Gas-metal reactions of a new Fe-Ni-Cr-W alloy in helium with reactive components and in an H2-CH4-H2S atmosphere in the temperature range 700-9500C

A new heat resistant e-Ni-Cr-W alloy (Thermon 4972) was developed within the scope of the prototype nuclear process plant project. This alloy shows mechanical properties and creep rupture properties similar to those of the nickel-based alloy Inconel 617 but, in addition, the new alloy forms protective oxide layers in atmospheres with very low O2 partial pressures. It is shown, by means of some examples, that a variation in the oxide morphology is caused by the modification of the alloy. However, the modifications lead to changes in the carbon activity of the alloy in comparison with the carbon activity of the atmosphere. Both activities must be adjusted to avoid processes such as carburization or decarburization. The results of experiments carried out for durations up to 2000 h at temperatures between 750 and 9500C are compared with those of the alloy Inconel 617. Experiments in sulphidizing and carburizing gas atmospheres were carried out to examine the protective behaviour of the layers built up in H2-CH4-H2S atmospheres with H2O contents between 10% and 10-3%. It is shown that, with an increase in the O2 partial pressure, the layers change from sulphide to oxide. At the same time there is a large variation in the specific mass change. The results are important for the application of the new alloy in plants for coal conversion and are compared with those obtained with the alloy Inconel 800 H. (orig.)