Question:
An Iron-Carbon alloy at room temperature has pro-eutectoid ferrite as a constituent in the microstructure, that formed above the eutectoid temperature. The alloy also has pearlite as another constituent that has formed below eutectoid temperature.
Which ONE of the following best describes this Iron-Carbon alloy?
An Iron-Carbon alloy at room temperature has pro-eutectoid ferrite as a constituent in the microstructure, that formed above the eutectoid temperature. The alloy also has pearlite as another constituent that has formed below eutectoid temperature.
Which ONE of the following best describes this Iron-Carbon alloy?
Which ONE of the following best describes this Iron-Carbon alloy?
Show Hint
Pro-eutectoid ferrite forms only when carbon content is below the eutectoid point.
Updated On: Aug 3, 2026
- Hyper-eutectic steel
- Hyper-eutectoid steel
- Hypo-eutectoid steel
- Eutectoid steel
Show Solution
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The Correct Option is C
Solution and Explanation
Step 1: Understanding the Question:
The alloy shows two things at room temperature: pro-eutectoid ferrite that formed above the eutectoid temperature, and pearlite that formed below the eutectoid temperature.
We need to name the steel type that gives exactly this combination.
Step 2: Recall what pro-eutectoid ferrite means:
On the Fe-C diagram, eutectoid steel (about 0.76 percent carbon) has no pro-eutectoid phase at all, it converts straight to 100 percent pearlite at the eutectoid temperature.
When carbon is below 0.76 percent, the steel is hypo-eutectoid, and as it cools through the austenite plus ferrite region, ferrite starts forming first, before the eutectoid temperature is reached, this is the pro-eutectoid ferrite.
When carbon is above 0.76 percent (and below about 2.14 percent), the steel is hyper-eutectoid, and it forms pro-eutectoid cementite first, not ferrite.
Step 3: Match the description to the right steel:
Check option (A), hyper-eutectic steel: the word eutectic (not eutectoid) applies to cast irons above about 4.3 percent carbon, it is a different transformation entirely, so this is wrong.
Check option (B), hyper-eutectoid steel: this forms pro-eutectoid cementite, not ferrite, so this is wrong.
Check option (C), hypo-eutectoid steel: this is exactly the case where pro-eutectoid ferrite forms above the eutectoid temperature and the remaining austenite turns to pearlite below it, so this matches.
Check option (D), eutectoid steel: this has no pro-eutectoid phase at all, only pearlite, so this is wrong.
Final Answer:
Pro-eutectoid ferrite is the signature of a hypo-eutectoid steel. \[ \boxed{\text{Hypo-eutectoid steel}} \]
The alloy shows two things at room temperature: pro-eutectoid ferrite that formed above the eutectoid temperature, and pearlite that formed below the eutectoid temperature.
We need to name the steel type that gives exactly this combination.
Step 2: Recall what pro-eutectoid ferrite means:
On the Fe-C diagram, eutectoid steel (about 0.76 percent carbon) has no pro-eutectoid phase at all, it converts straight to 100 percent pearlite at the eutectoid temperature.
When carbon is below 0.76 percent, the steel is hypo-eutectoid, and as it cools through the austenite plus ferrite region, ferrite starts forming first, before the eutectoid temperature is reached, this is the pro-eutectoid ferrite.
When carbon is above 0.76 percent (and below about 2.14 percent), the steel is hyper-eutectoid, and it forms pro-eutectoid cementite first, not ferrite.
Step 3: Match the description to the right steel:
Check option (A), hyper-eutectic steel: the word eutectic (not eutectoid) applies to cast irons above about 4.3 percent carbon, it is a different transformation entirely, so this is wrong.
Check option (B), hyper-eutectoid steel: this forms pro-eutectoid cementite, not ferrite, so this is wrong.
Check option (C), hypo-eutectoid steel: this is exactly the case where pro-eutectoid ferrite forms above the eutectoid temperature and the remaining austenite turns to pearlite below it, so this matches.
Check option (D), eutectoid steel: this has no pro-eutectoid phase at all, only pearlite, so this is wrong.
Final Answer:
Pro-eutectoid ferrite is the signature of a hypo-eutectoid steel. \[ \boxed{\text{Hypo-eutectoid steel}} \]
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