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Design and Manufacture 2 > Ferous Alloys and casting > Flashcards

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

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2
Q

Once a microstructure has formed eg pearlite can it be converted to another microstructure without being heated to ferrite first

A

No

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3
Q

Give an example of a slow cooling method

A

Full annealing

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4
Q

What microstructure does full annealing usually produce

A

Coarse Pearlite

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5
Q

Give an example of moderate cool

A

Normalising

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6
Q

What microstructure does normalising normally produce

A

Fine Pearlite

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7
Q

Name a method of fast cooling

A

Quenching

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8
Q

What microstructures does quenching usually produce

A

Pearlite or Martensite

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9
Q

How can a Bainitic Microstructure be achieve

A

Adding other alloying elements to the steel alloy

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10
Q

What sort of process is the process in which austensite becomes Martensite

A

A diffusion less process

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11
Q

How does the ductility of Tempered Martensite compare to that of Martensite

A

It is more ductile

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12
Q

What the hardest and strongest microstructure

A

Martensite

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13
Q

What is the most brittle microstructure

A

Martensite

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14
Q

What causes the residual stresses in martensite

A

The differences in densities

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15
Q

Spherodite is very….

A

Soft and Ductile

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16
Q

What is the most ductile microstructure of steel

A

Spherodite

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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

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18
Q

Spherodite consists of a ferrite phase containing particles of…

A

Cementite

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19
Q

Ferrite is a relatively……… &…………….. Microstructure

A

Soft and ductile

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20
Q

What are some of the characteristics of Cementite

A

Hard and brittle

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21
Q

What is pearlite made up of

A

Layers of cementite and ferrite

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22
Q

Which is stronger fine pearlite or coarse pearlite

A

Fine pearlite is stronger

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23
Q

What is stronger Pearlite or pearlite + cementite

A

Pearlite + Cementite

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24
Q

Is Bainite is stronger than Pearlite and ferrite

A

Yes stronger than both

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25
Q

Describe the process of annealing

A

Heat, Hold, slow cool

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26
Q

What is Annealing used for

A

To soften and make more ductile

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27
Q

What is process annealing used for

A

To negate the affects of cold working

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28
Q

How does cold working make a substance harder

A

Increases the number of dislocations which makes them harder to move

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29
Q

Process Annealing increases the ………….

A

Electrical Conductivity

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30
Q

What are some of the causes for internal stresses to develop

A

Plastic deformation during machining and non uniform cooling

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31
Q

What temperature does stress relief annealing cool to

A

Room Temperature

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32
Q

Does normalizing involve heating above or bellow eutectoid temperature

A

Above

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33
Q

Does Normalizing involve a phase change

A

No

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34
Q

Does spherodising take place above or bellow eutectoid temperature

A

Bellow

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35
Q

Does full annealing take place above or bellow Eutectoid temperature

A

Above (usually)

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36
Q

In normalising what causes the alloy to become more machinable

A

Refined grain size and uniform distribution of grain sizes

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37
Q

Normalising takes place 55-85 degrees above…….

A

Upper critical temperature

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38
Q

What sort of steel (in terms of carbon) is full annealing used to treat

A

Low or medium

39
Q

In full annealing the specimen is Austenised ………………. degrees above upper critical temperature

A

15-40

40
Q

Full annealing produces ………………. material than normalising

A

Softer

41
Q

What does the quenching medium control

A

The rate of heat extraction and therefor the amount of martensite that forms

42
Q

What does Tempering usually follow

A

Quenching

43
Q

What does tempering involve

A

Heating martenstitic steel for a specified time between 300-600 degrees bellow the eutectoid temperature

44
Q

What diffuses from microstructure during tempering

A

Excess carbon

45
Q

During tempering of martensite What precipitate forms to reinforce BBC alpha ferrite phase

A

Fe3C Iron Carbide

46
Q

What is Precipitation hardening only used for

A

Non ferrous alloys

47
Q

Name the 2 stages of precipitation hardening

A

Solution heat treatment

Precipitation heat treatment

48
Q

Describe the solution heat treatment stage of precipitation hardening

A

Heat until all solute is dissolved, just alpha phase present, then rapid cool or quench

49
Q

Describe the precipitation heat treatment stage of precipitation hardening

A

Reheat to intermediate temperature to allow precipitation of beta

50
Q

For precipitation hardening what causes the increase in strength and stiffness

A

The distortion of crystal lattice, this is caused by precipitation particles, these inhibit the motion of dislocations

51
Q

What is the shaping process chosen dependent on

A

Mechanical properties of material

52
Q

How does the carbon content effect the Yield strength and tensile strength of the steel

A

Increasing carbon content increases the tensile strength and yield strength

53
Q

How does increasing carbon content of steel effect the ductility

A

Increasing carbon content reduces the ductility

54
Q

Describe the yield strength and the ductility of wrought iron

A

Low strength and high ductility

55
Q

Ductile materials can be formed at…….

A

Room Temperature

56
Q

How does increasing the temperature effect the strength the ductility of a material

A

Makes it weaker but more ductile

57
Q

How does the quality of casting compare to forging

A

Lower quality

58
Q

What are the 2 main categories of metal alloys

A

Ferrous and non-ferrous

59
Q

What has higher carbon content, steels or cast iron and what are these contents

A

Steel has less, <1.4 and cast iron has 3-4.5

60
Q

What is the oldest way to extract iron from ore

A

Bloomary process

61
Q

What does the bloomary process involve

A

Heating the iron with charcoal until soft but not molten

62
Q

Describe the output of a blast furnace

A

A very high carbon (4-5 wt%) iron called big iron. which contains lots of impurities. Pig iron is very brittle

63
Q

What are the inputs and outputs of the blast furnace

A

Limestone, iron ore, coke and hot air in. Pig iron, Slag and exhaust gas out.

64
Q

What are the chemical reactions involved in the blast furnace

A 
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
Q

What is coke formed from

A

Coal

66
Q

What is a Cupola furnace used for

A

Making pig iron ready for casting

67
Q

What are puddling furnace’s used for

A

Remove excess carbon from pig iron

68
Q

What does the Bessemer process involve

A

Blowing air through molten iron to remove C as CO2

69
Q

What does a basic oxygen furnace involve

A

Blowing pure oxygen through molten iron to remove C as CO2

70
Q

Basic Oxygen furnace accounts for 70% of steel production in USA what is the other 30%

A

Electric arc Furnace- better quality but more expensive

71
Q

What types of iron contain flakes of Graphite and what cooling methods to produces each

A

White iron (fast cool) , pearlitic grey iron (moderate cool) and Ferritic grey iron (slow cool)

72
Q

What types of iron produce nodules of graphite and what are the cooling methods to produce each

A

Ductile pearlitic iron (moderate)

Ductile Ferritic iron (slow)

73
Q

What elements should be added to produce ductile iron

A

Mg/Ce

74
Q

How would you produce pearlitic and ferritic malleable iron which have graphite in rosettes

A

Reheat white iron at 700 degrees C for about 30 hours

75
Q

What are the carbon and silicon contents of grey iron

A

3-4wt% carbon and 1-3wt% silicon

76
Q

What are some of the properties of grey iron

A 
Weak and brittle under tension 
strong under compression 
good vibration dampening 
cheap 
cant be deformed
77
Q

What are some properties of white iron

A

hard but brittle
<1wt% Si
more cementite that grey iron
can be found on the surface of grey iron

78
Q

Which type of iron is ductile

A

Malleable iron

79
Q

What are some advantages of casting

A

Versatility
can be used for any molten metal
can be used to create complex shapes

80
Q

What are some disadvantages of casting

A

Porosity, poor tolerances and surface finishes

81
Q

What are some problems that can occur during casting

A

Turbulence while pouring and Gas entrapment

82
Q

What is equation for the velocity down the downsprue

A

v= (2gh)^1/2

83
Q

What is the equation of the flow rate from the continuity law

A

Q=Av

84
Q

What is the equation for the filling time of the mould

A

t=V/Q

85
Q

What is the equation of Reynolds number

A

(velocityDiameterDensity)/Viscosity

86
Q

What is the Reynolds number defined as

A

Inertial versus viscous forces of fluid flow

87
Q

if the Reynolds number is greater than………. it can cause damage

A

20000

88
Q

What happens to metals during solidification

A

They shrink

89
Q

What can the shrinkage of metals cause

A

A cavity to form in the inside the cast

90
Q

What part of a closed mould ensures that the cavity is filled

A

The riser

91
Q

What is the equation for solidification time

A

t= mould constant * (volume/area)^n

n=2

92
Q

In a dendritic what does the width of the mushy zone depend on

A

Length of freezing zone

93
Q

In dendritic structure what causes micro voids to form

A

Pockets of liquid trapped inside growing dendritic structure

94
Q

What are the limitations of quality in cast parts and what are the causes

A

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

Design and Manufacture 2 (5 decks)

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