3.1 Why is tempering of steel done after hardening? 3.2 Give ONE reason for EACH of the following heat-treatment processes on steel: 3.2.1 Case hardening 3.2.2 Annealing 3.3 Explain how to conduct a spark test to identify the type of steel - NSC Mechanical Technology Automotive - Question 3 - 2023 - Paper 1

The purpose of case hardening is to obtain a wear-resistant surface while ensuring that the core remains tough enough to withstand applied loads. This dual benefit protects the outer layer against wear without compromising the integrity of the core.

Annealing serves to relieve internal stresses in the steel. This process softens the material, making it easier to work with in subsequent machining processes, while also increasing the ductility of the steel and reducing its brittleness.

To conduct a spark test, hold the steel against a grinding wheel. As the steel makes contact with the wheel, observe the spark pattern generated. The characteristics of the sparks—such as their color, length, and frequency—can provide insights into the type of steel being tested.

For the filing test, use a file and apply it to the tip or near the edge of the metal. Observe the bite of the file on the material; this action will help determine the hardness of the steel being tested.

To conduct the bend test, subject the metal to deformation by bending it. Observe the amount of bending and the resulting rupture of the metal to evaluate its ductility and toughness.

Low-carbon steel typically produces a dull (low pitch) sound when subjected to a sound test.

High-carbon steel generates a loud and clear (high pitch) sound during a sound test.