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A simplified portion of the iron-carbon equilibrium diagram is shown - Leaving Cert Engineering - Question b - 2021
Question b
A simplified portion of the iron-carbon equilibrium diagram is shown. Identify the regions A, B, C and D shown. Identify and explain the microstructure which is pr... show full transcript
Worked Solution & Example Answer:A simplified portion of the iron-carbon equilibrium diagram is shown - Leaving Cert Engineering - Question b - 2021
Step 1
Identify the regions A, B, C and D shown.
Answer
Region A corresponds to austenite, which is a face-centered cubic (FCC) structure present at higher temperatures. Region B represents austenite and cementite. Region C is the area of ferrite and pearlite, where both structures exist together. Finally, region D consists of pearlite and cementite.
Step 2
Identify and explain the microstructure which is present at 0.83% carbon steel, up to 723°C.
Answer
At 0.83% carbon content, up to 723°C, the microstructure is known as pearlite. Pearlite is characterized by a layered structure containing alternating layers of ferrite and cementite. It exhibits a distinctive 'mother of pearl' sheen when fractured, indicating its layered composition.
Step 3
Describe the transformation that occurs at point X, with reference to temperature, composition and phase change.
Answer
Point X signifies the eutectic point, occurring approximately at 1140°C and 4.3% carbon content. At this point, the liquid steel undergoes a transformation into solid steel without passing through a completely solid phase, entering a pasty state instead. This eutectic transformation is crucial as it indicates the change in microstructural phases during cooling.