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.