热输入对深海X70粗晶区组织和韧性的影响

Effect of heat input on microstructure and toughness of CGHAZ of deep-sea X70

为解决深海X70管线钢在实际焊接中粗晶区(CGHAZ)的脆化问题,在不同热循环工艺下对X70管线钢进行了热模拟研究。采用Gleeble-3800热模拟机模拟X70管线钢CGHAZ,研究CGHAZ在10~60 kJ/cm不同热输入(HI)条件下组织和韧性的变化规律,并通过光学显微镜(OM)、扫描电镜(SEM)和夏比冲击试验等手段表征CGHAZ的组织和韧性。结果表明,不同热输入下试验钢的组织主要由粒状贝氏体(GB)、贝氏体铁素体(BF)和马-奥组元(M-A组元)组成;当HI不断增大时,BF比例减少,GB比例增加,M-A组元粗化,冲击吸收能先升高再降低;当HI为20 kJ/cm时,BF和GB可获得优异组合,断口为韧性断裂,冲击吸收能达到173.8 J;当HI大于20 kJ/cm时,断口解离断裂,冲击吸收能下降明显,最低为18.8 J。因此,较低的热输入可提高CGHAZ的韧性,使X70管线钢具有高强度、高韧性和良好的焊接性。研究结果可为优化焊接工艺提供理论依据。

In order to solve the embrittlement problem of coarse grain zone(CGHAZ)of deep-sea X70 pipeline steel in actual welding,the thermal simulation study of X70 pipeline steel was carried out under different thermal cycle processes.X70 pipeline steel CGHAZ was simulated by Gleeble-3800 thermal simulator to study the microstructure and toughness of CGHAZ under different heat input(HI)conditions in the range of 10~60 kJ/cm.The microstructure and toughness of CGHAZ were characterized by means of optical microscope(OM),scanning electron microscope(SEM)and Charpy impact test.The results show that the microstructure of the test steel under different heat input is mainly composed of granular bainite(GB),bainite ferrite(BF)and martensite-austenite component(M-A component).When HI increases continuously,the proportion of BF decreases,the proportion of GB increases,the M-A component coarsens,and the impact absorption energy first increases and then decreases.In the case of 20 kJ/cm,the excellent combination of BF and GB is obtained,the fracture is ductile fracture,and the impact absorption energy reaches 173.8 J;when HI is greater than 20 kJ/cm,the fracture is dissociated and fractured,and the impact absorption energy decreases obviously,with the lowest of 18.8 J.Therefore,lower heat input can improve the toughness of CGHAZ,make X70 pipeline steel have high strength,high toughness and good weldability,and provide some theoretical guidance for the optimization of welding process.