3. Consider the phase diagram below: 1600 1538°C: 1495°C. Liquid -1394 Liquid +

Question

3. Consider the phase diagram below: 1600 1538°C: 1495°C. Liquid -1394 Liquid + Cementite 21300 iquid + Austenite O 1200... 1154°C Austenite (r-Fe) 110 2.08% Austenite:+ Cementite 900 9122C Acm 0.68%/ 800 : 738°c (A,); 700-Ferrite (aFe); : Ferrite + Cementite 600 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 MASS PERCENT C 2006 calphad.com (a) Austenite is more ductile than ferrite; ferrite is more ductile [2] than cementite. Why? (b) Pearlite is a lamellar (layered) mixture of ferrite and cementite. Bainite is a dispersion of cementite particles in ferrite. Which do you expect to be more ductile? Why? (c) Consider a 0.5 wt% C steel and a 0.7 wt.% C steel. which [4] one has larger Young's modulus (stiffness), or are they the same in this regard? Why? (d) Consider a 1 wt.% C steel cooled from 1500 oC. List the phase transformations that you expect to occur from 1500 °C to room temperature. What do you expect to occur between 600 °C and room temperature?

Explanation / Answer

1. Austenite is more ductile than ferrite due to its fine crystal structure and homogeneity in its microstructure , and ferrite is more ductile than the cemetite due to more slippages present along the grain boundary.

2. Pearlite is more ductile than Bainite because of its lamellar layer of ferrite and cementite which allows slippage to occur and less so in dispersed phase of Bainite.

3. Steel with less carbon content tend to be more ductile but it has very limited impact on the young's modulus, it remains more or less same without much difference.

4. Different phase transformation that would occur are- liquidliquid+austeniteausteniteferrite+cementite.

Between 600°C and room temperature phase would not change although mechanical properties may change.

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