Lectures 12-14 Flashcards
(57 cards)
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
