DESENSITISATION OF AUSTENITIC STAINLESS STEELS USING lASER SURFACE MELTING

Abstract

Sensitised types 304 and 316 stainless steels were laser surface melted using a Nd–YAG laser of 300 W power and 9 ms pulse width at a traverse speed of 2.5 mm s^–l. Pulse energy, pulse repetition rate, and gas atmosphere were varied to give 24 different laser melting conditions. The melted specimens were tested according to ASTM A262 practice A (electrolytic etch test), and ASTM A262 practice E (immersion for 24 h in boiling Cu–CuS0₄ solution followed by a Ubend test) in order to assess the intergranular corrosion (IGC) resistance. The micro hardness values across the unmelted/melted region were measured and impact tests, with sensitised subsize specimens laser surface melted at the notch, were carried out. The results indicate that on lasersurface melting the sensitised microstructure disappeared and also that the specimens possessed higher IGC resistance. This is attributed to the creation of a desensitised microstructure of 200 μm thickness with dendritic–cellular structure and a heat affected zone between the melted and unmelted regions. The increase in the micro hardness values across the unmelted/melted region and the marginal 10% increase in the energy absorbed values of laser melted impact specimens indicated that laser surface melting led to an improvement in the strength and toughness of the specimens inaddition to the improved IGC resistance.