GRAIN-GROWTH IN HAZ OF DUPLEX STAINLESS-STEELS

The heat affected zone (HAZ) plays an important role in the final properties of a weld. In fact, this particular kind of heat treatment may give unwanted structural changes in the material. The present investigation, performed on weld simulated specimens from four duplex stainless steels, was focussed on the grain growth and the corresponding influence on impact properties. HAZ-simulations were proved to be in good agreement with the actual temperature distribution and structural changes obtained at welding. A mathematical relation was derived between grain size, D, and the cooling parameters DELTA-t8/5 and DELTA-t12/8 as D(m) approximately DELTA-t. This relation shows good agreement with grain size measurements on a wide DELTA-t interval for all steels tested. The impact properties were studied in more detail for the steel Sandvik SAF 2205 (UNS S31803). The Charpy V 27J transition temperatures were well below -50-degrees-C even for the maximum grain size. Yet the transition temperatures were considerably lower when the grain size decreased, irrespective of the HAZ austenite content within the range of 30-55%.