低碳微合金钢焊接热影响区软化机制分析

Softening mechanism analysis of welding heat affected zone of low carbon microalloyed steel

通过电子背散射衍射(EBSD)技术和透射电镜(TEM)等研究了低碳微合金钢经3种成熟的焊接工艺(打底焊、间隙焊和连续焊)焊接后的焊接接头热影响区软化区的本质及软化机理。结果表明:低碳微合金钢卷板经制管过程后亚晶界比例及位错密度显著提升,呈现典型的加工硬化效应,并伴随一定程度的细晶强化、固溶强化和第二相粒子强化。经3种焊接工艺后,再结晶晶粒比例增加,高应变区域减少,软化区的小角度晶界明显减小,位错密度下降。低碳微合金钢油管焊接软化区的形成机制主要是部分组织在焊接热循环的作用下,受形变的强化组织发生回复与部分再结晶,从强化机制角度看,具体表现为应变强化和细晶强化效应降低。

The softening mechanism of heat affected zone(HAZ)of low carbon microalloyed steel tube welded by three kinds of welding processes(backing welding,spacer welding and continuous welding)were studied by means of electron backscattered diffraction(EBSD)technique and transmission electron microscopy(TEM).The results show that the fraction of sub-grain boundaries and dislocation density of the low carbon microalloyed steel coil sheet after tube-making are increased remarkably,which shows typical work hardening effect,accompanied by fine grain strengthening,solid solution strengthening and second phase particle strengthening.After three welding processes,the recrystallization grain fraction increases,the high strain region decreases,and the low angle grain boundary and the dislocation density in the softening region decreases obviously.The formation mechanism of weld softening zone of the low carbon microalloyed steel is mainly due to the recovery and partial recrystallization of the deformed strengthened microstructure under the influence of welding thermal cycling.From the perspective of strengthening mechanism,the effect of strain strengthening and fine grain strengthening is reduced.