For mechanical structure and its manufacturing method for machine structural bar or wire

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PROBLEM TO BE SOLVED : To provide a steel member for machine structural use which has excellent machinability and cold forgeability or fatigue resistance. SOLUTION : The steel member for machine structural comprises, by mass, 0.01 to 0.8% C, ≤2.0% Si, 0.1 to 2.0% Mn, ≤0.1% P, 0.004 to 0.1% S and ≤0.1% Al, and further comprises one or more kinds of metals selected from Te, Se, Zr, Mg, Ca and rare earth metals by 0.0005 to 0.02%, respectively. The steel member has a form wherein the average aspect ratio (a) and the average Vickers hardness H in the cross-section parallel to the working direction (rolling direction or forming direction) in sulfide inclusions satisfy 1/a≥5.3×10-5×H2-0.0187×H+1.849. The steel member can comprise one or more kinds of metals selected from Cu, Ni, Cr, Mo, Nb, B, W and V as well. COPYRIGHT : (C)2004, JPO