采用Gleeble-3800型热模拟试验机对X120管线钢进行了焊接热模拟试验，研究了不同焊接热输入下X120管线钢焊接接头粗晶热影响区（CGHAZ）的显微组织和冲击韧性。结果表明：热输入为10 kJ·cm^-1时，粗晶热影响区组织主要由贝氏体和少量低碳马氏体组成，晶粒间的晶界为小角度晶界；热输入为20 kJ·cm^-1时，粗晶热影响区的组织由细小的板条贝氏体组成，板条束间为大角晶界；随着热输入的进一步增加，粗晶热影响区的组织主要为粗大的贝氏体，大角度晶界的占比降低；当热输入由10 kJ·cm^-1增加到40 kJ·cm^-1时，粗晶热影响区的冲击韧性先增后降，当热输入为20 kJ·cm^-1时，冲击韧性最好，断裂方式为韧性断裂；热输入为30 kJ·cm^-1时，断裂方式为脆性解理断裂和韧性断裂共存的混合断裂；热输入为10，40 kJ·cm^-1时，断裂方式为脆性解理断裂。

The welding thermal simulation tests of X120 pipeline steel were conducted with a Gleeble-3800 type thermal simulator, and the microstructure and impact toughness of the coarse grain heat-affected zone (CGHAZ) of welded joint of X120 pipeline steel under different heat input conditions were investigated. The results show that when the heat input was 10 kJ·cm^-1, the microstructure of CGHAZ was mainly composed of bainite and a small amount of low-carbon martensite with small-angle grain boundaries. As the heat input was 20 kJ·cm^-1, the microstructure of CGHAZ consisted of fine lath bainite with large-angle grain boundaries. With the increase of heat input, the microstructure of CGHAZ was composed of coarse bainite and the proportion of large-angle grain boundaries decreased. The impact toughness of CGHAZ increased first and then decreased with the heat input increasing from 10 kJ·cm^-1 to 40 kJ·cm^-1. When the heat input was 20 kJ·cm^-1, the impact toughness was the best and the fracture mode was ductile fracture. The combination fracture with ductile fracture and brittle cleavage fracture occurred when the heat input was 30 kJ·cm^-1 and the brittle cleavage fracture occurred when the heat input was 10, 40 kJ·cm^-1.