Iron Production
Asif Hosen
Lecturer
Department of MSE,
KUET
Introduction
Introduction
Iron Ore (Lump, sinter,
pellet) 𝐹𝑒𝑇 ≥ 65%
Pig Iron, 𝐹𝑒𝑇 =
90 − 92%
(Reduction + Melting)→ Gray Cast Iron
(Oxidizing+ Refining)→ Plain C Steel
3.5-4.5% C
<2% C
2.5% Si
<1% Si
1.5% Mn
<1% Mn
0.2% P
<0.05% P,S
0.1% S
Introduction
❖ The earth’s crust contains about 5% iron. However, it is present as a compound,
mostly as iron oxide.
❖ Iron is extracted as metallic Fe from the oxide by reduction with a reducing agent.
❖ The principal agent that is used is naturally occurring carbon in the form of coke, coal
or charcoal.
❖ For economic extraction of iron, relatively rich deposits of iron ore, with Fe contents
above 55–60%, are generally used.
❖ The most abundant iron oxide mineral is haematite (i.e. Fe2O3) followed by magnetite
(i.e. Fe3O4).
❖ Iron ores also contain oxide minerals of some other elements such as aluminium,
silicon, manganese and phosphorus.
❖ These minerals are physically mixed with earthy materials such as sand, rock and clay.
Introduction
❖ Some of these substances are harmful for the properties of the finished products.
❖ These are treated as impurities that ought to be removed during extraction.
❖ Iron has the ability to form alloys with many elements.
❖ Such alloying is done intentionally to produce various grades of iron alloys having the
properties required for various applications.
❖ Broadly speaking, iron products can be classified into three categories
1. Wrought iron,
2. Cast iron and
3. Steel.
❑ Today, steel is the most important product of iron, followed by cast iron, while
wrought iron is used in very small quantities for ornamental purposes.
1.1 EARLY HISTORY OF IRON (STEEL)
❖ This type of classification of iron into wrought iron, cast iron, steel, etc. was not
prevalent in the early days, i.e. these terminologies were not known.
❖ All the products were known as iron.
❖ This should be kept in mind while going through the topics that follow.
Early History of Iron Production
❖ The earliest sample preserved in the British Museum dates back to about 3500–4000
BC.
❖ Reduction of iron oxide by charcoal is possible at appreciable rates only above a
temperature of 900–1000°C.
❖ There is evidence that the first iron objects containing small percentages of nickel were
made from metallic iron present in the elemental state in meteorites.
❖ The first definite evidence of ironmaking by the reduction of oxide dates back to about
1500 BC.
Evolution in Iron Production
❖ The melting point of pure iron is 1536°C, but when iron absorbs carbon, the melting
point is lowered significantly. The lowest melting composition (i.e. the eutectic)
containing 4.26% carbon melts at 1153°C.
❖ The primitive furnaces that were used to extract iron were small in size and were
shaped like a deep bowl, about 1–1.5 m high with diameters ranging from 0.4 to 0.8 m.
The lining consisted mainly of dried clay, and charcoal was used as the reducing agent.
❖ Oxygen was supplied by blowing air through pipes kept in the mouth, and later on, by
bellows. The air supplied resulted in the partial combustion of carbon along with the
generation of carbon monoxide and heat, which raised the furnace temperature. The
actual reduction was carried out by CO:
Evolution in Iron Production
Evolution in Iron Production
Evolution in Iron Production
❖ In the small furnaces that were used, it was difficult to attain temperatures higher than
1100°C or so, in the zone of maximum temperature.
❖ Under these conditions, metallic iron could not absorb much carbon.
❖ Therefore, melting did not take place and hot iron that was obtained remained in the
solid state mixed with a low-melting slag containing very high percentages of FeO.
❖ Upon repeated heating followed by forging into various shapes using a hammer, most of
the slag got ‘squeezed out’ to leave solid iron (sponge) that was almost pure (with low
concentrations of carbon, etc.).
❖ This type of product became known as wrought iron (wrought meaning worked, i.e.
forged).
Evolution of Ironmaking in Europe
Self Study : Page 04 - 05
Major Developments in BF
1. Replacement of charcoal by coke
✓ Use of charcoal led to a large-scale destruction of forests in Great Britain before the Parliament
passed legislation to limit iron production.
✓ Coke, obtained by carbonisation of coal, was first used in a blast furnace by Dudley in 1709.
✓ Since coke is stronger than charcoal, the height of the blast furnace could be increased.
2. Use of steam engines for air blowing
✓ Steam engine-driven blowers were invented in 1760.
✓ These blowers were more powerful than the blowers used earlier and as a result, they were
soon employed in all blast furnaces.
✓ Bigger furnace sizes and higher production rates began to be obtained following this
development.
Major Developments in BF
3. Pre-heating of the air blast
✓ Neilson in 1829 introduced the concept of pre-heating the air blast.
✓ Earlier, about 8 tonnes of coal was required to manufacture coke sufficient to make one tonne
iron, but once pre-heating of air to about 150°C became possible, the consumption came down to
5 tonnes.
✓ Further modifications allowed the pre-heating temperature to reach about 600°C.
✓ In 1857, Cowper patented fire-brick lined stoves, which allowed the pre-heating temperature to
be increased even further.
✓ These stoves worked on the regenerative principle — two stoves being heated by combustion of
blast furnace gas, with one stove actually heating the air that was blown.
✓ This was done in a cyclic manner, much in the same way as is in vogue today.
Major Developments in BF
4. Utilization of blast furnace gas as fuel
✓ The hot gas that exits from the furnace top is referred to as blast furnace gas.
✓ It contains a high percentage of carbon monoxide, which can be burnt with air as a fuel to
provide heat.
✓ Earlier, the entire gas exiting from the furnace top used to be burnt for pre-heating the air blast.
✓ In 1845, Bunsen and Playfair pointed out that the bulk of the calorific value of the gas was being
wasted in this approach and suggested that the gas be transported through a pipeline for
utilization, not only for pre-heating of air, but also for using elsewhere in the iron works.
