Comprehensive Metallurgy: Iron, Steel, and Non-Ferrous Alloys

Steel Manufacturing and Transformation Processes

Insufflating oxygen removes excess carbon from cast iron alloys. The steelmaking process (or 'blow') typically lasts 30 minutes. The resulting products are approximately 300 tons of steel, 120 tons of slag, and 75 tons of gases.

Transformation of Iron and Steel

Lamination (Rolling)

The steel is passed between two rollers that rotate at the same speed and in opposite directions, reducing the cross-section and producing a lengthening. This process is easier at higher temperatures (T).

• Hot Rolling: Performed at high temperatures (800–1250°C).
• Cold Rolling: Performed at ambient temperature (T ambient).

Tubular Products

• Welded Tubes: Joined at one end by welding.
• Seamless Tubes: Produced by moving a heated billet against a punch, which opens the gap, using two cone-shaped cylinders (Mannesmann process).

Steel Rating and Classification Systems

Classification According to Chemical Composition

Non-Alloy Steels

Designated by St or C followed by a number representing 100 times the percentage of Carbon (100 x % C).

Alloy Steels

• Weakly Alloyed Steels: Percentage of other components is less than 5%.
  Example: 145 Cr 6 (0.145% C and 1.5% Cr).
• Special Steels: Designated with an 'X' if the percentage of alloying elements is high.
  Example: X2 CrNi18-9 (0.02% C, 18% Cr, 9% Ni).

Classification According to Application (F Designation)

Designated by 'F' and four figures, where the first series indicates the group and the subsequent figures specify characteristics.

• F1000 Series: General construction steels.
• F2000 Series: Special steels.
• F3000 Series: Stainless steels.
• F5000 Series: Tool steels.
• F8000 Series: Steels for molds and castings.

Cast Iron Alloys and Types

Cast irons are carbonic iron alloys containing 1.76% to 6.67% Carbon (C) and other components.

Types of Cast Iron

First Fusion Cast Iron (White Iron)

• Obtained directly in the blast furnace, typically 2.5–3% C.
• Characteristics: Hard, brittle, and not very machinable.

Second Fusion Cast Iron (Gray Iron)

• Obtained after remelting iron in cupola furnaces.
• Contains 3–3.5% C in the form of graphite flakes.
• Characteristics: More tenacious; used for complicated parts that absorb vibrations well.

Malleable Cast Iron

• Produced by annealing white iron.
• Characteristics: Malleable and ductile; used for complicated parts not subjected to high mechanical stress.

Ductile Cast Iron

• Gray iron treated with Ni, Mg, or Ce.
• Characteristics: Increased mechanical strength and properties similar to steel; used for parts subjected to high pressure.

Key Non-Ferrous Metals and Properties

Nickel (Ni)

• Density (D): 8.85 g/cm³
• Melting Point (Pt): 1450°C
• Resistivity (R): 0.11 µΩ·m
• Characteristics and Applications (C & Ap): Bright, silvery, easily polishable. Magnetic, resistant to oxidation and corrosion. Used to manufacture stainless steel, chemical equipment, and metal coatings.

Tungsten (W)

• Density (D): 19 g/cm³
• Melting Point (Pt): 3370°C
• Resistivity (R): 0.06 µΩ·m
• Characteristics and Applications (C & Ap): Very high melting point. Used for incandescent light bulb filaments and cutting tools for machines.

Cobalt (Co)

• Density (D): 8.6 g/cm³
• Melting Point (Pt): 1490°C
• Resistivity (R): 0.063 µΩ·m
• Characteristics and Applications (C & Ap): Properties similar to nickel but not magnetic. Used for hardening steels and as a tool material in hard metal cutting tools.

Ferrous Minerals and Ore Preparation

Common Iron Minerals

• Magnetite: FeO and Fe₂O₃. Contains 75% Fe (scarce).
• Hematite (Oligist): Fe₂O₃. Contains 70% Fe (very abundant).
• Limonite: Fe(OH)₃. Contains 60% Fe.
• Siderite: FeCO₃. Contains 50% Fe.
• Pyrite: FeS. Not exploited due to its high sulfur content.

Ore Preparation (Concentration)

1. Washing: Using water pressure.
2. Roasting: To remove moisture and sulfur.
3. Crushing: Followed by fine screening.
4. Separation: Mineral flotation or magnetism.
5. Sintering/Pelletizing: To form a compact mass (sinter) or pellets.

Iron Production: Blast Furnace and LD Converter

Zones of the Blast Furnace

• Superior Zone: Where raw materials are introduced and contains the exhaust system.
• Reduction of Oxides Zone: Pure Fe is obtained here. T ≈ 300°C.
• Heat Absorption Zone: Slag begins to melt. T ≈ 400–1200°C.
• Fusion Zone: Iron melts. T ≈ 1500°C.
• Bosh Zone: Oxygen combines with coke carbon. T ≈ 1650°C.
• Crucible Zone: Contains the two entrances (taps for iron and slag).

LD Converter Process

Hot metal (raw iron) arrives carried in torpedo cars, is poured into ladles, and scrap is added as a coolant. Fluxes are added to form slag, completing the steelmaking process.