EFFECT OF PHOSPHORUS ON THE MICROSTRUCTURE AND STRESS RUPTURE PROPERTIES IN AN FE-NI-CR BASE SUPERALLOY

This article describes the effect of phosphorus on the microstructure and stress rupture property at 650 degrees C in an Fe-Ni-Cr base super alloy. The results showed that phosphorus markedly improved the interg ranular precipitation in the range of 0.0005 to 0.016 wt pet, which fa cilitated M(23)C(6) and M(3)B(2) precipitation but inhibited the forma tion of MC carbide. A too high phosphorus addition (0.051 wt pet P) re sulted in an excessive precipitation at grain boundaries, while a too low phosphorus content (0.0005 wt pet P) led to many precipitate-free grain boundaries. Phosphorus also enlarged the size of the gamma' part icles and lowered its stability, that eta-Ni3Ti preferred to form in t he alloy with 0.051 wt pet P. Due to the improvement of the microstruc ture, appropriate amount of P content significantly prolonged the rupt ure life of the alloys in the range of 0.0005 to 0.016 wt pet. The pea k value was 660 hours at 0.016 wt pet, more than 4 times that of the a lloy with 0.0005 wt pet phosphorus, but phosphorus reduced the fractur e elongation. The mechanism by which phosphorus influenced the alloy i s discussed.