EVALUATION OF HOT CRACKING IN NITROGEN-BEARING AND FULLY AUSTENITIC STAINLESS-STEEL WELDMENTS

Stainless steels exhibiting a primary austenitic solidification mode a re particularly susceptible to hot cracking during welding. It is ofte n difficult to predict the behavior of such materials, since the crack ing is extremely sensitive to levels of impurity and minor elements su ch as P, S and N. In this work, the fusion zone and HAZ cracking behav ior of a nitrogen-bearing AISI Type 316LN steel and fully austenitic A lloy D9 were investigated using the Varestraint Test. The results of t he cracking tests were compared with that of a conventional primary fe rritic 316L composition. The crack length measurements revealed that t he 316LN was highly susceptible to fusion zone and HAZ cracking, while Alloy D9 was moderately susceptible. Analysis of the cracking data re vealed that the total crack length criterion provided a better estimat e of weldability than maximum crack length and brittleness temperature range criteria. Correlation of the composition and cracking susceptib ility including data obtained from the literature-indicated an interac tion between nitrogen and phosphorus in enhancing cracking. A high deg ree of base and weld metal HAZ microfissuring was produced in 316LN, i n comparison with 316L, which was attributed to the detrimental effect of nitrogen in this alloy. Heat-affected zone cracks were quite susce ptible to backfilling, presumably due to favorable capillary and therm al conditions in this region.