Making metals stronger

Understanding why heat treating is such an important process.

Photo courtesy of Thermex Metal Treating

Photo courtesy of Thermex Metal Treating

When thinking of metalworking, we often think of machining and fabricating. However, heat treating is a significant process in bringing many metal products closer to completion. Heat treating is necessary for many different industries including automotive, aerospace and defence, medical device, oil and gas, tooling, and industrial equipment. From extremely large turbine blades to tiny dental drill bits, heat treating transforms raw materials to hardened finished products.

Due to the unique nature of the process and the wide range of variables, heat treating is often left to the experts, with shops sending their products out to be processed. Some specialized shops have brought the process in-house; however, there are so many considerations to take into account, like material type, part size and intricacy, and hardness expectations, it is often best left to dedicated heat treating specialists.

Types of metals

When it comes to materials, there are so many different options available. However, not all metals and grades are heat treated the same. It is important to find the correct heat treating process for your specifications.

“Some grades share the same austentizing temperature,” explains Michael Schmidt, division manager for Böhler-Uddeholm Thermo-Tech in Mississauga, Ontario. “This is that elevated temperature, it ranges from 1800-1900°F, or up to 2200°F with high speed steels. So the different types of steel grades have different temperatures that are used.”

However, Schmidt does explain that there are only so many grades out there, and many families of steel. So there are really only “about 30-40 different recipes depending on the grades involved.”

As far as popularity of grades, it is more or less dictated by the industry needs. Schmidt deals with a lot of automotive related products, so H13, a hot work tool steel, is one of the more popular grades. Standard grades like A2, D2, S7, are pretty common in the industry.

“Usually, customers opt for plain carbon and alloy steel for their parts,” explains Surjit Bawa, General Manager of Metex Heat Treating, located in Brampton, Ontario. “Recently, with the push for lighter materials, we have started to see more diverse materials such as powder metal for induction hardening, neutral hardening and carburizing.”

Industry an application dictates the type of materials needed. In the automotive industry, the push towards lightweighting has forced heat treating facilities to adopt practices that accommodate these materials. The use of exotics has become more popular in the aerospace and medical industries, so does the need to heat treat these types of metals.

“We occasionally work with an Inconel or Incoloy, materials like Carpenter 465 [a custom stainless steel], or less exotic exotics like 304, 316,” says Norman Hanson, president and owner of Thermex Metal Treating, located in Edmonton, Alberta. Thermex primarily serves the resource and agricultural industries, like oil and gas, energy, mining, and forestry sectors. “We do work with some of those exotic materials with many different processes.”

How does heat treating work?

There are many different types of heat treating processes. The common ones include carburizing, liquid and gas nitriding, induction hardening, and through hardening (or quench and tempering).

For Böhler-Uddeholm Thermo-Tech, they really only get involved with nitrogen gas quenching, which can eliminate some of the materials and products. “We don’t see certain oil quenching grades like maybe a p20 or 4140 because they require oil as the quenching medium,” says Schmidt. However, due to their location, focusing on automotive-specific grades and processes made more sense.

Thermex, on the other hand, accommodates a broad scope, “We offer a wide range of different processes that are run on steel, stainless steel, tool steel, any iron based materials,” says Hanson. “We do all the common forms of heat treating that are done on steels.”

For the most part, a customer will buy a piece of steel (or the ever-more popular exotic materials) and rough machine it. When it comes to heat treating, there is often distortion, which is why it is important to rough machine, leaving a small amount of additional material on the part. At this point, the part is ready for heat treating.

Hanson explains that there are several discussions that need to happen before heat treating begins, though. The first discussion he has with a customer is whether the process they are asking for is compatible with the material they are using. The second discussion centres on aim properties they are looking for in terms of hardness, or case depth, if it’s a case hardening process. Is it appropriate and achievable for the part and material? If everything works, he will discuss dimensional changes and distortions that can occur.

The part is then ready for the heat treating process, “It will go into our furnaces where it undergoes metallurgical transformation,” says Schmidt. “During this time, you expose it to elevated temperatures, 1850-1900°F, then quenching it, which means cooling it quite rapidly to change the micro-structure. This process creates movement. Customers will call it distortion but it is movement in the steel which is byproduct of successful heat treatment.”

Quality Controls

For the most part quality assurances are dictated by the customers and specifications. It can be as easy as just certifying the process or as complicated as reviewing the micro-structure of a coupon. Many heat treating companies have dedicated quality departments to ensure their processes are done correctly, especially when it comes to industries requiring stringent standards, like aerospace.

Photo courtesy of Thermex Metal Treating

Photo courtesy of Thermex Metal Treating

One of the challenges heat treating facilities face is working with proprietary specifications. For Hanson, “working with the oil industry, most of the big players, like Haliburton or Schlumberger, they all have their own proprietary standards that we have to work towards, so often we will have a discussion with our customers about that as well.” They have developed an in-house metallurgical lab to test their products extensively to ensure they are meeting the requirements.

Understanding the different requirements both from customers and industry can make the heat treating process go more smoothly. “Most of the grades have their own unique recipes involved. It also requires more stringent parameters in the furnace itself. Some of the exotic materials and the industries they serve require tight temperature tolerances, so certain things can be run at a certain temperature with a ±25 thou temperature tolerance, other grades might require a ±5 or 10°,” says Schmidt, who explains there are a variety of testing that can be requested depending on the nature of the application and industry serving.

What are some challenges?

One of the most important challenges is just making sure that heat treating companies are able to meet the appropriate specifications. For Hanson, who’s primary customer is a machine shop selling to end users, this can be a challenge, because he has to ensure that he not only meets the shop’s specification but also the end user’s needs.

Different types of materials are required for different applications. There are specific heat-treatment processes associated with each to achieve optimum results. “Hence, when designing a part for a particular application, always analyze different steels to find the one that provides the balance of hardness, strength, amongst other characteristics to withstand the stresses the part will undergo in use as a finished part,” explains Bawa.

As a heat treating customer, it is important to ensure that part you provide is within the appropriate conditions for the process, which should include movement and distortion.

“Some customers tend to take this for granted,” says Schmidt. When you elevate the hardness of materials, it can make it harder to post-process machine. So customers will often machine to close to tolerance, being motivated to do as little machining after as possible. “There is a fine line and some risk involved,” he continues. “So they are rolling the dice by machining it too closely prior to heat treat. They may not be able to clean it up afterwards.”

When it comes to heat treating, there are many variable involved. Finding the correct heat treating facility for your needs will help ensure that the finished product is up to spec. Speak to the facility; their expert advice can help ensure that you’ve chosen the right process for the material and outcome expectations.

Heat treating is one of the key and fundamental steps used in producing machined or hardened metal parts. “It has applications across so many different industries and requirements. Any city, area, or region that wants to have a good strong metal parts manufacturing sector has to have good heat treating facilities available,” says Hanson.

About the Author
Canadian Metalworking / Canadian Fabricating & Welding

Lindsay Luminoso

Associate Editor

1154 Warden Avenue

Toronto, M1R 0A1 Canada

Lindsay Luminoso, associate editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.

Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.