| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heattreated steel for hot forging, used as a material for manufacturing machine parts, such as automobile engine crankshaft, having wear resistance capable of withstanding use even if surface hardening treatment after working is omitted, also having hardness within limits not prejudicially to machinability, and usable in an as-hot-rolled state. SOLUTION: The steel has an alloy composition consisting of, by weight, 0.40-0.70% C, <=0.50% Si, 0.90-1.80% Mn, 0.05-1.00% Cr, 0.010-0.045% sol.Al, 0.005-0.025% N, and the balance Fe with impurities. Further, the structure of this steel after hot forging is composed of ferrite+pearlite, and the area ratio of proeutectoid ferrite is regulated to <=10%.
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