U.S. patent application number 11/577976 was filed with the patent office on 2009-02-12 for process for the manufacture of a containment device and a containment device manufactured thereby.
This patent application is currently assigned to HILLE & MULLER GMBH. Invention is credited to Markus Helmut Maria Dotsch, Ruediger Hartung, Marcel Onink.
Application Number | 20090038718 11/577976 |
Document ID | / |
Family ID | 34928604 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090038718 |
Kind Code |
A1 |
Dotsch; Markus Helmut Maria ;
et al. |
February 12, 2009 |
PROCESS FOR THE MANUFACTURE OF A CONTAINMENT DEVICE AND A
CONTAINMENT DEVICE MANUFACTURED THEREBY
Abstract
A process for manufacturing a containment device including:
providing steel slab including (in wt. %) C: 0.05%-0.4%; Si:
.ltoreq.2.0%; Mn: .ltoreq.2.0%; P: .ltoreq.0.1%; N: .ltoreq.200
ppm; remainder iron and inevitable impurities; hot rolling the slab
to steel strip after reheating the slab, or utilizing the casting
heat by hot-charging the slab, or by direct rolling the slab after
casting, followed by cooling the strip to coiling temperature and
coiling; cold rolling the strip at between 40 and 95% thickness
reduction to form cold-rolled strip; continuous annealing by
reheating to temperature above Ac1, homogenising at least 5
seconds, followed by rapid cooling; producing the device. The
device has steel at least 10 vol. % martensite and/or bainite and
reduced properties of anisotropy. Containment device manufactured
by the process and producing isolation barrier material for high
temperature and/or pressure sealing for containment devices are
also disclosed.
Inventors: |
Dotsch; Markus Helmut Maria;
(Bottrop, DE) ; Hartung; Ruediger; (Bad Honnef,
DE) ; Onink; Marcel; (Dusseldorf, DE) |
Correspondence
Address: |
Dickinson Wright PLLC;James E. Ledbetter, Esq.
International Square, 1875 Eye Street, NW., Suite 1200
WASHINGTON
DC
20006
US
|
Assignee: |
HILLE & MULLER GMBH
Duesseldorf NRW
DE
|
Family ID: |
34928604 |
Appl. No.: |
11/577976 |
Filed: |
October 26, 2005 |
PCT Filed: |
October 26, 2005 |
PCT NO: |
PCT/EP05/11609 |
371 Date: |
October 31, 2008 |
Current U.S.
Class: |
148/530 ;
148/320; 148/518; 148/534; 148/603 |
Current CPC
Class: |
C21D 8/02 20130101; C22C
38/02 20130101; C22C 38/04 20130101; C21D 9/46 20130101 |
Class at
Publication: |
148/530 ;
148/603; 148/534; 148/320; 148/518 |
International
Class: |
C21D 8/02 20060101
C21D008/02; C21D 9/52 20060101 C21D009/52; C22C 38/00 20060101
C22C038/00; C25D 7/06 20060101 C25D007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2004 |
EP |
04077943.1 |
Claims
1. Process for the manufacture of a containment device comprising
the steps of a) providing a steel slab having a chemical
composition comprising (in weight percent) C: 0.05%-0.4%; Si: not
greater than 2.0%; Mn: not greater than 2.0%; P: not greater than
0.1%; N: not greater than 200 ppm; optionally also comprising, on a
weight basis at least one member selected from the group consisting
of Cr less than 1.0%, Mo less than 1.0% and/or at least one member
selected from the group consisting of Nb less than 0.1%, Ti less
than 0.1%, V less than 0.1%; remainder iron and inevitable
impurities; b) hot rolling the slab to a strip after reheating the
slab, or under utilisation of the casting heat by hot-charging the
slab, or by direct rolling the slab after casting, followed by
cooling the strip to a coiling temperature followed by coiling; c)
cold rolling the strip steel at a reduction in thickness of between
40 and 95% to form a cold-rolled strip; d) continuous annealing by
reheating to a temperature above Ac1, homogenising for at least 5
seconds, followed by rapid cooling, optionally followed by temper
rolling; e) producing the containment device, wherein the steel in
the containment device comprises at least 10% in volume of at least
one phase selected from a group of phases consisting of martensite
and bainite and wherein the containment device has a reduced
anisotropy of properties.
2. Process according to claim 1, wherein the steel in the
containment device comprises at least 20% in volume of a martensite
phase.
3. Process according to claim 1, wherein the steel in the
containment device comprises at least 80% in volume of a martensite
phase.
4. Process according to claim 1, wherein the steel is coated with
metallic coating.
5. Process according to claim 4, wherein the metallic coating is
selected from a group of metallic coatings consisting of Cu, Ni,
Co, Al, Zn, Ti, Cr or alloys thereof.
6. Process according to claim 4, wherein the metallic coating is a
nickel-based coating.
7. Process according to claim 1, wherein the steel is
aluminium-killed or aluminium-silicon killed.
8. Process according to claim 1, wherein the total nitrogen content
of the steel is greater than 5 ppm and/or not greater than 150
ppm.
9. Process according to claim 1, wherein the steel is temper rolled
after continuous annealing.
10. Containment device manufactured according to claim 1.
11. Containment device according to claim 10, wherein the
containment device is a gasket.
12. Containment device according to claim 10, wherein the
containment device is a cartridge for rimfire ammunition.
13. Containment device according to claim 10, wherein the
containment device is a battery case.
14. Process for the manufacture of an isolation barrier material
for high temperature and/or high pressure sealing applications
comprising the steps of: a. providing a steel slab having a
chemical composition comprising (in weight percent) C: 0.05%-0.4%;
Si: not greater than 1.0%; Mn: not greater than 2.0%; P: not
greater than 01%; N: not greater than 200 ppm; optionally also
comprising, on a weight basis at least one member selected from the
group consisting of Cr less than 1.0%, Mo less than 1.0% and/or at
least one member selected from the group consisting of Nb less than
0.1%, Ti less than 0.1%, V less than 0.1%; remainder iron and
inevitable impurities. b. hot rolling the slab to a strip after
reheating the slab, or under utilisation of the casting heat by
hot-charging the slab, or by direct rolling the slab after casting,
followed by cooling the strip to a coiling temperature followed by
coiling; c. cold rolling the strip steel at a reduction in
thickness of between 40 and 95% into a cold-rolled strip; d.
continuous annealing by reheating to a temperature above Ac1,
homogenising for at least 5 seconds, followed by rapid cooling; e.
producing the containment device wherein the steel in the
containment device comprises at least 10% in volume of at least one
phase selected from a group of phases consisting of martensite and
bainite and wherein the containment device has a reduced
anisotrophy of properties.
15. Process according to claim 1, wherein the steel in the
containment device comprises at least 20% in volume of a martensite
phase, the remainder comprising at least 60% in volume of
ferrite.
16. Process according to claim 1, wherein the steel in the
containment device comprises at least 90% in volume of a martensite
phase.
17. Process according to claim 1, wherein the steel is coated with
metallic coating by electroplating.
18. Process according to claim 4, wherein the metallic coating is a
nickel-based coating with a minimum nickel-content of at least
about 85%.
19. Process according to claim 1, wherein the total nitrogen
content of the steel is between 15 and 125 ppm.
20. Process according to claim 1, wherein the total nitrogen
content of the steel is between 25 and 100 ppm.
21. Process according to claim 1, wherein the steel is temper
rolled after continuous annealing, wherein the temper rolling
reduction is 10% or less.
22. Process according to claim 1, wherein the steel is temper
rolled after continuous annealing, wherein the temper rolling
reduction is at least 1.5%.
23. Process according to claim 1, wherein the steel is temper
rolled after continuous annealing, wherein the temper rolling
reduction is in the range from 1.5% to 10%.
24. Containment device according to claim 10, wherein the
containment device is an internal combustion engine gasket.
Description
[0001] The present invention relates to a process for the
manufacture of a containment device and a containment device
manufactured by said process and to a method of producing an
isolation barrier material for producing said containment
devices.
[0002] Containment devices are used to separate a first environment
from a second environment where it is important that both
environments do not come into contact with one another and where it
is important that the environmental conditions in the first
environment can be contained for a short period of time e.g. in
case of a rimfire cartridge, or for a sustained period of time e.g.
in case of an engine gasket. In a containment device such as an
engine gasket, which is for instance positioned between a cylinder
head and a cylinder block, which jointly define the combustion
chamber of an automotive engine, the internal environment of the
engine is separated from the outside environment. An engine gasket
is a sealing member having an opening, which generally has a
circular shape with essentially the same diameter as the cylinder
of the engine, and an annular bead, which is a ridge, formed by
beading so as to surround the opening. The bead functions as a
macro-seal since it is compressed between the cylinder head and
cylinder block and seals the interstice there between to prevent
leakage of combustion gas from the combustion chamber, cooling
water from cooling means for cooling the engine, and lubricating
oil from lubrication means for lubricating moving parts of the
engine. Additional micro sealing is provided by an elastomer, such
as a fluoro-elastomer. The gasket functions as a containment device
because its main purpose is to contain the different media (such as
gas, oil, water) in their proper environments. It is important to
note that a containment device is meant to act as a separator
device not only under static conditions, but also under dynamic
conditions.
[0003] A material for fabricating such an engine gasket is
therefore required to have high strength (high hardness and high
yield stress) sufficient to retain a bead against compression,
along with good workability, adequate corrosion resistance and
thermal stability, but also requires adequate formability during
forming of the gasket. It should also be noted that the fatigue
properties of containing device such as an engine gasket are of
major importance because the gasket is loaded and unloaded at each
explosion in any of the combustion chambers enclosed by the
cylinder, the piston and the cylinder head. A further requirement
is a low anisotropy of the properties of the material from which
the gasket is formed. It should be noted that when the term
anisotropy is used, this is to be understood as planar anisotropy.
Thermal stability of the properties is important as well because in
operation, temperatures of the gasket may be high, for instance
about 110.degree. C.
[0004] In a containment device such as a cartridge for ammunition
for firearms it is important to contain the internal exploding
atmosphere in the cartridge from the outside atmosphere as long as
possible in order to obtain a maximum transfer of energy from the
explosion to the bullet leaving the barrel of the firearm. During
the explosion the cartridge has to ensure sealing of the backside
of the barrel of the firearm to prevent energy loss by escaping gas
at the backside. This sealing is ensured by an elastic expansion of
the cartridge during the explosion. After the explosion the
cartridge relapses allowing easy removal of the cartridge from the
barrel. A good formability during forming of the cartridge is
required, in combination with a high yield strength of the final
cartridge. A high yield strength results in the required elastic
expansion of the cartridge during the explosion without plastic
deformation of the cartridge, which could cause it to stick in the
barrel. A further requirement is a low planar anisotropy of the
properties of the material from which the cartridge is formed to
prevent or reduce earing during forming of the cartridge.
[0005] In a containment device such as a battery case it is
important to contain the often harmful and corrosive content of the
battery from the outside environment to prevent corrosion,
pollution or health risks. To improve the capacity of a battery, it
is important to increase the volume of the battery case without
changing the external dimensions of the battery. Down gauging the
wall thickness of the case would result in such a volume increase.
However, in a battery, the internal pressure may easily exceed a
value of 30 bar. This high pressure must not result in plastic
deformation or failure of the battery. Hence a high strength and a
high yield point is required of the battery case, but a low yield
stress and high formability is required during the forming of the
case by draw-and-wall-ironing (DWI) or draw-and-redraw (DRD)
techniques. A further requirement is a low anisotropy of the
properties of the material from which the cartridge is formed to
prevent or reduce earing during forming of the battery case.
[0006] In order to meet the above-described requirements for engine
gaskets, a known solution is to use a metastable austenitic
stainless steel, such as SUS 301 stainless steel, which is a Cr-
and Ni-added stainless steel. Deformation of such a steel by cold
working, such as cold rolling and beading, causes the metastable
austenite in the deformed area to transform to martensite, which
has a greater hardness. Thus, the steel can exhibit a high work
hardenability with good initial workability.
[0007] However, such a stainless steel has the disadvantage that
its properties, particularly hardness, may fluctuate greatly, since
the increased hardness of the steel obtained by working may vary
significantly depending on the working ratio of the steel and the
temperature at which the steel is subjected to working. Therefore,
the quality, particularly the sealing quality of gaskets made from
the steel, may fluctuate significantly. Another disadvantage is
that the metastable austenitic steel is susceptible to stress
corrosion cracking. Furthermore, the steel contains a large amount
of nickel, which is expensive, thereby adding to the production
costs of the gaskets.
[0008] In order to cope with these problems, a Cr-based martensitic
stainless steel having a tempered martensitic structure has been
proposed for the fabrication of engine gaskets in JP 7-278758. In
general, martensitic stainless steels have an improved resistance
to stress corrosion cracking over the metastable austenitic
stainless steel described above. Moreover, it is relatively easy to
achieve a high hardness with martensitic stainless steel by means
of quenching from a high temperature, which causes transformation
to form hard martensitic phases. Furthermore, martensitic steel is
less expensive since it contains a lower nickel content.
[0009] However, since martensitic stainless steels in the
as-quenched condition have a decreased elongation and are difficult
to work, it is essential that the quenched martensitic steel be
subjected to heat treatment to a tempering heat treatment after
quenching. Such heat treatments add to the production costs of the
steel and may cause embrittlement of the steel due to formation of
carbides or a loss of corrosion resistance due to the formation of
Cr-deficient phases resulting from the formation of carbides.
[0010] The application of stainless steel for gaskets has a number
of disadvantages. Firstly, the costs of stainless steel are high
due to the high level of expensive alloying elements such as for
instance Chromium and Nickel. Furthermore, the final properties of
a stainless steel are very sensitive to the processing conditions
and these processing conditions are quite demanding. In addition,
stainless steels contain many alloying elements in significant
quantities. As a result of non-uniform distribution of the alloying
elements and the effect of fluctuations in processing conditions
thereupon, the mechanical properties of these steels also fluctuate
significantly. Therefore, the reproducibility and the anisotropy of
the mechanical properties of stainless steels is a constant
concern.
[0011] It is known that the yield strength of a steel can be
increased by subjecting it to a second cold rolling at a draft of
30% or more. The disadvantage of this second cold rolling step at a
draft of 30% or more is the large anisotropy, which is the result
of the second cold rolling.
[0012] It is an object of this invention to provide a process for
the manufacture of a containment device with a high
post-manufacture yield strength
[0013] It is another object of this invention to provide a process
for the manufacture of a containment device with a reduced
anisotropy of properties.
[0014] It is another object of this invention to provide a process
for the manufacture of a containment device made from an
economically attractive material.
[0015] It is still another object of this invention to provide a
process for the manufacture of a containment device with a reduced
sensitivity of the properties to the processing conditions.
[0016] According to the invention, one or more of these objectives
are achieved with a process for the manufacture of containment
device manufactured comprising the steps of: [0017] a. providing a
steel slab having a chemical composition comprising (in weight
percent) [0018] C: 0.05%-0.4%; [0019] Si: not greater than 2.0%;
[0020] Mn: not greater than 2.0%; [0021] P: not greater than 0.1%;
[0022] N: not greater than 200 ppm; [0023] remainder iron and
inevitable impurities; [0024] b. hot rolling the slab to a strip
after reheating the slab, or under utilisation of the casting heat
by hot-charging the slab, or by direct rolling after casting,
followed by cooling the strip to a coiling temperature followed by
coiling; [0025] c. cold rolling the strip at a reduction in
thickness of between 40 and 95% to form a cold-rolled strip; [0026]
d. continuous annealing by reheating to a temperature above Ac1,
homogenising for at least 5 seconds, followed by rapid cooling;
[0027] e. producing the containment device wherein the steel in the
containment device comprises at least 10% in volume of at least one
phase selected from a group of phases consisting of martensite and
bainite and wherein the containment device has a reduced anisotropy
of properties. The steel is preferably aluminium-killed or
aluminium-silicon killed.
[0028] With a process for the manufacture of a containment device
according to the invention, there is no need for a very costly
alloy basis such as in the case of a stainless steel. The steel
basis according to the invention, subjected to the process as
described hereinabove, will result in a steel strip with a
microstructure which comprises at least 10% in volume of at least
one phase selected from a group of phases consisting of martensite
and bainite. These phases contribute greatly to the strength of the
material. Due to the annealing above Ac1, the anisotropy of the
final product is greatly reduced because the phase transformation
from ferrite to austenite upon heating and the subsequent
re-transformation from austenite to the desired phases during rapid
cooling randomises the texture of the material to a great extent,
thereby reducing the anisotropy of the material.
[0029] Surprisingly, it was found that the containment device
produced according to the invention has a high bake hardening
potential. Upon heating the containment device, which has undergone
deformation to form it, to a temperature of for example between 100
and 200.degree. C. a very significant increase in yield strength
could be observed. This also results in excellent fatigue
properties.
[0030] Consequently, a bake-hardening treatment after forming the
part further increases the yield strength of the material in the
finished part. An advantage of the process according to the
invention is that no second cold rolling treatment is required to
achieve the desired final properties. An additional cold rolling
step would significantly increase the anisotropy of the properties,
which is undesirable for many containment devices. It should be
noted that a second cold rolling treatment is to be understood as a
rolling treatment involving a reduction of more than 10% since
these levels of deformation will deleteriously affect the
anisotropy of the product. Any cold rolling treatment involving a
reduction of at most 10% is considered to be a temper-rolling
treatment.
[0031] The containment device produced according to the invention
therefore favourably combines high strength, excellent fatigue
properties and a reduced anisotropy.
[0032] The cooling of the hot-rolled steel is optionally performed
using accelerated cooling equipment such as a laminar cooling unit,
or an ultra fast cooling unit, both units mainly using water as a
coolant, but it could also be performed using a mist cooling unit
or a gas-cooling unit. Typical cooling rates during accelerated
cooling would be between 10 and 200.degree. C./s, although using a
cooling of the ultra fast cooling type, the cooling rate could be
significantly higher, up to 1500.degree. C./s per unit thickness
(in mm) (i.e. 500.degree. C./s for a 3 mm strip).
[0033] The mechanical properties of the containment device can be
further tuned in embodiments of the invention wherein the chemical
composition of the steel also comprises, on a weight basis, [0034]
at least one member selected from the group consisting of Cr less
than 1.0%, Mo less than 1.0% and/or [0035] at least one member
selected from the group consisting of Nb less than 0.1%, Ti less
than 0.1%, V less than 0.1%.
[0036] Chromium and molybdenum are ferrite stabilising elements,
raise the transformation temperature from austenite to ferrite
(A.sub.3) and retard decomposition of austenite by slowing down the
diffusivity of carbon in austenite. Vanadium, titanium and niobium
have the same effect. All mentioned elements are also strong
carbide formers, resulting in a precipitation of carbides under the
proper thermo-mechanical conditions (i.e. temperature, strain and
strain rate). The addition of these elements consequently allows
tuning the microstructure of the steel as well as the mechanical
properties, resulting in a containment device with the desired
properties to perform its function.
[0037] In an embodiment of the invention, the silicon content of
the steel is at most 1.0%, preferably at most 0.5%. By reducing the
silicon content, the condition of the surface of the material
improves.
[0038] In an embodiment of the invention the cold rolling reduction
is between 50 and 95%, preferably between 70 and 90%, more
preferably between 75 and 88%. The anisotropy of the final
cold-rolled and annealed product at least partly depends on the
amount of cold rolling reduction. In combination with the annealing
treatment it was found that the cold-rolling reduction should
preferably be at least 50% but more preferably be at least 75%.
Although the cold rolling reduction of step c. is preferably
brought about in one process step, for instance in a multi-stand
rolling mill or in a reversible cold-rolling mill, step c may also
consist of two separate cold rolling steps with an intermediate
recrystallising annealing between the two separate cold rolling
steps. This is particularly relevant for less powerful cold rolling
mills. However, the total cold rolling deformation is the same as
for the single cold rolling step.
[0039] In an embodiment of the invention the steel in the
containment device comprises at least 20% in volume of a martensite
phase, the remainder preferably comprising at least 60% in volume
of ferrite. The increase in martensite content ensures a further
increase in strength. In this embodiment, the resulting structure
is commonly referred to as a dual-phase structure, although other
phases like bainite and/or retained austenite are known to be
possible in these steels, albeit in quantities not affecting the
beneficial properties associated with the dual-phase steel. In this
embodiment, the ferrite content needs to be at least 60% to ensure
sufficient hardness of the martensite phase. During annealing and
upon transformation during cooling carbon is rejected from the
ferrite and concentrates in the remaining austenite. If the carbon
enrichment is sufficient and the cooling rate is high enough, the
austenite may transform to martensite upon further cooling. The
hardness of the martensite depends at least partly on its carbon
content. The formability of the dual-phase structure is excellent
and the presence of the martensite embedded in the ferritic matrix
ensures a low initial yield stress, whereas the ultimate strength
of the material is high. After deformation, i.e. after forming the
containment device, the yield strength has increased significantly
thereby increasing the potential of the material to accommodate
elastic stresses, because plastic deformation does not occur until
the increased yield stress is exceeded.
[0040] In an embodiment of the invention the steel in the
containment device comprises at least 80%, preferably at least 90%
in volume of a martensite phase. This very high level of martensite
ensures a very high strength, and a very high yield stress.
Although the hardness of the martensite phase itself decreases with
increasing martensite fraction due to the lower carbon content in
the martensite, the large amount of martensite still ensures a
strong increase in strength. To achieve this high martensite
content, the continuous annealing of step d has to be performed by
reheating to a temperature near Ac3 or even above Ac3. After
forming the containment device the very high yield strength ensures
a very high potential of the material to take up elastic stresses,
because plastic deformation does not occur until the yield stress
is exceeded. The higher the martensite content, the higher the
strength of the material, usually at the expense of the
formability. In cases where limited formability is required, but a
very high elastic potential, the required martensite content could
be 90% or even higher. A fully martensitic steel would ensure a
very high strength. For applications where only limited formability
is required and a very high elastic potential, a containment device
formed from a steel with 90% in volume of a martensitic phase, or
even a fully martensitic structure, would be suitable.
[0041] Surprisingly, it was found that the containment device
produced according to this embodiment invention has a very high
bake hardening potential. Upon heating the containment device,
which has undergone deformation to form it, to a temperature of for
example between 100 and 200.degree. C. a very significant increase
in yield strength could be observed. This results in a significant
advantage over a containment produced from a conventional material
such as stainless steel, which have to be subjected to an
temperature of about 400.degree. C. to achieve the desired level of
precipitation. This implies that the material has to be subjected
to an additional process step. In addition, the curing of the
elastomer, which is used for additional microsealing, has to take
place in a separate process step at temperatures of between 100 and
200.degree. C. When subjecting a formed part of the material
according to the invention to said curing step, bake hardening of
the material occurs, thereby resulting in an increase of the yield
strength after forming the part. It should also be noted that a
temperature at the location of a gasket of between 100 and
200.degree. C. in an engine readily occurs. Therefore the use of
said material in an engine gasket results in a further increase of
the yield strength without the need for an additional process step.
This increase of the yield strength is an isotropic increase
because the bake-hardening effect is isotropic.
[0042] Consequently, a bake-hardening treatment after forming the
part further increases the yield strength of the material in the
finished part.
[0043] In an embodiment of the invention the steel is coated with a
metallic coating. This may be done before or after the continuous
annealing, partly depending on the type of coating. Although the
coating may be provided using a process such as PVD, in a preferred
embodiment the coating is applied by electroplating, preferably
prior to continuous annealing. In case the steel is also subjected
to a second cold-rolling step, the electroplating step may take
place prior to or after the second cold rolling step. The type of
metal or metals chosen for the metallic coating depends on the
specific requirements of the containment device and the
environmental conditions in which it is to function. In an
embodiment the metallic coating is selected from a group of
metallic coatings consisting of Cu, Ni, Co, Al, Zn, Ti, Cr or
alloys thereof. In a preferred embodiment of the invention, the
metallic coating is a barrier coating such as a nickel-based
coating, such as a nickel coating preferably with a minimum
nickel-content of at least about 85%. A nickel coating is a very
versatile coating, which provides the steel strip with protection
against the corrosive properties of the environment, even at high
temperatures. In another embodiment the metallic coating is
sacrificial to steel such as nickel-zinc or zinc.
[0044] In addition to, or instead of, a metallic coating it is also
possible to provide the containment device with an organic coating
for reasons of corrosion resistance or lubrication purposes.
[0045] In order to increase the hardness of the surface of the
containment device, a carburizing step or nitriding step may be
part of the process for manufacturing a containment device.
[0046] In an embodiment of the invention the total nitrogen content
of the steel is greater than 5 ppm and/or not greater than 150 ppm,
preferably wherein the total nitrogen content is between 15 and 125
ppm, more preferably wherein the total nitrogen content between 25
and 100 ppm. The amount of nitrogen enables to control the bake
hardening behaviour.
[0047] In any of the embodiments, the steel may be temper rolled to
provide the desired surface quality, roughness, shape or mechanical
properties wherein the temper rolling reduction is 10% or less,
preferably 8% or less, more preferably 5% or less, even more
preferably less than 3%. The temper rolling reduction is preferably
at least 1.5%, more preferably at least 2%. At temper rolling
reductions of above 10%, the anisotropy caused by the cold-rolling
step increases rapidly to unacceptable levels. The temper rolling
treatment, which may be replaced by a tension-levelling treatment,
produces the amount of cold deformation in the material to benefit
optimally from the bake-hardening potential of the material. The
lower boundary value for the temper rolling reduction is applied to
achieve a homogeneous bake-hardening effect, because if the temper
rolling reduction is too low or even zero, then the difference in
bake-hardening effect between the deformed parts of a formed part
such as the bead in a gasket and the undeformed part will become
too large, resulting in a higher susceptibility to fatigue of the
formed part, and in a lower base yield strength of the formed
part.
[0048] According to a second aspect of the invention, a containment
device is provided which is manufactured according to the process
as described hereinabove. Depending on the volume of at least one
phase selected from a group of phases consisting of martensite and
bainite, this containment device provides a high post-manufacture
yield strength and/or a reduced anisotropy of properties which is
made from an economically attractive material and which provides a
reduced sensitivity of the properties to the processing
conditions.
[0049] In an embodiment of the invention the containment device is
a gasket for use in an internal combustion engine.
[0050] The present inventors found that when producing a
containment device such as a gasket as described hereinabove, the
containment device having a high post-forming yield stress is
obtained. When the gasket is produced according to the embodiment
wherein the steel of the gasket comprises at least 60% of a ferrite
phase, the pre-forming yield stress is low, and the post-forming
yield stress has increased with respect to the pre-forming yield
stress. When the gasket is produced according to the embodiment
wherein the steel of the gasket comprises at least 80% of a
martensite phase the pre-forming yield stress is already high and
the post-forming yield stress has increased with respect to the
pre-forming yield stress. This high post-forming yield stress
results in good fatigue properties of the gasket with a low
anisotropy value. These fatigue properties are important because of
the cyclic loading of the gasket due to the repeated explosions in
the combustion chamber, or chambers of the engine. In case the
steel is coated with a suitable metallic coating, the gasket
possesses a corrosion resistance comparable to stainless steel
gaskets. The post-forming yield strength and/or overall strength
may be further increased by the bake-hardening potential of the
material. The inventors surprisingly found that a containment
device according to the invention, particularly if the containment
device comprises a large fraction of martensite, such as at least
80%, has a very large bake-hardening potential. This bake hardening
may take place ex-situ (i.e. before application of the gasket in
the engine) or in-situ (i.e. after application of the gasket in the
engine). In the latter case the heat developed in the engine
enables the bake-hardening process to occur. Since the amount of
deformation during production of the gasket is limited and
localised, preferably the material to be formed into a gasket has
been subjected to the temper rolling or tension levelling treatment
to promote the bake-hardening effect as described hereinabove. This
is also important to limit the difference in bake hardening effect
between the deformed and undeformed parts of the gasket after
forming the gasket.
[0051] In an embodiment of the invention the containment device is
a cartridge for rimfire ammunition. Such a cartridge can be formed
from a sheet metal by drawing a cup and further forming into a
cartridge. In this type of process it is important that the
material has a low earing property, i.e. a low in-sheet or planar
anisotropy of the properties of the material. After forming the
cartridge, the material of the wall of the cartridge is heavily
deformed. This material consequently has a very high yield stress.
When using the cartridge as a rimfire cartridge in a firearm, the
cartridge undergoes a very large load transient upon explosion of
the explosive in the cartridge. During the explosion the cartridge
has to ensure sealing of the backside of the barrel of the firearm
to prevent energy loss by escaping gas at the backside. This
sealing is ensured by an elastic expansion of the cartridge during
the explosion. After the explosion the cartridge relapses allowing
easy removal of the cartridge from the barrel. The high
post-forming yield strength results in the required elastic
expansion of the cartridge during the explosion without plastic
deformation of the cartridge, which could cause it to stick in the
barrel. Since the amount of deformation during production of the
cartridge is significant, the importance of the temper rolling or
tension levelling treatment to promote the bake-hardening effect as
described hereinabove is reduced but it may be relevant for the
flatness or roughness of the material.
[0052] In an embodiment of the invention the containment device is
a case for a battery. Such a battery case can be formed from a
sheet metal by drawing a cup and further forming into a case, a
process not unlike the process for forming a cartridge for
ammunition. Also for battery cases it is important that the
material has a low earing property, i.e. a low in-sheet anisotropy
of the properties of the material. The higher the earing, the more
material needs to be trimmed from the case (or cartridge) after the
final forming step. After forming the case, the material in the
wall of the case is heavily, deformed. This material consequently
has a very high yield stress. The material in the bottom of the cup
has undergone much less deformation, particularly in a DWI process,
resulting in a larger remaining thickness of the bottom. When using
the case to form a battery, the battery has to withstand a very
high internal pressure, without bulging. If the battery bulges, the
appearance of the battery is compromised and the larger diameter as
a result of the bulging could also cause the battery to get stuck
in the battery compartment of an apparatus such as a torch. If the
battery bulges at the bottom, the appearance of the battery is
compromised and it may cause the battery to get stuck in a battery
compartment. Because of the high yield stress of the walls, the
thickness of the battery wall can be reduced, thus enabling a
higher capacity of the battery. This is the result of the larger
internal volume of the case. The higher strength of the walls
compensates for the lower thickness of the case. Since the amount
of deformation during production of the case is significant, the
importance of the temper rolling or tension levelling treatment to
promote the bake-hardening effect as described hereinabove is
reduced but it may be relevant for the flatness or roughness of the
material.
[0053] In general, the containment device according to the
invention is produced from an isolation barrier material for high
temperature and/or high pressure sealing applications. The
invention is therefore also embodied in a process for manufacturing
said isolation barrier material according to the process described
hereinabove.
[0054] The thickness of the steel strip after the last and final
rolling step as described hereinabove preferably is below 1.5 mm,
preferably below 0.75 mm. The thickness is preferably at least 0.10
mm. The preferable thickness range depends on the type of
application. For the application of the containment device as a
gasket the preferable thickness range is between 0.15 and 0.60 mm.
For the application of the containment device as a rimfire
cartridge the preferable thickness range is between 0.35 and 0.50
mm and for the application of the containment device as a battery
case the preferable thickness range is between 0.15 and 0.25
mm,
[0055] Specific embodiments of the present invention will now be
explained by the following non-limitative examples.
[0056] The following steels were continuously cast and hot rolled
to 4.5 mm (Ex. 1) or 3.0 mm (Ex. 2) according to a conventional hot
rolling schedule in an 88 inch hot strip mill followed by cold
rolling to 0.96 mm in an industrial tandem cold-rolling mill.
TABLE-US-00001 TABLE 1 Chemical compositions of the studied alloys
(wt. %) C Mn Si P Cr N Ex. 1 0.09 1.72 0.26 0.02 0.58 31 Ex. 2 0.15
1.49 0.42 0.02 -- 30 Ex. 3 0.26 1.45 0.30 0.005 -- 45
[0057] These steels were subjected to three types of annealing
treatment in step d.: [0058] cycle #1, embodiment of claim 3: at
least 80% martensite [0059] cycle #2, embodiment of claim 2: at
least 60% ferrite and 20% martensite [0060] cycle #3, embodiment of
claim 2: at least 60% ferrite and 20% martensite
TABLE-US-00002 [0060] TABLE 2 Pre-forming tensile properties Ex. 1
after step d (at centreline thickness, RD = rolling direction, TD =
transverse direction). yield uniform stress tensile stress
elongation total elongation Cycle Orientation [MPa] [MPa] [%] A80
[%] #1 RD 615 904 6.2 10.1 #1 TD 545 845 6.6 9.1 #2 RD 353 743 13.9
20.4 #2 TD 355 756 12.7 16.0 #3 RD 300 672 13.4 17.2 #3 TD 309 675
14.6 21.1
TABLE-US-00003 TABLE 3 Pre-forming tensile properties Ex. 2 after
step d (at centreline thickness). yield total stress tensile
uniform elongation Cycle Orientation [MPa] stress [MPa] elongation
[%] A80 [%] #1 RD 405 801 14.9 19.4 #1 TD 423 797 11.4 15.8 #2 RD
318 760 18.3 22.4 #2 TD 328 758 14.6 15.4 #3 RD 322 689 18.3 22.4
#3 TD 340 686 16.1 20.3
[0061] Additional experiments were performed starting from a 2.0 mm
hot rolled steel strip with a composition according to Ex. 2. The
values for the r-value and .DELTA.r-value were determined in the
usual way from measurements of samples taken at angles of
0.degree., 45.degree. and 90.degree. to the rolling direction.
TABLE-US-00004 TABLE 4 Pre-forming tensile properties after step d
(at centreline thickness, 90.degree. to rolling direction, r-value
and .DELTA.r-value). Cold Martensite rolling yield tensile fraction
Reduction Cooling stress strength [%] [%] factor [MPa] [MPa]
r-value .DELTA.r-value <20 80 394 383 715 0.61 0.09 <20 88
295 416 621 0.80 -0.60 >80 47 592 462 762 0.97 -0.16 >80 68
547 746 1015 0.85 -0.23 >80 88 454 879 1185 0.98 -0.23
[0062] Cooling factor is a measure for the cooling rate after
annealing. The higher the cooling factor, the higher the cooling
rate. Typical cooling rates obtained in these experiments were
between about 100 and 200.degree. C./s. The hot rolled strip had a
thickness of 2.0 mm. It is apparent that the higher the cold
rolling reduction, the higher the strength. Also, the higher the
cooling factor, the higher the cooling rate, and hence the higher
the strength.
TABLE-US-00005 TABLE 5 Pre-forming tensile properties of Ex. 2
after step d (at centreline thickness, 90.degree. to rolling
direction, r-value and .DELTA.r-value). Cold Martensite rolling
yield tensile fraction Reduction Cooling stress strength [%] [%]
factor [MPa] [MPa] r-value .DELTA.r-value >80 80 260 539 660
1.21 -0.23 >80 80 283 586 679 1.07 0.08 >80 80 306 594 739
1.21 -0.22 >80 80 326 614 744 1.02 -0.34 >80 80 381 720 929
1.10 -0.25 >80 80 453 839 1058 0.63 -0.41
[0063] From Table 5 it is apparent that the strength increases with
increasing cooling factor.
[0064] Containment devices produced from the material in Table 4
and 5 provided excellent containment performance in any of the
aforementioned applications, such as engine gaskets. A very high
post-forming yield strength was combined with a low anisotropy and
excellent fatigue properties.
TABLE-US-00006 TABLE 6 Ex. 2 steels were subjected to annealing at
different temperatures in a continuous annealing line and cooled at
different cooling rates (a.u. is arbitrary unit: the cooling rate
is a function of the cooling power, the thickness of the strip and
the line speed), WH is the work hardening as a result of the 2%
deformation prior to bake- hardening, BH0 and BH2 values were
determined after 20 minutes at 170.degree. C. Annealing Parameters
Furn. Line Cool. Mechanical properties (tensile test) Temp speed
power Rm A80 BH0 BH2 WH Steel type (.degree. C.) (a.u.) (a.u.)
(MPa) YS/Rm (%) (MPa) (MPa) (MPa) Bainitic matrix 1020 7 700 693
0.83 18 <10 29 28 Multiphase A (BM A) Martensitic matrix 1020 6
900 945 0.77 9 70 152 192 Multiphase B (MM B) Martensitic matrix
1020 6 1100 1158 0.74 9 23 180 220 Multiphase C (MM C) Ferrite
Martensite Dual 950 6 1100 804 0.43 19 18 62 168 Phase D (FMDP D)
Ferrite Martensite Dual 950 7 1100 772 0.41 15 31 89 134 Phase E
(FMDP E)
[0065] It is clear from the data of Table 6 that the bake-hardening
effect in the Martensitic matrix Multiphase materials is
particularly strong. The total effect of the 2% work hardening and
the bake-hardening treatment amount to values over 300 MPa for MM B
(344 MPa) and MM C (400 MPa).
TABLE-US-00007 TABLE 7 An overview of the change in strength and
ductility observed for three orientations (tensile axis at
0.degree., 45.degree. and 90.degree. to the rolling direction)
during cold rolling of the Ferrite Martensite Dual Phase E steel
(FMDP E) and the martensitic multiphase C (MM C) steel. Steel type/
second Total cold Tensile strength Rm elongation: Yield rolling
(MPa) A50 (%) Strength (MPa) step (%) Rm.sub.0.degree.
Rm.sub.45.degree. Rm.sub.90.degree. 0.degree. 45.degree. 90.degree.
Rp.sub.0.degree. Rp.sub.45.degree. Rp.sub.90.degree. FMDP E/0 776
763 783 23 22 23 319 317 325 FMDP 858 840 844 17 13 16 746 667 620
E/10 FMDP 942 930 931 5 3 9 894 751 681 E/20 FMDP 999 966 983 3 5 3
921 783 745 E/30 FMDP 1090 1037 1070 4 4 4 944 844 853 E/40 FMDP
1111 1100 1089 5 6 6 981 867 815 E/50 MM C/0 1120 1106 1075 6 3 2
887 843 864
[0066] It is clear from the data of Table 7 that the anisotropy in
yield strength observed for the as annealed martensitic matrix
multiphase steel is much lower than the values obtained for the 50%
cold rolled FMDP E (i.e. the cold rolled condition which exhibits
comparable strength to that of the annealed MM C/0yield strength
variation observed for the as annealed variant is of the order of
20-45 MPa rather than the 100-200 MPa reported for the 50% cold
rolled DP. It is also clear that the anisotropy is maximal at a
cold deformation value of 20% and stabilises at higher
deformations. The increase of yield strength in the first 10% of
cold deformation is notable, whereas the further increase at higher
values is less strong.
[0067] Combination of the results of Table 6 and 7 shows that the
annealed martensitic matrix multiphase steel type already has a
high isotropic base strength and adequate formability, whereas
after it has been formed into a containment device such as a gasket
it will produce a bake-hardening effect resulting in a further
isotropic increase of the yield strength and hence excellent and
isotropic fatigue properties. Subjecting the MM C/0 to a
pre-deformation of 3% instead of 2% results in a WH value of 289
MPa and a BH3 value of 174 MPa.
[0068] A more detailed study of the influence of small deformations
such as those occurring in temper rolling revealed that the amount
of temper rolling should preferably be 10% or less, preferably 8%
or less, more preferably 5% or less, even more preferably less than
3%. The amount of temper rolling is preferably at least 1.5% more
preferably at least 2.0%. As shown in Table 7 temper-rolling values
of above 10% result in a strong increase of the anisotropy caused
by the cold-rolling step increases rapidly to unacceptable levels,
whereas the increase in yield stress saturates very rapidly. So a
combination of an increase in yield strength with low anisotropy
and a good bake hardening potential is obtained by a temper rolling
treatment within the range as given in this paragraph.
[0069] It is of course to be understood that the present invention
is not limited to the described embodiments and examples described
above, but encompasses any and all embodiments within the scope of
the description and the following claims.
* * * * *