4.1 Temperature affects the structure of steel with regard to iron and carbon - NSC Mechanical Technology Welding and Metalwork - Question 4 - 2016 - Paper 1
Question 4
4.1 Temperature affects the structure of steel with regard to iron and carbon. State TWO characteristics of each of the following:
4.1.1 Pearlite
4.1.2 Cementite
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Worked Solution & Example Answer:4.1 Temperature affects the structure of steel with regard to iron and carbon - NSC Mechanical Technology Welding and Metalwork - Question 4 - 2016 - Paper 1
Step 1
4.1.1 Pearlite
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Pearlite is characterized by:
Good ductility, allowing it to be formed without breaking.
Strong and tough nature, providing resistance to fracture.
Step 2
4.1.2 Cementite
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Cementite has the following characteristics:
It is intensely hard, making it suitable for applications requiring wear resistance.
Cementite is also brittle, which limits its use in some applications.
Step 3
4.2.1 Lower critical point (AC₁)
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The lower critical point (AC₁) is defined as:
The lowest temperature to which steel must be heated to achieve hardening.
The temperature at which the structure of the steel begins to change.
Step 4
4.2.2 Higher critical point (AC₃)
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The higher critical point (AC₃) is explained as:
The highest temperature to which the steel can be heated to achieve maximum hardness.
The temperature at which steel loses its magnetic properties fully.
Step 5
4.3 Which ELEMENT determines the hardness of steel?
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The element that determines the hardness of steel is carbon. It plays a crucial role in enhancing the hardness and strength of steel.
Step 6
4.4 Which STRUCTURE in steel determines the hardness?
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The structure that determines hardness in steel is cementite. This phase contributes to the overall hardness due to its brittle nature.
Step 7
4.5 Which STRUCTURE in steel determines the ductility?
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The structure responsible for ductility in steel is ferrite. Ferrite is more malleable and allows for deformation without fracture.
Step 8
4.6 Describe the austenite structure.
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Austenite is a solid solution of iron and carbon, characterized by its face-centered cubic (FCC) crystal structure. It is non-magnetic and maintains a stable form at higher temperatures. The presence of carbon within the austenitic structure significantly enhances its ductility and toughness.
