| 摘要 |
PROBLEM TO BE SOLVED: To provide a high-strength and high-toughness non-heat treated steel having high toughness as well as high strength of >=850 MPa tensile strength in as-rolled state and also excellent in drilling machinability. SOLUTION: This non-heat treated steel has a composition containing, by weight, 0.30-0.60% C, 0.01-1.0% Si, 0.1-2.0% Mn, 0.050<0.50% S, 0.5-5.00% Ni, >1.0-3.0% Cu, 0.0010-0.020% N, 0.0010-0.0050% O, and one or >=2 kinds selected from 0.01-0.50% V, 0.01-0.50% Nb, and 0.01-0.50% Ti and also has a structure composed of ferrite + pearlite structure of 20-80% ferrite volume ratio in as- rolled state.
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