JP3001136B2 - Composite metal sheet with excellent BH properties and workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to provide a composite metal sheet which is reduced in weight while maintaining the same rigidity, for a use in which a thin steel sheet is conventionally used, and is used for processing such as deep drawing. The present invention relates to a composite metal sheet which is suitable for use, and particularly hardens when placed at a temperature of, for example, 170 ° C. for baking paint after press molding, and further improves compatibility between press workability and strength.

[0002]

2. Description of the Related Art Weight reduction as a structural material such as an outer panel of an automobile is a major problem, and various means have been proposed. As one of the means for reducing the weight, there is a method in which aluminum is used in a portion where a conventional steel plate is used. However, although weight reduction and strength are theoretically possible with aluminum, aluminum itself has low rigidity and therefore must be considerably thicker than steel. For this reason, the effect of reducing the weight is reduced and the cost is disadvantageous. Further, aluminum and aluminum alloys are significantly inferior in workability to steel plates. From the above, at present, aluminum can be used only for limited applications.

In order to solve these problems, a thin plate having a baking hardenability (hereinafter referred to as BH) after processing, which is a three-layer composite plate composed of an iron layer on both sides and an aluminum layer at the center, is considered promising. Can be There are few practical examples of plate materials in which aluminum and iron are combined because their production is technically difficult. However, there is a practical example of a thick plate made of a 5 mm aluminum and a 15 mm thick steel plate made by the explosion method, but there is no practical example of a thin plate.

[0004] As a method for producing a thin sheet in which aluminum and iron are combined, a so-called lap rolling method is known. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-157774, 350 to 55
A method in which the steel material is heated to about 0 ° C., hot-rolled and joined to the iron material, and as disclosed in Japanese Patent Publication No. 56-52679, the surface of the iron material is previously plated with aluminum and heated to about 500 ° C. There is a method of hot rolling and joining with an aluminum material. However, there is a problem that the composite metal sheet manufactured by these methods has insufficient workability and hardly hardens by baking coating after press molding.

[0005] On the other hand, a single steel sheet having curability by baking coating has been studied so far, for example, Japanese Patent Application Laid-Open Nos. 2-197549 and 63-247338.
It has been found that this can be obtained by setting the amount of C, Ti or Nb in steel to a specific range and annealing under specific conditions, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. H11-163,086. However, since the steel sheets produced by these methods have a small total carbon content, the amount of bake hardening itself cannot be so high, and the steels disclosed in Japanese Patent Laid-Open No. 2-1975 / 1990 are not available.
At present, it is about 3 kgf / mm ² as disclosed in JP-A-49. Therefore, even if such a steel sheet can be combined with aluminum, a composite metal sheet having a high bake hardening amount cannot be expected. As described above, a composite plate of iron and aluminum having sufficient workability and bake hardenability has not been known so far.

[0006]

SUMMARY OF THE INVENTION In view of the above, the present invention has good workability, and furthermore, in order to reduce the weight by BH, a composite metal of iron and aluminum having a BH amount of 4 kgf / mm ² or more. It is intended to provide a board.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the composition and condition of the steel sheet and aluminum and found that a composite of iron and aluminum having good workability and bake hardenability is obtained. I found a metal plate.

That is, the present invention is a composite metal plate comprising three layers of iron on both surfaces and aluminum at the center, wherein the iron layer has a chemical composition of C: 0.01-0.055% by weight and S:
i: 0.1% or less, Mn: 0.04 to 0.5%, P:
0.1% or less, solAl: 0.002-0.1%,
N: 0.006% or less, solid solution C: 0.0003 to 0.0
020%, the balance consisting of iron and unavoidable impurities
The aluminum layer has a grain size of not less than 60 μm and not more than 60 μm.
This is a composite metal plate excellent in bake hardenability and workability, characterized by being made of aluminum alloy or Al alloy. Further, the aluminum layer constituting the composite metal plate is characterized in that it is an aluminum alloy containing at least one of 6% or less of Mg and 2% or less of Mn instead of the above components.
Further, in addition to the above components, 0.5% or less of Si,
1 or 2 of 0.5% or less of Cr and 0.5% or less of Zn
It is also characterized by containing the above.

[0009]

Hereinafter, the present invention will be described in detail. As the C content in the iron material increases, the average r value and the ductility deteriorate, the yield strength increases, and the workability decreases. Therefore, the smaller the amount of C, the better the press workability. Therefore, the content of C is preferably set to 0.055% or less. However, there is a problem that the cost of decarburization increases in order to make C lower than 0.010%. Therefore, the amount of C was limited to 0.055 to 0.010%.

Although a small amount of Si causes no problem, an increase in the content lowers the workability. Therefore, it must be 0.1% or less.

Mn is a component necessary to prevent hot embrittlement due to S present as an unavoidable content in steel. However, if it is less than 0.04%, FeS is formed and the effect is not obtained. On the other hand, if it exceeds 0.5%, the workability deteriorates. Therefore, the amount of Mn was limited to 0.04 to 0.5%.

If P is contained in a large amount, it segregates at the grain boundaries and becomes brittle, causing a reduction in workability. Therefore, the P content was limited to 0.1% or less.

Al is an element necessary for controlling the amount of oxygen in the steel, and is added as a deoxidizer before adding Ti. If the acid-soluble Al content in the steel is less than 0.002%, deoxidation is not sufficiently performed, and the yield of Ti is significantly reduced. However, if it exceeds 0.1%, inclusions increase and the workability of the steel sheet decreases. Therefore, the amount of Al was limited to 0.002 to 0.1%.

N, when solid-dissolved in steel, significantly lowers the workability and must be fixed as TiN by Ti. Also, the amount of generated TiN is preferably as small as possible. Therefore, the N content is set to 0.0060% or less.

The reason why the amount of solute C is specified is to harden the composite metal plate by baking coating performed after processing, which is a feature of the present invention. As the amount of solid solution C increases, the baking hardening amount can be increased, but there is a problem that workability is reduced due to aging. FIG. 1 is a graph showing annealing conditions for the amount of solute C in a steel plate portion when manufacturing a composite metal plate composed of a steel plate having the chemical components shown in Table 1 and an aluminum plate on both sides and a center made of an aluminum plate using the equipment shown in FIG. This shows the effect of the amount of solid solution C on the baking hardening amount and the amount of the stretcher strain after 6 months from the production when the amount was varied in the range of 0.2 to 30 ppm by changing the amount of C. As is clear from FIG.
It can be seen that if it is in the range of 0 ppm, a stretcher strain due to aging does not occur and a multi-layer steel sheet having a high bake hardening amount of 4 kgf / mm ² or more is obtained. Other than the above components, they consist of Fe and unavoidable impurities.

[0016]

[Table 1]

The crystal grain size of the iron material of the above component must be 10 μm or more and 60 μm or less in order to provide good workability. FIG. 2 shows that when a composite metal plate composed of a steel plate having the chemical components shown in Table 1 and an aluminum plate and having a steel plate on both sides and an aluminum plate in the center is manufactured by the equipment shown in FIG. 3, the annealing time of the steel plate portion is changed. FIG. 4 shows the influence of the crystal grain size on the average r value and elongation of the multilayer steel plate when the average crystal grain size of the steel plate portion of the multilayer steel plate is changed. As is clear from FIG. 2, it is found that a good average r value and elongation can be obtained when the average crystal grain size is 10 to 60 μm.

In the above investigation, it was found that good workability and bake hardenability were obtained even when the composition was changed within the range of the present invention. The method of manufacturing the steel sheet in the composite metal sheet is not particularly limited, and may be a method manufactured by hot rolling or a method manufactured through a cold rolling annealing step.

Next, conditions of the aluminum material will be described. The material of the aluminum material may be either pure aluminum or an aluminum alloy. Although the type of the aluminum alloy is not limited, an aluminum alloy containing at least one of Mg of 6% or less and Mn of 2% or less is particularly preferable. These alloy components increase the strength of aluminum in an annealed state, and do not significantly impair workability such as drawing. 6% of Mg
, Or when the amount of Mn exceeds 2%, the curing is remarkable,
Since the processability is impaired, the above ranges of these components are appropriate. Further, when 1 or 2 of 0.5% or less of Si, 0.5% or less of Cr, and 0.5% or less of Zn is added together with the above components, the strength is further increased while maintaining good workability. be able to. However, Si, Cr, Zn
If the amount exceeds the above range, the hardness becomes too high and the workability is impaired, so the above range is limited. The aluminum material of the above component may be either a cold-rolled material or an annealed material.

In the electric heating apparatus shown in FIG. 3, energizing rolls 11, 12, and 13 are provided on the iron layers 1 and 3 and the aluminum layer 2 as raw materials, respectively.
The composite plate 5 is manufactured by continuously feeding the sheet between the rolls 4 of the book. As the power supply, either a low-frequency AC power supply or a DC power supply can be used. The current of the power supply 21 flows from the energizing roll 11 of the iron layer 1 to the energizing roll 12 through the iron layer 1 and the aluminum layer 2. Similarly, the current of the power supply 22 flows through a series circuit of the aluminum layer 2 and the iron layer 3. If the phases of the two power supplies 21 and 22 are properly adjusted, the current of the aluminum layer 2 becomes the sum of the currents from the two power supplies. In this case, since the iron layer has higher electric resistance than the aluminum layer, if the iron layer and the aluminum layer have the same thickness, the iron layer generates more heat and becomes higher in temperature. If the heating temperature of the iron layer does not reach the target temperature, the auxiliary heating power supplies 23 and
Auxiliary heating is performed by energizing from 24.

When joining the iron layer and the aluminum layer,
A method in which an external force is applied between two rolls as shown in FIG. 3 or a method like a press may be used. The method of heating the joining material may be any method such as electric heating, induction heating, and heating by a heating furnace. By using a composite metal plate having an iron layer and an aluminum layer as described above, a composite metal plate excellent in bake hardenability and workability can be obtained.

[0022]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
A steel plate having a thickness of 0.4 mm and an aluminum plate having a thickness of 0.6 mm having the composition shown in Table 2 were used. At the same time, as shown in FIG. 3, an external force was applied by two rolls in contact with the iron layer to continuously join the iron layer and the aluminum layer. By changing the heating temperature and heating time of the steel plate portion, the crystal grain size and the amount of solute C in the steel plate portion were variously changed as shown in Table 2. Sample Nos. (1) to (14) are all within the scope of the present invention in terms of composition, crystal grain size of the steel plate portion and solid solution C, and (15)
Any one or more of (26) is out of the scope of the present invention. After joining, the materials of the obtained composite metal plate are shown in Table 3.
Shown in As can be seen from Table 3, the composite metal sheet within the scope of the present invention exhibits excellent bake hardenability and workability.

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

As described above, the composite plate of iron and aluminum according to the present invention has excellent workability and bake hardenability.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the amount of dissolved carbon in an iron layer on the amount of bake hardening of a composite plate and the amount of stretcher strain after aging.

FIG. 2 is a graph showing the influence of the crystal grain size of the iron layer on the r value and elongation of the composite plate.

FIG. 3 is a diagram showing an example of an apparatus used for manufacturing a composite plate.

[Explanation of symbols]

 1,3 iron layer 2 aluminum layer 4 roll 5 composite plate 11,12,13 energizing roll 14,15 auxiliary energizing roll 21,22 power supply 23,24 auxiliary heating power supply

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification symbol FI C22C 38/00 301 C22C 38/00 301S 38/06 38/06 (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 30/00

Claims (3)

(57) [Claims] 1. A composite metal plate comprising three layers of iron on both surfaces and aluminum at the center, wherein the iron layer has a chemical composition of 0.01 to 0.055% by weight in chemical ratio and 0.1 to 0.1% in Si. %Less than,
Mn: 0.04 to 0.5%, P: 0.1% or less, sol
Al: 0.002 to 0.1%, N: 0.006% or less,
Solid solution C: 0.0003 to 0.0020%, the balance being iron and unavoidable impurities, having a sized structure of 10 μm or more and 60 μm or less, and an aluminum layer containing 99% or more by weight of a chemical component of Al in the aluminum layer A composite metal sheet having excellent bake hardenability and workability, characterized by being made of an Al material or an Al alloy. 2. The aluminum layer other than Al has a weight ratio of 6%.
2. An aluminum alloy containing at least one of Mg of 2% or less and Mn of 2% or less.
The composite metal plate as described in the above. Wherein the aluminum layer is further than 0.5% of Si, 0.5% or less of Cr, according to claim 2, characterized in that it contains one or more of 0.5% or less of Zn Composite metal plate.