Toughness Scatter About FCAW-S Girth Weld for X80 Pipeline Steel

The toughness scatter about Flux-Cored Arc Welding Self for X80 pipeline steel was investigated to explore the reason that causes toughness scatter, and how to improve the toughness scatter. The type of the metallography, the volume fraction and the pattern distribution of M/A constituents, and the effects of them to the weld toughness were studied by weld thermal-cycle curves measurement, thermal simulation experiments, Charpy Impact Test, optical microscope observation and SEM. The results showed that the toughness scatter was observed in temperature region of A(c1)-A(c3), MA constituent directly related to the charpy impact toughness, toughness decreased with increasing of the volume fraction of MA constituent. It is considered that bacilliform MA is the main reason that cause toughness scatter, bulk MA is another reason that cause low toughness.