| 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/mm<2> . 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 deg.C, then to slow cooling at (5 to 12.5) deg.C/min cooling rate down to 500 deg.C to reduce residual stress, and further to rapid cooling at least down to 200 deg.C at a rate of >=10 deg.C/min to avoid the occurrence of 475 brittleness.
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