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    • 专利摘要:
    .
    公开号:BR112013029160B1
    申请号:R112013029160
    申请日:2012-04-23
    公开日:2018-11-21
    发明作者:Okuda Kaneharu；Takaki Naoki；Takagi Shusaku；Naito Tadashi；Fujita Takeshi；Sugiura Tomoaki；Tamai Yoshikiyo；Okitsu Yoshitaka
    申请人:Honda Motor Co Ltd；Jfe Steel Corp；
    IPC主号:
    专利说明:

    (54) Title: VEHICLE COLLISION ENERGY ABSORPTION ELEMENT (73) Holder: JFE STEEL CORPORATION. Address: 2-3, UCHISAIWAICHO 2-CHOME CHIYODA-KU, ΤΟΚΥΟ 1000011, JP -JAPAN, JAPAN (JP); HONDA MOTOR CO. LTD, Japanese Society. Address: 1-1, Minamiaoyama 2Chome, Minato-Ku ,, Tokyo, JAPAN (JP) (72) Inventor: SHUSAKU TAKAGI; KANEHARU OKUDA; YOSHIKIYO TAMAI; TAKESHI FUJITA; YOSHITAKA OKITSU; TADASHI NAITO; ΝΑΟΚΙ ΤΑΚΑΚΙ; TOMOAKI SUGIURA.
    Validity Period: 20 (twenty) years from 23/04/2012, subject to legal conditions
    Issued on: 11/21/2018
    Digitally signed by:
    Alexandre Gomes Ciancio
    Substitute Director of Patents, Computer Programs and Topographies of Integrated Circuits
    1/42
    Invention Patent Descriptive Report for VEHICLE COLLISION ENERGY ABSORPTION ELEMENT. Technique Field
    The present invention relates to a collision energy absorption element for a vehicle (also referred to as an axial deformation element for a vehicle) which smashes axially by colliding the vehicle to thereby absorb the collision energy and, more particularly, to the steady improvement in collision energy absorption performance.
    Background Technique
    In recent years, from the point of view of global environmental protection, there has been a demand for weight reduction in vehicle bodies. High-strength steel plates are widely used today for vehicle bodies, in particular, 15 for peripheral components in a passenger compartment (cabin), which contributes to the reduction in vehicle body weight by thinning the walls this. On the other hand, the strength of the high-strength steel plates used for an engine room and for frames (including a front frame and a rear frame) of a suitcase for the purpose of increasing the resistance amounts to a mere 780 MPa maximum. This is because the high strength steel sheet for use as a material for a front frame and a rear frame cannot be excessively increased because this involves the following problems and does not necessarily lead to so much increase in the amount of impact energy absorption compared to the increase in resistance. That is, the front frame or the rear frame, which serves as a collision energy absorption element that undergoes significant deformation through the collision, in order to absorb the collision energy, can suffer significant fracture due to deteriorated ductility, or have an unstable deformed shape due to the collision failure to achieve stable curvature, with the result that local fractures can
    Petition 870180067986, of 08/06/2018, p. 9/17
    2/42 occurs easily when the steel material has increased strength.
    Under the circumstances mentioned above, there is a demand for a collision energy absorbing element that has a property of absorbing energy efficiently through collision while increasing in strength for the purpose of promoting the resistance of the energy absorbing element of collision. collision forming a front frame or a rear frame and to achieve additional weight reduction in a vehicle body.
    In order to meet such a demand, for example, the Pa10 Tent Literature (PTL) 1 describes a collision energy absorption element formed from a steel sheet that has a microstructure that includes austenite in an area ratio of 60% or higher. PTL 1 further describes, as an example of the steel plate that has a microstructure that includes austenite in an area ratio of 60% or greater, an austenite 15 stainless steel plate containing 18% to 19% Cr and Ni at 8% to 12%, which illustrates that a collision energy-absorbing element formed using the aforementioned steel sheet can have enhanced deformation-propagating properties by collision to thereby ensure absorption performance of collision energy desired.
    PTL 2 describes a high-strength steel plate with good machinability and which has high resistance to dynamic deformation. The high-strength steel sheet illustrated in PTL 2 has a multiphase containing: ferrite and / or bainite, any of which is used as a main phase; and a tertiary phase containing austenite retained at 3% to 50% in volume fraction, and has high resistance to dynamic deformation in which, after a pre-deformation of more than 0% to 10% or less, a difference between a resistance under deformation quasi-static o s and a dynamic deformation resistance o d (a d . - σ 5 ) satisfies at least 60 MPa, and the quasi-static deformation resistance σ 5 is obtained when the steel sheet is formed in a stress rate of 5 χ IO 4 to 5 χ 10 ' 3 (1 / s), with resistance to dynamic deformation o d being obtained when the steel sheet is deformed at a stress rate of 5 χ 10 2 to 5 χ 10 3 (1 / s), and the exponent
    3/42 hardening in an effort of 5% to 10% satisfies at least 0.130. According to the technology described in PTL 2, an element manufactured using a steel plate that has (σ ρ - σ ε ) of at least 60 MPa is capable of absorbing the highest energy through collision, when compared to an estimated value from the strength of steel sheet material.
    In addition, PTL 3 describes a high-strength steel plate that has a multiphase microstructure formed by a ferrite phase and a hard secondary phase contained in an area ratio of 30% to 70% in relation to the entire microstructure, being that the ferrite phase and the hard secondary phase are dispersed on the steel plate, where the ratio of ferrite area having a crystal grain diameter of 1.2 pm or less in the ferrite phase is 15% to 90%, and a relationship between the average grain diameter ds of ferrite that has a crystal grain diameter of 1.2 pm or less and an average grain diameter dL of ferrite that has a crystal grain diameter that exceeds 1.2 pm satisfies dL / ds> 3. The technology described in PTL 3 is able to improve the balance between strength and ductility which is important by forming pressure to thereby obtain an excellent high strength steel plate in capacity absorption of energy by deformation at high speed, so that the plate d and high-strength steel obtained in this way can be applied to a vehicle body that requires high collision energy absorption performance.
    In addition, according to PTLs 4 and 5, studies were carried out, using a rectangular tubular element inserted in recess, in steel sheets capable of being deformed by deformation by axial collapse without collapse and cracking, and it was found that the amount and the size of ferrite, bainite, austenite, and precipitates can be controlled in order to allow the steel sheet to deform without causing collapse and cracking in the deformation mode upon collision.
    In addition, the Non-Patent Literature (NPL) 1 shows examples of hat profile parts that crush stably in a bellows shape by collision crushing. The element is formed by a thin steel sheet that has a tensile strength of 1155 MPa and a
    4/42 multiphase microstructure of ultrafine grains, where the n value is 0.205 for a real deformation in a range of 5% to 10%. The thin steel sheet described in NTL 1 has a chemical composition based on: 0.15% C 1.4% Si - 4.0% Mn - 0.05% Nb, and has a microstructure that includes ferrite and a secondary phase each in sub-micron size, the secondary phase containing austenite retained at 12% to 35%, which is high in value and in deformation hardening capacity.
    Citation List
    Patent Literature
    PTL 1: JP 2001-130444 A
    PTL2: JP H11-193439 A
    PTL 3: JP 2007-321207 A
    PTL 4: JP 2008-214645 A
    PTL 5: JP 2008-231541 A
    Non-Patent Literature
    NPL 1: Y. Okitsu and N. Tsuji; Proceedings of the 2nd International Symposium on Steel Science (ISSS 2009), pp. 253-256, Oct. 21-24, 2009, Kyoto, Japan: The Iron and Steel Institute of Japan.
    Summary of the Invention Problem of the Technique
    According to the technology described in PTL 1, the collision energy absorption element is formed by a steel plate that contains a large amount of austenite. Austenite has a cubic crystal structure with a centered face (fcc) and, therefore, it has a characteristic of being less susceptible to embrittlement and fracture, which can increase to a certain degree the amount of energy to be absorbed by the collision. However, the steel sheet that contains a large amount of austenite, as described in PTL 1, has a low tensile strength of about 780 MPa and, in addition, its strength is lower when compared to a steel sheet that has a body-centered cubic structure (bcc) when deformed at a high rate of effort, such as, through collision, which lacks sufficient strength for use as a ma5 / 42 material for a vehicle collision energy absorption element. In addition, the Ni content and the Cr content need to be increased in order to obtain a steel plate that contains a large amount of austenite, which leads to an increase in manufacturing cost. From this point of view, the PTL 1 steel sheet is unsuitable for use in a vehicle body element.
    According to the technology of PTL 2, the hat-like element was evaluated only for a steel plate that has a tensile strength of about 780 MPa at most. An element formed by a steel sheet that has a tensile strength less than 980 MPa is easily deformed into a bellows shape by means of collision deformation without suffering fracture and rupture and, thus, the energy to be absorbed by the element by means of collision strain can be estimated based on material properties. On the other hand, an element formed by a steel plate that has a tensile strength of 980 MPa or higher suffers fracture and rupture of the thin steel plate and, thus, the energy to be absorbed by the element through the collision often shows a lower than expected value from material properties. PTL 2's technology has difficulty in suppressing fracture and rupture by high-speed crushing of the element formed by a high-strength steel sheet that has a tensile strength of 980 MPa or higher in order to improve in a stable manner the energy to be absorbed by high-speed crushing.
    According to the technology described in PTL 3, the steel sheet has a mixed microstructure of nanocrystalline grains and microcrystalline grains, in which the type and fraction of microstructure of the hard secondary phase are optimized to obtain, in this way, a sheet high strength steel that is high in strength while having high ductility. However, PTL 3 does not provide any description of the formation of a collision energy absorbing element using the steel plate, and does not refer to the suppression of fracture and rupture that would otherwise be problematic when an element is formed by a steel sheet that has
    6/42 a tensile strength of 980 MPa or higher, in the element by means of the collision, in order to allow the element to be folded axially stable in a bellows shape to efficiently absorb the collision energy that, in this way , remains not evident.
    In addition, according to the technology described in PTLs 4 and 5, C, Si, Mn and Ti and / or Nb are contained in an appropriate amount, in order to properly control the amount of ferrite, bainite and austenite retained in the plate microstructure. of steel, the grain sizes of these, the concentration of C in the retained austenite, and the size and number of precipitates to carry out, in this way, the deformation by axial collapse without suffering collapse and cracking described above. However, this technology may find it difficult to perform axially collapsed deformation without collapsing and cracking, particularly on a steel sheet that has a tensile strength of 980 MPa or higher, and the stable energy absorption to be achieved. obtained through axial collapse deformation is only limited when the steel sheet has a combination of the chemical composition and microstructure mentioned above and, therefore, there is a demand for an element formed by a steel sheet with TS 980 MPa or upper that is capable of suppressing fracture and rupture by means of high speed crushing, in order to be stably folded into a bellows shape.
    According to the technology described in NPL 1, the element is formed by a steel plate enhanced in value n that serves as a measure of the deformation hardening capacity, in order to be formed as a collision energy absorption element that crushes in a bellows shape in the axial direction upon collision. However, the inventors of the present invention have carried out additional studies to find that even when a steel sheet having a value n higher than 0.205 is used to manufacture the collision energy absorption element (impact) and the element is deformed by impact in the axial direction, in some cases, the element may still fail to be stably curved (crushed) into a bellows shape.
    7/42
    The present invention was carried out in view of the problems mentioned above inherent to the conventional technique, and has the objective of providing: a vehicle collision energy absorption element formed by a high strength thin steel sheet that has a tensile strength TS of 980 MPa or higher, which also excels in axial collision energy absorption performance through collision; and a manufacturing method for that. Here, when an element excels in axial collision energy absorption performance through collision, this means that the element is curved stably in the axial direction and deformed by crushing into a bellows shape upon vehicle collision to thereby way, efficiently absorb the collision energy, which can also be referred to as excellent in axial collapse stability.
    Solution to the Problem
    In order to achieve the above objective, the inventors of the present invention manufactured an element that is formed by a high-strength thin sheet steel element and in the shape of a cross-section, and subject the element to axial collision deformation, to in order to carry out intensive studies on the deformation behavior of the element. As a result, the inventors understood that the bending property, in particular the U-shaped bending property at 180 ° of the high strength steel sheet is an essential factor, in addition to the n value of the high strength steel sheet used as the material, in order to have the element curved stably in the axial direction, in order to be deformed by crushing into a bellows shape. The inventors found that an element that has a low U-shaped bending property at 180 ° cannot be axially deformed by crushing into a bellows shape even if the n-value of the high-strength steel sheet is high, because the property of Low 180 ° U-shaped bending allows rupture and non-uniform deformation to occur in a deformed portion upon collision.
    Also, it was found that the crack that occurs when the e
    8/42 lement is axially crushed is generated mainly in the first bending portion and therefore crack generation in the first bending portion needs to be avoided because otherwise the stable bending fails to develop in the element and the element it may not be deformed by crushing into a bellows shape. Then, it was found that the generation of cracking in the bending portion of the element is preventable as long as the radius of curvature of the bending portion is equal to or greater than the limit bending radius in the U-shaped bending at 180 ° of the material of steel sheet. Here, the term limit bending radius refers to a minimum radius of curvature that does not crack the steel sheet surface. Hereinafter, 180 ° U-shaped bending is simply referred to as bending. The radius of curvature is substantially determined depending on the value n as long as the thickness of the steel sheet material is equal, and a larger n value leads to an increase in the radius of curvature in the bending portion.
    That is, even if the value n is higher and, thus, the radius of curvature in the curving portion is greater, the crack still occurs in the curving portion of the element when the limit curvature radius of the steel plate is greater than the radius of curvature of the curving portion. On the other hand, even if the value n is lower and, therefore, the radius of curvature in the bending portion is smaller, the generation of cracking in the bending portion of the element can be avoided when the steel sheet is excellent in property of bending and has a limit bending radius equal to or less than the radius of curvature in the bending portion.
    For the reasons mentioned above, it has been found that it is important to make the limit radius of curvature of the steel sheet equal to or less than the radius of curvature in the bending portion and thus achieve a good balance between the value n of the steel sheet. steel and the limit bending radius is an important factor in order to steadily bend the element in the axial direction.
    Figure 1 is a graph that schematically illustrates the basic idea (concept) of the present invention.
    9/42
    The curve in Figure 1 illustrates a relationship between the n value of the steel sheet material and the radius of curvature of the bending portion, where the radius of curvature of the bending portion is determined based on the value n when the plate thickness is equal. When the limit bending radius obtained for the steel sheet material is greater than the curve in Figure 1 (region of occurrence of breakage and rupture), that is, when the limit bending radius is greater than the radius of curvature of the portion bending rate determined based on the value η, the element breaks and breaks when deformed by collision, without being axially deformed by crushing in a bellows shape.
    However, when the limit bending radius obtained for the steel sheet material is equal to or less than the curve in Figure 1 (bellows-shaped crushing region), that is, when the limit bending radius is equal to or less than the radius of curvature of the bending portion determined based on the value η, the element is deformed to have a predetermined radius of curvature when deformed by collision, so that the element is curved stably in the axial direction in order to be deformed by crushing it into a bellows shape.
    In other words, even if the n-value of the steel plate material is equal, an element formed by a steel plate deteriorated in flexural properties due to an increase in the limit bending radius suffers breakage and rupture and fails to be bent stable manner in a bellows shape. When the n-value of a steel sheet is increased, the radius of curvature of the bending portion is also increased, which is determined based on the n-value, with the result that the element is curved stably in a shape of bellows even if the bending property is slightly deteriorated and the limit bending radius is increased.
    The present invention is based on the discoveries that are essential to form the element with a steel plate in which the relationship between the value in the bending property satisfies a predetermined relational formula, in order to have the element curved in a stable manner in a bellows shape when the element is deformed by collision in the axial direction.
    10/42
    Here, the bending property is generally evaluated based on U-shaped bending at 180 ° or bending in V-shape at 90 ° and, in the present invention, the steel sheet has been subjected to the U-shaped bending test 180 ° to assess its flexural property. Specifically, the U-shaped bend at 180 ° often has a limit bending radius greater than that of the V-shape bend at 90 °, the limit bending radius represents a break limit by bending and thus , serves as an index associated with flexion under a more severe condition. Therefore, the U-shaped flexion at 180 ° exhibits a good correlation with the value n as an index of the strain due to axial collapse. On the other hand, the limit bending radius obtained for V-shaped bending at 90 ° serves as an index for use in forming an element, such as a hat-shaped element that is formed by bending at about 90 ° and, therefore, the 90 ° V-shaped bending fails to show an appropriate relationship between the value n and the bending property in the axial collapse strain. Here, more importance is given to U-shaped bending at 180 ° than V-shaped bending at 90 °, because the curved / deformed portion that occurs when the element is crushed deformed into a bellows shape looks like a state deformed obtained through the U-shaped bending at 180 °.
    First, a description of the experimental results that serve as a basis for the present invention is provided.
    In general, to assess the axial collapse performance of a collision energy absorbing element, such as a side frame, an element having a square cross section is used. In this way, the collision energy absorbing elements (each having an axial height of 230 mm) each having a cross-section of Figure 2 (c) were manufactured using several high strength thin steel sheets with resistance to traction in a range from 980 MPa to 1180 MPa, and a weight of 110 kgf was caused to collide with each of the elements in their axial direction at a rate that is equivalent to 50 km / h to deform by shock the element in 160 mm. Subsequently, the elements
    11/42 that were curved in a stable manner in a bellows shape were selected, and submitted to the observation of the deformation state after the shock.
    The thin steel sheets used in this document have been subjected in advance to the investigation of their n-values, in addition to their tensile properties. The n values were calculated for an actual strain in a range of 5% to 10%. Here, if the uniform elongation in the tensile test falls below 10%, which means that a stress under the actual 10% strain cannot be calculated, the calculation was performed for a real strain in a range of 5% to a maximum real deformation calculable. The n value was calculated using the following equation.
    value η = (Ιησ 10 - Ιησ 5 ) / (InO, 1 - ln0.05) (where σ-ιο: real stress under 10% real strain, σ 5 : real stress under 5% real strain) )
    However, if the data under a 10% real deformation cannot be collected, the calculation is performed for a maximum real deformation obtainable and a real stress that corresponds to this.
    The bending radius R (J) of a crushed portion in a bellows shape after the aforementioned collapse deformation, i.e., a bending portion, was measured, and Figure 3 shows the results obtained in relation to the n values. In Figure 3, the results are normalized by the plate thickness t, and shown as R (J) / t. The radius of the curving portion was obtained as follows.
    That is, the radius of curvature of the bending portion of the element was measured using an R meter for measuring the radius of curvature, from which the plate thickness was subtracted to thereby obtain the bending radius of the portion curving.
    Referring to Figure 3, the results obtained for the relationship between the radius of curvature R (J) of the curved portion of element J that has a transversal shape of Figure 2 (c) and its n value can be simplified, as the relationship between R (J) / t and ln (n), to be found in Equation (a) below:
    12/42
    R (J) / t = 1.31 χ ln (n) + 5.21 (a); (where t: steel plate thickness (mm)).
    As described above, the bending radius of the bending portion is substantially determined based on the value n, thus a steel sheet that has a value obtained by dividing the limit bending radius by the plate thickness (the bending radius limit / plate thickness) which is located in a region below Equation (a), that is, in a region equal to or less than 1.31 x ln (n) + 5.21 allows element J to be curved stable manner in a bellows shape. However, a steel plate that has a value obtained by dividing the limit bending radius by the plate thickness (the limit bending radius / the plate thickness) which is located in a region above Equation (a), that is, , in a region greater than 1.31 χ In (rt) + 5.21, makes it difficult to obtain stable curving.
    Next, in order to eliminate the influence of the shape of the element, it is considered a case in which a steel plate for use was subjected to compressive bending in a flat plate shape without being shaped. This can be considered, evaluating the bending, as a case of bending by compression caused under the most severe condition. This bending assessment assumes more severe conditions, and the minimum obtainable radius of curvature R (P) in the bending portion was obtained through finite element analysis using the model illustrated in Figure 4. An explicit explicit method solver was used in the analysis finite element. A plate element (25 mm χ 40 mm χ 1.2 mm) was formed in a wrap model, where one end of it was fixed while the other end of it was displaced, so that the plate element is deformed bent to have a U shape, and the minimum radius of curvature inside the plate element was measured. The results obtained, in this way, can be simplified, regarding the relation between R (P) / t and ln (n), in Equation (b) below:
    R (P) / t = 1.31 χ ln (n) + 4.21 - (b).
    The relationship presented by Equation (b) is also shown in Figure 3 together with the relationship in Equation (a).
    13/42
    Here, a steel plate that has a value obtained by dividing the limit bending radius by the plate thickness (the limit bending radius / the plate thickness) which is located in a region below in Equation (b), that is , is equal to or less than 1.31 χ ln (n) + 4.21 allows an element to be curved stably in a bellows shape even if the element has a surface cross-sectional shape closer to a plate shape that makes it difficult to ensure stable curving.
    When R (J) / t and R (P) / t are compared to each other with the value n being the same, R (P) / t is less than R (J) / t. Therefore, the reason is considered due to the influence exerted by the limitations on the vertical wall of the element's cross-section, and it can be assumed that the limit radius of curvature R (J) of the bending portion is reduced to a minimum on a flat plate without a wall vertical.
    The results mentioned above shows that the element can be bent stably in a bellows shape in the axial direction in a region that satisfies Formula (1) below, where the limit bending radius Rc / t of the steel sheet material is equal to or below the curve presented by Equation (a) of Figure 3, that is, the limit bending radius Rc / t is equal to or less than R (J) / t of the curved portion of the element with a square cross section,
    Rc / t <1.31 χ ln (n) + 5.21 (1) (where Rc: limit bending radius (mm), t: plate thickness (mm), en: n value obtained between the actual deformation of 5% to 10%).
    Furthermore, in a region that satisfies Formula (2) below, where the limit bending radius Rc / t is equal to or below the curve presented by Equation (b) of Figure 3, that is, the limit bending radius Rc / t t is equal to or less than the radius of curvature R (P) / t obtained for a curved flat plate,
    Rc / t <1.31 χ ln (n) + 4.21 (2) (where Rc: limit bending radius (mm), t: plate thickness (mm), en: n value obtained between the actual deformation of 5% to 10%), the element can be bent stably in a bellows shape in the axial direction even if the element has a more shallow cross-sectional shape
    14/42 close to a flat plate shape that makes it difficult to ensure stable bending. As for the relationship between the limit bending radius and the n value in relation to the crushed state of the element, as a result of studies carried out on elements formed by different materials and in different formats and simplified by Formulas (1) and (2) above, which are shown in Figure 5 to be described later, it was confirmed that an element formed by a steel plate with deteriorated bending property due to the excessively increased limit bending radius Rc cannot be bent stably in a bellows shape even if the value n is substantially the same, whereas a value n greater allows an element to be curved in a stable manner even if the bending property has been deteriorated.
    Based on these findings and additional considerations, the present invention has been accomplished.
    That is, the subject in question of the present invention is as follows:
    (1) A vehicle collision energy absorption element formed by forming a high strength thin steel sheet, where the high strength thin steel sheet has a TS tensile strength of at least 980 MPa, and has a value n and a limit bending radius Rc that satisfy Formula (1) below:
    Rc / t <1.31 x ln (n) + 5.21 (1);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), and n: value n obtained for real deformation in a range of 5% to 10%.
    (2) A vehicle collision energy absorption element formed by forming a high strength thin steel sheet, where the high strength thin steel sheet has a TS tensile strength of at least 980 MPa, and has a value n and a limit bending radius Rc that satisfy Formula (2) below:
    15/42
    Rc / t <1.31 χ ln (n) + 4.21 - (2);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), and n: value n obtained for real deformation in a range of 5% to 10%.
    (3) The vehicle collision energy absorption element according to item (1) or (2), in which the thin high-strength steel plate includes a chemical composition containing mass%:
    C: 0.14% to 0.30%;
    Si: 0.01% to 1.6%;
    Mn: 3.5% to 10%;
    P: 0.060% or less;
    S: 0.0050% or less;
    Al: 0.01% to 1.5%;
    N: 0.0060% or less;
    Nb: 0.01% to 0.10%; and the rest being Fe and incidental impurities, in which the high-strength steel sheet has a microstructure that includes a ferrite phase at 30% to 70% in volume fraction in relation to the entire microstructure and a different secondary phase the ferrite phase, the ferrite phase which has an average grain size of 1.0 pm or less, the secondary phase which contains at least one austenite phase retained by at least 10% in volume fraction throughout the microstructure, the retained austenite phase that has an average spacing of 1.5 qm or less.
    (4) The vehicle collision energy absorption element, according to item (3), in which the chemical composition contains Si and Al, so that the total content of Si and Al (Si + Al)% in mass meets at least 0.5%.
    (5) A method of manufacturing an absorption element
    16/42 vehicle collision energy using, as a material, a high-strength thin steel sheet, which is formed in a predetermined shape, in order to provide a vehicle collision energy absorbing element in the predetermined shape , in which the material selectively employs a high-strength thin steel sheet which has a tensile strength TS of at least 980 MPa and which has a value n and a limit bending radius Rc that satisfy Formula (1) below;
    Rc / t <1.31 x ln (n) + 5.21 (1);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), and n: value n obtained for real deformation in a range of 5% to 10%.
    (6) A method of fabricating a vehicle collision energy-absorbing element using, as a material, a thin high-strength steel sheet, which is formed in a predetermined shape, in order to provide an element of vehicle collision energy absorption in the predetermined format, in which the material selectively employs a high-strength thin steel sheet which has a TS tensile strength of at least 980 MPa and which has a value n and a limit bending radius Rc that satisfy Formula (2) below;
    Rc / t <1.31 x ln (n) + 4.21 (2);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), and n: value n obtained for real deformation in a range of 5% to 10%.
    (7) The method of manufacturing a vehicle collision energy-absorbing element, according to item (5) or (6), in which the thin high-strength steel plate includes a 17/42 chemical position containing % in large scale:
    C: 0.14% to 0.30%;
    Si: 0.01% to 1.6%;
    Mn: 3.5% to 10%;
    P: 0.060% or less;
    S: 0.0050% or less;
    Al: 0.01% to 1.5%;
    N: 0.0060% or less;
    Nb: 0.01% to 0.10%; and the rest being Fe and incidental impurities, in which the high-strength steel sheet has a microstructure that includes a ferrite phase at 30% to 70% in volume fraction in relation to the entire microstructure and a different secondary phase the ferrite phase, the ferrite phase which has an average grain size of 1.0 μητι or less, the secondary phase which contains at least one austenite phase retained by at least 10% in volume fraction throughout the microstructure, the retained austenite phase that has an average spacing of 1.5 μηπ or less.
    (8) The method of manufacturing a vehicle collision energy absorption element, according to item (7), in which the chemical composition contains Si and Al, so that the total content of Si and Al (Si + Al)% by mass satisfies at least 0.5%.
    Advantageous Effect of the Invention
    The present invention allows for the easy and stable manufacture of a vehicle collision energy absorbing element, the element being formed by forming a high strength thin steel plate that has a TS tensile strength of at least 980 MPa while it excels in axial collision energy absorption performance to provide remarkable industrial effects in this way. In addition, according to the present invention, a high strength thin steel plate of 980 MPa or higher can be used as a material, which obtains the reinforcement of a collision energy absorption element, such as a frame
    18/42 front and a rear frame, which leads to a reduction in weight of the vehicle body.
    Brief Description of Drawings
    The present invention will be further described below with reference to the accompanying drawings, in which:
    Figure 1 is an explanatory graph that schematically illustrates how the relationship between a limit bending radius (Rc) and a n value of a vehicle collision energy absorption element influences the deformation behavior by axial collapse of the absorption element of vehicle collision energy through collision;
    Figure 2 is an explanatory diagram that schematically illustrates the shapes of the vehicle collision energy absorption element used in the Examples;
    Figure 3 is a graph showing the relationship between the radius of curvature at the moment of bending and the value n of an element J that has a square cross-sectional shape and that of a flat plate element shape P;
    Figure 4 is an explanatory diagram that schematically illustrates a finite element analysis model used to simulate compression curving of the flat plate element shape; and
    Figure 5 is a graph showing a relationship between the limit bending radius Rc / t and the value n obtained in the Examples.
    Description of Modalities
    First, a configuration of a vehicle collision energy-absorbing element in accordance with the present invention is described. The vehicle collision energy-absorbing element according to the present invention is formed by a thin, high-strength steel plate, the steel plate material being formed in a predetermined shape. The term predetermined shape used in this document, which is not necessarily particularly limited, may refer, preferably, to a cylindrical shape or a polygonal cross-sectional shape that is capable of efficiently absorbing colli energy
    19/42 are in the axial direction. In addition, there is no need to particularly limit the method of forming the sheet steel material to one format, and any method generally employed that includes, such as, for example, pressure forming and bending forming can be used.
    Then, the high strength thin steel sheet to be used as a material for the element of the present invention has a TS tensile strength of at least 980 MP, and also has a value n and a limit bending radius Rc that satisfy the Formula (1) or (2) below:
    Rc / t <1.31 x ln (n) + 5.21 (1) (where Rc: limit bending radius (mm), t: plate thickness (mm), en: value n obtained between the actual deformation of 5% to 10%), or
    Rc / t <1.31 x ln (n) + 4.21 (2) (where Rc: limit bending radius (mm), t: plate thickness (mm), en: n value obtained between the actual deformation of 5% to 10%). Here, the thin steel sheet in this document refers to a steel sheet that has a sheet thickness of 3.2 mm or less.
    When the element is formed by a thin sheet of high-strength steel that has a value n and a limit bending radius Rc that satisfy Formula (1) above, the element is allowed to be curved in a stable manner in the axial direction by means of vehicle collision in order to be crushed deformed into a bellows shape to thereby absorb the collision energy, even if the sheet steel material is a high-strength steel sheet that has a tensile strength TS 980 MPa or higher. When the value of the limit bending radius Rc of the steel sheet material fails to satisfy Formula (1) above, a portion of the bending deformation undergoes cracking (rupture) at the first bend when it crushes the element in the axial direction, which prevents the curving later develops into a bellows shape. As a result, the stable curving of the element cannot be ensured, failing to ensure that the desired property for the element absorbs collision energy efficiently and high.
    That is, when crushing the element in the axial direction, even
    20/42 if the n-value of the steel sheet material is equal and thus the radius of curvature of the bent portion of the element obtained at the time of bending, which is determined on the basis of the n-value, is also equal, the element it is still capable of bending in a stable manner to be deformed by crushing into a bellows shape without suffering from cracking in the bending portion when being crushed in the axial direction, provided that the steel plate material is a high strength steel plate that has a lower limit bending radius Rc that meets Formula (1) or (2) above. In addition, even a sheet steel material that has an n-value that is not as large, for example, an n-value of 0.20 or less is still capable of stable bending to be crushed deformed into a bellows shape without suffering from cracking in the bending portion when being crushed in the axial direction, provided that the steel sheet has a sufficiently small limit bending radius to satisfy Formula (1) above.
    Furthermore, when the element is formed by a high-strength steel plate that meets Formula (2) above, excellent crushing property can be obtained even if the element has a surface cross-sectional shape closer to a plate shape. flat.
    Here, the value n is obtained as follows. A test piece (test piece for JIS tensile test number 5: GL 50 mm) is collected from the thin high-strength steel plate, which is subjected to a tensile test according to JIS Z 2241, and a value obtained by the following equation defined as a two-point method in JIS Ζ 2253 for a real strain in a range of 5% to 10% is used as the value n in this document:
    value η = (Ιησι 0 - Ιησ 5 ) / (InO, 1 - ln0.05) (where σι 0 : real stress under 10% real strain, σ 5 : real stress under 5% real strain) .
    However, if the data under a 10% real deformation cannot be collected, the calculation is performed for a maximum real deformation obtainable and a corresponding real stress.
    21/42
    In addition, the limit bending radius Rc is obtained as follows. A test piece collected from thin high-strength steel plate (plate thickness: t mm) according to JIS Z 2248 was subjected to a U-shaped bending test at 180 ° by bending the test piece along a matrix that has a radius of curvature of the tip end R changed in a pitch of 0.5 mm, in order to obtain a minimum bending radius that does not cause a visually identifiable linear crack on the outside of the bending, and the minimum bending radius is defined as the limit bending radius Rc. The crack in this document does not refer to fine cracks resulting from inclusions. Generally, a crack of 1 mm or less in length is attributable to inclusions.
    The thin sheet of high strength steel for use as a material of the element of the present invention is not particularly limited, for example, to its composition and microstructure, provided that the steel sheet has a value n and a limit bending radius Rc that satisfy Formula (1) or (2) above.
    Here, in order to satisfy Formulas (1) and (2), it is particularly preferred that the steel sheet is formed as a thin steel sheet that includes: a chemical composition containing mass%: C: 0.14% a 0.30%; Si: 0.01% to 1.6%, Mn: 3.5% to 10%, P: 0.060% or less, S: 0.0050% or less, Al: 0.01% to 1.5%, N: 0.0060% or less, Nb: 0.01% to 0.10%, and the rest is Fe and incidental impurities, and has a microstructure that includes: a ferrite phase in 30% to 70% in volume fraction across the microstructure; and a secondary phase other than the ferrite phase, the ferrite phase that has an average grain size of 1.0 pm or less, the secondary phase that contains at least one austenite phase retained by at least 10% by volume fraction throughout the microstructure, the retained austenite phase that has an average spacing of 1.5 pm or less.
    First, a description is given of the reasons for limiting the content of each component of the preferred high strength thin steel sheet as a material to form the element of the present invention.
    Hereinafter, the mass% of ca22 / 42 of the component is simply denoted by%.
    C: 0.14% to 0.30%
    Carbon (C) is an element to increase the volume fraction of a hard phase by improving the cooling hardening capacity to thereby increase the strength of the steel while it is concentrated in austenite to stabilize austenite in order to allow austenite to be stabilized at room temperature. The C content needs to be at least 0.14% to obtain such an effect, as described above. On the other hand, the C content above 0.30% tends to incur a significant deterioration in the spot welding capacity and a significant reduction in the bending property. Therefore, it is defined that the C content is in a range of 0.14% to 0.30%, preferably 0.23% or less.
    Si: 0.01% to 1.6%
    Silicon (Si) is an element that contributes to the improvement of resistance through the reinforcement of solid solution and also improves ductility. The Si content needs to be at least 0.01% to obtain such an effect, as described above. On the other hand, in a case where the Si content exceeds 1.6%, Si is concentrated as an oxide on the steel plate surface, causing a failure in the chemical conversion treatment and bare point. Therefore, it is defined that the Si content is in a range of 0.01% to 1.6%, preferably in a range of 0.1% to 1.0%.
    Mn: 3.5% to 10%
    Manganese (Mn) contributes effectively to the improvement of resistance and also has the function of stabilizing austenite in order to improve elongation and the η value. The Mn content needs to be at least 3.5% to achieve such an effect, as described above. On the other hand, the Mn content that exceeds 10% observes significant segregation, and the microstructure suffers from localized variation at the transformation point due to the segregation of Mn, or similar. As a result, the steel sheet has a non-uniform microstructure in which a ferrite phase and a martensite phase exist in the form of bands, which have deteriorated the bending property. Furthermore, in this case, Mn is concentrated as an oxide on the surface
    23/42 steel sheet, which can cause leaf failure. Therefore, it is defined that the Mn content is in a range of 3.5% to 10%, preferably in a range of 4.0% to 7.0%.
    P <0.060%
    Phosphorus (P) contributes to the improvement of resistance, while deteriorating weldability. Such an adverse effect becomes significant when the P content exceeds 0.060%. Therefore, the P content is defined to be 0.060% or less. Here, an excessive reduction in the P content results in an increase in the cost of the steelmaking process and, therefore, the P content is preferably at least 0.001%. Preferably, the P content is 0.025% or less and, more preferably, 0.015% or less.
    S <0.0050%
    Sulfur (S) is an element that causes red brittleness, and can cause problems in the production process when contained in large quantities. In addition, S forms MnS as inclusions in the steel sheet, which remain as sheet-like inclusions after cold rolling and, thus, deteriorates the final deformability of the material to thereby confer the bending property. This adverse effect exerted by S becomes significant when the S content exceeds 0.0050%. Therefore, the S content is defined to be 0.0050% or less. Here, an excessive reduction in the S content results in an increase in the cost of desulphurisation in the steelmaking process and, therefore, the S content is preferably at least 0.0001%, and most preferably 0 , 0030% or less.
    Al: 0.01% to 1.5%
    Aluminum (Al) is an element that is effective as a deoxidizer in the steelmaking process and also useful for separating a non-metallic inclusion that can deteriorate the slag bending property. In addition, Al has the function of concentrating C on austenite, in order to stabilize austenite in order to improve elongation and the η value. The Al content needs to be at least 0.01% to achieve such an effect, as described above. On the other hand, the Al content that exceeds 1.5% results not only in an increase in material cost, but also in deterioration
    24/42 significant in weldability. Therefore, it is defined that the Al content is within the range of 0.01% to 1.5%, preferably 0.02% to 1.0%.
    N <0.0060%
    Nitrogen (N) forms a solute to improve resistance, considering that an excessive increase in N content reduces the ductility of the steel plate. In view of the purification of ferrite to improve ductility, it is preferred that the N content is kept to a minimum, considering that the effects of the present invention remain unaffected, provided that the N content is 0.0060% or less and thus, the N content is defined as 0.0060% or less. However, an excessive reduction in the N content results in an increase in the cost of steel production and, therefore, the N content is preferably at least 0.0001%.
    Nb: 0.01% to 0.10%
    Niobium (Nb) is an element that forms a C or N bond in order to form a fine carbide or fine nitride in a steel, and effectively contributes to: the refinement of ferrite grains after lamination-quenching cold; and uniform fine dispersion and improvement of austenite resistance as a hard phase. In particular, the adequate control of the heating rate in the tempering process allows the refinement of the ferrite and hard phase, which improves the bending property, with the result that the steel sheet can be curved in a stable manner in order to be deformed by crushing into a bellows shape when the element is crushed in the axial direction. The Nb content needs to be at least 0.01% to obtain such an effect, as described above. On the other hand, the Nb content above 0.10% saturates the effect and also leads to the hardening of the hot-rolled sheet, which causes an increase in the hot rolling load and in the cold rolling load, reducing the productivity. In addition, an excessive content of Nb generates excessive precipitates in the ferrite, which deteriorates the ductility of the ferrite, conferring elongation and flexion properties. Therefore, it is defined that the Nb content is in a range of 0.01% to 0.10%, preferably in a range of 0.03% to 0.07%.
    The basic components are illustrated above, and it is preferred that
    25/42 the total Si + Al content, each within the range mentioned above, is at least 0.5%.
    Si and Al are an element to suppress cementite precipitation, while allowing easy concentration of C in austenite. The total content of Si and Al is preferably at least 0.5% in order to more effectively retain austenite by 10% or more in the steel plate. The total content is, more preferably, at least 0.7%.
    The rest of the components mentioned above include Fe and incidental impurities.
    The high-strength thin steel sheet for use as a material of the element of the present invention has the chemical composition mentioned above, and additionally has a microstructure (multiphase) that includes, in fraction of volume, a 30% to 70% ferrite phase % and a secondary phase different from the ferrite phase. Here, the ferrite phase is formed by fine grains with an average grain size of 1.0 pm or less. With the ferrite phase being refined in this way, to have an average grain size of 1.0 pm or less, a desired high strength (TS: at least 980 MPa) can be ensured and the bending property can still be improved . However, the effect mentioned above can no longer be expected when the average grain size of the ferrite phase exceeds 1.0 pm. Consequently, the average grain size of the ferrite phase is defined as 1.0 pm or less, and preferably 0.8 pm or less.
    However, the secondary phase other than the ferrite phase is a hard secondary phase that contains at least one austenite phase retained by at least 10% in volume fraction in relation to the entire microstructure. The hard secondary phase contained, thus, leads to an improvement in strength and ductility. The retained austenite phase is contained in at least 10% by volume fraction and finely dispersed, in order to have an average spacing of 1.5 pm or less in the area of the retained austenite phase, which increases the value n while ensuring the excellent bending property to, in this way, allow the relationship between the value of the limit bending radius to be adjusted to be within a desired range. Ade
    26/42 more, the steel sheet which has an adjusted microstructure, as described above, allows the element to be deformed, when crushed, as it is curved in a stable manner into a bellows shape. The retained austenite phase contained in less than 10% or coarsely dispersed to have an average spacing above 1.5 μιτι fails to ensure, in particular, the desired bending property. The retained austenite phase is preferably contained in at least 15% by volume fraction with an average spacing of 1 μιτι or less. The retained austenite phase preferably has an average grain size of 0.1 μΓη to 1 μιτι.
    Here, the hard secondary phase may include, in addition to the retained austenite phase, a bainite phase (which includes tempered bainite), a martensite phase (which includes tempered martensite) and a cementite phase. Needless to say, it is also preferred that each secondary phase lasts beyond the retained austenite phase be finely dispersed in a similar manner to the retained austenite phase.
    In the following, a preferred method of manufacturing thin high strength steel sheet for use as a material of the element of the present invention is described.
    Preferably, the steel material having the chemical composition mentioned above can be subjected to the hot rolling process, pickling process, cold rolling process and tempering process, in order to thereby form a steel sheet high strength thin.
    The method of fabricating the steel material is not particularly limited, and any conventional steel melting method, such as a converter, can preferably be used to prepare molten steel which has the chemical composition mentioned above, which can be subjected to a method of continuous casting and a method of casting or ingot breaker, in order to obtain a thick plate (like steel material).
    The plate (steel material) obtained in this way is preferably subjected to the hot rolling process after being cooled once
    27/42 and then reheated, or directly without undergoing a heat treatment after casting.
    The heating temperature in the hot rolling process is preferably in the range of 1150 ° C to 1400 ° C. The heating temperature that falls below 1150 ° C fails to achieve sufficient uniformity, considering that the high heating temperature above 1400 ° C results in significant oxidation loss, which deteriorates the performance. The heating temperature is preferably at least 1250 ° C for the purpose of reducing the effect of Mn segregation, in order to improve the bending property.
    In the hot rolling process, the plate is subjected to crude and finished lamination in order to be obtained as a hot-rolled sheet, which is wound on a coil.
    The conditions of rough lamination are not specifically limited, as long as it is able to form a sheet bar in a desired dimensional shape. In addition, in the finished lamination, it is defined that the finishing delivery temperature is within a range of 850 ° C to 950 ° C. The finish delivery temperature that is outside the range mentioned above fails to standardize the hot-rolled sheet microstructure, leading to deterioration in machinability, such as elongation and bending properties.
    Upon completion of the finished lamination, the steel sheet is subjected to cooling at an average cooling rate of 5 ° C / s to 200 ° C / s over a temperature range of 750 ° C. In this way, it is possible to suppress the generation of band-like texture that includes two phases, that is, a ferrite phase and a pearlite phase. The winding temperature is defined to be in a range of 350 ° C to 650 ° C. The winding temperature that falls below 350 ° C increases the strength of the steel sheet excessively, which makes it difficult to move the sheet to the next step and also to perform cold rolling on it. On the other hand, the winding temperature that exceeds 650 ° C leads to the excessive generation of an internal oxidation layer on the steel sheet surface, which significantly reduces fatigue resistance.
    Then, the hot rolled sheet is subjected to the cold rolling process in which the sheet is subjected to pickling and then cold rolling in order to be obtained as a cold rolled sheet.
    The rate of reduction of cold rolling in cold rolling is preferably at least 30% for the purpose of refining the microstructure. Here, when the hot-rolled sheet is hard, it may be conceivable to have the sheet heated to about 500 ° C and subjected to hot rolling instead of cold rolling. However, according to the present invention, accumulation of deformation in the cold rolling process is critical in the refinement of the microstructure and, thus, the steel sheet is subjected to rolling at room temperature, instead of hot rolling at temperature which causes deformation recovery.
    Alternatively, the hot-rolled sheet can be annealed to be softened. The reduction rate of cold rolling is preferably suppressed by 60% or less because, otherwise, the rolling load is increased to make cold rolling difficult.
    Then, the resulting cold-rolled sheet is subjected to the hardening process by subjecting the steel sheet to hardening to obtain a cold-rolled annealed sheet.
    In the tempering process, the steel plate microstructure is controlled at the time of tempering and heating before being cooled, in order to optimize the volume fraction and the ferrite grain size to be finely obtained. In the present invention, a primary heating of 300 ° C to 600 ° C is carried out at a rapid average heating rate of 1 ° C / s to 50 ° C / s and then a secondary heating of 600 ° C until the tempering temperature it is carried out at an average heating rate of 0.1 ° C / s to 10 ° C / s to thereby heat the steel sheet to a tempering temperature of 650 ° C to 750 ° C.
    The primary heating carried out at a rapid heating rate of 1 ° C / s to 50 ° C / s on average allows the suppression of growth of
    29/42 ferrite grain and fine dispersion of the austenite phase in the ferrite matrix, with the result that the ferrite grains and the hard secondary phase can be finely dispersed in the microstructure. In addition, secondary heating carried out at a heating rate of 0.1 ° C / s to 10 ° C / s allows precise control of the tempering temperature.
    It is defined that the tempering temperature is in a range of 650 ° C to 750 ° C. A tempering temperature that falls below 650 ° C causes the deformations generated during cold rolling to remain, which deteriorates the bending property. On the other hand, a high tempering temperature above 750 ° C leads to thick crystal grains, which fail to obtain a desired fine microstructure.
    Here, it is preferred that the tempering temperature is maintained in the above-mentioned tempering temperature range for 10 seconds to 500 seconds. The retention time of less than 10 seconds causes deformations during cold rolling to remain, which deteriorates the bending property. However, even if the hardening carried out over a long period of time exceeding 500 seconds, hardly any structural change can be identified and, thus, the upper limit of the retention time is preferably defined as 500 seconds.
    After being maintained at the aforementioned tempering temperature, the steel sheet is cooled over a temperature range of 200 ° C or below at an average cooling rate of 1 ° C / s to 30 ° C / s. The cooling rate below 1 ° C / s takes a long time to cool, which incurs an increase in cost. On the other hand, rapid cooling at a cooling rate or higher than 30 ° C / s results in non-uniform cooling of the steel sheet, which makes the material quality unstable. Alternatively, the steel sheet can be cooled from the tempering temperature to a temperature range of 350 ° C to 500 ° C and then kept in the temperature range of 350 ° C to 500 ° C for at least 10 seconds, preferably for at least 120 seconds, before being cooled to room temperature.
    During cooling in the tempering process, the steel sheet
    30/42 can be subjected to galvanizing and annealing where the sheet is immersed in a hot dip galvanizing bath and then adjusted in quantity of zinc coating by means of, for example, gas cleaning, and additionally heated at a predetermined temperature. In addition, after the hardening process, the steel sheet can be subjected, without any problem, to zinc or nickel electroplating and hardening lamination, which are generally used in a steel sheet for a vehicle.
    EXAMPLES
    Example 1
    Each molten steel that has the chemical composition of Table 1 was prepared by steelmaking and cast on a plate (steel material) with a thickness of 300 mm. Then, the obtained plates were thus heated to the heating temperatures shown in Table 2 before being subjected to hot rolling which includes finished rolling under the conditions shown in Table 2, which were then cooled under the conditions shown in Table 2 and wound in a coil at the winding temperatures of Table 2, in order to be obtained as hot-rolled sheets.
    Then, the hot rolled sheets obtained in this way were subjected to cold rolling under the reduction rates of cold rolling shown in Table 2, in order to be obtained as cold rolled steel sheets. Subsequently, the cold-rolled steel sheets obtained in this way were subjected to the tempering process under the conditions shown in Table 2.
    The steel sheets (cold-rolled annealed sheet) obtained in this way were subjected to microstructure observation, tensile test, and flexion test. The test methods were as follows.
    (1) Microstructure observation
    A test piece for observation of microstructure was collected from each of the steel sheets obtained, which were subjected to polishing on a transversal surface and in a thickness direction of
    31/42 plate parallel to the rolling direction and then engraved with a 3% nital solution, so that a microstructure in a region ranging from a steel surface to 1/4 of the position in the direction of plate thickness be observed using a scanning electron microscope (from 1000 to 5000 magnifications) to identify, in this way, the microstructure and measure the crystal grain size of the ferrite phase by an interception method using the micrograph adopted in this way. In the interception method, straight lines with a length corresponding to 20 μιτι on the micrographic scale are drawn in a perpendicular and horizontal direction, respectively, to calculate, in this way, the average ferrite grain size. To obtain the microstructure fraction of the ferrite phase, the micrographic was processed using commercially available image processing software (Paint Shop Pro Ver. 9 (trade name) (released by Corei Corporation)) and binarized in the ferrite phase and in secondary phase, so that the proportion of the measured ferrite phase is defined as the volume fraction of the ferrite phase.
    In addition, the microstructure fraction (volume fraction) of the retained austenite phase was measured by X-ray diffraction. The steel plate was subjected to crushing to a position of 1/4 of the plate thickness from a surface of steel plate and then to an additional 0.1 mm chemical polish. On this crushed and polished surface, using an X-ray diffractometer using the Koc de Mo line, integrated intensities were measured by (200), (220) and (311) FCC iron faces and (200), (211) and (220) BCC iron faces. From the measurements above, the microstructure fraction (volume fraction) of the retained austenite was calculated. To obtain the distribution of the residual austenite phase, the FCC phase was identified by backscattered electron pattern (EBSP) at the position of 1/4 of the plate thickness, and based on the data obtained in this way, the average grain size and the Mean spacing was calculated for each FCC phase. The average grain size of retained austenite was calculated with a dissection method in which straight lines at a length corresponding to 20 μηη on the EBSP map scale were drawn in a per direction
    32/42 pendulum and in a horizontal direction on the EBSP map, and the sections were calculated. To obtain the average spacing of the retained austenite, 10 straight lines were drawn in random directions on the EBSP map, and the sections of ferrite grains between the retained austenite grains were measured, which were calculated to obtain the average spacing of the retained austenite.
    (2) Tensile test
    A JIS test piece number 5 that has a longitudinal direction (pull direction) in a 90 degree direction from the collected rolling direction, according to JIS Z 2201 from each steel sheet obtained was subjected to the traction according to JIS Z 2241 to obtain the traction property (TS tensile strength). The n value was calculated, based on the stress-strain data obtained in the tensile test, by the following equation defined as a two-point method in JIS Z 2253 for a real strain in a range of 5% to 10%.
    value η = Ιησιο - Ιπσ 5 / (InO, 1 - ln0.05) (where oio: a real stress under a real strain of 10%, 05: a real stress under a real strain of 5%)
    Here, if the data under the actual 10% strain cannot be calculated, the calculation is performed using a maximum calculable real strain and an actual stress that corresponds to it.
    (3) Bending test
    A bending test piece (30 mm wide χ 100 mm long) collected according to JIS Z 2248 from each of the steel sheets obtained was subjected to the U-shaped bending test at 180 ° by bending the test piece along a matrix that has a radius of curvature of the tip end R changed in a pitch of 0.5 mm pitch, and the outside of the folded portion was visually observed as there was no crack generated, the in order to obtain a minimum bending radius Rc (mm) that did not cause any cracking, and the minimum bending radius Rc was defined as the limit bending radius (mm). Here, the crack of 1 mm or less in length resulting from the inclusion has been excluded from the subjects of observation.
    33/42
    The results obtained are shown in Table 3.
    Next, a test material was collected from each of the thin high-strength steel sheets that have the properties mentioned above, and used to manufacture, through the formation of folds, an element that has a cross-sectional shape in Figure 2 , and the element formed in this way is connected to a 590 MPa class high-strength steel plate that serves as a backing plate to thereby obtain two types of crushing elements each having a height of 420 mm (W) and 260 mm (X), respectively. Here, the ratio between the shortest side b between the parallel sides, or perpendicular to the backing plate in a cross section of the element and the plate thickness t is obtained as bit - 33.3 for element X and as b / f = 33.3 for element W. A crush test was performed using these configured crush elements, as described above. The test method was as follows.
    (4) Crush test
    The crushing elements were crushed in the axial direction with a variable weight from 110 kgf to 190 kgf depending on the element at a rate that is equivalent to 50 km per hour, in order to be crushed at a height of 200 mm or 240 mm. After being crushed, these were visually identified as deformed elements, while the amount of energy absorbed up to a predetermined amount of crushing was calculated.
    The results obtained are shown in Table 4.
    Table 1
    Steel No. Chemical Compositions (% by mass) Ç Si Mn P s Al N Nb THE 0.16 0.5 4.1 0.02 0.0013 0.025 0.0021 0.054 B 0.16 1.0 3.9 0.03 0.0024 0.022 0.0014 0.057 Ç 0.15 1.5 3.9 0.02 0.0011 0.019 0.0025 0.058 D 0.19 0.3 3.6 0.02 0.0030 0.024 0.0029 0.071 AND 0.23 0.8 5.8 0.03 0.0012 0.017 0.0034 0.051 F 0.27 0.6 7.2 0.02 0.0029 0.033 0.0027 0.066
    34/42
    Steel No. Chemical Compositions (% by mass) Ç Si Mn P s Al N Nb G 0.16 0.5 2.4 0.01 0.0018 0.031 0.0040 - H 0.15 0.5 2.6 0.02 0.0010 0.032 0.0050 - 1 0.08 0.5 2.6 0.02 0.0010 0.032 0.0050 -
    35/42
    Table 2
    Quenching Process Cooling Rate after Retention (° C / s) **** uo O m 30 the CM 30 co uo O Retention time(s) 09 120 180 06 the xr CM 200 09 09 120 Temp. Temper (° C) 685 710 | 069 670 O00 CO 099 685 750 820 Heating rate(° C / s) Secondary Heating *** O 0.5 ro 0.5 O co CO O 0.5 Primary Heating ** OU LO 20 30 CM OU IO LD IO uo Process ofRolling aCold Cold Rolling Reduction Rate (%) 40 40 35 40 LO CO 35 40 40 40 Hot Rolling Process Temp. Winding (° C) 600 550 570 620 O OLO 600 009 '600 550 Average Cooling Rate (° C / s) * after Finishing Lamination 50 the CO 20 70 O o 40 50 50 30 Temp. Finishing Delivery (° C) 900 920 950 O0000 o o σ> 930 006 006 920 Temp. Heating (° C) 1350 1300 1350 1270 the CM CO 1250 1350 1350 1350 oo O -7 < z < m O Q LU u. □ I - Plateof steelNo. - CM CO xr IO coCO σ>
    ) Average rate between finishing delivery temperature and 750
    *) Average rate between 300 ° C and 600 ° C **) Average rate between 600 ° C and tempering temperature ***) Average rate between tempering temperature and 180 ° C
    36/42
    Table 3
    Comments ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleComparative ExampleComparative ExampleComparative Bending Properties Formula Satisfaction (2) satisfied satisfied satisfied satisfied satisfied satisfied ώ ωQ «*» CÜ XIç not satisfied not satisfiedL ------------ R Value of Formula (2) ** it cm rCM 2.7 cd cm 2.6 LOcm 0.3 O 6'0 Formula Satisfaction(1) satisfied satisfied satisfied satisfied satisfied satisfied not satisfied not satisfied not satisfied Formula R Value (1Γ LO and rCO 3.7 CDCO 3.6 3.5 ΓΟ r- CD Rc / tCM 2.5 CD CM ~ 2.5 LO cm CM cm ’ LO CM r, 2 <1> —-.Ο · Π5 rü c™ ό φ Ε or| _L —1 LO Cm ’ LO Cm ’ 3.0 LOCO 3.0 3.0 2.5 LOCsT 3.0 Traction Properties valuen * 0.28 0.31 0.32 CO CO o 0.29 0.28 0.05 0.07 0.08 Tensile strength TS (MPa) 1245 1125 1129 the o 1284 1376 1079 1025 983 Microstructure Austenite Mean spacing (pm) 0.98 0.82 0.83 rd 0.63 O 1 immeasurable immeasurable Average Grain Size (pm) 0.49 0.67 0.91 WithO 0.49 0.62 1 immeasurable immensefair Volume Fraction (%) CM COCM CM 26 28 1 - CM Ferrite ώ-o π .2 · -And '2 ® «3 E 0.53 0.72 0.84 LO0 ' 0.62 0.78 CD 9'9 8.3 Volume Fraction (%) 39 43 46 LO LO ! 37 32I 851 I 70 99 Type*** F + M + y + B F + M + y + B F + M + y + B > -++ l_L ++ l_L F + M + y φ + LL CD> ++ LL F + M + y + B Plate Thickness (mm) CM CM CM CM CM CM CM CM CM < 2 < m O D LU LL O I - Steel SheetNo. - CM COLO CDCO σ>
    *) value obtained based on the data for real deformations of 5% and 10%. When the uniform elongation does not reach 10%, the data obtained for a real strain of 5% and for a maximum real strain, and a real stress for each strain was used.
    **) Formula (1): Rc / t <1.31 x ln (n) + 5.21 ... (1) Formula (2): Rc / t <1.31 ln (n) + 4.21 ... (2) ***) F: Ferrite, M: Martensite, B.bainite, y: Austenite (retained γ), Θ: cementite
    37/42
    Table 4
    Element No. PlateSteel No. Element Format * Crushing Stroke (mm) Deformed State after Crushing Absorbed Energy (kJ) Comments 1 1 X 200 bellows shape 15.5 Inventive Example 2 2 w 240 bellows shape 15.3 Inventive Example 3 3 X 200 bellows shape 12.1 Inventive Example 4 4 X 200 bellows shape 12.6 Inventive Example 5 5 X 200 bellows shape 13.2 Inventive Example 6 6 X 200 bellows shape 11.5 Inventive Example 7 7 X 200 crack 10.3 Comparative Example 8 8 X 200 crack 9.9 Comparative Example 9 9 w 240 crack 11.3 Comparative Example
    *) See FIG. 2
    All Inventive Examples allow the element to be bent stably in the axial direction to be deformed by crushing it into a bellows shape when the steel sheet has a TS tensile strength as high as 980 MPa or higher and the ne radius value limit flexion meet Formulas (1) and (2). So, in this case, the energy absorbed by crushing is as high as 11.5 kJ or greater, which means that the element is excellent in the collision energy absorption performance. On the other hand, the Comparative Examples that are outside the range of the present invention experience the generation of cracking and suffer non-uniform deformation when the element is crushed in the axial direction and, in addition, the energy absorbed by the collision was less than 11.5 kJ, which means that the element is inferior in collision energy absorption performance when compared to the element that has been stably bent into a bellows shape.
    Example 2
    38/42
    The collision energy absorbing elements were manufactured using thin steel sheets (each with tensile strength of 980 MPa to 1300 MPa class) as materials, which have tensile properties, n values, and properties of flexion (bending radius 5 limit Rc) shown in Table 5. The collision energy absorption elements were formed in one of those shapes of the elements X, W and J of Figure 2. The support plates were formed by steel plate high strength 590 MPa grade, as in Example 1.
    A crush test was performed using these configured collision energy absorption elements, as described above. The test method was the same as that used in Example 1.
    The results obtained are shown in Table 5.
    39/42
    Table 5
    Comments ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleInventive o -t-J c (D E Π5 cn CO E CO LU(D Ό(O a> όσ Φd O t_ CL Crushing Stability stable stable stable stable stable stable Φ>v> stable stable stable stable Deformed State after Crushing bellows shape bellows shape bellows shape bellows shape bellows shape I format 'bellows Format ; bellows . bellows shape bellows shape bellows shape bellows shape Crushing Stroke (mm) 160 200 240 160 200 240 160 200 240 160 200 ijj E 1 -S - Nl LU (/) J- 13 nJ-LΦ ω ω ™ JZ jQ -o 33.3 33.3 33.3 40.0 OO 40.0 33.3 33.3 33.3 33.3 33.3 Element Format *** "3 X-> X- X”> X Properties of Thin Steel Plate for Use | Formula Satisfaction (2) satisfied satisfied satisfied satisfied satisfied satisfied not satisfied not satisfied not satisfied not satisfied not satisfied R value of Formula (2) ** OU cm ΙΩCM in cxí Γcm cm cm CM CM_ CM At the' 0.7 Formula Satisfaction (1) satisfied satisfied satisfied satisfied satisfied satisfied satisfied satisfied satisfied satisfied satisfied R value ofFormula (1) ** CO 3.5 u CO rco u-CO uCO CM CM ~ CM cm 2.2 Rc / t CM CM CM it cm LO CM LOCM CO CO CO Γ ^ -_Bending Radius Limit Rc (mm) 2.5 2.5 2.5 LO cm LO cm LO CM LO LO_r- LO_ 2.0 2.0 Valuen * 0.28 0.28 0.28 0.31 0.31 0.31 O The ~ CD 0.07 0.07 Tensile strengthTS (MPa) 1245 1245 1245 1125 1125 1125 1007 1007 1007 1215 1215 Plate Thickness t (mm) CM CN CM O_ O CD CM CM CM CM CM "----------Steel SheetNo. - - - O O O -- CM CM Element No. < A2 A3 £ CM B3 O C2 C3 Q D2
    40/42
    Comments ExampleInventive ExampleInventive ExampleInventive ExampleInventive ExampleComparative ExampleComparative ExampleComparative ExampleComparative ExampleComparative ExampleComparative ExampleComparative ExampleComparative Ο Ή Φ Ε 03 σ 03 Ε ω LUφ ΌV) CD(ϋ Τ3 φΟ. ο h— CL Crushing Stability stable stable stable (D> * 03 4— 1 tf) CD Φ> * 03tf) c unstable unstable unstable unstable unstable unstable unstable Deformed State after Crushing bellows shape bellows shape bellows shape bellows shape D TDQ φ JZ Ι-Ο2 crack crack crack crack crack crack cracked-frog Course ofCrushing (mm) 240 160 200 OCN the CO 200 240 160 200 240 160 200 o Ε => ω ra ra p, z>p> “o. N UJ W TJ ro ra Q ω ™ to -c - ° COCOCONUT OCD 40.0 O oΝ ’ coCOCONUT 33.3 33.3 25.0 25.0 25.0 33.3 33.3 I Element Format***1 §X~ O X §X IΛΛ -> X Properties of Thin Steel Plate for Use Formula Satisfaction (2) not satisfied ώ ro tf)* O * =. 52 c not satisfied not satisfied not satisfied not satisfied not satisfied not satisfied not satisfied not satisfied not satisfied not satisfied R value ofFormula (2) ** 0.7 σ> CbCO o “ 0.3 0.3 0.5 0.5 0.5 2.2 CN CN Formula Satisfaction (1) satisfiedi I satisfied satisfied <ü M— »Φ Ml · -tf) * - <tD <Λ not satisfied not satisfied don't leave unsatisfied not satisfied not satisfied i not satisfied not satisfied don't know• flawed R value of Formula (1) ‘* r- 2.9 2.9 O)CN co CO cO LÕ ID LD CN CQ 3.2 'Rc / tIOCN OCN OCN CN CN V ·CN CNCN CNCN 2.2 CN n - 4.2 Bending Radius Limit Rc (mm) 2.0 2.0 The CN The cn LO CN 2.5 IDCN m co ID co 3.5 the in 5.0 Valuen * Ζ0Ό 0.17 0.17 Γo ’ ID O ’ 0.05 0.05 0.06 0.06 90'0 0.21 0.21 Tensile strengthTS(MPa) 1215 1021 1021 CN O co co o 1038 1038 1340 1340 1340 1306 1306 Plate Thickness t (mm) CN (D <D O CN CN CN CD <D CD CNT ~ CN Π3 ÍT Q. Õ * ro <Μ Φ Ο Ό CN CO CO co Ν ’ Ν ’LO LO LO CD CD ElementNo. D3 LU E2 CO LU LL F2 F3 δ CN (D G3H2
    41/42
    ο ο ~ 9- 2 Ε 05 φ Οχ Ε LU Q ο
    οω c 0)> Ε £ιη Ε * -> (Λ LLI (0 Ç σι
    42/42
    All of the Inventive Examples were stably curved in the axial direction to be crushed deformed into a bellows shape.
    In addition, the results obtained for examples 1 and 2 were collectively shown in Figure 5 in relation to the limit bending radius and the n value. In Figure 5, white circles each corresponding to a case in which the element has been stably bent into a bellows shape, and black circles each corresponding to a case in which the element has undergone rupture and has not been crushed stably in a bellows shape.
    It can be understood from Figure 5 that the element is curved stably! in a bellows shape and has an excellent collision energy absorption performance in the axial direction upon collision when the value obtained by dividing the limit bending radius by the plate thickness (the limit bending radius / plate thickness) satisfy Formulas (1) and (2). For example, when the sheet steel material has a large value η, the element crushes stably in a bellows shape. However, even if the value n is somewhat small, for example 0.20 or less, the element is still allowed to be crushed in a stable manner, provided the value obtained by dividing the limit bending radius by the plate thickness (the limit bending radius / sheet thickness) satisfies Formulas (1) and (2). However, an element formed by a steel plate that does not satisfy Formula (1) undergoes the generation of rupture regardless of its shape, and is unable to obtain deformation by stable collapse.
    1/3
    权利要求:
    Claims (4)
    [1]
    1. Vehicle collision energy-absorbing element formed by forming a high strength thin steel sheet, where the high strength thin steel sheet has a TS tensile strength of at least 980 MPa, and has a value n a limit bending radius Rc that satisfy Formula (1) below:
    Rc / t <1.31 xln (n) + 5.21 (1);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), en: value n obtained for a real deformation in a range of 5% to 10%, characterized by the fact that the high-grade thin steel plate resistance includes a chemical composition containing% by mass:
    C: 0.14% to 0.30%;
    Si: 0.01% to 1.6%
    Mn: 3.5% to 10%;
    P: 0.060% or less;
    S: 0.0050% or less;
    Al: 0.01% to 1.5%;
    N: 0.0060% or less;
    Nb: 0.01% to 0.10%; and the rest being Fe and incidental impurities, and the high strength steel plate has a microstructure that includes a ferrite phase at 30% to 70% in volume fraction in relation to the entire microstructure and a secondary phase different from the phase of ferrite, the ferrite phase having an average grain size of 1.0 pm or less, the secondary phase containing at least one austenite phase retained by at least 10% in volume fraction throughout the microstructure, the austenite phase retained having an average spacing of 1.5 pm or less.
    [2]
    2. Vehicle collision energy absorption element forPetition 870180067986, of 06/08/2018, p. 10/17
    2/3 formed into a high strength thin steel sheet, where the high strength thin steel sheet has a TS tensile strength of at least 980 MPa, and has a value n and a limit bending radius Rc that satisfy Formula (2) below:
    Rc / t <1.31 xln (n) + 4.21 (2);
    Where
    Rc: limit bending radius (mm), t: plate thickness (mm), en: value n obtained for a real deformation in a range of 5% to 10%, characterized by the fact that the high-grade thin steel plate resistance includes a chemical composition containing% by mass:
    C: 0.14% to 0.30%;
    Si: 0.01% to 1.6%
    Mn: 3.5% to 10%;
    P: 0.060% or less;
    S: 0.0050% or less;
    Al: 0.01% to 1.5%;
    N: 0.0060% or less;
    Nb: 0.01% to 0.10%; and the rest being Fe and incidental impurities, and the high strength steel plate has a microstructure that includes a ferrite phase at 30% to 70% in volume fraction in relation to the entire microstructure and a secondary phase different from the phase of ferrite, the ferrite phase having an average grain size of 1.0 pm or less, the secondary phase containing at least one austenite phase retained by at least 10% in volume fraction throughout the microstructure, the austenite phase retained having an average spacing of 1.5 pm or less.
    [3]
    Vehicle collision energy-absorbing element according to claim 1 or 2, characterized in that the thin high-strength steel sheet includes a composition
    Petition 870180067986, of 06/08/2018, p. 11/17
    3/3 chemical containing% by mass:
    C: 0.14% to 0.30%;
    Si: 0.01% to 1.6%
    Mn: 3.5% to 10%;
    P: 0.060% or less;
    S: 0.0050% or less;
    Al: 0.01% to 1.5%;
    N: 0.0060% or less;
    Nb: 0.01% to 0.10%; and the rest being Fe and incidental impurities, the high strength steel sheet has a microstructure that includes a ferrite phase in 30% to 70% in volume fraction in relation to the entire microstructure and a secondary phase different from the ferrite, the ferrite phase having an average grain size of 1.0 pm or less, the secondary phase containing at least one austenite phase retained by at least 10% in volume fraction throughout the microstructure, the retained austenite phase having an average spacing of 1.5 pm or less.
    [4]
    4. Vehicle collision energy absorption element according to claim 3, characterized by the fact that the chemical composition contains Si and Al, so that the total content of Si and Al (Si + Al) in mass% satisfy at least 0.5%.
    Petition 870180067986, of 06/08/2018, p. 12/17
    1/4
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    同族专利:
    公开号 | 公开日
    CN103582714A|2014-02-12|
    KR20130140176A|2013-12-23|
    KR101570918B1|2015-11-20|
    RU2558779C2|2015-08-10|
    US20140103684A1|2014-04-17|
    JP5856002B2|2016-02-09|
    CA2835153C|2016-10-25|
    CN103582714B|2015-10-14|
    CA2835153A1|2012-11-15|
    BR112013029160A2|2017-01-31|
    US9452792B2|2016-09-27|
    EP2708610A4|2015-10-21|
    RU2013155176A|2015-06-20|
    EP2708610A1|2014-03-19|
    MX2013013193A|2014-08-21|
    TW201307126A|2013-02-16|
    TWI494237B|2015-08-01|
    MX351295B|2017-10-10|
    WO2012153471A1|2012-11-15|
    JP2012251239A|2012-12-20|
    EP2708610B1|2017-09-27|
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    法律状态:
    2018-05-08| B07A| Technical examination (opinion): publication of technical examination (opinion)|
    2018-09-25| B09A| Decision: intention to grant|
    2018-11-21| B16A| Patent or certificate of addition of invention granted|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 23/04/2012, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
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    JP2011107214|2011-05-12|
    JP2012095957A|JP5856002B2|2011-05-12|2012-04-19|Collision energy absorbing member for automobiles excellent in impact energy absorbing ability and method for manufacturing the same|
    PCT/JP2012/002778|WO2012153471A1|2011-05-12|2012-04-23|Vehicle collision energy absorbing member having high collision energy absorbing power, and method for manufacturing same|
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