Structure, Mechanical Properties and Features of Crack Growth Micromechanism of Maraging Steel Obtained by Hybrid Additive CMT Surfacing

The effect of heat treatment (quenching and aging) on the structure and mechanical characteristics of maraging steel Cr12Ni9Mo2Si (EP659A) obtained using a hybrid CMT surfacing technology consisting in multilayer cold metal transfer and layer-by-layer deformation hardening is investigated. Metallographic analysis of the samples is carried out using light and scanning electron microscopes. The local elemental composition of the surfacing is determined. Tensile tests at 20°C and impact tests at 20 and –100°C are performed. The micromechanisms of crack growth and their special features are investigated. The effect of structural segregation of the material during the CMT with deformation without heat treatment is detected. It is shown that the structural segregation in the surfaced layer disappears after the heat treatment; the strength characteristics and the impact toughness increase, and the elongation decreases slightly. The micromechanism of crack growth after the surfacing followed by heat treatment changes from a mixed viscous-quasi-brittle one to a viscous one. To obtain a set of high mechanical characteristics at room and negative temperatures in the material synthesized by CMT surfacing with interlayer forging, it is recommended to carry out a heat treatment involving water quenching from 940°C for 45 min and aging at 520°C for 240 min.