Materials - Metals 2

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What type of metal is iron?
Iron is polymorphic/allotropic which means it has different crystal stuctures at different temps. As temp increases to 912 degrees, BCC structure becomes FCC. Solubility of carbon in BCC is less, so this is a problem in cooling
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What are hypo and hyper eutectoids?
Hypoeutectoid - lower carbon content. Hypereutectoid - greater carbon.
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How does austenite change for hypoeutectoids?
For hypoeutectoids, ferrite grains form at austenite boundary and rest becomes pearlite, then transforms to ferrite and cementite, (Fe3C - carbon comes into it as solubility falls) after pro-eutectoid phase
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What is the product of austenite cooling?
The product of a hypoeutectoid reaction is the formation of pearlite which is made of ferrite and cementite with metal-ceramic likeness. Alternating layers with ferrite ductile and cementite strong but brittle
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What is product of hypereutectoid formation?
Fe3C forms at the austenite grain boundaries. In continuous brittle phase steel is brittle. Remaining austenite made to pearlite with cementite precipitating at austenite boundaries. More carbon means product more hard and brittle but stronger yield
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What is common carbon weight in steels?
Many steels contain carbon <0.8% wt
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What is the direction of the formation reaction?
Reaction is shown on diagram from left to right
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How is martensite made?
If cooling fast, phase diagrams invalid. Metastable phases form. If cooling is too fast, carbon can't diffuse, leads to a distorted body-centred lattice with locked carbon - martensite, 4.3% larger vol and body centred tetrahedral
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What is martensite structure?
Martensite has many interfaces with greater hardness due to C, harder than pearlite, high strongly varied local stresses around C, between laths, and between colonies of different orientation, leads to resistance of dislocation motion, brittleness,
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What is martensite used for?
Martensite is strong. Used in spanners and high tension bolts. Too brittle for most use so can then be tempered
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What is process of tempering for quenched and tempered steels? (Low temp blade use, high temps for shafts)
Tempering involves heat treatment to let carbon atoms diffuse, trades strength for toughness. At low temp, carbon precipitates as e carbides and internal stress gone, at 350-500 e-carbide precipitates to cementite, then at >temp coarsens
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How is stainless steel made?
Stainless steel has 11% chromium added. Leads to Cr2O3 film when oxidised and this film is inert and protective to corrosion. Can be made from austenitic, ferritic, and martensitic stainless steel. Austenitic less corrosion resistant
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How is pig iron made from coke, limestone and iron ore after coal, limestone and iron ore sintered?
Coal, limestone, and iron ore pass blast furnace. Coal heated forms coke. Coke reacts with oxygen to form CO2 at furnace, iron oxide reacts with this to form iron, and molten iron at bottom collected, covered by ****. Fe 4-4.5% C
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How does steel have carbon further reduced?
After blast furnace iron passes basic oxygen converter. Lined with magnesite bricks. O2 blown through water cooled lances and reacts with C in iron to form CO and CO2. Exhaust gas from this burned to heat boiler. Reduces C to 1.5%
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What is needed for electric arc furnace?
Electric arc furnace is filled with scrap steel and iron from blast furnace via crane. Lid is swung to position with electrodes. Electric current passes to make arc with O2 blown to steel and lime and fluorspar (CaF2) added for ****.
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How does electric arc furnace separate steel and ****?
Furnace is tilted to remove ****, molten steel poured to ladle for secondary steel making
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How is molten steel processed?
Molten steel passes continuous cannister or ingot moulds+primary mill to form blooms, billets and slabs. These can be rolled for flat products or tube milled for tubes
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What are environment impacts of steel?
1.7 tonnes of CO2 per tonne steel. But steel recyclable, durable, low embodied carbon, lightweight which saves energy and resource
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Other cards in this set

Card 2

Front

What are hypo and hyper eutectoids?

Back

Hypoeutectoid - lower carbon content. Hypereutectoid - greater carbon.

Card 3

Front

How does austenite change for hypoeutectoids?

Back

Preview of the front of card 3

Card 4

Front

What is the product of austenite cooling?

Back

Preview of the front of card 4

Card 5

Front

What is product of hypereutectoid formation?

Back

Preview of the front of card 5
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