In what structure does FCC steel exist when heated above a certain temperature?

When steel is heated above a certain temperature, it exists in a face-centered cubic (FCC) structure. This transformation occurs when temperatures reach the austenitic phase, typically above approximately 727°C (1340°F) for carbon steels. In the FCC structure, atoms are located at each of the corners and the centers of all the faces of the cube. This arrangement allows for a higher atomic packing factor and better ductility compared to other crystal structures, such as the body-centered cubic (BCC) structure, which is found in steel at lower temperatures.

The FCC structure plays a crucial role in the behavior of steel at different temperatures, particularly in its ability to dissolve more carbon, leading to different mechanical properties upon cooling. The stability of the FCC phase at elevated temperatures is vital for processes like welding and heat treatment, where materials are frequently subjected to varying thermal conditions.

In contrast, the body-centered cubic structure is typically associated with lower temperatures and is less ductile. The hexagonal close-packed structure is not characteristic of steel; instead, it is found in metals like magnesium and titanium. Lastly, amorphous structures lack long-range order, which is not applicable to crystalline metallic forms like steel when heated. Thus, the face-centered cubic structure is