Welding behaviour of DUPLEX and SUPERDUPLEX STAINLESS STEELS using LASER and PLASMA ARC WELDING processes

1.4462 (UNS S31803) duplex stainless steel (DSS) and EN 1.4410 (UNS 532750) superduplex stainless steel (SDSS) have been welded by fibre laser welding and plasma arc welding (PAW) processes without filler metal. Impact toughness testing at various temperatures from 20 degrees C down to -60 degrees C was carried out. Microstructural examination included macro and microphotographs of the cross-sections, ferrite content measurements and hardness survey of the weld zones. Weld metal impact toughness results on the order of 100 J were obtained while values between 30 J and 60 J were measured respectively for plasma arc and laser welds of the duplex and superduplex grades even at -60 degrees C test temperature. Ferrite content of the welds varied generally in an acceptable range which affected the microstructure and the toughness properties. Better toughness results of plasma arc welds of both duplex and superduplex material compared to the laser welds are attributed to the balanced microstructure of the weld metal having ferrite- austenite ratio close to 50:50% obtained by controlled heat input.