Microstructure characteristics and mechanical properties of a laser cladded Fe-based martensitic stainless steel coating

Abstract

In the present work, a Fe-based alloy (Fe60) coating was fabricated by laser cladding (LC) process. Heat treatment was conducted by heating the LC coating to 1050 °C by 30 °C/min, holding for 30 min and cooling in air. Microstructure characteristics of the coatings before and after heat treatment were studied using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and electron backscatter diffraction detector (EBSD). Micro-hardness, tensile strength of the coatings before and after heat treatment were also acquired. Before heat treatment, the LC coating was composed of martensite dendrite matrix with a small number of ferrite and retained austenite grains and a large number of fine carbides (Fe3C, M7C3 and M23C6) that are rich in Cr element in inter-dendritic area. After heat treatment, the martensite dendrite matrix was retained and a large number of new carbide particles precipitated in martensite dendrites, while the size and Cr content of inter-dendrite carbide particles increased. Micro-hardness of the coating decreased from 800 HV1 to 650 HV1 due to the release of residual stress and carbon atoms in the BCC structure lattice, elimination of high density defaults. However, ultimate tensile strength of the coating increased from 450 MPa to 550 MPa due to the precipitate hardening effect of new precipitated carbide particles in dendrites. The tear and cleavage appearance of the fractures proved that the fractures are quasi-cleavage fracture.