3.1 All heat-treatment processes involve the heating and cooling of metals according to a time-temperature cycle - NSC Mechanical Technology Fitting and Machining - 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 Fitting and Machining - Question 3 - 2021 - Paper 1
Step 1
Describe this cycle.
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Answer
The heat-treatment cycle consists of three primary stages: heating, holding, and cooling.
Heating: The metal is gradually heated to a specific temperature, allowing for uniform temperature distribution.
Holding: At the target temperature, the metal is maintained for a certain duration to ensure the transformation of its microstructure.
Cooling: The metal is then cooled at a controlled rate to achieve desired mechanical properties. This can involve quenching or air cooling, depending on the treatment.
Step 2
Name any THREE types of quenching mediums used during the heat-treatment processes.
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Answer
Water
Oil
Air
Step 3
Give ONE reason why steel is annealed.
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Answer
Steel is annealed to reduce internal stresses and improve its ductility, making it easier to work with in subsequent processes.
Step 4
Name the THREE groups.
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Answer
Low carbon steel
Medium carbon steel
High carbon steel
Step 5
In FIGURE 3.5 below the iron-carbon equilibrium diagram is shown. Label the diagram as indicated, from A to D.
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Answer
A - Percent liquid / cooling curve
B - Temperature in °C
C - AC3 line / higher critical temperature
D - AC1 line / lower critical temperature
