Patent ID: 10378079

Abstract:
A stainless steel is provided having good corrosion resistance and good low-temperature toughness. A stainless steel contains, in mass %, Cr: 15.5 to 18.0%. The stainless steel has a matrix structure having, by volume ratio, 40 to 80% tempered martensite, 10 to 50% ferrite and 1 to 15% austenite. When a microstructure image obtained by photographing the matrix structure at a magnification of 100 times is positioned in an x-y coordinate system and each of 1024×1024 pixels is represented by a gray scale level, β defined by Equation (2) is not smaller than 1.55: 1.0≤Mo+0.5W≤3.5  (1).Here, Mo and W are the Mo and W contents in mass %.In Equation (2), Su is defined by Equation (3), and Sv is defined by Equation (4):In Equations (3) and (4), F(u,v) is defined by Equation (5):In Equation (5), f(x,y) represents the gray level of the pixel at coordinates (x,y).