Effect of Welding Heat Input on Toughness of Coarse-grained Zone of X80 Pipeline Steel and Inside Weld in Welded Pipe

The effects of welding heat input on toughness and microstructure characteristics of coarse-grained heat-affected zone(CGHAZ) in X80 grade pipeline steel and inside weld in welded pipe were investigated by welding thermal simulation technology,microscopic analysis method and mechanical property testing.The results show that with the increase of welding heat input,the toughness distribution of CGHAZ of X80 pipeline steel base metal and inside weld in welded pipe is different.For the steel,when the heat input is 10～20 kJ/cm,CGHAZ get the best toughness and toughness values remain the same level with the base metal.When the welding heat input is greater than 20 kJ/cm,the toughness presents downward trend;when the welding heat input is greater than 35 kJ/cm,the toughness drops sharply.But for the inside weld in welded pipe,when the welding heat input is 17～35 kJ/cm,inside weld CGHAZ can get the best toughness level;when the welding heat input is less than 17 kJ/cm or greater than 35 kJ/cm,the toughness levels of X80 inside weld CGHAZ entirely decline.