| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that steel usable as a member applied with repeated stress even as plasma-cut is not present. SOLUTION: This steel has a steel composition containing 0.01 to 0.2% C, 0.1 to 0.6% Si, 0.4 to 1.60% Mn, 0.01 to 0.6% Cr, 0.01 to 0.5% Mo, 0.01 to 0.06% Nb and/or 0.005 to 0.03% Ti and moreover has a structure in which the hardenability index DI is >=18, and austenitic grain size in the hardened layer part in the plasma-cut part is <=20μm. The steel is excellent in the fatigue characteristics in the plasma-cut part and can be used as a member applied with repeated stress even as plasma-cut.
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