Lecture 1: Introduction to Iron and Steel Making

1. Course Overview & Scope

Course Structure: Split into two non-overlapping sections:
1. Iron Making (~17 lectures)
2. Steel Making (~17 lectures)
Key Topics: Material Balance, Thermodynamics, Kinetics, and Rist Diagrams.
Goal: To move beyond descriptive chemistry (Grade 12 level) to engineering principles governing the extraction and refining of iron.

2. Global and Indian Steel Scenario (2019 Statistics)

Production Statistics

Global Steel Production: ~1870 Million Metric Tonnes (MMT).
Top Producers:
1. China: ~1000 MMT (Dominant player, >50% global share).
2. India: ~111 MMT (2nd Largest).
3. Japan: ~100 MMT.

Per Capita Steel Consumption

A key index of a nation’s prosperity and development.

Global Average: ~225 kg/person.
Developed Nations (USA, Japan, Germany): 200–300 kg/person.
India: ~75–80 kg/person.
- Target: Government aims to increase capacity to 300 MMT by ~2030, raising per capita consumption to 160 kg.

3. Historical Evolution & Thermodynamics of Extraction

Why did the Bronze Age precede the Iron Age?

Despite iron being more abundant in the earth’s crust than copper or zinc, it was extracted much later.

Reason: The Iron-Oxygen bond in hematite ( $F e_{2} O_{3}$ ) is significantly stronger than the Cu-S or Cu-O bonds.
Thermodynamic Constraint: Primitive furnaces could not reach the high temperatures required to break this bond using Carbon.

Thermodynamics: The Ellingham Diagram

(Conceptual Reconstruction of Board Work)

The feasibility of reducing Iron Oxide with Carbon is determined by the intersection of free energy curves ( $Δ G^{\circ}$ vs $T$ ).

Line 1 ( $2 F e + O_{2} \to 2 F e O$ ): Slopes upwards (Stability of oxide decreases with T).
Line 2 ( $2 C + O_{2} \to 2 C O$ ): Slopes downwards (CO becomes more stable at high T).
Intersection Point: Approximately 900°C.

Interpretation:

T < 900°C: Iron has a higher affinity for Oxygen. Reduction by Carbon is thermodynamically difficult.
T > 900°C: Carbon has a higher affinity for Oxygen. Carbon can strip Oxygen from FeO to form CO.
Historical Context: Primitive man struggled to sustain T > 900°C, delaying the Iron Age.

Melting Points & Solid State Reduction

Pure Iron Melting Point ( $T_{m}$ ): 1539°C.
Primitive Iron Making:
- Ancient furnaces could not reach 1539°C.
- Iron was produced in the solid state (spongy/porous mass known as bloom or wrought iron).
- Reaction: Solid-Gas reaction dominated by diffusion (slow process).
  
  $F e_{2} O_{3} (s) + C O (g) \to F e (s) + C O_{2} (g)$

4. Reduction Mechanism (Step-by-Step)

Reduction of hematite to metallic iron does not happen in one step. It occurs via intermediate oxides with decreasing Oxygen-to-Iron ratios.

Board Work: Reduction Sequence

Oxide / State	Formula	O/Fe Ratio (Atomic)	Characteristics
Hematite	$F e_{2} O_{3}$	1.50	Hard to reduce initially.
Magnetite	$F e_{3} O_{4}$	1.33	Intermediate phase.
Wustite	$F e O$	1.05	Stable only above 570°C.
Metallic Iron	$F e$	0.00	Final Product.

Instructor Note: The removal of the last oxygen atom (FeO $\to$ Fe) is the most difficult step kinetically and thermodynamically.

5. Structure of the Indian Steel Industry

India typically follows three distinct routes for steel production, unlike most countries that rely on just two.

Sector 1: Integrated Steel Plants (ISP)

Route: Blast Furnace (BF) $\to$ Basic Oxygen Furnace (BOF).
Feedstock: Iron Ore + Coal/Coke.
Product: Liquid Iron (Hot Metal) $\to$ Liquid Steel.
Scale: Mammoth (e.g., 4–5 Million Tonnes Per Annum per furnace).
Key Players: TATA Steel, JSW, SAIL (Bhilai, Bokaro, etc.), RINL.
Contribution: ~70 MMT (~63% of total).

Sector 2: Electric Arc Furnace (EAF) / Secondary Sector

Route: DRI/Scrap $\to$ Electric Arc Furnace.
Feedstock: Steel Scrap + Direct Reduced Iron (DRI/Sponge Iron).
Product: Specialty Steels (High strength, fatigue resistant for auto/aerospace).
Scale: Medium (50–100 Tonnes capacity furnaces).
Contribution: ~10 MMT.

Sector 3: Induction Furnace (IF) Sector

Route: Melting in Induction Furnace.
Feedstock: 100% Scrap (recycled from automobiles, railways, etc.).
Product: Mild Steel (Long products like TMT bars for construction).
Scale: Small/Micro (~3–10 Tonne furnaces).
Units: >3000 small units scattered across India.
Contribution: ~30 MMT.

6. Comparison of Furnaces (Ancient vs. Modern)

Parameter	Ancient Shaft Furnace	Modern Blast Furnace
Height	~15–16 feet	~35 meters (~115 feet)
Diameter	Small (~1-2 meters)	~15 meters (Hearth diameter)
Production	~350 kg/day	~13,000–15,000 Tonnes/day
State of Iron	Solid (Porous Bloom)	Liquid (Hot Metal)

Important Instructor Remarks

Iron vs. Steel: Iron is an intermediate product; Steel is the finished engineering material.
Slag Generation: Approx. 30% of output is slag (waste). For 1870 MMT steel, ~600 MMT slag is generated globally. Modern engineering focuses on recycling this slag.
Carbon’s Role: Carbon acts as a reducing agent (removes Oxygen) and an alloying element (lowers MP of Iron).
- Fe-C Phase Diagram: Addition of Carbon depresses the melting point of Iron, allowing liquid iron production at lower temperatures than 1539°C.

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Lecture 01