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
Heat treatment involves heating metals to a specific temperature, holding them at that temperature for a designated time, and then cooling them down. This process allows for the adjustment of the material's microstructure, altering its mechanical properties. The cycle typically consists of three main phases:
Heating: The metal is gradually heated to a predetermined temperature to avoid thermal shock.
Soaking: The metal is maintained at this temperature long enough for its structure to transform, ensuring uniformity throughout the material.
Cooling: The metal is cooled, which can be done at different rates depending on the desired mechanical properties, leading to different microstructural formations.
Step 2
Name any THREE types of quenching mediums used during the heat-treatment processes.
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Answer
Water
Oil
Salt solutions
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 further manufacturing processes.
Step 4
Name the THREE groups.
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Answer
The three groups of carbon steel are:
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 – Percent cooling rate/ cooling content
B – Temperature in °C
C – AC3 line/ Higher critical temperature
D – AC1 line/ Lower critical temperature
