Pulsed laser surface melting of AISI H13 steel and investigating the effect of TiC powder particle size and concentration on the morphology of MC carbides in the composite coating

In this research, the microstructure of the pulsed laser surface melted AISI H13 tool steel was studied. Then, by laser surface alloying with TiC powder, the effect of particle size and powder concentration on superficial composite microstructure was investigated. For this purpose, TiC powders with particle sizes of 1 micrometer and 45 micrometers in layers of different thicknesses were pre-placed on the surface of H13 steel and then subjected to pulsed laser operation. The results showed that in the surface melting, an intermittent cell/dendritic structure developed from the depth to the surface of the molten pool with a higher concentration of alloying elements in the boundary network. With the selected laser parameters, the cooling rate was estimated at one million K/s. In the surface alloying process, the preplaced TiC particles were completely (fine powders) or a partially (coarse powders) dissolved in the melt pool. During subsequent cooling, TiC-type MC carbides precipitated from the melt. Increasing the thickness of the preplaced layer caused the morphology of carbides to be more diverse. The size of precipitated MC carbides was reduced by decreasing the concentration of TiC powder in the melt pool and increasing the particle size of preplaced TiC powder. As the number of MC carbides increased, the cellular/dendritic structures of the steel matrix replaced by coaxial grains.