热输入对X120管线钢焊接接头粗晶热影响区组织和冲击韧性的影响

Effect of Heat Input on Microstructure and Impact Toughness of Coarse Grain Heat Affected Zone of Welded Joint of X120 Pipeline Steel

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10kJ·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20kJ·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10kJ·cm^(-1)增加到40kJ·cm^(-1)时,粗晶热影响区的冲击韧性先增后降,当热输入为20kJ·cm^(-1)时,冲击韧性最好,断裂方式为韧性断裂;热输入为30kJ·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10,40kJ·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.