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外文资料原文与译文
中英文对照外文翻译
(
文档含英文原文和中文翻译
)
原文
:
Heat
Treatment of Steel
Types of
Heat Treating Operations
Five
Operations
are
detailed in this lesson as the basis of
heat treatment.
Explanations of these
operations follow.
Full
annealing
Full annealing is the
process of
softening steel
by a
heating and cooling
cycle,
so
that
it may
be bent or cut
easily. In annealing, steel is heated above a
transformation
temperature
and
cooled
very
slowly
after
it
has
reached a suitable
temperature. The distinguishing
characteristics of full annealing are:
(a) temperature above
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外文资料原文与译文
the
critical
temperature
and
(b)
very
slow
cooling,
usually
in
the
furnace.
Normalizing
Normalizing is identical with annealing,
except that the steel is air cooled;
this is much faster than
cooling
in
a
furnace.
Steel
is
normalized
to
refine
grain
size,
make its structure
more uniform, or to improve machinability.
Hardening
Hardening
is
carried
out
y
quenching
a
steel,
that is, cooling it
rapidly from a temperature above the
transformation
temperature.
Steel
is
quenched
in
water
or
brine
for the most rapid
cooling, in oil for some alloy steels, and
in
air
for
certain
higher
alloy
steels.
After
steel
is
quenched,
it
is
usually
very
hard
and
brittle;
it
may
even
crack
if
dropped.
To
make the steel more ductile, it must be tempered.
Tempering
Tempering
consistes of reheating a quenched
steel
to a suitable temperature below the transformation
temperature for an appropriate time and
cooling back to room
temperature. How
this process makes steel tough will be
discussed later.
Stress
relieving
Stress relieving is the
heating of
steel to a temperature below
the transformation temperature,
as in
tempering, but is done primarily to relieve
internal
stress
and
thus
prevent
distortion
or
cracking
during
machining.
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外文资料原文与译文
This is
sometimes called process annealing.
Reasons for Heat Treating
Heat treatment of steel is
usually
intended to accomplish any one of the following
objectives:
?
Remove stresses induced by cold working
or to
remove
stresses
set
up
by
nonuniform
cooling
of
hot
metal
objects;
?
Refine the grain structure of hot
worked steels
which may have developed
coarse grain size;
?
Secure the proper grain structure;
?
Decrease
the
hardness
and
increase
the
ductility;
?
Increase
the
hardness
so
as
to
increase
resistance
to wear or to
enable the steel to withstand more service
conditions;
?
Increase
the
toughness;
that
is,
to
produce
a
steel
having
both a high tensile strength and good ductility,
enabling it to withstand high impact;
?
Improve the
machinability;
?
Improve the electrical properties;
?
Change
or
modify
the
magnetic
properties
of
steel.
Heat
Treatment
The hardest condition for
any givens
steel
is
obtained
by
quenching
to
a
fully
martensitic
structure.
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外文资料原文与译文
Since
hardness is directly related to strength, a steel
composed of 100% martensite is at its
strongest possible
condition.
However,
strength
is
not
the
only
property
that
must
be
considered
in
the
application
of
steel
parts.
Ductility
may
be
equally important.
Tempering
Ductility is the ability of a metal
to change
shape
before
it
breaks.
Fleshly
quenched
martensite
is
hard
but
not
ductile; in fact, it is very brittle. Tempering is
needed
to impart ductility to the
martensite, usually at a smell
sacrifice in strength. In addition,
tempering greatly
increases the
resistance of martensite to shock loading.
The effect of tempering may be
illustrated as follows. If
the head of
a hammer were quenched to a fully martensitic
structure, it probably would crack
after the first few blows.
Tempering
during manufacture of the hammer imparts shock
resistance with only a slight decrease
in hardness. Tempering
is
accomplished
by
heating
a
quenched
pert
to
some
point
below
the transformation temperature, and
holding it at this
temperature for an
hour or more, depending on its size. Most
steels are tempered between 205 and
5,95
0
C. As higher
temperatures
are
employed,
toughness
or
shock
resistance
of
the
steel is increased, but the hardness
and strength decrease.
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外文资料原文与译文
Annealing
the two-stage
heat treating process of
quenching and
tempering is designed to produce high strength
steel capable of resisting shock and
deformation without
breaking. On the
other hand, the annealing process is intend
to make steel easier to deform of
machine. In manufacturing
steel
products, machining and severe bending operations
are
often employed. Even tempered steel
may not cut or bend very
easily and
annealing is often necessary.
Process
annealing
Process
annealing
consists
of
heating
steel
to a temperature just below the lowest
transformation
temperature for a short
time. This makes the steel easier to
form.
This
heat
treatment
is
commonly
applied
in
the
sheet
and
wire industries, and the
temperatures generally used are from
550 to 650
o
C.
Full
annealing
Process
annealing,
where
steel
is
heated
50 to 100
o
C
above the third transformation temperature for
hypoeutectoid steels, and above the
lowest transformation
temperature
for
hypereutectoid steels,
and
slow
cooled,
makes
the
steel
much
easier
to
cut,
as
well
as
bend.
In
full
annealing,
cooling must take place very slowly so
that a coarse pearlite
is
formed.
Show
cooling
is
not
essential
for
process
annealing,
since any cooling rate from
temperatures below the lowest
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外文资料原文与译文
transformation temperature will result
in the same
microstructure and
hardness.
During
cold
deformation,
steel
has
a
tendency
to
harden
in
deformed
areas,
making
it
more
difficult
to
bend
and
liable
to
breakage. Alternate deforming and
annealing operations are
performed on
most manufactured steel products.
Normalizing
The process of
normalizing consists of
heating to a
temperature above the third transformation
temperature and allowing the pert to
cool in still air. The
actual
temperature
required
for
this
depends
on
the
composition
of the steel,
but is usually around 870
o
C.
Actually, the term
normalize does not
describe the purpose. The process might be
more
accurately
described
as
a
homogenizing
or
grain-refining
treatment.
Within any piece of steel, the composition is
usually
not
uniform
throughout.
That
is,
one
area
may
have
more
carbon than the area
adjacent to it. These compositional
differences affect the way in which the
steel will respond t
heat treatment. If
it is heated to a high temperature, the
carbon can readily diffuse throughout,
and the result is a
reasonably
uniform
composition
from
one
area
to
next.
The
steel
is
then
more
homogeneous
and
will
respond
to
the
heat
treatment
in a more uniform
way.
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