Microstructure, microhardness, composition, and corrosive properties of stainless steel 304 I. Laser surface alloying with silicon by beam-oscillating method.

Abstract.

Laser surface alloying (LSA) with silicon was conducted on austenitic stainless steel 304. Silicon slurry composed of silicon particle of 5 μm in average diameter was made and a uniform layer was supplied on the substrate stainless steel. The surface was melted with beam-oscillated carbon dioxide laser and then LSA layers of 0.4–1.2 mm in thickness were obtained. When an impinged energy density was adjusted to be equal to or lower than 100 W mm⁻², LSA layers retained rapidly solidified microstructure with dispersed cracks. In these samples, Fe₃Si was detected and the concentration of Si in LSA layer was estimated to be 10.5 wt.% maximum. When the energy density was equal to or greater than 147 W mm⁻², cellular grained structure with no crack was formed. No iron silicate was observed and alpha iron content in LSA layers increased. Si concentration within LSA layers was estimated to be 5 to 9 wt.% on average. Crack-free as-deposited samples exhibited no distinct corrosion resistance. The segregation of Si was confirmed along the grain boundaries and inside the grains. The microstructure of these samples changed with solution-annealing and the corrosion resistance was fairly improved with the time period of solution-annealing.