(Solved): a) Differentiate between eutectic, eutectold, and peritectic regions. Locate them on the phase diag ...

Expert Answer

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a) Eutectic, eutectoid, and peritectic regions are specific regions on a phase diagram that describe the behavior of alloy systems.

1. Eutectic Region: The eutectic region is a region on the phase diagram where a liquid phase transforms into two solid phases upon cooling. In this region, a eutectic reaction occurs. The eutectic reaction involves the simultaneous solidification of two components (usually metals) from a liquid solution to form a eutectic mixture of distinct solid phases. The eutectic composition is the composition at which this reaction occurs. On the phase diagram, the eutectic region is typically located between the liquidus and the solidus curves.

2. Eutectoid Region: The eutectoid region is a region on the phase diagram where a solid phase transforms into two different solid phases upon cooling. In this region, a eutectoid reaction occurs. The eutectoid reaction involves the transformation of a single solid phase into two different solid phases at a specific temperature and composition. The eutectoid composition is the composition at which this reaction occurs. On the phase diagram, the eutectoid region is typically located between the upper critical temperature (A3) and the lower critical temperature (A1).

3. Peritectic Region: The peritectic region is a region on the phase diagram where a solid phase and a liquid phase react to form a different solid phase upon cooling. In this region, a peritectic reaction occurs. The peritectic reaction involves the transformation of a solid phase and a liquid phase into a different solid phase at a specific temperature and composition. The peritectic composition is the composition at which this reaction occurs. On the phase diagram, the peritectic region is typically located between the solidus and the peritectic curve.

b) At 0.65 wt% C, the microstructure development in steel depends on the cooling rate. Assuming a slow cooling rate, the following microstructure will form:

The steel will undergo a eutectoid reaction. The eutectoid composition of steel is approximately 0.76 wt% C. At 0.65 wt% C, the microstructure that forms is pearlite. Pearlite consists of alternating layers of ferrite ( ??iron ) and cementite (Fe3C). It is a lamellar microstructure and is formed through the transformation of austenite ??iron ( ) during slow cooling.

c) For a 1 wt% C steel at a temperature just below the eutectoid:

I. The compositions of components:
- The eutectoid composition of steel is approximately 0.76 wt% C.