4.1 State TWO properties of the cementite structure of carbon steel - NSC Mechanical Technology Automotive - Question 4 - 2016 - Paper 1

Case hardening is performed to:

1. Ensure hardness to the surface: This increases the wear resistance of the camshaft, which experiences high friction and stress during operation.

2. Ensure a soft and tough inside/core: This allows for better shock absorption and ductility, reducing the risk of fracture and failure under load.

Tempering hardened steel is essential for:

1. Reducing brittleness: After hardening, steel can become extremely brittle. Tempering helps to relieve stresses and make the material more ductile.

2. Increasing toughness: This process improves the impact resistance of the steel, allowing it to withstand greater forces without fracturing.

The iron-carbon equilibrium diagram illustrates various phases and their corresponding carbon contents and temperatures. The following elements should be represented:

1. Carbon content from 0% to 1.4%: This range should be clearly marked along the x-axis.

2. Temperature of 0 °C to 1 000 °C: This temperature range should be represented along the y-axis.

3. AC1-line: This line indicates the transformation of austenite to pearlite.

4. AC3-line: This line indicates the temperature at which austenite begins to form from ferrite and cementite.

5. Austenite structure: This phase appears in the diagram within its specific temperature and carbon content range.

6. Ferrite structure: This phase is located in the lower carbon content and lower temperature range.

7. Pearlite structure: This structure is found within a specific range of carbon content, associated with temperatures between the AC1 and AC3 lines.