TWI Industrial Member Report Summary 286/1985
By J Honeycombe and T G Gooch
The effects have been examined of welding conditions and weld metal composition on the ferrite/austenite balance of welded duplex steels. Alloys containing 22Cr/5Ni/2.5Mo/N and 25Cr/5Ni/2.5Mo/Cu/N were obtained in 3 and 12mm thicknesses and welded with the TIG and MMA processes. Weld metal composition was varied by employing a range of consumable types with different dilution levels. Throughout, ferrite/austenite balance was determined by a point counting technique. Weld thermal cycles were monitored by thermocouples and correlated with predictions from The Welding Institute HEAT-2T computer program. It was found that the austenite content developed in the heat affected zone and weld metal was not greatly dependent on arc energy over the range studied. However, austenite formation may be suppressed by rapid cooling and a preliminary nomogram is proposed for selection of welding conditions avoiding low austenite contents. The Schaeffler diagram does not give accurate prediction of weld metal structure from the composition, and modified versions are presented, together with an alternative approach based on an empirical compositional parameter.