Abstract
CO2 laser beam was applied to the cladding of WC dispersed stellite on carbon steel using a preplaced powder method. The hardness and microstructure of the clad layer were investigated by changing the laser power and number of clad layers. The average hardness of the clad layer obtained was 600～700HV 0.1 (matrix), when the conditions were as follows : laser power of 2300W to 2900W, clad number of one layer to two layers (thickness of clad layer ; 0.80～1.60mm), cladding speed of 400mm/min, defocusing distance of 30mm, oscillation width of 7mm, and argon as the shielding gas. The microstructure of the clad layer was completely transformed into a fine dendritic structure (secondary dendrite arm spacing ; 3μm) and eutectic structure because of rapid solidification, and tungsten carbide crystals were dispersed in the matrix. A heat affected zone was produced on the surface of the carbon steel and a martensitic structure could be observed. The heat affected zone was then heat treated also with CO2 laser beam. The martensitic structure of the heat affected zone was transformed into troostite. The hardness of clad layer was unchanged with heat treatment. EPMA line analysis indicated that an alloyed layer (thickness ; 30μm) exists between the clad layer and base metal. These results show that CO2 laser beam cladding of WC dispersed stellite serves as a new surface treatment process for carbon steel.
