Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
  • B62D—MOTOR VEHICLES; TRAILERS
  • B62D21/00—Understructures, i.e. chassis frame on which a vehicle body may be mounted
  • B62D21/15—Understructures, i.e. chassis frame on which a vehicle body may be mounted having impact absorbing means, e.g. a frame designed to permanently or temporarily change shape or dimension upon impact with another body
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60J—WINDOWS, WINDSCREENS, NON-FIXED ROOFS, DOORS, OR SIMILAR DEVICES FOR VEHICLES; REMOVABLE EXTERNAL PROTECTIVE COVERINGS SPECIALLY ADAPTED FOR VEHICLES
  • B60J5/00—Doors
  • B60J5/04—Doors arranged at the vehicle sides
  • B60J5/042—Reinforcement elements
  • B60J5/0422—Elongated type elements, e.g. beams, cables, belts or wires
  • B60J5/0423—Elongated type elements, e.g. beams, cables, belts or wires characterised by position in the lower door structure
  • B60J5/0426—Elongated type elements, e.g. beams, cables, belts or wires characterised by position in the lower door structure the elements being arranged at the beltline
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60J—WINDOWS, WINDSCREENS, NON-FIXED ROOFS, DOORS, OR SIMILAR DEVICES FOR VEHICLES; REMOVABLE EXTERNAL PROTECTIVE COVERINGS SPECIALLY ADAPTED FOR VEHICLES
  • B60J5/00—Doors
  • B60J5/04—Doors arranged at the vehicle sides
  • B60J5/042—Reinforcement elements
  • B60J5/0422—Elongated type elements, e.g. beams, cables, belts or wires
  • B60J5/0423—Elongated type elements, e.g. beams, cables, belts or wires characterised by position in the lower door structure
  • B60J5/0429—Elongated type elements, e.g. beams, cables, belts or wires characterised by position in the lower door structure the elements being arranged diagonally
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60J—WINDOWS, WINDSCREENS, NON-FIXED ROOFS, DOORS, OR SIMILAR DEVICES FOR VEHICLES; REMOVABLE EXTERNAL PROTECTIVE COVERINGS SPECIALLY ADAPTED FOR VEHICLES
  • B60J5/00—Doors
  • B60J5/04—Doors arranged at the vehicle sides
  • B60J5/042—Reinforcement elements
  • B60J5/0422—Elongated type elements, e.g. beams, cables, belts or wires
  • B60J5/0438—Elongated type elements, e.g. beams, cables, belts or wires characterised by the type of elongated elements
  • B60J5/0443—Beams
  • B60J5/0444—Beams characterised by a special cross section
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
  • B62D—MOTOR VEHICLES; TRAILERS
  • B62D29/00—Superstructures, understructures, or sub-units thereof, characterised by the material thereof
  • B62D29/007—Superstructures, understructures, or sub-units thereof, characterised by the material thereof predominantly of special steel or specially treated steel, e.g. stainless steel or locally surface hardened steel
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium

Definitions

• the present invention relates to an impact beam for use in a vehicle. More specifically, the invention relates to an impact beam and related assembly, the impact beam comprising precipitation hardenable stainless steel, and a method of producing such a beam.
• Impact beams can, for example, be designed to protect passengers in the vehicle by absorbing impact energy in a collision, through plastic and/or elastic deformation. Furthermore, impact beams can also be designed to protect objects outside the vehicle, such as pedestrians or animals. In a collision between two or more vehicles, for example in a head-on collision, an impact beam can limit the damage caused by the colliding vehicle to the oncoming vehicle, resulting in less risk of passengers in the oncoming vehicle being seriously injured. Impact beams can also be used to prevent vital machinery inside the vehicle from being damaged. In addition to absorbing impact energy an impact beam can also be designed to transmit impact energy to the vehicle frame, i.e. the chassis without the running gear, and/or the vehicle body structure, such as a door, or another impact beam.
• Running gear in this context includes, inter alia, engine, drive shaft, transmission and suspension.
• High strength carbon steel (tensile strength ⁇ 800 MPa) is commonly used for vehicle components designed for crash protection due to physical properties, such as high strength, good formability, and inherent capability to absorb impact energy in a crash situation.
• ultrahigh strength carbon steels tensile strength >800 MPa
• boron steels can be used.
• ultra-high strength carbon steels may involve formability problems as well as low ductility, which can lead to brittle cracking.
• An example of an impact beam is disclosed in EP 1520741 , wherein the beam is described as an automobile strength member comprising a rectangular steel tube.
• Brittle cracking is identified as a problem, which arises for high strength members having tensile strengths exceeding 1470 MPa.
• the preferred production methods include e.g. drawing, rolling or extrusion.
• WO 02/064390 manufacturing of a lightweight vehicle door, comprising a supportive door frame that includes at least one impact beam, by hot forming particularly hot stamping, is disclosed.
• Tensile strengths of over 1000 MPa up to 1500 MPa are expected when using boron steel.
• one object of the present invention is to provide an impact beam for use in vehicles, which provides improved impact absorbing properties per unit of weight, wherein the impact beam can be formed by conventional hot forming techniques.
• the stated object is achieved by the present invention in accordance with claim 1.
• the impact beam according to the invention, comprises precipitation hardenable stainless steel, wherein the steel has a composition, all in percent by weight, of:
• a precipitation hardenable stainless steel in an impact beam, provides a vehicle component with improved impact absorbing properties per unit of weight, which may for example facilitate significant weight reduction of the impact beam while preserving the same energy absorption properties.
• the present invention also relates to a method of producing an impact beam, comprising said precipitation hardenable stainless steel by hot forming, such as for example hot stamping or press hardening.
• Press hardening is a manufacturing process for low weight, ultra-high strength components, in which simultaneous forming and quenching is utilized.
• press hardening formation of complex geometries is made possible due to the high formability of the hot steel, and the quenching results in a component with very high yield and tensile strength, as well as high dimensional accuracy.
• new design opportunities are available and complex designs are enabled, which, for example, may lead to space savings when assembling the vehicle body.
• the design can also aim at controlling the absorption of the impact energy, by controlling the deformation of the beam.
• Figure 1 illustrates examples of impact beams in an automobile, which can comprise precipitation hardenable stainless steel, according to the present invention.
• Figure 2 illustrates a vehicle door with a waist rail reinforcement beam and a side impact beam.
• Figure 3 illustrates a cross section having two intersecting tangents.
• Figure 4 illustrates examples of cross section geometries for impact beams.
• Figure 5 illustrates examples of complex cross section geometries for impact beams.
• Figure 6 illustrates the setup used in the FEA (Finite Element Analysis) for a beam with circular cross section.
• Figure 7 illustrates the setup used in the FEA for a beam with C-shaped cross section.
• Figure 8 illustrates results from FEA comparing steel according to the present invention to boron steel of type Mat. No. 1.5528, using a beam with circular cross section and a wall thickness of 1.5 mm.
• Figure 9 illustrates results from FEA comparing steel according to the present invention to boron steel of type Mat. No. 1.5529, using a beam with circular cross section and a wall thickness of 1.5 mm.
• the figures should not be considered drawn to scale, since some features may have been exaggerated in order to clearly illustrate the invention.
• the impact beam should comprise steel with ultra-high strength
• Ultra-high strength precipitation hardenable stainless steel provides high tensile strength combined with excellent impact absorbing properties, and is an alternative to ultra-high strength carbon steel.
• the amount of material in the component can be reduced due to the improved energy absorbing capacity per unit of weight. Thereby, the total weight of the component, and in the end the weight of the vehicle, is reduced. This can be achieved by for example reducing the wall thickness of the impact beam.
• an increase of strength can be achieved by manufacturing an impact beam using an ultra-high strength steel, with preserved amount of impact absorbing material.
• An impact beam designed for crash protection can be used in several types of vehicles, such as automobiles, motorcycles, buses, trucks, caterpillars, crawlers, and tractors.
• the beam can be joined to, or be a part of, the vehicle frame, i.e. the chassis without the running gear, or the vehicle body structure.
• the impact beam can also be used in other types of vehicles such as motorboats, snowmobiles, or airborne vehicles such as helicopters or airplanes.
• impact beams are important components in the floor structure of helicopters.
• Figure 1 illustrates examples of impact beams in an automobile.
• the following components are identified in the figure: bumper beam 1 , side member 2, A-pillar reinforcement 3, front header 4, roof beam 5, B-pillar reinforcement 6, floor beam 7, door beam 8, cross member 9 and waist rail reinforcement 10.
• Impact beams which are situated in more than one location for example side members 2 and A-pillar reinforcements 3, are normally placed at corresponding sides in the vehicle and are therefore not indicated in Figure 1.
• Examples of impact beams in a vehicle door 21 comprising a waist rail 22 and a side impact beam 23 are illustrated in Figure 2.
• a beam is considered as a structure comprising a cross section with at least two intersecting tangents, illustrated in Figure 3 as t1 and t2 for an angle beam 31 , and t1 ' and t2 ' for beam with a circular cross section 32, wherein the tangents define a two-dimensional plane, and wherein the structure is extended in a direction essentially perpendicular to the plane.
• the beam can be designed in a number of different shapes and sizes.
• Figure 4 shows some examples of basic cross sectional shapes of impact beams: circular 41 , elliptical 42, U-shaped 43, C- shaped 44 or hat shaped 45.
• the cross section can also be of essentially square shape, essentially triangular shape, essentially tetragonal shape, essentially pentagonal shape, as well as of irregular shapes.
• the cross section of the beam can contain one or more open sections, such as the open area A defined by t1 and t2 in Figure 3, and/or one or more closed sections, such as the area B in Figure 3.
• the shape and/or the size of the cross section can either be identical or vary throughout the extension of the beam.
• the impact beam can be adapted so as to absorb impact energy, through controlled deformation of the beam.
• the impact beam can also be adapted so as to transmit impact energy to other parts of the vehicle frame and/or the vehicle body structure, thus directing the impact energy away from the impact zone.
• FIG. 5 examples of complex geometrical forms of cross sections of impact beams are illustrated.
• the cross sections illustrated in Figure 5 are examples of a floor beam 51 , a waist rail in a vehicle door 52, a side impact beam in a vehicle door 53 and a roof bow 54.
• the precipitation hardenable stainless steel should be suitable for hot forming.
• not all precipitation hardenable stainless steels can be formed by hot forming techniques without becoming too hard during the process. If the hardness of the steel increases too much during the hot forming process, it can lead to detrimental brittle fractures and poor impact absorbing properties, which is not desirable in an impact beam.
• precipitation hardenable stainless steels that meet the requirements stated above, inter alia excellent impact absorbing properties and possibility of hot forming are UNS S45500, UNS S45503 and UNS S46500.
• the precipitation hardenable stainless steel is of UNS S45500 type.
• Compositions of said precipitation hardenable stainless steels, in percent by weight, are displayed in Table 1. The balance is Fe and normally occurring impurities.
• the precipitation hardenable stainless steel can be processed in the shape of a tube, sheet or bar, for further forming into various geometrical shapes.
• the impact beam can either consist entirely of precipitation hardenable stainless steel, according to the invention, or comprise a member of a precipitation hardenable stainless steel in combination with another member of another material, for example other steel grades or carbon fiber.
• Commonly used stainless steel in this application is for example AISI 301 type, and commonly used boron steel is, for example, material number (Mat. No.) 1.5528 or Mat. No.15529.
• the material strength is affected by the degree of processing and the conditions of any heat treatments performed.
• the impact beam is manufactured by any conventional hot forming technique.
• the temperature applied during hot forming is generally equal to, or exceeding, 750 0 C, typically around 900 0 C.
• the hot forming technique is press hardening.
• the press hardening can be followed by a precipitation hardening step.
• the starting material for press hardening is usually in the form of a sheet, a tube or a strip, preferably the starting material is a steel sheet.
• the impact beam may be shaped to fit an available space in the vehicle and/or shaped to provide the best impact absorption.
• the impact beam can be a part of an impact beam assembly, wherein the impact beam is joined to at least a part of the vehicle frame, and/or the vehicle body structure, for example a vehicle door or another impact beam, by conventional techniques, for example, bolting, welding, gluing or seaming.
• the surface of the beam is pre- treated to improve the shearing strength of an adhesive joining.
• the surface can be ground and/or chemically treated to remove most of the native oxide scale and thereafter coated with a primer, such as a silicon based primer.
• the primer will create a surface structure which interacts well with the glue and thereby strengthens the glued joint.
• Surface pre-treatment using a primer is performed after hot forming.
• FEA finite element analysis
• Table 3 The balance is Fe and normally occurring impurities.
• Mat. No. Material number, also known as Werkstoff number.
• the beam comprising the precipitation hardenable stainless steel according to the invention displays an increased energy absorption, in beams with both circular and U-shaped cross sections, by on average at least 20 % compared to a beam comprising boron steel of the type Mat. No. 1.5528.
• the beam according to the invention displays an increased energy absorption by on average at least 7 %.
• the true energy absorption may be even higher than suggested in these FE-analyses due to the large elongation to fracture in the beam according to the invention, compared to a beam comprising boron steel. Impact beams with lower fracture toughness can experience cracking when the beam is deformed, which locally leads to a considerable reduction of the ability to absorb energy.
• Width 100 mm
• an impact beam comprising precipitation hardenable stainless steel, according to the present invention which has up to 50 % higher tensile strength than conventional steel types used for impact beams, a considerable weight reduction of at least 20 % on average can be obtained for the final component.
• High tensile and yield strengths, of the precipitation hardenable stainless steel used according to the invention, in combination with high ductility and high toughness, result in a superior ability to absorb impact energy in a collision, through plastic and/or elastic deformation, making the steel highly suitable for use in impact beams.
• the high elongation at rupture, associated with this precipitation hardenable stainless steel results in less risk of cracking.
• the precipitation hardenable stainless steel, used according to the invention is corrosion resistant there is no need for any additional corrosion protection throughout the expected life time of the vehicle.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Transportation (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Architecture (AREA)
• Structural Engineering (AREA)
• Body Structure For Vehicles (AREA)
• Vibration Dampers (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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Cited By (3)

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Citations (2)

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• 2007
  • 2007-06-12 SE SE0701436A patent/SE531252C2/sv not_active IP Right Cessation
• 2008
  • 2008-05-29 US US12/664,121 patent/US20100180990A1/en not_active Abandoned
  • 2008-05-29 WO PCT/SE2008/050630 patent/WO2008153480A1/en active Application Filing
  • 2008-05-29 EP EP08779313A patent/EP2158340A4/en not_active Withdrawn

Patent Citations (3)

Non-Patent Citations (1)

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