METHOD FOR PRODUCING electric resistance welded steel pipes and welded steel pipes with a high Si content or high Cr

摘要

The present invention provides a method of production of electric resistance welded steel pipe able to stably reduce weld defects due to oxides by firing plasma and furthermore able to reduce plasma jet noise and comprises shaping steel plate 1 into a tube and electric resistance welding the abutting end faces 4 during which blowing on at least the abutting end faces 4a in the region 6 at the welding upstream side from the weld point 9 where the temperature becomes 650°C or more a reducing high temperature (pseudo) laminar plasma obtained by applying voltage to a reducing gas containing H 2 gas: 2 to 50 vol% to which is added a balance of Ar gas alone or a mixed gas of Ar gas to which N 2 gas, He gas, or both are added. At that time, it is preferable to make the applied voltage over 120V and the make the plasma blowing conditions satisfy the following formula (1). 150 4 × ˆ‘ G i M i À × D × ¼ ave , T = 7000 400