SANDVIK 12RN72 is a 19Cr-25Ni austenitic steel with additions of molybdenum, titanium, and boron. In this paper structure, mechanical properties, and high-temperature corrosion properties of 12RN72 are presented.

The structure of 12RN72 in the solution heat treated condition consists of a fully austenitic matrix with some undissolved carbides and nitrides of type TiC and TiN. During creep, M₂₃C₆ precipitates in the grain boundaries, and both M₂₃C₆ and finely dispersed TiC-particles precipitate in the grains. The small TiC-particles, which precipitate at dislocations, are very stable and their growth rate is low.

The precipitates of TiC and M₂₃C₆ greatly contribute to a high creep-rupture strength. For instance, at 700°C the 100 000 h creep-rupture strength of 12RN72 is at least twice that of TP316 and TP347 and about 50 percent higher than that of Alloy 800H. Another prominent feature is the high creep ductility with a transcrystalline rupture behavior.

The high chromium and nickel contents of 12RN72 account for an improved corrosion resistance at elevated temperature in comparison with the standard austenitic steels. Up to about 1000°C, the corrosion properties are similar to those of Alloy 800H that has been verified by tests in air, steam, and impure helium.