EFFECTS OF WELDING PARAMETERS ON HARD ZONE FORMATION AT DISSIMILAR METAL WELDS

An experimental study was conducted to determine effects of welding pa rameters and to optimize those parameters that have the most influence on eliminating or reducing the extent of hard zone formation al dissi milar metal welds (DMWs). Preheat, base metal thickness and welding el ectrode composition were found to have the most influence. Maintaining an optimum preheat for a given base metal thickness and controlling t he maximum interpass temperature throughout welding resulted in drasti c reduction and often complete elimination of hard zones at DMWs fabri cated with ENiCrFe-3 electrodes, but not those welds fabricated with E 309 stainless steel electrodes. This finding indicates that depending on the cooling rare and composition of the welding electrode, hard zon es in DMWs can be eliminated. The cooling rate must be slow enough to avert formation of hard allotropic structures (i.e., martensite) and f ast enough to avoid precipitation of hard intermetallic phases. The op timum welding electrode composition is one that will retard formation and precipitation of intermetallic phases during welding while the pre heat needed to prevent the formation of allotropics is being maintaine d. Unfortunately, this unique characteristic is not available in most, if not all, austenitic stainless steel electrodes; nickel-based weldi ng electrodes have been demonstrated to be more receptive.