EFFECT OF NITROGEN ON CREEP CHARACTERISTICS OF ALPHA-FE-W AND ALPHA-FE-MO SOLID-SOLUTIONS

The effects of nitrogen on the creep characteristics of substitutional alpha solid solutions, the Fe-W and Fe-Mo systems, have been investigated at 1100 K. Three stress regions in the power-law creep regime are-observed in these solid solutions, except the Fe-Mo-N solid solution. In Region L, nitrogen strengthens the Fe-W solid solution, while it weakens the Fe-Mo solid solution. The effect of nitrogen on the creep strength of the Fe-W solid solution is negligibly small in Regions M and H. In the Fe-Mo solid solution, however, the transition stress between Regions M and H increases with the addition of nitrogen and the steady-state creep-rate decreases in Region H. The effects of nitrogen on the creep characteristics depend on the substitutional solute in these solid solutions. The difference in the effects of nitrogen can be attributed to the difference in the interaction between. interstitial and substitutional elements. In the Fe-Mo solid solution, nitrogen interacts strongly with molybdenum and so-called ''IS effect'' causes the increase of transition stress between Regions M and H in this system. In contrast, the interaction between nitrogen and tungsten is weaker than that of nitrogen and molybdenum, so that little changes in the transition stress are observed in the Fe-W solid solution. It becomes obvious that the addition of interstitial elements affects creep characteristics in the temperature range above 0.5 Tm (Tm: melting point), but accumulation of experimental results and detailed considerations are needed to understand the rate-controlling mechanism in Region L.