Ferous Alloys and casting Flashcards
1
Q
If an alloy is heated but does’nt to reach the lines on a phase diagram then cool what will its microstructure consist off
A
Martensite
2
Q
Once a microstructure has formed eg pearlite can it be converted to another microstructure without being heated to ferrite first
A
No
3
Q
Give an example of a slow cooling method
A
Full annealing
4
Q
What microstructure does full annealing usually produce
A
Coarse Pearlite
5
Q
Give an example of moderate cool
A
Normalising
6
Q
What microstructure does normalising normally produce
A
Fine Pearlite
7
Q
Name a method of fast cooling
A
Quenching
8
Q
What microstructures does quenching usually produce
A
Pearlite or Martensite
9
Q
How can a Bainitic Microstructure be achieve
A
Adding other alloying elements to the steel alloy
10
Q
What sort of process is the process in which austensite becomes Martensite
A
A diffusion less process
11
Q
How does the ductility of Tempered Martensite compare to that of Martensite
A
It is more ductile
12
Q
What the hardest and strongest microstructure
A
Martensite
13
Q
What is the most brittle microstructure
A
Martensite
14
Q
What causes the residual stresses in martensite
A
The differences in densities
15
Q
Spherodite is very….
A
Soft and Ductile
16
Q
What is the most ductile microstructure of steel
A
Spherodite
17
Q
Is spherodite formed by heating above or bellow eutectoid temperature and how long is it left for
A
Bellow and 18-24 hours
18
Q
Spherodite consists of a ferrite phase containing particles of…
A
Cementite
19
Q
Ferrite is a relatively……… &…………….. Microstructure
A
Soft and ductile
20
Q
What are some of the characteristics of Cementite
A
Hard and brittle
21
Q
What is pearlite made up of
A
Layers of cementite and ferrite
22
Q
Which is stronger fine pearlite or coarse pearlite
A
Fine pearlite is stronger
23
Q
What is stronger Pearlite or pearlite + cementite
A
Pearlite + Cementite
24
Q
Is Bainite is stronger than Pearlite and ferrite
A
Yes stronger than both
25
Describe the process of annealing
Heat, Hold, slow cool
26
What is Annealing used for
To soften and make more ductile
27
What is process annealing used for
To negate the affects of cold working
28
How does cold working make a substance harder
Increases the number of dislocations which makes them harder to move
29
Process Annealing increases the .............
Electrical Conductivity
30
What are some of the causes for internal stresses to develop
Plastic deformation during machining and non uniform cooling
31
What temperature does stress relief annealing cool to
Room Temperature
32
Does normalizing involve heating above or bellow eutectoid temperature
Above
33
Does Normalizing involve a phase change
No
34
Does spherodising take place above or bellow eutectoid temperature
Bellow
35
Does full annealing take place above or bellow Eutectoid temperature
Above (usually)
36
In normalising what causes the alloy to become more machinable
Refined grain size and uniform distribution of grain sizes
37
Normalising takes place 55-85 degrees above.......
Upper critical temperature
38
What sort of steel (in terms of carbon) is full annealing used to treat
Low or medium
39
In full annealing the specimen is Austenised ................... degrees above upper critical temperature
15-40
40
Full annealing produces ................... material than normalising
Softer
41
What does the quenching medium control
The rate of heat extraction and therefor the amount of martensite that forms
42
What does Tempering usually follow
Quenching
43
What does tempering involve
Heating martenstitic steel for a specified time between 300-600 degrees bellow the eutectoid temperature
44
What diffuses from microstructure during tempering
Excess carbon
45
During tempering of martensite What precipitate forms to reinforce BBC alpha ferrite phase
Fe3C Iron Carbide
46
What is Precipitation hardening only used for
Non ferrous alloys
47
Name the 2 stages of precipitation hardening
Solution heat treatment
| Precipitation heat treatment
48
Describe the solution heat treatment stage of precipitation hardening
Heat until all solute is dissolved, just alpha phase present, then rapid cool or quench
49
Describe the precipitation heat treatment stage of precipitation hardening
Reheat to intermediate temperature to allow precipitation of beta
50
For precipitation hardening what causes the increase in strength and stiffness
The distortion of crystal lattice, this is caused by precipitation particles, these inhibit the motion of dislocations
51
What is the shaping process chosen dependent on
Mechanical properties of material
52
How does the carbon content effect the Yield strength and tensile strength of the steel
Increasing carbon content increases the tensile strength and yield strength
53
How does increasing carbon content of steel effect the ductility
Increasing carbon content reduces the ductility
54
Describe the yield strength and the ductility of wrought iron
Low strength and high ductility
55
Ductile materials can be formed at.......
Room Temperature
56
How does increasing the temperature effect the strength the ductility of a material
Makes it weaker but more ductile
57
How does the quality of casting compare to forging
Lower quality
58
What are the 2 main categories of metal alloys
Ferrous and non-ferrous
59
What has higher carbon content, steels or cast iron and what are these contents
Steel has less, <1.4 and cast iron has 3-4.5
60
What is the oldest way to extract iron from ore
Bloomary process
61
What does the bloomary process involve
Heating the iron with charcoal until soft but not molten
62
Describe the output of a blast furnace
A very high carbon (4-5 wt%) iron called big iron. which contains lots of impurities. Pig iron is very brittle
63
What are the inputs and outputs of the blast furnace
Limestone, iron ore, coke and hot air in. Pig iron, Slag and exhaust gas out.
64
What are the chemical reactions involved in the blast furnace
```
Heat generation
C+02=C02
Reduction of iron ore
CO2+C=2CO
3CO+Fe2O3=2Fe+3CO2
Purification
CaCO3=CaO+CO2
CaO+SiO2+AL2O3=Slag
```
65
What is coke formed from
Coal
66
What is a Cupola furnace used for
Making pig iron ready for casting
67
What are puddling furnace's used for
Remove excess carbon from pig iron
68
What does the Bessemer process involve
Blowing air through molten iron to remove C as CO2
69
What does a basic oxygen furnace involve
Blowing pure oxygen through molten iron to remove C as CO2
70
Basic Oxygen furnace accounts for 70% of steel production in USA what is the other 30%
Electric arc Furnace- better quality but more expensive
71
What types of iron contain flakes of Graphite and what cooling methods to produces each
White iron (fast cool) , pearlitic grey iron (moderate cool) and Ferritic grey iron (slow cool)
72
What types of iron produce nodules of graphite and what are the cooling methods to produce each
Ductile pearlitic iron (moderate)
| Ductile Ferritic iron (slow)
73
What elements should be added to produce ductile iron
Mg/Ce
74
How would you produce pearlitic and ferritic malleable iron which have graphite in rosettes
Reheat white iron at 700 degrees C for about 30 hours
75
What are the carbon and silicon contents of grey iron
3-4wt% carbon and 1-3wt% silicon
76
What are some of the properties of grey iron
```
Weak and brittle under tension
strong under compression
good vibration dampening
cheap
cant be deformed
```
77
What are some properties of white iron
hard but brittle
<1wt% Si
more cementite that grey iron
can be found on the surface of grey iron
78
Which type of iron is ductile
Malleable iron
79
What are some advantages of casting
Versatility
can be used for any molten metal
can be used to create complex shapes
80
What are some disadvantages of casting
Porosity, poor tolerances and surface finishes
81
What are some problems that can occur during casting
Turbulence while pouring and Gas entrapment
82
What is equation for the velocity down the downsprue
v= (2gh)^1/2
83
What is the equation of the flow rate from the continuity law
Q=Av
84
What is the equation for the filling time of the mould
t=V/Q
85
What is the equation of Reynolds number
(velocity*Diameter*Density)/Viscosity
86
What is the Reynolds number defined as
Inertial versus viscous forces of fluid flow
87
if the Reynolds number is greater than.......... it can cause damage
20000
88
What happens to metals during solidification
They shrink
89
What can the shrinkage of metals cause
A cavity to form in the inside the cast
90
What part of a closed mould ensures that the cavity is filled
The riser
91
What is the equation for solidification time
t= mould constant * (volume/area)^n
| n=2
92
In a dendritic what does the width of the mushy zone depend on
Length of freezing zone
93
In dendritic structure what causes micro voids to form
Pockets of liquid trapped inside growing dendritic structure
94
What are the limitations of quality in cast parts and what are the causes
Voids caused by air entrapment
Damaged mould caused by turbulence
Cavities due to shrinkage
Micro cavities when solidifying mushy zone
Rapid cooling can produce concentration gradients
