Excellent mechanical structural steel and its manufacturing method in cold forging of

摘要

PROBLEM TO BE SOLVED: To provide a steel for machine structure excellent in cold forgeability when it is hot-rolled as it is or after being spheroidized as well stably at a low cost.;SOLUTION: The steel has a composition which contains, by mass%, C: 0.30-0.55%, Si: 0.03-0.30%, Mn: 0.50-1.50%, P: 0.018% or less, S: 0.02% or less, Al: 0.010-0.060% and Cr: 1.2-2.0% in a range satisfying the following expression (1) [%C]-[%Si]/2+[%Mn]/5+2[%Cr]≥3.2, and the balance Fe with inevitable impurities, is hot-rolled under the condition of a finishing temperature: 1,000°C or below.;COPYRIGHT: (C)2011,JPO&INPIT