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3. (a) (i) Explain the difference between hardening and annealing of metals - Leaving Cert Engineering - Question 3 - 2013
Question 3
3. (a) (i) Explain the difference between hardening and annealing of metals. (ii) Name a heat treatment process used to produce a hard surface on mild steel comp... show full transcript
Worked Solution & Example Answer:3. (a) (i) Explain the difference between hardening and annealing of metals - Leaving Cert Engineering - Question 3 - 2013
Step 1
Explain the difference between hardening and annealing of metals.
Answer
Hardening is a process designed to produce the hardest condition possible in a metal. This leads to increased resistance to wear and scratching; however, it results in brittleness due to internal stresses. The process involves heating the metal to a red color and then rapidly cooling it, often by quenching in water.
Annealing, on the other hand, aims to relieve these internal stresses and create a more ductile state. The metal is heated to a predetermined temperature and is allowed to cool slowly, which facilitates atomic arrangement and reduces hardness.
Step 2
Step 3
Explain how the twist drill shown below is hardened during manufacture.
Answer
To harden the twist drill, it is first heated in a crucible or a tube of red-hot lead until it attains a glowing red color. After this initial heating, the drill is quickly quenched in a bath of lukewarm water, which helps achieve the hardness necessary for effective drilling.
Step 4
Step 5
State two safety precautions to be observed when using water for cooling during the heat treatment of metals.
Answer
- Always wear protective clothing to guard against water splashes and rising steam, which can cause burns.
- Components should be plunged into the water vertically and moved in a circular motion to ensure uniform cooling, preventing cracking due to thermal shock.
Step 6
Explain any two of the following terms: Work hardening, Brittlness, Tempering.
Answer
Work hardening refers to the process where a metal becomes harder and stronger as it is mechanically deformed. This occurs because dislocations accumulate within the material's structure, hindering further movement.
Tempering is a heat treatment technique applied after hardening. It reduces the brittleness of hardened materials, allowing for some ductility and toughness. This involves heating the metal to a certain temperature for a specific duration and then allowing it to cool.