Design of steady-state magnetic field and effect of current intensity on microstructure of Fe55 alloy coating by laser cladding

Using self-designed steady-state magnetic field device, combined with laser cladding process, by adjusting current intensity to obtain corresponding steady-state magnetic field and put the magnetic field on laser molten pool, Fe55 alloy coatings was fabricated on 45 substrate steel surface. The microstructure, chemical composition and phase characteristics of the cladding coatings were characterized by scanning electron microscope(SEM), energy disperse spectroscopy(EDS) and X-ray diffraction (XRD). The results show that Fe55 alloy coating is mainly composed of -(Fe, Cr) solid solution, (Fe, Ni) solid solution, (Cr, Fe)23C6 carbide and a small amount of Cr9.1Si0.9. The interdendritic Cr element content in laser cladding Fe55 alloy coating with steady-state magnetic field is higher than that of the laser cladding without magnetic field, and dendrite internal Fe element content also increased. To a certain extent, the steady-state magnetic field can promote the mass transfer process in laser melten pool, which is beneficial to the diffusion of Fe, Cr elements and the formation of (Fe, Cr) solid solution. When the current intensity is 4.0 A, steady-state magnetic field greatly reduces the temperature gradient of solid-liquid interface in laser molten pool, and increases the nucleation rate in liquid metal molten pool. A large number of columnar dendrites and dendritic crystals are changed into directions different equiaxed grains in coating, and the microstructure of Fe55 alloy coating has been significantly optimized.