Note: Descriptions are shown in the official language in which they were submitted.
~3~
--2--
METHOD AND APPARATUS FOR
HEAT TRE~TING STEEL
BACRGROUND OF THE INVENTION
The pres~nt invention relates to a method and appa-
ratus for hardening steel and more particularly to a
method and apparatus for hardening steel pipes of sub
stantial thickness and length.
Steel is essentially an alloy of iron and carbon.
Additionally, it may contain small amounts of manganese,
phosphorus, or silicon, which may be added to enhance such
properties as hardness, strength, ductility, and toughness.
While a trace amount of carbon is dissolved in the
iron to form a constituent known as ferrite, most of the
carbon in steel exists as an intermetallic compound known
as iron carbide or cementite, which form-~ a configuratior.
with the ferrite known as pearlite. When a pearlite
carbon steel is heated to a sufficiently high temperature,
known as the critical transformation temperature, a
face-centered cubic lattice crystal structure, known as
austenite, begins to form, dissolving substantial amounts
of carbon in the steel. The transformation temperature
for most steels is generally in the range of 1340~F
(725C~ to 1450F (790-C).
When austenite steel is subsequently cooled below
its critical transformation temperature, it decomposes
into other forms such as pearlite, bainite, martensite, or
combinations thereof. These constituents determine the
array of properties possessed by the steel. The formation
of these constituents is a function of both the type of
steel and the rate of cooling from the critical trans
formation temperature. Thus, the form into which the
austenite decomposes, and hence the exact nature of the
~3~5g
--3--
resulting steel, depends not only upon the initial compo-
sition of the steel, but also the sequence of cooling. At
one extreme, very rapid cooling or quenching to about -
450CF (232C) and then to about 250F ~121~C~ prod~ces a
very hard constituent, known as martensite. At the other
extreme, slow cooling, as in ambient air, produces a
coarse pearlite. Between these two extremes in cooling
a wide variety of constituents may result. However, the
minimum rate of cooling is often severely limited if the
formation of pearlite is to be avoided.
Over the years there have developed a variety of
methods to facilitate the production of large segments
of steel. These methods involve the use of alloys~ which
alter the point at which a given constituent will form;
variations in the amount of carbon, which affect the
formation of martensite and there~ore hardness; and
specific cooling sequences and me~hods~
It has long been a common practice to harden steel by
heat treating followed by quenching. Typically, the steel
is heated above the critical transformation temperature at
which it becomes austenitic and is then cooled fast
enough, usually by quenching into a liquid such as water
25 or oil, to avoid any transformation of t~e austenite until
the steel reaches the relatively low temperature range
within which it transforms to a hard, martensitic micro-
structure. The steel is subsequently reheated or tempered
to remove the internal stresses caused by the inherent
expansion of the martensite.
Martempering and austempering, which may be tho~ght
of as modifications to the traditional heat treating and
quenching process, represent two widely used commercial
35 processes.
5~
4--
~oth martempering and austempering produce high
strength steels. In martempering, rapid cooling from the
critical transformation temperature is interrupted just
above the martensitic transformation temperature, e.g.,
about 450F (232C), which varies according to the steel's
composition. The surface of the steel is then held at a
constant temperature until this temperature is equalized
throughout the piece. Then it is cooled to room tempera-
ture in order to minimize cracking caused by severe
diferential cooling stresses set up in the brittle
martensite. The steel is subsequently tempered as in
regular heat treating and quenching. No bainite is
allowed to form.
In austempering, the steel is quenched to a fixed
temperature and held at that temperaturer e.g. 500 to
7509F (260 to 399C) depending on the steel, until the
austenite completely transforms to bainite and the harden-
ing transformation is complete. This process involves
less total time since no additional tempering is needed.
The resulting bainite structure has a higher level of
toughness for a given hardness.
The general superiority in mechanical properties of
austempered steel over martempered steel is shown in the
Table 1 for a 0.74~ carbon steel for two given temperature
sequences. The data is taken from Grossmann and ~ain~
Principles of Heat Treatment (5th Edition 1972), p. 179.
~2~3~5~
TABLE 1
Austempered Martempere~
Mechanical Properties Steel _ Steel
S
Rockwell C hardness50.4 50.2
Ultimate strength, psi282,700246,700
Yield point, psi151,300 121,700
Elongation, ~ in 6 inches 1.9 0.3
Reduction of area, %34.5 0.7
Impact, ft-lb 35.3 2.9
Ausforming represents a modification of martempering.
In ausforming the cooling sequence is interrupted in the
600-800F ~315-427'C) temperature range and subjected to
plastic deformation pricr to transformation to martensite
and subsequent tempering. Although only certain alloy
steels are capable of undergoing ausforming, the combina-
tion of strain-hardening and quench-hardening, followed by
tempering, produce a very strong product.
All of these processes suffer from a number of
limitations. For example, even though carbon is inexpen
sive and constitutes the most important source of hard-
ness, the carbon content of a martensitic steel is limited.As the amount of carbon increases for a given steel, the
martensitic transformation temperature lowers and the
martensite formed becomes harder. Since steel is less
plastic at lower temperatures and so less able to accom-
modate the internal stresses caused by the volume changesaccompanying the formation of martensite, the addition of
carbon enhances the chance of cracking. Consequently, the
amount of carbon and hence the maximum hardness obtainable
in a martensitic steel is limited.
s~
--6--
Additionally, exact temperature ~ontrol over time is
often required if specific results are to be obtained.
For example, quenching, martempering, and austempering _
all require very rapid cooling, particularly in the
temperaeure range around 1050 to 950F (570 to 510C)
within which relatively soft pearlite would form with very
little delay.
Given the importance of the cooling rate in producing
the desired properties and regulating internal stresses in
a given steel, the production of large pieces of steel has
always presented particular difficulties, since the tem-
perature drop at the center lags the temperature drop
at the surface. The quenching of steel from its critical
transformation temperature to the martensitic transforma-
tion temperature requires a rather severe cooling rate if
the formation of pearlite is to be avoided. If the steel
is to be austempered after initial quenching, it must be
maintained within a relatively narrow temperature range
above the initial martensitic transformation temperature.
~owever, if the piece is cooled sufficiently to avoid
formation of pearlite, it is often not possible to prevent
significant portions of the steel from falling below the
marten~itic transformation temperature. Similarly, if the
steel is to be subject to martempering or`modified martem~
pering, the cooling rate must be significantly slower near
or through the martensitic transformation temperature
range due to the high expansion and resultant internal
stresses caused by the formation of martensi~e. Yet,
regulation of the cooling rate or maintenance of a con-
stant temperature is often difficult.
A number of processes have been developed in an
attempt to address these problems. ~etal alloys, such as
s~
manganese, silicon, nickel, or chromium have been added to
retard the formation of pearlite to allow for a slower
initial quehch and to otherwise enhance the final proper-
ties of the steel. Although metal alloys and increased
amounts of carbon have been used to make steel amenable to
austempering in larger sections, alloys add considerably
to the expense of the steel.
Additionally, the toughness and strength produced
~o with alloys in steels having a carbon content of roughly
0.65% or less is often very close for austempering and
martempering. Accordingly, austempering has not been m~ch
utilized in larger sections with alloy constructional
steels having a low carbon content since martempering
procudes similar toughness and strength~
Althoygh high strength and high toughness can be
achieved by austempering high carbon alloy steels, exces-
sively long time intervals are required for complete
transformation to the bainite structure. In austempering
the steel must be quickly reduced to a given temperature
throughout and then held at that temperature until the
austenite completely transforms to bainite. Given the lag
in the change between surface and internal temperatures
and the need for subsequently maintaining a constant
temperature as bainite transformation occurs, the size of
a piece of carbon steel which may be austempered is
severely limited. Rods or other shapes having an effec-
tive diameter of much more than 0.25 inches tO.64 cm) have
probably not generally been effectively austempered.
Similarly, austempering has not heretofore proven effec-
tive for pipes having a wall thickness of approximately
.125 inches (.32 cm) or greater.
--8--
A variety of quenching materials and related pro-
cesses have developed in an attempt to control temperature
transformations in hardening steel. As to the quenching
medium, a water quench is generally preferable due to
availability, reduced health hazards, effectiveness in
removing scale from the surface of steel parts, and high
heat capacity. However, the high rate of cooling creates
and causes problems in controlling temperature, especially
where larger pieces of steel are being treated. This is
particularly the case where a water bath is employed.
In salt quenching, the steei is generally quenched in
a salt bath at 800-F (427'C) and then cooled in air.
However, salt is more expensive than water as a cooling
medium and air cooling is nonuniform, thus causing hot
spots leading to weak pcints in the steel. Additionally,
the molten salt generally prcvides a comparatively poor
quench. Although the molten salt successfully avoids any
temperature drop below the temperature of the salt bath,
the attainable rate of ~ooling is not particularly fast,
especially when compared with water.
Oil quenches have been used to reduce the rate of
cooling of hot steel~ However, the reduced rate of ~ool-
ing can result in the formation of pearli~e. Addition-
ally, oil quenching is expensive, relatively slow, and
creates pollution problems.
A variety of methods and devices have been developed
in an attempt to properly control heat transfer from both
the exterior and interior surface of pipes while using
water, as well as other substances, as a cooling medium.
5~
g
A variety o~ methods and devices use spray nozzles
to impact droplets of water against a pipe. For exam-
ple, U.SO Patent No. 3,294,599 discloses an internal
quench head which works in conjunction with an external
quench head to spray water against the inside and outside
surfaces of the pipe, while U.S. Patent No. 3,682,722
discloses an oil quench from rotating nozzles, which
direct a stream of spray against a tubular article.
U.S. Patent No. 4,165,24S discloses a process for
heat treating steel pipes with a wall thickness ranging
from 16 to 36 mm. A steel pipe is first heated over a
cross section of the pipe wall to the critical trans-
formation temperature. The pipe is then passed on rollers
to a cooling zone where water from no~zles encircles the
surface of the pipe to quench the surface below the mar-
tensitic transformation temperature. As the mar~ensite is
formed, heat supplied from the internal unquenched portions
of the pipe or an independent source, tempers the martensite
surface layer, while the unquenched internal layers form
an interstage structure. The speed of the pipe through
the process is greater than the critical cooling speed.
U.S. Patent No. 4,204,892 discloses another method
for heat treating steel tu~es which also involves the
cooling of a surface layer to form martensite followed by
self-tempering due to internal cooling. In one embodiment
the self-tempering step is followed by a second quench
such that the properties of the center of the steel depend
on the equalization temperature of the second cooling
step. The second cooling step is timed such that the
equalization temperature is obtained before transformation
of the residual austenite into bainite.
;~2~P34LSi~
-10-
Other processes immerse the surface in the cooling medium.
For example, in U.S. patent No. 3,623,716, there is disclosed
an apparatus for hardening long pipes by passing a cooling
medium, such as water, from a nozzle in a helical pattern
through the inside of a hot pipe which is immersed in a bath
of cooling liquid.
Another steel hardening apparatus, disclosed in U.S. patent
No. 3,877,685, attempts to control the relative rates of cooling
in the interior and exterior surfaces of a pipe. Two streams
of water are respectively directed to the inside and outside
surfaces of the pipe. The inside surface of the pipe is more
effective]y cooled due to the speed and helical nature of flow
inside the pipe. After the initial quenching stage as the
steel enters the martensitic transformation range, the rate
of cooling is reduced by the diversion of increasing amounts
of water from the inside to the outside of the pipe. A sleeve
mechanism, which is located in concentric feed conduits, is
used to reduce the flow to the inside portion of the pipe.
U.S. patent No. 2,307,694 discloses a cylindrical quenching
device which directs water against the cylindrical surface
of a hollow barrel as a pipe passes through the barrel.
Other patents disclose devices with a variety o~ quenching
mechanismsusing quenching baths and the like.
These and other devices and methods suffer from one or
more of several limitations in addition to those already
discussed. For exmaple, none of the prior devices are suitable
for quenching, rnartempering, austempering, and ausforming
without substantial modification. Additionally, prior devices
fail to make efficient use of the inherent heat of the pipe
produced by the initial raising of the pipe temperature above
the critical transformation temperature. Prior devices and
methods using water as a quenching medium also fail to produce
a steel pipe of substantial size having a carbon content of
~21~3~S9
grea-ter than 0.50%. Additionally, many prior devices fail
-to provide efficient heat transfer from the steel pipe.
Furthermore, the thickness of a steel pipe which may be
successfully austempered or martempered is generally believed
to be limited to approxima-tely one inch (2~54 cm) more or less.
These and other limitations of prior processes and methods
are substantially minimized, if not eliminated, by the present
invention.
SVMMARY OF THE INVENTION
The invention in one aspect pertains to a process for
heat treating a piece of steel comprising the steps of heating
the piece of steel and then quenching each segment of the piece
of steel by directing a sufficient amount of a cooling medium
directly against a surface of each segment to rapidly lower-the
temperature of the segment to a desired temperature while
vaporizing substantially all of the cooling medium to create
a vapor blanket around at least one surface of each segment
so cooled, the vapor blanket being maintained to control the
temperature of the segment.
In one embodiment of this process, a steel pipe is heated
above its critical transformation temperature and then each
longitudinal segment of the pipe is sequentially quenched by
substantially simultaneously sending a sufficient amount of
water against the inside and outside surfaces of each segment
to reduce thetemperature of the segment to within a
predetermined range while vaporizing substantially all of the
water to create a steam blanket around the segment. The steam
blanket or envelope is then maintained on at least the inside
surface of each segment in order to control the temperature
change of each segment until the pipe is subjected to further
processing. According to the invention the rate of passage
of each segment through the quenching zone and the amount of
water directed against the pipe may be varied in relation to
each other.
~3~5~
-12-
Another aspect of the invention comprehends an apparatus
for segmentally cooling successive segments of preheated steel
pipe comprising a preheater for heating the steel pipe and
a flow chamber configured to receive successive segments of
the steel pipe from the preheater and adapted to flow
selectively and continuously a cooling medium over the outer
surface of successive segments of the steel pipe. There is
a plug having a diameter less than the internal diameter on
the steel pipe and an internal feeder having an inlet and an
outlet, the outlet being located in the flow chamber and the
internal feeder being adapted in conjunction with the plug
to flow selectively and continuously a cooling medium over
the inner surface of the same successive segments of steel
pipe. At least one of the flow chamber and internal feeder
is further adapted to control the flow of cooling medium such
that the temperature of each segment can be lowered to a desired
temperature in the flow chamber and thereafter controlled by
using the inherent heat of the segment to vaporize substantially
all of the cooling medium to create a vapor blanket along a
surface of each segment so cooled to thereby control the
temperature of the surface.
In another embodiment the apparatus includes a flow chamber
with a hollow cylinder having an inside diameter larger than
the outside diameter of the pipe. The cylinder has an inlet
and an outlet for the pipe and a series of vanes on the inside
walls of the cylinder are adapted to throw a cooling medium
toward the center of the hollow cylinder. A cooling medium
inlet, adapted to bring the cooling medium in contact with
the vanes, and a cooling medium outlet are also provided.
~2l~45~
In another embodiment the apparatus includes a pre-
heater; a flow chamber; a feeder adapted to feed the steel
pipe at a variable rate from the preheater and through
pipe inlet and outlet of the flow chamber: and a plug of
sufficient size to slidably seal the inside cross section
of the steel pipe as it passes into the flow chamber. The
plug has a tapered front portion adapted to receive the
steel pipe as it passes from the preheater to the flow
chamber pipe inlet and a contoured end portion opposite
the tapered end portion. An internal feeder having an
outside diameter less than that of the steel pipe is located
so as to direct a cooling medium against the contoured end
portion of the plug to thereby selectively bring the cooling
medium into contact with the inside surface of a segment
of the steel pipe.
By using the apparatus and process of the present
invention, steel pipe with increased carbon content,
reduced alloy content, increased thickness, improved
properties, or some combination thereof may be produced
with savings in energy and reductions in water consump-
tion. The apparatus and process may be used in a variety
of heat treatments including conventional heat treating/
quenching, martempering, austempering, and ausforming.
Examples of the more important features of this
invention have thus been summarized rather broadly in
order that the detailed description thereof that follows
may be better understood, and in order that the contribu-
tion to the art may be better appreciated. There are; ofcourse, additional features of the invention that will be
described hereinafter and which will also form the
subject of the claims appended hereto.
~2~3~
E~RIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is an elevation view, partially in schem~tic
form, of a preferred embodiment of the present invention;
FIGURE 2 is a front view taken from line 2-2 in
Figure 1;
FI~URE 3 is a close-up view of a portion of the
embodiment shown in Figure 1; and
FIGURES 4-6 are isothermal transformation diagrams
illustrating conventional qu~nching, martempering, and
austempering, recpectively.
Reference to these drawings will further explain the
invention when taken in conjunction with the description
of a preferred embodiment.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to Figures 1-3, there will now be
described a process and apparatus for heat treating steel
pipe in accordance with the present invention. Generally,
the apparatus includes an initial heating means 10; a
flow chamber 20; an internal feeder 40; a plug means 50;
intermittent support means, indicated at 60 and 65; pipe
feed control means, indicated by drive units 70, 71, and
72; optional plasticizing means 80 and treatment chamber
10~.
Initial heating means 10 may comprise a furnace 11 or
heating steel pipe 16 above its critical transformation
temperature. The furnace 11 is equipped with drive rolls
-~5-
(not shown) to push the preheated pipe 16 out of the door
or opening 14 in the furnace wall 12 and into engagement
with the plug means 50 and flow chamber 20 as shall
hereinafter be more fully described. The austenizing
furnace 11 is equipped with an insulated extension 15
which is attached to furnace wall 12. Insulated extension
15 helps to maintain the temperature of the pipe 16 above
the cri~ical transformation temperature between furnace 11
and flow chamber 20.
The flow chamber 20, along with drive unit 70 and
clamp or support means 60, is located a sufficient dis-
tance downstream of furnace 12 to avoid any damage to
those units. Flow chamber 20 is adapted to bring a
cooling medium, such as water, into contact with the
outside surface 17 of the pipe lS. The flow chamber 20
comprises a hollow cylinder 23, the inside diameter of
which is larger than the outside diameter of the largest
pipe 16 to be treated. As shown in Figure 3, flow chamber
cylinder 23 is equipped with adjustable vanes 29 which are
adapted to airect the cooling medium away from the surface
of flow chamber cylinder 23 and towards the outer pipe
wall 17.
~5 Flow chamber cylinder 23 is connected to cooling
medium inlet 21 by means of upper guide conduit 25 and
lower guide conduit 24. As can be seen in Figure 1, the
outer surface of the interior walls of conduits 24 and
25 are tapered to guide the pipe 16 into flow chamber
cylinder 23. The closest distance between tapered walls
27 and 28 is such that the inlet opening 34 ~o the flow
chamber cylinder 23 is just slightly more than the outside
diameter of the pipe 16. Thus, as the pipe 16 passes
through the inlet 34 it i~ closely surrounded by the end
portions of external walls 27 and 28.
~2~5~
-16-
Guide conduits 24 and 25 are adapted to impart a
helical motion to the cooling medium passing from inlet
21 into the flow chamber cylinder 23. The adju~table
vanes 29 then direct the swirling water with sufficient
pressure against the outer pipe wall 17, as shall herein-
after be more fully described.
The flow chamber outlet 35 is of slightly larger
diameter than the inlet 34 such that the outer pipe wall
17 and the outlet 35 form an annulus.
The flow chamber 20 is also equipped with optical
sensors 30, 31, and 32, or other appropriate sensing
devices, which measure the progress of the pipe 16 through
the flow chamber cylinder 23, and an upper chamber 26
which i5 adapted to receive the vaporized cooling medium
and so facilitate i~s passage through the flow chamber
body 23 and flow chamber outlet 22.
Flow chamber 20 is also equipped with thermocouples
or other appropriate temperature sensing mechanisms, for
example as shown a~ 33, 3Ç, 37, and 38.
The forward segment of the flow chamber 20 comprising
25 the inlet 21 and the guide conduits 24 and 25 may be
detachably mounted to the flow chamber cylinder 23 in
order to facilitate adjustment for differing sizes of
pipe. ~lternatively, the tapered walls 27 and 28 may be
movably mounted or provided with appropriate extensions to
facilitate sealing engagement with varying sizes of pipe.
The size of the various components of flow chamber 20
is such that a cooling medium may be supplied to inlet 21
in sufficient quantity to direct a uniform continuou
3~5~
-17--
stream of the cooling medium to the appropriate portion of
the hori~ontally disposed pipe 16. The cooling medium
is at a pressure sufficient to cause complete contact ~ith
the appropriate surface portion or segment passing through
the flow chamber at any given time.
An internal feeder or feed mechanism indicated gener-
ally at 40 comprises a floating lance 41 which is con-
nected at one end to a swing-away feed pipe or detachable
conduit 42 and at the other end to shaft 51 and spiral
vanes 57 of plug mechan;sm 50. The floating lance 41,
which comprises a hollow cylinder or conduit with an
external diameter less than that of the pipe 16, is
detachably connected to swing-away conduit 42 by means of
connectors 43. Packing 44 insures an adequate seal at the
juncture of feed pipe 42 and floating lance 41.
Detachable conduit 42 is rotatably mounted in pipe
connector 45 and is equipped with an appropriate mech-
anism, such as an hydraulic cylinder and piston arm (notshown) to move the conduit 42 in and out of engagemen~
with the floating lance 41 and out of the path of pipe
16 as it enters chamber 100.
The plug mechanism 50 is equipped at one end with a
header 52. The header 52 is tapered such that it slopes
away from the direction of the advancing pipe 16. The
header 52 and the end of tapered body portion 54 are
spaced to create a notch or clamp groove 53 adapted to
30 receive clamping members 61 of clamp 60. Header 52 and
tapered body portion 54 of the plug mechanism 50 serve to
guide the pipe 16 as it passes from austenizing furnace
11 into inlet 34 of flow chamber 20
~2~3~5~
-18-
Plug mechanism 50 is equipped with wheels 55 located
at the opposite end of tapered body portion 54 from header
52. The wheels 55 facilitate the movement of pipe 16 past
plug mechanism 50 while serving to insure an adequate seai
between the plug 50 and inner pipe wall 18.
Shaft 51 is inserted a sufficient distance into
floating lance 41 to insure adequate support for spiral
vanes 57 as well as the end of floating lance 41 itself.
As the spiral vanes 57 are integrally mounted tG the
inside wall of floating lance 41, ~he curved or arcuate
sur~ace 56 of plug 50 remains a fixed distance from the
outlet of floating lance 41. Additionally, spiral vanes
57 and shaft 51 cooperate to support the end of floating
lance 41. Thus, the $loating lance 41 is always supported
by plug mechanism 50 regardless of whether plug mechanism
50 is held in place by clamp 60 or ~y the pipe 16 and
floating lance 41.
The shaft 51 and spiral vanes 57 are of sufficient
dimensions tc impart a helical or swirling motion to the
cooling medium flowing from conduit 42 through lance 41
and into flow chamber 20. The curved surface 56 of plug
mechanism 50 serve to reverse this helical flow and throw
the wa~er or other cooling medium with sufficient force to
insure complete contact of the cooling medium with the
inner pipe wall 18.
As austenizing furnace 11 is operated at high tem-
peratures such as 1500E' ~816C), the interior of thefurnace 11 is at a slightly positive pressure. Thus, the
seal created between the inner pipe wall 18 ~nd plug
~echanism 50 should be such as to prevent the furnace
pressure from causing any material disturbance of th~
g5~
--19--
helical flow patterns created by spiral vanes 57 and
reversed and directed by arcuate surfaces 56.
The pipe 16 is supported and moved during its passage
from austenizing furnace 11 through flow chamber 20 and
into unit 100 by drive units 70, 71 and 7~. Each of these
units comprises a pair of grooved circular rolls 76 having
an axial portion 77. Thus, as the pipe passes between the
two grooved circular rolls, its upper portion is encom-
passed by the groove of the upper rolls while the lowerportion of the pipe rests in the groove of the lower
rolls. ~s shown in Figure 1, drive roll 70 is closed
around an engaging pipe 16, while drive rolls 71 and 72
are disengaged.
Intermittent support means 60 and 65 support plug
mechanism 50 and floating lance 41 J respectively. Each
intermittent support means or clamp comprises jaws 61
attached to arms 62. The arms 6~ are operatively con-
nected to a hydraulic cylinder and control mechanism 63such that arms 62 bring members 61 in and out of engage-
ment with floating lance 41 or notch or clamp groove 53 of
plug mechanism 50. As shown in Figure 1, clamp 60 is in
the open position, i.e., disengaged, while clamp 65 is
supporting one end of floating lance 41.
Wall 102 of unit t00 is provided with an opening 101
adapted to receive the pipe 16 as it passes beyond drive
uni~ 72.
Optional platicizing means 80 may be provided down-
~tream of flow chamber 20. For example, ~he plasticizing
means may comprise a pair of drive rolls capable of
exerting sufficient pressure to deform the surface of the
3~
-20-
pipe wall sufficiently for ausforming. As with drive units
70, 71 and 72, plasticizing unit 80 may comprise a pair of
two grooved circular rolls 82 mounted on a shaft 83O
In operation a pipe 16 to be heat treated is heated
above its critical transformation temperature in furnace
11. At this time clamping members 61 of clamp 60 are
engaged with notch or clamp groove 53 in order to provide
- support for plug mechanism 50. Drive rolls 70, 71 and 72
are disengaged, while clamp 65 supports floating lance 41
in much the same fashion that clamp 60 supports the end of
plug 50.
Just as the pipe 16 is to be rolled out from austen-
izing furnace 11, hydraulic cylinder control mechanism63 is activated and arms 62 swing outwardly thus disengag-
ing clamping members 61 from notch or clamp groove 53 of
plug mechanism 5D. Additionally, drive motor and control
mechanism 75 of drive unit 70 is activated to bring
2~ grooved circular rolls 76 into engagement with pipe 16 as
it is run out of furnace 11, over lance header 52 and
tapered body portion 54 of plug mechanism 50, and into
inlet 34 of flow chamber 20. Wheels 55 of plug 50 facili-
tate the movement of pipe 16 as plug 50 comes into sealing
engagement with inner pipe wall 18.
As the pipe continues on its path into flow chamber
cylinder 23 optical sensor 30, through an appropriate
control mechanism (not shown), triggers the flow of water
30 into inlet 21 of flow chamber 20 and into conduit 42 and
floating lance 41. In accordance with the present inven-
tion, the amount of water channeled into floa~ing lance 41
as well as the pressure and rate of flow are controlled
along with the speed of the pipe 16 so that substantially
~345~
-21-
all of the water entering the annulus formed by the outer
~all of floating lance 41 and inner pipe wall 18 is
vaporized as it comes into contact with the inner pipe~
wall 18. Similarly, the flow of water passing through
inlet 21 and upper and lower guide conduits 24 and ~5 is
such that substantially all of the water is vaporized as
it comes into contact with outer pipe wall 17. Thus, as
each segment of inner pipe wall 18 and outer pipe wall 17
enters into flow chamber 20 it is quenched in a quenching
zone by the water stream ~hrown against it and then
blanketed or enveloped by the resulting steam.
Thermocouples 33, 36, 37, and 38 along ~ith optical
sensors 30, 31, and 32 monitor the pipe speed and the
temperature near the pipe surface. As understood by ~hose
s~illed in the art the location and number of the various
optical and thermal sensors may be varied as appropriate.
The information from the sensors is fed into a con-
trolling mechanism (not shown) used to regulate both the
speed of the pipe as it passes from furnace 11 to unit 100
as well as the pressure and flow of water into floating
lance 41 and flow chamber 20 such that the inherent heat
of each segment of pipe is sufficient to vaporize substan-
tially all of the water flowing against outer pipe wall 17and the inner pipe wall 18. As substantially all of the
water vaporizes, a blanket of steam envelopes the inner
and outer pipe wall segment as it passes through the flow
chamber 20. Depending upon the preferred cooling rate, it
may be preferable in some cases to control the speed of
the pipe and flow of water such that the water i5 not
substan~ially completely vaporized until water is being
directed against the next segment of the pipe.
~2t~ 5~
-2Z-
Although the size of the segment which passes prior
to vaporization of all of the water may vary depending
upon the cooling sequence desired, it is to be understo~d
that the process is an incrementally continuous process
such that each segment or increment of pipe may be quite
small. Additionally, as the process is a continuous one
the distinction between segments will generally be blurred
As the pipe 16 passes through oulet 35 of flow
chamber 20 the steam created by the inherent heat of the
pipe 16 escapes from the annulus created by the outer pipe
wall 17 and the outlet 35. Similarly, steam also escapes
from the ever lengthening annulus formed by inner pipe
wall 18 and the outer surface of floating lance 41. The
length of the annulus formed by pipe surface 17 and the
walls of cylinder 23 may be partially or fully extended,
if desired, by means of a cylindrical covering or plate
(not shown) attached to the flow chamber near or congruent
with outlet 35. Drive unit 71 may be moved downstream if
necessary. With such a full or partial extension of the
walls of cylinder 23, the time during which the outer pipe
17 is exposed to ambient air can be greatly reduced.
As the pipe approaches drive unit 71, it is activated
and circular rolls 76 of drive unit 71 engage the pipe in
the same fashion as those of drive unit 70. As the front
end of the pipe continues to move toward chamber 100, the
inner pipe wall 18 remains enveloped by steam. Thus,
although the outer pipe wall 17 is now exposed to ambient
air, the temperature drop at the outer pipe wall surface
can be minimized and the temperature of the inner pipe
wall 18 can be maintained. If desired, additional heating
means (not shown~ may be provided to maintain or raise the
temperature of the outer pipe wall 17. ~owever, such
additional heating means is not generally required.
-~3-
In accordance with the present invention after the
water initially contacts the pipe, water does not impinge
upo~ the pipe 16 but rather wraps pipe 16 in a vapor
blanket. The existence of the vapor blanket is in turn
controlled by water flow into inlet 21 of flow chamber 20
and lance feed conduit 41 as well as the speed of pipe 16
as it passes from furnace 11 to chamber 100. ~hus,
generally only three variables, i.e., the two different
flow rates and the speed of the pipe, need be controlledO
As the front end of the pipe 16 approaches clamp 65,
hydraulic cylinder mechanism 63 moves arms 62 and so brings
clamp 61 out of engagement with floating lance 41. Drive
unit 7~ then engages the pipe as it passes through its drive
rolls in much the same fashion as drive unit 71. The flow
of water through floating lance 41 is then cut off and
detachable conduit 42 is disengaged from floating lance 41
by means of an arm and a hydraulic cylinder or other suit-
able mechanism (not shown). The front end of the pipe 16
then passes into chamber 100 through opening 101 in wall
102.
As the rear portion of the pipe 16 passes through the
various units and stages, the components are brought back
to their original positions in preparation for receiving
another pipe. For example, as the end of the pipe passes
lance head 52 and tapered body portion 54 of plug 50, the
hydraulic cylinder control mechanism 63 of clamp 60 oper-
ates on arms 62 to bring clamp 61 into engagement with notch
or clamp groove 53 of plug 50. The end of plug 50 is thus
once again supported by clamp 60.
As the end of pipe 1S passes through drive unit 70
grooved circular rolls 76 are retracted and as the end of
3~
~2~3~g
-24-
the pipe passes through inlet 34 of flow chamber 20t the
flow of water into inlet 21 is suspended. Similarly,
rolls 76 of drive unit 71 and drive unit 72 open and
clamping members 61 of clamp 65 once again engage the
outer surEace of floating lance 41 in order to support the
same, while detachable conduit 42 is placed in communica-
tion with floating lance 41.
Although the foregoing description is in terms of a
single pipe, one skilled in the art will appreciate that
the mechanism and inventive concepts may be readily
adapted to the sequential processing of a large number of
pipes of varying sizes.
Adjustable vanes 29 in hollow cylinder 23 and spiral
vanes 57 in cooperation with arcuate surface 56 of plug
50 serve to throw the water or otheF cooling medium
against the pipe surfaces. This flow pattern in coopera-
tion with the vaporization of the water by the inherent
heat of the pipe to be heat treated provide rapid cooling
capable of accommodating a very severe quench to a pre-
determined temperature at which the pipe can then be
maintained prior to further processing. Both the rate of
speed of the pipe as controlled by variable speed drive
motors 75 of drive units 70, 71, and 72 and the flow rate
and pressure of the cooling medium entering flow chamber
~0 and floa~ing lance 41 combine to control the tempera-
ture sequence through which each segment of the pipe
passes. Thus, in accordance with the present invention,
appropriate process controls may be employed to control
the flow rate of the cooling medium and the speed of the
pipe as it progresses from furnace 11 to chamber 100 and
so closely regulate the cooling se~uence of each segment
of the steel pipe 16. The details of the various pro-
cess controls which may be used to regulate the cooling
~r~341~59
sequences will be apparent to those skilled in the artrom the descriptions contained herein.
According to one aspect of the present invention the
floating lance 41 of internal feeder 40 is adapted to
allow each pipe to pass substantially directly from
heating means 10 to chamber 100. There is no need to
remoYe the pipe laterally after it passes over floating
lance 41 prior to passing the pipe to chamber 100 for
further treatment. Thus, in a preferred embodiment the
floating lan~e 41 is stationary in relation to flow
chamber 20 due to the operation of clamp or intermi~tent
support means 60, plug 50, clamp 65, and detachable
conduit 42. As swinging conduit 42 is de$achable from
floating lance 41 and may swing out of the path of the
pipe as it passes over the end of floating lance 41
nearest chamber 100, the pipe may pass directly to
chamber 100.
Reference will now be made to Figures 4-6 to describe
conventional heat treating/quenching, martempering, and
austempering as accomplished in accordance with the
present invention.
Each isothermal transformation diagram or S curve
represents a graph which charts the transformation of
austenite as a function of temperature and time. The
diagram permits an approximation of how a given steel
will respond to a particular cooling sequence. The cross-
hatched areas between lines Ms-Ai and M~-Aj represent the
regions of transformation from austenite to other forms
such as pearlite, bainite, and martensite. This area is
partially bounded on one side by line Ms~ which indicates
the temperature at which martensite star~s to form on
31 2~?3~
-26-
quenching from the critical transformation temperature
indicated by Tc. The area is further bounded by curved
line Ai, which represents the temperature at which trans-
formation to pearlite or bainite will b~gin after a given
amount of time. 80rizontal line Mf and curved line Af
serve to define the other boundary of the transformation
area. The horizontal line Mf indicates the temperature
at which 100~ martensite is formed, while Af represents
a completed transformation to pearli~e or bainite, depend-
ing upon the location on the curve.
The ~orm of the Ai, Af curves as well as the loca-
tion of the Ms and ~f lines is a function of a given
steel's composition, including carbon and alloy content,
and the grain size of the austenite which is undergoing
tranformation. In mos~ cases an increase in alloy content
generally retards isothermal transformation, i.e., moves
the curve toward the right, at any temperature higher than
about 900~F (482C), where the initial transforma~ion
curve, Ai, comes closest to the zero time axis.
As the amount of carbon in a given steel increases,
the hardness of the martensite subsequently formed in-
creases while the martensitic transformation temperature
(Ms) decreases. This in turn enhances the possibility of
cracking, particularly where a fast rate of cooling is
maintained through the martensite transformation range,
i.e., as the temper~ture decreases from Ms to Mf~
3~ Before proceeding to discuss the individual processes,
some other points concerning the isothermal transformation
curves should be noted. First, time is on a 109 scale.
Thus, the time available in which to avoid the nose or
knee of the initial transformation curve (Ai) at a point
-2~-
where pearlite begins to form is minimal. In most cases
it i5 on the order of a few seconds.
Second, the various transformation curves are only
approximations. For example, the martensitic transforma-
tion temperature Ms may vary somewhat for any gi~en point
on a piece of steel. Thus, it is often necessary to
operate in a region somewhat removed from a given trans-
formation curve in order to avoid formation of a given
- 10 structure.
Third, the curve marked surface represents the
cooling rate curve for the outer surface of a piece of
steel pipe whereas the curve marked center represents the
cooling rate curve for the center of the pipe wall. As
the temperature change in the center will naturally lag
the temperature change at the surface, the distance
between these two cooling curves will increase with an
increase in thickness of the steel for a given method of
cooling.
Figure 4 shows the cooling sequence for customary
quenching and tempering. As indicated in Figure 4 the
austenite steel is quickly cooled or quenched from a
temperature above the critical transformation temperature
Tc to a temperature below the complete martensite trans-
formation temperature Mf. As the martensite expands, the
resulting martensitic steel is unstable and must be
tempered to produce the final product, a tempered marten-
site.
In prior processes, the thickness of steel pipe whichcould be quenched was limited to a thickness of approxi-
mately 1 inch ( 20 54 cm), since at any grea~er thickness
3~
~2~34S~
-28-
the central cooling curve would cross the knee or nose of
the initial transfor~ation curve (Ai), thus resulting in
the formation of undesirable pearlite. Although the
addition of alloys moved the nose or knee of the initial
transformation curve to the right and hence provided more
leeway in cooling the center, the use of alloys substan-
tially increases the cost of the steel.
In accordance with the present invention, the water
is vaporized as soon as or soon after it impinges upon the
steel. Additionally, a helical flow is created by spiral
vanes 57 and curved surfaces 56 on the interior of the
pipe and by adjustable vanes 29 on the exterior of the
pipe. This combina~ion of helical flcw and substantial
vaporization produces more efficient transfer of heat than
heretofore possible in the heat treatment of steel. Thus,
a quench in accordance with the present invention serves
to move ~he surface and center cooling curves to the left
and so minimizes or eliminates the need for expensive
alloys to move the knee of the initiai transformation
curve to the right~ After initial quenching in the flo~
chamber 20, the steam blanket maintains the temperature as
shown in Figure 4 until the pipe passes into chamber 100
for tempering.
Referring now to Figure S, as already indicated mar-
tempering allows the use of a steel with a higher carbon
content, since the rate of martensite transformation is
accomplished over a longer span oE time. However, as a
practical matter, prior processes are generally limited to
the martempering of steels with a carbon content of
approximately 0.50~ or less. By way of example a one-sided
quench of a steel pipe is limited to a steel with a carbon
content oP about 0.45~, while a two-sided quench is limited
5g
-29-
to a steel with a carbon content of approxi~ately 0.33% or
less. This is due to the fac~ that sufficiently exact
temperature control is not possible, particularly afte~
the severe quench often necessitated by the need to avoid
the nose of the initial transformation curve ~Ai). For
example, if a steel pipe was plunged into a bath of ice
water in order to provide a sufficiently severe quench in
the center of the pipe wall; the surface would then dip
below the martensitic transformation temperature Ms,
thus setting up immediate transformation of a portion of
the steel to martensite accompanied by the concomitant
problems of martensitic expansion and crac~ing.
In accordance with the present inventionJ a steel
15 pipe having a carbon content of from 1.0 to 105% or
greater and a thickness of up to 2.5 inches (6.4 cm) and
greater can be successfully martempered. ~his is due to
the fact that in accordance with the present invention
there is provided a process which allows a sufficiently
severe quench to a fixed temperature followed by a con-
trolled and gradual change in temperature such that the
increased stresses due to higher carbon content may be
accommodated, Thus, a given martempered steel may have a
lower alloy content~ a greater carbon conten~, greater
thickness or some improved combination of these not
previously possible.
In martempering the pipe 16 may be severely quenched
by the vaporization of water flowing from flo2ting lance
41 and inlet 21. However, due to the presence of the
steam blanket or envelope, the temperature does not
fall below a given ~emperature above the martensitic
transformation temperature Ms. As the pipe passes from
the flow chamber 20, it then begins to cool gradually in
~3~15~
~3~-
the air as it approaches chamber 100, thus providing a
controlled cooling rate. Control of the amount o~ water
fed through inlet 21 and floating lance 41 along with t~e
rate of speed of the pipe as it progresses from furnace 11
to chamber 100 provides control of the slope of the cool-
ing curve through the martensite ~ransformation region,
i.e., between lines Ms and Mf, since ~his in turn allows
control of the temperature and the extent of the internal
and external steam blankets. As ~ith customary quenching
and tempering, the pipe may be tempered downstream of
drive unit 72 and conduit 42 in chamber 100~
Referring now to Figure 6, as already discussed
austempering is a hardening process based upon isothermal
transformation of austenite to bainite. As indicated in
Fiyure 6 the steel must again be severely quenched such
that the cooling curve for the center of the pipe wall
avoids the knee of the initial transformation curve Ai.
However, unlike martempering the steel must then be
~o maintained within a narrow temperature range above the
martensitic transformation temperature until transforma-
tion to bainite is completed.
Prior processes have been unable to successfully
austemper steel pipes with a wall thickness of greater
than approximately one inch (2.54 cm) more or less, since
prior processes were not able to provide a sufficiently
severe quench and still avoid the formation of martensite
on the surface of the pipe. Howevery the present inven-
tion reduces the temperature lag between the surface andcenter cooling curves and moves them to the left. The
present invention also allows the subsequent maintenance
of the ste~l at a constant temperature until it may be
transferred to an oven or furnace to complete the trans-
formation to bainiter Thus, unlike prior art processes
-31-
steel pipe of fairly large ehicknesses can now be success-
fully austempered.
As each portion of the pipe enters the flow chamber
20 both the exterior and interior surfaces of the pipe are
quenched by water coming from floating lance 41 and inlet
21 of flow chamber 20. Thus, each segment is quickly
quenched from the critical transformation temperature to
the appropriate temperature just above the martensitic
transformation temperature. In accordance with the
present invention the vapor blankets or envelopes which
surround the inside and outside surfaces of the pipe 1~
are maintained for an appropriate distance along the pipe
once produced by the inherent heat of the pipe 16. The
flow of water and speed of the pipe are controlled such
that the supply of heat radiated from the pipe 16 equals
or exceeds the amount of heat needed to form the appro-
priate amount of vapor per unit surface area of the steel
pipe 16. As the vapor envelope acts as an insulator,
such that cooling occurs principally by radiation through
the vapor film of the pipe, the temperature remains
essentially constant for whatever period of time necessary
to facilitate the transformation of austeni~e to bainite.
As with martempering, a given austempered steel may
have a lower alloy content, a greater carbon content,
greater thickness~ improved properties or some combination
of these. By way of example, given an appropriate alloy
content, a steel pipe austempered by traditional processes
might have a yield strength as high as about 150,000-
160,000 psi. Now, yield strengths of 250,000 psi or
possibly higher may be obtained by practice of the present
invention.
-32-
The present invention may also be used to advantage
in ausforming a given steel pipe. In ausforming the steel
is guenched to te~peratures between about 600 and 800F
(316 to 427C) and then isothermally transformed to pear-
lite. The pearlitic steel is then converted to martensiteafter being plasticly deformed by mechanical working.
Thus, in accordance with the present invention, the flow
of water and speed of the pipe are regulated to quench
the steel to a desired temperature (for example 600-800~F
or 316-427~C). The steel is then isothermally deformed by
austempering roll 81 and transferred to chamber 100 for
appropriate tempering. Again, larger thicknesses of pipe
may be ausformed than heretofore possible and under more
favorable conditions given the improved temperature
control provided by the ~ormation of controlled amoun~s of
steam from the inherent heat of the pipe.
Although in most cases the temperature of the water
fed into inlet 21 and floating lance 41 is not believed to
be particularly critical in obtaining the benefi~s of the
present invention, it is preferable if the water has a
temperature of about 80DF (27~C) and preferably 70F
t21C) or less, since the cooling power of water increases
rapidly as water temperature decreases beyond about 75F
(24C). In fact, this los~ of cooling power i5 almost
expotential such that water at a temperature of 120~
(49~C) has only about 20% of the cooling power of water at
70-F (21-C~. ~owever, use of water at a higher tempera-
ture can still prove advantageous when compared to prior
processes using water of a similar temperature due to the
favorable flow pattern created by the vanes and the
vapori~ation of the water as well as use of ~he heat of
vaporization for cooling.
~3~
-33-
As the foregoing discussion indicates and unlike
the prior art processes, the apparatus of the present
invention may be used to accomplish conventional quench~
ing, martempering, modified martempering, austempering and
ausforming without modification. Additionally, varying
sizes of pipe may be accommodated by varying the diameter
of the flow chamber inlet.
As will be appreciated by one s~illed in the art
having the benefit of this disclosure, including the
following examples, the present invention results in the
production of steel pipes with improved properties not
heretofore possible for a given thickness of pipe. More-
over, in some cases the attainable array of properties
is greater than previously possible for a given thickness
of steel pipe. Additionally, the present invention
accomplishes these results at reduced costs through use of
the inherent heat of the pipe and smaller qua~ti~ies of a
given cooling medium such as water.
The following examples further illustrate the inven-
tive concept disclosed herein. Naturally, ~hese examples
are in no way meant to limit the scope of the present
invention, but rather are illustrative only. The examples
are based on data taken from the third edition of an Atlas
of Isothermal Transformation Diagrams published by United
States Steel Corporation.
EXAMPLE 1
A modified 1060 grade steel pipe with a carbon con-
tent of .~4~ a manganese content of 1.13~ an~ a silicon
content of .09% could be austempered by passing it through
the flow chamber at a controlled speed such tha~ water
- 35
5~
-3~-
flowing through the floating lance and the flow chamber
would quench the pipe at an overall rate of approximately
950-F in 5 seconds to a temperature of approximately
600F. The blanket of steam would initially hold each
quenched portion of the pipe at 600F such that the steel
would undergo a uniform transformation to bainite. The
resulting steel pipe would have a RC hardner number of
approximately 52 with a tensile strength of approximately
250,000 psi.
EXAMPLE 2
The process of example 1 could be repeated for a 4068
grade steel pipe with a carbon content of .68~9 a manga-
nese content of .87%, a molybden content of .24~, and asilicon content of .26%, as weil as residual amounts of
nickel (.01%), chromium t.03%), and copper (.03%), could
be quenched to ~bout 500-F. The blanket of steam would
initially hold each quenched portion of the pipe at 500F
and the resulting steel should have an RC hardness number
of 56 and a tensile strength of about 300,000 psi.
Of course, a number of modifications and substitu-
tions may be made in the foregoing apparatus and method
without departing from the spirit and scope of the present
invention. For example, a portion of the plug 50 may be
constructed of an insulating material. Additionally,
although water is the preferred quenching medium, it is to
be understood that other liquids or solutions can be used
to advantage. Furthermore, although the description o
the preferred embodiment is restricted to ~teel pipe, the
inventive concept may be employed with other annular or
cylindrical shaped pieces of steel. Similarly, the
apparatus of the present invention may be employed in
~'3~
conventional isothermal annealing as well as modified
martempering, wherein the quench through the martensite
region is less severe than in regular martempering, an~
other heat treating processes.
Further modifications and alternative embodiments
of the apparatus and method of this invention will be
apparent to those skilled in the art in view of this
description. Accordingly, this description is to be
construed as illustrative only and is or the purpose of
teaching those skilled in the art the manner of carrying
out the invention. It is to be understood that the forms
of the invention herewith shown and described are to be
taken as the presently preferred embodiments. Various
changes and modifications may be made in the size, shape
and arrangement of parts. For example, equivalent ele-
ments or materials may be substituted for those illu5-
trated and described herein, parts may be reversed, and
certain features of the apparatus and process of the
invention may be utilized independent of the use of other
features, all of which would be apparent to one skilled in
the art after having the benefit of this description of
the invention. It is intended that the following claims
be interpreted to embrace all such modifications and
changes as would be apparent to those skilled in the ar~.
