Microstructure and corrosion behavior of laser welds between dissimilar stainless steels

In recent years, laser beam welding becomes very popular in joining dissimilar materials for improving performance and reducing cost of the engineering components because of its accuracy, precision, repeatability and low distortion. In the present study, six autogenous dissimilar welds with the combinations of austenitic (S30400 and S31603) and duplex (S31803 and S32760) stainless steels were fabricated by laser welding using a 2.5 kW CW Nd:YAG laser in an argon atmosphere. The phases present and compositions in the resolidified zone of the welds were analyzed by X-ray diffractometry and energy dispersive spectroscopy (EDS) respectively. The microhardness of the welds was measured by means of a microhardness tester. The corrosion behavior of the welds in 3.5% NaCl solution at 23 oC was studied by means of cyclic potentiodynamic polarization. XRD and EDS analysis showed that the phases present in the welds depended on the mixing of the elements and the combinations of the parent steels (austenitic-austenitic, austenitic-duplex and duplex-duplex). The welds between austenitic-austenitic and austenitic-duplex steels contained γ as the major phase and δ-ferrite as the minor phase, while the duplex-duplex welds retained δ-ferrite as the major phase. The hardness of the dissimilar welds was comparable to that of the similar welds. All dissimilar welds exhibited passivity. The pitting corrosion resistance of the welds between S31603-S32760 and S31803-S32760 is comparable to the unwelded S32760 as evidenced by a high pitting potential.