Lectures 12-14 Flashcards
Iron is allotropic meaning that Iron has
more than one crystal structure
Pure iron below approx. 912C has what type of structure?
BCC - body centred cubic
Pure iron between approx. 912C and 1394C has what type of structure?
FCC - face centred cubic
Changes in the crystal structure of the metal canaffect what other feature of that metal?
Volume
On the Iron-Iron Carbide phase diagrams, alpha is known as
Ferrite
On the Iron-Iron Carbide phase diagrams, gamma is known as
Austentite
On the Iron-Iron Carbide phase diagrams, beta is known as
Beta ferrite
Fe3Cis known as
cementite
Fe3C has a specific composition. What category does this fall into?
Intermediate compound
Fe3C is a solid solution. Which type of solid solution is it?
Interstitial solid solution - C atoms are between the lattice of Fe atoms
Commonly, steel has —– wt% to —– wt% C
0.008 ~ 2.14
Low carbon steel as it is, is usually
soft and weak
Medium carbon steel as it is, is usually
high strength and wear resistant
High carbon steel as it is, is usually
hardest and strongest
Eutectic Austentite that is cooled below the eutectoid temp forms what
ferrite and cementite
Below the eutectoid temp the structure of the metal is lamellae with layers of alpha ferrite and Fe3C Cementite. What is this structure known as?
Pearlite
Name the two types of pearlite you are able to get
Coarse and fine
What affects the thickness of the lamellae in pearlite?
Cooling rate
Very slow cooling of austentite results in the pearlite to come out with
thicker layers in the lamellae formed
Slightly faster cooling of austentite results in the pearlite to come out with
thinner layers in the lamellae formed
At room temperature, hypoeutectoid and hypereutectoid alloys consist of
regions of pearlite and ferrite
Hypoeutectoid alloys have contiuous areas of —– that give it ductility
ferrite
Increasing the C content in hypoeutectoid alloys results in a higher proportion of —-. Which leads to?
pearlite, leads to increased strength and reduced ductility
Increasing the C content in hypereutectoid alloys results in a higher proportion of —-. Which leads to?
cementite, leads to increased hardness but can lead to reduced strength due to more brittle
Hypereutectoid alloys have areas of —– that give it hardness, but is also —–
cementite, brittle
Spheroidise annealing is used generally for —– alloys
hypereutectic
Spheroidising improves —– and prepares the metal for forming and machining by —–
ductility, softening
How do you spheroidise steel?
Heated to 30C degrees below the eutectoid temp, for 15-25 hrs.
What structure in the steel restructures during spheroidising? What shapes do they become?
The cementite restructures to become spheres
Normalising leads to what kind of grain structure
a fine grain structure
If you would like to cold work a piece, should it go through normalising or full annealing?
Full annealing
If you would like to cold work a piece, should it go through normalising or full annealing?
Normalising
Normalising a alloy, how is it cooled
In air
Full annealing of an alloy, how is it cooled
Very slowly in a furnace
To harden steel, how is it cooled?
Rapidly in water or oil
What is quenching
Cooling rapidly, in oil or water
The rapid cooling of steel via quenching leads to
slight deformation in the crystal structure
Martensite is
steel with a high C content that has lead to deformation
Tempering of steel is when
the hardened steel is reheated to temps around 200-650C degrees
Rank in hardness from highest to lowest;
tempered martensite, fine pearlite, martensite
martensite, tempered martensite, fine pearlite
What test is used to determine a materials hardenability?
Jominy-end test (water sprayed on a small nail looking thing)
Hardenability is the rating of
how uniformly hardened an alloy can be from cooling
Stainless steel is highly resistant because
there is a thin Chromium oxide layer that forms on the surface
Cast iron has a much lower melting point than steels. Therefore is is good for
casting processes
Name the three main groups of stainless steel
- Ferritic
- Austentitic
- Martensitic
Pure Aluminium is approx. —- the density of steel
1/3
2 good properties of Copper
- high electrical conductivity
- good corrosion resistance
How can coppers strength be improved?
Alloy the copper
Brass is the alloy made out of
copper and zinc
Bronze is the alloy formed from
copper and tin
4 natural good features about the properties of titianium alloys
- High corrosion resistance
- High strength to weight ratio
- High melting point
- Highly ductile
Titanium alloys can easily be —– for special applications
alloyed
Titanium alloys can also be used in the medical industry. This is known as
biocompatible
2 main pros of Magnesium alloys
- Extremely light weight
- Low density
Magnesium alloys can be hazardous to work with due to its
high reactivity
Nickel alloys show good
corrosion resistance
Superalloys can prevent dislocation slip by
having other elements added to it to create second phase particles
