Using the isothermal transformation diagram for an iron-carbon alloy of eutectoid composition, answer question 6 8

6. (5 pts) Suppose that a steel of eutectoid composition is cooled to 550C (1020F) from 760C (1400F) in less than 0.5 s and held at this temperature. How long will it take for the austenite-to-pearlite reaction to go to 50% completion?

a) 2.5 s

b) 10 s

c) 25 s

d) Cant say

7. (20 pts) Describe the nature of the sample after each of the follow heat treatments. I am looking for the materials/phases present as well as ballpark estimates (10%, 25%, 50%, etc.) of these phases. In each case assume that the specimen begins at 760 C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure:

(1) Cool rapidly to 400 C, hold for 20s, then quench to room temperature.

(2) Rapidly cooled to 500 C, then hold at this temperature for 5 s, then rapidly cooled to 300C, and hold for 30s, and finally quenched to room temperature.

8. (10 points) Sketch and label time-temperature paths on this diagram to produce the following microstructures (one process to get the following microstructure):

25% coarse pearlite, 50% bainite, and 25% martensite