3.1 All heat-treatment processes involve the heating and cooling of metals according to a time-temperature cycle - NSC Mechanical Technology Automotive - 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 Automotive - Question 3 - 2021 - Paper 1
Step 1
Describe this cycle.
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Answer
The time-temperature cycle in heat treatment involves three primary steps:
Heating: The metal is heated slowly to a specified temperature where it begins to undergo phase changes. This allows for a uniform temperature across the entire metal piece.
Soaking: Once the desired temperature is reached, the metal is held at this temperature for a certain period. This soaking period ensures that the temperature is uniform throughout the metal, which is crucial for achieving the desired metallurgical properties.
Cooling: After soaking, the metal is cooled at a controlled rate to room temperature. This cooling process varies depending on the heat treatment method (e.g., quenching, normalizing) and is critical in determining the final microstructure of the metal.
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 in the material, which improves its ductility and makes it easier to machine.
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 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
