JP3207232B2 - Exterior structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exterior structure having excellent resistance weldability and press formability, and is particularly suitable as an exterior material for transportation equipment and home electric appliances, and can reduce the weight of the product. And a high-strength exterior structure.

[0002]

2. Description of the Related Art Conventionally, as an exterior structure for transportation equipment such as automobiles, railway vehicles, containers and the like and home electric appliances, SS34,
Rolled steel materials for general structures such as SS41 and rolled steel materials for welded structures such as SM41A are generally used. The rolled steel material contains 0.1 to 0.6% of carbon (C), 0.15 to 0.25% of silicon (Si), and 0.3 to 0.8% of manganese (Mn) by weight ratio. It is a general-purpose carbon steel containing and is used in many industrial fields.

For example, in an automobile manufacturing plant, a roll-shaped rolled steel sheet supplied from a mill maker is cut into a predetermined length and then punched using a press forming machine.
A molded body of a predetermined shape is formed by performing plastic working such as deep drawing or stretch forming, and then the obtained molded body is pressed and fixed to a body frame or another molded body, and an automatic welding robot or the like is used. They are used for mass production of vehicles by joining them together mainly by resistance welding.

[0004] Therefore, it is essential for the structural material used in the above-mentioned mass-produced products to have not only structural strength but also excellent press formability and resistance weldability as material properties.

However, in recent years, as for transportation equipment and home electric appliances typified by the above-mentioned automobiles, high utilization of energy resources and lower prices of the products themselves are increasing as social demands.
On the other hand, there is an increasing demand for reducing the weight of the product to reduce the weight and further reducing the operating cost. For example, for vehicles such as automobiles, research has been conducted to reduce the weight of structural members without impairing the strength and to improve the consumption rates of fuel and electric power.

As specific examples, studies have been made to use a high-strength steel material whose strength characteristics are several times that of a conventional structural steel material by making it thinner, or to use an aluminum alloy having a smaller specific gravity than the conventional material. .

[0007]

However, the high-strength steel and the aluminum alloy have poor resistance weldability, and it is particularly difficult to join them by spot welding, which is the mainstream of automatic welding machines. The difficulty in forming a mass production line using a machine is a technical barrier to practical application.

[0008] Further, high-tensile steel contains more carbon than ordinary carbon steel, and thus has the disadvantage that it is easily cracked when quenched after welding, and has a low ductility. There are drawbacks in that the press formability is low, for example, plastic working is difficult, and the press mold is significantly worn and the life of the processing equipment is short.

[0009] On the other hand, although aluminum alloys are lightweight, they have high thermal conductivity, so that even if a small current is applied for a long time during resistance welding, resistance heat is dissipated and the purpose of welding may not be achieved. Therefore, in the case of resistance welding of an aluminum alloy, it is necessary to flow a large current of tens of thousands of amps in a short time. However, since the electrodes of general-purpose resistance welding machines have low high-temperature strength, there are disadvantages such as that the electrode material alloys at the contact interface with the aluminum alloy as the material to be joined and frequently causes so-called sticking fusion. Was. Then, every time fusion occurs, it is necessary to stop all the lines in the welding process and perform re-polishing of the electrodes and repairing of the parts to be joined with high frequency, thereby reducing the operation efficiency of the production line. There was a problem.

The aluminum alloy material has low adhesion to the resin coating material, and has a problem that it cannot sufficiently satisfy the specifications as an exterior material for an automobile or the like that requires particularly high coating film strength.

The present invention has been made in order to solve the above problems, and has excellent resistance weldability and paintability, and is particularly capable of automatic welding, while being subjected to press forming such as deep drawing and overhanging. It is an object of the present invention to provide an exterior structure which does not easily generate cracks and the like even when the method is carried out, has excellent press moldability, and can respond to a demand for lighter products.

[0012]

From the above viewpoints, the inventors of the present invention have made it possible to obtain an exterior body which is less likely to impair the strength characteristics of the structure and has excellent press formability and weldability. Various kinds of alloy materials were prepared for the purpose, and experiments to compare and examine their properties were repeated. As a result, when a predetermined amount of Cu was alloyed to the iron material, an exterior structure excellent particularly in press formability and weldability was obtained. The present invention has been made based on the above findings.

That is, the exterior structure having excellent resistance weldability and press formability according to the present invention comprises copper at a weight ratio of 5.
4-30%, with the balance being iron and unavoidable impurities.

The copper (Cu) constituting the exterior structure having excellent resistance weldability and press formability according to the present invention imparts precipitation hardening properties, increases the strength and corrosion resistance of the iron material, and further increases the strength and corrosion resistance of the iron material. 1 to 30% by weight to improve weldability
Is added. When the content of copper in the alloy material is less than 1 wt%, the strength and corrosion resistance of the alloy material decrease, while when the content exceeds 30 wt%, the thermal conductivity of the entire alloy material increases, and the resistance increases. The weldability is reduced. Therefore, the content of copper in the alloy material is set to 1 to 30 wt%. In particular, by setting the copper content to 5.4 wt% or more, the hardness (Hv) of the alloy material can be made 130 or more, and the strength of the alloy material can be improved.
The content of copper is, for example, about 1.5 wt% and 5.4.
The hardness (H
Although v) is obtained, a hardness (Hv) exceeding 130 is not obtained.

As an element for improving the properties of the alloy material, C, Al, Ti, Zr, Cr, etc., in addition to the above-mentioned copper, may be added in such a manner as to partially replace iron. That is, C does not form a solid solution with copper but forms a solid solution only with Fe, and it is preferable to add C by 0.1% by weight or less based on the total amount of iron in order to harden the alloy structure and increase strength. Al, Ti, Zr, and Cr form an oxide film on the surface of the alloy material to exhibit a rust-preventive effect.
It is good to add in the range of t%. Note that these auxiliary elements may be formed as a dense thin film on the surface of the alloy material by a surface treatment method such as thermal spraying, or may be mixed in the raw material in advance. Aluminum and the like mixed in the raw materials are concentrated on the surface of the alloy material during a heating operation such as hot treatment to form a dense thin film.

Further, Cr added to the alloy material can increase the strength and corrosion resistance of the alloy material.

The exterior structure having the desired properties of the present invention can be obtained by casting a material having the above composition by, for example, a high frequency melting method or the like to form an ingot. After the solution treatment for 5 to 3 hours, it is formed into a predetermined shape such as a strip by hot rolling, scratching and cold working, and further subjected to aging heat treatment at a temperature of 450 to 900 ° C. for 1 to 5 hours. Is done. Further, instead of the solution treatment, the hot rolling temperature is set to 850 to 100.
The temperature may be set at 0 ° C. for processing.

In addition to the above-mentioned conventional manufacturing method, a material having the above composition is melted in a high-frequency melting furnace or the like, and a uniformly mixed molten metal is injected between a pair of rolls facing each other with a predetermined gap. It is also possible to rapidly cool and solidify and produce a thin plate having a predetermined thickness. According to the manufacturing method using the twin rolls, it is possible to directly manufacture a plate material having a predetermined thickness from a molten material at a high speed without going through complicated manufacturing processes such as conventional forging and hot rolling operations. Thus, the manufacturing cost of the plate material can be significantly reduced. In addition, since the plate is manufactured by quenching from a molten metal, the metal structure of the plate is finely crystallized, and a plate having excellent corrosion resistance and strength can be formed.

The plate-like and band-like copper-iron alloy materials thus produced are excellent in press formability and resistance weldability.
It is extremely useful as an exterior structure for mass-produced products such as automobiles, railway vehicles, transportation equipment such as containers, and home electric appliances.
In addition, since the strength is higher than that of the conventional mild steel material, when designed with the same strength, the used plate thickness can be relatively reduced, and the entire product can be significantly reduced in weight.

[0020]

Next, the exterior structure having excellent resistance weldability and press formability according to the present invention will be described more specifically with reference to the following examples.

Reference Example and Examples 1 to 3 Purity was 99.9% so as to have the composition shown in the left column of Table 1.
And pure iron having a purity of 99.9% were blended and uniformly melted in a high-frequency melting furnace to prepare Fe-Cu alloy-based ingots, respectively. Next, each of the ingots was forged, heated at a temperature of 900 ° C. for 1 hour, and hot-rolled to produce a copper-iron alloy plate having a thickness of 2 mm. Further, after removing the oxide of the alloy plate, cold rolling was performed to a thickness of 1 m.
m, and heat-treated at a temperature of 800 ° C. for 2 hours. Furthermore, cold-rolled, finally 0.6mm thick
And the copper-iron alloy plates according to Examples 1 to 3 were prepared, respectively.

Comparative Examples 1 to 5 On the other hand, the case where the content of copper is set to an excessively small amount of 0.5 wt% (Comparative Example 1) and the case where the content of copper is set to an excessive amount of 33.2 wt% (Comparative Example 2) By treating under the same conditions as in Examples 1 to 4, copper iron alloy sheets according to Comparative Examples 1 and 2 were prepared, respectively.

As Comparative Examples 3 to 5, commercially available automotive steel plates (SM41) each having a thickness of 0.8 mm, high-strength steel plates (WEL-TEN80) having a thickness of 0.6 mm, and Al alloys having a thickness of 1.0 mm A plate (4% Cu-Al) was prepared.

The following test measurements were performed on each of the sheets prepared or prepared in Reference Examples, Examples 1 to 3 and Comparative Examples 1 to 5 in order to evaluate the strength characteristics, resistance weldability and press formability. Was.

That is, as for the strength characteristics, Vickers hardness (Hv) exhibiting a value proportional to the structural strength and the proof stress.
Was measured. The resistance weldability was measured using a commercially available resistance welder equipped with chromium copper alloy electrodes. Each of the superposed sheets was continuously spot resistance welded, and the width of the electrode tip was changed to the initial width by thermal deformation. It was measured as the number of continuous resistance welding operations performed up to 2 mm or more from the time when welding failure occurred due to electrode welding or the like, and it became necessary to re-polish the electrode or repair the joint.

The press formability was measured by an Erichsen test performed to determine the deep drawing characteristics of a thin plate. In the Erichsen test, the periphery of a 90-mm-wide strip was placed and fixed between a wrinkle presser and a die, and the center was pushed in with a punch. This is a test for obtaining an Erichsen value representing the depth of penetration in mm units.

The results of the above detection and measurement are shown in Table 1 below.

[0028]

[Table 1]

As is clear from the results shown in Table 1, Cu
In the sheet materials of Reference Examples and Examples 1 to 3 formed of a copper-iron alloy containing 1 to 30% by weight of steel, the resistance weldability and the press formability were excellent and compared with the conventional mild steel sheet for automobiles (Comparative Example 3). As the hardness increases, the strength increases. Therefore, when the same strength is given, the thickness of the used plate can be relatively reduced, and the weight of the product can be reduced.

On the other hand, as shown in Comparative Example 1, a sheet material having a low copper content has low hardness and insufficient structural strength. Further, in the sheet material of Comparative Example 2 in which the copper content was excessive, welding occurred frequently, and it was difficult to perform welding for a long time continuously. It was also found that the high-strength plate of Comparative Example 4 and the Al alloy plate of Comparative Example 5 both had sufficient hardness and press formability, but had low weldability and were difficult to apply to mass-produced products.

[0031]

As described above, according to the exterior structure having excellent resistance weldability and press formability according to the present invention,
Because it is formed of an iron-based alloy containing a predetermined amount of copper,
Excellent press formability, paintability and resistance weldability,
It is extremely useful as an exterior structure for transportation equipment such as automobiles, railway vehicles, containers, etc., and home electric appliances. In addition, since the strength is higher than the conventional mild steel material, it is possible to relatively reduce the used plate thickness when designed with the same strength,
The entire product can be significantly reduced in weight.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoko Takeuchi 1 Toshiba-cho, Komukai-shi, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute, Inc. (72) Yoshikazu Oda Komukai-Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa No. 1 Toshiba Research Institute, Inc. (56) References JP-A-5-179395 (JP, A) JP-A-3-232953 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) ) C22C 38/00-38/60

Claims (3)

(57) [Claims] 1. An exterior structure excellent in resistance weldability and press formability, characterized by containing 5.4-30% by weight of copper and the balance being iron and unavoidable impurities. 2. The exterior structure according to claim 1, wherein the exterior structure contains 0.1% by weight or less of carbon based on the total amount of iron. 3. The exterior structure according to claim 1, further comprising 0.1 to 1% by weight of at least one of Al, Ti, Zr and Cr.