TWI Industrial Member Report Summary 321/1986
By D N Noble and T G Gooch
The ferrite/austenite balance in duplex stainless steels is critical to obtain optimum corrosion resistance and mechanical properties. Parent steel usually contains a ferrite/austenite ratio of about 50:50, but this can be significantly changed by fusion welding. This report presents data on the influence of material composition and weld thermal cycle on the ferrite/austenite balance developed in the heat affected zone (HAZ) and weld metal. The MMA, TIG and submerged-arc welding processes were employed with a number of consumable/parent steel combinations to generate welds covering a range of arc energies and weld metal compositions. The base steels were of the commonly used 22Cr/5Ni/2.5Mo/N type, and ranged in thickness from 13-20mm. The effects of arc energy, reheating, and the position within the weld run were incorporated in weld thermal cycle studies, and the composition data were correlated to austenite contents with the aim of deriving a prediction technique. In all cases, weld metal and HAZ austenite/ferrite ratios were determined by point counting.