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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 Hardening ... 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
The properties that can be obtained from heat-treatment processes include:
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Toughness: This property allows the material to absorb energy and deform without fracturing, making it ideal for applications requiring resistance to shock and impact.
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Hardness: Heat treatment can enhance the hardness of materials, making them more resistant to wear and abrasion, thus prolonging their service life.
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Ductility: This property refers to the ability of a material to be drawn into wires or bent without breaking, which is important for manufacturing and forming processes.
Step 2
Describe the following heat-treatment processes: Tempering
Answer
Tempering is a heat treatment process applied to hardened steel. It involves the following steps:
- Heating the hardened steel to a temperature below its critical temperature, which can be determined using a color chart.
- Soaking the steel at this intermediate temperature for a specified period.
- Quenching or cooling it rapidly in a medium such as water, brine, or oil to achieve the desired mechanical properties.
Step 3
Describe the following heat-treatment processes: Hardening
Answer
Hardening is another critical heat-treatment process, characterized by:
- Heating the steel slightly above the upper critical temperature.
- Soaking the steel at this elevated temperature for sufficient time to achieve uniformity.
- Rapidly quenching the steel in water, brine, or oil to lock in the metallurgical structure and increase hardness.
Step 4
Give TWO examples of case-hardened products used in the industry.
Answer
Two common examples of case-hardened products include:
- Bearing cases: These are typically case-hardened to enhance their wear resistance and durability in high-stress environments.
- Crankshafts: These components benefit from case hardening to provide a hard surface that can resist wear while maintaining toughness.
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 or distortion. This method allows for a more uniform cooling rate, minimizing the risk of creating localized spots that could lead to cracks or other structural imperfections.