MÉTODO PARA FABRICAÇÃO DE TUBULAÇÃO OU TUBO DE AÇO INOXIDÁVEL MARTENSÍTICO

摘要

There is provided a method capable of manufacturing a martensitic stainless steel pipe or tube with high efficiency by reducing the time required for cooling for quenching in a heat treatment step. The method for manufacturing a martensitic stainless pipe or tube according to the present invention has a heat treatment step comprising: a heating step of heating the steel pipe or tube until the external surface temperature thereof reaches a predetermined 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 predetermined 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 predetermined 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. 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.