What process holds a soft spot in your heart? Tempering or annealing? For Valentine's Day, turn up the heat -- errr heat treatments -- with this look at the differences in tempering and annealing! Heat TreatToday has resources for you to spark some thought and learning on these processes.
Sentiments and strong feelings can certainly be heightened this Valentine's Day. While tempering and annealing may not lend themselves easily to the holiday, we hope you enjoy a bit of a nod to the day in our headings below. Make use of the Reader Feedback button, too, and keep us in the loop with questions and comments on what heat treatment you love.
Problem with Annealing? Get to the Heart of the Issue
An automotive parts manufacturer was running into problems with cracking parts. The variable valve timing plates were returning from heat treatment with this problem. To determine why those parts were cracking after the annealing process, an investigation was launched by metallurgists at Paulo.
The presence of nitrogen combining with the aluminum already present in the particular steel being used was forming aluminum nitrides. What could be done? Read more in the case study article below to find out a workable solution that allowed the annealing to create a crack-free product.
Induction, Rapid Air, Oven and Furnace Tempering: Which One do You Love?
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This article gives some perspectives, from experts in the field, on what kinds of tempering are available and for what the processes are used.
Hear from Bill Stuehr of Induction Tooling, Mike Zaharof of Inductoheat, and Mike Grande of Wisconsin Oven with some basics and background information on tempering. Those reasons alone make this resource helpful with information like this: "tempering at higher temperatures results in lower hardness and increased ductility," says Mike Grande, vice president of sales at Wisconsin Oven. "Tempering at lower temperatures provides a harder steel that is less ductile."
More specific in-depth study is presented as well. The Larson-Miller equation is considered, and the importance of temperature uniformity is emphasized. Read more of the perspectives: "Tempering: 4 Perspectives — Which makes sense for you?"
Cast or Wrought Radiant Tubes in Annealing Furnaces - is Cheaper Really What to Fall For?
Marc Glasser, director of Metallurgical Services at Rolled Alloys, takes a look at radiant tubes. He particularly discusses the cast tubes and wrought tubes. For use in continuous annealing furnaces, there are several factors contributing to choice of radiant tube type.
Marc says, "Justification for the higher cost wrought alloy needs to take into consideration initial fabricated tube cost, actual tube life, AND the lost production of each anticipated downtime cycle as these downtime costs are often much more than material costs." He probes into areas that may not be considered when thinking of all the costs involved. Read more of his article "Radiant Tubes: Exploring Your Options."
Tempering Furnaces: Improvements are Thrilling
The expert behind this piece shows the importance of tempering, particularly in automotive fastener production. Tim Donofrio, vice president of sales at CAN-ENG Furnaces International Limited examines what's working in the tempering furnaces. The products are meeting and exceeding expectations.
To wrap up this Technical Tuesday post on tempering and annealing, head over to this additional resource to round out the scope of each process. "What is the Difference: Tempering VS. Annealing" gives a summary perspective on the heat treatments discussed above.
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What are the heat treat tech trends we're seeing in Heat TreatToday? Perhaps you read the Tech Trends article earlier this year predicting what trends in the industry will continue to develop in 2022. We can see that a point made by Jim Oakes, president of Super Systems, Inc., overlaps all of the trends in this line up: "The pillars in technology remain quality and efficiency with a growing emphasis on connectivity and carbon footprint visibility." Check out the 6 trends below!
Thermal Efficiency To Decrease Carbon Footprint
The technical thoughts that we're seeing surrounding this awareness for thermal efficiency surround the technology of induction. "[Induction] is also a very efficient process," commented Michael J. Zaharof, manager customer information & marketing at Inductoheat, "as induction power supplies are only powered on when needed compared to batch processing (like those requiring an oven)." Additionally, Girish Dahake, senior vice president of Global Applications at Ambrell Corporation, describes this efficient process saying, "The workpiece is placed in the coil where this field induces a current, generating heat in the workpiece. The water-cooled coil is cool to the touch and is placed around or adjacent to the work piece. It does not touch the workpiece and heat is generated by the induced current flowing in the workpiece."
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In the news, there have been companies looking to replace old gas generators with no automatic process controls and lacking in dew point efficiency. The resulting significant CO2 savings for heat treating operations is in line with the trend of pursuing efficiency for the sake of decreasing carbon footprint.
Technology for Remote Monitoring and Integrated Control
We've seen this in the episode with Matt Wright at C3 Data in his description of integrated control of various systems. Additionally, he related that flow of information in heat treat facilities is a major challenge: "When I look at our industry, one of the things that is the biggest challenge is the flow of information — getting information from where it resides to where it needs to be in the format that it needs to be. I think the technologies that have been successful in our industry are technologies that help lubricate that flow, if you will."
This hot -- or rather salty -- topic appeared on Heat Treat Radio with Bill Disler at AFC-Holcroft noting that modern processes allow for 99% of salt in quenching to be reclaimed. The manner that salt is used as a quenchant is different from oil: "With salt, you’ll come out of the quench with some liquid salt on it, you’ll go into a washer but that salt then dissolves back into the water. Generally, there is a multiphase wash with a wash/rinse/rinse. Then, after we get a certain percentage of salt in the wash solution, we thermally evaporate the water off leaving the salt back where it can be reintroduced into the quench tank."
Another representative from the company, Bill Coburn, was recently quoted in a press release that highlighted this feature in a recent installation at an agricultural product manufacturer. While these examples are so far quite consistent within the company, we expect more conversations about this reuse-and-recycle opportunity to be forthcoming.
Looking back at the months of June and July, the press release ratio of atmosphere to vacuum furnace focus was 3:9. Check out the latest news in the industry in these press releases:
One of our partners, heat processing interviewed Mark Bula at H2 Green Steel in a feature revealing how the company was commited to electric generation as part of the industrial process. While there is a fair amount of criticism from the energy sector about what this conversion value could realistically look like, the attempts to make electric happen continue to grow.
Digital Transformation and Application of IIoT Technologies
This trend will take a variety of forms, particularly with the catchy term, "predictive maintenance." Learn more about IIoT here, but for some technical conversations that have continued into 2022, turn to the Heat TreatRadio podcast with Fives North American Combustion.
[blockquote author="Justin Dzik, Fives North American Combustion" style="1"]The CertiFire™ is, as you already stated, an automated tuning device for temperature uniformity certifications. I think pretty much everybody that’s going to watch this podcast is probably going to know that they can be extremely time consuming to do, they take a lot of time and a lot of intelligence to actually tune the process. This device takes all of that and does it all itself. It does all the automated burner tuning, all the valve adjustments, it locks it all in and tunes it for whatever class uniformity you need.[/blockquote]
Tempering. A vitally important step in the hardening process and a process that is used extensively throughout the heat treatment industry. There are three main schools of thought on how to achieve a properly tempered part. Here we have asked three experts to share their knowledge on the specific approach they feel works best for tempering: Bill Stuehr of Induction Tooling, Mike Zaharof of Inductoheat, and Mike Grande of Wisconsin Oven. Learn how each approaches tempering and why they feel it works well for them.
Please note that mechanical properties and microstructure, in addition to hardness, need to be carefully considered when choosing any tempering process so as to help ensure the part is fit for its intended purpose.
This Technical Tuesday article first appeared inHeat Treat Today’sMay 2022 Induction Heating print edition.
Induction Tempering: Captive Heat Treating
By William I. Stuehr, President/CEO, Induction Tooling, Inc.
William I. Stuehr President/CEO Induction Tooling, Inc.
I can only speak to this subject through a lens of 46 years and thousands of induction hardening applications. That said, I have had many tempering inductor requests within the domain of captive heat treating. The commercial induction heat treaters that I service most always use oven tempering because it is accurate, economical, and easy.
Figure 1. Wheel bearing hub and spindle sectioned and etched to show the selective hardened surfaces. Source: Induction Tooling, Inc.
For the captive heat treat departments processing high volume components, the interest in induction tempering as an in-line process sparked in the mid-1970s with the production “cell” concept. This was most evident in the manufacturing of modular wheel bearing assemblies – raw forgings were fed into the cell and completed units exited. Modular wheel bearings are composed of a hub and a spindle. Within the production cell both needed selective induction hardening and tempering. The specification for the wheel spindle required a casehardened profile to provide wear and strength and for the wheel hub, the bearing races were hardened. Equipment manufacturers designed and built specialized high-volume parts handlers, integrated with the proper induction power supplies to operate efficiently within the cell. The inductors, both hardening and tempering, were designed, built, and characterized to produce a specification hardened part (Figure 1).
Figure 2. Thermal image of a wheel spindle Source: Induction Tooling, Inc.Figure 3. Truck axle and truck axle temper inductor Induction Tooling, Inc.
Induction hardening for the hub and spindle is quick – usually five seconds or less; induction tempering is a much longer heating process. Both parts required a low power soak until the optimum temperature was achieved. For the two wheel bearing components, tempering had to be accomplished either in a long channel-type inductor or several multi-turn inductors to keep pace with hardening. The long channel inductor was designed to hover over a conveyor belt. The belt would move the hardened hub or spindle at a slow, even pace allowing the precisely controlled induction energy to migrate throughout. Care was taken in the design and length of the channel inductor to assure temperature uniformity. Multi-turn inductors are circular solenoid designs that required the hub or spindle to lift and slowly rotate at three or four locations in order to complete the temper. As in hardening, the temper installation required its own induction power supply. Thermal imaging confirmed the results (Figure 2).
Truck axle shafts are another high production component that is induction hardened and tempered. Often the axle shafts are robotically loaded in a vertical or horizontal inductor. The shaft is rotated, heated, and then shuttled to a quench position. The loading robot then moves the hardened axle shaft to another inductor, usually within the same unit, specifically designed for the tempering process. A separate induction power supply controls the input energy. The temper time can be equal to the induction hardening time added to the quenching time. This will allow for the proper input of uniform induction temper energy (Figure 3).
Today, high production automotive driveline components are routinely induction tempered. Among the examples explained are CV joints, gears, and camshafts. Monitoring of the induction energy is different compared with furnace tempering. When heating parts with complex geometries, it is necessary to focus upon where the induction energy is concentrated. Heat conduction can be carefully monitored to confirm that an overheat condition does not occur at the target temper areas. Power input, soak time, and inductor characterization control these
fundamentals.
Induction tempering is sometimes attempted using the hardening inductor. For some very low volume parts, depending upon the part geometry and induction power supply frequency, the results may be acceptable. Careful power control and timing along with thermal imaging is needed to confirm the results. Again, since tempering takes longer, output will be much slower. Experience has demonstrated that a part specific tempering inductor coupled with a dedicated induction power supply works best.
About the Author: Bill Stuehr is the founder and president of Induction Tooling, Inc, a premier heat treat inductor design and build facility. The holder and partner of many induction application patents, Bill shares his expertise and generously donates his time and facility resources to mentor young students entering the heat treat industry.
By Michael J. Zaharof, Customer Information & Marketing Manager, Inductoheat
Michael J. Zaharof Customer Information & Marketing Manager Inductoheat
Induction tempering is the process of heating a previously hardened workpiece to reduce stress, increase toughness, improve ductility, and decrease brittleness. A medium-to-high carbon steel (i.e., 1045, 1050, 4140, 5160) heated above the upper critical temperature causes a high-stress shear-like transformation into very hard and brittle martensite. This untempered martensite is generally undesirable and too brittle for postprocessing operations such as machining and can pose a concern for poor performance in high fatigue applications. Therefore, tempering is needed to reduce internal stresses, increase durability, and reduce the possibility of cracking.
In most cases, induction tempering occurs in-line and directly after the induction heating, quenching, and cool-down operations. Traditionally, workpieces are moved to a tempering spindle or separate machine after hardening. Once moved, the part is then inductively heated and often force cooled to ambient temperature. The induction tempering process itself generates temperatures on the workpiece (typically) well below the curie point (248°F-1112°F/120°C-600°C – solid blue line in Figure 1). This phenomenon is referred to as “skin effect,” where the current density is highest at the surface of the material. Therefore, a lower inverter frequency is most desirable in order to increase the electrical reference depth.
However, while most cases reflect a secondary/separate station for induction tempering, this is not always the case. Recent advancements in power supply technology permit “real-time” frequency and power adjustments. These next-generation induction power supplies have brought tremendous flexibility into the market and have allowed induction hardening and tempering to occur at the same station, on the same induction coil. Using such a novel approach with induction heating often speeds up production while reducing the number of part movements. Induction tempering is a preferred method for many manufacturers as it offers several notable advantages. In production applications, it is viewed as a fast-tempering method, as the parts are heated quickly, cooled, then moved on to the next operation, reducing potential bottlenecks.
There is no need to collect the parts, place them into batches, and wait for long subsequent processes to finish before moving them down the production line.
Figure 1. The induction tempering process itself generates temperatures on the workpiece (typically) well below the curie point. Source: Inductoheat
Induction is a clean process and does not rely on combustible gases or chemicals that may be harmful to the environment. Additionally, it is also a very efficient process as induction power supplies are only powered on when needed compared to batch processing (like those requiring an oven). Ovens must be preheated prior to use and can often stand idle for long periods between batches, as the pre-heat/cooldown cycles can be lengthy. Induction heating equipment is also physically smaller in most cases and occupies much less real estate on the manufacturing floor.
Individual part traceability and data collection are possible when utilizing induction tempering. If paired with a quality monitoring system (QAS), data can be evaluated in real-time and compared to a known good “signature” for the part during the induction tempering process. This allows precise control of the process and the ability to reject parts that deviate outside of established metrics. It is also an effective tool for detecting process issues early when a variation occurs minimizing potential scrap and helping to prevent delivery of “bad” parts to the end customer.
Induction tempering offers many advantages over other methods of tempering and is an effective choice in many applications. Due to the benefits of speed, efficiency, repeatability, and environmental cleanliness, induction technology is widely accepted and is being used throughout many industries today.
References:
[1] “In-Line Tempering on Induction Heat Treating Equipment Relieves Stresses Advantageously,” by K. Weiss: Industrial Heating, Vol. 62, No. 12, December 1995, p. 37-39.
[2] “Induction Heat Treatment: Basic Principles, Computation, Coil Construction, and Design Considerations,” by V.I. Rudnev, R.L. Cook, D.L. Loveless, and M.R. Black: Steel Heat Treatment Handbook, G.E. Totten and M.A.H. Howes (Eds.), Marcel Dekker Inc., Monticello, N.Y., 1997, p. 765-871.
About the Author: Michael Zaharof is a customer information & marketing manager at Inductoheat in Madison Heights, Michigan. He has been with the company since 2011 and has worked in the sales application, digital media, outside sales, and engineering departments. Michael has a bachelor’s degree in computer science in information system security.
By Mike Grande, Vice President of Sales, Wisconsin Oven
Mike Grande Vice President of Sales Wisconsin Oven
Tempering (also known as “drawing”) is a process whereby a metal is heated to a specific temperature, then cooled slowly to improve its properties. It is commonly performed on ferrous alloys such as steel or cast iron after quench hardening. Quenching rapidly cools the metal, but leaves it brittle and lacking toughness, which is a desirable characteristic that represents a balance of hardness and ductility. After quenching, the material is tempered to reduce the hardness to the required level and to relieve internal stresses caused by the quenching process. The resulting hardness is dependent on the metallurgy of the steel and the time and temperature of the tempering process. Tempering is performed at a temperature between approximately 255°F (125°C) and 1292°F (700°C). In general, tempering at higher temperatures results in lower hardness and increased ductility. Tempering at lower temperatures provides a harder steel that is less ductile.
Draw batch ovens: the high-powered workhorses of the tempering process Wisconsin Oven
Tempering is performed in a convection oven using a high volume of air circulating through and around the load of steel being tempered. The air is heated in a plenum separated from the load, then delivered to the load at high velocity through distribution ductwork using a recirculation blower. Since the air is the medium used to carry the heat from the source (a gas burner or heating elements) to the load, it is important that the blower recirculates a high volume of air through the heating chamber. Further, since air becomes significantly less dense at higher temperatures, the recirculated air volume must be higher for ovens operating at higher temperatures in order to provide sufficient mass (pounds or kilograms) of air to transfer the heat from the source to the load.
For example, a typical batch tempering oven designed to process a 2,000 lb. load with dimensions of 4′ x 4′ x 4′ might have a recirculation rate of 10,000 cubic feet per minute (CFM). At this airflow volume, the oven recirculating system operates at 156 air changes per minute, which means all the air passes from the recirculating blower through the heating chamber 2.6 times per second. At a temperature of 1000°F (538°C), for example, the weight of the air being recirculated is 290 lbs. (132 kg) per minute, or 17,400 lbs. (7,909 kg) per hour. It is this high volume of air that provides good heat distribution to the load being processed and ensures tight temperature uniformity within the load during tempering.
The higher the mass of air being recirculated, the tighter the temperature uniformity will be. The temperature uniformity (±10°F or 6°C, for example) defines how much the temperature is allowed to vary within the load being tempered. If the oven operates too far outside of this tolerance, the parts may not be tempered uniformly, and the hardness might vary among different parts in the same load. It is important that the temperature uniformity of a tempering oven be verified (“certified” or “qualified”) by testing, and that this is repeated periodically, as well as after any changes or repairs are made that could affect the uniformity.
About the Author: Mike Grande is the vice president of Sales at Wisconsin Oven with a bachelor’s degree in mechanical engineering and over 30 years of experience in the heat processing industry. Over that time, he has been involved with convection and infrared technologies, and several industrial oven energy efficiency design advancements.
The next type of tempering we’d like to address is rapid air tempering. This process involves “any tempering technology taking advantage of rapid heating methods combined with shortened soak times at temperature based on those predicted by use of the Larsen-Miller calculator.”1 Here “rapid heating” is defined as “any heating method that accelerates conventional furnace heating.”2
Table 1.3 Thermal profile of conventional tempering and vertical rapid air furnaces
Rapid air tempering takes advantage of the use of a higher initial heating temperature (i.e., the use of a so-called heat head) to drive heat into the part more quickly. Additionally, rapid air tempering shortens soak time at temperature (from the more conventional furnace tempering times).
The Larson-Miller calculator is used in rapid air tempering to provide a comparison of hold times at various tempering temperatures and the results of tempering time change is assumed be the same (see example below); however, the interpretation of the data and results are left to the end user.
Larson-Miller Calculator
There are various reports describing the use of the Larson-Miller equation for assessing stress-relieving and tempering process conditions.4 “The relationship between time and temperature can be described as a logarithmic function in the form of the Larson-Miller equation, which shows that the thermal effect (TE) is dependent on the temperature and the logarithm of time:
“This thermal effect is also interpreted as the tempering parameter. For example, a material that is required to be tempered at a temperature of 740°F for one hour has the same TE as a material treated at 800°F for 6 minutes (Fig. 1).”5
Figure 1.5 The “TE” is a logarithmic function of time
References:
[1] Roger Gingras, Mario Grenier, and G.E. Totten, “Rapid Stress Relief and Tempering,” Gear Solutions, May 2005, pg. 27-31.
[2] N. Fricker, K.F. Pomfret, and J.D. Waddington, Commun. 1072, Institution of Gas Engineering, 44th Annual Meeting, London, November 1978.
[3] Thomas Neumann and Kenneth Pickett, “Rapid Tempering of Automotive Axle Shafts,” Heat Treating Progress, March/April 2006, pg. 44.
[4] Lauralice C.F. Canale, Xin Yao, Jianfeng Gu, and George E. Totten, “A Historical Overview of Steel Tempering Parameters,” Int. J. Microstructure and Materials Properties, Vol. 3, Nos. 4/5, 2008, pg. 496.
[5] Roger Gingras and Mario Grenier, “Tempering Calculator,” in ASM Heat Treating Society, Heat Treating: Proceedings of the 23rd ASM Heat Treating Society Conference September 25-28, 2005, David L. Lawrence Convention Center, Pittsburgh, Pennsylvania, USA, Daniel Herring and Robert Hill, eds., Materials Park, Ohio: ASM International, 2006. pg. 147-152.
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An induction heat treat equipment supplier is offering customized, process-specific training seminars to a leading automotive part manufacturer. With the growing need for training and education among new and less experienced employees, these highly effective training strategies are growing in popularity.
This article shows how one induction heat treat equipment supplier, Inductoheat, has helped Stellantis, a leading automotive manufacturer, improve its in-house heat treat operations and further excel its technology.
Stringent demands to dramatically minimize transmission noise in hybrid and electric vehicles (EV) as well as in modern internal combustion powered vehicles (ICE) call for innovative technologies allowing to suppress distortion of heat-treated parts, while further enhancing their metallurgical quality and performance characteristics.
Light-weighing initiatives have become essential in vehicle designs. To minimize weight and cost of automotive components, designers might choose to drill holes, reduce cross sections, make intricate transitions, cutouts, re-entrant corners, and custom shapes. In some cases, such attempts result in a component’s geometries that might be prone to cracking during heat treating or might be associated with excessive distortion. Many times, complex geometries of components are linked to intricate hardness patterns and specific requirements for magnitude and distribution of residual stresses.
To be competitive and successfully develop high performance/low distortion components, induction heat treatment users must have a clear understanding of not only principles of electromagnetic induction and associated metallurgical subtleties, but also have awareness of recent theoretical discoveries and technological breakthroughs to further advance part designs.
On multiple recent occasions, Inductoheat has been approached by automotive industry and heat treat suppliers to develop process-specific training seminars as a knowledge-sharing eff ort to give insights on various aspects associated with induction thermal technology. As a response, Inductoheat has developed several practical-oriented training seminars for the automotive industry. These seminars allow present and potential users of induction technologies to understand basic and advanced knowledge associated with electromagnetic induction and to learn novel theoretical achievements, process developments, technological breakthroughs, and practical recommendations.
Another goal in developing these technical seminars is to minimize the negative impact of a generation gap by helping young professionals involved in induction heating to better understand its subtleties and metallurgical intricacies and clarify common misconceptions and confusions existing in different publications.
Best practices and simple solutions for typical induction heating challenges, as well as do and don’t items in designing and fabricating coils are explained. The subject of induction hardening of complex geometry parts (including but not limited to gears, gear-like and shaft-like parts, raceways, camshafts, and other critical components) is also thoroughly discussed, describing inventions and innovations that have occurred in the last three to five years.
Understanding a broad spectrum of interrelated factors associated with various failure modes of heat treat components is an important step in designing new products and developing robust and sustainable processes. Aspects related to failure analysis, part longevity, process monitoring, quality assurance, and robustness of induction systems, novel semiconductor inverter technologies, as well as specifics of implementing Industry 4.0 operating strategy in induction heat treating are also addressed in these seminars. Various design concepts and advanced process recipes/protocols are analyzed to help reduce the energy consumption of induction equipment and enhance cost effectiveness.
Some people traditionally view induction heating as a standalone process or system. Presented materials clearly reveal a necessity to consider induction equipment as part of an integrated system that includes all elements (such as previous process stages and their metallurgical implications, stress analysis, load matching capabilities, and many others) that must be considered to accomplish the process goal.
Finally, Inductoheat conducts these technical video seminars free of charge, addressing specific subjects defined by a particular automotive manufacturer or heat treat supplier.
Technical Seminars for Stellantis
Inductoheat recently conducted two free technical video seminars addressing subjects selected by Stellantis that included aspects related to modern induction thermal processing for traditional ICE vehicle and EV markets.
The first seminar in April was devoted to “Troubleshooting Failures and Prevention in Induction Hardening: General Useful Remedies, Impact of Geometrical Irregularities and Improper Designs.”
In May, the second seminar focused on “Novel Developments and Prospects of Using Induction Heat Treating for Electrical Vehicles (EV).”
Both seminars had the same format: 90 minutes of oral presentations by Inductoheat’s team followed by 20 minutes of Q&A sessions. Attendees included heat treat practitioners, engineers, metallurgists, managers, and scientists involved in induction heating technologies in application to the automotive industry. There were 220 professionals from Stellantis North America registered for the first seminar alone.
Figure 1
Step-by-Step Remedies to Minimize the Probability of Abnormal Outputs
A virtually endless variety of components are routinely induction hardened for different sectors of the industry (Figure 1). Many of these components have their own “personalities” that affect the outcome of heat treatment. Troubleshooting tips and practical remedies to prevent unspecified outputs associated with induction hardening have been developed by industry experts and shared with professionals involved in induction thermal processing. This enhances the knowledge of designers of automotive components and minimizes the probability of cracking and excessive distortion in industrial practice.
Possible abnormal outputs associated with induction hardening include:
Inappropriate microstructures (undesirable phases or their mixtures)
Unacceptable hardness levels (too high or too low)
Inadequate hardness case depths (too deep or too shallow)
Hardness inconsistency/inappropriate hardness pattern (e.g., a deviation of a run-off region)
Excessive grain coarsening, decarburization, oxidation, and scaling
Unfavorable transient stresses/undesirable magnitude and distribution of residual stresses
Crack development and propagation
There is a variety of factors that need to be considered to ensure that abnormal heat treat outputs do not occur. Those factors can be divided into four large groups: 1, 2
Prior microstructure and composition of incoming material
Parts geometry related
Inductor design related
Process protocol related
Inadequate equipment selection or unsuitable heat treat process protocols may be unfit for certain geometrical features of parts or required hardness patterns. It is difficult to overestimate the importance in having a sufficient degree of familiarity with the hardening equipment and process specifics of a particular machine under investigation. Underestimating geometrical irregularities of components (including a presence of holes, keyways, grooves, shoulders, flanges, undercuts, sharp corners, and other geometrical irregularities) by novices as well as a danger of misjudging an impact of different process factors on the outcome of heat treatment have been reviewed in these seminars. Numerous practical case studies and solutions to prevent abnormal outputs have been shared.
Figure 2. Transmission and engine components may contain multiple longitudinal (axial) and/or transverse (radial) holes, as well as angled or cross holes.
Presence of Holes on Selecting Appropriate Inductor Style and Process Protocol
It is not unusual for transmission and engine components to contain multiple longitudinal (axial) and/or transverse (radial) holes, as well as angled or cross holes (Figure 2). Induction practitioners can face certain challenges when dealing with parts containing holes. Distortion of the eddy current flow in the hole area can result in the undesirable combination of “hot” and “cold” spots, excessive shape distortion, and unwanted metallurgical microstructures, which weakens grain structure and substantially increases brittleness and sensitivity to intergranular cracking.
It is important to carefully evaluate the imaginary eddy current flow lines in the vicinity of oil holes. Surprisingly, in many cases, a proper selection of induction hardening technique (for example, single-shot vs. scanning vs. static hardening) in combination with other factors can be essential in helping to dramatically improve heat uniformity and eliminate regions with localized grain boundary liquation that could act as crack-initiation sites.
There are several helpful practical solutions and knowhow shared with heat treaters during these seminars helping to develop robust and failure-free induction hardening processes. For example, appropriate coil copper profiling often allows dramatically reducing or eliminating hot spots in the vicinity of holes. Some of those solutions allow selectively controlling heat source distribution along the oil hole perimeter by providing preferable channels for eddy current flow. Several patented design concepts have been revealed.
It should be recognized that temperature surplus alone might not result in cracking. There are other factors that can contribute to overheating, thereby increasing crack sensitivity. Steel chemical composition is one of those factors. Steels having higher carbon contents are more prone to cracking. Besides carbon content, an unfavorable combination of alloying elements and residual impurities could promote a tendency to crack initiation; the extent depends on the amount and combination of elements present.
For example, sulfur and phosphorus amounts should be minimized to reduce steel brittleness and crack sensitivity. Sulfur reacts with iron, producing hard, brittle iron sulfides (FeS) that concentrate at grain boundaries. FeS also has a relatively low melting temperature, potentially leading to grain boundary liquation and increased sensitivity to heat surplus. FeS in carbon steels is minimized by the addition of manganese to form MnS creating a less brittle microstructure. A high level of phosphorus, copper, and tin can also weaken steel’s grain boundaries causing excessive brittleness and a tendency to crack initiation.
Impact of metallic residual elements can be differentiated based on their presence (e.g., in solid solution), precipitation specifics (for example, a capability to form inclusions such as carbides, sulfides or nitrides), as well as characteristics of formed inclusions (including amount, size, distribution, etc.), and their tendency for segregation.
It is important to keep in mind that transient stresses are primarily responsible for great majority of cracking in induction hardening. Thus, it is essential to have a clear understanding regarding the specifics of their formation. A complex stress state in the vicinity of the oil holes takes place during the heating and quenching cycles. Dynamics of a formation of transient stresses during spray quenching in the locality of the oil hole may have a unique double hump appearance, where the second peak of tensile residual stress might have appreciable greater magnitude compared to the first one resulting in a potential to exceed the strength of the material. This phenomenon must be taken into consideration when developing process protocols.
Additional challenges can appear when the part consists of several closely spaced holes positioned in-line or across from eddy current flow. Case studies have been reviewed and practical suggestions on enhancing microstructures in the vicinity of multiple oil holes were given addressing a double hump of transient stresses. Practical remedies were given to diminish probability of crack initiation when a part consists of multiple, closely positioned oil holes.
Experience shows that in many cases, the proper choice of design parameters (applied frequency, power density, inductor profiling, quench considerations, etc.) allows one to obtain the required hardened pattern around holes free of cracks, even in those cases that may seem first unsuitable for heat treating by induction.
Novel Developments
Newly developed induction thermal technologies occur quite regularly, offering impressive benefits. In its continuing tradition to further excel existing processes, Inductoheat is developing advanced technologies that enhance traditional processes. For example, thanks to newly developed inductor design, one of the world’s largest suppliers of automotive parts has achieved more than a ten-fold increase in a coil life of a single-shot hardening inductor compared to industry average life of conventional single-shot inductors. Enhancement has been verified by the manufacturer’s tool-room tag. Reasoning for such a dramatic coil life enhancement has been explained during seminars. Other benefits of this remarkable technology include a measurable improvement in process robustness and dramatically reduced process sensitivity.
Additional innovations are related to the unique ability of some of Inductoheat’s inverters to independently control power and frequency (like a CNC machine) during the scan hardening or a single-shot hardening, which helps further optimize thermal conditions.
Seminars provided an objective assessment of rapid tempering and stress relieving compared to longer-time oven tempering. An evaluation of mechanical properties and performance characteristics of components produced by different tempering techniques (e.g., longer-time oven tempering vs. induction rapid tempering), impact of steel’s chemical composition (including a carbon content and alloy composition), as well as an impact of hardness case depth and other practical factors when assessing applicability of induction tempering have been reviewed.
It is imperative to be aware that numerous studies recently conducted by various researchers worldwide clearly suggest that under specific conditions, a rapid tempering can be superior to oven tempering in helping to eliminate or dramatically minimize such undesirable phenomena as temper embrittlement (TE) and temper martensite embrittlement (TME) and measurably enhance toughness and ductility of rapid tempered steels.
Conclusion
It is our hope that the materials presented at these technical video seminars will help you to better understand the intricacies of thermal processing using electromagnetic induction and to deliver your company a competitive advantage to become a “world-class” user of this remarkable technology.
References
[1] G. Doyon, V. Rudnev, R. Minnick, T. Boussie, Troubleshooting and Prevention of Cracking in Induction Hardening of Steels, Lessons Learned – Part 1, Thermal Processing, September 2019, p.26-33.
[2] G. Doyon, V. Rudnev, R. Minnick, T. Boussie, Troubleshooting and Prevention of Cracking in Induction Hardening of Steels – Part 2, Thermal Processing, October 2019, p.30-37.
For more information, please contact: Inductoheat, Inc. in Madison Heights, Michigan or visit www.inductoheat.com or www.inductothermgroup.com.
Welcome toHeat Treat Today'sThis Week in Heat TreatSocial Media. As you know, there is so much content available on the web that it’s next to impossible to sift through all of the articles and posts that flood our inboxes and notifications on a daily basis. So, Heat Treat Todayis here to bring you the latest in compelling, inspiring, and entertaining heat treat news from the different social media venues that you’ve just got to see and read!
This week, we are looking at where rockets are flying next and exploring the heat treat conversations that people are having through social media. A few graphs, charts, and interview resources are further down.
"Under the new Rocket Cargo Vanguard, the DAF will seek to leverage these commercial advances and position the DoD to be an early adopter of the new commercial capability." Read the entire article at "USAF wants to deliver cargo around the world with reusable rockets."
The US Air Force has announced the development of a new type of rocket-powered transporter to deliver cargo around the world https://t.co/0SOBd3gqTE
— Aerospace Manufacturing (@AerospaceTweets) June 7, 2021
2. Join the Conversation
A few quick tours around your heat treat shops: what have heat treaters accomplished this past year? Have you done anything similar? Let us know and tag @HeatTreatToday on your next post!
An Aerospace Question to the Heat Treaters
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Breaking it Down: Annealing, Hardening, Tempering
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The Ladies With Elbow Grease
3. A Little Heat Treat Kudos
Social media is a great place to celebrate your advances with your coworkers and clients. Check out some of the kudos that has been circulating around the inter-web.
A New Measurement System
It's Always Hot in Houston
Click Image to see gallery of images on LinkedIn
Structural Integrity of an Open Die
4. Reading and Podcast
Tune into these interviews and fun conversations this weekend, or check out the reading snippets from around the industry.
Internet Security in the Industry World
Learn how Oldcastle uses SecureLink to manage vendor privileged access for multiple users across 85 locations and how they were able to resolve pain points associated with using VPNs for vendor access. You have to submit your contact information, and then you can read more here: "Oldcastle Infrastructure, Inc. Strengthens Security and Centralizes Remote Access"
So, Then, Can I Really Trust IoT Security
You desire to implement and maintain the best manufacturing practices in your workplace. With technological solutions pressing a connected work system, you may very well be hesitant to adopt them as they come with a different set of security concerns. Read about the "Top 10 Best Practices for Zero Trust IoT Manufacturing."
A Selection from Heat Treat Radio
Click the selections to hear what's new from Heat TreatRadio!
5. What Do You Get When An Automobile Renovates a Restaurant?
If you are going out to eat this weekend, would you prefer your waiter to act like this? I mean, who doesn't love a little dinner theatre?
Alternatives to internal combustion engines have long dominated conversations in the automotive world. Discover why induction heating is playing a vital role in the production of the electric vehicle in this Technical Tuesday original content article written by Michael Zaharof, regional sales and marketing manager at Inductoheat.
This article first appeared inHeat TreatToday's May 2021 Induction print edition. Find the digital upload and other past editions here.
Michael Zaharof Regional Sales and Marketing Manager Inductoheat
The electric vehicle (EV) sector of the automotive market is gaining momentum. Government mandates, fuel economy standards, and increasing consumer interest are all driving the push to EV. Some platforms are further along in the process, while others are just starting to enter the space. Many new ideas and vehicle configurations are being developed to deliver the best alternative to the internal combustion engine (ICE).
This industry is learning about the best way to configure drive mechanisms and control acceleration, be it a centralized power source operating a driveline or multiple motors powering different areas of the vehicle. Heat treating the necessary components properly to impart enough strength for the much higher torque delivery is more critical than ever compared to the traditional performance characteristics of those equipped on a standard ICE platform. Induction heating plays a critical role in the EV market as it permits several unique benefits over other thermal processing methods. Whether it is heat treating, shrink fitting, curing, or surface hardening, induction heating is one technology that has already proven itself to be beneficial for the manufacturing of electric vehicles.
Deeper Case Depth
Because of the almost instant torque delivery and fast acceleration characteristics of electric motors, EV driveline components must be more robust to handle the added torsional stresses. Combined with the need for wear resistance and fatigue life, these components must be heat treated to deliver these critical properties.
Induction heat treating of an automotive pinion
The powertrain components generally made with carbon steels (such as bearings, raceways, constant velocity joints, pinions, shafts, hubs, and gears), must be sufficiently hardened to provide enough strength, while remaining ductile enough to prevent premature failure. Induction hardening is ideal in many cases since it can deliver deeper hardened case depths, if desired, compared to other methods like conventional gas carburizing and nitriding. These alternative heat treatment methods must rely on diffusion mechanisms associated with a sustained and prolonged environment.
Alternatively, induction utilizes subsurface heating through electromagnetic current applied to a specified and customizable area achieving the desired casehardened depths. Because heat can be applied quickly to the specific area, electromagnetic induction produces much less metallurgical distortion compared to thermochemical methods that rely on through-heating and diffusion processes at high temperatures, which in some instances eliminates or diminishes the need for post heat treatment grinding or machining.
Fast & Flexible
The speed of manufacturing is an essential factor in keeping a supply chain moving and having enough product available. Many manufacturers and automotive part suppliers have adopted just in time (JIT) manufacturing workflow methodologies to increase speed to market while controlling production and inventory costs.
Induction heating of an automotive CV inner race
Induction hardening allows for parts to be processed as needed and in a way that does not require hours of processing time in contrast to alternative thermochemical heat treating methods. Because of the constant flow of individual parts and almost instantaneous time to heat, production can be incremental and consistent while still being flexible enough to adjust rates as needed. This flexibility and lean approach to inventory management can be more difficult when batches of parts are being processed together.
Also, because material distortion after induction heat treatment can be much lower, as previously mentioned, post-heat-treatment manufacturing operations can be reduced or eliminated.
Single Part Flow: Repeatability & Traceability
Part process flow is an important consideration when repeatability and traceability become essential, like in automotive manufacturing. When multiple parts are being processed simultaneously, such as in a furnace operation, individual parts cannot be validated while the heat treatment is in process. The part variability in batch operations can be impacted by part spacing, location in the furnace, gas concentration, and temperature from one batch to another.
Many quality standards require tight control of the heating process and data collection during heat treatment to ensure that acceptable parts are being made. Induction heating allows precise monitoring and real-time evaluation of each stage in the heat treat process. The parameters of the process cycle – such as quench temperature, quench concentration percentage, quench pressure, quench flow, energy used, frequency, and part rotation – are just some of the points that can be analyzed by today’s sophisticated sensors and signature monitoring systems.
Signature monitoring system by Inductoheat
Some of the more advanced monitoring systems, like those offered by Inductoheat, allow the user to “teach” the induction machine what a “good part” signature looks like as all the data points of the process are plotted throughout the cycle and compared to established acceptable limits. As the process runs in production, the user can validate that all critical factors being monitored are in specification.
In the event of an issue in which one or more points are out of specification, the part will be rejected by the quality system. The cycle processing data can be instantly associated with each heattreated piece through part marking/reading or the most suitable such as radio frequency identification (RFID),u for example, for storage and later use by the manufacturer.
Environmentally Friendly
Induction heating uses electricity as its means of heat generation. Other methods such as carburizing and different batch heating processes employ gases such as ammonia and other chemicals in conjunction with fossil fuel-powered furnaces. Induction heating is considered a clean and environmentally friendly option for heattreating.
The process uses electrical energy and can quickly cycle through the desired operation and then sit idle until needed again. Most alternative systems require warm-up and cooldown time before and after production runs. In some cases, it is less expensive to keep the furnace running while continuing to burn natural resources and vent exhaust gases into the environment compared to shutting the system down in between uses.
More Efficient
Induction heating is a fast and efficient operation and can be scaled up easily to meet production requirements. Induction heating machines generally take up much less floor space than gas-powered batch furnaces. As mentioned above, they can be operated when needed without lengthy preheat or cooldown sequences.
Induction heating is associated with greater heat intensity, transferring more power directly to the workpiece in a concentrated fashion, compared to most other methods that rely on heating a surrounding environment. Induction coils can be designed to apply the required current density into an exact area of the part to be heat-treated instead of heating the entire piece.
The induction process is also more efficient as energy output can be controlled precisely to apply only the necessary power needed to obtain the desired temperature profiles at the desired production rate.
Induction heating of an automotive input shaft
Conclusion
Induction heating is a proven and environmentally friendly process that has a long history of precision and repeatability. The ability to heat parts quickly and more effectively is why many companies have opted for induction heating over other heat treat methods. Some other popular applications utilizing induction heating employed in EV production include shrink fitting, brazing, bonding, curing, battery production, stamping, forming, and varnishing of motor components.
Induction heating technologies are also dynamic, changing every day to meet new requirements and manufacturing goals. The use of multiple power levels and frequencies from a single induction inverter is one such innovation changing how some parts are being engineered and produced. Induction heating is a solution that will continue to assist the automotive manufacturing industry for years to come.
About the Author: Michael Zaharof is a regional sales and marketing manager at Inductoheat in Madison Heights, Michigan. He has been with the company since 2011 and has worked in the sales application, digital media marketing and outside sales departments. Michael has a bachelor of computer science in Information System Security. Michael currently works with customers in several states with their induction heat treating and induction forging needs.
In preparation for Heat TreatToday's May Induction magazine, here is a best of the web to end your week on.
How do they do it? What happens to metals when they are being induction heated? If you've had experience with heat treating using induction, how does it compare to other forms of heat treatment? This helpful article runs down the basics of induction and includes a video with different phases of the process. Check it out!
"As current flows through a medium, there will be some resistance to the movement of the electrons. This resistance shows up as heat (The Joule Heating Effect). Materials that are more resistant to the flow of electrons will give off more heat as current flows through them, but it is certainly possible to heat highly conductive materials (for example, copper) using an induced current."
Welcome to Heat Treat Today'ssecond installment of This Week in Heat TreatSocial Media.As you know, there is so much content available on the web that it's next to impossible to sift through all of the articles and posts that flood our inboxes and notifications on a daily basis. So, Heat Treat Todayis here to bring you the latest in compelling, inspiring, and entertaining heat treat news from the different social media venues that you've just got to see and read!
1. Plibrico Company Sponsors Project for Shriner's Hospitals for Children
The Plibrico Company recently sponsored a Happy Craft Day for Shriner's Hospitals for Children, during which many locations took part in assembling craft kits for kids needing a smile.
2. Innovations and Services on the Front Line
During this difficult and uncertain time, many companies are offering support to fight the spread of COVID-19, and some have come up with unique innovations.
Stack Metallurgical Group has announced its support for manufacturers in fighting the pandemic:
Similarly, Inductoheat has made a statement in the same vein:
ION HEAT has come out with the first prototype of its mechanic lung ventilator:
And Proceq USA Sales Manager Tom Ott demonstrates how to recharge a Proceq UT8000 flaw detector using a common USB power pack:
3. Good Friday Furnace Repair
Capital Refractories' Research & Development Manager Julie Hardy shared images of a 12 ton holding furnace repair that took place on Good Friday:
4. Reading and Podcast Corner
You may have a bit more time to catch up on the reading and podcast listening you've been yearning to do. May we recommend two brief written items of interest and an informative podcast.
Park Ohio Turns 100
Ipsen USA recommends their paper on vacuum furnace maintenance
And, for your listening pleasure, be sure to download the latest Heat Treat Radio episode entitled, Heat Treat Modeling with Justin Sims.
5. 101 Uses for Heat Treat Today Tape
Roseanne Brunello of Mountain Rep came up with a festive use of Heat Treat Today packing tape:
"Heat Treat Today comes through again..."
6. Launch into Your Socially Distanced Weekend with the Family Lockdown Boogie
No explanations necessary. Happy Friday, everyone!
One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s101 Heat TreatTipsis another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.
Today’s tips come to us from Rob Medeira and Florie Grant of Inductoheat, covering Induction Heating. This includes advice about correcting irregular part distortion and finding solutions to cracked parts.
Situation: Part is distorting irregularly after induction heat processing
Solution:
1. Check quench concentration, flow, & pressure.
2. Make sure there is proper quench uniformity.
3. Check TIR of the spindles and part holding fixtures
4. Check to ensure the part dimensions are accurate & center drills are on center.
5. Check part nest clearance when the part is cold.
6. Check to make sure the heating time is not too long.
HINTS:
· Check the part holding fixtures and spindles to ensure proper positioning.
· Some processes use a negative quench delay, quench on before heating stops, typically 0.05-0.3 seconds to improve TIR of the part.
· The part nest should not fit snug when the part is col – it will grow during the heating & warp the part.
· If the spline area has distortion or the “Go” gage is tight, try a quench delay of 0.2 to 0.4 seconds.
Heat Treat Tip #14
Cracked Parts?
(source: Inductoheat)
Situation : Cracked Parts
Solution:
1. Check parts positioning.
2. Make sure there are no unexpected hot spots; lack of rotation may be the cause.
3. Check for excessive grain growth around the crack surface area.
4. Check if quench condition is out of spec.
5. Check surface finish of part prior to hardening.
6. Apply temper ASAP.
7. Confirm & inspect steel conditions.
HINTS:
· If the part has excessive grain growth, that may lead to cracking.
· If cracking appears around hole area, then the proper chamfering might help.
· Parts out of higher carbon steels (0.55%C or higher) use higher quenching concentration & avoid surface overheating.
What process holds a soft spot in your heart? Tempering or annealing? For Valentine's Day, turn up the heat -- errr heat treatments -- with this look at the differences in tempering and annealing! Heat Treat Today has resources for you to spark some thought and learning on these processes.
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
Rapid Air Tempering
