Question

Name the microstructural products of eutectoid iron-carbon alloy (0.76 wt% C) specimens that are first completely transformed to austenite, then cooled to room temperature at the following rates:

(a) 200°C/s,
(b) 100°C/s, and
(c) 20°C/s.

Answer 1

The microstructural products of eutectoid iron-carbon alloy specimens at different cooling rates include fine-grained pearlite, coarser-grained pearlite, and a mix of pearlite and bainite.

Step-by-step explanation:

The microstructural products of eutectoid iron-carbon alloy specimens, which are first completely transformed to austenite and then cooled to room temperature at different rates, can be determined using the iron-carbon phase diagram. The eutectoid composition of iron-carbon alloy is 0.76 wt% C. At different cooling rates, the resulting microstructures will be different.

(a) At a cooling rate of 200°C/s, the alloy will form a fine-grained pearlite microstructure consisting of alternating layers of ferrite and cementite.

(b) At a cooling rate of 100°C/s, the alloy will also form a pearlite microstructure, but with slightly coarser grains compared to (a).

(c) At a cooling rate of 20°C/s, the alloy will form a mix of pearlite and bainite microstructures, with the proportion of bainite increasing compared to (b). Bainite is a microstructure that forms at slower cooling rates and has a finer structure compared to pearlite.