Induction Heating

Boronizing — What Is It and Why Is It Used?

/ Featured, HARDENING TECHNICAL CONTENT, Manufacturing Heat Treat Technical Content

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

This informative piece was first released in Heat Treat Today’s April 2025 Induction Heating & Melting print edition.

Of all the case hardening processes, boronizing (a.k.a. boriding) is perhaps the least understood and least appreciated. Let’s learn more.  

In this era of using coating technologies (e.g., PVD, CVD, DLC) to produce hard, wear-resistant surface layers on component parts, one often forgets that there is a thermo-chemical treatment that often can outperform many of them.  

Boronizing (a.k.a. Boriding)  

Table 1. Examples of hardness levels achieved by boronizing*
*The hardness of the boride layer depends on the compound formed. For example, FeB is 1900–2100 HV, Fe2B is 1800–2000 HV, while Ti2B is 3000 HV.

Boronizing is a case hardening process that produces a very high surface hardness in steels and is used for severe wear applications (see Table 1). The layer of borides (FeB and Fe2B) formed also significantly increases corrosion resistance of the steel.

Boron is added to steels for its unique ability to increase hardenability and lower the coefficient of (sliding) friction. In addition, boron is used to control phase transformation and microstructure since the time-temperature-transformation curve for the material when boron is diffused into the surface is shifted to the right. 

The Process

The boronizing process is typically run in a solid (pack), liquid, or gaseous medium. Each of these methods involves the diffusion of boron into the steel’s surface, but they differ in how boron is introduced and the conditions under which they operate. 

  • In the pack boronizing, a powder mixture of boron compounds (typically boron carbide or sodium tetrafluoroborate) is packed around the steel workpieces. This pack is placed in a retort-style furnace where it is heated, typically with an argon cover gas, to temperatures ranging from 1300°F to 1832°F (700°C to 1000°C). The heat causes the boron to diffuse into the steel surface, forming a boride layer (Figure 1). 
    • A key advantage of this method of boronizing is that it is highly effective for producing uniform boride coatings. It is particularly suitable for large parts or components that may not be suitable for immersion in a liquid or exposure to gaseous boron compounds. 
  • In liquid boronizing, the steel is immersed in a molten bath containing boron-bearing compounds, typically a mixture of sodium tetraborate and other chemicals. The steel absorbs boron from the bath, forming a boride layer. The liquid process tends to be faster than the solid method and can be more economical for certain applications. 
    • One of the challenges with liquid boronizing is that the process can be difficult to control in terms of coating thickness and uniformity. Therefore, this method is often used for smaller, simpler parts rather than large or complex geometries. 
  • Gaseous boronizing involves exposing the steel to a boron-containing gas, typically diborane (B2H6) or boron trifluoride (BF3), at elevated temperatures. The boron diffuses from the gas onto the surface of the steel, forming the boride layer. Gaseous boronizing allows for better control over the process compared to the other two methods, but it requires specialized equipment to handle the toxic and reactive nature of the boron gases. 
    • The advantage of gaseous boronizing lies in its ability to produce a uniform and controlled boride layer, especially for complex parts or those with intricate geometries. 

When working with any boron-containing compounds, adequate ventilation and other safety precautions (e.g., masks, gloves) are required. If boron tetrafloride is present, extra precautions are necessary since it is a poisonous gas.  

Typical processing temperature is in the range of 1300°F–1832°F (700°C–1000°C) with time at temperature from 1 to 12 hours. Typical case depths achieved range from 0.003″–0.015″ (0.076 mm to 0.38 mm) or deeper (Figure 2). Case depths between 0.024″ and 0.030″ require longer cycles up to 48 hours in duration. 

Figure 1. Typical microstructure of a boronized component

The mechanical properties of the borided alloys depend strongly on the composition and structure of the boride layers. The most desirable microstructure a er boronizing is a single-phase boride layer consisting of Fe2B2. Plain carbon and low alloy steels are good candidates for boronizing, while more highly alloyed steels may produce a dualphase layer (i.e., boron-rich FeB compounds) because the alloying elements interfere with boron diffusion. The boron-rich diffusion zone can be up to seven times deeper than the boride layer thickness into the substrate. 

The hardness of the borided layer depends on the composition of the base steel (Table 1). Comparative data on steels that have been borided versus carburized or carbonitrided, nitrided or nitrocarburized are available in the literature (see Campos-Silva and Rodriguez-Castro, “Boriding,” 651–702). The surface hardness achieved through boronizing is among the highest for case hardening processes. The boride layers typically exhibit hardness values in the range of 1000 to 1800 HV. This level of hardness helps prevent surface deformation under load, which is particularly beneficial in applications involving high contact pressures, such as gears, bearings, and automotive components. 

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Boronizing can also lower the coefficient of friction on the surface of the steel. This is particularly useful in applications where reduced friction is necessary, such as in sliding or rotating parts that operate under high pressures. The reduced friction helps to minimize wear and energy consumption, improving the overall efficiency and longevity of the components. 

Unlike other surface-hardening methods that can compromise the core properties of the material, boronizing tends to retain the toughness and ductility of the base steel. This means the steel remains strong and resistant to cracking or breaking while also benefiting from a hard, wear-resistant surface. 

By contrast, when boron is used as an alloying element in plain carbon and low alloy steels, it is added to increase the core hardenability and not the case hardenability. In fact, boron can actually decrease the case hardenability in carburized steels. Boron “works” by suppressing the nucleation (but not the growth) of proeutectoid ferrite on austenitic grain boundaries. Boron’s effectiveness increases linearly up to around 0.002% then levels off.  

Figure 2. Hardness-depth profiles on different borided steel*
* Notes:
1. The boriding temperature was 1740°F (950°C) with six (6) hours of exposure
2. Hardness conversion: 1 GPa = 102 HV (Vickers hardness)
3. Depth conversion: 10 micrometers = 0.00039 inches

Boronizing Applications 

Given the range of benefits that boronizing offers, it has found widespread use across many industries. Some of the most common applications include: 

  • Automotive industry: Gears, camshafts, and valve components are often boronized to enhance wear resistance and extend their service life. 
  • Aerospace: Parts exposed to high temperatures and wear, such as turbine blades, landing gears, and other critical engine components, benefit from the hard, wear-resistant coatings created by boronizing. 
  • Cutting tools and dies: The high surface hardness and resistance to abrasion make boronized tools highly effective for machining and forming hard materials. 
  • Mining and earthmoving equipment: Equipment like drill bits, shovels, and conveyor parts subjected to abrasive conditions can be boronized to improve their performance and reduce downtime. 
  • Oil and gas: Valves, pumps, and other equipment exposed to corrosive fluids in the oil and gas industry benefit from the enhanced corrosion resistance of boronizing. 

In Summary

Boronizing is not for everyone, but it is safe to say that it is the “forgotten” case hardening process, one that will find increasing use in the future as demand for better tribological properties increases. It is a highly effective surface treatment process that imparts significant benefits to steel, including enhanced wear and corrosion resistance, increased surface hardness, and improved frictional properties. By carefully selecting the boronizing method and optimizing process parameters, manufacturers can produce components with superior performance in demanding applications. As industries continue to push the boundaries of material performance, boronizing can be an essential technique for producing long-lasting, high-performance steel components.  

References

Campos-Silva. I. E., and G. A. Rodriguez-Castro, “Boriding to Improve the mechanical properties and corrosion resistance of steels.” In Thermochemical Surface Engineering of Steels, edited E. J. Mittemeijer and M. A. J. Somers. Woodhead Publishing, 2014. 

Herring, Daniel H. Atmosphere Heat Treatment, vol. I. BNP Media, 2014.  

Kulka, Michal. “Current Trends in Boriding: Techniques.” Springer Nature, 2019. 

Senatorski, Jan, Jan Tacikowski, and Paweł Mączyński. “Tribological Properties and Metallurgical Characteristics of Different Diffusion Layers Formed on Steel.” Inżynieria Powierzchni 24, no. 4 (2019).  

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

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

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

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

Find heat treating products and services when you search on Heat Treat Buyers Guide.Com

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EFD Induction and IPT Technology Will Become New Brand — ENRX

/ FEATURED NEWS, MANUFACTURING HEAT TREAT

HTD Size-PR Logo

Industrial induction heating expert EFD Induction and inductive charging and power supply innovator IPT Technology will combine to form ENRX. On March 27, 2023, the new brand will officially launch. Under the new name, ENRX will provide induction technology for inductive heating, charging, and power supply with low or no carbon footprint.

Bjørn Eldar Petersen
CEO of ENRX
Source: ENRX

Magnus Vold
CCO of ENRX
Source: LinkedIn

“We are a new company with more than 70 years of experience in induction heating,” says Bjørn Eldar Petersen, CEO of ENRX. “We now have a new brand, ENRX, and many products in the pipeline.”

ENRX, with locations in North America and headquarters in Skien, Norway, has 1,100 employees. The new brand bringing EFD Induction and IPT Technology together will hold over 1,200 patents for induction technology.

“Inductive wireless charging and contactless power supply are technologies for the future,” says Magnus Vold, CCO of ENRX. “In the new world that is emerging, everything is based on automation, digitalization and electrification."

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

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Forging and Metalcasting Resources To Keep You Informed

/ FEATURED NEWS, FORGING TECHNICAL CONTENT, FOUNDRY CASTING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT

OCWe've assembled some of Heat Treat Today's resources on forging and metalcasting. Read or listen to what the experts have to say on these important topics in the heat treat industry.

This Technical Tuesday original content piece will help you wade into an introduction of these heat treatment processes. Follow the links to dive deeper into the studies.

The span of articles, radio episodes, and TV clips below are compiled to learn more about forging and casting. Heat treating is developing and changing through the years, and it's wise to keep swimming with the current of information.

Simulating Induction Heating for Forging

What can simulation software do for you? Manufacturers are able to run the software to act upon the steel billet prior to forging. Read more about the process here. The simulation shows results in the metal to help the user best plan for desired results. One of the decisions that can be helped is, "the selection of right forging temperatures for plain carbon and alloy steels to avoid possible damage by incipient melting or overheating."

A Look at Steel and Iron

Dan Herring
"The Heat Treat Doctor"
The HERRING GROUP, Inc.

Read or listen to this episode of Heat Treat Radio with expert Dan Herring who discusses metals such as stainless steel, tool steel, cast iron, high and low carbon steels, and more. He looks at their production and their uses.

"I wanted to set the stage for it to say that it’s the end-use application by the customer that fuels the type of steel being produced and fuels the form in which the steel is produced," says Herring.

Investment Casting in Turbine Blades

Take a look at how an alumina and silica (quartz) mix are improving metal casting for support rods used in aerospace manufacturing. "LEMA™, a range of proprietary alumina-based materials that provide double the mechanical strength of quartz while providing significantly improved leaching times, compared with typical high purity alumina," provides many benefits for metal casting. Jump into this piece to find out more about this metal casting example.

Direct From the Forge Intensive Quenching

President
Akron Steel Treating Co & Integrated Heat Treating Solutions, LLC

In this discussion, expert Joe Powell says, "My thing is  to develop a robust process that can be applied and implemented using automation and new equipment with the proper pumps and material handling that is all integrated into a seamless process." He plunges in to talking about immediate quenching pieces in water after heat treating and what they are learning at the forge shop.

Heat Treat TV

Here are a few episodes to keep you afloat while moving into deeper waters.

 

Click on these two illustrations to watch the full episodes.

 

Search for heat treat services and products on Heat Treat Buyers Guide.com

 

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How to Improve the Performance and Longevity of Induction Tooling Components

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

OCWhat is the most common cause of induction tooling failures? What is essential for the longevity of induction tooling? What is a vital component for induction tooling’s successful performance? This informative article shares the answers to these questions and provides valuable guidance for your induction needs.

This Technical Tuesday is provided by David Lynch, vice president of Engineering at Induction Tooling, Inc. and was featured in the Heat Treat Today’s 2021 May Induction print edition. Check out more original content articles in this digital edition or other editions here.

David Lynch
Vice President, Engineering
Induction Tooling, Inc.

Most induction heat treating applications are challenged with a harsh environment often dealing with high frequencies, high power, heat, smoke, steam, dirt, oil, quench fluid, quench additives, and contaminates. How induction tooling components are maintained in these harsh environments greatly impacts their performance and longevity.

The induction power supply, workstation, and material handling system should all be properly grounded. The work holding system should be level, square, and have proper alignment between the inductor coil and the workpiece for it to be heat treated. Part-holding fixtures should be held to a dimensional tolerance to ensure proper positioning and repeatability with minimal runout. The heat-treating process should include documentation of parameters including positioning (the air gap of the inductor coil relative to the workpiece), scan rates (in/sec), power (kw), frequency (kHz), heat time (sec), dwell time (sec), and quench time (sec). If auxiliary quench lines or nozzles are used, recording positioning data with pictures will guarantee repeatability of the process. Keeping track of quench water temperature, pressure, and flow along with percentage of polymer (aka viscosity) will help ensure consistent results. Keeping track of cooling water temperature, pressure, and flow is important in troubleshooting water cooling issues. The power supply should be routinely serviced and calibrated along with having an active preventative maintenance schedule.

Ball Race Inductors

Inductor coils should be properly designed to not only produce a heat treat specification, but also be of high quality, manufactured from quality materials with maximized water cooling and robust construction. Flux intensifiers should be properly matched to the operating frequency and attached to the inductor coil securely. Teflon insulators should be virgin grade and replaced if damaged or worn. Fasteners, fittings, and hose clamps should be non-ferrous such as brass or 300 series stainless steel. Hoses should be specified non-conductive and rated to meet or exceed supplied water pressure. Epoxies used should be rated for high temperatures and allow for expansion and contraction. Electrical contacts should be silver plated to provide superior contact and prevent oxidation.

Gear Tooth Scan Inductor

Manufacturing inductor coils is a skill that takes years to develop and several more to master. These tools can be made from copper tubing utilizing fabrication techniques with the use of bending fixtures and forming dies. Most tools today are machined from solid, raw materials often with complex geometries. To ensure quality and consistency, 5-axis CNC machining is often used. Thirty to forty percent silver braze should be used for joining the inductor coil components and sealing water-cooling passages. Designs should avoid sharp corners and provide smooth transitions for optimal current flow and minimal stress risers. Computer-solid models, engineering drawings, and process forms following ISO 9001:2015 certified standards guarantee a quality manufactured induction coil.

Ring Bearing Inductor

Inductor coils are precision handmade tools and should be treated as such. Inductor coils should be supplied in a heavy-duty case with packing materials to provide the proper support and protection during shipping and storage. Identification should be clearly marked on the case. Many cases are lockable as theft may be a concern. When inductor coils are removed from service, they should be cleaned with soap and water using a Scotch-BriteTM cleaning pad. Steel wool and steel bristle brushes should be avoided as the steel can imbed into the copper and may cause more harm than good. Once the inductor is cleaned, it should be closely evaluated for signs of wear or damage. If there are any signs of wear or damage, it should be sent out for maintenance or repair so it will be ready for the next use. After tools are cleaned and evaluated, cooling passages should be blown out with air and the inductor should be dry before sealed in the case and put into inventory. Notes and pertinent data related to the inductor can also be stored with it such as the number of parts processed, any modifications made to the inductor coil, and recorded setup data.

All of what was stated above about design and manufacture of inductor coils also applies to bus bars and quick-change adapters. These devices are used between the workstation and the inductor coil to bridge the gap closer to the workpiece. Originally developed for the automotive industry, quick-change adapters can drastically reduce changeover time, often without the use of hand tools. Since these devices are typically kept on the machine for long periods of time, it is important to check the condition and perform maintenance when needed. Scheduled maintenance of removal and cleaning of these devices will exceedingly increase their life. As with inductor coils, soap, water and a Scotch-BriteTM cleaning pad is all that is needed for these items; steel wool and steel bristle brushes should be avoided.

Multi-Turn O.D. Scan & Quench

When installing bus bars, adapters, and inductor coils with a bolted contact, it is extremely important to make sure that each of the mating surfaces are clean and free from debris. When dirt accumulates or ferrous debris is contained between the contacts, severe arcing and melting can occur.

It is also very important to use proper fasteners. For correctly fastening contact surfaces, 300 series stainless steel bolts with heavy brass washers are preferred. The heavy brass washers help distribute the load evenly and help prevent damaging the copper. The bolt threads should be inspected for wear and replaced new if there is any sign of wear or damage. It is also very important to verify that the length of the bolts will properly clamp without bottoming out before tightened. The recommended torque procedure for 3/8-16 stainless steel bolts is to tighten each bolt twice at 35 to 40-foot pounds. Special "break-away" bolts are available that are designed to fail beneath the washer if they are over tightened. This prevents damage to the threaded insert inside the copper contact. The remainder of the bolt can then be removed with pliers. This is much easier and less expensive than having to repair a bus bar contact or workstation transformer.

O.D. Scan with Quench

The workstation contacts, bus bars, adapters, and inductor coils are all electrical components that when energized are a live circuit, often with high power. The inductor coil produces a strong magnetic field used to heat the workpiece. There are also stray magnetic fields in the surrounding area. It is very important that everything in the surrounding area of these components be non-ferrous to prevent them from heating up. Something as simple as a steel hose clamp in close proximity to the magnetic field could heat up, causing a hose to melt, or a hose to come off, preventing water cooling and severely damaging the induction tooling or the induction machine. Steel fittings can rust and contaminate a water system very rapidly, choking the water flow internally and causing premature failure from low water flow. Any support structure to the induction tooling components should be a quality non-porous insulating material. Non-porous materials prevent liquid and contaminates from being absorbed and ultimately may cause a short circuit.

Proper water cooling is essential to the performance and longevity of tooling components. Both the induction power supply components and induction tooling components need to be properly cooled. Most power supply manufactures have a closed loop cooling system requiring deionized or distilled water. Most power supply manufacturers require that the cooling water temperature be maintained from 80 to 90 degrees Fahrenheit to prevent condensation inside the cabinet and on the circuitry. For cooling the inductor coil, bus bars, and adapters, deionized or distilled water is not necessary. Cooling water for these induction tooling components is best to be kept below 70 degrees Fahrenheit. This may require a separate cooling supply. Through laboratory experimentation and real-world production trials, it has been proven that lower cooling water temperatures can drastically increase the life of these components, especially in high volume, high power, short cycle applications.

The internal water-cooling passages of the inductor coil can play a significant factor in performance and longevity. Each inductor design should focus on maximizing water flow while minimizing sharp transitions.

The cooling water supply should come from a clean water source with a filtration unit of 25 microns placed just before it enters the induction tooling components. This guarantees that contaminates are filtered out, which may otherwise cause a low-flow or no-flow condition.

Quality non-ferrous fittings should be properly sized and configured to ensure the hoses are attached correctly to the induction tooling. It is very common to see 3/8" quick-change fittings used for cooling lines and 1/2" or 3/4" quick-change fittings used for quench lines. Using quick-change sockets for supply lines and quick-change plugs for return lines ensures the proper connections are made every time. Color-coding the hoses also helps in identifying water lines. It is very common to see blue hose for supply lines, red hose for return lines, and black hose for quench lines.

Single Shot Stem Inductor

Some inductor coils can be very small, having very limited water-cooling passages due to physical space. With these small inductors, it is even more important to have proper water cooling. In these situations, the use of a high-pressure booster pump may become necessary. These pumps can ensure cooling water continues to flow through these tight passages. Positive displacement pumps can also overcome steam pockets and help prevent vapor locks.

Problems with a cooling system can be detrimental to the performance and longevity of induction tooling components. Contamination in the cooling system can lead to low water flow. Problems with the water pump can also cause a low water flow condition. Then, low water flow can cause a steam vapor lock in the inductor coil leading to a rupture at a braze joint, a rupture through the tubing in a fabricated inductor coil, or a breach in the copper exposing the cooling chamber. Low water flow can also cause laminar flow internally which leads to thermal failure, resulting in exposed surface cracks through to the cooling chamber. Low water flow is sometimes identified by darkening of copper with purple color tones on the cooling return side of the inductor coil.

Wheel Bearing Single Shot Hardening

Induction tooling components cannot survive without water cooling. Symptoms include darkening of copper with purple color tones, melted copper, and catastrophic failure. Catastrophic failures caused by a no-water condition cannot be patched and require a major rebuild or replacement. It is a wise investment to have a flow indicator on the machine that prevents operation if there is no water flow or a low water flow condition.

All of what is stated earlier about the design and manufacture of inductor coils, bus bars, and adapters can also apply to quenches. These devices are used to evenly cool the part after heating to transform the structure consistently. Let’s discuss some of the important details in a quench system such as their design, fitting and hose requirements as well as pumps, filtration, and maintenance.

Quenches should be designed to provide a sufficient amount of quench to fully transform the metallurgical structure as specified. The quench pattern should be a uniform array of holes to quench the part at a proper impingement angle. The volume of water required should be matched with a supply having an inlet to outlet ratio not to exceed 1 in: 2 out. Hoses should be specified non-conductive and rated to meet or exceed supplied water pressure. Fittings should be high quality, non-ferrous without auto shutoffs, which can hinder quenching action and tend to clog more often.

Quenches can be a component that is kept on the machine for long periods of time. It is important to check the condition of these devices and perform routine maintenance. Scheduled maintenance of removal and cleaning these devices will exceedingly increase their life. Soap, water and a Scotch-BriteTM cleaning pad works well, and again, steel wool and steel bristle brushes should be avoided. Having a quench designed with bolted removable quench plates allows easy clean out.

Quench water needs to be filtered and contaminates kept at a minimum to improve performance and increase longevity of induction tooling components. A typical quench filter consists of a stainless-steel filter housing and a 100-microns bag filter. It is also very important to have a system for magnetic particle removal. Magnetic rod filters are available in many configurations, some that install inside the filter housing with the bag filter. Automatic separators are also often used. A low-cost alternative is to install a rubber coated magnet in the quench tank. In a non-ferrous tank, it can simply be dropped to the bottom. In a ferrous tank, it must be suspended to prevent the tank itself from becoming magnetized. All these methods can work, but only if they are properly maintained. A solid preventative maintenance schedule for these filters is essential.

Low Water Flow Failure

When filters are not used or maintained, tooling repairs are required more frequently. Common contaminates found inside quenches include oil dry, metal chips, and chewing tabaco. We see inductor coils come in for rebuild with a heavy patina of dirty, crusty contaminates. These contaminates are commonly a buildup of magnetic particles attracted by the magnetic field generated by the inductor coil. This patina accumulates and can create a short circuit, damaging the inductor coil.

To summarize, contamination is by far the most common cause of induction tooling failures. Water cooling is essential for longevity of induction tooling. Maintenance is essential for the performance of induction tooling. High quality, well-designed, robust induction tooling should be used for best results and consistency. Analyze induction tooling failures when they occur. Troubleshoot induction tooling rebuilds for possible machine issues. Look for methods of improvement with each opportunity. In closing, the best way to improve the performance and longevity of induction tooling components is to have open and frequent lines of communication with your tooling vendor.

About the Author: David Lynch is vice president of engineering at Induction Tooling, Inc. with 36 years of experience and is also the Deputy of the ISO quality system. He has created and developed the system and templates being used today for creating and tracking engineering drawings, job history, rate tracking, and job performance. David holds several design patents, has authored several published articles, and has often presented at technical sessions. He enjoys working closely with customers to develop valued solutions across a wide range of induction heating applications from initial design concepts to implementation, customer support and troubleshooting.

For more information, Contact David at dlynch@inductiontooling.com.

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Red Hot Basics: The World of Induction

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

Source: Inductoheat.com

In preparation for Heat Treat Today'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."

Read more: "What is Induction Heating?"

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International Military Equipment Heat Treaters Receive Vacuum Furnace

/ FEATURED NEWS, MANUFACTURING HEAT TREAT, VACUUM FURNACES NEWS

Maciej Korecki
Vice President of the Vacuum Furnace Segment
SECO/WARWICK
(source: SECO/WARWICK)

AHTD Size-PR Logon international arms and military equipment manufacturer in Brazil needed to quickly expand and was recently able to receive a new vacuum furnace to meet their manufacturing demands.

The solution was provided by the parent company to North American SECO/VACUUM, SECO/WARWICK. Their furnace, the VECTOR®, is a single-chamber vacuum furnace that uses gas quenching and can be used for multiple metal heat treatment applications and processes. In this configuration, equipped with a round graphite heating chamber, it may be used for most standard processes including hardening, tempering, annealing, solutionizing, brazing and sintering.

"A situation where we have a product almost ready to be collected is rare. This time, the customer was indeed looking for a standard solution," said Maciej Korecki, vice president of the Vacuum Furnace Segment at the SECO/WARWICK Group.

(source: vidar nordli mathisen at Unsplash.com)

(source: SECO/WARWICK)

 

 

 

 

 

 

 

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Dr. Valery Rudnev on Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 3

/ FEATURED NEWS, 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 third in a discussion on equipment selection for one of four popular induction hardening techniques focusing on single-shot hardening systems.

Previous articles in the series on equipment selection for single-shot hardening are here (part 1) and here (part 2). To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. 

Single-Shot Inductors for Non-Cylinder Parts

Single-shot inductors can be successfully used for hardening not only components of classical cylinder geometries but other geometries as well. This includes workpieces of general conical shapes, such as elliptic, parabolic, hyperbolic geometries—and the list can grow. As an example, Figure 1 shows induction surface-hardened ball joints (ball studs) and the single-shot inductors used to harden them. Ball studs are used in automotive, off-road, and agricultural machinery and can be different in shape and size (Compare images on the left in Figure 1 with images on the right.), requiring noticeably different hardness patterns.

Figure 1. Surface-hardened ball joints (ball studs) and single-shot inductors used for its hardening. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)

In any attempt to scan harden workpieces with appreciable diameter changes, the scan coil must have a sufficient gap to clear the largest diameter. When scanning the section(s) of the workpiece with smaller diameters, an inductor-to-shaft air gap might be very large, resulting in low electrical efficiency and potentially exhibiting difficulties in load matching as well as in controlling the austenitizing pattern along the length of the part producing "cold" and "hot" spots. Additional difficulties may appear in controlling the hardness pattern in regions (e.g., near geometrical irregularities) where good control is most needed.

Thus, the substantially different workpiece-to-inductor electromagnetic coupling variations might not permit using classical multiturn solenoid coils or scan inductors. In contrast, single-shot inductors allow not only better electromagnetic coupling along the entire length of heat treated components (Figure 2) but also better address the geometrical irregularities of heat treated workpieces, producing the required hardness patterns at minimum process times with superior metallurgical quality.

Figure 2.  Single-shot inductors allow better electromagnetic coupling along the length of heat treated components properly addressing the geometrical complexity of the workpiece. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)

As stated in Part 1 of this series, in contrast to scan hardening, a single-shot inductor can be contoured along the length of the part properly addressing the geometrical complexity of the workpiece. Furthermore, the use of flux concentrators helps drive the current into the desired areas and allows producing a well-defined hardness profile with minimum distortion. The trade-off here is that more finesse is required in the design stage to produce the properly profiled single-shot inductor at the lowest possible cost.¹ Errors are costly since these inductors are each custom made for a given part or application and modifications can be quite costly. Thus, computer modeling is a helpful assistant as an attempt to keep the development cost down and shorten the "learning curve".

Proper hardening of such components as output shafts, flanged shafts, planet carriers, yoke shafts, sun shafts, intermediate shafts, driveshafts, turbine shafts, and some others may require extensive copper profiling, making a single-shot hardening inductor a complex electromagnetic device.

Certain geometrical features such as flanges, diameter changes, bearing shoulders, grooves, undercuts, splines, etc., may distort the mag­netic field generated by an inductor, which, in turn, can cause tem­perature deviations, making it challenging to achieve certain hardness patterns.

For components containing fillets, it is often necessary to increase the heat intensity in the fillet region owing to the geometrical specifics. Also, the larger mass of metal in the proximity of the heated fillet and behind the region to be hardened produces a substantial thermal “cold sink” effect.¹ This draws heat from the fillet due to thermal conduction, which must be compensated for by generating additional heating energy in the fillet area.

Needed energy surplus can be achieved by narrowing the current-carrying face of the crossover segment of the single-shot inductor (Figure 3). Here is a simplified illustration of an impact of a copper profiling of the inductor’s heating face: if the current-carrying portion of the inductor heating face is reduced by 50 percent, there is a corresponding increase in current density. This will be accompanied by an increase of the eddy current density induced within the respective region. According to the Joule effect, doubling the induced eddy current density increases the induced power density roughly by a factor of four. Also, attaching a magnetic flux concentrator to certain areas of the hardening inductor further enhances the localized heat intensity.

Figure 3.  Longitudinal leg sections of single-shot indicators and their crossover segments can be profiled by relieving selected regions of the copper to accommodate workpiece geometrical features. Attaching a magnetic flux concentrator to certain areas of the inductor further enhances localized heat intensity. (From V. Rudnev, A. Goodwin, S. Fillip, W. West, J. Schwab, S. St. Pierre, Keys to long-lasting hardening inductors: Experience, materials, and precision, Adv. Mater. Processes, October 2015, pp. 48–52.)

When using a single-shot inductor, it is particularly important that the workpiece is properly located in the heating position because seemingly minor dislocations may noticeably affect the heat treat pattern and metallurgical quality of hardened parts.

Traditionally designed single-shot inductors may exhibit high process sensitivity that is associated with the electromagnetic proximity effect.¹ A change in positioning of the workpiece inside the single-shot inductor attributed to excessive bearing wear of the centers, improper machining of the centers and fixtures, incorrect part loading, and other factors may produce a correspondent appreciable variation in the hardness pattern (particularly within the fillet region, undercut areas, and the part’s end zone). A reduced hardness case depth and the formation of unwanted microstructural products associated with incomplete phase transformation may be the result of that. Magnitude and distribution of transient and residual stresses might also be altered. Thus, attention should be paid to part’s reliable positioning during heating and quenching cycles.

As can be concluded, there are good reasons for using single-shot hardening, scan hardening, or continuous/progressing hardening approaches in induction hardening applications. The decision must be well thought out based on many factors such as geometry specifics, product quality, production rate, design proficiency, limitations of available equipment, reliability requirements, cost considerations, and some other factors.

The next installment of this series, “Dr. Valery Rudnev on .  . . ”, will continue the discussion on 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, "Dr. Valery Rudnev on . . . Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 1", Heat Treat Today, July 9, 2019.
  3. V.Rudnev, A.Goodwin, S.Fillip, W.West, J.Schwab, S.St.Pierre, "Keys to long-lasting hardening inductors: Experience, materials, and precision", Adv. Mater. Processes, October 2015, pp. 48–52.

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Simulation of Induction Heating of Steel Billets for Forging

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This article was written by Dr. Vadims Geza, chief scientist at CENOS. More information on CENOS Platform can be found here.

Induction is becoming an increasingly popular choice for heating steel billets prior to forging due to its ability to create high heat intensity quickly and within a billet, which leads to low process-cycle time (high productivity) with repeatable high quality, occupying minimal space on the shop floor. It is more energy-efficient and inherently more environmentally friendly than most other heat sources for steel billets.

In this article, the author demonstrates a simulation example on how to optimize a progressive induction heating system for a steel billet. The method used is CENOS Platform, a 3D simulation software which focuses specifically on induction heating and uses open source components and algorithms.

CENOS platform is capable of simulating various types of induction heating for forging. It is possible to simulate both static heating and progressive heating where the billet is moved through the coil with constant velocity. In accomplishing this simulation, coil design is not a limitation: both single coil and multi-coil are possible to simulate. Besides the coil, it is also possible to simulate any material and frequency.

The functional performance of the software

CENOS is a finite element method-based, computer-aided engineering desktop software for 2D and 3D physical process simulation and computational modeling of induction heating, induction hardening, brazing, annealing and tempering of steel, aluminum, copper, and other materials.

The simulation process consists of three steps:

  • Choose the workpiece geometry (from built-in templates or create your own CAD file).

  • Define induction heating parameters (frequency, voltage, time, etc.).

  • Run 2D or 3D simulation of your choice.

At the conclusion, results like temperature and magnetic field are displayed in 3D renderings, plots, and more. Apparent power, induced heat, and inductance are logged into an Excel file.

3D Simulation example—comparison of two heating systems

In the simulation, two systems under consideration—two-stage and three-stage systems—in the progressive heating of the billet. The target for the simulation was to reach 2192°F (1200°C) ± 122°F (50°C). To check both systems, the user has to create set up for both of them, set physical parameters (material properties, frequency, current, etc.), and start the simulation.

After the simulation is done, the user will have access to different output variables, including:

  • Temperature distribution
  • Current density and Joule heat distribution
  • Magnetic field lines
  • Total, reactive and apparent power
  • Inductance of the coil
  • Coil current, voltage

In our example of billet heating, it is possible to compare both cases and the output.

 

It is observable how a three-stage system can decrease power consumption and increase the production rate for this specific case. It is also possible to plot the distribution of temperature, Joule heat, magnetic field, etc. Resulting temperature distribution in the billet across the radius is shown in Figure 1. As can be seen, better temperature homogeneity is obtained in the three-stage system.

Figure 1. Temperature distribution along the billet radius at the outlet of the heating system

 

Figure 2. Temperature distribution in the long billet during scanning (progressive) induction heating.

Figure 2 shows how different systems lead to different temperature distribution. In the two-stage system, the temperature required for forging is reached with shorter coils, thus also with smaller scanning speed. This leads to worsened temperature uniformity and smaller production rates. On the other hand, the three-stage system heater gradually increases the temperature of the billet and the resulting temperature difference between core and surface is smaller.

Platform users are free to change all the input parameters and assemble the system of any number of stages required for their process.

Should the same system need to be used for scanning of shorter billets where end effects play a more significant role, it is possible to set up a simulation with a moving billet. An example of temperature dynamics in such simulation are shown in GIF images below:

A simulation with a moving billet in a two-stage system.

A simulation with a moving billet in a three-stage system.

 

Simulation helps make better decisions for production set-up and planning

As demonstrated in the simulation example, it is possible to compare two different systems and get results. The scope and variety of different simulations are unlimited; it all depends on what problem the user wants to solve:

  • Dr. Vadims Geza

    Heating system design—to optimize induction heating performance, improve product quality, and avoid unpleasant surprises related to subsurface overheating

  • The selection of power, frequency, and coil length in induction billet heating applications

  • The selection of right forging temperatures for plain carbon and alloy steels to avoid possible damage by incipient melting or overheating.

 

 

Main Photo Image via CENOS, courtesy of efd-induction.com

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

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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 »

Induction Heat Treat: Considerations for Inductor Design

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Source: Fluxtrol.com

Induction heat treaters know that proper coil design is crucial to increasing longevity, improving production quality, and cutting costs. Among the topics addressed in this paper about induction heat treat coil design and fabrication (presented by R. Goldstein, W. Stuehr, and M. Blackby at ASM International) are these:

  • The design and fabrication of induction heating coils over the years
  • The Variable of Flow and the Influence of Frequency
  • Control and Presentation
  • Structure, Quenching, and Cooling
The paper closes out with a case study using computer simulation to show typical temperature distributions in a single-shot induction hardening coil.
A good place to start whenever preparing parts for induction heat treating is the consideration of inductor design. The authors provide this list (an excerpt):
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Considerations for Inductor Design

Induction heat treating coils are available in many shapes and sizes and must perform a variety of tasks in a given induction heat treating application. Depending on the application, the induction coil design requirements include:

  • Meet heat treatment specifications in desired production rates
  • Be robust enough to tolerate manufacturing variations
  • Mount into the induction machine
  • Have electrical parameters that match the induction power supply
  • Deliver quench
  • Have a satisfactory lifetime
  • Have satisfactory efficiency
  • Be repeatable from inductor to inductor

In developing a new induction heat treating coil and process, the first question is whether the component will be produced on an existing system or if a new machine must be built. In many cases, the part producer’s desire is to develop new tooling for an existing machine with spare capacity. This reduces the degree of freedom and can make the induction coil design procedure more complicated because a less-than-optimal frequency or coil style will be necessitated to fit the existing machine (Ref 16).

To determine the ability to use existing equipment, it is necessary to make an analysis of the part to be heat treated. Part material, prior processing, geometry, production rate, and heat treatment specifications all play roles. The part material and prior processing determine what the minimum heat treatment temperature should be, along with how much time is allowed for cooling. The part geometry and heat treatment specifications indicate how much energy is required, what the preferred frequency ranges are, and what type of induction method (i.e., single shot, scanning) is best suited for the application. Finally, the production rate determines how much power and/or how many spindles or stations are required.

Read more: "Design and Fabrication of Inductors for Induction Heat Treating"

 

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