Fázové diagramy binárních soustav
Odmísemí a spinodální rozpad
Aktivita složek v binárních diagramech
Fázové přeměny
Křivky chladnutí
NaCl-H20
Stanovení FD z křivek chladnutí
Vzájemná rozpustnost
Úplná vzájemná rozpustnost
Částečná rozpustnost
Degree of solubility depends on temperature
At max. solubility, 183 C: lead holds up to 19.2 wt%
tin in a single phase solution, and tin holds up to
2.5wt% lead and still be a single phase.
Rovnováhy organických látek
Fázový diagram Fe-C
Fáze soustavy Fe-C
,(present only at extreme temperatures)
Austenite, (FCC, high formability, high solubility of C,
over 2%C can be dissolved in it, most of heat
treatments begin with this single phase).
Ferrite, BCC, stable form of iron below 912 deg.C, only
up to 0.02 wt% C in solid solution and leads to two
phase mixture in most of steels.
Cementite (iron-carbide), stoichiometric intermetalic
compound, hard, brittle, exact melting point
unknown.
Currie point (770 deg. C), atomic level nonmagneticto-magnetic
transition.
ferrite−δ
Fázové reakce Fe-C
Peritectic, at 1495 deg.C, with low wt% C
alloys (almost no engineering
importance).
Eutectic, at 1148 deg.C, with 4.3wt% C,
hapends to all alloys of more than
2.11wt% C and they are called cast irons.
Eutectoid, at 727 deg.C with eutectoid
composition of 0.77wt% C, alloys bellow
2.11%C miss the eutectic reaction to
create two-phase mixture. They are
steels.
Oceli
CBCCCFCCC CementiteFerriteAustenite %67.6;%02.0;%77.0 +→
4.5 Eutectoid Steel
At 0.77%C by cooling from
austenite (FCC) changes
to BCC-ferrite (max
0.02%C) and excess C
forms intermetalic
cementite.
Chemical crystalline solid
separation gives fine
mixture of ferrite and
cementite. Perlite (right),
1000X.
4.5 Hypoeutectoid Steel
With less than 0.77%C from
austenite by cooling
transformation leads to growth
of low-C ferrite growth. At
727deg.C austenite transforms
in to pearlite.
Mixture of proeutectoid ferrite
(white) and regions of pearlite
forms.
Magnification 500X.
4.5 Hypereutectoid Steel
With more than 0.77%C, from
austenite transformation leads to
proeutectoid primary cementite
and secondary ferrite. At 727
deg.C austenite changes to
pearlite.
Structure of primary cementite
and pearlite forms.
Magnification 500X.
4.6 Cast Irons
Iron-Carbon alloys of
2.11%C or more are cast
irons.
Typical composition: 2.0-
4.0%C,0.5-3.0% Si, less
than 1.0% Mn and less
than 0.2% S.
Si-substitutes partially for
C and promotes
formation of graphite as
the carbon rich
component instead Fe3C.
4.6 Gray Cast Iron
Composes of: 2.5-4.0%C, 1.0-
3.0%Si and 0.4-1.0% Mn.
Microstructure: 3-D graphite flakes
formed during eutectic reaction.
They have pointed edges to act as
voids and crack initiation sites.
Sold by class (class 20 has min.
tensile strength of 20,000 psi is a
high C-equivalent metal in ferrite
matrix ). Class 40 would have
pearlite matrix.
4.6 Gray Cast Iron
Properties: excellent compressive strength,
excellent machinability, good resistance
to adhesive wear (self lubrication due to
graphite flakes), outstanding damping
capacity ( graphite flakes absorb
transmitted energy), good corrosion
resistance and it has good fluidity needed
for casting operations.
It is widely used, especially for large
equipment parts subjected to
compressive loads and vibrations.
4.6 White Cast Iron
Composes of: 1.8-3.6%C, 0.5-1.9%Si and 0.25-
0.8%Mn.
All of its carbon is in the form of iron-carbide
(Fe3C). It is called white because of
distinctive white fracture surface.
It is very hard and brittle (a lot of Fe3C).
It is used where a high wear resistance is
dominant requirement (coupled hard
martensite matrix and iron-carbide). Thin
coatings over steel (mill rolls).
4.6 Malleable Cast Iron
Formed by extensive heat treatment
around 900 degC, Fe3C will dissociate
and form irregular shaped graphite
nodules. Rapid cooling restricts
production amount to up to 5 kg. Less
voids and notches.
Ferritic MCI: 10% EL,35 ksi yield
strength, 50 ksi tensile strength.
Excellent impact strength, good
corrosion resistance and good
machinability.
4.6 Pearlitic Malleable Cast
Iron
Pearlitic MCI: by rapid cooling through
eutectic transformation of austenite to
pearlite or martensite matrix.
Composition: 1-4% EL, 45-85 ksi yield
strength, 65-105 ksi tensile strength. Not
as machinable as ferritic malleable cast
iron.
Ductile Cast Iron
Without a heat treatment by addition of
ferrosilicon (MgFeSi) formation of smooth
spheres (nodules) of graphite is promoted.
Properties: 2-18% EL, 40-90 ksi yield strength,
60-120 ksi tensile strength.
Attractive engineering material due to: good
ductility, high strength, toughness, wear
resistance, machinability and low melting
point castability.
4.6 Malleable Cast Iron
Ductile iron with ferrite
matrix (top) and pearlite
matrix (bottom) at 500X.
Spheroidal shape of the
graphite nodule is
achieved in each case.
Microstructure
Globular cast iron
Diskuse
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