Abstract: The present invention relates generally to an improved method and apparatus for induction heat treating and restraint quenching structural members of carbon steel, to a uniform martensitic structure, such that distortion of the member due to rapid quenching is controlled to a minimum. More specifically, the member is generally heated by induction in two stages generally to austenitizing temperature in the range of 1450.degree. to 1750.degree. F. Then the member is liquid quenched under restraint to below 1000.degree. F. to minimize distortion and finally tempered under restraint at a temperature in the range of 750.degree. to 1250.degree. F. Such structural members attain minimum physical properties after heat treating in the range of 110,000 psi yield strength and 125,000 psi tensile strength.

Abstract: This invention relates to a method of induction heat treating and restraint quenching structural members, particularly those of low carbon alloy steel (lean content), to a uniform martensitic structure, such that distortion of the member due to rapid quenching is controlled. The members would generally be of a channel shape and they would be heated by induction preheating in several stages to austenitizing temperature, namely 1450.degree. to 1750.degree. F., and then liquid quenching the channel member and restraining the channel on both its web and its flanges to below 900.degree. F. to minimize distortion and then tempering the channel at a temperature of 750.degree. to 1000.degree. F. and again restraining it while cooling to avoid distortion. These would generally be truck side rails and they would be low carbon alloy steels (lean content), approximate carbon content of 0.22-30%, manganese 1.00 to 1.35%, sulfur 0.05% max., phosphorus 0.04% max.