Super duplex stainless steel welds with and without Cu and varying levels of W have been investigated for their pitting resistance. Variations in N2 content and addition of Co was also explored. Tests were made in 10% FeCl3.6H2O solution per ASTM G48A. The welds were designed to a PREN around 40 calculated by PREN = Cr+3.3Mo+16xN.

In the as-welded condition, it was observed that the AWS 5.4 -type 2553 welds showed relatively low critical pitting temperatures (CPTs). This was irrespective of their PREN values, which did not appear to correlate well with the CPT. Besides chemical composition, metallurgical stability apparently played a more crucial role in the pitting resistance of the weld metal than suspected.

Addition of W and Co with and without Cu was tried for improving CPT. The results have been highly promising. As against a CPT of 20°C and below for Cu containing 2553 welds, CPTs as high as 42.5°C was reached in W alloyed welds under similar welding conditions and testing techniques.

Metallurgical examinations revealed distinctive precipitation of secondary phases in the welds. The W alloyed weld metal behaved differently from Cu containing welds in both nature and quantity of g 2 and other secondary phases. No sigma was detected in W-containing welds. Both types of welds showed intragranular g 2 Pptn. in varying amounts; no grain-boundary g 2 was observed. Mechanical properties showed no unusual increase in tensile or deterioration in ductility in both W and Cu containing weld metal. Microhardness tests however showed more inhomogeneities in Cu-alloyed weld metal.

In welding super duplex stainless steels, the weld metal design with W is thought to be beneficial to the usability of the welds in the as-welded condition. Besides normal mechanicals, high pitting resistance and better structural stability is anticipated. The investigations being carried out under controlled conditions of welding and testing, it is however recommended that further work be done under field conditions to establish this approach.