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.

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.