Surface modification of Q550 HSLA steel with Co–Fe–Cr composite coatings manufactured by fibre laser cladding

The surface of Q550 steel was modified with Co–Fe–Cr/WC composite coatings deposited by fibre laser cladding. Coating microstructure, elemental distribution, phase constitution and microhardness were investigated. Results showed that the composite coating was mainly composed of dendrites and eutectic lamellar of carbides. Phases of composite coatings were comprised of Co3Fe7, Fe–Cr, CFe15.1, Cr7C3, and M6C (M represents for W, Co and Fe). Owing to the dilution of base metal, large amount of Fe was transformed into molten pool. Martensite laths were easily formed at the front of fusion line due to the rapid solidification process in laser cladding. Plenty of M6C carbides were synthesised by in-situ reactions between W, Co, Fe and C. Carbides were prone to form eutectic lamellar with growth directions perpendicular to each other. The microhardness of coatings added with wt.50% WC was significantly increased to 668HV0.1, which was about 2.4 times that of Q550 steel.