The present paper summarises the research work performed for a group sponsored project initiated by the Belgian Welding Institute about fracture toughness and fracture behaviour of duplex and super duplex stainless steel weldments. The main objective of the project was to amend or further develop toughness recommendations specifically applicable for duplex stainless steels operating at low temperature service conditions.

The investigation has been focussed on 40mm thick shielded metal arc, submerged arc and flux cored arc weldments. The broad programme of notch impact and CTOD fracture toughness tests has been expanded by realistic large scale tensile tests performed at -40C on full-thickness specimens containing large surface breaking defects extended by fatigue and positioned at the lowest toughness areas of the welded joints.

Part of the project has highlighted the effect of flame straightening on the fracture toughness of duplex stainless steel base metal, heat affected zone and real weldments. This examination has shown that local sustained heating at for instance 850°C may jeopardise most of the microstructures present in duplex stainless steel welds. Great caution should thus be exercised during flame straightening of this type of materials.

The available data base allows for a relaxation of existing rules imposed by formal regulations concerning minimum required levels of toughness and temperature ranges, which initially were extrapolated from specifications applicable for other types of steel. The present conclusions show indeed that duplex stainless steel weldments may be considered fit-for-purpose for use in highly stressed components working at temperatures below those permitted at present. A reconsideration of present requirements would certainly enhance the perspectives of commercially available steel grades and welding processes and would therefore stimulate their use in constructions where adequate toughness and superb corrosion resistance are demanded.