The effect of hydrogen and cooling rate on the mechanical and corrosion properties of SAF 2507 duplex stainless steel welds

Since the microstructure of super duplex stainless steels consists of approximately equal amounts of austenite and ferrite, the response of these two constituent phases to hydrogen is of significant importance for potential applications. A study has been carried out of hydrogen additions in argon shielding gas welding of a super duplex stainless steel (SAF 2507) employing the use of TIG welding process. The percentage of hydrogen in the argon shielding gas was set to 10% and welds were carried out in both hydrogen enriched as well as pure argon shielding gases. Moreover, weldments were performed at a variety of cooling rates. Extensive metallographic observations of weldments were carried out employing the use of an image analysis system and a calculation of the volume fraction of phases across weld zones has been performed. The pitting corrosion of welds in chloride solutions, as well as the intergranular corrosion were studied and observed using a SEM microscope fitted with an EDS-X-ray Microanalysis system. The embrittlement of welds was also investigated employing the use of impact testing at various temperatures.