OIL COUNTRY TUBULAR GOODS EXCELLENT IN COLLAPSE CHARACTERISTICS AFTER EXPANSION AND METHOD OF PRODUCTION THEREOF

摘要

The present invention provides a method of production of oil country tubular goods having a small drop in collapse pressure after expansion and having a collapse pressure recovering by low temperature ageing at about 100° C. and oil country tubular goods obtained by this method of production. ;This method of production comprises hot rolling a steel slab having amounts of addition of C, Mn, P, S, Nb, Ti, Al, and N in specific ranges and having a balance of iron and unavoidable impurities and shaping the steel strip coiled at a temperature of not more than 300° C. as it is into a tube. Alternatively, it comprises heating steel pipe having amounts of addition of C, Mn, P, S, Nb, Ti, Al, and N in specific ranges and having a balance of iron and unavoidable impurities to a temperature of the Ac₃ [° C.] to 1150° C., then cooling it in a range of 400 to 800° C. at a rate of 5 to 50° C./second.