**5.2 Austenitic steels**

A main driver for the development of HNS austenitic steel was the power generation in the 1980´s. A material for retaining rings was required that could resist the mechanical loads but also stress corrosion cracking. This has finally led to the introduction of X8CrMnN 18-18 also known as P900 or 18-18. This alloy combines superb mechanical properties, e.g. high ductility at elevated strength level with good corrosion resistance.

Further developments have also come up with Mn-stabilized austenites, e.g. X13CrMnMoN 18-14-3 (P2000). This alloy can achieve strength level (YS) beyond 2000 MPa, still with good ductility and corrosion resistance. One should consider heat treatment conditions and corresponding part dimensions with regards to the precipitation of Cr2N.

Another market is powder metallurgy, i.e. thermal spraying and metal injection moulding (M.I.M.). The powders are gas atomized and very homogenous in terms of nitrogen and chemical composition. Main consumers are jewelry and general engineering.

Corrosion Resistance of High Nitrogen Steels 79

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Fig. 26. Generator shaft with retaining rings, X8CrMnN 18-18 [ETE-11].

Fig. 27. Retaining ring. X8CrMnN 18-18 [ETE-11].
