Methods for their preparation steel bar or high-strength steel wire, high strength and molded article having excellent cold workability

摘要

PROBLEM TO BE SOLVED: To provide a steel wire or steel bar in which conventionally used steels of general-purpose type and component system can be used to maintain the manufacturing cost for a steel ingot or cast billet on the conventional level and, further, the necessity of softening treatment, such as spheroidizing annealing, prior to cold working for a formed article, such as screw and bolt, by means of cold heading etc. can be obviated and also the necessity of the application of quench-and-temper treatment to the formed article after the cold working can be obviated and also to provide a formed article using them.;SOLUTION: Warm working is applied at 350 to 800°C to a steel ingot, cast billet, steel billet or steel semifinished product having 0.01 to 0.45 mass% C content to prepare a material having ≤3μm average crystal grain size in a cross section perpendicular to the longitudinal direction. Subsequently, cold working is applied to form a ferrite main-phase structure of ≤500 nm average crystal grain size in a cross section perpendicular to the longitudinal direction.;COPYRIGHT: (C)2006,JPO&NCIPI