| 摘要 |
PROBLEM TO BE SOLVED: To provide a non-heat-treated bar steel for direct cutting whose use can be limited as possible even in the case V is not contained or is contained, and whose high yield strength, yield ratio and toughness can be obtained as-cooled after hot working. SOLUTION: The non-heat-treated bar steel for direct cutting has a chemical composition comprising 0.37 to 0.53% C, 0.05 to <0.50% Si, 1.55 to 1.90% Mn,≤0.040% P, 0.010 to <0.030% S, 0.15 to 0.80% Cr,≤0.06% Al, 0.005 to 0.025% N and 0.010 to 0.050% Nb, and the balance Fe with impurities, and satisfying 1.90<Mn+Cr≤2.50, and has a microstructure in which the ratio of a ferrite-pearlite structure is≥90%, and also, the grain size of old austenite is≤150μm. One or more selected from <0.15% V,≤0.010% Ca and≤0.35% Pb may be incorporated therein. COPYRIGHT: (C)2011,JPO&INPIT
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