media is typically sprayed on to the part rather than submerging it into a bath. Quench concentration, temperature, flow, and pressure must all be monitored closely for a robust process. These parameters all function to guarantee that the part is quenched properly and consistently to ensure the correct hardness is achieved and crack susceptibility is minimized. Quench media must also be filtered to remove any process waste that could potentially clog the quench spray holes.

    Inspection – Like most other forms of heat treatment, the two most common specifications with induction hardening are case depth and hardness. Most specifications will require surface hardness measurements along with effective case depths to determine the depth of hardening.

    Materials – The most common materials to be induction hardened are medium to high carbon and alloy steels, cast irons, and powder metal. Induction is also becoming a popular heat treat method on certain stainless steels in different industries.

    Induction hardening in action

    What to Look Out For

    Cracking – The rapid expansion of the part during heating followed by shrinkage from the accelerated cooldown during quenching increases crack susceptibility of induction hardened parts. Not all parts have a high risk of cracking, but part characteristics such as internal holes, sharp edges, and certain higher carbon materials will require more consideration. If cracking is an issue, the first two areas to investigate are overheating and quench severity. Reducing the quench severity (increasing quench temperature and concentration, reducing flow and pressure) is typically the most effective means of reducing cracking within an induction hardened part.

    Distortion – Another side effect of the rapid expansion and contraction is part distortion. It is impossible to not distort the part with induction hardening due to the phase changes in the metal. However, with a robust and carefully monitored process, it is possible to minimize and accurately predict process distortion. Faster heating times and technical expertise in fixturing methods are two common methods to reduce distortion.

    Conclusion

    Although this information just begins to scratch the surface of the terminology and fundamentals of the process, hopefully it provides a starting point to those with limited experience. Like many other forms of heat treatment, it can take years to develop the knowledge and skills to gain expertise in induction hardening. I have been involved in induction for almost fifteen years, and I find there is always a new application that gives me the opportunity to learn even more.

    About the Author: Kyle Hummel is a licensed Professional Engineer who has worked for Contour Hardening for 15 years as a metallurgical engineer and currently manages operations of Contour’s Indianapolis location.

    For more information, contact Kyle at khummel@contourhardening.com or 317.876.1530 ext. 333

    Induction Hardening: Understanding the Basics Read More »

    Dr. Valery Rudnev on Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 2

    / FEATURED NEWS, HARDENING, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

    This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Six previous installments in Dr. Rudnev’s series on equipment selection addressed selected aspects of scan hardening and continuous/progressive hardening systems. This post is the second in a discussion on equipment selection for one of four popular induction hardening techniques focusing on single-shot hardening systems.

    The first part on equipment selection for single-shot hardening is here; the third part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. 

    Traditional Designs of Single-Shot Inductors

    Figure 1 shows a typical shaft-like component (Figure 1,top-left) suitable for a single-shot hardening inductor, as well as a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces. Sometimes, these inductors are also referred to as channel inductors.

    A conventional single-shot inductor consists of two legs and two crossover segments, also known as bridges, “horseshoes,” or half-loops [1]. The induced eddy currents under the legs primarily flow along the length of the part (longitudinally/axially) with the exception of the regions of the workpiece located under the crossover segments where the flow of the eddy current is half circumferential. Unlike scanning inductors, traditional designs of single-shot inductors can be quite complicated.

    Figure 1. A typical shaft-like component (top-left image) suitable for a single-shot hardening and a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces (Courtesy of Inductoheat Inc., an Inductotherm Group company)
    Figure 1. A typical shaft-like component (top-left image) suitable for a single-shot hardening and a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces (Courtesy of Inductoheat Inc., an Inductotherm Group company)

    With a predominantly longitudinal eddy current flow, the heat uniformity in the diameter change areas of the stepped shafts is dramatically improved and the tendency of corners and shoulders to be overheated is reduced significantly compared to applying a single-turn or multi-turn solenoid coils commonly used in scan hardening and continuous/progressive hardening.

    Because the copper of single-shot inductors does not completely encircle the entire region required to be heated, rotation must be used to create a sufficiently uniform austenitized surface layer along the workpiece perimeter. Upon quenching, a sufficiently uniform hardness case depth along the circumference of the part will be produced. For single-shot inductors, the rotation speed usually ranges from 120 to 500 rpm.

    Different types of magnetic flux concentrators (also called flux intensifiers, flux controllers, flux diverters, magnetic shunts, etc.) complement the copper profiling of an inductor, helping to achieve the required hardness pattern. Flux concentrators may provide several considerable benefits when applied in single-shot inductors. This includes an increase of coil electrical efficiency, a noticeable reduction of coil current, and a significant reduction of the external magnetic field exposure.

    As an example, Figure 2 shows a transverse cross-section of a single-shot inductor and a straight shaft. Computer-modeled electromagnetic field distribution of a bare inductor (Figure 2, left) compared to an inductor with a U-shaped flux concentrator (Figure 2, right) is shown. Note that the magnitude of magnetic field intensity on both images is different. The use of U-shaped magnetic flux concentrators in single-shot hardening applications typically results in a 16% to 27% coil current reduction compared to using a bare inductor while having a similar heating effect. A reduction of the external magnetic field exposure while applying flux concentrator is even more dramatic (Figure 2, right).

    Figure 2.  Computer-modeled EMF distribution in the transverse cross-section of a bare inductor (left) compared to an inductor with U-shaped flux concentrator (right). Note: the scale of magnetic field intensity on both images is different [1].
    Figure 2.  Computer-modeled EMF distribution in the transverse cross-section of a bare inductor (left) compared to an inductor with U-shaped flux concentrator (right). Note: the scale of magnetic field intensity on both images is different [1].
    Different applications may call for various materials used to fabricate magnetic flux concentrators including stacks of silicon-steel laminations, pure ferrites, and various proprietary multiphase composites. The selection of a particular material depends on a number of factors, including the following [1]:

    • applied frequency, power density, and duty cycle;
    • operating temperature and ability to be cooled;
    • geometries of workpiece and inductor;
    • machinability, formability, structural homogeneity, and integrity;
    • an ability to withstand an aggressive working environment resisting chemical attack by quenchants and corrosion;
    • brittleness, density, and ability to withstand occasional impact force;
    • ease of installation and removal, available space for installation, and so on.

    It should be noted that, though in most single-shot hardening applications flux concentrators will improve efficiency, there are other cases where no improvement will be recorded, or efficiency may even drop. A detailed discussion regarding the subtleties of using magnetic flux concentrators is provided in [See References 1, 2.].

    Sufficient rotation is critical when using any single-shot inductor design. As an example, Figure 3 shows the sketch of a single-shot induction hardening system.

    Figure 3.  Sketch of single-shot induction hardening of an axle shaft. Note: The right half of this induction system is computer-modeled in Fig. 4 [3].
    Figure 3.  Sketch of single-shot induction hardening of an axle shaft. Note: The right half of this induction system is computer-modeled in Fig. 4 [3].
    Taking advantage of symmetry, only the right side of such a system was modeled using finite-element analysis. Figure 4 shows the result of computer simulation of initial, interim, and final heating stages, taking into consideration the shaft rotation. Insufficient part rotation resulted in a non-uniform temperature distribution along the shaft perimeter (Figure 4, left). Proper shaft rotation results in a sufficiently uniform temperature pattern (Figure 4, right).

    Figure 4.  Results of numerical simulation of heating an axle shaft by using a single-shot inductor [3].
    Figure 4.  Results of numerical simulation of heating an axle shaft by using a single-shot inductor [3].
    There should be at least eight full rotations per heat cycle (preferably more than 12 rotations), depending on the size of the workpiece and the design specifics of the inductor, though, as always in life, there are some exceptions. Shorter heating times and narrower coil copper heating faces require faster rotation during the austenitization cycle.

    An appropriate inductor design with a closely controlled and monitored rotation speed will produce a hardness pattern with minimum circumferential and longitudinal temperature deviations, which will result in sufficiently uniform hardness patterns (Figure 5, left four images). Failure to ensure proper rotation as well as the use of worn centers (lacking grabbing force resulting in slippage and excessive part wobbling) could lead to an unacceptable heat non-uniformity, severe local overheating, and even melting (Figure 5, right). Manufacturers of induction equipment such as Inductoheat have developed various proprietary tools, holders, fixtures, and monitoring devices to ensure proper rotation and high quality of single-shot hardened parts.

    Figure 5.  Inductor design with closely controlled rotation speed will produce a hardness pattern with minimum circumferential temperature deviations (left four images). Failure to ensure proper rotation speed as well as the use of worn centers (lacking grabbing force resulting in slippage) could lead to unacceptable heat non-uniformity and can even cause a localized melting (right image).
    Figure 5.  Inductor design with closely controlled rotation speed will produce a hardness pattern with minimum circumferential temperature deviations (left four images). Failure to ensure proper rotation speed as well as the use of worn centers (lacking grabbing force resulting in slippage) could lead to unacceptable heat non-uniformity and can even cause a localized melting (right image).

    The next installment of this column, "Dr. Valery Rudnev on . . . ", will continue the discussion of design features of induction single-shot hardening systems.

    References

    1. V.Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.
    2. V.Rudnev, "An objective assessment of magnetic flux concentrators", Heat Treating Progress, ASM Intl., December 2004, pp 19-23.
    3. V.Rudnev, "Simulation of Induction Heat Treating", ASM Handbook, Volume 22B, Metals Process Simulation, D.U. Furrer and S.L. Semiatin, editors, ASM Int’l, 2010, pp 501-546.

     

    Dr. Valery Rudnev on Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 2 Read More »

    Comparative Study of Carburizing vs. Induction Hardening of Gears

    / AEROSPACE HEAT TREAT, AEROSPACE HEAT TREAT NEWS, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, INDUCTION HEATING TECHNICAL CONTENT

    Modern rotary-wing aircraft propulsion systems rely on different types of gears to transmit power from the turbine engines to the rotors. The basic requirements of these gears are that they are high strength, sustain long life, meet weight considerations, and have a high working temperature and low noise and cost, among others.

    Most importantly, these gears require a hard, wear-resistant surface with a ductile core.

    Gas carburizing is the current heat treat method used to produce these aircraft quality gears, but this method of heat treatment is costly due to the large number of process steps, huge footprints, energy consumption, and environmental issues. Moreover, the final grinding of gear teeth to correct distortion produced during quenching reduces effective surface compressive stresses.

    An investigation into low-cost alternatives for surface hardening aerospace spur gears was conducted where specimens of the selected gears were induction hardened using a patented process. Dimensional and microstructural analyses were conducted, and residual stress studies were performed. This article is a summary of the steps and observations of the case study that resulted from this investigation, which can be summarized this way:

    The proposed induction process is a low-cost alternative to conventional gas carburization. In some applications, a 25% savings is estimated.

    The first step to gear manufacturing demands a total understanding of aerospace gear requirements. As the gear transmits torque, the teeth are subjected to a combination of cyclic bending, contact stresses, and different degrees of sliding or contact behavior. It is, therefore, critical for a gear to have the proper case and core structure to withstand these loading conditions.

    With every revolution, a cyclic bending load is applied, resulting in tensile stress at the root region of the gear. The core of the gear has to be soft to absorb impact load and prevent brittle failure. Due to high-speed contact between adjacent gear teeth, peak shear stresses generated at the surface act in the normal direction to the surface. Pitting, spalling, or case crushing types of failures can occur due to low residual stress or inadequate case depth.

    For aircraft quality gears, typical surface hardness is around 58Rc to 60Rc. The case depth is in reference to 50Rc and is controlled by diametral pitch.

    Carburization

    Carburization hardening is the most widely used technique for surface hardening of aerospace quality gears. A brief introduction to carburization is necessary to understand the potential benefits of this process and how other surface transformation can improve on some of the drawbacks of this commonly used process.

    After raw material is received, it is forged to achieve proper grain structure and core hardness. The alloy most commonly used is ASM 6260 (AISI 9310). This low carbon alloy steel exhibits high core toughness and ductility.

    Parts are loaded in a furnace and heated to 1650ºF – 1750ºF in a carbon rich atmosphere, where approximately 1% carbon potential is maintained. The depth and level of carbon absorption depend on carbon potential, temperature, time inside the furnace, and the alloy content of the material. After the desired carbon gradient is achieved, the gears are cooled slowly. Then the parts are heated to austenitizing temperature and quenched.

    The process depends on the size, geometry, dimension tolerances, and other gear requirements.

    The heat treat cycles shown above are two commonly used carburization processes. The difference in post carburization steps depends on the alloy used and final product requirement.

    The characteristic of carburization is the inherent distortion associated due to the difference in cooling rates between the thin web and thicker rim. Distortion can occur as a size growth, a change in involute profile, or the loss of crown in spur gears.

    Case Hardening by Selective Heat Treatment

    The number of process steps required to case carburize a gear can be significantly reduced only if the gear tooth surface areas are heat treated.

    Processes for locally heating only the tooth surface include induction, flame, laser, and electron beam.

    In order to use induction, steel with a minimum of 0.5% carbon must be used. Several different alloy steels were experimented with, such as AMS 6431, AlSl 6150, and AlSl 4350/4360/4370. These steels were selected due to their combination of toughness, temper resistance, hardenability, and strength. The hardened case is obtained by heating a specific volume of the tooth surface above the transformation temperature for that material. Rapid contour heating produced a case of martensitic structure around the profile-hardened area, resulting in high compressive residual stress at the surface at the root fillet. This compressive stress increases the tooth bending fatigue life, where tensile stress exists due to tooth bending.

    Transformation hardening allows a significant reduction in process steps and associated fabrication costs, due to two different factors:

    1. Since sufficient carbon is already present in the base material, copper masking, plating, stripping and carburization steps are eliminated.
    2. In selective hardening, the area of the heated zone is limited to only the hardened sections, and distortion is minimal and predictable.

    Surface hardening applications are generally controlled by three process parameters, namely frequency, power level, and time. In this respect, several different hardening processes have been used for gear hardening. The proposed method discussed in this presentation is known as Dual Pulse Induction Hardening (DPIH).

    DPIH Process

    The DPIH is a patented process (U.S. patent #4,639,279). The process uses single frequency for both the preheat and final heat cycles. Two different power levels are used. This allows the entire process to be performed in one setup, using a single solid-state power supply.

    The DPIH process consists of the steps described below:

     

     

    The heat treatment process steps for both the carburized and DPIH processes for the aircraft gear are compared below:

     

     

    An 85% reduction in heat treat process steps occurs when the gear hardening method is changed from conventional gas carburization to DPIH.

     

    Conclusion:

    Comparison of the above data and the conventional carburization process to DPIH process.

    Carburizing grade material has to be changed from low carbon to medium carbon steel for induction hardening. In both the processes, surface hardness achieved is comparable, but the characteristic of induction hardening is that the gear section maintains a constant hardness value from the surface up to the transition zone, where it rapidly drops to core hardness levels, unlike a more gradual decrease in hardness in case of carburized gears. Low distortion of induction hardening gear is also a major cost reducing factor.

     

    Acknowledgment:

    This work was performed at AGT, Division of General Motors.

    Madhu Chatterjee is founder and president of AAT Metallurgical Services LLC in Michigan with extensive experience in advanced engineering, research and development, and process and product improvement. He is also one of the original dozen consultants that inaugurated Heat Treat Today’s Heat Treat Consultants resource page. You can learn more about Madhu Chatterjee here.

     

     

     

     

    Look for more on aerospace heat treating in the upcoming special aerospace manufacturing edition of Heat Treat Today.

    Comparative Study of Carburizing vs. Induction Hardening of Gears Read More »

    Suit of Armor Receives Heat Treatment

    / FEATURED NEWS, HARDENING, MANUFACTURING HEAT TREAT NEWS, TEMPERING

      Source: Metlab

    Combining the ancient craft of blacksmithing with heat treating processes, artisan Robert (Mac) McPherson obtained the finish he wanted for a suit of armor designed after a late 15th-century statue of the patron saint of firefighters. The suit was fashioned with 125 hand-formed, then hardened and tempered metal plates.

    Read more: Metlab Applies Black Oxide to a Suit of Armor by Metlab Blog

    Suit of Armor Receives Heat Treatment Read More »