Metals

Question 1

metals - density

Answer 1

metals are generally most dense

Question 2

stiffness

Answer 2

the resistance to elastic deformation measured in pascals

Question 3

metals - stiffness

Answer 3

have a high modulus

Question 4

strength

Answer 4

the resistance to permanent deformation measured in pa

Question 5

metals -strength

Answer 5

strong but not the strongest

Question 6

toughness

Answer 6

resistance to cracking, fracture

Question 7

metals - toughness

Answer 7

are the toughest

Question 8

metals -thermal conductivity/electrical conductivity

Answer 8

can have much higher conductivity, but not always

Question 9

metals - cost

Answer 9

metals have a v large range of prices

Question 10

the strengthening mechanisms

Answer 10

1 atoms in solution, different sizes deflect and create distortions (alloy)
2 dispersion strengthening, adding enough of another element to make a second phase
3 work hardening
4 reduce grain size,more boundaries present , more deflections

Question 11

casting

Answer 11

pouring a melt into a mould

low cost but can lead to defects

Question 12

rolling

Answer 12

properties are better if material is deformed - stronger
squeezes out pores 
refines microstructure 
work hardening 
good for producing long bits, eg rails

Question 13

forging

Answer 13

hot softened metal pushed/ flattened into shape

produces good microstructure high strength

Question 14

extrusions

Answer 14

can produce complex materials
steel needs high temp so not practical method
common for aluminium or polymers

Question 15

austenite (gamma)

Answer 15

high temp phase
fcc structure
(can be present in stainless steels and non magnetic metals)

Question 16

Ferrite (alpha)

Answer 16

high purity- a lot of carbon
v small region in phase diagram
bcc structure
present in most steels not as a single phase

Question 17

cementite (fe3C)

Answer 17

a ceramic like material, intermetallic
line compund, fixed composition
effects all mechanical properties

Question 18

pearlite

Answer 18

not a single phase
two phase region of ferrite and cementite
has practical implication on how fraction travel in materials

Question 19

martensite

Answer 19

not on phase diagram
isn an equi phase
produced by fast cooling
hard and brittle

Question 20

Extraction - Blast furnace

Answer 20

iron ore+coke+limestone
hot air blown in bellow
coke acts as a heat source, reducing agent accepting electrons from other reactions.
liquid metal and waste (slag) tapped of periodically
5% C - poor strength, not useful

Question 21

Steel making - Basic oxygen

Answer 21

molten iron poured into converter
oxygen blow 
oxidation of impurities, gives more heat (can melt some scrap)
~300 tonne, 30-40 min cycle 
large scale

Question 22

Steel making - electric arc furnace

Answer 22

iron and scrap steel
electrodes supply power
will melt 100 tonnes in 90 mins

Question 23

secondary steel making

Answer 23

small composition adjustments

creates certain alloys

Question 24

casting

Answer 24

requires a melt
tipping/injecting melt into a mould
low cost BUT can lead to defects

Question 25

rolling

Answer 25

``` properties better if deformed - work hardening -squeezes out pores -refines microstructure -work hardening good for long products, eg rails ```

Question 26

forging

Answer 26

dies can be flat, open die forging shaped and closed die forming often done with hot softened metal produces good microstructure

Question 27

extrusion

Answer 27

produces complex cross sections in one long direction not good for steel, need high temp commonly used for polymers and aluminium

Question 28

Pearlite - phases

Answer 28

``` ferritie and Fe3C alternating plates, lamellae plates are boundaries, stronger slow cooling final product can be controlled ```

Question 29

martensite - phases

Answer 29

quick cooling no time for ferritie and Fe3C to form carbon doesnt fit in bbc ferrite structure is distorted- v hard brittle material

Question 30

wrought steels

Answer 30

``` steels shaped by deformation carbon is low= weld-ability high strength low alloy (hsla) -grain size reduction -second phase strongest and toughest of regular steels ```

Question 31

cast steels

Answer 31

not used structurally casting is easier and cheaper martensite at the surface, v brittle difficult to machine

Question 32

stainless steel

Answer 32

has protective surface oxide expensive -used for aesthetics/long-life structures strong good in certain application, not structural tho

Question 33

non ferrous structural metals

Answer 33

all metals not based on fe mostly more expensive have attractive properties

Question 34

aluminium

Answer 34

``` lightweight usually alloyed for strengthening food strength to weight ratio susceptible to degradation from heat used in, transport -panelling -internal fitting -cladding -bridges -roofs ```

Question 35

titanium

Answer 35

more expensive than aluminium high strength to weight ratio used for -cladding -aircraft

Question 36

copper

Answer 36

``` not primary load support use din -roofing -flashing and cladding easy to form difficult to weld oxidation gives a green surface colour ```