Patent ID: 8366843

Claim:
A method of manufacturing a seamless martensitic stainless steel pipe comprising the steps of: a) piercing a billet to form a pierced billet, b) subjecting the pierced billet to a hot working step to form a mother pipe and then subjecting the hot worked mother pipe to an immediate quenching step, wherein the method does not involve cooling and reheating of the hot worked mother pipe prior to performing quenching, and wherein the hot working step is either: 1) hot working the pierced billet using a mandrel mill reducer to form the mother pipe, wherein the hot working includes a final rolling occurring between the piercing step and the immediate quenching step, the final rolling having a finishing temperature of 850-960° C., the pierced billet having a chemical composition comprising, in mass percent, C: 0.15-0.21%, Si: 0.16-1.0%, Mn: 0.35-1.0%, Cr: 10.5-14.0%, P: at most 0.020%, S: at most 0.005%, Al: 0.005-0.050%, and a remainder of Fe and impurities, or 2) hot working the pierced billet using a mandrel mill reducer to form the mother pipe, wherein the hot working includes a final rolling occurring between the piercing step and the immediate quenching step, the final rolling having a finishing temperature of 800-850° C., the pierced billet having a chemical composition comprising, in mass percent, C: 0.15-0.21%, Si: 0.16-1.0%, Mn: 0.35-1.0%, Cr: 10.5-14.0%, P: at most 0.020%, S: at most 0.005%, Al: 0.025-0.050%, and a remainder of Fe and impurities, and further wherein the immediate quenching step is at a cooling rate greater than or equal to that of air cooling to produce a quenched pipe, and c) tempering the immediately quenched pipe of step (b) to provide a seamless martensitic stainless steel pipe having HRC of 22 or less, vTrs of 0° C. or lower and a tensile strength of at least 657 MPa.