PURPOSE: To elevate toughness of a weld, by adding to a conventional shape fixing stage for manufacturing an electric welded steel pipe, a stage for eliminating work hardening due to the fixing of the shape, and also anneal-treating the weld at a temperature which does not spoil dimensional accuracy, of the pipe, of an electric welded steel pipe manufacturing process.
CONSTITUTION: In an electric welded steel pipe manufacturing line, an annealing heat treatment process of a weld is added at a heating temperature of about 400W700°C, to the stages through molding-electric welding-normalizing heat treatment of a weld-shape fixing stages. As a result, toughness can be recovered by dropping its hardness which has been raised by fixing shape of the weld. Also, in case when a heating temperature is ≤ about 700°C, no influence is affected on dimensional accuracy of the pipe, and on the other hand, in case when it is ≤ about 400°C, too much time is required for softening the weld, therefore, it is not practical.
YASUGI SEIJIROU
SUGAMASA TETSUAKI
NAGAHAMA YUTAKA
KONAWA TSUTOMU
KOUNO KENSAKU
