JPH0841652A - High temperature coated stainless steel plate with excellent oxidation resistance and corrosion resistance - Google Patents

Abstract

PURPOSE:To produce a coated stainless steel sheet for high temp. use excellent in oxidation resistance and corrosion resistance by forming a specified amt. of chromate treated layer on the surface of a stainless steel sheet and furthermore forming a lubricant coating material layer on the same treated layer. CONSTITUTION:On the surface of a stainless steel sheet, a chromate treated layer is formed by 5 to 100mg/m<2> as Cr coating weight, and moreover, on the surface of the same chromate treated layer, a lubricant coating material (coating material layer obtd. by incorporatmng wax into epoxy resin) is formed by about 3 to 5mum thickness. Thus, a coated stainless steel sheet for high temp. use excellent in oxidation resistance and corrosion resistance is obtd., which is suitable as the material for combustors. Moreover, since lubricating oil is not used at the time of forming process in this coated stainless steel sheet, a degreasing after forming process is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated stainless steel plate having excellent oxidation resistance and corrosion resistance after oxidation, which are used for exhaust mufflers of automobiles, parts around engines and parts for heating appliances.

[0002]

2. Description of the Related Art Combustion equipment parts such as exhaust mufflers, engine parts, and heating appliances of automobiles are exposed to an environment where a cycle of normal temperature-high temperature-normal temperature is repeated, and the maximum operating temperature reaches 800 to 900 ° C. Become hot.

Under such an environment, even if stainless steel shows sound oxidation resistance under normal atmosphere, the oxidation resistance is lowered when oil or the like is attached. That is,
When heated in a state where oil is attached, abnormal oxidation occurs in which only that portion undergoes remarkable oxidation, and as a result, the scale thickness of the abnormally oxidized portion increases and scale peeling occurs. Corrosion resistance after oxidation because a deep Cr deficient layer is locally formed on the base metal surface of this abnormal oxidation portion (hereinafter, the corrosion resistance of the base metal after oxide scale formation is simply referred to as corrosion resistance)
Is also deteriorated.

When stainless steel whose corrosion resistance is deteriorated in this way is heated, moisture in the combustion gas or moisture in the air is condensed on the surface of the steel sheet, and the condensed water contains sulfur or the like in the combustion gas. When mixed, it corrodes stainless steel.

Further, rock salt is sprayed on roads in cold regions to prevent freezing. When rock salt on the road scatters and adheres to exhaust mufflers and parts around the engine while the vehicle is running, this salt is oxidized. Fe ₂ O ₃ contained in the scale,
Red rust is generated in a short period of time by reacting with Fe ₃ O ₄ .

Therefore, stainless steel used for automobile exhaust mufflers, parts around engines, etc. is required to have oxidation resistance and corrosion resistance after oxidation.

As a countermeasure against such abnormal oxidation and deterioration of corrosion resistance, conventionally, means for adjusting the composition of the stainless steel has been mainly used. For example, high-purity ferritic stainless steel with reduced impurities such as C and N, and increased Si content,
There are ferritic stainless steels containing one or more of Ti, Nb, Zr and Al. JP-A-62-202056 discloses a stainless steel having excellent oxidation resistance and corrosion resistance, and JP-A-62-139853.
The publication discloses stainless steel having excellent oxidation resistance.

[0008]

It is not always sufficient to prevent abnormal oxidation and deterioration of corrosion resistance only by adjusting the composition of the above-mentioned steel. The object of the present invention is not a method by adjusting the composition of the composition of steel, but by carrying out a surface treatment of stainless steel, abnormal oxidation and scale which tend to occur in automobile exhaust mufflers, engine parts, combustion parts of heating appliances, etc. −
The purpose of the present invention is to provide a coated stainless steel sheet which prevents peeling of the aluminum and has excellent corrosion resistance.

[0009]

As described above, the oxidation resistance and corrosion resistance of a stainless steel plate can be generally dealt with by the operating temperature and the chemical composition of the material, but even a healthy stainless steel plate can be lubricated during forming. Partial abnormal oxidation and scale exfoliation may occur due to oil adhesion.

Further, in the state where such abnormal oxidation and scale exfoliation occur, the oxidized scale becomes porous and salt invades into the scale, and Fe ₂ O ₃ , which easily reacts with the salt,
The corrosion resistance of stainless steel deteriorates due to Fe ₃ O ₄ and the Cr-deficient layer formed on the surface of the base material.

Therefore, the present inventors have focused on preventing abnormal oxidation and improving corrosion resistance from the viewpoint of treating the surface of stainless steel, not from adjusting the composition of stainless steel,
As a result of earnest research, the following findings were obtained.

A) If a chromate-treated layer is provided on the surface of the stainless steel sheet before being heated to the operating temperature, the chromate-treated layer will effectively exert the effect even if it is subsequently heated to a high temperature and the oxidation resistance will be improved.

B) The chromate-treated layer preferably has a Cr deposition amount of 5 to 100 mg / m ² .

C) By providing a lubricating coating layer on the chromate-treated layer, the chromate-treated layer can be protected during the molding process, and the use of lubricating oil is unnecessary during the molding process.

The present invention has been made on the basis of the above findings, and the gist of the present invention is that "the surface of a stainless steel plate has a chromate treatment layer having a Cr deposition amount of 5 to 100 mg / m ² , and It is a high temperature coated stainless steel plate having a lubricating coating layer on the chromate treatment layer and having excellent oxidation resistance and corrosion resistance. "

[0016]

Next, the reason and function of limiting the coated stainless steel plate of the present invention as described above will be explained.

1) Chromate Treatment Layer Chromate treatment is generally used in a coated steel sheet to improve the adhesion between metal and paint, but in the present invention, to improve oxidation resistance and corrosion resistance after oxidation. It is provided in. If the Cr deposition in the chromate treatment is less than 5 mg / m ² , the oxidation resistance and corrosion resistance after oxidation are insufficient, while if the Cr deposition is more than 100 mg / m ² , the workability deteriorates and the treatment process increases. Therefore, the amount of deposited Cr is set to the range of 5 to 100 mg / m ² .

The reason why the oxidation resistance is improved by the chromate treatment is that the surface of the stainless steel is covered with dense and stable Cr ₂ O ₃ because of the chromate treatment.
It is presumed that the supply of O ₂ to the stainless steel surface is suppressed and the oxidation is less likely to proceed.

Similarly, the corrosion resistance after oxidation is also Cr ₂ O ₃
It is presumed that the formation of Fe ₂ O ₃ , Fe ₃ O ₄ and Cr deficient layer is suppressed by being covered with.

2) Lubricating paint layer Lubricating oil is usually used to improve the workability in the forming of stainless steel sheets. Since the workability deteriorates when chromate treatment is applied to stainless steel, lubrication at the time of molding is important, but in the present invention, a lubricant coating layer is used instead of the conventional lubricating oil. By providing a lubricant coating layer on the chromate treatment layer as a lubricant before the molding process, the lubricating oil that was normally used as a lubricant during the molding process and was one of the causes of abnormal oxidation becomes unnecessary. Therefore, abnormal oxidation is prevented. The lubricating coating layer also has an effect of protecting the brittle chromate-treated layer during molding.

It is not necessary to limit the type of the lubricant coating, and any commercially available lubricant may be used. For example, a paint containing a wax in an epoxy resin, a paint containing a wax in a urethane resin or an epoxy resin, and the like can be mentioned.

The thickness of the lubricating coating layer may be such that the effect of lubrication can be obtained, and the thickness is usually about 3 to 6 μm.

The type of stainless steel is not limited and may be selected according to the application. Ferrite-based stainless steel is used for automobile exhaust mufflers and heating appliances, and representative ones include SUS430, SUS409L, SUS436L and the like.

[0024]

Example An oxidation resistance test piece having the following dimensions and a corrosion resistance test piece after oxidation were prepared from a ferritic stainless cold-rolled steel sheet having a thickness of 1.5 mm and a chemical composition shown in Table 1. After cleaning the surface of this test piece by alkaline degreasing, chromate treatment with Zinchrome 1320 manufactured by Nippon Parkerizing Co., Ltd.
It provided variously changed chromate treatment layer of Cr deposition amount within the range of ^{g / m 2 ~100mg / m 2} . Further, a lubricating paint composed of acrylic resin and wax manufactured by Kansai Paint Co., Ltd. was applied on the chromate-treated layer to form a lubricating paint layer having a thickness of 5 μm, and the test was conducted. Further, the test piece as degreased with the alkali was used as a comparative material.

[0025]

[Table 1]

Using the above test pieces, an oxidation resistance test and a corrosion resistance test after oxidation were carried out under the following conditions.

Oxidation resistance test Specimen dimensions: plate thickness 1.5 mm, width 20 mm, length 30 mm Heating temperature by electric furnace: 600-900 ℃ (100 ℃ interval) Heating atmosphere: In air Heating time: Continuous 200 hours After oxidation Corrosion resistance test Specimen size: Plate thickness 1.5 mm, width 70 mm, length 150 mm Cr adhesion amount: Inventive material 5 mg / m ² Comparative material 0 Same as the oxidation test conditions of [Oxidation conditions] Test: 5% NaCl, 35 ° C Spraying time: 10 hours After conducting the test under the above conditions, the oxidation resistance and scale thickness were measured in the oxidation resistance test. Also, in the corrosion resistance test after oxidation, the occurrence of red rust was observed.

FIG. 1, Table 2 and FIG. 2 show the test results. FIG. 1 is a diagram showing the effect of the amount of Cr deposited by the chromate treatment on oxidation, and Table 2 shows the Cr by the chromate treatment.
FIG. 2 is a table showing the relationship between the adhered amount and the thickness of the produced scale, and FIG. 2 is a diagram showing the results of an examination of corrosion resistance after oxidation by a salt spray test. From Fig. 1 and Table 2, the Cr deposition amount is higher than that of the comparative material without the treated layer and the comparison material with a small Cr deposition amount of 1 mg / m ^2.
It can be seen that the material of the present invention, which has been subjected to a chromate treatment of 5 mg / m ² or more, has a remarkably small amount of increased oxidation and a small scale thickness.

[0029]

[Table 2]

As is clear from FIG. 2, the results of the salt spray test after oxidation show that the stainless steel sheet of the present invention is much less likely to cause red rust than the unpainted stainless steel sheet of the comparative material. Compared to the test piece with a low oxidation temperature, the test piece with a high oxidation temperature generated less red rust because the scale produced by oxidation at a high temperature was more stable than the scale produced by oxidation at a low temperature.
Because it is covered with Cr ₂ O ₃ , red rust hardly occurs.

[0031]

The coated stainless steel sheet of the present invention is superior to ordinary stainless steel sheets in oxidation resistance and corrosion resistance after oxidation, and is suitable as a material for combustion equipment. Further, when the coated stainless steel sheet of the present invention is used, no lubricating oil is used during the forming process, so that the degreasing step after the forming process is unnecessary.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a Cr deposition amount and an oxide scale increase amount.

FIG. 2 is a diagram showing the results of an examination of corrosion resistance after oxidation by a salt spray test.

Claims (1)

[Claims] 1. A Cr deposit amount of 5 on the surface of a stainless steel plate.
~ 100 mg / m ² chromate treated layer, which has a lubricating paint layer on top of the chromate treated layer, and has excellent oxidation resistance and corrosion resistance. steel sheet.