Photo AI
3. (a) Describe any two of the following heat treatment processes: (i) Annealing; (ii) Normalising; (iii) Carburising - Leaving Cert Engineering - Question 3 - 2012
Question 3
3. (a) Describe any two of the following heat treatment processes: (i) Annealing; (ii) Normalising; (iii) Carburising. (b) A flame hardening process is shown below.... show full transcript
Worked Solution & Example Answer:3. (a) Describe any two of the following heat treatment processes: (i) Annealing; (ii) Normalising; (iii) Carburising - Leaving Cert Engineering - Question 3 - 2012
Step 1
Describe any two of the following heat treatment processes: (i) Annealing
Answer
Annealing is a heat treatment process that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. The process involves three main steps:
- Heating: The material is heated to a specific temperature, known as the annealing temperature, which is above its recrystallization temperature.
- Soaking: The material is held at this temperature for a sufficient duration to allow internal changes, such as grain growth or phase transformations, to take place.
- Cooling: After soaking, the material is cooled down slowly, often in the furnace, to ensure uniform heating and reduce internal stresses. This gradual cooling helps in refining the grain structure.
Step 2
Describe any two of the following heat treatment processes: (ii) Normalising
Answer
Normalising is another heat treatment process that aims to refine the grain structure and improve the mechanical properties of materials. It involves the following steps:
- Heating: The material is heated to a temperature above its upper critical temperature, typically to around 40°C above this point.
- Cooling: The material is then cooled in air rather than in the furnace, which leads to a more uniform microstructure.
- Results: The main benefits of normalising include reduced residual stresses and improved hardness and toughness of the material.
Step 3
A flame hardening process is shown below. (i) Describe the principle of operation of this flame hardening process.
Answer
Flame hardening involves heating the surface of a metal object, usually to around 850°C, using an oxy-acetylene flame. The high temperature causes the austenitic transformation at the surface. The heated surface is then rapidly quenched, typically in water or oil, which transforms the austenite to martensite, significantly increasing surface hardness. The depth of hardening can be controlled by the rate of heating and the duration of exposure to the flame.
Step 4
A flame hardening process is shown below. (ii) Outline one application for this process.
Answer
One common application of flame hardening is in the manufacture of machine components that require a hard surface but a tough core, such as lathe slideways or the surfaces of machine beds. This process helps enhance wear resistance while maintaining the overall toughness of the underlying material.
Step 5
Step 6
A simplified portion of the iron-carbon equilibrium diagram is shown. (ii) Identify and describe the points X and Y.
Answer
X - Eutectoid point: This is a reaction point that occurs in the solid state when solid austenite changes to solid pearlite. It happens at 723°C for the iron carbon alloy with 0.83% carbon.
Y - Eutectic point: A liquid to solid change occurs at this point. It happens at 1140°C for the iron carbon alloy with 4.3% carbon, where the liquid changes to solid austenite and cementite.