JP2013230593A - Laminated steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated steel plate that is light, has high rigidity and shock resistance, has small anisotropy, is excellent in workability such as shearing, bending, deep drawing, and extending, and shape stability after processing.SOLUTION: In a laminated steel plate, a truss structure body made of steel wires is laminated between steel plates. It is preferable that the carbon concentration is at least 0.24 mass% among components of the steel wires, a distance between apexes of the truss structure body is 30 times or more of the steel thickness, an angle formed by the wires comprising the truss structure body and the steel plate is 30 to 60°, and the truss structure body and the steel plate are bonded with a blaze material or an adhesive whose melting point is 400°C or less.

Description

  The present invention relates to a laminated steel sheet, and more particularly to a laminated steel sheet in which steel sheets are laminated on both surfaces of a core layer.

Lightweight, high rigidity and strength in various applications such as automobile parts, home appliance housings, furniture, and office equipment parts, and workability such as shearing, bending, deep drawing, and overhanging, and stable shape after processing There is a wide demand for steel sheets having excellent properties. In recent years, CO ₂ emissions have been severely regulated as a measure against global warming, and especially in the use of automobile parts, not only the need for weight reduction is particularly high in order to reduce CO ₂ emissions. High performance is required for rigidity, impact resistance, workability and shape stability after processing. As a solution to such a demand, various laminated steel sheets in which a core layer made of a processed metal plate, a honeycomb, metal fibers and the like are laminated between steel sheets have been proposed.

  Specifically, a laminated steel sheet has been proposed in which a metal plate processed into a core layer is used to introduce voids into the core layer, maintain strength, and enhance the light weight effect. For example, Patent Document 1 proposes a plate in which a flexible metal sheet with unevenness is laminated between cover layers made of a metal plate or a resin sheet, and Patent Document 2 proposes a large number of plates between metal face sheets. A manufacturing method of a plate in which cores with groove-shaped materials arranged in parallel have been proposed, and in Patent Document 3, a superplastic metal material is processed into a hat shape on a surface layer plate made of a superplastic metal material and stacked Is proposed, and Patent Document 4 proposes a structure in which a dimple-processed steel plate with micro-dents is laminated as a core layer between steel plates.

  In addition, a laminated steel sheet has been proposed which uses a core layer formed of an extremely thin plate and has a honeycomb shape and is intended to improve heat insulation and sound insulation. For example, Patent Documents 5 to 8 propose metal plates in which a honeycomb plate filled with foamed resin is used as a core layer and laminated between metal plates.

  Further, for the purpose of further reducing the weight of the core layer, a laminated steel sheet using metal fibers for the core layer has been proposed. For example, Patent Document 9 proposes a metal plate obtained by laminating an organic or metal fibrous porous body covered with a thermoplastic resin between metal plates as a core layer. In Non-Patent Document 1, short fiber SUS fibers are proposed. As the core layer, a structure in which the steel plates are blazed and laminated is proposed. For example, Patent Document 10 proposes a plate in which a wire mesh formed in a net shape using a steel wire is laminated as a core layer. In Patent Documents 11 to 12, a wire mesh is laminated as a core layer between metal plates. A seam welded laminated plate has been proposed, and Patent Document 13 proposes a plate in which a corrugated wire mesh is used as a core layer between steel plates.

Special table 2003-508270 gazette JP-A-5-269898 JP-A-8-230098 International Publication No. 2008/097984 Japanese Patent No. 2838982 JP-A-8-82021 JP-A-8-105127 JP-A-8-20086 International Publication No. 2006/050610 JP 2011-031482 A JP 58-55242 A Japanese Patent Laid-Open No. 9-19986 JP-A-2-171232

D. Mohr, Int. J. et al. Mech. Sci. , Vol. 45. , P.M. 253 (2003)

  In the above Patent Documents 1 to 4, the metal layer is processed so that the core layer introduces voids, so that the weight can be reduced. Moreover, since a metal plate is used, Young's modulus and yield strength are high compared to a core layer using other materials. Therefore, the techniques disclosed in Patent Documents 1 to 4 are effective for increasing the rigidity and the strength.

  However, since the metal layer processed in a certain direction is arranged in the core layer structures of Patent Documents 1 to 3, the gaps are continuous. Therefore, when processing the metal plate which laminated | stacked the said core layer, the processing defect which a surface steel plate sinks on a space | gap may generate | occur | produce depending on the direction which loads force. Defects can be prevented by reducing the space between the gaps, but when the air gap is reduced, the core layer is made of a metal plate, so that the increase in weight becomes significant.

  In Patent Document 4, since the dimples are isotropically arranged, the influence of the anisotropy of the core layer structure during processing is slightly mitigated. Since mild steel that is thin and easy to process is used, the yield strength of the core layer is small.

  The laminated steel sheets described in Patent Documents 5 to 8 are metal plates intended for building material panel applications such as heat insulation panels and sound insulation panels for construction, and are considered to be effective as panel-like parts. It is done.

  However, since the honeycomb structure which is the core layer of the laminated steel sheets described in Patent Documents 5 to 8 is a structure in which the metal foil and the ultrathin board are arranged perpendicular to the surface steel sheet, the force in the direction perpendicular to the surface steel sheet ( A large resistance force is exerted on the compression force), but it is very weak against a force parallel to the surface steel plate (shear force). As a result, when strong processing such as bending is performed after lamination, the core layer often undergoes shear failure and often becomes a defect.

  In addition, the laminated steel sheet described in Patent Document 9 defines a suitable porosity of the fibrous porous body constituting the core layer, and is intended to realize light weight and high rigidity in a balanced manner. it is conceivable that.

  However, Patent Document 9 does not define any appropriate structure of the core layer (particularly, the structure of the holes). Also, when the core layer is porous, the portion of the surface steel plate laminated on the pores in the core layer is weaker than the portion laminated on the filled portion in the core layer. . As a result, if a core layer with an appropriate structure is not formed, stress concentrates on the portion laminated on the pores during tensile deformation, and the elongation decreases, or the surface steel plate falls into the pores during bending deformation. In some cases, it may cause defects.

  Further, in the structure described in Non-Patent Document 1, since short fiber fibers are used, the yield strength and shear strength of the core layer are small, and defects are often generated during strong processing.

  In addition, the laminated steel sheet described in Patent Document 10 is considered to be lightweight and capable of increasing the yield strength of the core layer by using a wire mesh using a steel wire having a high tensile strength as compared with a sheet.

  However, when the core layer thickness is increased, it is necessary to increase the wire diameter of the wire, and it is considered that the light weight effect may be reduced with a wire mesh spacing that can maintain good workability.

  Moreover, it is thought that the laminated steel plates described in Patent Documents 11 to 12 can increase the bonding strength between the core layer and the steel sheet by the wire mesh between the steel sheets during seam welding.

  However, in Patent Documents 11 to 12, since the core layer is crushed to increase the bonding strength, it is difficult to maintain the thickness of the core layer, and it is difficult to increase the rigidity efficiently.

  Moreover, it is thought that the laminated steel plate described in Patent Document 13 can increase the core layer thickness without increasing the wire diameter by processing the wire mesh into a corrugated shape.

  However, in Patent Document 13, a method for processing a wire mesh is not defined, and when the corrugated shape is formed by processing, the core layer has directionality, and thus the plate on which the core layer is laminated has a large anisotropy.

  Thus, the laminated steel plates that have been proposed so far have light weight, high rigidity, high impact resistance, small anisotropy, and excellent workability (shear workability, bending workability, deep drawing) There has been a problem that not all the performances such as the property, the stretchability and the like and the excellent shape stability after processing have been satisfied.

  Therefore, the present invention has been made in view of such problems, is lightweight, has high rigidity and impact resistance, has low anisotropy, and has workability such as shearing, bending, deep drawing, and overhanging. It aims at providing the laminated steel plate which is excellent in the shape stability after a process.

  As a result of intensive studies to solve the above problems, the inventors of the present invention laminated a truss structure using a steel wire, and further controlled the composition of the steel wire and the shape of the truss structure, thereby reducing the weight. The present invention has been completed on the basis of this finding, and has found that all of excellent workability and excellent shape stability after processing can be satisfied.

The present invention has the following gist.
(1) A laminated steel sheet, wherein a truss structure made of a steel wire is laminated between steel sheets.
(2) The laminated steel sheet according to (1), wherein a carbon concentration is at least 0.24% by mass among the components of the steel wire rod.
(3) The laminated steel sheet according to (1) or (2), wherein a carbon concentration is at least 0.60% by mass among the components of the steel wire rod.
(4) The laminated steel sheet according to any one of (1) to (3), wherein the distance between the vertices of the truss structure is 30 times or less the thickness of the steel sheet.
(5) The laminated steel sheet according to any one of (1) to (4), wherein the distance between the vertices of the truss structure is 10 times or less the thickness of the steel sheet.
(6) The laminated steel sheet according to any one of (1) to (5), wherein an angle formed between the wire constituting the truss structure and the steel sheet is 30 ° to 60 °.
(7) The laminate according to any one of (1) to (6), wherein the truss structure and the steel plate are joined together with a blaze material or an adhesive having a melting point of 400 ° C. or less. steel sheet.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide a laminated steel plate with lightweight and large rigidity by arrange | positioning a steel plate on both surfaces of the truss structure which consists of steel wires. Furthermore, by configuring the core layer with a truss structure made of steel wire, while suppressing an increase in weight, the void of the core layer that becomes a processing defect portion of the laminated steel sheet is reduced, and a quasi-isotropic core layer and By doing so, it becomes possible to provide a laminated steel sheet having excellent workability.

It is a side view of the laminated steel plate which concerns on embodiment of this invention. It is a schematic diagram of the laminated steel plate which concerns on embodiment of this invention. It is a mimetic diagram of a truss concerning an embodiment of the present invention. It is a mimetic diagram of a truss structure object concerning an embodiment of the present invention. It is a top view of the wire mesh which concerns on embodiment of this invention.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[Configuration of laminated steel sheet]
As shown in FIGS. 1 and 2, the laminated steel sheet 1 according to the present embodiment has a structure in which steel sheets (hereinafter referred to as “surface steel sheets”) 5 (5A, 5B) are laminated on both surfaces of a core layer 10, respectively. That is, the core layer 10 is laminated on the surface steel plate 5 </ b> A, and the surface steel plate 5 </ b> B is laminated on the core layer 10. The core layer 10 is a truss structure 11 made of a steel wire. When the core layer 10 is composed of two truss structures, these truss structures are stacked in a state where the vertices of the truss structure 11 are in contact with each other, or the vertices of the truss structure are overlapped. It consists of a structure that is arranged in a state that does not become.

  Since the core layer is a truss structure made of a steel wire material, voids can be introduced in the plane direction (direction perpendicular to the plane of FIG. 1) and the thickness direction. As a result, the density can be greatly reduced as compared with a single metal, and the weight of the laminated steel sheet can be reduced. Similarly, even if a core layer processed with a metal plate is compared with a truss structure, the former is a surface, whereas the latter is a wire, so the truss structure can be made lighter. .

  There is a wire mesh as a structure made of a wire, but the truss structure and the wire mesh of the present invention are distinguished by the following structural differences.

  In the case of a normal wire mesh, the intersection of the vertical line and horizontal line of the wire rod completely overlaps, so that there is no gap in the thickness direction in that part, and the product thickness is the diameter of the wire rod constituting the wire mesh. Doubled. In addition, the space | gap of the thickness direction in this case is defined as a space | gap, when it is 1/5 or more of core layer thickness.

  On the other hand, in the case of the truss structure, since the intersection portion is bent, a gap can be introduced in the thickness direction, and the weight can be reduced efficiently.

Moreover, although mentioned later in detail, in the laminated steel plate 1 which concerns on this embodiment, a carbon concentration is at least 0.24 mass% among the components of the steel wire which comprises the truss structure 11, and truss structure It is preferable that the distance W between vertices is 30 times or less of the thickness ts of the surface steel plate 5 and the angle θ ₁ between the steel wire constituting the truss structure 11 and the surface steel plate 5 is 30 ° or more and 60 ° or less. In addition, in FIG. 1, the core layer 10 has shown the example which consists of one truss structure. Hereinafter, each member which comprises the laminated steel plate 1 is demonstrated in detail.

[Composition of steel wire]
Here, among the components of the steel wire constituting the truss structure 11 in the present embodiment, the carbon concentration is preferably at least 0.24% by mass. By setting the carbon concentration of the steel wire to 0.24% by mass or more, the tensile strength of the steel wire can be secured, and the steel wire density in the core layer 10 is required (plate density (of the steel wire in the core layer 10). The tensile strength and the yield strength of the core layer 10 (in this embodiment, the truss structure 11) required for processing the laminated steel sheet 1 and the processed product can be ensured even if the mass ratio is reduced to (mass ratio). Therefore, the laminated steel sheet 1 can be sufficiently reduced in weight while keeping the rigidity and impact resistance of the laminated steel sheet 1 high. Further, since the tensile strength of the steel wire can be increased by increasing the carbon concentration and the tensile strength of the core layer can be further strengthened, the carbon concentration of the steel wire is at least 0.60% by mass (0 .60% by mass or more). However, when the carbon concentration of the steel wire exceeds 0.86% by mass, the ductility of the steel wire decreases, and when the laminated steel sheet is processed, the core layer may be broken. The upper limit of the concentration is preferably 0.86% by mass or less.

  On the other hand, if the carbon concentration of the steel wire is less than 0.24% by mass, the tensile strength and yield strength of the steel wire are reduced, and this is required unless the steel wire strength in the core layer 10 is increased and reinforced. Thus, the tensile strength and yield strength of the core layer 10 cannot be ensured, and the weight reduction of the laminated steel sheet 1 may be insufficient. Specifically, as the steel wire, one containing a steel component specified in JIS-G-3506 (2004) can be suitably used, but is not limited thereto, and the steel wire satisfying the above carbon concentration. If it is, it can be used as a steel wire constituting the truss structure 11 according to the present embodiment.

[Configuration of truss structure]
First, the configuration of the truss structure 11 according to the present embodiment will be described in detail with reference to FIGS. FIG. 3 is an explanatory diagram showing an example of the configuration of the truss structure 11 according to the present embodiment, where (a) is an n-pyramidal truss, (b) is a quadrangular pyramid truss, and (c) is a triangular pyramid truss. Is shown. FIG. 4 is an explanatory view schematically showing the truss structure body 11 according to the present embodiment.

  As shown in FIGS. 3 and 4, the truss structure 11 is a structure in which n-pyramidal trusses formed by n bars of equal length connected at one point are periodically continuous. The rod needs to be made of the steel wire, and a truss structure formed of a triangular pyramid truss made of three steel wires as shown in FIG. , A), and a truss structure composed of four pyramid trusses made of four steel wires as shown in FIG. 3B is called a quadrangular pyramid (FIG. 4, b). In addition, among the n-pyramid trusses, trusses having equal lengths connecting the n rod ends are referred to as regular n-pyramidal trusses, and a truss structure in which regular n-pyramidal trusses are periodically continued. The body is called a regular n-pyramidal truss structure. From the viewpoint of reducing the influence of anisotropy, a preferable truss structure is a regular n-pyramidal truss structure. Considering the balance between the weight and strength of the core layer, a triangular pyramid truss structure is preferable, and a regular quadrangular pyramid truss structure is more preferable. In addition, as will be described in detail later, since the truss structure is made of steel wire, it suppresses the increase in weight, reduces the voids in the core layer directly below the surface steel plate (the cause of surface steel plate intrusion), and is a quasi-isotropic core Layers can be built.

  Here, since the truss structure is a structure in which n pyramids are periodically continuous with n steel wires, the wire diameter of the wire mesh steel wire is larger than that of a conventionally used wire mesh. Therefore, since the core layer thickness can be increased and voids can be introduced in the thickness direction of the core layer, further weight reduction can be expected. In addition, since the core layer is a truss structure, the anisotropy is reduced because the air gap is isotropically arranged as compared with the corrugated plate in which the air gap is continuous in a certain direction.

For example, as shown in FIG. 2, a portion where the n steel wires of the truss structure 11 are connected is referred to as a vertex 113 of the truss structure 11. The inter-vertex distance W of the truss structure 11 is the distance between the apexes of the adjacent truss structures 11. For example, in the case of a quadrangular pyramid truss structure, the longitudinal direction (that is, the longitudinal direction of the surface steel plate 5). of the vertex distance W _L of the truss structure _11, the width direction (i.e., the width direction of the surface layer steel plate 5) sometimes to distinguish path length of the truss structure 11 and W _B.

Here, vertex distance W _L of the truss structure _11, the portion of W _B becomes a void layer portion right under the surface layer steel laminated steel 1, the compression resistance is lowered. As a result, at the time of processing the laminated steel sheet 1, the surface steel sheet may intrude into the core layer void portion of the surface steel sheet. Therefore, from the viewpoint of preventing the intrusion of the surface steel plate, the inter-vertex distance W is preferably 30 times or less, more preferably 10 times or less the thickness ts of the surface steel plate 5. However, if the distance between the vertices is reduced, there is a concern about an increase in the specific gravity of the plate. Therefore, in order to achieve both lightness and workability, the distance between the vertices of the truss structure is 5 times or more the thickness ts of the surface steel plate. It is desirable.

Incidentally, the four case of pyramidal truss structure, vertex distance W _L, W _B are different, there is a possibility that the distance anisotropy in compression resistance is too big difference occurs. Thus, the preferred _{W L} and _{W B} ratio _(W L / _{W B)} is preferably 0.5 to 2.0. For truss structure quadrangular pyramid type, vertex distance W _L, at least one of W _B is 30 times or less than 5 times the thickness ts of the surface layer steel (more preferably, 10 times or less) enough., It is more preferable that both the vertex distances W _L and W _B are 5 times or more and 30 times or less (more preferably 10 times or less) the thickness ts of the surface steel plate.

Moreover, as shown in FIG. 3, the angle | corner which the steel wire and the surface steel plate which comprise a truss structure make is called (theta) ₁ . Here, when the laminated steel sheet 1 is bent and deformed, a compressive force and a shearing force in the thickness direction are generated in the core layer 10. When the compressive strength of the core layer 10 is small, the core layer 10 of the laminated steel sheet 1 is crushed and it is difficult to maintain the thickness of the core layer. As a result, it becomes difficult to develop desired mechanical properties, and molding defects occur during processing. Moreover, when the shear strength of the core layer 10 is small, it becomes difficult for the surface steel plates 5 on both sides of the core layer 10 to be integrally deformed, and the bending rigidity and strength of the laminated steel plates are reduced. Accordingly, it is necessary to improve the compressive strength and shear strength of the core layer 10. From this viewpoint, the angle θ ₁ formed by the steel wire and the surface steel plate is preferably 30 ° or more and 60 ° or less, and more preferably 45 ° or more and 60 ° or less.

  As described above, the truss structure body 11 constituting the core layer 10 according to the present embodiment may be one or two may be laminated. When stacking two truss structures, it is possible to promote weight reduction of the core layer by stacking the trusses so that the vertices of the trusses overlap, and fixing the vertices of the truss structure with a bonding material. is there.

  In addition, by arranging the two truss structures so that the vertices of the truss structure do not overlap, it is possible to reduce the distance between the truss vertices and improve the workability while preventing the intrusion of the surface steel plate. . Specifically, in the case of a regular quadrangular pyramid truss structure, it is possible to arrange one truss structure to be arranged without overlapping by rotating 45 degrees in the plate width direction. Further, in the case of a triangular pyramid truss structure, it can be arranged without overlapping by rotating 180 ° in the plate width direction.

  When two truss structure bodies 11 are laminated, each truss structure body 11 can be joined by using an adhesive, a blaze agent, or the like, which will be described later.

  The height of the truss structure is not particularly limited, but the height t of the truss structure is preferably 1 mm or more and 5 mm or less in consideration of the balance between the workability of the laminated steel sheet and the lightening effect.

The truss formation method, as long as it satisfies the angle theta ₁ conditions the carbon concentration and the truss structure of the steel wire rod described above, forming method is not particularly limited. For example, a connecting portion of n steel wire rods is fixed with a bonding material, an n-pyramidal truss is manufactured, and the truss structure is formed by continuously arranging the trusses and fixing the intersections of the steel wires of adjacent trusses with the bonding material. The body is obtained. There is also a method for forming a truss structure by bending an intersection of a wire mesh made of a steel wire rod. Compared to the method of forming a truss structure with a bonding material, the method of forming a truss structure by bending makes it possible to produce a truss structure with a large area at once by bending. From this point of view, a method of forming a truss structure by bending a wire mesh made of a steel wire is more preferable. Examples of suitable forms of the truss structure that can be formed by processing a wire mesh made of a steel wire material include a triangular pyramid shape, a regular quadrangular pyramid shape, and a quadrangular pyramid type truss structure. The structure of the wire mesh used for forming the truss structure will be described later.

[Composition of wire mesh]
First, the configuration of the wire mesh 12 suitable for forming the truss structure will be described in detail with reference to FIG. FIG. 5 is an explanatory view showing an example of the configuration of the wire mesh 12 according to the present embodiment, and shows a plan view.

  As shown in FIG. 5, the wire mesh 12 is knitted so that the vertical lines 111 and the horizontal lines 112 of the steel wire intersect. Here, as shown in the figure, the vertical line 111 means a steel wire that runs in the x direction among all the steel wires constituting the wire mesh 12, and the horizontal line 112 means all the steel that constitutes the wire mesh 12. Among the wire rods, it means a steel wire rod that runs in the y direction intersecting with the vertical wire 111.

The distance l (vertical direction, horizontal direction, diagonal direction) between the intersections of the vertical line 111 and the horizontal line 112 of the steel wire 12 of the wire mesh 12, the wire diameter d of the steel wire, and the angle θ ₂ formed by the vertical line 111 and the horizontal line 112 are However, it is not particularly limited, and can be determined as appropriate depending on the desired core layer thickness and the angle θ ₁ formed by the steel wire constituting the truss structure 11 and the surface steel plate.

  In addition, the wire diameter d of the vertical line 111 and the horizontal line 112 may not be the same as long as it does not impair the light weight effect. However, the preferable ratio of the wire diameters (the wire diameter of the vertical line 111 / the wire diameter of the horizontal line 112) is 0.8 or more and 1.2 or less.

  The shape of the wire mesh 12 can be appropriately determined depending on the shape of the truss structure. For example, a square wire mesh is preferable for a quadrangular pyramid truss structure, a diamond wire mesh is used for a square pyramid truss structure, and a turtle-shaped wire mesh is preferable for a triangular pyramid truss structure. Further, as a method of forming the wire mesh 11, it is not limited to weaving or knitting, but welding may be used. That is, the vertical line 111 and the horizontal line 112 may be joined by welding to form a net shape.

  When forming a truss structure by bending a wire mesh, it is more preferable to select a wire mesh forming method in consideration of the ductility of the steel wire rod. For example, in the case of a low ductility steel wire, the steel wire may break during bending. Therefore, by selecting a wire mesh in which the intersection point of the vertical line and the horizontal line of the wire mesh is not fixed, a shift deformation occurs at the intersection point, and breakage can be prevented. Therefore, in the case of a wire mesh made of a low ductility steel wire material, a weld wire mesh in which the intersection is welded may be inappropriate. In addition, when the intersection is joined with a bonding material such as an adhesive, the shape of the truss structure can be prevented while preventing breakage of the steel wire by using a bonding material having a deformability capable of withstanding the displacement deformation during bending. This is preferable because it can be maintained.

[Bonding material]
Next, in this embodiment, the joining of the truss structure 11 and the surface steel plate 5 will be described.

  First, a suitable adhesion force between the truss structure 11 and the surface steel plate 5 can be evaluated by peel strength. However, the truss structure 11 and the surface steel plate 5 in this embodiment have a peel strength of 5 N / cm or more. It is preferable to be joined. When the peel strength is less than 5 N / cm, the surface steel plates 5 on both surfaces of the core layer 10 are not deformed integrally when the laminated steel plate 1 is bent or tensile deformed, and the rigidity and bending strength of the laminated steel plate 1 are exhibited. It may not be possible to In order to reduce the deviation of the surface steel sheets on both surfaces of the core layer 10 due to shear during bending deformation of the laminated steel sheet 1, the peel strength is more preferably 25 N / cm or more, further preferably 40 N / cm or more, It is still more preferable to set it as 40 N / cm-60 N / cm. Here, if the strength is 60 N / cm, the surface steel plate and the core layer will not peel at the time of strong processing, so even if the peel strength is increased, the effect becomes saturated and uneconomical, so the upper limit is 60 N / Cm is preferable. The peel strength can be evaluated by a T peel test based on JIS-Z-0238. Here, the peel strength is a value obtained by dividing the maximum load at the time of peeling by the width of bonding.

  As a method for joining the truss structure 11 and the surface steel plate 5, a known steel joining method can be applied. Specifically, for example, adhesive joining, blaze joining, seam welding, or the like can be used. .

  In the case where the truss structure 11 and the surface steel plate 5 are bonded by adhesive bonding, an adhesive is used as a bonding material. However, in order to maintain heat-resistant shape stability even after processing, the adhesive 100 ° C to 160 ° C. The storage elastic modulus G ′ is preferably 0.05 MPa or more and 100 GPa or less. If it is less than 0.05 MPa, when the molded product of the laminated steel sheet 1 is heated to the temperature (100 ° C. to 160 ° C.) due to the residual stress at the steel sheet / adhesive interface generated when the laminated steel sheet 1 is formed, the adhesive layer May creep deform, and the adhesive layer may be destroyed, or peeling may be caused starting from the adhesive layer. In order to more reliably prevent creep deformation of the adhesive layer, G ′ is more preferably 1.0 MPa or more, and G ′ is more preferably 5 MPa or more. On the other hand, if it exceeds 100 GPa, the G ′ at room temperature becomes larger, so that the process following ability is deteriorated and breaks at the time of processing, and there is a possibility that peeling starting from the adhesive layer is likely to occur. The storage elastic modulus G ′ of the adhesive can be evaluated by the maximum value of the storage elastic modulus of the adhesive measured at a frequency of 0.1 to 10 Hz. In the case of a thermosetting adhesive, an adhesive film that has been crosslinked and cured by applying the same heat history as the lamination conditions is used. In the case of a thermoplastic adhesive, the adhesive film is formed into a known dynamic viscosity. It can be measured with an elasticity measuring device.

  Further, the ratio tan δ (= G ″ / G ′) of the loss elastic modulus G ″ and the storage elastic modulus G ′ at 100 ° C. to 160 ° C. of the adhesive is preferably tan δ <1, and tan δ <0.8. Is more preferable, tan δ <0.5 is further preferable, and tan δ <0.1 is even more preferable. As tan δ is smaller, even when heated, creep deformation of the adhesive layer due to residual stress can be suppressed, and the shape can be stabilized. When tan δ ≧ 1, when the processed product is heated to 100 ° C. to 160 ° C., the adhesive layer may viscously flow, the shape may become unstable, or creep deformation breakage may cause separation.

  In addition, from the viewpoint of ensuring the heat resistance and durability of the adhesive, a structural adhesive based on an epoxy resin is preferable. Among them, a one-component heat curable adhesive preliminarily mixed with a curing agent is a handling property. From the viewpoint of, it is further preferable.

  Moreover, as an adhesive used for joining the truss structure 11 and the surface steel plate 5 in the present embodiment, a conductive adhesive is preferable from the viewpoint of ensuring the weldability of the laminated steel plate 1. Examples of the conductive adhesive include those obtained by adding a predetermined amount of metal powder such as aluminum powder, nickel powder, and iron powder to the adhesive as described above.

  In the case where the truss structure 11 and the surface steel plate 5 are joined by blaze joining, a blaze agent is used as a joining material. Examples of the blaze agent usable at this time include lead, tin, antimony, and cadmium. Soft solder (solder) made of an alloy such as zinc, Ni-Cr solder, copper brazing, gold brazing, palladium brazing, silver brazing, aluminum brazing, and the like.

  When joining the truss structure 11 and the surface steel plate 5 by welding, a known welding method can be used. Specific welding methods include, for example, resistance welding such as spot welding and seam welding, Examples include electron beam welding, laser welding, and arc welding.

  In order to maintain the strength of the steel wire rod of the truss structure 11, it is important to maintain the initial metal structure of the steel wire rod. From such a viewpoint, the joining temperature when joining the wire mesh 11 and the surface steel plate 5 is preferably 400 ° C. or less, and more preferably 300 ° C. or less, at which no phase transition of the steel structure of the steel wire material occurs. Preferably, it is 200 degrees C or less, More preferably, it is 100 degrees C or less. Moreover, if the metal mesh 11 and the surface steel plate 5 can be joined at 100 ° C. or lower, the bake hardening of the surface steel plate 5 can be prevented, and strong processing becomes easy.

  Furthermore, as a method for joining the truss structure 11 and the surface steel plate 5, it is particularly preferable from the viewpoint of ensuring the productivity and weldability of the laminated steel plate 1 that the joining is performed with a heat-resistant conductive adhesive or the melting point. Is joining with a blaze agent (for example, solder) of 400 ° C. or lower.

[Configuration of surface steel plate]
Although it does not specifically limit as the surface steel plate 5 which concerns on this embodiment, Specifically, steel plates for cans, such as tinplate, a thin tin plating steel plate, an electrolytic chromic acid processing steel plate (tin free steel), a nickel plating steel plate, etc., for example. And hot dip galvanized steel sheets, hot dip galvanized steel sheets, hot dip zinc-aluminum-magnesium alloy plated steel sheets, hot dip aluminum-silicon alloy plated steel sheets, hot lead-tin alloy plated steel sheets, etc. Use surface-treated steel sheets, cold-rolled steel sheets, hot-rolled steel sheets, stainless steel sheets, etc., such as steel plates, electro-galvanized nickel-plated steel plates, electro-zinc-iron alloy-plated steel plates, electro-zinc-chromium alloy-plated steel plates Can do. Further, the surface steel plate 5 may be a surface-treated steel plate such as a coated steel plate, a printed steel plate, or a film laminated steel plate.

  Further, the core layer 10 can be laminated between steel plates of different steel types. Specifically, in applications that require bending, drawing, etc., the core layer 10 is laminated between steel plates with different strengths, mild steel is used for the hard surface with a small radius of curvature, and strength is applied to the other surface. For securing, it is possible to use high-strength steel.

  In addition, a known surface treatment can be applied to the surface of the surface steel plate 5 according to the present embodiment in order to improve adhesion and corrosion resistance. Examples of such surface treatment include, but are not limited to, chromate treatment (reaction type, coating type, electrolysis) and non-chromic treatment, phosphate treatment, organic resin treatment, and the like.

  Moreover, the thickness of the preferable surface steel plate 5 is 0.2 mm-2.0 mm. If the thickness of the surface steel plate 5 is less than 0.2 mm, it may be easily buckled during bending. On the other hand, when the thickness of the surface steel plate 5 exceeds 2.0 mm, the lightening effect tends to be insufficient. From the viewpoint of weight reduction, the thickness of the surface steel plate 5 is preferably 1.0 mm or less.

  Furthermore, the thickness of the surface steel plates 5A and 5B may not be the same as long as the light weight effect is not impaired. By increasing the thickness of one of the surface steel plates 5A and 5B, it becomes easy to avoid buckling and fracture of the surface steel plates during strong working. The preferred ratio of the thickness of the surface steel plates 5A and 5B (the thickness of the surface steel plate 5A / the thickness of the surface steel plate 5B) is 0.8 or more and 1.2 or less.

  In addition, when the surface steel plates are different, the distance between the vertices of the truss structure described above is defined based on the thinner plate thickness.

[Production method]
As mentioned above, although the structure of the laminated steel plate 1 which concerns on one Embodiment of this invention was demonstrated in detail, the manufacturing method of the laminated steel plate 1 which has the above structures is demonstrated in detail continuously.

  The laminated steel sheet 1 according to the present embodiment can be manufactured by applying a known steel sheet laminating method. Specifically, it can be produced by the following steps.

(1) As described above, a truss structure is manufactured using a steel wire.
(2) A bonding material (adhesive, blaze agent, etc.) is applied to both surfaces of the core layer 10 (truss structure composed of one or two or more wire meshes 11) as necessary, and the surface steel plate 5A and the core layer 10 are applied. Then, the surface steel plates 5B are laminated in this order, and are pressurized at room temperature or while heating.

  In the step (2), it is also possible to apply a bonding agent to one surface of the surface steel plates 5A and 5B, sandwich the core layer between the applied surfaces and laminate them, and pressurize while producing at normal temperature or heating.

  In addition, since specific examples of the bonding material and the bonding method are as described above, detailed description thereof is omitted here.

  As described above, the laminated steel sheet according to the present embodiment can provide a laminated steel sheet that is lightweight, has high rigidity, and is excellent in workability by disposing steel sheets on both sides of a truss structure made of steel wire. It becomes possible.

  Furthermore, by setting the carbon concentration to at least 0.60% by mass among the components of the steel wire rod, the tensile strength of the core layer is improved, and the strength and impact resistance of the laminated steel sheet can be further enhanced. It becomes.

  Furthermore, the distance between the vertices of the truss structure is set to 10 times or less of the thickness of the steel sheet, and the angle between the steel wire constituting the truss structure and the steel sheet is controlled to 30 ° to 60 °. Further strong processing such as processing becomes possible.

  Furthermore, the shape stability after processing is further improved by joining the truss structure and the steel plate using a blaze agent or an adhesive having a melting point of 400 ° C. or less.

  Hereinafter, the present invention will be described more specifically with reference to examples.

(Used steel plate, truss structure, joining method of truss structure and steel plate)
In this example and a comparative example, the steel plate shown in Table 1 was used, the wire mesh using the steel wire shown in Table 2 was processed into the truss structure shown in Table 3, and the laminated steel plate was manufactured. Moreover, as for the bonding agent between the truss structure and the surface steel plate, a structural adhesive (base material: epoxy resin, coating amount 200 g / m ² , storage elastic modulus 1-30 MPa, tan δ 0.3), solder (low-temperature brazing agent) , Sn-Pb series, melting point 183 ° C.) Blaze agent 1 (15 g / m ² ), Ni—Cr series brazing agent (trade name: Coclburn 2003, melting point 1040 ° C.) Blazing agent 2 (15 g / m ² ) And used each.

(Manufacture of laminated steel sheets)
As a specific manufacturing method of the laminated steel sheet in this example and comparative example, the laminated material in the order of the joining material and the wire mesh produced by processing the joining material and the wire mesh on the 300 mm × 300 mm surface steel sheet, Increase to a predetermined temperature under vacuum (180 ° C when adhesive is used as bonding material, 300 ° C when blaze agent 1 is used as bonding material, 1100 ° C when blaze agent 2 is used as bonding material). Warm up. Subsequently, the laminated surface steel plates, the bonding material, and the truss structure are heat-bonded for 20 minutes with a pressure force of 10 to 40 kgf / cm ² (0.98 to 2.92 MPa), then cooled to room temperature and opened to the atmosphere. Each laminated steel plate shown in Table 4 was obtained.

  In addition, the laminated steel plate of Example 18 was thermocompression bonded after laminating the same joining material used between the steel plate and the truss structure also between the truss structure vertices, They were joined together. Further, in order to arrange the laminated steel plates of Example 19 so that the apexes of the two truss structures do not overlap, one truss structure is rotated by 45 ° in the plate width direction, and the two truss structures are The laminated steel sheet was obtained by the same method as in Example 1.

  In addition, for the truss structures 14 and 15 in Table 3, six steel wire rods 1 having a length of 1.7 mm and 3.5 mm are used, respectively. First, the connecting portions of the six steel wire rods are joined together (soft brazing material). , Sn—Pb system) to prepare a hexagonal pyramid truss. Then, the laminated steel plate was obtained in the procedure similar to the above. In addition, the plate was sandwiched between the heating plates so as to have a predetermined thickness between the upper and lower surface steel plates at both ends of the laminated steel plate, and heat-pressed for 20 minutes, and then cooled to room temperature and released into the atmosphere to obtain a laminated steel plate. .

(Comparative Example 1)
Laminated steel sheets with a wire mesh (porosity: 66%, plate density: 0.26 g / cm ² ) made of a steel wire (carbon concentration: 0.26% by mass) with a wire diameter of 0.5 mm and a tensile strength of 1000 MPa as a core layer Prepared as in Example 1.

(Comparative Example 2)
According to Patent Document 4, a steel sheet having a thickness of 0.2 mm (tensile strength: 270 MPa) was subjected to dimple processing to give square-shaped irregularities of 2 mm × 2 mm × height 0.5 mm at intervals of 2 mm. A depression of 0.5 mm × 0.5 mm × depth 0.2 mm was provided in the center of the convex portion. The blaze agent 2 was applied to the convex portions, and two dimple processing plates were laminated so that the convex portions were in contact with each other. A steel plate coated with blazing agent 2 (tensile strength: 300 MPa, hot dip galvanized steel plate, weight per unit area: 60 g / m ² ) is laminated on both sides of the laminated steel plate, and heated and pressed under the same conditions as in Example 20 to laminate A steel plate was obtained. In addition, the dimple process which provides the unevenness | corrugation of the said size with the high-tensile steel of intensity | strength exceeding 270 Mpa was impossible.

(Comparative Example 3)
A laminated steel sheet having a SUS honeycomb (SUS thickness: 0.1 mm, honeycomb shape: regular hexagon, total thickness: 1 mm, density 0.28 g / cm ³ ) as a core layer was produced in the same manner as in Example 1.

(Comparative Example 4)
A surface layer steel sheet (tensile strength 300 MPa, hot dip galvanized steel sheet, plated, with a corrugated surface of 0.3 mm thick (tensile strength: 270 MPa) and 1 mm height applied with adhesive. A basis weight of 60 g / m ² ) was laminated and heated and pressed under the same conditions as in the example to obtain a laminated steel sheet. Since the corrugated plate is used as a core layer, voids are continuous in a certain direction. Therefore, two types of laminated steel sheets were prepared so that the gaps were continuous in the longitudinal direction and the width direction, respectively.

(Physical properties, processing / weldability test of laminated steel sheets)
A test piece (25 mm × 150 mm) was cut out from the laminated steel sheet of each example obtained as described above in accordance with ASTM D-790, the distance between fulcrums was set to 50 mm, and the speed was set to 5 mm / min. The test was conducted. Since the laminated steel plates of Examples 3 to 6, 18 and 27 have different truss apex distances W in the longitudinal direction and the width direction, the test pieces were placed so that W was in the longitudinal (W _L ) and width (W _B ) directions, respectively. Cut out. The bending stiffness D was calculated by substituting the slope k of the measured strain-load curve (calculated using a load up to 1/3 of the maximum load) into the equation (i). Further, the bending moment M in the plastic region of the laminated steel sheet was calculated by the equation (ii). In addition, since it is known that the impact resistance of the steel sheet has a correlation with the bending moment in the plastic region, the bending moment in the plastic region calculated by the equation (ii) was used as an index of impact resistance.

^{D = kl 3/48 ··· (} i)
M = Pl / 4b (ii)

  Here, in the above formulas (i) and (ii), P: measured maximum bending load, l: distance between fulcrums, and b: width of test piece.

  Further, a 125 mm × 30 mm test piece was cut out from the laminated steel sheets of Examples 1 to 27, and a square deep drawing experimental apparatus (r = 100 mm, BHF (blank hold force): 2 ton) of an Erichsen 20T comprehensive testing machine. A U-shaped hat bending specimen was prepared.

Since the laminated steel sheets of Examples 3 to 6, 18, and 27 have different truss apex distances W in the longitudinal direction and the width direction, the test pieces should be arranged so that W is in the longitudinal (W _L ) and width (W _B ) directions, respectively. Cut out.

  Further, a test piece (150 mm × 30 mm) was cut out from the laminated steel plates of Examples 1 to 9, 13, 15 to 23, and 25 to 27, two test pieces were laminated by 30 mm square, and the center of the laminated portion was pressurized. Spot welding was performed under the conditions of 3.5 kN, current 6.2 kA, and energization time 10 cycles. The spot-welded test piece was subjected to a shear tensile test with a 50 kN universal tensile tester manufactured by Shimadzu Corporation at a tensile speed of 5 mm / min.

(Evaluation)
<1. Lightweight evaluation>
The plate density ρ of each laminated steel plate was calculated by dividing the measured mass by the area of the sample.

Furthermore, the rigidity D obtained in (i) formula to calculate the plate thickness t _p of the surface layer steel sheet alone required to express the same flexural rigidity and laminated steel with (iii) wherein the area of the unit the mass _{W p} per obtained in (iv) expression. The lightness when the bending rigidity was made constant was evaluated by the ratio (W / W _p ) of the mass W per unit area of the laminated steel sheet and the mass W _p per unit area of the steel sheet of the formula (iv).

t _p = 12D / E _s (iii)
_{W p = ρ s t p ···} (iv)

Here, in (iii) above formula and (iv) expression, _{E s} is Young's modulus of the surface layer steel (210 GPa in this embodiment), _{W p} is per unit area of the steel plate having the same stiffness and laminated steel plate Mass.

<2. Evaluation of bending rigidity and impact resistance>
Rigidity D _p of the steel sheet itself having a mass W and the same weight per unit area of the laminated steel sheet was calculated by (v) expression. Further, the ratio (D / D _p ) between the rigidity D _p obtained by the equation (v) and the rigidity D of the laminated steel sheet was calculated, and the rigidity of the laminated steel sheet was evaluated (if D / D _p > 1, the steel sheet It is estimated that the rigidity is reasonably increased compared to the case of the single case).

^{_{D p = E s t p 3}} /12 ··· (v)

Similar to the evaluation of bending rigidity, the bending moment M _{p of a} single steel plate having the mass per unit area is calculated by the equation (vi), and the ratio of M _p to M obtained by the equation (ii) (M / M _p ), the magnitude of impact resistance was evaluated (if M / M _p > 1, it is evaluated that the impact resistance is reasonably increased compared to the case of a steel sheet alone).

^{_{M p = T S t p 2}} /4 ··· (vi)

  Here, in the above formula (vi), Ts is the tensile strength of the surface steel plate.

<3. Evaluation of processing soundness>
Observe the cross-section of the hat bend specimen visually and with an actual microscope, peeling the surface steel plate, breaking the surface steel plate and invading the core layer (the surface steel plate biting into the pores of the core layer), damage to the core layer The presence or absence was inspected, and when there was no abnormality, it was evaluated that it was excellent in processing soundness, and it was indicated by ○ in Table 5 (hat bending column). Moreover, the said processed piece was inserted into the oven heated at 180 degreeC, and after hold | maintaining for 30 minutes, it took out from the oven and cooled to normal temperature. Heated shape soundness after processing (peeling of surface steel plate, core layer destruction) is evaluated, and if all are normal, it is evaluated that heat shape soundness is excellent, and in Table 2 (180 ° C heat resistant column) ○ indicates. In addition, the fracture | rupture of a surface steel plate shows that a crack arises on the surface of a surface steel plate, and it fractures. In addition, the intrusion into the core layer of the surface steel plate is related to the bending radius R of the upper and lower surface steel plates in the vicinity of the bending deformation portion (upper surface steel plate bending radius R) = (lower surface steel plate bending radius R) + (core layer) The case where the (thickness) was not satisfied was judged as an intrusion of the surface steel plate. The determination of the fracture of the core layer after processing was made by observing the presence or absence of breakage of the steel wire from the X-ray photograph of the test sample.

<4. Evaluation of spot weldability>
When spot welds are evaluated for external appearance (defects such as cracks and blisters) and shear tensile tests are performed, and the weldability is evaluated by observing the appearance defects and the delamination form. Is indicated by ○ in Table 5 (spot weldability column). Appearance defects include swelling around the weld and peeling due to welding of the surface steel plate to the spot welding electrode.

(Evaluation results)
The above evaluation results are shown in Table 5.

The laminated steel plates of Examples 1 to 27 have W / W _p <1.0, and it was found that the plate density is small and the light weight is excellent as compared with steel plates having the same rigidity. Furthermore, the laminated steel plates of Examples 1 to 27 have D / D _p > 1.0 and M / M _p > 1.0, and the bending rigidity and the bending moment in the plastic region are higher than those of the same plate density. It was found to be large, highly rigid and excellent in impact resistance.

Furthermore, the laminated steel plates of Examples 1 to 3, 5 to 23, and 27 have no hat bending, no peeling of the surface steel plate, no breakage of the surface steel plate, no intrusion into the core layer, no damage to the core layer. It was found that soundness after processing and heating after processing can be maintained. Moreover, in the laminated steel plate of Example 4, 24-26, it turned out that the soundness after heating after a process can be hold | maintained in the sample in which the indentation did not generate | occur | produce. Moreover, the laminated steel plates of Examples 1 to 9, 13, 15 to 23, and 25 to 27 had no appearance defect in the evaluation of spot weldability, and the peeled form after the shear tensile test was plug rupture (of laminated steel plates). One side was completely perforated and attached to the other laminated steel sheet), and the shear tensile strength was 120 to 160 MPa. In addition, since the total thickness of Examples 10-12, 14, and 24 was very thick, the spot welding test was not implemented. Moreover, in the laminated steel plate of Example 4, the indentation of the surface steel plate occurred only in a part of the sample cut out so that W was in the longitudinal (W _L ) direction. This vertex distance W _L of the truss structure has more than 10 times the thickness of the surface layer steel sheet, the stress concentration is presumably because that occurred portion is no apex of the truss structure of the surface layer the steel plate.

  Further, in the laminated steel sheet of Example 20 in which the truss structure having the same shape as that of Example 1 was used as the core layer, the thickness was smaller than M of Example 1. This is presumably because the strength of the wire constituting the truss structure is as low as 1/5.

  The M of Example 22 is larger than Example 23 because the blaze temperature is high in Example 23 and the tensile strength of the steel wire constituting the truss structure is reduced.

Moreover, in the laminated steel plates of Examples 24, 25, and 26, part of the indentation into the core layer of the surface steel plate occurred during hat bending. In the laminated steel plates of Examples 24 and 25, the distance between the vertices of the truss structure is more than 10 times the thickness of the surface steel plate, and stress concentration is partially generated in the portion located above the holes in the surface steel plate. It is estimated that In the laminated steel plate of Example 26, it is considered that the angle θ ₁ formed by the steel wire forming the truss structure and the surface steel plate is as small as 25 °. As a result, since the compressive strength of the core layer is small as compared with the laminated steel sheets of other examples, it is presumed that the core layer is partially compressed and broken.

The total thickness of the laminated steel sheets of Comparative Examples 1 and 2 is the same as that of the laminated steel sheets of Examples 3, 4, and 8, but the plate mass per unit area is large and heavy, and D / D _p , M Since / _Mp was small, it can be seen that the laminated steel sheet of the present invention is inferior in terms of lightness, rigidity and impact resistance. This is because, in the present invention, the steel wire is processed into a truss structure, so even a high-strength steel material can easily provide fine pores and further provide a gap in the thickness direction to reduce weight. Therefore, it is considered that light weight, rigidity, and impact resistance can be achieved more easily than when the wire mesh and the dimple processed plate are used as the core layer.

  Furthermore, in the laminated steel sheet of Comparative Example 3, the intrusion into the core layer of the surface steel sheet occurred during the three-point bending test. This is presumably because the pore portion is more than 10 times the thickness of the surface steel plate, and stress concentration occurred in the portion of the surface steel plate located above the pore.

  Furthermore, in the laminated steel sheet of Comparative Example 4, the indentation of the surface steel sheet occurred in the test piece in which voids continued in the width direction during hat bending. This is considered to have occurred because the compressive strength is almost zero in the void portion of the core layer. That is, since the anisotropy is large even in the same laminated steel sheet, it is presumed that the processing direction is limited and the degree of freedom in workability is low.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Laminated steel plate 5 (5A, 5B) Surface steel plate 10 Core layer 11 Truss structure 12 Wire mesh 111 Vertical line 112 Horizontal line 113 Vertex t Truss structure height ts Surface steel plate thickness W Vertex distance W _L length direction path length W angle theta ₂ vertical lines _B width direction of the vertex distance theta ₁ steel wire rod and the surface steel sheet and horizontal angle between

Claims (7)

A laminated steel sheet, wherein a truss structure made of steel wire material is laminated between steel sheets. The laminated steel sheet according to claim 1, wherein, among the components of the steel wire rod, the carbon concentration is at least 0.24 mass%. The laminated steel sheet according to claim 1 or 2, wherein a carbon concentration is at least 0.60 mass% among the components of the steel wire rod. The laminated steel sheet according to any one of claims 1 to 3, wherein the distance between the vertices of the truss structure is 30 times or less the thickness of the steel sheet. The laminated steel sheet according to any one of claims 1 to 4, wherein the distance between the vertices of the truss structure is 10 times or less the thickness of the steel sheet. The laminated steel sheet according to any one of claims 1 to 5, wherein an angle formed by the wire constituting the truss structure and the steel sheet is 30 to 60 degrees. The laminated steel sheet according to any one of claims 1 to 6, wherein the truss structure and the steel sheet are joined together with a blazed material or an adhesive having a melting point of 400 ° C or lower.

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