低炭素316ステンレス鋼のクリープ破断強度に及ぼすN量の影響

抄録

The influence of nitrogen addition on creep rupture strength of low carbon Type 316 austenitic stainless steel has been investigated.
The creep rupture strength of this steel remarkedly increased with increasing nitrogen content and in the steels with more than about 0.085mass%N, the rupture strengths were almost equivalent to or higher than those of comercial Type 316 austenitic stainless steels. It is thought that its beneficial effect is due to the solid solution hardening controlled by Mo-N atomic pairs in the matrix. Increasing the nitrogen content from 0.085 to 0.12mass% suppressed the precipitation of intermetallic phases such as sigma(FeCr) and Laves(Fe₂Mo), but accelerated the precipitation of the Cr₂N.
From the result of analysis of creep deformation behavior using the modified θ projection concept for the steel with 0.085%N, the strengthening effect made into molybdenum and nitrogen solutes can give the highest creep resistance, but in a longer term condition, the lowering in strength was occurred by the precipitation of Laves phase, which was related to the removal of molybdenum in solution and to the precipitation behavior of Laves phases.