Austinite also known as gamma phase ion
is a metallic non-magnetic allotrope of
iron or a solid solution of iron with an
alloying element in plain carbon steel
austenite exists above the critical
eutectoid temperature of 1,000 decay
other alloys of Steel have different
eutectoid temperatures it is named after
Sir William Chandler Roberts Austen
allotrope of iron from 912 to 1394a a
degree Celsius alpha iron undergoes a
phase transition from body centered
cubic to the face centered cubic
configuration of gamma iron also called
austenite this is similarly soft and
ductile but can dissolve considerably
more carbon this gamma form of iron is
exhibited by the most commonly used type
of stainless steel for making hospital
and food service equipment
austenitization austenitization means to
heat the iron iron based metal or steel
to a temperature at which it changes
crystal structure from ferrite to
austenite an incomplete initial
austenitization can leave on dissolved
carbide in the matrix for some ions iron
based metals and Steel's the presence of
carbides may occur during the
austenitization step the term commonly
used for this is two-phase
austenitization offs tempering of stem
purring is a hardening process that is
used on iron based metals to promote
better mechanical properties the metal
is heated into the austenite region of
the iron cementite phase diagram and
then quenched in a salt bath or other
heat extraction medium that is between
temperatures of 300 euro 375 a degree
Celsius the metal is annealed in this
temperature range until the austenite
turns to bainite or ospa right by
changing the temperature for
austenitization
the Austen purring process can yield
different and desired micro structures a
higher austenitization temperature can
produce a higher carbon content in
austenite whereas a lower temperature
produces a more uniform distribution of
AA stem perd structure the carbon
content in austenite is a function of
Austin purring time
has been established behavior in plain
carbon steel as austenite cools it often
transforms into a mixture of ferrite and
cementite is the carbon diffuses
depending on alloy composition and rate
of cooling pearlite may form if the rate
of cooling is very Swift the alloy may
experience a large lattice Distortion
known as martensitic transformation in
which it transforms into a BCT structure
instead of into cubic lattice ferrite
and cementite in industry this is a very
important case as the carbon is not able
to diffuse due to the cooling speed
which results in the formation of hard
martensite the rate of cooling
determines the relative proportions of
martensite ferrite and cementite and
therefore determines the mechanical
properties of the resulting steel such
as hardness and tensile strength
quenching followed by tempering will
transform some of the brittle martensite
into tempered martensite if a low harden
ability steel is quenched a significant
amount of austenite will be retained in
the microstructure behavior in cast iron
heating white hypothetic cast iron above
727 a a degree Celsius causes the
formation of austenite in crystals of
primary seven tight this Osten ization
of white iron occurs in primary
cementite at the interphase boundary
with ferrite when the grains of
austenite form in cementite they occur
as lamellar clusters oriented along the
semmen tight crystal layer surface
austenite is formed by withdrawal of
carbon atoms from cementite into ferrite
stabilization the addition of certain
alloying elements such as manganese and
nickel can stabilize the austenitic
structure facilitating heat treatment of
low alloy steels
in the extreme case of austenitic
stainless steel much higher alloy
content makes this structure stable even
at room temperature on the other hand
such elements as silicon molybdenum and
chromium tend to destabilize austenite
raising the eutectoid temperature
austenite is only stable above 910 AAA
degree celsius in bulk metal form
however the use of a face centered cubic
or diamond cubic substrate allows the
epitaxial growth of FCC transition
metals the epitaxial growth of austenite
on the diamond face is feasible because
of the closed lattice match in the
symmetry of the diamond faces FCC more
than a monolayer of I cubed iron can be
grown because the critical thickness for
the strained multi layer is greater than
a monolayer the determined critical
thickness is in close agreement with
theoretical prediction austenite
transformation and Curie point in many
magnetic alloys the Curie point the
temperature at which magnetic materials
cease to behave magnetically occurs at
nearly the same temperature as the
austenite transformation this behavior
is attributed to the paramagnetic nature
of austenite while both martensite and
ferrite are strongly ferromagnetic
thermo optical emission during heat
treating a blacksmith causes phase
changes in the iron carbon system in
order to control the materials
mechanical properties often using the
annealing quenching and tempering
processes in this context the colour of
light or blackbody radiation emitted by
the workpiece is an approximate gauge of
temperature temperature is often gauged
by watching the color temperature of the
work with the transition from a deep
cherry red to orange red to 871 a a
degree Celsius corresponding to the
formation of austenite in medium and
high carbon steel in the visible
spectrum this glow increases in
brightness as temperature increases and
when cherry red the glow is near its
lowest intensity and may not be visible
an ambient light therefore blacksmiths
usually Austin eyes steel in low-light
conditions to help accurately judge the
color of the glow maximum carbon
solubility in austenite is 2.03 percent
C at 1420 okay see also heat treatment
gamma loop allotropes of iron references
external links
Feifei 3 c phase diagram