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Class 2 (2nd Engineer) MEKG 📅 Mar 2026

Exam Question

Q3 (a) Describe the key phases and microstructures present in the iron-carbon equilibrium diagram and explain their significance in the heat treatment of steel. (8) (b) How do the different regions of the iron carbon diagram influence the mechanical properties of steel, such as hardness, toughness, and ductility? Provide examples of how specific compositions and heat treatments can achieve desired properties. (8)

Reference Answer

### Part (a): Key Phases, Microstructures, and Significance in Heat Treatment
The iron-carbon equilibrium diagram is a fundamental map that illustrates the relationship between temperature, carbon content, and the resulting phases and microstructures in steel and cast iron under slow cooling (equilibrium) conditions. Its understanding is paramount for controlling the properties of steel through heat treatment.
#### 1. Key Phases
Phases are physically distinct, chemically homogeneous, and mechanically separable regions of a system. In the iron-carbon system, the key solid phases are:

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