| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heat treated steel for hot forging, without remarkably increasing the content of V added for precipitation strengthening, which can obtain high strength (high proof stress) compared with a steel having a V content equal to the conventional one. SOLUTION: The non-heat treated steel for hot forging has a composition comprising, by mass, 0.30 to 0.50% C, 0.05 to 1.00% Si, 0.50 to 1.50% Mn, 0.040 to 0.100% S,≤0.50% Cr,≤0.05% Mo, 0.20 to 0.40% V,≤0.050% Al,≤0.0060% N and <0.02% Nb, and the balance Fe with inevitable impurities, and in which Ceq=C+Si/7+Mn/5+Cr/9+V satisfies≥0.9, and hardness after air cooling subsequently to hot forging is≥340 Hv, and has a structure of ferrite-pearlite in which the area ratio of bainite is≤10%. COPYRIGHT: (C)2011,JPO&INPIT
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