The machine structural steel null which is superior in machinability, resistance grain conversion property and the resistance for case

摘要

PROBLEM TO BE SOLVED: To provide a steel for machine structural use, excellent in machinability, capable of inhibiting the coarsening of austenite grains even if high-temp., short-time treatment is performed at the time of surface hardening treatment such as carburizing, and increased in resistance to case crush. ;SOLUTION: The steel has a composition consisting of, by weight, 0.3-0.5% C, 1.0% Si, ≤2.0% Mn, ≤0.03% P, 0.02-0.15% S, ≤2.0% Cr, ≤0.4% Ti, ≤0.4% Zr, ≤0.008% N, ≤3.5% Ni, ≤1.0% Mo, ≤1.0% W, ≤0.005% B, ≤0.1% Nb, ≤0.3% V, ≤0.3% Pb, ≤0.1% Ca, ≤0.1% Al, and the balance Fe with impurities and satisfying Ti(%)+Zr(%)=0.025 to 0.4%.;COPYRIGHT: (C)1999,JPO