The Effect of Magnesium on the Microstructure and Stress Rupture Properties of Hastelloy X Superalloy

In the present study, the effects of magnesium on the microstructural characteristics and stress-rupture properties of Hastelloy X superalloy were investigated. In this regard, four alloys with different amounts of Magnesium (0, 17, 33, 47 ppm) were cast via the vacuum induction melting and then purified via the electro slag remelting. Microstructural observations were carried out through optical and scanning electron microscopes and phase analysis was performed by x-ray diffraction. The stress rupture test was carried out at 815 °C/130 MPa. The results showed an almost significant effect of Magnesium on decreasing grain size and sulfur content and increasing M6C carbides volume fraction. Magnesium changed the morphology of carbides from course and continuous to finely divided one. Mg segregated at the grain and carbide boundary, decrease the lattice parameters of matrix and change the composition of M6C. Magnesium increased the rupture life by 46%. The most important causes for improving the rupture life of the Hastelloy X in the presence of Magnesium are the increasing carbides volume fraction, improving its morphology and decreasing sulfur content.