2.
Phase transformations and microstructural control in Fe-C alloysystem For the Fe-C alloy of eutectoid composition(shown below in the left graph):
1100
' 800 T TT
500
I I I I I I I I
a + Fe3C
100
M(50%) A/(90%)
1 10
50%
102 103 104 105 Time (s)
400_ I01.0 2.0 10_1
Composition (wt% C)
a) Name the possible types of micro-constituents inmicrostructures achieved by austeniticphase transformation whensubjected to various isothermal heat treatments. [1]
b) Mark these micro-constituents directly on thetime-temperature-transformation (ill)diagram (shown above in theright graph). [2]
c) Rank microhardness of these micro-constituents in increasingorder. [1]
d) Using the TTT diagram, specify the final microstructure (interms of micro-constituentsand approximate percentages of each) ofa small specimen that has been subjected to the followingtime-temperature treatments. In each case, assume that the specimenbegins at 760 °C and that it has been held at this temperature longenough to have achieved acomplete and homogeneous austeniticstructure. [5]
