| 摘要 |
PURPOSE: To produce a stainless steel for oil well pipe, having high strength and high toughness, by specifying respective contents of Al and N in an A1S1420 type 13Cr steel. CONSTITUTION: This steel has a composition which consists of, by weight ratio, 0.15-0.22% C, <=1.0% Si, 0.25-1.0% Mn, 12.0-14.0% Cr, <=0.020% P, <=0.010% S, <=0.03% Al 0.015-0.03% N, and the balance Fe with inevitable impurities and in whichΔN represented byΔN=(Total N%)-(14/27)Al% is regulated to >=0.0050. This steel is subjected to pipe making into a seamless steel pipe, to heating up to 960-1000 deg.C, to air cooling down to room temp., and further, to tempering treatment at a temp. not higher than the Ac1 point of this steel. By adopting these methods, proper amount of precipitation of Cr2 N can be maintained, and, after heat treatment, an oil well pipe having >=552MPa yield strength and having high strength and superior toughness can be obtained.
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