Patent ID: 8168014

Claim:
A method for manufacturing a martensitic stainless steel pipe or tube, having a heat treatment step comprising: a heating step of heating the steel pipe or tube until the external surface temperature thereof reaches a selected temperature not lower than A3 transformation point+20° C. and not higher than 980° C.; a first cooling step of water cooling the heated steel pipe or tube until the external surface temperature thereof reaches a selected temperature not lower than 350° C.; a second cooling step of air cooling the water cooled steel pipe or tube until the external surface temperature thereof reaches a selected temperature not higher than 250° C.; and a third cooling step of water cooling or air cooling the air cooled steel pipe or tube until the external surface temperature thereof reaches normal temperature, wherein the cooling rate of the steel pipe or tube in the first cooling step is determined according to the wall thickness of the steel pipe or tube so that the amount of heat recuperation for the external surface temperature of the steel pipe or tube in the second cooling step is not higher than 50° C.