1.
Crystallography (12 Hrs)
Q1. Explain the atomic structure of metals and the difference between crystalline and non-crystalline
materials.
Answer:
Atomic Structure of Metals: Metals have a crystalline structure where atoms are arranged in a
repeating pattern. Most common structures: BCC, FCC, and HCP.
Crystalline Materials: Have long-range order; atoms are arranged in a periodic pattern. Example: Iron
(α-Fe).
Non-Crystalline (Amorphous): Lack a defined structure; atoms are randomly arranged. Example:
Glass.
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Q2. What are crystal defects? Explain point and line defects.
Answer:
Crystal Defects: Imperfections in the regular arrangement of atoms.
Point Defects:
Vacancy: Missing atom.
Interstitial: Extra atom in a space.
Substitutional: Atom replaced by a different one.
Line Defects (Dislocations):
Edge Dislocation: Extra half-plane of atoms.
Screw Dislocation: Spiral distortion in lattice.
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2. Phase Transformation (09 Hrs)
Q3. Draw and explain the Iron-Carbon Equilibrium Diagram.
Answer:
Show all critical temperatures (A1, A3, Acm), phases (austenite, ferrite, cementite), and reactions
(eutectoid, eutectic, peritectic).
Important point: Eutectoid reaction at 0.8% C and 727°C:
γ (Austenite) → α (Ferrite) + Fe₃C (Cementite)
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Q4. What is a TTT diagram? Explain its significance.
Answer:
TTT (Time-Temperature-Transformation) Diagram: Shows transformation of austenite at constant
temperature.
Helps to decide heat treatment process (e.g., quenching, annealing).
Shows pearlite, bainite, and martensite regions.
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3. Heat Treatment (09 Hrs)
Q5. Define and differentiate between Annealing, Normalizing, Hardening, and Tempering.
Answer:
Annealing: Heating then slow cooling – improves ductility and removes stresses.
Normalizing: Cooling in air – refines grain size.
Hardening: Rapid cooling (quenching) – increases hardness.
Tempering: Reheating hardened steel to reduce brittleness.
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Q6. Explain surface hardening and flame hardening.
Answer:
Surface Hardening: Hardens the outer surface, core remains soft.
Examples: Carburizing, Nitriding, Cyaniding.
Flame Hardening: Heating with flame then quenching. Used for gears and shafts.
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4. Ferrous Metals and Their Alloys (06 Hrs)
Q7. What are the effects of alloying elements like Si, Mn, Ni, Cr, Mo, and Al on steel properties?
Answer:
Si (Silicon): Increases strength and hardness.
Mn (Manganese): Improves hardness and tensile strength.
Ni (Nickel): Improves toughness and corrosion resistance.
Cr (Chromium): Increases hardness, corrosion resistance.
Mo (Molybdenum): Increases strength at high temperatures.
Al (Aluminum): Grain refiner, removes oxygen.
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Suggested 5-Question Exam Set for Practice:
1. Define and classify crystal structures with examples.
2. Explain the Fe-C diagram and mark eutectoid, eutectic points.
3. Discuss heat treatment processes with neat diagrams.
4. Explain TTT diagram and its use in transformation.
5. Discuss the effect of alloying elements on steel.
