4. Austenitic-ferritic steels

4.1 Composition

Austeno-ferritic steels, also known as two-phase alloys, were discovered by chance in the 1930s. Today, they are shaped in an electric furnace, then refined, ensuring faithful reproduction of the chemical compositions crucial to determining the intrinsic properties of these alloys, notably the distinctive two-phase structure with 50% α-phase (ferrite) and 50% γ-phase (austenite).

The basic chemical composition comprises carbon, chromium and nickel. It is finely tuned so that, in the temperature range from 1,000 to 1,100°C, the alloy displays a two-phase structure, consolidating a ferrite-austenite aggregate.

A representative alloy, X 5 Cr Ni Mo Cu 21-08, illustrates the austeno-ferritic nature of these steels. The...