Laser surface alloying of AISI 304-stainless steel with molybdenum for improvement in pitting and erosion-corrosion resistance

Abstract

The present study concerns laser surface alloying (LSA) of AISI 304 stainless steel (304-SS) with predeposited Mo (by plasma spraying) to enhance pitting and erosion-corrosion resistance of the substrate. A parametric correlation between the alloyed zone (AZ) depth (w) vis-a-vis incident laser power density (Q) and linear scanning speed (υ) indicates that w is directly related to Q but varies inversely with υ. Both microstructure and chemistry of the AZ are strong functions of the LSA parameters. LSA seems to improve the microhardness level in the AZ by 2-3 times that of the substrate. The optimum LSA conditions in terms of predeposit thickness, Q and υ have been identified to achieve the desired microstructure, composition and mechanical properties. LSA under such optimum conditions significantly improves the pitting corrosion resistance in terms of critical potential for pit formation (E(PP1)) and pit growth (E(PP2)). In addition, the erosion-corrosion resistance in 20 wt.% sand in 3.56 wt.% NaCl solution registers a marked improvement. Thus, it is concluded that LSA of 304-SS with Mo is an appropriate technique to enhance the resistance to pitting and erosion-corrosion in stainless steel.