Abstract
The good mechanical and corrosion resistance properties of duplex, ferritic-austenitic steels depend critically on the phase balance. While typical commercial wrought products display 50/50 ferrite/austenite, this can be significantly, and adversely, affected by a weld thermal cycle. Work was carried out to derive a predictive system for phase balance in single pass weld metals. Single run beads were produced on UNS S31803 steel using the SMAW, TIG and submerged arc welding processes, and varying consumable compositions, to give a range of deposit compositions and microstructures. Weld metal cooling rates were recorded. The Austin-Rickett equation was used to describe transformation behaviour, and comparison was made between anstenite contents measured and calculated from an equilibrium value at 1000°C. Austenite contents of single pass weld metals from about 5 to 95% were predicted from their composition and the cooling cycle experienced. At the 50% level, predicted values were within about ±10% of the measured value. From the predictive model, the change in austenite content due to varying the cooling time from 1200 to 800°C was assessed. The change in austenite content is expected to be greatest in weld metals having an equilibrium austenite content of 50%. Weld metals having higher or lower equilibrium austenite contents are less sensitive to variations in welding conditions.
