Hardenability Flashcards
What is hardenability?
Ability of a steel to transform to hard martensite, which is controlled by its microstructure and cooling rates
How can alloying aid hardening?
Addition of alloying elements, such as Mn, displaces pearlite nose to right = martensite formation is easier and more extensive
How can hardenability be used in sword making?
Quenching water: surface will have high cooling rate = martensitic = high TS; interior will have lower cooling rate = fine pearlite = ductile and some strength
What are four iron ores?
Carbonate, haematite, liminite, bog iron ores
What are carbonate ores?
FeCO3. Roasting drives off CO2 –> FeO. Further roasting –> Fe2O3
What are haematite ores?
Fe2O3. Valued for purity due to small phosphate content compared to iron ores form the Continent
What are liminite ores?
Hydrated ores; Fe2O3.H2O
What are bog iron ores?
Found mainly in highland zone; consists of a deposit of iron ore occurring in sub-Arctic conditions; formed by precipitation where iron-bearing surface water meets organic material. Deposition is continuous at a few mm each year
What is wrought iron?
Up to 4% C
What is the overall process used to manufacture wrought iron?
Washing to remove gangue; roasting to convert the ore; smelting reduces iron oxide to relatively pure Fe; slag is produced; hammering improves properties of wrought iron
How is CO for smelting produced?
Generated by partial combustion of charcoal in air; charcoal itself is partially combusted wood, with the volatiles driven off
How is iron oxide smelted?
CO is pumped through tuyere by bellows; Fe2O3 + 3CO –> 2Fe + 3CO2 (based on Ellingham diagram); bowl over bowl furnace to seal off from environment; heat to ~1150 Celsius for 5 hours; heating above intersect allows higher rate of reaction; liquid slag collects at bottom of furnace as cinder; bloom is obtained; bloom still contains slag as inclusions, making product too brittle to be usable; bloom reheated; slag becomes liquid; bloom hammered to squeeze out slag; wrought iron formed with improved mechanical properties
What does slag consist of?
Fe2CO3, SiO2, P
Why is alpha ferrite formed?
Low temperature = solid = low rates of diffusion of C through grains of ferrite
What might happen if the temperature of the furnace is too high?
Conditions may become oxidising, reducing amount of final iron product
