Swords and iron Flashcards
What is the process of carburisation?
Heating in a C-rich atmosphere, e.g. from charcoal; diffusion of C from exterior to interior microstructure
What does carburisation do to properties of the object?
Improves local mechanical properties; in combination with quenching, forms a (strong) martensitic exterior and (ductile) pearlite core
What is an alternative to carburisation?
Nitridisation
What are the three stages of the boiling curve?
Nucleate boiling, transition boiling, film boiling
What happens during nucleate boiling?
Water penetrates surface flaws, but surface tension prevents from reaching apex of flaw; as temp increases, bubble becomes larger and is released; cold water collapses onto surface to replace the bubble; hot material against the cooler water allows for heat transfer by conduction/ convection
What happens during transition boiling?
Vapour film forms and collapses
What happens during film boiling?
Film vapour (~0.5cm) covers surface and insulates liquid from solid, so must use conduction as heat transfer
What is heat flux?
Heat transfer rate
Where is the critical heat flux?
At the top of the curve
What is pattern welding?
A by-product of using welding sheets with different individual C content
Why are swords not made of a homogeneous material?
Properties at edge should be different to at centre; thin sheets of carburised iron are homogeneous as no quenching occurs due to thinness, but welding different sheets together gives mechanical advantage
What is an example of a heterogeneous pattern-welded sword’s composition?
Core has medium-C content (0.5%); either side of core backed with soft iron strip (0.1%C); core and sides are piled and twisted together; cutting edge welded to core and sides is plain C-steel (0.3%C)
What is Damascening?
A method formed in Damascus; same as pattern welding but with finer and more steel strips; takes up to 75 hours and 128 reheats to make; uses layers of higher-C (cementite) steel or cast iron fragments, mixed with low-C bloom steels
Outline the process of cementation.
Wrought iron bars into furnace; heat to 1100 Celsius; heat for a week; carbon diffuses into steel; blister steel forms (0.1% C); bars cut, forged, and reheated; more homogeneous composition of shear steel formed
What is Huntsmans’ crucible steel?
Liquid Fe with high C
What are two overarching methods of making steel?
Carburising wrought iron; de-carburising cast iron
How was Huntmans’ crucible steel formed from carburisation of wrought iron?
Use coke (devolatilised coal) to obtain a high furnace temperature (1200-1300 Celsius); blister steel melts in pots with a flux; cast to shape; due to liquid form, C pick-up from coke was high; C content of steel increased
How was Huntsmans’ crucible steel formed from decarburisation of cast iron?
Use a Bessemer converter: blow in air; O2 reacts with C in iron –> CO2; C content of steel decreased, but O2 still dissolved in melt which would make brittle; deoxidise to remove embrittling O2
What are the four stages of modern steel-making?
Blast furnace; oxygen blowing; deoxidising; alloying
What occurs in the blast furnace in modern steel-making?
Iron found as Fe2O3 and Fe3O4 is reduced by reaction with C from coke; occurs at high temperatures; Fe2O3 + CO –> 2Fe + 3CO2; high C content liquid iron formed
What occurs in oxygen blowing in modern steel-making?
Lance blows O2 through liquid steel; O2 + 2C –> 2CO; reduced C content, high O content liquid iron formed
What occurs in deoxidising in modern steel-making?
Add elements with high reactivity with O2 (Si, Al); deoxidation products float out of steel and removed with slag
What occurs in alloying in modern steel-making?
Held under vacuum to degas: N removed; reaction with slag: removes impurities (S and P); addition of ferroalloys (Mn, Cr, Ni): alters composition and properties; stir with Ar gas: makes temperature and composition uniform
When was malleable iron invented?
In China c. 300BC; was patented in England in the 1670s
