Production of electrical resistance welded steel tubes with welds having improved toughness

摘要

A process for producing an ERW tube having welds which have been improved in toughness without adversely affecting the toughness of the parent metal of the tube is disclosed. The process comprises forming a continuous low alloy steel strip into a tubular shape through a series of forming rolls, continuously carrying out electrical resistance welding of a seam which is formed from the opposite side edges of the hoop and which extends in the longitudinal direction to produce an electrical resistance welded tube, heating the welds of the thus obtained electrical seam welded tube to a temperature not lower than the Ac3 point, then cooling the heated welds at cooling rate of 15 DEG -30 DEG C./sec for at least between 800 DEG C. and the Ar1 point, and tempering the thus cooled welds of the tube at a temperature of 450 DEG -800 DEG C.