Evaluation of Hot Cracking in Nitrogen-Bearing and Fully Austenitic Stainless Steel Weldments

摘要

Stainless steels exhibiting a primary austenitic solidification mode are particularly susceptible to hot cracking during welding. It is often difficult to predict the behavior of such materials, since the cracking is extremely sensitive to levels of impurity and minor elements such as P, S and N. In this work, the fusion zone and HAZ cracking behavior of a nitrogen-bearing AISI Type 316LN steel and fully austenitic Alloy D9 were investigated using the Varestraint Test. The results of the cracking tests were compared with that of a conventional primary fer-ritic 316L composition. The crack length measurements revealed that the 316LN was highly susceptible to fusion zone and HAZ cracking, while Alloy D9 was moderately susceptible. Analysis of the cracking data revealed that the total crack length criterion provided a better estimate of weldability than maximum crack length and brittleness temperature range criteria. Correlation of the composition and cracking susceptibility — including data obtained from the literature— indicated an interaction between nitrogen and phosphorus in enhancing cracking. A high degree of base and weld metal HAZ microfissuring was produced in 316LN, in comparison with 316L, which was attributed to the detrimental effect of nitrogen in this alloy. Heat-affected zone cracks were quite susceptible to backfilling, presumably due to favorable capillary and thermal conditions in this region.