S355钢激光-MIG复合焊接头显微组织和残余应力

Investigation of microstructure and stress in laser-MIG hybrid welded S355 steel plates

采用激光-MIG(metal inert gas welding,MIG)复合焊接方法对12 mm厚S355钢板进行焊接,分析了9 kW激光功率下复合焊接头显微组织和硬度分布规律.建立了适合低合金高强钢激光-MIG复合焊接的双椭球+三维锥体复合热源模型来描述复合热源的能量分布,采用SYSWELD软件计算了1.0,1.5,2.0 m/min三种焊接速度下激光-MIG复合焊的温度场和接头的残余应力,分析了焊接速度对焊接过程的温度场和残余应力分布的影响.结果表明,三种焊接速度下粗晶热影响区(coarse grained heat affected zone,CGHAZ)的组织为马氏体,接头的硬度水平较高,最高硬度均在350 HV以上.焊接速度增加,熔池最高温度下降,焊后冷却速度增加.等效残余应力水平较高,HAZ位置出现了应力集中;随着焊接速度增加,等效残余应力、纵向残余应力、横向残余应力和厚度方向的残余应力峰值均上升;但焊接速度从1.5 m/min增加到2.0 m/min时,各应力分量的拉应力峰值上升较少,而压应力峰值显著上升.

12 mm thick S355 steel plates were butt welded using laser-metal inert gas(MIG)hybrid welding with 9 kW laser power.Microstructure and hardness distribution in hybrid welded joints were analyzed.A heat source model combined with upper double ellipsoid heat source and lower three dimensional conical heat source was proposed to represent the energy distribution of the combined arc-laser heat input.Sequential coupled thermal-mechanical analysis under welding speed of 1.0,1.5 and 2.0 m/min was performed using SYSWELD finite element software.Influence of welding speed on temperature field and residual stress field was investigated.Microstructure in coarse grained heat affected zone(CGHAZ)under three welding speeds mainly consists of martensite which causes maximum hardness levels above 350HV in three welded joints.Peak welding temperature decreases and postweld cooling speed increases with increasing welding speed.Level of Von Mises equivalent stress is high with stress concentration occurs in HAZ.As welding speed increases,the magnitude of Von Mises equivalent stress,longitudinal stress,transverse stress and through-thickness stress increase.However,as the welding speed was increased from 1.5 m/min to 2.0 m/min,tensile stress magnitude of the three stress components increases slightly while compressive stress magnitude of the three stress components increases remarkably.