The denitrogenation behaviour during vacuum induction melting of Ni base superalloy using CaO crucible was studied, and the nitrogen solubility under different vacuum levels as well as Al and Ti addition amounts at 1873 K were also calculated. The experiment results show that Al addition had bene® cial effect, but Ti addition had adverse effect to denitrogenation. The increase of vacuum level is a powerful measure to accelerate the denitrogenation process. The denitrogenation mechanism has been discussed for a nitrogen content of below 10 ppm. MST/5046

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The effects of phosphorus, sulfur, and silicon on the microstructure and the stress rupture properties of a N&Fe base superalloy were studied. Phosphorus had no effect on the grain size of the alloy, but sulfur reduced and silicon enlarged the gram size of the alloy. The 'net' alloy with the lowest amount of the minor elements had a problem of short rupture life. It was determined by analysis that the dislocations in the 'net' alloy were not firmly pinned by the segregation of the minor elements and could move easily, which increased the creep rate and reduced the rupture life of the alloy. In this case, a small addition of any minor element resulted in the same effect, significantly increasing the rupture life but drastically decreasing the rupture elongation. The concentration of the minor elements at the dislocations might reach the saturation point at a very low addition level. When the addition of the minor elements was above the level, their effect of inhibiting the dislocation movement did not increase again, and other influencing mechanisms by the elements took effect. In the late eighties, some minor elements were suggested to be controlled as low as possible to get premium quality superalloys with homogeneous microstructure and mechanical properties.Because the elements, including phosphorus, sulfur, and silicon, The effects of phosphorus, sulfur, and silicon on the microstructure and stress rupture properties of the alloy were investigated and compared in this study. The goal of this paper is to manifest the influencing mechanism of these elements. Materials and ExDerimentalThe materials were prepared in a vacuum induction furnace using high-purity raw materials. To minimize the compositional variations among the heats, the master alloy was prepared, and its composition (wt. %) was CO.011, Cr12.89, Ni43.54, W3.12, Mo1.59, A11.71, Ti3.64, B0.003, SiO.059, SO.003, and Fe balance.And the master alloy was remelted to give ten IOkg ingots. The ingots were added into different contents of phosphorus, sulfur, and silicon, with the same content of carbon and boron. The remelting also made the alloy much more homogeneous. The contents of carbon, boron, phosphorus, sulfur, and silicon were