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

The purpose of case hardening on a camshaft is to:

1. Ensure hardness: Case hardening provides a hard outer surface that resists wear, which is crucial for the camshaft's performance.
2. Enhance wear resistance: It protects the softer inner core, ensuring durability against mechanical stresses and wear.

Tempering hardened steel serves two main purposes:

1. To reduce brittleness: Tempering helps to decrease the brittleness that arises from hardening, making the steel less likely to fracture under impact.
2. To increase toughness: It improves the overall toughness of the steel, allowing it to absorb more energy and deform without breaking.

In the iron-carbon equilibrium diagram, the carbon content can be represented along the horizontal axis from 0% to 1.4%, with distinct phases such as ferrite, austenite, and cementite plotted as well.

The temperature range of 0 °C to 1 000 °C is illustrated on the vertical axis of the iron-carbon equilibrium diagram, indicating phase changes that occur as the temperature increases.

The AC1-line on the diagram indicates the temperature at which austenite begins to form as the temperature increases with a given carbon content.

The AC3-line marks the temperature at which cementite transforms to austenite at higher carbon contents.

Austenite is represented on the diagram, characterized by a face-centered cubic (FCC) structure, stable at high temperatures and critical for steel's mechanical properties.

Ferrite is depicted as having a body-centered cubic (BCC) structure in the diagram, stable at lower temperatures, and shows good ductility.

Pearlite appears in the diagram as a combination of ferrite and cementite, showing lamellar structure and acting as a microstructural feature that provides a mixture of strength and ductility.