抗大变形管线钢焊接粗晶区的组织和韧性

Microstructure and Toughness of Heat-affected Zone of Weld Joint for Pipeline Steels with High Deformability

采用Gleeble-3800模拟研究了抗大变形管线钢中不同Nb含量和不同热输入时的焊接热循环过程,并通过光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)及冲击载荷试验等研究了抗大变形管线钢焊接粗晶区(CGHAZ)的微观组织特征和冲击韧性。结果表明:随着热输入量的增加显微组织逐渐从板条贝氏体到粒状贝氏体过渡,M/A尺寸增大,比例提高,同时显微组织的平均有效晶粒尺寸也增大;在热输入相同的条件下,高Nb钢中原始奥氏体细化明显,组织中M/A尺寸细小,分布更加弥散;随着焊接热输入量的增加实验钢的冲击韧性急剧降低,高Nb钢的韧性急剧降低的热输入临界值约为35 k J/cm,低Nb钢韧性降低的热输入临界值约为25 k J/cm,在整个实验参数范围内,高Nb钢的冲击韧性值明显比低Nb实验钢的高。

Welding thermal cycle process of test steels containing different Nb was investigated under different heat inputs with a Gleeble-3800 thermo-mechanical simulator.The microstructural characteristics of the coarse-grained heat-affected zone（CGHAZ） were observed by using optical microscope（OM）,scanning electron microscope（SEM） and electron backscatter diffraction（EBSD）,while their impact toughness was tested.The results indicate that with the increasing heat input,lath bainite transformed gradually into granular bainite,and the size and proportion of M/A islands increased,while the average grain size also increased.Under the same heat input,austenite in high Nb steel was refined obviously,with more dispersive and refined M/A islands distributed in the microstructure of high Nb steel,and the proportion of high angle boundaries was high.With the increasing heat input,the impact toughness of steels decreased sharply.The critical heat input value for a sharp decrease in impact toughness were approximately 35 k J/cm for high Nb steel and 25 k J/cm for low Nb steel.However,the impact toughness of the high Nb steel was significantly higher than that of the lower Nb steel in the range of experimental parameters.