Explain how you will conduct the following tests to identify various metals: 3.1.1 Sound test 3.1.2 File test What is the purpose of the heat treatment of steel? What is the purpose of the case hardening of steel? Describe the tempering process of steel - NSC Mechanical Technology Fitting and Machining - Question 3 - 2020 - Paper 1

To perform the file test, use a metal file to scrape the surface of the metal in question. Observe the bite of the file; if the file bites deeply, the metal is softer. Conversely, if the bite is minimal, the metal is harder.

The primary purpose of heat treatment is to alter the properties of steel. This process can enhance strength, ductility, and hardness, enabling the steel to perform better for specific applications. It may also aim to change the grain structure to improve the overall performance characteristics of the steel.

The purpose of case hardening is to create a hard outer surface on steel while maintaining a tough inner core. This method enhances wear resistance, making the steel components more durable and resilient in high-stress environments.

The tempering process involves heating the steel to a temperature below its critical point. First, heat the steel until it reaches a specific temperature that is determined by desired properties. Next, maintain that temperature for a suitable period to allow for uniform heat distribution. Finally, cool the steel down in an appropriate medium, such as water, oil, or air, to achieve the required properties.

1. Heating temperature / Carbon content: The temperature at which steel is heated is crucial, as it affects the properties achieved in the final product.
2. Soaking time (time period at temperature): The duration for which the steel is held at temperature influences the effectiveness of the heat treatment.
3. Cooling rate / Quenching method: The method and rate at which steel is cooled after heat treatment define the final hardness and microstructure of the steel.