4.1 Temperature affects the structure of steel with regard to iron and carbon - NSC Mechanical Technology Welding and Metalwork - Question 4 - 2016 - Paper 1

1. Cementite is known for its intensely hard nature.
2. It is also brittle, making it susceptible to fracture under stress.

1. The lower critical point (AC1) is defined as the lowest temperature to which steel must be heated to be hardened.
2. It also represents the lowest temperature where the structure of the steel begins to change.

1. The higher critical point (AC3) is the maximum temperature to which steel can be heated to achieve maximum hardness.
2. At this temperature, the steel also completely loses its magnetic properties and achieves its finest structural state.

The element that primarily determines the hardness of steel is carbon.

The structure in steel that determines the hardness is cementite.

The structure that determines the ductility in steel is ferrite.

Austenite is a solid solution of iron and carbon, also known as iron carbide. This structure is face-centered cubic (FCC), which contributes to its high ductility and ability to retain carbon in solution.