Ironmaking and Steelmaking Flashcards
Where did the invention of ferrous metallurgy occur?
Protoliterate Vinca Culture based in the lower Danube where it empties into the Black Sea
What is the first step of iron making?
Minerals from iron ore need to be removed by washing and/ or roasting, this changes the composition making it more easily processed
Name 4 iron ores found in Britain
Carbonate ores
Haematite ores
Liminite ores
Bog iron ore
Describe Carbonate ores
FeCO3 (iron carbonate), roaring this ore drives off CO2 = FeO
Further roasting + Fe2O3, haematite
Describe Haematite ores
Fe2)3, valued to its purity, contained little P, compared to iron ores from the continent
Describe Liminite ores
Also known as hydrated iron oxide ores, with absorbed water (fe2O3.H2O)
Probably dug out of outcrops i.e. open cast mining.
Describe bog iron ore
Found mainly in the highland zone.
Consist of a deposit of iron ore occurring in sub-Artic conditions, caused by precipitation where iron-bearing surface water meets organic material. Deposition is continuous, at the rate of.a few mm/ year
Why was iron smelting realised relatively late?
(Not due to high mp 1538oC) but means required for its reduction, which takes place at ~800oC
Name some common impurities in iron
oxides of other elements
a common one is silica SiO2
What is slag
Fragments of iron ore form a charge for reduction and melting, but also contain large amounts of SiO2, which in combination with iron oxide (Fe2O3) form a slag (fayalite)
Slag is detrimental to properties
How is slag removed
Removed by liquidation, requires high T 1150oC, above T @ which FeO reduced but below mp pure Fe
What is bloom
A single sponge-like solid state, produced after removal of slag
Consists of iron interspersed with L slag
Some of L slag drains away in the furnace, remainder “squeezed-out” by subsequent re-heating and hammering
How is the temperature obtained that is needed to make the slag molten
Need fuel to burn, insulation to maintain the T achieved by burning the fuel
What was initially used in the second stage of ironmaking?
Simple bowl furnace, consisting of a layer of insulating brick, through which a tuyere would be introduced
What does the iron smelting process use
Carbon monoxide, generated through partial combustion of charcoal in air pumped through tyre, using bellows to reduce iron oxide to iron
Increase the T in furnace and allows some of L slag to run out of the bottom of the furnace
What is the equation to reduce iron oxide
Fe2O3 + 3CO –> 2Fe+3CO2
What is cinder
The liquid slag that runs out of the bottom of the furnace
What happens if the temperature in a bowl furnace becomes too high
Heating conditions can become more oxidising
If rate of oxidisation of iron is increased, this reduces the amount of iron finally obtained
What was obtained 5 hours after heating an iron ore?
Bloom obtained, consisting of mostly iron but still containing some slag
What happens in the third stage of iron making
bloom is reheated and hammered
Reheated to around 1150oC to make slag fluid
Hammering forces L slag to flow between the iron grains in the bloom, to be extruded out of the bloom
Improves properties –> piece of wrought iron
What is the microstructure like after the third stage of iron making
Simple
Relatively pure
Reduced FeO so largely C free
Why is further pick up of C in wrought iron rare?
Because it is processed in solid state
What is the microstructure of wrought iron
grains of ferrite (ductile) interspersed with stringers of slag
What is fluxing
The addition of compounds to lower the mp of the slag, so processing can take place at lower temperatures
What is a shaft furnace
It’s like a bowl furnace, but has a tall chimney above 5-10 ft high
Allows air to be drawn in, rather than pumped in by bellows = more efficient process
When were shaft furnaces used and when is there little evidence
common practice in roman times
To retrieve the bloom the furnace would be dismantled
In the Iron Age what was the size of the blooms produced
10kg in weight
uses bowl furnaces of ~ 0.5m in size
What was characteristic of the blooms produced
They had high P pick up
from a P-bearing mineral difficult to remove from the iron ore
Where was coinage used
Coinage that came into use in the Lowland Zone of Britain in ~50BC
(Probably as a result of the Gallic wars of Julius Caesar)
Consisted of gold staters and silver and bronze units
What was found in the Highland Zone
Long straight bars of iron found
(e.g. on the malvern Hills, and at Bourton-on-the-Water in the Cotswolds)
interpreted as means of currency
What did the bending of one end of the currency bar indicate
Interpreted as showing the quality of the bar - if bent = ductile = high quality
currency bars seen as currency as could be converted into swords
How long and heavy were Iron Age swords
3 ft long, ~600g
same shape and size as currency bars
typically up to ~0.5% C
How were Iron Age swords made
edges of the sword were either hammered to make OR work harden –> retain a ground edge on the weapon
OR
by hammering together leaves of thinner iron plates
LATER
Blades had edges hardened by carburising
What is Carburising
edge of blade being placed in a C-rich atmosphere (e.g. packed with charcoal)
Causes C atoms to diffuse into the structure
Increases the C content locally = grater pearlite content = tougher and able to receive a ground edge
Compare iron and bronze swords
Iron Age: relatively ductile, might bend in combat - could be straightened then used again
Bronze sword: more brittle, would fracture in combat - could not be used agian
When was the Delhi Iron pillar erected?
~400 AD
How was the Delhi iron pillar said to be made
By bloomers process described above, blooms being beaten into discs, piled on top of each other until they fused
Why is the Delhi iron pillar remarkable
for its lack of corrosion - attributed to high purity of the alloy
Contains a certain amount of P, which has led to the suggestion that the corrosion resistance is due to the formation of a P-containing passive layer
