Laser surface alloying of type 304 stainless steel for enhanced corrosion resistance

For imparting localised corrosion resistance to AISI type 304 stainless steel, its surface alloying with chromium, nickel and molybdenum has been studied using a carbon dioxide laser. Effect of laser processing parameters, such as, scan speed, power and spot size was studied. Microstructural characterization of the alloyed surfaces was carried out using optical and scanning electron microscopy and localised corrosion susceptibility was studied using steady state corrosion potential vs time as well as by carrying out potentiodynamic polarisation, in aqueous chloride media. Analysis of the alloyed zone has revealed austenitic phase, with fine cellular dendritic micro-structure and good compositional homogeneity. Various surface alloys with molybdenum content ranging from 3 to 12 weight percent were obtained. Among these, the one containing 11 wt% molybdenum, exhibited enhanced passivity and possessed the best compositional homogeneity.