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Effects of microstructural and mechanical testing variables on the toughness of quenched and...
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Effects of microstructural and mechanical testing variables on the toughness of quenched and tempered 4340 steel
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http://www.ohsu.edu/xd/education/library/services/theses-dissertations/rights-statement.cfm
Title
Effects
of
microstructural
and
mechanical
testing
variables
on the
toughness
of
quenched
and
tempered
4340
steel
Creator.PersonalName
Datta
,
Kanti
P
.
Thesis.Degree
Ph.D.
Thesis.Major
Materials Science
Thesis.DateDegreeAwarded
September
1979
Institution
Oregon Graduate Center
Department
Dept. of Materials Science
Thesis.Advisor/Mentor
Wood, William E.
Thesis.Committee
Eror, Nicholas G.
Elliott, Richard A.
Atteridge, David G.
Subject.LCSH
Steel
Notched bar testing
Call Number
Q183.5.OGC D38 1979
Description.Abstract
The
effects
of
notch
root
radii
on the
toughness
of
quenched
and
tempered
4340
steel
were
studied
in
greater
details
by
instrumented
and
slow-bend
Charpy
tests
. Also
studied
was the
effect
of
tempering
after
both
high
and
conventional
austenitizing
temperatures
by
fracture
toughness
,
slow-bend
Charpy
and
instrumented
Charpy
tests
. The
effects
of
bainitic
isothermal
transformations
from
high
temperature
austenitization
of
4340
steel
were
studied
by
fracture
toughness
and
tensile
tests
.
Microstructural
investigation
was
carried
out
by
optical
,
transmission
and
scanning
electron
microscopy
as
well
as
X-ray
diffraction
. The
effects
of
notch
root
radii
on the
toughness
results
showed
that
initially
the
toughness
increased
as the
notch-root
radius
increased
and then
after
a
critical
notch-root
radius
was
reached
, the
toughness
dropped
. The
loss
in
toughness
was
coincident
with an
intergranular
fracture
initiation
mode
. Also, the
critical
root
radius
at
which
the
drop
in
toughness
was
noticed
was
strongly
temperature
and
strain
rate
dependent
but
independent
of the
prior
austenitic
grain
size
. The
critical
stress
or
strain
model
applies
for the
initial
rise
of the
toughness
with
notch
root
radius
.
Beyond
the
critical
notch
root
radius
,
fracture
criteria
based
on '
strain
energy
density
'
is
consistent
with the
observed
drop
in
toughness
. A
physical
model
involving
double
slip
band
for the
intergranular
fracture
initiation
mode
is
also
discussed
. A
new
explanation
for the
differences
in
toughness
behavior
between
the
sharp
crack
and
blunt
notch
behavior
for the
two
heat-treatments
is
provided
.
ε-carbide
precipitation
in
as-quenched
martensite
from
high
temperature
austenitization
is
proposed
to
improve
the
toughness
in '
sharp
crack
'
testing
. In
blunt
notch
testing
, the
importance
of
grain
size
is
stressed
. Here,
larger
grain
size
resulted
in
inferior
toughness
.
Finally
the
results
indicated
that the
limited
bainitic
heat-treatments
from
high
austenitizing
temperature
studied
in this
investigation
were not
conducive
to
either
toughness
or
tensile
strength
. The
impairment
of
mechanical
properties
is
attributed
to
large
bainitic
ferrite
grain
size
. The
tempering
behavior
from
high
austenitizing
temperature
showed
that
up
to a
tempering
temperature
of
about
175°C
,
toughness
increased
continuously
;
however
,
toughness
dropped
at a
tempering
temperature
as
low
as
225°C
for the
high
austenitizing
case
,
whereas
no
such
drop
was
observed
in that
tempering
temperature
range
for the
low
austenitizing
temperature
case
.
SEM
,
TEM
and
X-ray
studies
have
indicated
that the
loss
in
toughness
was
associated
with a
change
in
fracture
mode
,
i.e
. from
microvoid
coalescence
to
intergranular
fracture
, and was also
coincident
with
cementite
precipitation
.
It
is
believed
that the
prior
austenite
grain
boundary
segregation
coupled
with
cementite
precipitation
triggered
the
above
embrittlement
.
Language
eng
Type
Text
Format.Use
Needs Adobe Acrobat Reader to view.
Format.FileType
pdf
Format.FileSize
10085.016 KB
OCLC number
10648439
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