| 摘要 |
PROBLEM TO BE SOLVED: To improve the corrosion resistance in a water environment particularly contg. chlorine or chloride by allowing the grain boundaries and/or grain sub-boundaries in the surface layer of steel having a specified compsn. or in the surface and back layer regions of the steel to have a specified structure and controlling the intensity ratio of the (100) plane in the crystalline texture parallel to the rolling face to the specified value. SOLUTION: This steel is composed of, by weight, 0.04 to 0.25% C, 0.01 to 1.0% Si, 0.3 to 2.0% Mn and <=0.01% S, and the balance Fe with inevitable impurities. Then, it has a structure of <=3μm average grain size essentially consisting of ferrite or bainite, in which, in the surface layer of the steel or in the surface and back layer regions of >=5% of the diameter or thickness of the respective steel from the surface and back layer of the steel sheet, a cementite phase or a carbonitride phase of <=0.5μm is provided in the grain boundaries and/or grain sub-boundaries, and moreover, the fractional ratio of pearlite is <=10%, and also, the intensity ratio of the (100) plane in the crystalline texture parallel to the rolling face is >=1.5.
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