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Explain any two of the following: (i) Case hardening - Leaving Cert Engineering - Question 3 - 2015
Question 3
Explain any two of the following: (i) Case hardening. (ii) Annealing. (iii) Work hardening. Describe how the head of the engineering hammer shown could be harden... show full transcript
Worked Solution & Example Answer:Explain any two of the following: (i) Case hardening - Leaving Cert Engineering - Question 3 - 2015
Step 1
Explain any two of the following: (i) Case hardening.
Answer
Case hardening is a method used to increase the hardness of low carbon steel by enriching its surface with carbon. This is done through a process called carburizing, where the steel is heated in a carbon-rich environment. The outer layer of steel, which becomes hardened, receives a 'skin' of carbon that enhances its wear resistance while leaving the inner part malleable. The process involves heating the part, allowing it to absorb carbon, and then quenching it in a rapid cooling step.
Step 2
(ii) Annealing.
Answer
Annealing is a heat treatment process aimed at softening metal to reduce hardness and improve ductility. It involves heating the material to a specific temperature where internal stresses are relieved, followed by a controlled cooling process that allows for the formation of a more uniform microstructure. The process is vital in preparing metals for further machining or forming by making them less brittle.
Step 3
Describe how the head of the engineering hammer shown could be hardened and tempered.
Answer
To harden the head of the hammer, it would first be heated to red-hot temperatures until it reaches the required hardness before quenching in either water or oil. Once hardened, the hammer needs to be tempered; this is done by reheating it to a lower temperature, usually just below the critical point, and then allowed to cool. This process reduces the brittleness while retaining hardness, ensuring the tool is strong yet tough.
Step 4
State two safety precautions to be observed when handling hot metals during heat treatment.
Answer
- Always use appropriate personal protective equipment (PPE), such as heat-resistant gloves and aprons, to protect against burns from hot materials.
- Ensure proper ventilation or use fume extraction systems to avoid inhaling fumes produced during heating and quenching processes.
Step 5
Outline the effects of using each of the following, when cooling metals during heat treatment: Water.
Answer
Water is a fast cooling medium that can significantly harden metals, but it poses risks of cracking or warping due to rapid temperature changes. It leads to higher hardness but at the expense of increased brittleness, often making the metal less ductile.
Step 6
Oil.
Answer
Oil is a slower cooling medium compared to water and provides more controlled cooling rates. It reduces the risk of cracking, although it might not achieve the same hardness levels as water. The oil can also leave a protective film on the metal, which can further prevent oxidation during subsequent processes.