a. If we cool the first sample quickly to 750 o C, hold for 1000 seconds, and as

Question

a. If we cool the first sample quickly to 750oC, hold for 1000 seconds, and assume that equilibrium is reached:

What phase(s) will be present?

What will the composition of each phase be in wt. % C?

How much of each phase will be present (in wt. %)? Show your calculations.

b. If we then very rapidly quench this sample to room temperature, what microstructure and phases will be present? (2 points)

c. If we very rapidly cool a second sample from 900oC to 700oC, hold for three hours at that temperature, and then very rapidly quench to room temperature, what microstructure and phases will be present? (2 points)

d. If we very rapidly cool a third sample from 900oC to 400oC, hold for 20-25 seconds at that temperature, what microstructure and phases will be present at that instant of time?

g. If we now rapidly cool this third sample to 300oC, what microstructure and phases will be present at that instant of time?

h. If we now hold this sample at 300oC for three days, and then very rapidly quench to room temperature, what microstructure and phases will be present?

Explanation / Answer

(a) ans-austanit and cementite phase will present in microstructure.because it is above the eutectoid temprature temprature.

composition of cementite is 6.7% carbon and composition of austanite is 0.76% of carbon

weight % of phases-0.37/5.94*100% cementide and 5.57/5.94*100% austanite will be present.

(b) if we quench at room temprature than cementide and martensite will we present. on the grain boundary cementide will present.

(c) cementite and pearlite will present in michrostructur. cementide will be on grain boundary and pearlite will be in the inner portion of grain boundary.

(d)the half of austanite will convert in banite in this temp. in the microstructure austanite , upper banite and cementite will present. cementite will be on the grain boundary.

(g)nothing going to change. all thing will be as usual.

(h)in the final phase 50% austanite convert in upper banite , 50%in lower banite and cementide will be present. cementide will be at grain boundary.than upper banite and than lower banite will present in micro structure.

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