Effect of nitrogen on the dynamic strain ageing behaviour of type 316L stainless steel

Abstract

The dynamic strain ageing (DSA) behaviours of type 316L stainless steels containing different nitrogen contents (0.01-0.15 wt% N) were studied in tension under varying strain rates (1 x 10(-2)-2 x 10(-4) s(-1)) and the test temperatures (R.T -1023 K). The temperature range for DSA was moved to higher temperature for increasing nitrogen contents. The critical strain, ec for the onset of serration increased with nitrogen content at 773 K and then became almost constant at 873 K. Type A and B serrations were observed at 873 K with the value of the strain required to effect the transition from type A to type B serration increasing for nitrogen contents up to 0.1 wt% and then becoming saturated. The activation energy for DSA was 23.4-26.2 kcal mol(-1) (97.8-109.5 kJ mol(-1)) at the onset and 65.0-76.6 kcal mol(-1) (271-320.2 kJ mol(-1)) at the end of serration. The lower activation energy was related to vacancy diffusion and the higher activation energy was attributed to the diffusion of chromium to dislocations. The activation energy for DSA was slightly increased with nitrogen addition. DSA was retarded by an increase in the nitrogen content since nitrogen reduced the chromium diffusion to dislocations due to a strong interaction between the nitrogen and chromium. (C) 1998 Chapman & Hall.