Effect of nitrogen on the creep-fatigue behaviors of type 316L(N) stainless steel

Creep-fatigue tests including hold time of 10 minute at the maximum tensile strain were conducted for type 316(N) stainless steels containing different nitrogen content of 0.04 and 0.10 wt% at 600 .deg. C and 2x10-3/sec in air atmosphere. Creep-fatigue life was decreased with the hold time but was increased with the addition of nitrogen. Fracture modes were intergranular regardless of nitrogen content. Dislocation structures were changed from cell to planar with the addition of nitrogen. Carbides (M23C6) were precipitated at grain boundaries and acted as the site for cavitation. Carbides were continuous in the low nitrogen content steel but discontinuous in high nitrogen content steel. The increase of creep-fatigue life with the addition of nitrogen is attributed to the distribution of carbides at grain boundaries rather than the change of dislocation structures