Continuous wave Nd:YAG laser cladding of stellite 6 multi-track layers on mild and AISI 4016 steel

The level of sliding friction between the mating top centre and centre bowl liner components of a rail freight truck centre bearing provides both positive and negative effects on rail vehicle dynamics. Currently used centre bearing surfaces include AISI 1053 steel top centres mating against unlubricated and lubricated Hadfield steel, and polyethylene centre bowl liners. The wear life of the unlubricated AISI 1053 steel top centre against Hadfield steel is short, whilst the low friction of the lubricated and polyethylene surfaces can be detrimental to vehicle dynamics. It is proposed to use laser clad Stellite 6 as one of the bearing surfaces. Stellite 6 multi-track layers were laser cladded on mild and AISI 4016 steel substrates with a continuous wave Nd:YAG laser at 1800 W laser source power using four different processing speeds: 600, 900, 1200, and 1500 mm/min, whilst the laser power, defocused laser spot size, and powder feed rate were constant. The cladding samples were characterised using optical microscopy and scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS). Microhardness profiles of the cladded layer and heat affected zone were determined. The effect of processing speed on cladded layer height, depth of penetration and dilution has been examined. The main difference between the samples clad onto the two different substrates was the microstructure and hardness of the heat affected zone. Untempered martensite was observed in the heat affected zone of the AISI 4016 steel substrate at 1500 mm/min. For both substrates the optimum processing speed is between 600 and 900 mm/min.