Effects of nitrogen and carbon on void swelling in austenitic stainless steels

Abstract

Void swelling of 316 austsnitic stainless steels and the effects of nitrogen and carbon were investigated by in-situ observation using a high voltage electron microscope. Specimens used were solution treated or 20% cold worked. Electron irradiation was performed at 600 C. Swelling increased linearly with dose after incubation period. In solution treated specimen, swelling decreased with nitrogen and carbon concentration, and this decrease was attributed to the decrease of the swelling rate rather than the incubation dose of swelling which was almost independent of nitrogen and carbon concentration. Void number density first decreased, and then increased with nitrogen and carbon concentration in solution treated specimen. Average void diameter exhibited reverse dependency, i.e. it first increased and then decreased. In cold worked specimen, the swelling rate was nearly the same as that of solution treated specimen in case of the same kind of steel, but the incubation dose became shorter than in solution treated specimen. Void number density increased and average void diameter decreased with nitrogen and carbon concentration in cold worked specimen. The differences between the contributions of nitrogen and carbon in solution treated specimens and those in cold worked specimens are discussed.