Temperature field simulation and microstructure evolution of Fe-based coating processed by extreme high-speed laser cladding for re-manufacturing locomotive axle

With the rapid development of Chinese railway network in the last decade, the number of scrapped locomotive axles is increasing year by year due to various damages. Re-manufacturing is an effective way to save resources and reduce carbon footprint for developing an environmental-friendly society. In the present work, Fe-based alloy powder was deposited on the surface of a 25CrMo4 steel using extreme high-speed laser cladding (EHLA). The optimum processing parameters were determined through range analysis, and the thermal effect to the substrate was studied by numerical simulation. The depth of heated-affected zone (HAZ) was obtained by both experimental method and numerical simulation approach, and the results showed good agreement. The microstructure evolution, phase composition, and mechanical properties of the cladding layer were investigated systematically. The cladding layer was mainly consisted of austenite, ferrite, and carbides. The microstructure evolution exhibited a gradient variation from the interface to the top of cladding layer, which was similar to conventional laser cladding (CLA). Furthermore, the quenching effect to the substrate changed the microstruc- ture from sorbite to martensite, leading to the formation of hardening layer beneath the cladding layer. The cladded sample exhibited higher tensile strength but lower elongation compared with 25CrMo4 substrate, which was detrimental to the service life of locomotive axles.