SIRIUS S15 grade is a fully austenitic stainless steel containing 21 Cr, 1.7 Si, 0.17N and Rare Earth elements (Cerium, Lanthane,...) which make the alloy particularly well designed for high temperature applications.

The nitrogen additions stabilize the austenitic microstructure, particularly at high temperatures. The alloy is less susceptible to embrittlements effects occuring after long term exposure. Creep properties are enhanced, due to high Chromium and Nitrogen. Rare Earth elements (Ce, La,...) are added in order to anchor the oxide protective film and improve the resistance of the steel to oxide spaling. As a result, the alloy is much more resistant to high temperature thermal cycling effects in oxidizing atmospheres compared to 310.

SIRIUS S15 grade may be used up to 1100°C (2012°F) in oxidizing environments. Thermal cycling effects, sulphur containing atmospheres and low oxygen contents reduce the high temperature resistance of the steel.