Applied Thermal referenced in Cutting Tool Engineering magazine.
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Making steel hard—but not too hard
In warsaw, ind., Applied Thermal Technologies Inc. specializes in vacuum heat treating and brazing steels and exotic materials. Equipped with nine vacuum furnaces and eight tempering furnaces, the company serves the orthopedic and aerospace industries, said Micky Bradican, president of Applied Thermal. “While medical implants are usually made of titanium, surgical instruments are typically stainless steel, and aerospace runs that gamut from Inconels to cobalt alloys, titanium and stainless steels,” he said.
Methods of heat treating the metals to increase hardness and tensile strength vary. Steel, a ferrous metal, generally undergoes a two-step process called “quench and temper hardening.” Depending on the chemistry and size of the part, the steel is heated to 1,400° F or higher for a minimum of 30 minutes. Heating repositions the carbon atoms and strengthens the atomic bonds. Th e steel is then quickly quenched in water, oil or air, locking the carbon atoms in place. Tempering, the next step, involves reheating the steel from 200° F to 800° F to reduce some of the hardness, yet retain enough for the part’s intended use.
While quench and temper is used for most steels, it’s not the sole method of heat treating the material. Th e specific chemical composition (percentage of carbon, iron and other alloys) is the determining factor. For instance, the 17-4 PH stainless steel plate for the camera mount cited at the beginning of the main article contains iron, nickel and chromium, and would have required a single-step process (heating at 900° F for 1 hour) to achieve a hardness of 45 HRC.