HIGH STRENGTH NONTEMPERED STEEL PARTS AND ITS MANUFACTURE

摘要

PROBLEM TO BE SOLVED: To manufacture high strength parts excellent in machinability including the hot forging, direct oil quenching and drilling of steel in the manufacture of automobile parts by hot forging and also excellent in buckling resistance and fatigue resistance. ;SOLUTION: A steel, which contains by weight, 0.05-0.20% C, 0.05-0.50% Si, 0.50-2.00% Mn, 0.30-1.50% Cr, 0.0005-0.0050% B, 0.010-0.100% Al, ≤0.010% N and the balance F with inevitable impurities, further whose hard facing parameter P1 calculated by P1=C+(Mn/20)+(Cr/20) is within 0.15-0.25% and whose internal hardness parameter P2 calculated by P2=Mn+Cr is within 1.20-2.80%, is hot-forged and then is directly oil-quenched to obtain the still whose Rockwell C hardness of the surface is ≥25 to 35, and internal Rockwell C hardness of the part 2 mm or below from a surface layer is lower than the surface hardness and is ≥20 and 30, thereafter the steel is machined.;COPYRIGHT: (C)2001,JPO