HIGH-STRENGTH, HIGH-TOUGHNESS STAINLESS STEEL EXCELLENT IN RESISTANCE TO DELAYED FRACTURE

摘要

The present invention makes the best use of a low-cost chemical composition in providing a high strength and high corrosion resistance stainless steel, which has improved delayed fracture resistance and toughness in particular, for building and construction uses, and as, for example, a stainless steel tapping screw.;The present invention is, specifically, a stainless steel and a stainless steel screw with high strength and high toughness and excellent in delayed fracture resistance, characterized by: comprising, by mass, 0.01 to 0.25% of C, 0.05 to 1.0% of Si, 0.1 to 2.0% of Mn, 0.1 to 3.0% of Ni, 11.0 to 16.0% of Cr, 0.01 to 0.15% of N, and 0.01 to 3.0% of Mo; containing, optionally, 0.001 to 0.005% of B and/or one or more of 0.05 to 0.5% of Ti, 0.05 to 0.5% of Nb, and 0.05 to 0.5% of W; having less than 10% of ferrite in the center portion of the material; and having a mixed structure of martensite and 3 to 30% of austenite in the surface layer from the outermost surface to the depth of at least 1 µm, and a method to produce the same.