Exam Question

### (a) Causes of Formation of Mill Scale on Steel Plate (4 Marks)
Mill scale is a brittle, flaky surface of iron oxides that forms on steel plates during the manufacturing process. Its formation is a high-temperature oxidation phenomenon with the following primary causes:
1. **Hot Rolling Process**: Mill scale is predominantly formed when steel slabs or billets are heated to high temperatures (typically above 1200°C) and then passed through rollers to be shaped into plates. This process is known as hot rolling.
2. **High-Temperature Oxidation**: At these elevated temperatures, the surface of the steel reacts directly with atmospheric oxygen. This chemical reaction, or oxidation, creates layers of iron oxides on the steel surface. The reaction proceeds through several stages, forming a composite layer.