In an iron-nickel alloy, at what percentage of nickel does it become austenitic at room temperature?

In an iron-nickel alloy, the characteristic transition to an austenitic structure at room temperature occurs around 28% nickel content. Austenite is a face-centered cubic (FCC) phase of iron, which is stable under specific conditions, particularly at elevated temperatures and specific alloy compositions.

The presence of nickel is crucial in stabilizing the austenitic phase at lower temperatures. As the nickel content increases, it disrupts the body-centered cubic (BCC) phase of ferrite in iron, making it more favorable for the alloy to maintain an FCC structure even under room temperature conditions.

At approximately 28% nickel, the thermodynamic stability of austenite becomes prominent, allowing it to remain in this phase as the temperature decreases. This understanding is important for industries that depend on specific properties of austenitic alloys, such as enhanced toughness and corrosion resistance, which are critical in applications like stainless steel manufacturing and other structural applications. Therefore, the transition of iron-nickel alloys to an austenitic structure is significantly influenced by achieving that specific nickel percentage.