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Explain any two of the following terms: (i) Case hardening, (ii) Annealing, (iii) Work hardening - Leaving Cert Engineering - Question 3 - 2012
Question 3
Explain any two of the following terms: (i) Case hardening, (ii) Annealing, (iii) Work hardening. Describe how the point A of the chisel shown is hardened and tempe... show full transcript
Worked Solution & Example Answer:Explain any two of the following terms: (i) Case hardening, (ii) Annealing, (iii) Work hardening - Leaving Cert Engineering - Question 3 - 2012
Step 1
Explain any two of the following terms: (i) Case hardening
Answer
Case hardening is a method of making low carbon steel very hard on the outside while leaving its core tough. This is achieved by increasing the amount of carbon in the steel surface by a process called 'carburising'. The steel is heated to a cherry red and allowed to cool in a carbon-rich material. The steel part will then have a skin or 'case' rich in carbon. Finally, it is heated to a cherry red and quenched to produce a hardened skin with a tough core.
Step 2
Explain any two of the following terms: (ii) Annealing
Answer
Annealing involves heating the metal to a specific temperature to soften it and relieve internal stresses. The metal is subsequently allowed to cool down slowly, which aids in reducing hardness and enhancing machinability. This controlled cooling process helps to restore ductility and reduce brittleness.
Step 3
Describe how the point A of the chisel shown is hardened and tempered.
Answer
The point A of the chisel is hardened by first heating it to a cherry red temperature and then quickly cooling it in clean water. The rapid cooling process transforms the microstructure of the metal, increasing its hardness. In the tempering process, the point is polished with emery cloth to remove excess hardness, followed by reheating it while controlling the temperature to achieve the desired toughness at the cutting edge.
Step 4
Explain why it is important to temper point A of the chisel.
Answer
Tempering point A of the chisel is essential because after hardening, the metal tends to become brittle with a tendency to break under stress. Tempering reduces this brittleness by removing some hardness and ensuring that the chisel retains sufficient strength and toughness for effective use.
Step 5
State two safety precautions to be observed when heat treating the point of the chisel.
Answer
- Always wear protective clothing such as gloves and goggles to shield from water/oil splashes and molten metal during the heat treatment process.
- Conduct the heat treating process in a well-ventilated area away from busy environments to minimize hazards.