Study On Welding Thermal Susceptibility For X80 Pipeline Steel

In this paper, the microstructure characteristic, toughness and fractograph of X80 pipeline steel HAZ was studied by using welding thermal simulation technique, Charpy impact test, microscope and SEM, with the different thermal cycles. The results are as follows, the toughness of the CGHAZ is all bad and the rigidity is better when the peak temperature of the X80 pipeline steel is 1300℃.The coarse-grained brittle and coarse M-A are the principal reasons of bad toughness, fractograph is quasi-cleavage crack. When the peak temperature is 800℃, CGHAZ generates some slender lath ferrite and Bainite, which makes the toughness larger, and the hardness less.In the multi-pass welding, when the first top temperature is 1300℃and the second top temperature is 800℃, it is found the local brittle zone of inter-critically reheated coarse-grained HAZ(IRCGHAZ).The reasons are the formation of massive ferrite, long-chain M-A is generated in crystal boundary, and the coarse austenite is remained by single peak temperature action, the impact energy value is 71J, fractograph is cleavage fracture. When the top temperature is placed in the other trial temperature, the toughness of IRCGHAZ is improved. After the effects of peak temperature 800℃and then that of the second peak temperature of 1300℃, the impact toughness is low far from that of the base metal's. The coarse crystal zone is embrittled seriously and the fracture is cleavage.On the base of deposit welding experiment, the best welding parameters of handwork arc welding are recommended.