A newly developed 18Ni based maraging steel without Ti and Al was welded and then subjected to a thermo-mechanical treatment.Microstructure evolution and property change during the welding,high temperature annealing,rolling,recrystallization heat treatment and aging processes were characterized,and the effects of thermo-mechanical treatment on the microstructure,phase and mechanical properties of the welding seam were analyzed.The results show that the initial welding seam includes melting zone,transition zone and heat affected zone,which is significantly different from the matrix,but the phase is basically martensite.After high temperature annealing at 1050 ℃,72.7％cold rolling and recrystallization annealing at 900 ℃,the difference in microstructure between the welding seam and the matrix gradually disappears.After recrystallization,the microstructure,phase,microhardness,tensile strength,elongation and other properties of the welding seam tend to be consistent with the matrix.There is no strain concentration or fracture at the welding seam under tensile loading.The strength of the welding seam after aging at 450 ℃ is close to 2 GPa,which indicates that the difference in microstructure between the welding seam and the matrix of the novel maraging steel can be eliminated by proper thermo-mechanical treatment.
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