SURFACE MODIFICATION OF FERRITIC STAINLESS-STEEL BY LASER ALLOYING

Laser surface alloying (LSA) of AISI 430 stainless steel (SS) with silicon nitride was investigated. Energy dispersive spectroscopy showed that the silicon content in the LSA layer varied with processing conditions and changed slightly with the thickness within the LSA layer. A surface alloying layer with a silicon content as high as 20 wt.% could be produced. Both Auger electron spectroscopy and wavelength dispersive spectroscopy also revealed a slight alloying of nitrogen, oxygen and carbon in the surface layer. The hardness in the LSA layer, which was found to be a strong function of silicon content, could reach as high as 1100 Hv. Potentiodynamic polarization curves obtained in neutral 3.5 wt.% NaCl solution showed that the passive region greatly expanded and the pitting initiation potential was shifted approximately 460 mV towards the noble direction for the LSA layer with 10 wt.% Si as compared with those of the 430 SS.