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Describe how to carry out each of the following heat treatment processes: (i) Case hardening; (ii) Annealing - Leaving Cert Engineering - Question 3 - 2017
Question 3
Describe how to carry out each of the following heat treatment processes: (i) Case hardening; (ii) Annealing. (b) (i) Describe how the point of the centre punch... show full transcript
Worked Solution & Example Answer:Describe how to carry out each of the following heat treatment processes: (i) Case hardening; (ii) Annealing - Leaving Cert Engineering - Question 3 - 2017
Step 1
Case hardening;
Answer
Case hardening is a process used to increase the hardness of the surface of low-carbon steel while leaving the core soft. The process involves several steps:
- Preparation: Clean the steel component to remove any surface contaminants.
- Carburising: The steel is heated in a carbon-rich environment, usually in a furnace, at temperatures around 900°C (1652°F). This introduces carbon into the outer layer of the steel.
- Quenching: After carburising, the steel is rapidly cooled, typically by immersion in water or oil. This hardens the outer layer, creating a 'case' while preserving a softer core.
Step 2
Annealing.
Answer
Annealing is a heat treatment process that softens metal and relieves internal stresses. Here’s how it is carried out:
- Heating: The metal is heated to a temperature of around 800°C (1472°F) until it reaches a cherry red color.
- Soaking: The metal is kept at this temperature to ensure that the heat penetrates all parts of the material, allowing for a uniform temperature.
- Cooling: The furnace is allowed to cool down gradually. This slow cooling process can take several hours, enabling the metal to become softer and more workable.
Step 3
Describe how the point of the centre punch is hardened and tempered.
Answer
The point of the centre punch is hardened and tempered through a two-step process:
- Hardening: The punch is heated to approximately 800°C (cherry red) to harden the metal. This process changes the structure of the steel, making it very hard.
- Tempering: After hardening, the punch is reheated to a temperature between 230°C and 350°C (light brown color) and then cooled down in water. This tempering process reduces brittleness, allowing for a balance between hardness and toughness.
Step 4
Explain why it is necessary to temper the point of the centre punch shown.
Answer
Tempering is necessary for the point of the centre punch because the initial hardening process can make the metal excessively brittle. Brittle materials are prone to cracking or breaking under stress. By tempering, the microstructure of the steel is modified, which increases toughness and resilience, ensuring that the centre punch can withstand impact without shattering.
Step 5
Identify any two items of protective clothing that should be worn when using water as a coolant during heat treatment.
Answer
When using water as a coolant during heat treatment, workers should wear:
- Goggles: To protect the eyes from splashes and steam that can be generated during the quenching process.
- Gloves: Heat-resistant gloves should be worn to protect the hands from burns and hot materials.
Step 6
Step 7
Explain any two of the following terms: Tensile strength.
Answer
Tensile strength is the maximum amount of tensile (pulling) stress that a material can withstand before failure. This property is essential in construction materials, as it ensures that structures can endure loads without breaking. For example, steel has a high tensile strength, making it suitable for construction and manufacturing.