不同焊接工艺下FB780钢焊接接头热影响区的显微组织和冲击韧性

用Gleeble-3500型热模拟试验机模拟单道次焊接条件下FB780钢焊接接头热影响区(HAZ)的热循环过程,研究了在不同焊接峰值温度及不同t8/5(由800℃冷却到500℃的时间)下HAZ的显微组织,并测试了不同焊接条件下HAZ的显微硬度和冲击韧性。结果表明:在t8/5相同的条件下,随着峰值温度的升高,HAZ组织粗化;当峰值温度一定时,随着t8/5的增加,铁素体板条变宽并逐渐融合,M/A组元粗化,粗大铁素体晶粒与细小准多边形铁素体晶粒混合,组织的均匀性恶化;在相同的峰值温度条件下,HAZ的硬度和冲击功均随着t8/5的增加而降低;在峰值温度为1 175℃,t8/5为6s条件下,HAZ的低温(-20℃)冲击断口形貌为韧窝花样,韧窝尺寸较大,HAZ的低温韧性与母材的相匹配,同时硬度较高,该工艺为最佳的单道次焊接工艺。

Microstructure and Impact Toughness of Heat Affected Zone of FB780 Steel Welded Joint with Different Welding Processes

The thermal cycle process of the heat affected zone(HAZ)of FB780 steel welded joint under single pass welding condition was simulated by the Gleeble-3500 thermomechanical simulator.The microstructures of HAZ at different welding peak temperatures and for different t8/5times(cooling time from 800 ℃ to 500 ℃)were studied,and the micro-hardness and impact toughness of HAZ under different welding conditions were tested.The results show that when the t8/5 was the same,the microstructure of HAZ coarsened with the increase of peak temperature.When the peak temperature was constant,with the increase of t8/5,the ferrite lath widened and gradually intergrated;the M/A component coarsened;the coarse ferrite grains were mixed with the fine quasipolygonal ferrite grains;the metallographic homogeneity deteriorated.At the same peak temperature,the hardness and impact energy of HAZ decreased with the increase of t8/5.At the peak temperature of 1 175℃and t8/5of 6s,the impact fracture morphology of HAZ at low temperature(-20℃)showed dimple pattern,and the dimple was relatively large;the toughness of HAZ at low temperature matched with that of the base metal;the hardness was relatively high;all indicated that the process was the best single pass welding process.