Formation and control of the residual delta-ferrite in 9% Cr-HAZ of Alloy 617/9% Cr dissimilar welded joint

The formation and control of the residual delta-ferrite in Alloy 617/9% Cr dissimilar welded joint manufactured by the single-layer or multi-layer multi-pass overlaying technique were comparatively investigated. The residual delta-ferrite was identified based on its lower microhardness and carbon content than the surrounding martensite matrix and being free from precipitates. Patch-shape residual delta-ferrite was found in the heat-affected zone (HAZ) of 9% Cr steel adjacent to the fusion line for the single-layer overlaying weldment, while less and smaller residual delta-ferrite could be achieved by employing the multi-layer multi-pass overlaying technique. Attributing to the optimisation of the subsequent thermal input and heat transfer, the technique utilised in this study was proved to be effective to control the formation of residual delta-ferrite.