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3.1 State THREE properties that can be obtained from heat-treatment processes - NSC Mechanical Technology Automotive - Question 3 - 2022 - Paper 1
Question 3
3.1 State THREE properties that can be obtained from heat-treatment processes. 3.2 Describe the following heat-treatment processes: 3.2.1 Tempering 3.2.2 Hardenin... show full transcript
Worked Solution & Example Answer:3.1 State THREE properties that can be obtained from heat-treatment processes - NSC Mechanical Technology Automotive - Question 3 - 2022 - Paper 1
Step 1
State THREE properties that can be obtained from heat-treatment processes.
Answer
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Toughness: The ability of a material to absorb energy and plastically deform without fracturing.
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Ductility: A measure of a material's ability to deform under tensile stress, allowing it to be stretched into a wire.
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Hardness/Wear resistance: The resistance of a material to deformation, indentation, or scratching, which enhances its wear properties.
Step 2
Describe the following heat-treatment processes: Tempering.
Answer
Tempering is a heat treatment process applied to hardened steel. It involves the following key steps:
- Heating the hardened steel to a temperature below its critical temperature, which is determined using a colour chart.
- Soaking the steel at this reduced temperature for a specified period to relieve stresses.
- Quenching or cooling the steel rapidly, typically in water, brine, or oil, to achieve the desired properties.
Step 3
Describe the following heat-treatment processes: Hardening.
Answer
Hardening is a process that enhances the strength and hardness of steel. The process includes:
- Intial Heating: The steel is heated slightly higher than its upper critical temperature to ensure uniformity.
- Soaking: The steel is maintained at that temperature for the necessary duration to allow for crystal structure transformation.
- Quenching: The steel is then cooled rapidly by quenching in water, brine, or oil to lock in the desired properties.
Step 4
Step 5
Why is steel cooled in still air, away from a draught, during the normalising process?
Answer
Steel is cooled in still air, away from draughts, to prevent sudden cooling that could cause localised spots of distortion or cracks. This controlled cooling process ensures uniform microstructural properties across the material.