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A simplified portion of the iron-carbon equilibrium diagram is shown - Leaving Cert Engineering - Question b - 2022
Question b
A simplified portion of the iron-carbon equilibrium diagram is shown. (i) Identify the point A, and describe the transformation which occurs at this point. (ii) Id... show full transcript
Worked Solution & Example Answer:A simplified portion of the iron-carbon equilibrium diagram is shown - Leaving Cert Engineering - Question b - 2022
Step 1
Identify the point A, and describe the transformation which occurs at this point.
Answer
Point A on the diagram corresponds to the eutectoid point. At this point, the phase transformation occurs where pearlite changes to austenite at a carbon content of 0.83% and a temperature of 723°C. This transformation is a solid-to-solid transition, representing a change in crystal structure without any phase change to a liquid state.
Step 2
Identify and describe the heat treatment process which occurs when 0.6% carbon steel is cooled very slowly from 1000°C, as indicated on the diagram.
Answer
The heat treatment process that occurs is known as annealing. During annealing, the 0.6% carbon steel is heated to 1000°C and held at this temperature until the entire workpiece is thoroughly heated. After reaching 1000°C, the temperature of the furnace is gradually reduced, causing the steel to cool slowly. This slow cooling process results in the transformation of structure, making the steel softer and allowing its grains to recrystallize, which enhances the material's machinability and ductility.
Step 3
Describe one method of accurately measuring furnace temperature when heat treating steel.
Answer
One method of measuring furnace temperature is through the use of an optical pyrometer. This device measures the intensity of light emitted from a filament compared to the colour of the furnace. The optical pyrometer is equipped with an adjustable variable resistor to match the filament's colour with that of the furnace. The accuracy can be monitored in three ways: if the filament appears too bright, it indicates that the temperature is too low; if it matches correctly, the temperature is accurate; and if it appears to disappear, this signals that the furnace temperature might be too high. Thus, accurate temperature readings can be obtained.