Structure and properties of austenitic steels after different periods of operation

Conclusions

• 1. The structure and the properties of austenitic steels change during use. The strength has a tendency to increase, while the ductility decreases considerably. The greatest changes occur during the first 4000 h of use.

• 2. Aside from carbides, the α- or σ-phase (or both simultaneously) is formed in steels which contain more chromium than nickel. In 1Kh14N18V2B, 1Kh14N18V2BR, and 1Kh14N14MV2T steels, in which the amount of chromium is equal to or smaller than the amount of nickel, these phases are not formed.

• 3. The distribution of the α- and σ-phases along the grain boundaries is responsible for the great decrease in ductility. The ductility is not affected when these phases precipitate within the austenite grains.

• 4. Stabilizing additional elements (titanium and niobium) do not protect the steels against intercrystalline corrosion when the α-phase precipitates along the grain boundaries.

• 5. Steels susceptible to the formation of the σ-phase along the grain boundaries become brittle during use. These steels should not be used.