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Answer any two of the following: (i) Identify two methods of measuring furnace temperature; (ii) Describe the influence of allotropy in carbon steel; (iii) Explain the term soaking in relation to the annealing process; (iv) Distinguish between the properties of grey cast iron and white cast iron - Leaving Cert Engineering - Question Question 1 - 2007
Question Question 1
Answer any two of the following: (i) Identify two methods of measuring furnace temperature; (ii) Describe the influence of allotropy in carbon steel; (iii) Explai... show full transcript
Worked Solution & Example Answer:Answer any two of the following: (i) Identify two methods of measuring furnace temperature; (ii) Describe the influence of allotropy in carbon steel; (iii) Explain the term soaking in relation to the annealing process; (iv) Distinguish between the properties of grey cast iron and white cast iron - Leaving Cert Engineering - Question Question 1 - 2007
Step 1
Identify two methods of measuring furnace temperature
Answer
Two methods for measuring furnace temperature include:
- Optical pyrometer: This device measures the temperature of an object based on the light emitted from it.
- Thermo-electric pyrometer: Utilizes thermocouples to measure temperature by generating a voltage that correlates to the thermal potential difference.
Step 2
Describe the influence of allotropy in carbon steel
Answer
Allotropy is the ability of an element to exist in different crystalline forms. In carbon steel, allotropy significantly affects the material's properties, particularly its hardness and strength. The transformation from alpha iron (ferrite) to gamma iron (austenite) changes the microstructure, which has crucial implications for processing and hardening techniques in steel.
Step 3
Explain the term soaking in relation to the annealing process
Answer
Soaking in the context of the annealing process refers to holding the metal at a specified high temperature for a period sufficient to enable uniform heat distribution. This practice ensures that the entire volume of the material reaches the required temperature, which minimizes internal stresses and facilitates more effective recrystallization during the cooling phase.
Step 4
Distinguish between the properties of grey cast iron and white cast iron
Answer
Grey cast iron contains flake graphite, which enhances its machinability and provides good wear resistance, but makes it relatively brittle. On the other hand, white cast iron has a higher carbon content and appears white due to its cementite structure, making it harder and more brittle than grey cast iron, thus less suitable for machining.
Step 5
Step 6
Identify and describe the significance of points X and Y
Answer
Point X marks the eutectoid point, where solid austenite changes to solid pearlite at 723 °C for an alloy containing 0.83% carbon. Point Y denotes the eutectic point, occurring at 1140 °C for the alloy with 4.3% carbon, where a liquid phase solidifies into a mixture of austenite and cementite.
Step 7
Name three quenching media and order them in terms of speed of cooling
Answer
Three common quenching media are:
- Brine (salt water) - fastest cooling rate
- Water - moderate cooling rate
- Oil - slowest cooling rate
This order represents the typical effectiveness of each medium in extracting heat quickly from the material.
Step 8
Outline, with the aid of a suitable diagram, the principle of induction hardening
Answer
Induction hardening involves placing a steel component inside an induction coil, where an alternating current generates a magnetic field. This induces surface currents that rapidly heat the surface layer of the component to austenitizing temperature, followed by rapid cooling in water or oil to achieve hardening. The effectiveness of this method depends on the frequency of the current, which influences the depth of hardening.