| 摘要 |
PROBLEM TO BE SOLVED: To produce bar steel and steel wire for machine structure in which softening equal to or above that of the conventional spheroidizing annealed material is attained, moreover good in hardenability and excellent in cold workability and to provide a method for producing the same. SOLUTION: This steel has components contg., by weight, 0.1 to 0.5% C, 0.01 to 0.15% Si, 0.2 to 1.7% Mn, 0.0005 to 0.05% Al, 0.005 to 0.07% Ti, 0.0003 to 0.007% B and 0.002 to 0.2% N, in which the content of P is limited to <=0.02%, and 0 to <=0.003%, and the balance Fe with inevitable impurities, its microstructure is composed of ferrite and spheroidal carbides, the crystal grain size of ferrite is No. >=8, and the number of the spheroidal carbides per mm2 unit area is <=1.5×106 pieces×C% in accordance with the C content.
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