Study on Microstructure and Properties of CGHAZ of X100 Pipeline Steel Using Thermal Simulation Technique

The microstructure and impact toughness of coarse-grained heat affected zone（CGHAZ） in X100 pipeline steel were studied by thermal simulation technique.The results indicate that when the cooling time t8/5is 5-21 s, the CGHAZ has small grain size, and bainitic ferrite lathes in the grains ensure that the CGHAZ has good impact toughness. When the cooling time t8/5is 32-130 s, the grain size increases and quasi-polygonal ferrite and large size M-A islands appear in the grains, therefore the impact toughness of CGHAZ decreases sharply.