Question

600 4. Chapter 10: Example Problem 10.3 (30 points, 10 points each) Using the isothermal transformation diagram for an iron-carbon -Eutected mere 1400 alloy of eutectoid composition (Figure 10.23), specify the nature roo- of the final microstructure in terms of microconstituents present and approximate percentages) of a small specimen that has been subjected to the following time-temperature treatments. In each case, assume that the specimen begins at 760°C (1400°F) and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. (a) Rapidly cool to 350°C (660°F), hold for 10 s, and quench to 200 room temperature. (b) Rapidly cool to 250°C (480°F), hold for 100 s, and quench to MSOMI room temperature. MSON) (c) Rapidly cool to 650°C (1200°F), hold for 20 s, rapidly cool to 400°C (750°F), hold for 10's, and quench to room 10 10 10 10 104 105 temperature. Temperaturen Time) Solution:

Answer 1

esort srout 40€ + 360°ct 300 F 25014 sila) 4 bainite ab i martensite Meat Hubo TMF 3 Lot I Os 10 c 4 pearlite & bamite Scanned with CamScanner

Ok we tried mapping the processes on TTT diagram .

For part a). We can see the it is cooled to 350°C and it is still completely austenite and thenit is hold for 10000s , during which it crosses to Bainite region implies it transforms to Bainite completely and then quenched . So it will have Bainite (100%)

For part b) we can see it is cooled to 250°C and then hold for 100 s during which no transformation acts and it remains as austenite . After this it is coooled to room temp , thus it cuts martensitic start and finish line , implies it converts to martensite (100%)

For part c) we can see it is cooled at 650°C and hold for 20s , in this pearlite transformation is started but not completed as it doesn't cut pearlite finish line and then it is cooled to 400°C and then hold for 1000s , during which remaining austenite converts to Bainite as it cuts bainite finish line and then cooled to room temp.

So it contains pearlite and bainite mixture as final product.