| 摘要 |
PROBLEM TO BE SOLVED: To provide a 655 Nmm-2 class low-C high-Cr alloy oil well pipe capable of being used without causing stress corrosion cracking even under the atmosphere containing much hydrogen sulfide while improving simultaneously the strength, stress corrosion cracking resistance, and toughness of the conventional martensitic stainless steel and also maintaining corrosion resistance, and its manufacturing method. SOLUTION: An alloy steel, which has a composition consisting of, by weight, 0.005-0.05% C, 12-16% Cr, <=1.0% Si, 0.05-0.3% Mn, 3.5-6.0% Ni, 1.5-2.5% Mo, 0.01-0.05% V, <=0.02% N, and the balance Fe with inevitable impurities and satisfying the relation of 705-25[%Ni]+5[%Cr]+25[%Mo]>=680, is used. This steel is hot worked, austenitized at temperatures between the Ac3 point and 980 deg.C, cooled, subjected to the first tempering at temperatures between the Ac1 point and the Ac3 point, cooled, and further subjected to the second tempering at temperatures between 550 deg.C and the Ac1 point.
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