JPH0525602A - Production of aluminum plated austenitic stainless steel having excellent plating adhesion - Google Patents

Abstract

PURPOSE:To provide the process for production of the aluminum plated austenitic stainless steel sheet having excellent plating adhesion. CONSTITUTION:The steel sheet is subjected to repetitive bending at the radius of >=200 times the sheet thickness >=2 times in the directions varying in the thickness direction while the surface temp. of the plated sheet remains at 150 deg.C upon solidification of the surface after aluminum plating, by which microcracks are generated in the alloy layer. The microcracks are generated in the alloy layer in the process of production in this way and the plating adhesion at the time of practicable molding is improved. Consequently, the replacement of the fields where materials, such as porcelain, castings, and ceramics, are heretofore used with the inexpensive iron and steel products by this invention is possible and a contribution is made to a cost reduction in many fields.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum-plated austenitic stainless steel sheet having excellent plating adhesion even when subjected to bending, drawing, or a combination of these.

[0002]

Exhaust gas mufflers for automobiles and motorcycle engines, and exhaust pipes before and after them (hereinafter collectively referred to as mufflers) are installed in the lower floor of automobiles as axles, fuel tanks, various shafts, etc. Forced to coexist. As a result, the space to be installed is limited, so that it is processed into a strict shape. In addition, after being actually mounted on a vehicle or the like, the outer surface is exposed to various salts for the purpose of preventing freezing spattered on the road surface.

On the other hand, from the inner surface of the muffler, condensed corrosive liquid generated from engine exhaust gas (high-temperature exhaust gas generated in the engine is discharged through an exhaust manifold, a converter, etc., and then through a center pipe, a muffler, and a tail pipe. Since the temperature of the muffler is low when the engine is started, the condensate, which is water-condensed in the exhaust gas, adheres to the inner wall surface of the muffler and stays at the bottom of the muffler. ₃ ^2- ,
NH ₄ +, SO ₄ ²⁻ , NO ₃ ⁻ , other Cl and a trace amount of organic substances are contained, which affects the corrosion resistance of the muffler), and is exposed to high temperature and high humidity conditions. The environment inside and outside the muffler has a very bad influence on the corrosion of the material. With this background, automobile manufacturers and material manufacturers have begun to use stainless steel for muffler materials.

[0004]

It has been a long time since the demand for the stainless steel plate itself began to expand in applications where its unique properties such as corrosion resistance, high temperature oxidation resistance, and high temperature strength are utilized. Conventionally, the muffler has been manufactured by a so-called three-piece type in which an outer cylinder formed by winding a flat plate in a circumferential shape and front and rear end plates are assembled by tightening, but recently, the muffler is economically manufactured. In order to do so, a two-piece muffler has been put into practical use, in which a pair of upper and lower "Monaka type" parts are manufactured by press molding, and then they are assembled by welding.

Among stainless steels, ferritic stainless steel sheets have some problems in press formability (deep drawing),
The austenitic stainless steel sheet typified by SUS304 is applied to this application because it is unsuitable for this application where it is pressed into a complicated shape, making use of excellent deep drawing. Further, depending on the type of vehicle and the driving area, Japanese Patent Publication No. 56-11749 and JP-A No. 55-97460.
As is known in the official gazettes such as the No. issue, products in which austenitic stainless steel plates are plated with aluminum are used. However, in the case of molding into a muffler having a complicated shape, the aluminum coating layer often peels off in the process of completing the shape, which is a problem. In addition, the development of steel products that have plating adhesion, corrosion resistance, and high-temperature characteristics in applications such as furnace walls such as high-temperature heating furnaces and dust incinerators, cooling pipes, and heat exchange systems is awaited. Was there.

[0006]

In view of these needs, the present invention relates to a method for producing a surface-treated stainless steel sheet which can greatly improve the life and performance, and its purpose is bending, drawing, flattening and flattening. Provided is an aluminum-plated austenitic stainless steel sheet having improved adhesion of a plating film when being formed into various shapes such as pipes, container cans and the like by undergoing pipe expansion processing or composite processing thereof. As a result of detailed examination of the plated layer of the cross-section of the steel sheet, which has been formed by performing hot-dip aluminum plating on various stainless steel sheets, the present inventors have found the following facts. Among them, in the aluminum-plated austenitic stainless steel sheet, the peeling phenomenon of the plating film concentrates on the boundary between the base steel and the alloy layer (Fe-Al), and the degree thereof is greater than that of ordinary steel sheet and ferritic stainless steel sheet. It was A major cause of the peeling phenomenon is that the coefficient of thermal expansion of the austenitic stainless steel sheet is higher than that of other steel types. Table 1 shows the thermal expansion coefficient of each steel.

[0007]

[Table 1]

Aluminum plating bath temperature is 660-70
In the cooling process immediately after hot-dip aluminum plating at 0 ° C., the coefficient of thermal expansion differs between the base iron and the alloy layer having a Hv hardness of 1000 to 1200, and a large internal stress occurs. In other words, in the molten aluminum plating bath, the base iron of the austenitic stainless steel and the alloy layer expand at the same rate immediately after they are formed, but they contract in accordance with the coefficient of thermal expansion of each in the cooling process after plating, Therefore, much larger internal stress occurs than ordinary steel and ferritic stainless steel. This internal stress causes peeling of the plating film when forming into various product shapes. Furthermore, the present inventors have tried various experiments based on such assumptions.

As a result, it has been found that the plating adhesion is significantly improved by repeatedly performing bending in the high temperature range of the cooling process of the aluminized austenitic stainless steel sheet that has passed through the molten aluminum plating bath. The present invention is configured on the basis of this finding, the gist thereof is in the cooling process of an aluminized austenitic stainless steel sheet that has passed through a molten aluminum plating bath, at a temperature immediately below the solidification temperature of the deposited aluminum plated metal to 150 ° C, This is a method for producing an aluminum-plated austenitic stainless steel sheet having excellent plating adhesion, in which bending with a curvature of 200 times or less of the steel sheet thickness is performed twice or more in different directions.

The present invention will be described in detail below. After passing the austenitic stainless steel plate manufactured through the normal manufacturing process and having the cleaned steel surface, after passing through an aluminum plating bath in which pure Al and Al-Si alloys are melted,
In the cooling process, the bending process with a curvature of 200 times or less of the plate thickness of the steel plate is repeated twice or more at a temperature just below the solidification temperature of the aluminum-plated metal welded to the steel plate to 150 ° C. This processing improves plating adhesion.

FIG. 1 shows the influence of the working temperature and working curvature on the plating adhesion when an aluminum-plated austenitic stainless steel plate having a plate thickness of 1.0 mm is bent at various temperatures during cooling immediately after plating. It is a thing. That is, the processed steel plate improves the plating adhesion (compared to the non-processed steel plate), and the degree of the improvement is greatly improved when the processing temperature is 150 ° C. or higher and the curvature is 200 times or less the steel plate thickness. In this case, if the working temperature is higher than the solidification of the aluminum-plated metal deposited on the steel plate, there is a problem in that it adheres to the bending roll and remarkably increases the peeling of the plating. Such an effect is obtained by repeating the bending process twice or more.

FIG. 2 shows the influence of the winding angle and the number of repetitions on the plating adhesion during bending of the aluminum-plated austenitic stainless steel sheet tested in FIG. As is clear from FIG. 2, the influence on the plating adhesion reaches the saturation region almost twice when the number of bending processes is two or more, regardless of the winding angle. The present invention is constructed on the basis of the above test results and limits each condition.

The phenomenon of plating adhesion improvement due to repeated bending can be explained for two reasons. First, the first point is the form of the alloy layer as shown in the representative example of FIG. The alloy layer of the product which has not been subjected to the repeated bending work exists almost as it is. This is because the alloy layer is solidified with a large amount of stress and strain inside due to the large shrinkage of the plating material (austenitic stainless steel). On the other hand, it is presumed that a large number of microcracks are generated in the alloy layer of the product that is repeatedly bent, and most of the internal stress generated during solidification shrinkage is released.

Needless to say, the presence or absence of internal stress, and to some extent, peeling of the coating (plating layer or plating layer or the like when the product is put to practical use in the market (projection process, drawing process, overdrawing composite molding process, severe bending process, etc.)) Since it is an important controlling factor for both the plating layer and the alloy layer, the product of the present invention, which is considered to have less internal stress, is less likely to peel off during processing during practical use.

The second point is the effect of microcracking of the alloy layer on absorption of the amount of coating elongation deformation during practical processing.
Peeling during the practical processing of an aluminum-plated product often occurs between the substrate and the alloy layer having an extremely high hardness (Hv: 1000 or more). Aluminum plating layer (generally Al alone or Al-Si component. Each contains impurities) against the poor workability of the alloy layer due to hardness.
Has a very high degree of ductility. The fact that the high-hardness alloy layer has rough microcracks disperses the entire elongation during practical processing into minute units. As a result, the overall elongational deformation is absorbed by the plated layer of high elongation, reducing damage to the entire coating such as cracking, flaking, or flaking.

[0016]

[Example] Based on the results of various basic experiments described above,
Austenitic stainless steel sheets were actually aluminum-plated on a continuous plating line, and the effect of bending immediately after plating on the plating adhesion was confirmed.
Table 2 shows those examples. In the bending temperature range in the table, the high temperature side shows the steel sheet temperature before entering the processing apparatus, and the low temperature side shows the steel sheet temperature immediately after leaving the apparatus.

[0017]

[Table 2A]

[0018]

[Table 2B] Note Plating adhesion test conditions and judgment standard CUP test [Conditions] Blank diameter 50 mm, drawing depth
10mm, die diameter 32mm, die shoulder radius 2mm [Judgment] (Observation of the outer wall surface of the drawing process) A: No abnormalities B: Two or three spots lifted up / peeled off in the scale of the plating layer C: Partial peeling of the plating layer D: 50% or more peeling of the plating layer E: Completely peeling of the plating layer Repeated impact [Procedure] --V-shaped impact bending test with a plunger whose tip width is twice the thickness x Impact bending --Inverted sample Flattened in the opposite direction to, and under the same conditions as [Judgment] 0 ← −−−−−−−−−−− → 100

[0019]

[Advantages of the Invention] Since the plating adhesion of austenitic stainless steel sheet aluminized products is greatly improved, molding processability, corrosion resistance, high temperature oxidation resistance, white appearance, etc., which cannot be applied in the past, are required. The product of the present invention can now be put to practical use. As a result, it has become possible to replace inexpensive steel products in fields where materials such as ceramics, castings, and ceramics have been used until now, and epoch-making cost reductions in both industrial products and private demand. I was able to do it.

[Brief description of drawings]

FIG. 1 shows the effect of working temperature and curvature in repeated bending work immediately after plating on plating adhesion.

FIG. 2 is a result of an experiment basically investigating the effects of the number of times of bending and the winding angle.

Claims (1)

Claim: What is claimed is: 1. In the cooling process of an aluminum-plated austenitic stainless steel sheet that has passed through a molten aluminum plating bath, the curvature of the steel sheet has a curvature at a temperature just below the solidification of the deposited aluminum-plated metal to 150 ° C. Of 20
A method for producing an aluminum-plated austenitic stainless steel sheet having excellent plating adhesion, which comprises bending 0 times or less twice or more in different directions.