Question

2.

Phase transformations and microstructural control in Fe-C alloy system 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 in microstructures achieved by austeniticphase transformation when subjected to various isothermal heat treatments. [1]

b) Mark these micro-constituents directly on the time-temperature-transformation (ill)diagram (shown above in the right graph). [2]

c) Rank microhardness of these micro-constituents in increasing order. [1]

d) Using the TTT diagram, specify the final microstructure (in terms of micro-constituentsand approximate percentages of each) 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 and that it has been held at this temperature long enough to have achieved acomplete and homogeneous austenitic structure. [5]

Answer 1