SULFUR FREE CUTTING STEEL FOR MACHINE STRUCTURAL USE

摘要

A sulfur free cutting steel for machine structural use which contains by weight 0.10 to 0.55 % C, 0.05 to 1.00 % Si, 0.30 to 2.50 % Mn, <= 0.15 % P, 0.050 to 0.350 % S, >0.010 % to 0.020 % Al, 0.015 to 0.200 % Nb, 0.0015 to 0.0150 % O, and <=0.02 % N, and further contains one or more selected from among 0.03 to 0.50 % V, 0.02 to 0.20 % Ti, and 0.01 to 0.20 % Zr, characterized in that the S/O content ratio ranges from 15 to 120 and that one or more selected from among oxide (see Fig. 1), carbide, nitride and carbonitride of Nb act as nuclei for the precipitation of an MnS inclusion.