Influence of shielding gas composition on the residual stresses of DP600 steel joints welded by GMAW process

ABSTRACT The automotive industry has been investing in new manufacturing processes that improve productivity without loss of quality. However, the presence of residual stress (RS), generated in all manufacturing processes, is one of the major problems encountered in the metalworking industry, since these can add up to external loading stresses and cause catastrophic failures in equipment and components. Since welding is one of the most widely used manufacturing processes, it is necessary to know how the welding parameters impact on the nature and magnitude of the residual stresses generated. The shielding gases are used in some welding processes and can be influence the conductivity of the electric arc, which can be affected the residual stresses behavior in the welded joints. In this work an experimental study was carried out about the influence of the percentage of CO2 on the argon-based shielding gases in the residual stresses generated on joints of high strength steel DP600 welded by GMAW process (widely used in the automotive industry). The residual stresses were measured by X-ray diffraction by the sin2ψ method. An assessment of the microstructural morphology by optical microscope (OM) was made. The results showed that the residual stresses have a tensile nature, of the order of 120 MPa, in all samples, which used shielding gas with a lower percentage of CO2.

摘要
汽车制造业一直致力于研发既能提升生产效率又不降低产品质量的新型制造工艺。然而，所有制造过程中都会产生残余应力（Residual Stress, RS），这是金属加工行业面临的主要难题之一：残余应力会与外部加载应力叠加，最终引发设备与构件的灾难性失效。由于焊接是应用最为广泛的制造工艺之一，因此有必要明确焊接参数对所产生残余应力的性质与大小的影响机制。部分焊接工艺会使用保护气，而保护气会影响电弧的导电性，进而改变焊接接头的残余应力特性。本研究针对汽车工业广泛应用的气体金属电弧焊（Gas Metal Arc Welding, GMAW）工艺焊接的高强度钢DP600接头，开展了基于氩基保护气中CO₂占比对残余应力影响的实验研究。采用X射线衍射法结合sin²ψ法对残余应力进行了测量。借助光学显微镜（Optical Microscope, OM）对接头的微观组织形貌进行了表征分析。结果表明，所有使用低CO₂占比保护气的试样，其残余应力均为拉应力，量级约为120 MPa。