焊接热循环对ASTM4130钢热影响区组织及韧性影响

Effect of welding thermal cycle on microstructure and toughness of heat-affected zone of ASTM4130 steel

采用金相、扫描电镜(SEM)和焊接热模拟方法,研究了不同峰值温度和焊接线能量对ASTM4130钢焊接热影响区(HAZ)显微组织、冲击韧性和断口形貌的影响。结果表明,ASTM4130钢热影响区除回火软化区外均发生脆化现象。当峰值温度为1200℃和1350℃时,由于晶粒粗大,且产生了贝氏体、未回火马氏体和M-A组元等非平衡组织,其冲击韧性损失达母材的94.5%,脆化现象最严重。当峰值温度为950℃,冲击韧性较低的原因是该区产生了未回火马氏体和块状铁素体。当峰值温度为800℃时,晶界附近碳化物聚集和不均匀分布,以及块状铁素体的存在,造成该区发生脆化。焊态下焊接线能量对ASTM4130钢粗晶区的冲击韧性影响较小。

Effects of peak temperature and welding heat input on microstructure,impact toughness and fracture morphology of the heat-affected zone（HAZ） of ASTM4130 steel were investigated by using OM,SEM and welding thermal simulation test.The HAZ was divided into coarse-grained（CG）,fine-grained（FG）,inter-critical（IC）,and subcritical（SC） HAZ depending on peak temperature.The results show that impact toughness of the HAZ decreases remarkably except the subcritical HAZ（SCHAZ）.When the peak temperature is 1200 ℃ and 1350 ℃,the impact toughness of the HAZ is only 5.5% of the substrate due to its large prior austenite grain size and formation of non-equilibrium microstructure such as bainite,untempered martensite and M-A constituents.At peak temperature of 950 ℃,the impact toughness decreases due to the generation of untempered martensite and blocky ferrite in the HAZ.The embrittlement of the HAZ also occurs when the peak temperature is 800 ℃.This is attributed to the aggregation and uneven distribution of carbides along grain boundaries and the existence of blocky ferrite.The welding heat input has little influence on impact toughness in the CGHAZ of ASTM4130 steel.