Direct laser deposition as repair technology for a low transformation temperature alloy: Microstructure, residual stress, and properties

Fe-Cr-Ni-Mn-Mo-Nb-Si steel with low transformation temperature was fabricated by direct laser deposition (DLD) and its microstructure, residual stress and properties were investigated. The results demonstrated that the microstructure consisted of martensite laths with a lath spacing in the nano-scale range and a small amount of nano-sized polycrystalline precipitates. There was no grain boundary segregation, and the chemical elements were homogeneously distributed. The tensile strength, yielding strength, elongation and impact energy were 1275 MPa, 1032 MPa, 12% and 57 J respectively. The comprehensive mechanical properties were equivalent with those of the wrought precipitation hardening martensitic stainless steel. There was no Cr-depleted zone at the interface between the matrix and the precipitates as well as the interior at the precipitates, and the corrosion resistance was better than that of FV520B stainless steel. The neutron diffraction (ND) stress analysis results showed that the residual tensile stress level in the cladding layer was relatively low due to the effect of solid phase transition. Consequently, due to the excellent integrated mechanical properties and the residual stress state, there was no need to conduct stress relief and precipitation hardening heat treatment, thus avoiding the influence of heat treatment on the base material properties, and saving resources and funds.