Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese

Definitions

• 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.
• 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.
• 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.
• 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.
• 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 0 C.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• a Cr-based martensitic stainless steel having a tempered martensitic structure has been proposed for the fabrication of engine gaskets in JP 7-278758.
• martensitic stainless steels have an improved resistance to stress corrosion cracking over the metastable austenitic stainless steel described above.
• 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.
• martensitic steel is less expensive since it contains a lower nickel content.
• 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.
• one or more of these objectives are achieved with a process for the manufacture of containment device manufactured comprising the steps of: a. providing a steel slab having a chemical composition comprising (in weight percent)
• N not greater than 200 ppm; 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 after casting, followed by cooling the strip to a coiling temperature followed by coiling; c. cold rolling the strip 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 Ad , homogenising for at least 5 seconds, followed by rapid cooling; e.
• 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.
• 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 0 C a very significant increase in yield strength could be observed. This also results in excellent fatigue properties.
• 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.
• 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.
• the containment device produced according to the invention therefore favourably combines high strength, excellent fatigue properties and a reduced anisotropy.
• 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 °C/s, although using a cooling of the ultra fast cooling type, the cooling rate could be significantly higher, up to 1500°C/s per unit thickness (in mm) (i.e. 500 °C/s for a 3 mm strip).
• 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,
• Chromium and molybdenum are ferrite stabilising elements, raise the transformation temperature from austenite to ferrite (A 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.
• the silicon content of the steel is at most 1.0%, preferably at most 0.5%.
• the condition of the surface of the material improves.
• the cold rolling reduction is between 50 and
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the continuous annealing of step d has to be performed by reheating to a temperature near Ac3 or even above Ac3.
• 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.
• the required martensite content could be 90% or even higher.
• a fully martensitic steel would ensure a very high strength.
• a containment device formed from a steel with 90% in volume of a martensitic phase, or even a fully martensitic structure, would be suitable.
• the containment device produced according to this embodiment invention has a very high bake hardening potential.
• a very significant increase in yield strength could be observed.
• the material has to be subjected to an additional process step.
• 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 0 C.
• 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.
• 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.
• 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.
• the metallic coating is selected from a group of metallic coatings consisting of Cu, Ni, Co, Al, Zn, Ti, Cr or alloys thereof.
• 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.
• the metallic coating is sacrificial to steel such as nickel-zinc or zinc.
• the containment device 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.
• a carburizing step or nitriding step may be part of the process for manufacturing a containment device.
• 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.
• 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%.
• 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.
• a containment device 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.
• the containment device is a gasket for use in an internal combustion engine.
• 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.
• 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.
• 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.
• 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.
• the containment device is a cartridge for rimfire ammunition.
• a cartridge can be formed from a sheet metal by drawing a cup and further forming into a cartridge.
• the material has a low earing property, i.e. a low in-sheet or planar anisotropy of the properties of the material.
• the material of the wall of the cartridge is heavily deformed. This material consequently has a very high yield stress.
• the cartridge undergoes a very large load transient upon explosion . of the explosive in the cartridge.
• 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.
• the containment device is a case for a battery.
• 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.
• 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.
• 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 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.
• 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,
• 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 °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.
• 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 7 An overview of the change in strength and ductility observed for three orientations (tensile axis at 0°, 45° and 90° 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.
• FMDP E Ferrite Martensite Dual Phase E steel
• MM C martensitic multiphase C
• 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%.
• 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.

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• 2005
  • 2005-10-26 WO PCT/EP2005/011609 patent/WO2006045622A1/en active Application Filing
  • 2005-10-26 JP JP2007538345A patent/JP2008518102A/ja active Pending
  • 2005-10-26 US US11/577,976 patent/US20090038718A1/en not_active Abandoned
  • 2005-10-26 EP EP05806088A patent/EP1807543A1/de not_active Withdrawn

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