The Effect of Nitrogen on the Mechanical Properties of an SAE 1045 Steel 920667

A cold worked and induction hardened SAE1045 steel component exhibited excessive distortion after cold working and straightening, as well as cracking during straightening after induction hardening. Since the problems occurred only in certain heats of electric furnace (EF) steel, in which nitrogen content can vary widely and in some cases be quite high, and never occurred for basic oxygen furnace (BOF) steel for which nitrogen contents are uniformly low it was suspected that the source of the problem was low temperature nitrogen strain aging in heats of EF steel with a high nitrogen content. The measured distortion and mechanical properties at various stages in the fabrication process showed that while nitrogen content had no significant effect on the hot rolled steel the component distortion and strength after cold working and after induction hardening increased with increasing nitrogen content. It appears that low temperature strain aging, which increased distortion and strength and decreased ductility in high nitrogen heats of EF steel, was responsible for the resistance to straightening after cold working and the high distortions after induction hardening that caused cracking during straightening.