JP2822141B2 - Method for producing high Al-containing ferritic stainless steel foil - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a ferrite stainless steel foil having a high Al content. In particular, A
l Excellent in the uniformity of the content distribution, and the plate thickness variation is small,
The present invention relates to a method for producing a ferritic stainless steel foil having excellent high-temperature oxidation resistance and electric heat resistance. The ferrite stainless steel foil obtained by the production method of the present invention is suitable for materials such as a heating element and a catalyst carrier of an automobile exhaust gas purifying apparatus.

[0002]

2. Description of the Related Art Ferritic stainless steel sheets containing a large amount of Cr are excellent in oxidation resistance and corrosion resistance, and are widely used in various industrial fields taking advantage of these characteristics. In order to impart more oxidation resistance to ferritic stainless steel, it is effective to add Al to the steel. However, the addition of a large amount of Al makes the material extremely brittle, so that not only cold rolling but also hot rolling becomes difficult. For this reason, it is extremely difficult to manufacture a high Al stainless steel sheet by a combination of ordinary rolling and annealing. Due to such difficulties in production, high-Al ferritic stainless steel sheets have not yet been fully utilized, despite having high electrical resistance and excellent oxidation resistance and corrosion resistance.

[0003] In a normal stainless steel mass-production process, due to a problem such as reduction in toughness of a steel strip during hot working, A
It is extremely difficult to produce a ferritic stainless steel containing l. As a means to solve this, Al is clad on a low-Al content stainless steel with excellent manufacturability,
Diffusion heat treatment after cold rolling to a predetermined thickness,
Production methods for obtaining a high Al-containing stainless steel without impairing the productivity are disclosed in JP-A-2-133562 and JP-A-2-1-1.
33563.

JP-A-2-133562 and JP-A-2-136
The production method of 133563 is to stack an Al or Al alloy plate on both sides or one side of stainless steel so as to have a ratio corresponding to the amount of Al to be contained, pass this between rolls to form a laminated pressure-welded plate, The laminated press-bonded plate (clad material) or a plate obtained by rolling the
In a temperature range of 00 ° C., high Al comprising diffusion heat treatment under conditions where the Al layer is alloyed without melting.
It is a manufacturing method of the containing stainless steel. In the present invention, the use of a ferritic stainless steel containing no Al as the base stainless steel is also advantageous in rolling and forming the clad material. Further, in the example in the publication, a SUS430 steel plate having a thickness of 1 mm was used as a material, and 0.05% was used.
It is said that the high-temperature oxidation resistance of the high-Al-containing ferrite stainless steel obtained by cladding an Al plate having a thickness of about 0.20 mm, rolling the sheet to 0.3 mm, and performing diffusion heat treatment is superior to SUS430.

[0005]

However, the thickness of Al occupied in the laminated pressure-welding plate (cladding material) made of Al or Al alloy (both are collectively referred to as Al) and stainless steel, or the diffusion from the time of clad rolling is large. If the total rolling ratio before the heat treatment is too high, there is a problem that the shape of the stainless steel phase in the clad material becomes non-uniform (the stainless steel layer becomes constricted and the thickness becomes non-uniform). The non-uniform shape of the rolled clad material is reported in the Bulletin of the Japan Institute of Metals, Vol. 26, No. 11, Plasticity and Processing Vol. 29, No. 332, etc. This problem is caused by the difference in the plastic deformation resistance of the constituent phases of the clad material. When the stainless steel phase is constricted, the thickness of the stainless steel phase and the Al coating amount change in the clad material, and as a result, the Al content in the high Al-containing stainless steel after the diffusion heat treatment becomes uneven.
Further, since the thickness variation of the obtained product becomes large, there is a problem that the high-temperature oxidation resistance, electric heat resistance, and moldability of the foil are deteriorated.

Generally, it is common sense to perform the Al diffusion heat treatment in a vacuum or in a reducing atmosphere. However, since the diffusion heat treatment requires time, it is difficult to perform the heat treatment in such a special atmosphere for a long time. It is a factor that worsens the sex. When trying to shorten the time required for diffusion heat treatment by raising the processing temperature in order to increase productivity, deformation of the foil and solid-phase bonding of the foils are likely to occur. Becomes difficult. In addition, if an attempt is made to shorten the heat treatment time by increasing the heating rate, Al melting tends to occur in a temperature range higher than the melting point of Al,
There is also a problem that the Al content in the product becomes non-uniform due to the flow of the gas.

An object of the present invention is to provide a method for producing a ferrite stainless steel foil having excellent A1 content distribution uniformity, a small thickness variation, and excellent high-temperature oxidation resistance and electric heat resistance. I do.

[0008]

In order to solve the above-mentioned problems, a method for producing a ferritic stainless steel foil according to the present invention comprises the steps of:
A cladding step of pressing the clad material overnight to obtain a clad material, and a diffusion heat treatment step of heating the obtained clad material to diffuse and infiltrate A1 into ferritic stainless steel;
A method for producing a high A1 content (over 5%) ferritic stainless steel foil of 0-200 μm;
５０50 μm, the hardness of A1 foil is Hv40 or less, the total rolling ratio from the clad material (base plate and A1 foil) to the diffusion heat treatment step is 15 to 87%, and the A1 / cladded material thickness ratio of the clad material is 0.12 or less.

The gist of the present invention is to use a ferrite stainless steel strip containing Al as a cladding material, reduce the thickness of the Al or Al alloy strip required to obtain the amount of Al to be contained, and further reduce the thickness of the material. By reducing the cumulative rolling ratio from the time of clad rolling to the time of diffusion heat treatment to suppress the occurrence of uneven shape (constriction) of the stainless phase in the clad material, and the unevenness of the Al amount after diffusion heat treatment. This is to suppress the thickness variation.

In the present invention, in the diffusion heat treatment step, the treatment atmosphere is the atmosphere, and the temperature is raised at a rate of 10 ° C./mi.
n or less, and the holding temperature is preferably 850 to 1000 ° C.

The present inventors have studied in detail the diffusion heat treatment method for the Al / SUS clad band. As a result, the atmosphere during the diffusion heat treatment was set to the air atmosphere, and the Al oxide A layer is formed and this is
It has been found that a physical coating that can prevent outflow of the molten layer can be obtained. Even when heated at a temperature increasing rate that causes Al melting due to the covering of the oxide, the molten Al is retained to some extent, and uneven Al content due to Al melting when heat treatment is performed at a high temperature increasing rate can be suppressed. Thereby, the diffusion heat treatment time is shortened, the productivity is increased, and the manufacturing cost is reduced because the atmosphere is in the atmosphere.

The high-Al-containing ferritic stainless steel foil (band) to be used in the present invention has an Al content of more than 5% and a thickness of 30 to 200 μm. Al of about 5% or less
This is because if it is contained, it can be industrially manufactured in a normal stainless steel mass production process, and it is superior in productivity and inexpensive. Regarding the range of plate thickness, the plate thickness is 200 μm
If it exceeds, Al is not easily diffused uniformly in the thickness direction, and a hard and brittle high Al portion remains in the surface layer portion, so that the ductility is remarkably deteriorated. If it is 30 μm or less, foil deformation is likely to occur during diffusion heat treatment, and it is difficult to obtain a good product.

In the present invention, it is preferable that the clad material be a ferrite stainless steel strip containing Al in a range that can be easily produced in the stainless steel mass production process. Since ferrite stainless steel easily diffuses Al as compared with austenitic steel, diffusion heat treatment can be performed at a low temperature in a short time. Therefore, it is advantageous as a target material of the present invention. The amount of Al contained in the material ferritic stainless steel is not particularly limited,
Since the production of stainless steel containing Al exceeding about 5% is difficult in a general stainless steel mass production process, the clad material ferritic stainless steel preferably has an Al content of about 5% or less. REM may be added to steel in order to improve high-temperature oxidation resistance.

In the present invention, the components of the Al (including Al alloy) foil are not particularly limited. From the viewpoint of improving high-temperature oxidation resistance, an Al alloy foil to which a small amount of Zr, Si, or the like is added may be used.

In the present invention, the thickness of the Al foil is set to 10 to 50 μm.
m. If it is less than 10 μm, wrinkles are likely to occur during clad rolling. If the thickness exceeds 50 μm, the clad rolling ratio required to obtain a bonding force between Al and SUS that does not cause the peeling of Al during cold rolling after clad rolling increases, so that the rolled material meanders during clad rolling to control the shape. It becomes difficult to do.

In the present invention, the hardness of the Al or Al alloy foil is set to Hv 40 or less, and for example, an annealing material is used as the foil material. When a hard material having a Vickers hardness of more than Hv40 is used, when the foil is further rolled after clad rolling, Al peeling is apt to occur during foil rolling, and the productivity is significantly reduced.
Further, even when heat treatment is performed to enhance the bonding strength of the clad material, blisters are easily generated in a hard material, and peeling occurs during foil rolling. Even if the rolling is not performed after the clad rolling, blisters are generated in the temperature rising process during the Al diffusion heat treatment, and the Al in the blister portion is melted, causing a non-uniform amount of Al. Generally, the rolling reduction required to obtain a strong bonding force is 30 to 40% or more at room temperature. However, under the manufacturing conditions of the present invention, the same Al rolling ratio is obtained at a cladding rolling reduction of 15% to 20%. / SUS bonding strength is obtained, and Al does not peel off during cold rolling. Therefore, the meandering control and the shape control are facilitated, and the generation of Al wrinkles can be prevented. This is presumably because the workability of the surface layer of the rolled material is higher than the workability of the inside of the rolled material, so that a new surface required for joining is more likely to occur during clad rolling. Further, it is considered that the heat generated during the rolling of the roll is easily transmitted to the Al / SUS interface due to the thin Al band, which is advantageous for the joining. A method of obtaining a strong bonding force even at a low rolling reduction by heating the clad material or heat treatment after clad rolling is known, but according to the present invention, these heat treatments can be omitted.

In the present invention, the ratio of Al / cladding plate thickness of the cladding material is set to 0.12 or less, and the total rolling ratio from the cladding material to the high Al-containing ferrite stainless steel foil (cladding foil) is 15 to 87. %.

In the range of the material thickness and the product thickness of the present invention, when the rolling reduction exceeds 87% or the Al / cladding plate thickness ratio exceeds 0.12, the constriction of the stainless phase in the cladding material occurs, and the Al / SUS is confined. The thickness ratio fluctuates in the longitudinal direction of the clad band. If the cumulative rolling ratio is less than 15%, when rolling is performed after clad rolling, warm cladding or heat treatment after clad rolling is required to prevent Al peeling, resulting in reduced productivity. If the rolling is not performed after the clad rolling, if the cumulative rolling reduction is less than 15%, blisters occur at the time of raising the temperature during the diffusion heat treatment, and this causes Al melting and tends to cause uneven Al content.

In the diffusion heat treatment step of one embodiment of the present invention, the temperature range of the diffusion heat treatment is 850 to 1000 ° C. If the temperature is lower than 850 ° C., the diffusion of Al is slow,
Above this, foil deformation or foil-to-foil solid phase bonding occurs.
The optimum temperature is around 850 to 950 ° C., which has the highest high temperature oxidation resistance.

[0020] In the diffusion heat treatment step of one embodiment of the present invention, the atmosphere of the diffusion heat treatment is air. In a vacuum or reducing atmosphere, the thickness of the oxide layer formed on the Al surface is not sufficient, and the molten Al cannot be retained. However,
If the heat treatment is performed in a state where the air easily flows around the sheet material, the surface is excessively oxidized and the amount of consumed Al becomes large. Therefore, it is preferable to perform the diffusion heat treatment in a tightly wound coil state. Further, the winding tension at that time is 5 (3 to
7) Desirably around kg / mm ² . If the tension is excessively high, problems such as deformation of the diffusion heat-treated material and solid-phase bonding occur.

In the diffusion heat treatment step of one embodiment of the present invention, the rate of temperature rise during the diffusion heat treatment is set to -10 ° C./min. If the temperature exceeds 10 ° C./min, molten Al cannot be held by the oxide layer formed on the Al surface. . This is considered to be because the speed of the Fe-Al alloying of the Al layer by the interdiffusion is lower than the generation speed of the molten Al. The lower limit of the heating rate is preferably 5 ° C./min. If it is less than this, the time required for raising the temperature of the diffusion heat treatment becomes longer, and the productivity decreases.

[0022]

【Example】

Example 1 Both surfaces of a ferritic stainless steel strip having a composition shown in Table 1 were polished with a roll brush, and an Al foil strip having a composition shown in Table 2 was cooled on both surfaces thereof at a plate thickness configuration and a rolling ratio shown in Table 3. Inter clad rolling was performed.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

Next, the obtained clad coil was cold-rolled to a sheet thickness shown in Table 3 according to a conventional method. After that, as a diffusion heat treatment, 9
The mixture was heated to 00 ° C., held for 6 hours, and cooled.
Table 3 shows the results of the Al content and the uniformity. The invention material did not cause constriction in the stainless steel phase of the clad foil. El
As a result of investigating the presence or absence of a gradient of the Al concentration with an ectron Prove Micro Analyzer Line Profile, it was confirmed that the Al content after the diffusion heat treatment was uniform in both the thickness direction and the plane direction.

In the range of the production conditions of the present invention, it has been confirmed that even if the rolling ratio of the cold clad rolling is 20% or less, a sufficient Al / SUS bonding force that does not cause Al peeling in the subsequent cold rolling can be obtained. did.

In sample 3, which is a comparative material, the cumulative rolling reduction was 8
Since it was as high as 7.2%, the stainless steel was constricted in the foil clad state, and undulations of about 10% were caused in the plate thickness. In addition, the Al concentration varied within the range of 9.5 to 12%. In sample 4, the cumulative rolling reduction was as high as 87.4%,
Also, since the Al layer / cladding plate thickness ratio was as high as 0.123%, swelling of 13% was generated in the plate thickness ratio, and the Al concentration was non-uniform as in Sample 3. Sample 7 with large material thickness
In the productions of Nos. 8 and 8, when the reduction ratio of the clad was 20% or less, only a bonding strength at which Al was peeled off in a bending test was obtained. In Sample 9, the Al / clad plate thickness ratio was 14.
Since it was as high as 2%, the bonding strength between Al and stainless steel at the time of cladding was not sufficient, and constriction of the bonding surface was also recognized. In Sample 10 using Hv42 hard Al foil,
Al exfoliation was caused by rolling after clad rolling, and when this was subjected to diffusion heat treatment, remarkable unevenness of Al amount in the plane direction occurred. In Sample 11, the amount of Al in the surface direction was non-uniform due to blisters generated during the temperature rise process.

Example 2 A 0.050 mm thick clad foil coil manufactured under the material conditions and rolling conditions of Sample 1 in Example 1 was subjected to a diffusion heat treatment in air under the heat treatment conditions shown in Table 4. A
Table 4 shows the results such as the uniformity of the amount of l.

[0030]

[Table 4]

Regarding the uniformity of Al content, Electron Prove
A line profile in which no Al concentration odor was observed in the thickness direction and the plane direction in the line profile of the Micro Analyzer was designated as Δ. At 1050 ° C. and 1100 ° C., deformation and fusion bonding of the foil (samples 7, 8, 9) occurred. The bonded sample was unable to unwind the coil after diffusion heat treatment.
In a temperature range of 850 to 1000 ° C. in which foil deformation and fusion bonding do not occur, if the holding is performed for about 6 hours, the amount of Al in the sheet thickness direction is uniform, but heating is performed at a heating rate exceeding 15 ° C./min. Then, the amount of Al in the plane direction became non-uniform (sample 3). Sample 4 treated at 800 ° C. also had an uneven amount of Al. In the invention materials (samples 1, 2, 5, and 6), the Al amount was non-uniform in the sheet thickness direction and the plane direction, foil deformation,
It was confirmed that no fusion bonding occurred.

[0032]

As is apparent from the above description, the present invention can suppress the occurrence of uneven shape (constriction) of the stainless steel phase in the clad material, so that the A1 content distribution is excellent and uniform. It is possible to provide a ferrite stainless steel foil having a small thickness variation and having excellent high-temperature oxidation resistance and electric heat resistance.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 20/00-20/04 B32B 15/01

Claims (2)

(57) [Claims] 1. A cladding step of pressing an Al foil against a surface of a ferritic stainless steel thin plate (original sheet) to obtain a clad material, and a diffusion heat treatment for heating the obtained clad material to diffuse and infiltrate Al into the ferritic stainless steel. A high Al-containing (5% or more) ferritic stainless steel foil having a thickness of 30 to 200 μm, comprising: an Al foil having a thickness of 10 to 50 μm, and a hardness of the Al foil of Hv 40 or less. The total rolling ratio from the clad material (original sheet and Al foil) to the diffusion heat treatment step is 15 to 87%, and the Al / clad material thickness ratio of the clad material is 0.12 or less. A method for producing an Al-containing ferritic stainless steel foil. 2. The high Al-containing ferritic stainless steel foil according to claim 1, wherein in the diffusion heat treatment step, the treatment atmosphere is the atmosphere, the temperature is raised at a rate of 10 ° C./min or less, and the holding temperature is 850 to 1000 ° C. Manufacturing method.