Study Notes: Ferrous Alloys and Related Material Classifications

Types of Engineering Materials:
- Metals
- Plastics
- Ceramics
- Composites
- Others
Metals:
- Ferrous
- Nonferrous
Plastics:
- Thermoplastics
- Thermosets
- Elastomers
Ceramics:
- Oxides
- Nitrides
- Carbides
- Amorphous
Examples of Other Materials:
- Acrylics
- ABS
- Nylons
- Polyethylenes
- PVC
- Epoxies
- Phenolics
- Polyimides
- Rubbers
- Silicones
- Polyurethanes
- Glasses
- Graphite
- Diamond
- Reinforced Plastics
- Metal-Matrix Composites
- Ceramic-Matrix Composites
- Laminates
- Glass Ceramics

Ferrous Alloys Classification:
- Ferrous Steels:
- Low alloy (less than 5% alloying elements)
  - Low-carbon
  - Medium-carbon
  - High-carbon
- High alloy (more than 5% alloying elements)
  - Tool
  - Stainless
- Cast Irons:
- Gray iron
- Ductile (nodular) iron
- White iron
- Malleable iron
- Compacted graphite iron

Characteristics:
- Most produced type of steel
- Carbon content: less than 0.25 wt% C
- Unresponsive to heat treatments meant for martensite
- Strengthening via cold work
- Microstructure: ferrite and pearlite
- Properties: soft, weak but ductile and tough
- Machinability: good
- Weldability: excellent
- Cost: lowest production cost among steels
Typical Applications:
- Automotive body components
- Structural shapes (I-beams, channel iron, angle iron)
- Sheets for pipelines, buildings, bridges, and tin cans
Mechanical Properties:
- Yield strength: 275 MPa
- Tensile strengths: 415 - 550 MPa
- Ductility: 25% EL

Characteristics:
- Another category of low-carbon alloys
- Alloying elements (Cu, V, Ni, Mo): up to 10 wt%
- Higher strength than plain low-carbon steels
- Heat treatment capability: tensile strengths greater than 480 MPa
- Ductile, formable, machinable
- Corrosion resistance superior to plain carbon steels
Applications:
- Bridges
- Towers
- Support columns in high-rise buildings
- Pressure vessels

Characteristics:
- Carbon concentration: 0.25 - 0.60 wt%
- Heat treatment via austenitizing, quenching, and tempering
- Typical microstructure: tempered martensite
- Low hardenability: effective only in thin sections with rapid quenching
- Alloying additions (Cr, Ni, Mo): enhance heat-treatment capacity
- Properties: stronger than low-carbon steels, reduced ductility and toughness
Applications:
- Railway wheels and tracks
- Gears
- Crankshafts
- High-strength structural components requiring strength, wear resistance, toughness

Characteristics:
- Carbon content: 0.60 - 1.4 wt%
- Hardness: hardest and strongest among carbon steels
- Ductility: lowest
- Typically used in hardened and tempered states
- Wear resistance: exceptional, able to hold sharp edges
Applications:
- Cutting tools
- Dies for forming materials
- Knives, razors, hacksaw blades, springs, high-strength wire

Characteristics:
- High corrosion resistance in various environments
- Predominant alloying element: chromium (at least 11 wt%)
- Enhanced corrosion resistance with Ni and Mo
- Classes based on microstructure:
- Martensitic
- Ferritic
- Austenitic
Microstructure Effects:
- Martensitic steels can be heat-treated
- Austenitic steels retain austenite phase at room temperature
- Ferritic steels consist of α-ferrite (BCC) phase
- Austenitic steels: non-magnetic and highly corrosion resistant
- Martensitic and ferritic steels: magnetic properties

Phase Diagram Insights:
- Effect of 17% chromium on iron-carbon phase diagram
- At low-carbon contents, ferrite is stable at all temperatures
- Section of phase diagram for 18% Cr-8% Ni
- At low-carbon contents, austenite is stable at room temperature

Designation System Elements:
- Element Factor:
- Cr, Co, Mn, Ni, Si, W: 4
- Al, Be, Cu, Mo, Nb, Pb, Ta, Ti, V: 10
- Ce, N, P, S: 100
- B: 1000
Mild Steels:
- Less than 1% Mn: Cx
- Example: C45 (0.45% carbon content)
- More than 1% Mn; alloyed steels: NE…x-x-x
- Example: 55NiCrMoV6-2-2-1 (0.55% carbon content with alloy elements)

Designation Format:
- HSx-x-x-x:
- W, Mo, V, Co: in order of appearance
- Chromium content: 3.5-4.5%
- Example: HS6-5-4 (carbon content 1.3%, 4.6% Mo, 5.6% W, 3.95% V)

Categories of Steel Designations:
- S: Structural steel engineering
- P: Pressure vessel construction
- Examples: $235JR$, $S355J0$, $P265GH$
- L: Pipeline construction
- E: Engineering steels
- B: Reinforcing steels
- Examples: $P355M$, $L360A$, $L360QB$, $E295$, $E360$
- YY: Prestressing steels
- R: Steel for rails
- H: Cold rolled flat rolled steels with higher-strength
- D: Flat products made of soft steels for cold reforming

General Definition:
- Ferrous alloys with carbon content that causes eutectic reactions during solidification
Types of Cast Iron:
- Gray Cast Iron
- White Cast Iron
- Malleable Cast Iron
- Ductile or Nodular Cast Iron
- Compacted Graphite Cast Iron

Microstructure of Cast Irons:
- Cast irons viewed as steels with carbon-rich phases (graphite or cementite)
Gray Iron:
- Characteristics: Graphite flakes in ferrite matrix, leading to brittleness
Nodular Iron:
- Characteristics: Graphite nodules improving toughness and ductility
White Iron:
- Characteristics: Cementite plates in pearlite matrix, leading to high hardness and brittleness
Malleable Iron:
- Characteristics: Graphite clusters improving toughness and ductility
Gray Iron Applications:
- Effective at damping vibrational energy
- Used for machine base structures exposed to vibrations
- High wear resistance and good fluidity for casting intricate shapes
Additional Notes:
- Molten gray iron exhibits low casting shrinkage

This lecture focused on the classification, properties, and applications of ferrous alloys, specifically various types of steels and cast irons, along with their microstructural implications and alloying characteristics.