LARGE-SIZED CASTING AND FORGING, MADE OF DUPLEX STAINLESS STEEL EXCELLENT IN CORROSION RESISTANCE AND TOUGHNESS, AND THEIR PRODUCTION

摘要

PROBLEM TO BE SOLVED: To stably obtain a large-sized casting of a duplex stainless steel excellent in corrosion resistance and toughness by specifying a composition consisting of C, Si, Mn, Ni, Cr, Mo, N, and Fe and also specifying the crystalline particle size of ferritic phases. ;SOLUTION: The large-sized casting and forging of duplex stainless steel excellent in corrosion resistance and toughness can be obtained by providing a composition consisting of, by weight, ≤0.10% C, ≤2.0% Si, ≤3.0% Mn, 3-10% Ni, 20-35% Cr, ≤6.0% Mo, ≤0.3% N, and the balance Fe with inevitable impurities and regulating the average crystalline grain size of ferritic phases to ≥50μm and preferably controlling residual stress to ≤300N/mm². These casting and forging can be obtained by casting a molten steel of the prescribed composition, further applying forging if necessary, subjecting the resultant casting or forging to heating up to ≥1000°C, then to slow cooling at (5 to 12.5)°C/min cooling rate down to 500°C to reduce residual stress, and further to rapid cooling at least down to 200°C at a rate of ≥10°C/min to avoid the occurrence of 475 brittleness.;COPYRIGHT: (C)1997,JPO