Effect of processing parameters of laser on microstructure and properties of cladding 42CrMo steel

Due to the abrasion of sprocket wheel socket and high cost, the failure 42CrMo steel is remanufactured using the laser cladding technology with paraxial powder feed. The remanufacturing was carried out through an 8-kW CO2 laser device with rectangular spot of 3 x 24 mm and the self-developed Fe-based powder. The effect of processing parameters on macromorphology, microstructure, and microhardness of cladding layer and heat-affected zone (HAZ) was investigated. The results showed that the quality of cladding layer is improved with the increase of laser energy density (P/A). Under the same energy density, the quality of cladding layer is superior when decreasing the scanning speed. The microhardness of heat-affected zone which is 1.5-2.5 mm in width ranges from 210 to 450 HV. The HAZ is composed of completely quenched zone, incompletely quenched zone, and tempered zone. The microhardness of cladding layer which is approximately 1.8 mm in thickness is between 210 and 450 HV and is double even tripled as substrates. From the fusion line to surface, the microstructure of cladding layer is plane crystal, cellular crystal, and dendrite crystal, in turn. With the increase of laser energy density, the microhardness of HAZ and cladding layer increases; meanwhile, the width of HAZ shows a fluctuant rising trend. The microhardness of coatings was improved on account of the martensite, fine grains, solid solution, and precipitated phases. Especially, the latter two are decisive factors under the higher laser energy.