What is the expected as-cooled microstructure of a eutectoid steel that experiences the following cooling path: (1) Cooled instantly from 800oC to 630oC (2) Held at 630oC for 10 seconds (3) Cooled to 400oC and held for 200 seconds (4) Quenched to room temperature.

Answer/Explanation:

From the isothermal transformation diagram for a eutectoid steel, the following can be deduced

1 and 2

Cooled Instantly from 800 to 630 C and held for 10 seconds.

No transformaton and 100% austenite will be there in the microstructure specimen

3) Cooled to 400oC and held for 200 seconds

During the rapid cooling 400°C and held for 200seconds, approximately 50℅ will have transformed into coarse pearlite, and 50% of remaining 50% will have transformed into Bainite.

(4) Quenched to room temperature.

Upon quenching to room temperature, 25% of the original specimen transforms to martensite.

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