Materials Science - Ferrous & Non-Ferrous Materials + Heat Treatment
Materials Science – Complete Revision Notes
Ferrous Materials, Heat Treatment & Non-Ferrous Alloys
1. Ferrous Materials: Iron & Steel Manufacture
Raw Materials
- Iron ore (Hematite Fe₂O₃), Coke (C), Limestone (CaCO₃)
Major Furnaces
| Furnace | Product | Temperature | Key Reaction |
|---|---|---|---|
| Blast Furnace | Pig Iron (3.5–4.5% C) | ~1500°C | Direct reduction |
| Open Hearth | Steel (slow, obsolete) | ~1650°C | Oxidation of impurities |
| LD Converter (Basic Oxygen) | Steel (fast, modern) | ~1700°C | O₂ blowing |
| Electric Arc Furnace (EAF) | Steel (from scrap) | ~1600°C | Arc melting |
| Induction Furnace | High-quality steel | — | Electromagnetic |
Types of Cast Irons
| Type | Carbon Form | Microstructure | Properties & Uses |
|---|---|---|---|
| Gray CI | Flake graphite | Ferrite/Pearlite + flakes | Excellent machinability, damping → Machine beds |
| White CI | Cementite | Pearlite + massive cementite | Very hard, brittle → Wear parts |
| Malleable CI | Temper carbon (nodules) | Ferrite + temper graphite | Ductile → Pipe fittings |
| Ductile (SG) Iron | Spherical graphite | Ferrite + nodules | High strength & ductility → Crankshafts |
Carbon Steels Classification
| Type | C % | Properties | Applications |
|---|---|---|---|
| Low Carbon (Mild) | < 0.3% | Soft, ductile, weldable | Sheets, wires, structural |
| Medium Carbon | 0.3–0.6% | Good strength + ductility | Shafts, gears, rails |
| High Carbon | 0.6–1.5% | Very hard, brittle | Cutting tools, springs |
Alloy Steels (Important Elements)
- Ni → Toughness, corrosion resistance (Stainless steel)
- Cr → Hardness, wear & corrosion resistance (SS, tool steel)
- Mo, V → High-temp strength (creep resistance)
- Mn → Hardenability
- Examples: 18-8 Stainless (18% Cr, 8% Ni), HSS (High Speed Steel)
2. Heat Treatment of Steels
Important Heat Treatment Processes
| Process | Purpose | Method | Resulting Structure |
|---|---|---|---|
| Annealing | Soften, relieve stress | Heat to >A₃ → slow cool (furnace) | Coarse pearlite + ferrite |
| Normalizing | Refine grain, uniform structure | Heat to >A₃ → air cool | Fine pearlite |
| Hardening (Quenching) | Maximum hardness | Heat to austenite → rapid cool (water/oil) | Martensite (BCT, brittle) |
| Tempering | Reduce brittleness, improve toughness | Reheat martensite (150–650°C) | Tempered martensite |
| Case Hardening | Hard surface + tough core | Carburizing/Nitriding + quench | Hard case (martensite) |
TTT Diagram (Time-Temperature-Transformation)
- Also called Isothermal Transformation Diagram
- C-shaped curves for Pearlite, Bainite, Martensite
- Nose at ~550°C → Critical cooling rate to avoid pearlite
- Martensite forms athermally (instant) below Mₛ – Mꜰ (no time dependence)
- Used to design heat treatment cycles (austempering, martempering)
3. Non-Ferrous Metals & Alloys
Important Non-Ferrous Metals
| Metal | Crystal Structure | Key Properties | Applications |
|---|---|---|---|
| Copper | FCC | Excellent conductivity, ductility, corrosion resistance | Wires, utensils |
| Aluminium | FCC | Light (2.7 g/cc), good strength/weight, corrosion resistant | Aircraft, foils |
| Nickel | FCC | High corrosion & heat resistance | Superalloys, coins |
| Titanium | HCP → BCC | High strength, low density, biocompatible | Aerospace, implants |
Copper Alloys
| Alloy | Composition | Properties | Uses |
|---|---|---|---|
| Brass | Cu + Zn (up to 40%) | Golden color, ductile, corrosion resistant | Decorative, fittings |
| Bronze | Cu + Sn (5–12%) | Harder than brass, excellent corrosion resistance | Bearings, statues |
| Gun Metal | Cu + 10% Sn + 2% Zn | High strength, wear resistant | Gears, valves |
Aluminium Alloys
- Duralumin: Al + 4% Cu + Mg, Mn → Age hardenable → High strength aircraft alloy
- Y-alloy: Al + Cu + Ni + Mg → Good high-temp strength (pistons)
- Al-Si alloys (Silumin): Excellent castability
Bearing Materials
- Babbitt (White metal): Sn/Sb/Cu → Low friction
- Bronze bearings
- Al-Sn alloys
Advanced Materials (Brief)
- Superalloys (Ni-based): Gas turbines
- Titanium alloys (Ti-6Al-4V): Aerospace
- Shape Memory Alloys (Nitinol): Medical stents
- Maraging steel: Ultra-high strength
- Metal Matrix Composites (MMC)
Quick Revision Summary
| Material | Key Feature | Typical Use |
|---|---|---|
| Mild Steel | Ductile, weldable | Construction |
| High Carbon Steel | Very hard | Tools |
| Gray Cast Iron | Machinability | Machine beds |
| Ductile Iron | Strength + ductility | Auto parts |
| Stainless Steel | Corrosion resistance | Kitchen, medical |
| Duralumin | High strength-to-weight | Aircraft |
| Brass | Beautiful + workable | Musical instruments |
This completes your full Materials Science syllabus notes!
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All the very best for your exam!