DEVELOPMENT OF MICROSTRUCTURE IN LASER SURFACE ALLOYING OF STEEL WITH CHROMIUM

Laser surface alloying (LSA) was used to form in situ Fe-Cr-C alloys on AISI 1018 steel substrates. Chromium powders of different particle sizes were mixed together to obtain optimum packing density of the powder deposited on the substrate. The surface was then melted using a 2kW CW carbon dioxide laser. The processing conditions were related to solute (chromium) content, microstructural refinement of the laser alloyed zone and the heat affected zone (HAZ). The microstructure of the laser surface alloyed region was investigated by optical, scanning and transmission electron microscopy, and X-ray microanalysis techniques. Microstructural study showed a high degree of grain refinement and an increase in solid solubility of alloying element. This process produced a fine distribution of complex type of carbide precipitate in the martensite-ferrite matrix because of the high cooling rate. An alloy of this composition does not show any retained phase. The nature of alloying and chemical diffusion profile as a function of intertrack separation distance affects the final content of alloying element in the surface layer. © 1990 Chapman and Hall Ltd.