2001 Volume 41 Issue 3 Pages 262-267
Thermo-mechanical control process (TMCP) applied to high nitrogen austenitic stainless steels could produce high-strength thick plates with a 0.2% proof stress of higher than 600 MPa. The effects of nitrogen, niobium and molybdenum on the strengthening have been examined by hot compression tests around 1223 K. The hardness of the compressed specimens linearly increased with increasing the nitrogen content, and the increment in hardness was larger than that of the specimens in a recrystallized state. This could be explained in terms of enhanced work-hardening by nitrogen addition during hot compression. In fact, the flow stress linearly increased with increasing the nitrogen content. The planar dislocation structure observed in the specimens with high nitrogen contents also gave evidence that nitrogen affected the workhardening behavior. Although it was not clear that nitrogen affected dislocation glide or dynamic recovery, it could be predicted that nitrogen addition was effective in increasing the dislocation density. Since niobium (0.1 mass%) had a marked effect on retarding the static recrystallization, probably owing to the fine precipitates of NbN, niobium addition is an effective way to prevent softening before accelerated cooling in TMCP.