Surface Melting of Cast Iron: Laser Parameters, Processing Conditions, Surface Morphology

Laser surface melting (LSM) of an alloy cast iron containing undercooled speroidal graphite was investigated using high power CO₂-lasers by variation of laser power, beam distribution, beam diameter, and traverse speed resulting in different power densities, interaction times, and heating times in order to achieve different heating and cooling rates and case dephts. In supplement to experimental results reported recently /1,2/ the investigations were performed either in the melting mode of processing without plasma formation or in the plasma mode of processing with plasma formation in the near surface region changing simultaneously the composition and the flow characteristics of the shielding gas. The resulting improvements in finish and cracking of overlapping melt tracks covering substantial surface areas relates processing conditions, solute content, microstructural refinement of the laser melted and heat affected zone, and resultant metallurgical and mechanical properties. The approach facilitates the selection of processing conditions to obtain reproducibly the compositions, microstructures and surface roughness necessary for gainful utilization of laser surface melt cast iron without additional machining.