| 摘要 |
PURPOSE:To improve the corrosion resistance, strength, toughness, corrosion fatigue strength, etc., of the title steel having specified composition and structure by holding the steel at a specified solid soln. temp. for specified hours, and then cooling the steel by forced air. CONSTITUTION:The casting of the title steel consisting of <=0.03% C, <=1% Si, <=2% Mn, 23-25% Cr, 3.5-5.5% Ni, 2-4% Mo, 0.5-1.5% Co, <=1% Cu, 0.15-0.25% N, and the balance Fe and wherein the ferrite amt. in the two-phase structure of austenite and ferrite is controlled to 50-70% in terms of an area ratio is prepared. The casting is held at a solid soln. temp. of 1000-1150 deg.C for 0.5-2hr per inch thickness, and then cooled by forced air. When the solid soln. temp. is lower than that above mentioned or the holding time is shorter, the solid soln. rate of the alloy elements and the homogenizing of the structure are insufficient. Meanwhile, when the temp. is higher and the time is longer, a state of sensitization is caused, and the corrosion resistance is deteriorated. Since the cooling is carried out by forced air, residual stress is reduced, and a specified soln. heat treatment effect can be secured. |
