Steel

Question 1

What does the lever rule show?

Answer 1

The relative amount of each phase in the 2 phase region

Question 2

What do tie lines show

Answer 2

The composition of phases in 2 phase regions

Question 3

What are the key steel manufacturing processes?

Answer 3

• Blast Furnace
• Basic Oxygen converter
• Electric arc furnace

Question 4

What are the main slow cooled microstructures?

Answer 4

• Austenite
• Ferrite
• Cementite
• Pearlite

Question 5

What are the main rapid cooled microstructures

Answer 5

Martensite

Tempered martensite

Question 6

What kind of reaction is the cooling of steel?

Answer 6

Eutectoid

One solid to two different solids

Question 7

What temperature does iron transform from bcc -> fcc

Answer 7

912 C

Question 8

What is the solubility of iron in ferrite?

Answer 8

(alpha-iron, bcc) 0.02 wt%

austenite (gamma-iron, fcc): 2.1 wt%

Question 9

What are the 3 eutectoid compositions?

Answer 9

<0.8% - hypoeutectoid
0.8% - eutectoid
>0.8% - hypereutectoid

Question 10

What happens in the hypoeutectoid composition?

Answer 10

(Ferrite and pearlite)
Ferrite grains formed from austenite
Remaining austenite goes to ferrite and cementtiete
Pearlite is formed

Question 11

What is pearlite?

Answer 11

Fine lamenar structure formed from ferrite and cementite - it is like a metal-ceramic nano-composite

Question 12

What determines the fineness of the ferrite?

Answer 12

the cooling conditions

Question 13

What temperature is pearlite formed at?

Answer 13

723 C

Question 14

What is the eutectoid composition of steel?

Answer 14

@723 C Austenite –> ferrite + Fe3C

Pearlite

Question 15

What is the hypereutectoid composition of steel?

Answer 15

austenite +Fe3C
Below 723 C:
Ferrite + Fe3C
cementite and pearlite

Question 16

What are the properties of hypereutectoid steel?

Answer 16

Brttle, as conitnuous brittle phase

Question 17

What kind of steels do we generally use in engineering?

Answer 17

Binary alloys of iron and carbon @<0.8 wt % C

Question 18

How much manganese, phosphorous and sulphur do carbon steels usually contain?

Answer 18

Manganese (0.45 - 0.9 %)
Phosphorous (0.025 - 0.06 %)
Sulphur (0.03 - 0.05 %)

Question 19

Do phase diagrams show rapid cooling?

Answer 19

No

Question 20

What is the effect of rapid cooling on the composition steel?

Answer 20

The crystal lattic tries to switch from fcc (austenite) to bcc (ferrite).
Excess carbon –> distorted body centered lattice –> martensite

Question 21

What is the benefit of iron carbon martnesites?

Answer 21

• Many interfaces
• Interiors of ‘laths’ heavily - - twinned or dislocated
• high and strongly varying stresses

very high resistance to dislocation motion

Question 22

What are the poperties of martensite?

Answer 22

Hard and brittle

too brittle to be useful

Question 23

What can be done to make martensite less brittle?

Answer 23

can be tempered

Question 24

What are the applications of tempered matrensite?

Answer 24

Crankshafts, spanners, high tension bolts

Question 25

What is tempering of martensite?

Answer 25

Heat treatment at 200-600 C
allows C atoms to diffuse out of martnsite

alpha’ -> alpha + Fe3C

Question 26

How is Fe3C present in tempered martensite?

Answer 26

Uniform distribution of fine round precipates –> high strength and toughness

Question 27

What happens if martensite is tempered <350 C

Answer 27

Precipitates as epsilon-carbide
~Fe2C5

Internal stresses dissapear

Question 28

What happens if martensite is tempered between 350 - 500 C

Answer 28

epsilon carbide precipitates to form cementite

Question 29

What happens if martensite at >500 C?

Answer 29

Cementite precipitates coarser, larger and more widely spaced
“spheriodised”

Question 30

What makes stainless steel?

Answer 30

Adding >11% wt % Cr

Question 31

What protects against corosion in stanless steel?

Answer 31

Adherent Cr2O3 film

prootection against corrosion and oxidation

Question 32

What are most stainless steels?

Answer 32

Austenitic

Question 33

What is a useful test for Austenitic stainless steel?

Answer 33

It is not magnetic

Question 34

How is molten steel produced

Answer 34

• Limestone + Iron ore
• into sinter plant (fueled by coke ovens)
• Blast furncae produces molten iron
• this is fed into a basic oxygen vessel
• this produces molten steel

Question 35

How does an electric arc furnace work?

Answer 35

Recycled/ scrap steel fed in
electric arc furnace feeds to secondary steelmaking
This then produces molten steel

Question 36

How does a blast furnace work?

Answer 36

• Iron ore coke and limestone added at the top
• Oxygen in air reacts with coke to produce carbon monoxide
• This passes up the furnace transforming iron oxide to iron
• liquid iron collects at the bottom of the furnace, covered by a layer of molten slag
• the iron is tapped at the bottom, andnd the slag is also tapped off from a seperate hole
• This produces pig iron

Question 37

What is the function of a basic oxygen converter?

Answer 37

Further reduces C content
8m in diammeter and 11m high

it is lined with ~1m of magnesite bridge

Question 38

To what C content does a basic oxygen converter convert C to

Answer 38

0 and 1.5%

Question 39

What is the process behing and electric arc furnace?

Answer 39

Charged with “cold” material - normally scrap or iron from blast furnace

• steel is tipped into the EAF
• lid is swung into a position that contains electroes
• electric current is passed throuh the electrodes to form an arc
• O2 is blown into the steel Lime and fluorspar are added to form slag
• the furnace is tilted to remove slag
• molten steel in porued into a ladle for secondary steel making

Question 40

How much steel does and EAF make in 90 minutes?

Answer 40

150 tonnes

Question 41

How much CO2 is produced per tonne of steel?

Answer 41

1.7 tonnes

Question 42

How many tonnes of CO2 per year come from steel?

Answer 42

2.73 billion