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Solving Problems with Heat Treatment

Why is metal heat treated?

December 9, 2020

Metals are professionally heat-treated for various reasons, but the short of it is this: heat-treated metals perform better, physically and mechanically, than raw material. Without thermal processing companies, certain industry standards simply could not be met - many mechanical parts could not be realized from concept to field use.

Heat-treated metals have had their microstructure manipulated to influence their mechanical properties such as hardness, toughness, and ductility. Our multi-certified team performs various thermal processes to help you acquire the properties you need. This concept applies to all industries in the world, namely aerospace, medical, and power generation.

Some applications require a softer material to assist in the ease of forming, machining, or cold working. Common processes that can reduce the hardness of a material include annealing, normalizing, solution treating, or spheroidizing. Each of these methods serves to eliminate dislocations and recrystallize grains. Solution annealing applies to martensitic stainless steels that are capable of precipitation hardening and austenitic. It serves to dissolve precipitates into solid solution and ease dislocation motion. Solution annealing can also be performed on non-ferrous metals such as aluminum, titanium, and nickel alloys. Spheroidizing is known to produce the softest and most ductile microstructure in steels, which forms spheroidal carbides throughout the material matrix.

Strengthening of steels is the most sought process in heat treatment. Increasing the strength of a metal involves both increasing the hardness and tensile properties of a material. Typical alloy steels are strengthened through austenitizing, quenching, and tempering. Precipitation hardening materials are strengthened via aging. This is holding the material at a temperature that brings precipitates out of solid solution which impedes dislocation motion. Surface treatments also provide wear resistance in critical surfaces such as gear teeth. This is facilitated through carburizing or nitriding, which diffuses either carbon or nitrogen into the surface of the steel to increase only the outer strength.

Tool steels are a common example of high-strength steels that undergo quench and temper processing. They are raised at a temperature above the upper transformation temperature until the grains have transformed entirely to austenite. They then undergo a quench, or rapid cooling, commonly in inert gas or oil. This causes a sheer transformation in the austenite grains and forms martensite. Martensite is the hardest and most brittle phase in alloy steels. The material cannot be used in the as-quenched condition due to the aforementioned brittleness of martensite. It is necessary to temper the material at a temperature below the austenite transformation range, typically in the range of 300 °F-1200 °F. This serves to resolve some brittleness while retaining a majority of the strength.

These processing methods can be carried out in a variety of ways that can alter the surface finish of the parts. Processing atmosphere is a significant consideration for the final properties of your parts. Atmospheric processing can ultimately produce a higher hardness in most steels due to more effective heat transfer and typically more aggressive quenching. Parts processed in a protected atmosphere or quenched in oil can suffer from distortion on the surface. This may require further machining or straightening operations to rectify. Vacuum processing is available to ensure the surface finish is of premium quality. Vacuum prevents scale and discoloration from forming and quenching in inert gas limits dimensional distortion.

All of these processes are integral to the products we use every day. No car or plane would function if their internal components were not properly processed. That is why it is important for every industry to choose their heat treater with care. Vacu Braze consistently demonstrates great commitment to quality processing and customer service. We understand that everything we do ensures our world functions properly.

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