Production manner of the steel for soft nitriding and the soft nitriding part null which uses its

摘要

PROBLEM TO BE SOLVED: To provide a soft-nitrided parts having superior fatigue resistance and wear resistance and a method of manufacturing a steel material for soft- nitriding, used as a stock for the parts and excellent in machinability. ;SOLUTION: (1) A steel, which has a chemical composition consisting of 0.15-0.45% C, 0.10-0.50% Si, 0.2-2.5% Mn, 0.002-0.2% S, 0.5-2% Cr, 0.05-0.5% V, ≤1.0% Ti, ≤1.0% Zr, 0.01-0.3% Al, ≤0.008% N, ≤0.35% Pb, ≤0.01 Ca, and the balance Fe with impurities and satisfying Ti+Zr=0.04 to 1.0% and Ti+Zr-1.2 S 0% and in which the maximum diameter of Ti carbon sulfides and Zr carbon sulfides in the steel is made to ≤10 μm and also the sum of their amounts is made to ≥0.05% by cleanliness, is subjected to hot working and to spheroidizing annealing to make hardness to ≤Hv180 and then to cold working to make hardness to ≥Hv250. The chemical composition of the steel material may contain either or both of Mo and W besides the components in (1), while Si content is made to 0.05-0.50%. The soft-nitrided parts are obtained by using, as a stock, the steel material for soft-nitriding manufactured by the above method and have ≥Hv600 surface hardness, ≥0.1 mm effective case depth, and ≥Hv250 core hardness.;COPYRIGHT: (C)1999,JPO