Metallurgy microstructure and properties of a new nitride strengthened nickel-chromium superalloy

The nitrogen content of Ni-base superalloys for high temperature service is generally kept below about 0.05 wt.-% to avoid detrimental precipitation of nitrides. These nitrides are said to have a harmful influence on mechanical properties and workability of these alloys. However, some recent studies and research conducted with nitrogen strengthening of Ni-Cr-alloys have resulted in an alloy with excellent physical and mechanical properties. The applied PESR (Pressurized Electro-Slag Remelting)-Technology provided up to 1.0 wt-% nitrogen in a NiCr7030-alloy.The homogeneously distributed nitrides prevent the alloy from excessive grain growth thus providing stable mechanical properties, i.e. impact toughness even after long term exposure. The new alloy easily exceeds R-m= 850 MPa at room temperature and 600 MPa at 600 degrees C as relevant design values. This paper introduces this new alloy with its very special metallurgy, microstructure, and its physical and mechanical properties.