Abstract: The effect of welding current 70A, 80A, 90A on the microstructure and mechanical properties of steel 40CrNiMoA weld joint is investigated. With the increase of welding current, the appearance quality of the welding seam is better. With the increase of welding current, the temperature of molten pool and the austenite grain size increase, which lead to coarsening of martensite. The microstructure of the weld is martensite and very small amount of residual austenite. The hardness of welding seam is much higher than that of base metal, and the hardness fluctuates greatly. The hardness of the heat affected zone (HAZ) increases gradually from base metal to weld metal. The longitudinal stress at weld center is compressive, while the external compressive stress gradually decreases. The longitudinal stress at the boundary of welding color zone is tensile stress, and the maximum tensile stress is found at this point. The transverse stress of weld center is tensile stress, and it gradually increase outward. The maximum transverse tensile stress is obtained at the boundary of welding color zone, and with increasing the welding current and heat input, the toughness of the material reduces, the ferrite in the structure increases, and the welding residual stress is the cause of brittle fracture. The optimum welding current intensity of 40CrNiMoA homogeneous electrode plate butt welding process is 80 A.

Key words: Steel 40CrNiMoA, Welded Joint, Microstructure, Properties ,

摘要： 分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。