Corrosion behavior of laser and TIG welded austenitic stainless steel

ABSTRACT

The corrosion behaviour and the effect of microstructural changes of 304 austenitic stainless steel induced by the processes of gas tungsten arc welding [GTAW] or TIG and laser beam welding [LBW] have been investigated. For each experiment, base metal and heat affected zone [HAZ] have been selected. The microstructure and the phases present in the HAZ of the laser and TIG weld specimens were investigated and analyzed by optical microscopy, scanning electron microscopy and energy dispersive X-ray. Very fine grains were formed at the HAZ in comparison to the base metal carbide precipitations formed at the grain boundaries. Beside the main austenite phase a ferrite phase is present at the HAZ at the grain boundaries and inside the grain. The ferrite content was higher in laser weld zone than TIG weld zone. Electrochemical measurements using poteniodynamic cyclic polarization in 0.5M NaCI solution have been carried out for welded and unwelded specimens. The pitting potential was estimated reflecting higher pitting resistance for base metal than laser and TIG weld, respectively. The decrease in pitting resistance for laser and TIG weld could be related to the presence of carbide and ferrite phases in their microstructure