超细晶粒钢普通CO2气体保护焊HAZ晶粒长大行为研究

研究了400MPa级超细晶粒钢普通CO2气体保护焊HAZ晶粒长大行为，并对晶粒长大的影响因素进行了分析．结果表明：过热区内晶粒明显长大，并随着热输入量的增加，晶粒粗化程度加重，热影响区总宽度变宽．超细晶粒钢细小的晶粒尺寸使其在受热时晶粒长大驱动力增大，但焊接时热影响区内的温度梯度将对奥氏体晶粒长大产生热钉扎效应，有利于减小晶粒长大的趋势；CO2气体分解时吸热，在焊接过程中能起到冷却作用。也减弱了HAZ晶粒长大趋势．实验条件下，对于400Mpa级超细晶粒钢，采用1．68～2．8kJ／cm线能量的普通CO2气体保护焊，HAZ晶粒虽有长大行为但程度并不严重，证明400MPa级超细晶粒钢具有良好的焊接性，细丝、中小线能量的普通CO2气体保护焊适用于400MPa级超细晶粒钢的焊接．

Research on HAZ Grain Growth Behavior of Ultra-fine Grain Steel under General CO2 Gas Protection Welding

The grain growth behavior of 400MPa ultra-fine grain steel under general CO2 gas protection welding has been researched and the influencing factors of grain growth have been analyzed. The result showed that the grain growth of overheated zone was obvious. With the increase of heal input, the degree of grain coarsening was worsened and the width of HAZ was wider. The grain size of ultra-fine grain steel was small that resulted in the increase of driving force of grain growth when it was heated. But the temperature gradient of HAZ had thermal pinning effect for grain growth of austenite and was beneficial to reduce the tendency of grain growth. Endothermic decomposition of CO2 could play a role in cooling that reduced the tendency of grain growth too. When 400 MPa uhra fine grain steel was welded by general CO2 gas protection welding with 1.68--2.8 kJ/cm line energy under experimental condition; the grain of HAZ had growth behavior but the degree was not serious. It is proved that the 400 MPa ultra-fine grain steel had good welding properties; and fine wire and medium-small line energy general CO2 gas protection welding was suitable for the welding of 400MPa ultra-fine grain steel.