| 摘要 |
PURPOSE:To produce a high tensile steel pipe having excellent weldability and having, for example, >=30mm. thickness and 65kg/mm.<2> tensile strength by rolling the steel which is decreased of equiv. of C relatively and is increased of content of Cu then cooling the same acceleratively according to need to make a steel plate, and subjecting the steel plate to a tempering treatment under specific parameters after making the same into a pipe. CONSTITUTION:The steel contg., by weight, <=0.15% C, <=0.80% Si, 0.7-2.0% Mn, 0.8-1.4% Cu, as basic components, and if necessary, contg. >=1 kind among <=3.0% Ni, <=0.06% Nb, <=0.10% V, and <=0.10% Ti is prepd. After the steel plate obtd. by heating said steel to a prescribed temp. then rolling the same and air cooling the rolled plate down to <=600 deg.C is heated to 950-1,250 deg.C, the steel plate is subjected to controlled rolling at >=30% cumulative draft at temp. lower than the unrecrystallization temp. and 650-750 deg.C finish rolling temp. After the resultant steel plate is made into a pipe, the pipe is subjected to a tempering treatment at and for the temp. and time within the 14.7X10<3>-17.2X10<3> range of a tempering parameter P=T(logt +20) (T: temp. deg.C, t: time hr), whereby the intended high tensile steel is obtd. |
