JPH11216791A - Steel structure member and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel structure member particularly suitable to an application to an automotive body by improving an energy absorption capability at the time of rapidly deforming with a rigidity while suppressing an increase in a weight of a structure and an adhesive durability between a resin and a steel sheet. SOLUTION: The resin-poured foam steel structure member has an inner surface of a steel structure having a hollow part and electrodeposition painted and filled with any of an urethane foam, a phenol foam and a polyolefin foam therein with a compression strength of 0.5 kg/cm<2> or more. In this case, when a hard polyurethane foam using a water as a foaming agent is used, it is better.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel structural member having a hollow portion filled with a hard foam, and a method for producing the same, which is particularly suitable for an automobile body.

[0002]

2. Description of the Related Art A steel structure used for an automobile body or the like is usually assembled by joining parts formed by pressing a thin steel plate by a method such as press forming or roll forming. These structures are made into a space with a small interior that contributes to the second moment of area in order to achieve both improvement in rigidity and weight reduction, for example, a molded steel plate assembled into a box-shaped cross-section structure,
In many cases, a steel pipe or a steel pipe is formed by bending or hydraulic bulging.

[0003] In recent years, in order to further improve the safety of occupants of automobiles, studies have been made to increase the strength and rigidity of the vehicle body structure and the ability to absorb collision energy. The strength of a steel structure is greatly affected by the dimensions and strength of the material, the joining strength of parts, and the like. The rigidity is greatly affected by structurally dependent factors such as the second moment of area of the steel structure, in addition to the above characteristics. There is a method of adding reinforcement to increase the rigidity of the steel structure, but if the weight of the vehicle increases due to the addition of reinforcement, the fuel consumption rate during car driving decreases, so there is a limit to reinforcement by reinforcement. .

[0004] When parts are joined together, the weld bond method of applying a structural adhesive to an overlapped portion such as a flange to be joined and performing spot welding is used to reduce the rigidity and absorbed energy of a steel structure during high-speed deformation. It is said to be effective for improvement. However, this method utilizes the phenomenon that an epoxy-based thermosetting type structural adhesive is cured by heating during electrodeposition coating, and has a limited rigidity improvement effect, poor adhesion durability, and low cost. High is the problem.

Japanese Patent Application Laid-Open No. 62-279932 discloses a panel structure in which a reinforcing resin block is interposed between two panels and bonded to reinforce the panel, thereby increasing rigidity while suppressing weight increase. Is disclosed. In this panel structure, a plate-shaped sponge having rubber-based closed cells with many holes is placed on a steel plate, the perforated portion is filled with a thermosetting resin, and then another steel plate is placed on the upper surface. These are stacked and pressed, and heated and held to cure the thermosetting resin. However, the force holding the two steel plates of the panel structure between the two steel plates depends on the strength of the thermosetting resin dispersed and arranged, and thus there is a limit to the rigidity improvement effect of the structure. In addition, the production requires a heat treatment and an apparatus for curing the thermosetting resin, which requires man-hours and costs.

Japanese Patent Application Laid-Open No. 1-29787 discloses a hollow body frame of a small vehicle in which a frame having a hollow structure is filled with a sound absorbing material or a vibration damping material. In the frame disclosed herein, a semi-rigid foamed polyurethane resin, which is a viscoelastic material, is considered to be the most excellent as an example of a filler that achieves a sound absorbing action and a vibration damping action. However, no consideration is given here to improving the rigidity of the structure or improving the energy absorbing ability during high-speed deformation. Further, neither the adhesion durability nor the structural durability between the foam and the body frame has been studied.

Japanese Patent Application Laid-Open No. 61-205119 discloses a method for filling a foam. In the method disclosed here, polystyrene, polyethylene, polypropylene, and the like are filled in the interior of a pillar, a locker, a wheel house, a front tire member, or the like of an automobile, and are foamed by applying a certain pressure and heating using steam. Is the way. However, in this method, since the foam shrinks after foaming and re-expands in the air at room temperature, there is a problem that the size and shape of the component may change.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel structural member which is particularly suitable for use in an automobile body and which has improved rigidity and energy absorbing ability at high speed deformation while suppressing weight increase. It is to provide a manufacturing method thereof.

[0009]

The gist of the present invention resides in a steel structural member described in the following (1) and a method of manufacturing the same described in (2).

(1) The hollow portion of a steel structure whose inner surface is electrodeposited is filled with a foam made of polyurethane foam, phenol foam or polyolefin foam and having a compressive strength of 0.5 kg / cm ² or more. Steel structural members.

(2) After the inner surface of the hollow portion of the steel structure is electrodeposited, a liquid foamable polyurethane raw material using water as a foaming agent is injected into the hollow portion, foamed, and filled with polyurethane foam. The method for producing a steel structural member according to the above (1), wherein:

The present inventors have studied various methods for improving the rigidity of the structure of an automobile and the energy absorbing ability when the structure is rapidly deformed without increasing the weight of the structure. As a result, for example, a steel structure (hereinafter simply referred to as “steel structure”) in which a hollow portion of a steel structure having a closed cross section such as a front side member of an automobile body is filled with a hard resin foam excellent in adhesion to steel. Members) are light in weight, have excellent flexural rigidity during high-speed deformation, and significantly improve the energy absorption capacity when axially compressed at high speed.

A resin foam containing a large number of cells therein (hereinafter, also referred to as “foam”) is classified into a soft foam and a rigid foam. A flexible foam is mainly composed of open cells, and is lightweight and has excellent properties of heat insulation and sound absorption. However, it has many air bubbles and is not suitable as a filling material for structural members. Rigid foams are closed cells for at least 90% of the cell structure and are inferior in weight to flexible foams, but have high compressive strength and are suitable as filling materials for structural members.

As the foaming agent used for forming the rigid polyurethane foam, a fluorocarbon having a high volatility or an alternative fluorocarbon has been conventionally used (hereinafter, the fluorocarbon and the alternative fluorocarbon are simply referred to as “fluorocarbons, etc.” A foam using these is referred to as a “CFC-based foam”). This is because, for example, Freon 11, which is often used as a foaming agent, has a low boiling point of 24 ° C., and is easily vaporized and gasified by reaction heat generated when isocyanate and polyol are mixed,
This is because there is an action of forming bubbles inside the resin. Since the bubbles contain Freon gas having a low thermal conductivity, the heat insulating effect of the foam is extremely excellent.

However, there is a problem in using a CFC-based foam as a filling material for a structural member. The biggest problem is that CFCs and the like are one of the causative substances that damage the global environment. Furthermore, since the condensation temperature of the CFC 11 in the air bubbles is 24 ° C., if the environmental temperature changes around this temperature, the volume of the foam changes significantly. For this reason, the dimension and shape of the structural member filled with the CFC-based foam may change depending on the environmental temperature. Changes in dimensions and shapes are not preferred because they change the appearance and may adversely affect rigidity. If water is used as the blowing agent, such a problem can be avoided. When water is used as a foaming agent, carbon dioxide gas is generated during the foaming reaction, and bubbles are formed based on the carbon dioxide gas. In this case, the foam contains carbon dioxide gas.

FIG. 5 is a diagram showing an example of the result of an investigation on the influence of the foaming agent on the dimensional change of the foam when the environmental temperature changes. The condensation temperature of carbon dioxide is -78 ° C. Therefore, since it is gaseous within the range of the normal environmental temperature, unlike the chlorofluorocarbon system, the volume of the foam hardly changes even if the external temperature changes. At high temperatures, carbon dioxide gas generally scatters and the volume of the foam tends to shrink, but in the case of water foaming, a dense non-foamed skin layer is formed at the interface with steel during foam molding. Therefore, scattering of carbon dioxide gas is prevented, and the volume change in a high temperature range is small.

Further, if the inner surface of the steel structure is electrodeposited before injecting the resin, the adhesion between the resin and the steel structure is further strengthened, and the rigidity of the steel structure is dramatically increased. It is improved and good adhesion can be ensured even when exposed to a corrosive environment. The present invention has been completed based on these findings.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of a steel structural member filled with the foam of the present invention will be described in detail below.

Steel structural member: The outer shell of the steel structural member filled with the foam of the present invention is made of a steel plate, a steel pipe, or a molded product thereof. It may be one formed by joining several molded products. The shape and dimensions of the steel structure are not particularly limited, and can be applied to any shape and any size, such as a beam, a plane, or a combination thereof. Further, a member provided with a reinforcing member in the hollow portion may be used.

The inner surface of the hollow portion of the steel structure is subjected to an electrodeposition coating which is excellent in a joint property of the steel sheet and a coating property to the end portion in order to improve the corrosion resistance of the steel surface and the adhesion to the foam. Is done. The type of the paint may be a known paint such as a melamine paint or an epoxy paint. Although the thickness of the coating film is not particularly limited, it is 20 μm because the corrosion resistance of the painted portion is improved.
It is preferable to make the above. As a pretreatment for the electrodeposition coating, a chemical conversion treatment such as a known phosphate treatment is preferably applied to the steel surface in advance according to a conventional method. Because such a pretreatment and painting are applied to the steel surface, not only immediately after filling the foam,
For a long period of time including secondary adhesion, good adhesion between steel and foam can be maintained.

In order to improve the rigidity and impact energy absorbing ability of the steel member filled with the foam, the foam filled inside the steel structure has a compressive strength of 0.5 kg / cm ^2. The above is assumed. When the compression strength of the foamed resin is less than 0.5 kg / cm ² , the rigidity of the structural member and the effect of improving the impact energy absorbing ability are insufficient. The higher the compressive strength of the resin, the greater the effect of improving these properties. Therefore, a resin having a compressive strength of 5 kg / cm ² or more is more preferable. The compressive strength of the foam specified in the present invention is such that a foam sample cut out from a steel structural member is subjected to a compression test at 25 ° C. in accordance with the method specified in JIS-K-7220, and the compressive strain reaches 10%. The load is measured and determined.

The inner surface of the steel structural member of the present invention has been subjected to chemical conversion treatment and electrodeposition coating. In order to avoid impairing the performance of these coating films, in the present invention, a resin foaming raw material which can be foamed without external heating is used without using a foaming treatment by an external heating method. Of course, after foaming, it is necessary to have the above-mentioned compressive strength. Any type of foam may be used as long as these requirements can be satisfied, and polyurethane foam, polyolefin foam or phenol foam is suitable. Polyurethane foam having excellent adhesion to steel is particularly preferred.

These foams may use a CFC-based foaming agent. However, in the CFC-based foam, the dimensional shape of the structural member may change due to a change in environmental temperature. Also, in steel structural members filled with CFC-based foam, when salt water enters the bonding interface with steel when using a car body, a chemical reaction occurs and chlorine ions are generated, impairing the adhesion between the resin and the steel, The compressive strength of the structural member may be deteriorated (hereinafter, such a defect is also simply referred to as “secondary adhesion defect”). In order to avoid these problems, a foam using water as a foaming agent is more preferable.

Manufacturing method: The steel structure constituting the outer shell of the steel structural member is formed by forming a steel plate or a steel pipe by a known method and joining it by welding or other known methods, or
These are further obtained by hydroforming.

The inner surface of the hollow portion of the steel structure is subjected to chemical conversion treatment and electrodeposition coating. The chemical conversion treatment may be a conventionally used one such as a zinc phosphate-based or iron phosphate-based treatment. The coating is performed by an electrodeposition coating method that is excellent in the ability of the paint to be applied to the joints and the ends of the steel. The kind of the coating film for electrodeposition coating may be a known one, and can be arbitrarily selected such as a melamine-based paint and an epoxy-based paint. Although the thickness of the coating film is not particularly limited, it is preferable to apply the coating so that the dry film thickness is 20 μm or more in order to secure the corrosion resistance of the coated portion. The baking conditions after coating may be any conditions that are normally applied, for example, a baking temperature of 170 to 200 ° C. and a baking time of 20 to 25 minutes. When coating the inner surface of the hollow portion, it is preferable to simultaneously apply a desired coating to the outer surface of the steel structure.

After coating the inner surface of the hollow portion, a liquid foaming material is injected and foamed. When an opening is provided in addition to the injection hole, a lid is temporarily provided at the opening so that the liquid foaming material does not leak. Since the steel structure of the present invention is not heated during foaming, it can be covered with a simple method.

When a polyurethane foam is formed, a foaming raw material comprises a stock solution mainly containing isocyanate having two or more NCO (isocyanate) groups (hereinafter simply referred to as “isocyanate component solution”) and a plurality of OH groups. Two kinds of undiluted solutions, which are mainly composed of polyols such as alcohols (hereinafter simply referred to as “polyol component solution”), are used as main materials. These raw materials are not particularly limited, and those that have been conventionally used in the production of foams may be used. For example, as the isocyanate, tolylene diisocyanate (TDI), a product obtained by reacting a part of TMD with a polyol, or an isocyanate component such as methylene diphenyl diisocyanate (MDI) can be used. As a polyol,
Mixtures of shoe-close type, sorbitol type and the like conventionally used for hardening can be used.
The polyol component liquid contains a foaming agent,
Additives usually used for the production of polyurethane foam, such as a catalyst and a stabilizer, are mixed to form a polyol component liquid.

As the foaming agent, a conventionally used fluorocarbon or the like (for example, R-11) may be used. However, the dimensional change of the steel structural member due to the change of the environmental temperature or the bonding interface with the steel may be used. It is more preferable to use water in order to avoid poor secondary adhesion which may occur when salt water enters. When water is used, when the isocyanate component liquid and the polyol component liquid are mixed, the isocyanate group reacts with water to generate carbon dioxide gas, and foam is formed based on the carbon dioxide gas. According to water foaming, unlike fluorocarbons, it does not react with salt water, so that even if salt water enters the interface, the secondary adhesion is not impaired. The catalyst may be a known one, and amines and organometallic compounds can be used. The curing time of foaming can be adjusted by these types and amounts. The stabilizer is added for the purpose of generating dense air bubbles, and may be a commonly used silicone oil or the like. The polyol component liquid may contain a small amount of a flame retardant, a filler, or the like, in addition to the above additives.

The isocyanate component liquid and the polyol component liquid are mixed at a predetermined ratio, and are foamed by injection or spraying into a hollow portion. Mixing and pouring methods are known in the art, such as a method of weighing and mixing each component liquid in a batch manner, or a method of continuously injecting into a mixer at a constant ratio by a constant proportional pump or the like, stirring, mixing and pouring. The method may be performed. The component liquid sent at a fixed rate may be sprayed using a spray gun. The liquid foaming material foams by chemical reaction in the hollow part,
Leave to cure for 20 minutes.

The compressive strength of the polyurethane foam can be adjusted by adjusting the mixing ratio of the blowing agent to the polyol and changing the foaming ratio to change the density of the foam. When water is used as the foaming agent, it is preferable to change the compressive strength by changing the mixing ratio of water. For example,
To make the compressive strength 5 kg / cm ² or more, water may be mixed in an amount of 1 part by weight or more with respect to 100 parts by weight of the polyol.

Phenol foam is mainly composed of benzyl phenol, and foams are formed by the reaction of "urea bond (urea bond) + carbon dioxide gas" between isocyanate and water without external heating. The polyolefin foam may use polypropylene as its main raw material liquid, and may use any of water, chlorofluorocarbon and butane as the blowing agent. As in the case of the urethane foam, these foams are formed by mixing, stirring and injecting commonly used additives such as a foaming agent, a catalyst and a stabilizer at a predetermined ratio.

Since the inner surface of the steel structural member of the present invention has been subjected to chemical conversion treatment and electrodeposition coating, in order not to impair the performance of these coating films, no heat treatment is performed after resin injection. For this reason, there is an advantage that the size and shape of the structural component are not changed at all during the foaming operation, and the foaming operation can be performed easily and easily.

In the steel structural member of the present invention, by combining high tensile strength steel with the above-mentioned resin foam, the rigidity of the member can be improved, and the thickness and weight can be further reduced. In addition, when a resin such as a rigid polyurethane foam is used, there is no problem since it can be collected and reused as shredder dust when the vehicle body is discarded.

The present invention is suitable for structural members such as, for example, pillars, lockers, front side members of automobiles, and frames of motorcycles.
It can also be used to reduce the weight of lids having many flat parts such as doors, roofs and floors. The structural member of the present invention is applicable not only to passenger cars and two-wheeled vehicles, but also to vehicle body structural members such as large trucks and buses.

[0035]

FIG. 1 is an external view of a box-shaped test specimen simulating a steel structural member. In FIG. 1, a component 1 is manufactured by bending a steel plate, and has a bottom width: 60 mm, a side wall height: 85 mm, a flange width: 20 mm, and a total length of 500 m.
m is a hat-shaped molded part, and 1a is referred to as its bottom surface. Parts 1 and 2 both have a thickness of 1.6 mm and a tensile strength of 470
One that uses a hot-rolled high-strength steel sheet of MPa and a thickness of 1.2 m
m and a type using a cold-rolled high-strength steel plate having a tensile strength of 610 MPa. A patch plate 2 having a width of 100 mm and a length of 500 mm was spot-welded to the flange surface. The spot welding condition is that the tip diameter is 6m
using a dome-shaped electrode with a pressure of 400 kg
f, energization time: 20 cycles, current: 9000 A,
The interval of spot welding was set to 50 mm. Then, tensile strength 390 MPa, thickness 10 mm, width 1
An end plate 3 having a length of 50 mm and a length of 150 mm was assembled by arc welding. At the center of the end plate 3a, a round hole 4 having a diameter of 40 mm was provided as an injection hole for a foaming raw material. The inner and outer surfaces of the steel structure were degreased using a solvent according to a conventional method, washed with water and subjected to a chemical conversion treatment, and then electrodeposited so that the film thickness after drying was 20 μm, and baked at 170 ° C. for 25 minutes. did.

(Example 1) TDI was used as an isocyanate component liquid for forming a polyurethane foam. The polyol component liquid was prepared by adding water as a foaming agent, an organic tertiary amine as a catalyst, and silicone oil as a stabilizer to a polyether having three or more OH groups.
The apparent density was changed by changing the mixing ratio of water in the range of 3 to 0.15 parts by weight with respect to 100 parts by weight of the polyol.
The respective component liquids were weighed so that the above-mentioned polyol component liquid was 100 parts by weight with respect to 120 parts by weight of the isocyanate component liquid, and these were stirred and mixed, and injected into the hollow portion of the above-mentioned simulated structure, and foamed. The sample was cured at room temperature for 10 to 20 minutes to prepare test samples 1 to 3 filled with a resin foam.

(Embodiment 2) Both parts 1 and 2 have a thickness of 1.6.
mm, using the above-described simulated structure using a hot-rolled high-tensile steel sheet having a tensile strength of 470 MPa, polyol 1 as a foaming agent
1.8 parts by weight of alternative Freon (R-1)
Specimen 4 was produced under the same conditions as in Specimen 1 of Example 1 except that 1) was used.

(Embodiment 3) Both parts 1 and 2 have a thickness of 1.6.
mm, using the above-described simulated structure using a hot-rolled high-strength steel sheet having a tensile strength of 470 MPa, using undiluted solution using benzylamine as a foaming main raw material, water as a foaming agent, and a tertiary amine as a catalyst. It was injected into the hollow portion of the simulated structure, foamed and cured at room temperature to prepare a test body 5 filled with phenol foam.

(Embodiment 4) Both parts 1 and 2 have a thickness of 1.2.
mm, using the above-described simulated structure using a cold-rolled high-tensile steel sheet having a tensile strength of 610 MPa, using a stock solution using polypropylene as a main foaming material, water as a foaming agent, and a tertiary amine as a catalyst as described above. Injected into the hollow part of the structure,
The sample was foamed and cured at room temperature to prepare a test body 6 filled with a polyolefin foam.

Comparative Example 1 Both parts 1 and 2 have a thickness of 1.6.
Specimen 7 for comparison under the same conditions as Specimen 1 except that a hot-rolled high-tensile steel sheet having a tensile strength of 470 MPa and a simulated structure not subjected to chemical conversion treatment and electrodeposition coating was used in the hollow portion. Was prepared.

(Comparative Example 2) Both parts 1 and 2 have a thickness of 1.6.
mm, a hot rolled high-strength steel sheet having a tensile strength of 470 MPa, a simulated structure having a hollow portion subjected to a chemical conversion treatment and an electrodeposition coating, and a water mixing ratio of 0.06 wt. Specimen 8 for comparison was prepared under the same conditions as Specimen 1 except that the parts were used.

(Conventional Example 1) Both parts 1 and 2 have a thickness of 1.6.
A hot-rolled high-strength steel sheet having a tensile strength of 470 mm and a tensile strength of 470 mm was used, and a test piece 9 having no foam in the hollow portion was produced.

The performance of these test specimens was evaluated by the following method.

Apparent density of foam: The density of a sample obtained by cutting a sample of the foam from the test body was measured.

Compressive strength of foam: A sample of the foam was cut out from the test piece and subjected to a compression test at 25 ° C. in accordance with the method specified in JIS-K-7220.
Was measured by measuring the load at the time of reaching.

Torsional rigidity: The end of the test piece on the 3a side is fixed to a fixed wall, and a jig for applying a torsional torque around the center axis C of the test piece is attached to the end of the 3b side. ,
The torsional torque around the C axis was applied to the 3b end to measure the torsional angle at the 3b end, and the torsional rigidity was measured by calculating using the following equation within the range where the relationship between the torsional torque and the torsional angle was linear. GJ = T × L / θ, where GJ: torsional rigidity, T: torsional moment, L: member length, θ: torsional angle at the load point, and the unit of rigidity value is [× 10 ⁸ kg / m
m ² ]. The stiffness unit mm ² is the cross-sectional area of the steel sheet.

Absorbed energy when the specimen is subjected to impact compression in the axial direction: the specimen is fixed on the pedestal with the center axis C vertical with the end on the 3a side down, and attached to the end plate 3b from above. The weight was dropped, and the specimen was compressed and deformed in the axial direction. The weight is 600 kg and the collision speed is 40 km / h
The height of the weight at the start of the fall was adjusted so that The distance after the collision between the upper and lower end plates was measured using a laser displacement meter, the load applied to the test piece was measured by a load cell provided inside the weight, and a compression deformation-load curve was obtained.

FIG. 2 shows an example of the obtained load curve. From the area surrounded by the load curve up to 100 mm of deformation,
The energy absorbed until the upper end plate was compressed by 100 mm was determined.

Impact bending absorption energy of test specimen: Specimen with the backing plate 2 on the lower surface (the 1a surface of the hat-shaped part is on the upper surface) on a bending jig consisting of two supports with a fulcrum spacing of 400 mm. And place it at the center in the longitudinal direction of the specimen.
A 50-kg weight is applied on the a-side, and the collision speed is 40 kph.
m, and a three-point bending test by an impact load was performed. The displacement of the 1a surface was measured using a laser displacement meter, and the impact load was measured using a load cell provided inside the weight to obtain a bending deformation-load curve.

FIG. 3 shows an example of the obtained bending deformation-load curve. The energy absorbed until the deformation was 40 mm was calculated from the area surrounded by the load curve up to the deformation of 40 mm.

Adhesion of foam: thickness 10 mm, size 3
A 0-mm square steel sheet was subjected to degreasing, chemical conversion treatment, and electrodeposition coating under the same conditions as those for coating the simulated structure. Two of these steel plates were arranged in parallel on the pedestal at a distance of 2 mm, and the side of the space formed between the two steel plates was closed with a side plate so that the foamed raw material did not leak. A liquid foaming raw material was injected into this space, mixed and foamed to prepare a test piece having a sandwich structure composed of a steel plate / foamed resin / steel plate.

Some test pieces were subjected to a peel test at room temperature to evaluate primary adhesion. In the peeling test, two steel plates were peeled in a direction perpendicular to the steel plate surface using an Instron type universal tensile testing machine, and the maximum peeling load was divided by the bonding area to determine the peeling load. Some test pieces were stored for 30 days in an atmosphere of 65 ° C. and a relative humidity of 95% assuming a corrosive environment of a vehicle body, and then subjected to a peeling test in the same manner as above to evaluate secondary adhesion. The adhesion is good when the peeling load is 10 MPa or more (indicated by ○ in Table 1). When the peeling load is less than 10 MPa or 8 MPa or more, it is slightly good (indicated by Δ in Table 1). Was determined.

The results are summarized in Table 1.

[0054]

[Table 1]

As can be seen from Table 1, all of the test pieces 1 to 6 have a compressive strength of the foam of 0.5 kg / mm ² or more and have excellent adhesion. 5 × 1 for torsional rigidity
0 ⁸ kg / mm ² or more, and the impact absorption energy was 5 kJ or more in the axial compression deformation and 500 J or more in the bending deformation, and all showed extremely excellent performance as compared with the test piece 9 of the conventional example. In particular, as shown in the results of the test pieces 1 to 3, the urethane foam using water as the foaming agent showed excellent performance. On the other hand, the test piece 7 did not have good adhesion because the surface of the steel sheet was not electrodeposited, had low torsional rigidity, and had low impact energy absorbing ability. Specimen 8 had low torsional rigidity and low absorbed energy due to the low compressive strength of the foam.

[0056]

Since the resin-injected foamed steel structural member of the present invention has a hard foam having good adhesion inside the steel structure, the rigidity and the high-speed deformation at the time of high-speed deformation are not accompanied by a significant weight increase of the member. Absorbed energy can be greatly improved. INDUSTRIAL APPLICABILITY The steel structural member of the present invention is useful for improving vehicle body rigidity and collision safety without impairing the running fuel consumption rate of an automobile or the like.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a box-shaped test body simulating a steel structural member.

FIG. 2 is a schematic diagram showing a relationship between a deformation amount and a load when a test body is subjected to impact compression deformation in an axial direction.

FIG. 3 is a schematic view showing a relationship between a deformation amount and a load when a test body is subjected to impact bending deformation.

FIG. 4 is a view showing the influence of a foaming agent on a dimensional change rate of a foam according to temperature.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hat-shaped molded part, 1a ... Bottom, 2 ...
Patch plate, 3 end plate, 4 injection hole.

Claims (2)

[Claims] 1. A hollow portion of a steel structure having an inner surface electrodeposited and coated with a foam made of any of polyurethane foam, phenol foam and polyolefin foam and having a compressive strength of 0.5 kg / cm ² or more. Steel structural members. 2. An inner surface of a hollow portion of a steel structure is subjected to electrodeposition coating, and then a liquid foamable polyurethane raw material using water as a foaming agent is injected into the hollow portion, foamed, and filled with a polyurethane foam. The method for producing a steel structural member according to claim 1, wherein: