Effect of Cooling Time Following Welding on Microstructure of Welding Coarse Grain Heat Affected Zone of X80 High-Strain Pipeline Steel

The effect of cooling time following welding (t8/5)on welding coarse grain heat affected zone(CGHAZ) microstructure of X80 high-strain pipeline steel was studied by Gleeble-3500 thermo-mechanical simulator. The results show that ferrite and a small quantity of pearlite were obtained in CGHAZ microstructure when t8/5 was more than 1 000 s, the CGHAZ microstructure was mainly composed of granular bainite when t8/5 was 300-60 s, the CGHAZ microstructure mainly comprised of lath bainite when t8/5 was 15 s, and martensite appeared in CGHAZ primarily when t8/5was smaller than 3 s.