Influence of Inclusions on Strength and Toughness of X70 Pipeline Steel Girth Weld

Abstract

In this paper, SEM, EPMA, and micro shear experimental method were applied to analyse the structure, inclusion morphology and composition, micro-area strength and toughness of the X70 pipeline steel girth weld joint. The results show that inclusions are mainly nonmetallic oxides, sulfides and calcium compounds. The length of inclusions can be up to 1mm, which have substantially reduced the strength and toughness of weld joint. By the combining effect of internal and external force, cracks tend to initiate around inclusions and propagate along the direction of inclusions, and finally reduce the impact toughness of girth weld.