| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel for machine structure having cold-workability equal to that of a low carbon steel and having characteristics of levels of medium and high carbon steels by heat treatment. SOLUTION: This steel for machine structure has the compsn. contg., by weight, 0.3 to 0.8% C, >0.15 to <0.30% Si, 0.05 to 0.6% Mn, 0.01 to 0.5% W, 0.005 to 0.10% Al, 0 to 0.5% Cu, 0 to 0.5% Ni, 0 to 0.2% Cr, 0 to 0.3% Mo, 0 to 0.05% Nb, 0 to 0.2% V, 0 to 0.2% Ti, 0 to 0.2% Zr, 0 to 0.5% Pb, 0 to 0.5% Bi, 0 to 0.1% Te, 0 to 0.1% Se, 0 to 0.01% Ca, <=0.03% P, <=0.05% S and the balance Fe with impurities, and has the structure composed of ferrite of 5 to 10 JIS size number by grain size, graphite having <=20μm maximum diameter and cementite and having <=120 HV hardness. The steel is produced by applying hot working, cold working at 5 to 50% reduction of area, and annealing at 650 to 720 deg.C for 5 to 20 hr.
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