| 摘要 |
PROBLEM TO BE SOLVED: To improve the corrosion fatigue resistance of steel for structural purpose, particularly the corrosion fatigue resistance in a water environment contg. chlorine or chloride by controlling the structure of steel. SOLUTION: As to the steel for structural purpose excellent in corrosion fatigue resistance and a method for producing it, the structure in which the ferrite crystal grain boundaries and/or crystal sub-grain boundaries in the surface layer part of steel or the surface and back layer parts of a steel sheet are provided with cementite and/or the carbonitrides of Nb, Ti and Ta of <=0.5μm, and in which the pearlite fractional ratio is controlled to <=10% and the balance is essentially composed of ferrite or bainite with <=3μm average grain size is obtained.
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