3.1 All heat-treatment processes involve the heating and cooling of metals according to a time-temperature cycle - NSC Mechanical Technology Welding and Metalwork - Question 3 - 2021 - Paper 1
Question 3
3.1 All heat-treatment processes involve the heating and cooling of metals according to a time-temperature cycle. Describe this cycle.
3.2 Name any THREE types of q... show full transcript
Worked Solution & Example Answer:3.1 All heat-treatment processes involve the heating and cooling of metals according to a time-temperature cycle - NSC Mechanical Technology Welding and Metalwork - Question 3 - 2021 - Paper 1
Step 1
Describe this cycle.
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Answer
The time-temperature cycle for heat treatment typically includes three main steps: heating, soaking, and cooling.
Heating: The metal is heated slowly to a specific temperature. This step is crucial as it ensures uniform temperature distribution within the metal.
Soaking: The metal is held at this temperature for a predetermined time to allow for internal transformations to occur within the material structure.
Cooling: Finally, the metal is cooled at a controlled rate to room temperature, preventing the formation of internal stresses and ensuring the desired mechanical properties.
Step 2
Name any THREE types of quenching mediums used during the heat-treatment processes.
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Answer
Water
Oil
Brine
Step 3
Give ONE reason why steel is annealed.
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Answer
Steel is annealed to relieve internal stresses, which helps improve the machinability of the steel and enhances its ductility.
Step 4
Name the THREE groups.
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Answer
Low carbon steel
Medium carbon steel
High carbon steel
Step 5
Label the diagram as indicated, from A to D.
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Answer
A: Percentage carbon / carbon content
B: Temperature in °C
C: AC3 line / Higher critical temperature
D: AC1 line / Lower critical temperature
