Let's break down the question step by step: **Question:** Consider an iron carbon alloy of eutectoid composition. While doing heat treatment, the following time-temperature treatment is done: 1. Rapidly cooled to 500°C, held for 5 seconds, 2. Rapidly cooled to 300°C, held for 10,000 seconds, 3. Quenched to room temperature. Assume the specimen begins at 760°C (austenite). **Ask:** Specify the nature of the final microstructure. --- ### **Analysis:** - **Austenite at 760°C:** The alloy is fully austenitic. - **Rapid cooling to 500°C and held for 5 seconds:** This is too short for significant transformation, so mostly still austenite. - **Rapid cooling to 300°C and held for 10,000 seconds:** At 300°C, bainite forms if held for enough time. 10,000 seconds is sufficient for austenite to fully transform to bainite at this temperature. - **Quench to room temperature:** Anything left as austenite would transform to martensite, but since 10,000 seconds at 300°C is enough for complete bainite transformation, there should be no austenite left. --- ### **Conclusion:** The **final microstructure** will be **100% bainite**. --- ### **Correct Answer:** **100% bainite.**