JPH07180036A - Surface treated steel sheet - Google Patents

Abstract

PURPOSE:To simply and easily produce a steel sheet without requiring any positioning, to simplify the process, and to provide the steel sheet light in weight, low in cost, neglectedly small in heterogeneous structure of a base metal, high in temp. oxidation resistance and durability and suppressed in the mutual diffusion between brazing components and steel sheet components, to obtain sufficient joining strength, and having good heat resistance. CONSTITUTION:This surface treated steel sheet is provided with an aluminum oxide layer formed on the surface of a steel sheet and a brazability alloy film of 0.1 to 20mum contg. 5 to 40wt.% Cr and 1 to 20wt.% of one or two kinds of B and Si, and the balance Ni with inevitable impurities formed on at least one side of the aluminum oxide layer. Thus, the surface treated steel sheet excellent in brazability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet provided with a brazing film, particularly to a surface-treated steel sheet required to have brazing property and heat resistance. The present invention relates to a surface-treated steel sheet effective for producing a carrier substrate to which a catalyst is attached in a catalytic converter for cleaning gas.

[0002]

2. Description of the Related Art As a metal carrier for an exhaust gas purifying catalyst for automobiles, there has been known one in which a heat-resistant flat plate-shaped steel plate and a corrugated plate-shaped steel plate are stacked and rolled into a honeycomb shape. In the metal carrier, the flat plate-shaped steel plate and the corrugated plate-shaped steel plate of the honeycomb body and the outer cylinder and the honeycomb body are joined by brazing to secure the strength as a structure.

As a known technique for improving the heat resistance of the base steel sheet, Al-containing stainless steel containing 3 to 8% by weight of Al is used, and after heat treatment, the Al in the steel is used to form α on the surface of the stainless steel. a method of precipitating -Al ₂ O ₃ (see JP-a 58-96728). Further, a method of forming α-Al ₂ O ₃ whiskers after plating and heating Al on a stainless steel plate having an Al content of less than 1% by weight (see JP-A-63-232850), and a surface of ferritic stainless steel. There is known a method in which Al is plated on Al and then Al is heated and diffused in ferritic steel, and then oxide whiskers are formed on the surface by heating in the atmosphere (JP-A-2-
40734 and JP-A-2-214545).

On the other hand, regarding the brazing method, as a known brazing joining method, a brazing foil is inserted between a flat plate and a corrugated plate,
Alternatively, there is a method in which a brazing filler metal component is applied to a flat plate or a corrugated plate by a roll, the flat plate and the corrugated plate are wound in a roll shape, and then the two are heat-bonded (see JP-A-3-60740). In this case, the brazing material is Ni-based (Japanese Patent Laid-Open No. 2-2
6443, refer to JP-A-3-278815), Fe-
Various brazing materials such as Cr-Si are used. However, braze foil (or braze component to be applied)
Is expensive (see Japanese Patent Laid-Open No. 1-171641). Also, in terms of strength, it is not necessary to intervene over the entire surface,
A brazing foil may be partially inserted (Japanese Patent Laid-Open No. 3-86329).
JP-A-3-86370, JP-A-3-278815
(See Japanese Patent Application Laid-Open No. 3-65244), or by partially coating or adjusting the weight of the brazing material foil within a certain range with respect to the foil serving as the substrate (see Japanese Patent Laid-Open No. 3-65244). Is being reduced.

On the other hand, in order to improve the heat resistance of the honeycomb molded body and the heat resistance of the base material and the heat resistance of the brazed portion at the same time, the stainless steel plate is coated with Al to form a powder or foil-like Ni-based material. A brazing material is applied or interposed (see JP-A-2-26643).

[0006]

However, the conventional structure for improving the heat resistance of the substrate has the following problems. That is, (1) When an Al-containing stainless steel containing 3 to 8% Al is cold-worked to form a metal foil, it is difficult to work, the yield is poor, and the productivity is deteriorated.

(2) Al plating is performed and after heating Al ₂ O ₃
When using whiskers, it is not suitable for brazing because the surface is covered with oxide and its adhesion to metal is insufficient. It is necessary to perform a special process such as

Further, the conventional brazing joining has the following problems. For example, the method of inserting the brazing material foil has the following problems. (1) It is difficult to form a thin film because the brazing filler metal foil has poor ductility, and the thickness of the brazing filler metal is large, from 20 to 50 μm, so the material cost of the brazing filler metal component is high. Poor performance and high cost of using brazing foil.

(2) It is not easy to insert the brazing material foil and the positioning is difficult. (3) Since the amount of brazing filler metal is large, as the temperature during brazing rises, the brazing filler metal diffuses more into the base material and changes from the ferrite structure of the base material to the austenite structure. Thermal strain occurs due to the difference in thermal expansion. Further, as the temperature rises during engine operation, the brazing filler metal diffuses into the base material, deteriorating the high temperature oxidative property.

Further, the method of applying the brazing material has the following problems. That is, (4) since the brazing material itself cannot be applied, it is necessary to mix the brazing material with the resin binder and then apply it.
Therefore, it is difficult to reduce the coating thickness, and there are the same problems as the problems (1) and (3) of the brazing foil.

(5) Further, there are problems that the thickness of the coating film varies greatly and the adhesion of the coating film is poor.
Therefore, when the flat steel plate and the corrugated steel plate coated with the brazing filler metal mixed with the resin binder are overlapped and wound in a roll, the coating film is partially peeled, or the peeled coating film However, there is a problem in that the brazing joint strength after that becomes unstable because it adheres to another place and is caught.

[0012]

The present invention relates to a heat resistant steel plate
After the heat-resistant steel plate is plated with Al, the Al oxide layer is formed by heating in the atmosphere. Then, a brazing film of a Ni-Cr based alloy plated on the Al oxide layer by dry plating or the like is formed. When the Ni—Cr alloy component is heated in the brazing heat treatment, Ni and B of the coating component interdiffuse with Fe that is the base component, and the melting point rises, so that there is a problem that bonding becomes difficult. The Al oxide layer has an effect of suppressing this diffusion during heating.

The base material preferably has a ferrite structure for the purpose of suppressing thermal expansion at high temperatures. The formation of the Al oxide on the surface of the substrate can be obtained by coating the Al oxide with a coating, or by coating the substrate with Al and then performing atmospheric heating in a temperature range of 200 to 1000 ° C. to oxidize the substrate. The Al oxide layer may not have a whisker-like structure. Further, when oxidizing after Al coating, it is not necessary to make all of the Al coating part an Al oxide layer, and only the surface layer (distance up to 3 μm from the surface) is A
It is sufficient if it is an 1-oxide layer.

That is, in both the method of coating with Al oxide and the method of coating and oxidizing with Al, the preferable thickness of the Al oxide layer is 3 μm or less, particularly, 0.
It is 1 μm to 2.0 μm. The present invention has a structure of steel plate / Al oxide layer / brazing layer and steel plate / Al layer / Al
Includes both oxide / brazed layer configurations.

When a honeycomb core is formed of a steel sheet having an Al oxide layer, the thickness of the honeycomb core is 30 μm or more and 200 μm or more in view of ensuring strength of the honeycomb core, moldability and weight reduction.
It is preferably m or less. Then, the shape thereof is a flat plate shape or a corrugated plate shape for forming a honeycomb core, and the honeycomb core is formed by combining and winding the flat plate steel plate and the corrugated steel plate.

This brazing film has a thickness of 0.1 μm or more 2
It shall have a film thickness of 0 μm or less. The reason for limiting the film thickness to this range is as follows. If the thickness is less than 0.1 μm, it is difficult to secure the bonding force. In addition, if the amount exceeds 20 μm and the adhesion amount is excessive, the production cost increases.

Ni-Cr alloy as a brazing film,
In particular, Ni-Cr-B type alloys, Ni-Cr-Si type alloys,
The Ni-Cr-Si-B alloy coating is effective in terms of high temperature oxidation resistance. The preferred composition of these alloys is Cr5-40
% By weight, 1 to 20% by weight of one or two of B and Si, and the balance Ni and inevitable impurities. These alloys are excellent in brazing property and high temperature oxidation resistance, and can form a film of a desired component by plating, particularly dry plating. The reason for adding the components of this alloy and the reason for limiting the preferable content range thereof are as follows.

Cr is added in order to prevent abnormal oxidation and ensure high temperature oxidation resistance, but if the Cr content is less than 5% by weight, high temperature oxidation resistance is not ensured, and if it exceeds 40% by weight, N is added.
The amount of i decreases and the high temperature oxidation resistance deteriorates.

One or two kinds of B and Si are added in order to lower the melting point of the brazing filler metal component, but if it is less than 1% by weight, the liquidus temperature does not lower as compared with the Ni-Cr alloy without addition, It does not exert its effect. On the other hand, if it exceeds 20% by weight, boride is formed in the B-added material and silicide is formed in the Si-added material, resulting in embrittlement. In the surface-treated steel sheet, the preferable range in which the brazing property is particularly good is 2% by weight or more and 12% by weight or less.

The brazing film (brazing property and high temperature oxidation resistant alloy film) is preferably formed by dry plating, which can adhere to the Al oxide on the surface of the base steel sheet with good adhesion. From this point of view, vacuum deposition or ion plating is preferable.

[0021]

In the surface-treated steel sheet according to the present invention, an Al oxide layer having heat resistance (high temperature strength) is formed between the steel sheet and the brazing film, and the brazing film (brazing resistance and resistance Since it forms a high-temperature oxidative alloy film, it has both heat resistance and brazing properties.

The Al oxide layer is formed by, for example, a method of directly forming the Al oxide layer on the surface of a steel plate such as vacuum plating, ion plating or sputtering on the substrate. Alternatively, it can be obtained by heating an Al-coated steel sheet obtained by coating Al in the atmosphere.
The coating of Al is not limited to vapor deposition such as vacuum deposition, ion plating and sputtering, or plating such as hot dip plating, and may be an Al clad steel plate. In addition, the Al oxide layer has both an amorphous structure formed at a low temperature and a crystalline Al oxide, for example, an Al ₂ O ₃ structure generated by heating in the air at a high temperature of about 900 ° C. But it's okay. In particular, it is preferable to form the Al oxide layer at a low temperature because the heat treatment cost can be reduced.

The Al oxide layer enhances the heat resistance of the base material to be plated, and at the same time, in the heating process from room temperature to the bonding temperature during brazing and bonding, the diffusion of the brazing film coated on the Al oxide layer. Acts as a barrier. That is, the interdiffusion of Ni and B in the plated brazing film with Fe in the steel sheet is blocked by the Al oxide layer as the intermediate layer during the heating process during brazing and joining.

In forming the brazing film, it is preferable to use a dry plating method in order to obtain adhesion with the Al oxide layer. This is because the wet plating method cannot form the Ni-based alloy plating containing Cr, so that the high temperature oxidation resistance of the brazeable film is deteriorated. Since the brazing film is formed by plating, the thickness of this film can be reduced to a desired value as compared with the conventional one. Further, if the well-known plating technique is applied to adjust the chemical composition, a brazing film can be formed on a desired portion of the metal member on which the Al oxide is formed.

Since the surface-treated steel sheet of the present invention is pre-coated with a brazing filler metal component in advance, if this steel sheet is used, the working process is more than that in the case of manufacturing a honeycomb core by a method of molding using a brazing foil. Can be simplified, and no positioning error occurs when the brazing foil is provided.

Therefore, the surface-treated steel sheet of the present invention thus obtained is used in a high temperature environment of 600 ° C. or higher, particularly a metal carrier which is used for an exhaust gas purifying apparatus for automobiles and motorcycles and which needs to be joined by brazing. It is useful as a base material (honeycomb core). To form a honeycomb core using this surface-treated steel sheet, prepare a corrugated plate-shaped surface-treated steel sheet and a flat plate-shaped surface-treated steel sheet on which an alloy film is formed, And the surface not to be plated are brought into contact with each other and brazed. Then, by covering the honeycomb body with an outer cylinder and joining them by spot welding or brazing, a carrier base material (honeycomb core) for an exhaust gas purifying apparatus is manufactured. Then, an exhaust gas purifying device is made by attaching a catalyst to the carrier substrate.

As a technique similar to the present invention, Japanese Patent Laid-Open No.
There is an insert material for diffusion bonding described in No. 2-38784. This is an insert material for joining two metal members, and the material supporting the diffusion bonding layer functions only as a carrier of the bonding layer and does not function as a structure. for that reason,
There is a possibility that a difference in strength will occur between the insert material and the base material and distortion will occur. On the other hand, in the present invention, since the material itself forms the structure, the purpose of the present invention is different from that of the above-mentioned invention and no distortion occurs.

[0028]

EXAMPLES Examples of the present invention will be described. A as the base foil
In the case of directly coating the oxide layer, 30 to
A ferritic stainless steel plate having a thickness of 200 μm, that is, a Fe-20 wt% Cr-5 wt% Al-REM-added steel plate, a SUS430 steel plate, and a SUS410 steel plate were used.
When the Al layer was coated and the Al oxide layer was formed on the surface by heating in the air, an Al clad stainless steel plate and an Al-plated stainless steel plate having a plate thickness of 30 to 200 μm were used. A vacuum deposition method and an ion plating method were used as a method for plating the Ni-Cr alloy film on the base foil. As the composition of the alloy film, Ni-Cr based plating species shown in Table 1 were used.

The bondability between the plated surfaces and the bondability (brazing property) between the plated surface and the base material not plated is a method for simulating the manufacturing process of the honeycomb molded heat-resistant structure (metal carrier) described below. I looked it up.

First, a base material foil plated with a brazing film and a base material foil not plated are each 15 mm × 1.
It was cut into a size of 5 mm. The hemispherical projections at three points shown in FIG. 1 were formed on either one of them by pushing into a position of an equilateral triangle as viewed from above. Next, a base foil having protrusions (plated base foil or non-plated base foil) and a heat-resistant stainless steel foil having no protrusions (plated base foil) are overlaid on top of each other. A weight of 2 to 10 g of a circular stainless steel plate was placed on. Then 10 ^-4 Tor
10 at 1100 to 1250 ° C. in a vacuum atmosphere of r
The bonding test was performed under the condition of holding for 120 minutes. After that, it was cut into three pieces including the protruding portion shown in FIG. 2, a hole having a diameter of 1 mm was made in the non-contact portion, a wire was passed through to peel off the joint portion, and the strength and fracture form were examined. As a result, those in which the breakage was observed in the base material foil part without being broken in the joint part were regarded as acceptable. The obtained results are summarized in Table 1 together with the film forming method and the brazing and joining conditions.

Next, the evaluation of the bondability of the metal carrier will be described below. FIG. 3 is a perspective view showing an example of the honeycomb heat-resistant structure 1 manufactured by using the surface-treated steel sheet according to the present invention. The honeycomb body 4 composed of the corrugated steel sheet 2 and the flat steel sheet 3 which are wound is shown. The outer cylinder 5 is covered and brazed. FIG. 4 is a diagram showing a manufacturing process of the honeycomb molded heat-resistant structure in the present invention. In the present invention, a step of preparing a base foil (a steel sheet having an Al oxide layer) and a brazing component are plated on the base foil. It is classified into a process, a process of forming a corrugated steel plate, and a joining process of brazing the corrugated steel plate 2 and the flat steel plate 3.

In the examples shown in Table 1, an Al oxide layer was first plated, and a base foil having an Al oxide layer 6 on its surface was prepared. In the examples shown in Table 2, first, the Al-clad stainless steel foil and the Al-plated stainless steel foil were exposed to air at 50
By heat-treating in a temperature range of 0 to 1000 ° C., a base foil having the Al oxide layer 6 on the surface was prepared.

The plating step, molding step and joining step will be described based on the single-sided plating method. First, at least one surface of the base material foil is plated with Ni—Cr alloy to form an alloy coating 7
To form. Next, in the forming step, a part of the steel sheet (foil) on which the alloy film 7 is formed is prepared as the flat steel sheet 3 as it is. Further, a part of the flat plate-shaped steel plate 3 is corrugated by a corrugating device to prepare a corrugated plate-shaped steel plate 2 in which predetermined linear corrugations of a corrugated plate are continuously bent. These corrugated plate-shaped steel plates 2 and flat plate-shaped steel plates 3 are wound in multiple layers while being alternately wound from a certain center. In the joining step, the corrugated steel sheet 2 and the flat steel sheet 3 are joined by heating after the forming step. That is, the Ni-based component laminated in the brazing component plating step is melted by heating and joins both the corrugated steel plate 2 and the flat steel plate 3. And
The heat-resistant structure 1 is manufactured through these manufacturing steps, that is, the preparation step, the brazing component plating step, the molding step, and the joining step.

When performing double-sided plating, Ni-Cr alloy plating is applied to both sides of the base material foil in the plating step, and then the plate foil 3 is prepared as it is, and the base material foil that is not plated is used as a corrugator. Corrugated and prepared, corrugated steel sheet 2 in which the predetermined linear corrugated irregularities of the corrugated sheet are continuously bent and formed, and are melted by heating and joined together. In addition, N is applied to both sides of the steel plate (foil) in the plating process.
In some cases, after the i-Cr alloy plating is performed, corrugation is performed by a corrugating device to form corrugated plate-shaped steel plate 2 in which unevenness is continuously bent and formed, and flat plate-shaped steel plate 3 that is not plated is joined by heating. . FIG. 5 shows the relationship between the plating film structure and the joining method. The test piece was cut out so that the joining property of the flat plate-shaped steel plate 3 and the corrugated plate-shaped steel plate 2 of the metal carrier produced in this way was included and the joining property was evaluated. The results obtained are shown in Table 1.

Experiments were also conducted on comparative examples in which the film thickness of the film of the brazing component is out of the range of the present invention, and comparative examples using the brazing foil, and the results are also shown in Table 1. From Table 1 below, in the case of the comparative example in which the film thickness and the alloy composition are out of the range of the present invention and the comparative example using the brazing material foil, the bonding strength is deteriorated or the productivity is deteriorated. On the other hand, according to the present invention, it is apparent that good bonding strength can be obtained and that productivity and economy are excellent.

[0036]

As described above, according to the present invention,
When brazing is performed on a steel sheet coated with an Al oxide layer using a surface-treated steel sheet coated with a Ni—Cr brazing film having a defined film thickness and alloy composition, the following effects are exhibited.

Firstly, it is not necessary to perform positioning as compared with the conventional one which is arranged between the brazing foil and the steel plate (in the case of the honeycomb body, between the flat plate-shaped steel plate and the corrugated plate-shaped steel plate). Therefore, the manufacturing process can be simplified and the manufacturing process can be simplified.

Secondly, as compared with the conventional brazing foil, the brazing component layer is thin, and the dissimilar organization of the base metal is so small that it can be ignored. Therefore, high temperature oxidation resistance and durability are improved. Thirdly, since the expensive brazing component layer is thin, the weight is reduced and the cost is reduced.

Fourth, the Al oxide layer is present between the brazing component layer and the steel sheet. For this reason, mutual diffusion of the brazing component and the steel plate component is suppressed, and there is little change in the alloy component of the brazing layer, and sufficient joint strength can be obtained. Fifth, since it has an Al oxide layer as an intermediate layer, it has good heat resistance.

[0040]

[Table 1]

[0041]

[Table 2]

[Brief description of drawings]

FIG. 1 is an explanatory view of a bonding test simulating honeycomb molding.

FIG. 2 is a diagram showing a method for measuring bonding strength.

FIG. 3 is a perspective view for explaining a heat resistant structure according to the present invention.

FIG. 4 is a diagram illustrating a manufacturing process of the honeycomb molded heat-resistant structure according to the present invention.

FIG. 5 is a diagram showing the relationship between the coating composition of the surface-treated steel sheet and the joining method according to the present invention.

[Explanation of symbols]

1 ... Heat resistant structure, 2 ... Corrugated steel plate, 3 ... Flat steel plate, 4
... Honeycomb body, 5 ... Outer cylinder, 6 ... Al oxide layer, 7 ... Alloy film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Kozaki 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Tetsuro Toyota 1-13-12 Nishi-Shinjuku, Shinjuku-ku, Tokyo Showa Aircraft Industry Co., Ltd.

Claims (5)

[Claims] 1. An excellent brazing property, comprising a steel sheet, an aluminum oxide layer formed on the surface of the steel sheet, and a brazing film of 0.1 to 20 μm formed by plating on the aluminum oxide layer. Surface treated steel sheet. 2. An aluminum-coated steel sheet, an aluminum oxide layer formed on the aluminum-coated surface of this steel sheet, and 0.1 to 0.1 plated on the aluminum oxide layer.
A surface-treated steel sheet having a brazing property of 20 μm and having excellent brazing properties. 3. The brazing alloy film according to claim 1, wherein the brazing alloy film comprises 5 to 40% by weight of Cr, 1 to 20% by weight of one or two of B and Si, and the balance Ni and unavoidable impurities. Surface-treated steel sheet with excellent attachability. 4. The surface-treated steel sheet excellent in brazability according to claim 1, wherein the alloy coating is a dry plating coating. 5. The surface-treated steel sheet excellent in brazability according to claim 1, 3 or 4, wherein the steel sheet coated with aluminum oxide or aluminum is a ferritic stainless steel sheet.