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In relation to the properties of metals, explain the difference between hardening and annealing - Leaving Cert Engineering - Question a - 2016
Question a
In relation to the properties of metals, explain the difference between hardening and annealing. Describe how to carry out each of the following heat treatment proc... show full transcript
Worked Solution & Example Answer:In relation to the properties of metals, explain the difference between hardening and annealing - Leaving Cert Engineering - Question a - 2016
Step 1
In relation to the properties of metals, explain the difference between hardening and annealing.
Answer
Hardening and annealing are two crucial heat treatment processes that alter the physical properties of metals.
Hardening involves heating a piece of metal to a specific temperature where the structure of the metal changes, typically to austenitic form, and then rapidly cooling it, often by quenching in water or oil. This process creates a hard, wear-resistant surface by inducing a higher hardness level and increased brittleness.
On the other hand, annealing entails heating the metal to a high temperature and then allowing it to cool slowly, usually in the furnace or air. This process helps relieve internal stresses and produces a softer metal with improved ductility and malleability. Thus, unlike hardening that increases hardness at the expense of ductility, annealing enhances ductility while reducing hardness.
Step 2
Describe how to carry out each of the following heat treatment processes: Hardening.
Answer
To carry out hardening, follow these steps:
- Heat the metal to a cherry red color (approximately 900°C).
- Once the metal reaches the target temperature, quench it immediately in cold water. This rapid cooling locks the carbon structure in a hardened state, forming martensite.
Step 3
Describe how to carry out each of the following heat treatment processes: Annealing.
Answer
To carry out annealing, follow these steps:
- Heat the metal to a cherry red color (approximately 900°C).
- Allow the metal to cool down as slowly as possible. This can be achieved by leaving the metal in the furnace until it cools down naturally, which helps to relieve internal stresses and restores ductility.