Theoretical Approach to Influence of Nitrogen on Solidification Cracking Susceptibility of Austenitic Stainless Steels

Abstract

The effect of nitrogen on the solidification cracking susceptibility of austenitic stainless steels (SUS316L and SUS310S) was quantitatively evaluated by transverse-Varestraint test. The amount of nitrogen in Ar shielding gas during GTA melt-run welding was varied in order to vary the nitrogen content in the weld metals. The solidification brittle temperature range (BTR) of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, while that of SUS310S was very slightly increased with an increase in the nitrogen content. Numerical analysis of solidification segregation during welding revealed that the solid-liquid coexistence temperature range of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, whereas that of SUS310S was almost constant regardless of the nitrogen content. A nitrogen itself essentially had a negligible effect on the solidification cracking susceptibility of fully-austenitic stainless steels, because a nitrogen neither solidification-segregated in the weld metal nor reduced the solidified temperature during welding. However, a nitrogen increased the solidification cracking susceptibility of austenitic stainless steels with two-phase solidification, because the solidification segregation of P and S was promoted by reducing the amount of δ-ferrite in the weld metal.