List the percentage of the amount of the final microstructures present for the f

Question

List the percentage of the amount of the final microstructures present for the following heat treatment schedule for eutectoid steel with the given TTT diagram. Start at 760oC Rapid cool to 650oC and hold for 20s Rapid cool to 450oC and hold for 10s Quench to room temperature.

If the microstructure is not present, enter zero. Please round to the nearest 10s or 5s (ie, 33 would become 35). Don't enter the "%" sign.

QUESTIONS: (5 NUMBERS TOTAL)

Pealite

Bainite

Tempered Martensite

Martensite

Spheroidite

800 1400 Eutectoid temperature 700 1200 600 1000 500 800 3 400 300 M(start) 50% 200 M +A 400 M( 5096) M( 9096) 100 10-1 10 10 10 10410 Time (s)

Explanation / Answer

After cooling to and holding at 650°C for 20 s, approximately 50% of the specimen has transformed to pearlite (medium). During the rapid cooling to 450°C no transformations occur. At 450°C we start timing again at zero time; while holding at 450°C for 10 s, approximately 50 percent of the remaining unreacted 50% (or 25% of the original specimen) will transform to bainite. And upon cooling to room temperature, the remaining 25% of the original specimen transforms to martensite. Hence, the final microstructure consists of about 50% pearlite (medium), 25% bainite, and 25% martensite.

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