MANUFACTURING METHOD AND MANUFACTURING EQUIPMENT FOR SEAMLESS STEEL PIPE OR TUBE WITH EXCELLENT TOUGHNESS

摘要

It is difficult in the related art to realize not only a decrease in material variability due to non-uniform microstructure distribution in the wall thickness direction of a pipe body but also the maintenance of satisfactory productivity of the whole heat treatment line at the same time. A method includes determining in advance whether or not the pipe body is made of a steel grade having an Ms point lower than 200°C; leaving the pipe body of a steel grade having an Ms point lower than 200°C additionally at room temperature (it is preferable to be transported to a holding bed 6 and left) until the temperature difference between the portion having the highest temperature and the portion having the lowest temperature in a cross section in a direction at a right angle to the pipe axis becomes less than 2.0°C after the quenching treatment has been performed, and then performing the tempering treatment; and, on the other hand, performing a tempering treatment on the pipe body of a steel grade not having an Ms point lower than 200°C without leaving the pipe body at room temperature after a quenching treatment has been performed.