JPS607706B2 - Manufacturing method of satin-textured austenitic stainless steel material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an austenitic stainless steel material having a satin texture with a degree of surface texture larger than that of a subordinate steel. The present invention relates to a method for manufacturing an austenitic stainless steel material having a satin texture with a surface roughness greater than that of conventional materials, which takes advantage of the property that chromium-deficient areas that occur in adjacent areas are easily corroded.

Recently, austenitic stainless steel materials, especially steel sheets, have been used in various applications that require a high surface roughness of the satin texture, such as coating with inorganic or organic substances, or in order to make the contrast of the satin texture clear. .

By the way, conventional methods for manufacturing satin-finished austenitic stainless steel materials include methods such as applying shot-plast or hairlining to the surface, methods such as liquid awning, or methods using corrosive liquids such as ferric chloride solution or nitrofluoric acid. Methods that corrode the surface are generally used, but in these methods, even if an abrasive with the coarsest particle size is used, or even if it is carried out under optimal corrosion conditions, the surface roughness that can be used for the above-mentioned purposes cannot be achieved. It was difficult to manufacture satin-textured steel materials.
In other words, a satin-textured austenitic stainless steel plate was processed using the shot-plast processing method (glass beads with a grain size of #80 were sprayed at a pressure of 6k9), the endless paper polishing method (
using endless vapor made of alumina powder with particle size #30), ferric chloride solution corrosion method (heating a mixed acid containing 3% by weight of ferric chloride and 5% by volume of hydrochloric acid to a temperature of 50 to 6000,
immersion in nitric acid for 8 minutes), and nitric-fluoric acid solution corrosion method (nitric acid 5 min.
A mixed solution containing 50 to 600% by volume and 5% by volume of hydrofluoric acid
When the surface roughness of the product manufactured by heating to 0 and soaking for 8 minutes was measured using a stylus type surface roughness meter (hereinafter simply referred to as a roughness meter), the surface roughness was as shown in Figure 1. At most Rmax
There are 20 to 30 Buddhas. If the surface roughness is as large as this, even if the coating is coated with an austenitic stainless steel plate, a sufficient anchoring effect will not be obtained and the adhesion of the coating will be poor. It was insufficient, and even when used without the coating, the contrast of the satin finish could not be sufficiently understood at a slight distance. The present invention provides a method for producing a satin-finished austenitic stainless steel material, which has a surface roughness greater than that produced by conventional methods, has superior adhesion to a covering due to the anchor effect, and has a clear satin-finished contrast. The purpose is to

In order to achieve the purpose of the present invention, the manufacturing method devised by the present inventors is to create numerous microscopic parts on the surface of the steel material that are easily eroded locally by a corrosive liquid, and then corrode those parts with the corrosive liquid. be. The method devised by the present inventors is to perform sensitization heat treatment as a method of creating numerous microscopic portions that are easily locally eroded by the corrosive liquid. This sensitizing heat treatment is disliked in stainless steel, where corrosion resistance is of utmost importance, as it is the treatment that makes the corrosion resistance the worst, but in the case of the present invention, it is intentionally applied to take advantage of it. It is. That is, when austenitic stainless steel is slowly cooled in the range of 400 to 850oC or heated to this range, chromium carbide (Cr23C6) is precipitated at the grain boundaries as shown in Figure 2A, and as a result, The amount of chromium in the adjacent area decreases, creating a chromium-deficient area (heat treatment within this chromium precipitation temperature range to precipitate chromium carbide is called sensitization heat treatment).

By the way, since the size of crystal grains is on the micron scale, chromium carbide precipitation occurs locally in numerous microscopic shapes.
As a result, chromium-deficient areas occur under the same circumstances. Therefore, the chromium-deficient area is preferentially corroded when a corrosive solution is applied, so a highly corrosive salt solution or acid solution such as ferric chloride solution, sulfuric acid or nitric-fluoric acid, or a mixture thereof may be used. When a solution is applied, the material is preferentially and easily corroded, and as a result, the crystal grains present on the surface fall off, resulting in a matte surface with a large degree of surface texture that cannot be obtained by conventional methods.
The surface roughness of the austenitic stainless steel material manufactured using this method is measured with a roughness meter and is Rmax50~
60 France, which is considerably larger than those produced by conventional methods, has a deeper contrast in the satin finish, and also shows good film adhesion when painted with various commercially available synthetic resin paints. . However, if the surface is simply roughened with a corrosive solution after sensitization heat treatment, chromium carbide will precipitate throughout the grain boundaries, including inside the steel, resulting in poor corrosion resistance and poor workability.
There may be restrictions on usage.

For this reason, steel materials are subjected to solution heat treatment after being exposed to a corrosive liquid to improve their corrosion resistance and workability. Figure 2B shows the structure of the steel material in Figure 2A subjected to solution heat treatment at 1050 qo x 2 minutes, and the chromium carbide is completely solutionized.5 The method for this solution heat treatment is ammonia cracking. There is a bright treatment that does not generate scale, which is performed in a reducing atmosphere such as gas or hydrogen gas, and a general treatment that generates scale, which is performed in an oxidizing atmosphere such as combustion gas or the atmosphere. It is necessary to remove scale by pickling or pickling. By the way, in the case of ordinary austenitic stainless steel materials, especially steel plates, the grain size is 6 to 9 as specified in JIS G 0551 (austenite grain size test method for steel).
(particle size 55 to 15 French), so even if particles of this size are corroded with a corrosive solution after sensitization heat treatment, the surface roughness will not be as high as 5.
You can only get satiny skin with a rating of 0 to 60.

Therefore, in order to produce a satin-textured austenitic stainless steel material with a surface degree larger than this, the crystal grains must be made larger before the sensitization heat treatment, and the crystal grains that fall off when a corrosive solution is applied are made larger. do it. A suitable method for enlarging the crystal grains is to perform cold working, preferably in the cold worked state, and then sintering at a recrystallization temperature. For example, an as-cold-rolled austenitic stainless steel plate is recrystallized annealed at 1150 pm for 5 minutes to coarsen the crystal grains to about No. 3 (grain size 130 to 150 peaks) specified in the JIS mentioned above, and then sharpen. After chemical heat treatment and corrosion treatment, the surface roughness level is 70 on a roughness meter.
An austenitic stainless steel sheet with a rough satin finish of ~80 mm, which could not be predicted by conventional manufacturing methods, can be obtained. The satin contrast of this steel sheet is even deeper and more pronounced than that of the steel sheet that is not recrystallized and annealed, and the adhesion of the coating is further improved, and it shows extremely excellent adhesion that would be unimaginable with conventional methods. In addition, depending on the processing and use, corrosion resistance and workability may be required for this satin-textured austenitic stainless steel material with coarsened crystal grains, as described above. Solution heat treatment may be performed to improve the above properties, and if the solution heat treatment is the aforementioned general treatment, descaling may be performed by pickling or the like.

As described above, in contrast to the conventional method for producing satin-textured austenitic stainless steel materials, which only improves the method for forming the matte-finished surface without making any improvements to the material, the present invention provides the following improvements in the manufacturing process: By adding heat treatment to the material, the surface texture of the satin finish is made even greater than that produced using conventional manufacturing methods, making it suitable for applications that require coatings or deep contrast of the satin finish. It is characterized by the fact that it is made as follows.

Next, examples will be given.

Example 1 SUS304 steel plate specified in JIS G 4305 (cold rolled stainless steel plate) (thickness 0.7 side, JIS G 4305 (cold rolled stainless steel plate)
G.0551 (grain size 8, surface finish is finished) was used as a material, and after being subjected to sensitization heat treatment at a temperature of 650 qo for 30 minutes to precipitate chromium carbide, it was treated with 5% by volume of nitric acid at a temperature of 50 to 60 qC. The surface was corroded by immersing it in a mixed acid solution containing 5% by volume of hydrofluoric acid for 8 minutes.

The surface roughness of the matte surface of this steel plate was measured using a roughness meter.
It was max 61mm. FIG. 2A shows the crystal structure after the sensitization heat treatment, and FIG. 3A shows a surface roughness measurement chart. As is clear from FIG. 2A, chromium carbide is precipitated at grain boundaries. Example 2 Using the same material as in Example 1, sensitization heat treatment was performed at a temperature of 600°C for 40 minutes to precipitate chromium carbide at grain boundaries, and then a 4% by weight ferric chloride solution at a temperature of 50 to 60 qo was applied. The surface was corroded by immersion in water for 8 minutes.

The surface roughness of the matte surface of this steel plate was measured using a roughness meter.
There were a maximum of 54 mountains. FIG. 3b shows a surface roughness measurement chart of this steel plate. Example 3 A satin-textured steel sheet manufactured using the same material and the same method as in Example 1 was heated at a temperature of 1050 pm in an atmospheric atmosphere for 2 hours.
It was subjected to a lacquer-forming heat treatment for 5 minutes, and then immersed in a 5 volume % nitric acid solution at a temperature of 50 qo for 5 minutes to remove scale generated on the surface.

The surface roughness of this steel plate was measured using a roughness meter.
It was max 55 Buddha.

FIG. 2B shows the crystal structure after solution heat treatment, and as is clear from the figure, chromium carbide has been solutionized. Example 4 SUS304 steel plate (plate thickness 2
．． 0 legs, austenite grain size No. 7 according to JIS G 0551, surface finish fox finish) is used as the material, 65
% cold rolling to a plate thickness of 0.7%, followed by recrystallization sintering at a temperature of 115,000 for 5 minutes to obtain austenite grain size No. 3 as specified in JIS G 0551. After that, the temperature becomes 650.
A sensitizing heat treatment was carried out for 3 minutes at 0.0° C., and then the surface was corroded by immersion in a mixed acid solution containing 5% by volume of nitric acid and 5% by volume of hydrofluoric acid at a temperature of 50 to 6000°C.

The surface roughness of the matte surface of this steel plate is around R as measured with a roughness meter.
There were a maximum of 74 mountains. FIG. 3c shows a surface roughness measurement chart of this steel plate. Example 5 The same materials and methods as in Example 4 were used until recrystallization and dulling, followed by sensitization heat treatment at a temperature of 600q0 for 40 minutes, and further 4% by weight ferric chloride at a temperature of 50 to 6020 The surface was corroded by immersion in the solution for 8 minutes.

When the satin surface texture of this steel plate was measured using a roughness meter, R
It was a maximum of 80 mountains. Figure 3d shows a surface roughness measurement chart of this steel plate. Example 6 A satin-textured austenitic stainless steel sheet manufactured by the conventional method described above (excluding those using the endless paper polishing method) and a satin-finished austenitic stainless steel sheet manufactured by the methods of Examples 1, 2, 4, and 5. Each steel plate is coated with various commercially available synthetic resin paints so that the dry film thickness is 30 to 60 mm, dried under the optimum drying conditions for each paint, and then tested according to JIS G 3312 ( A cross-cut cellotape peeling test was conducted in which a cross-cut grid was drawn using the method specified in 8.5 Cross-cut test for colored galvanized iron sheets), and then cellophane tape was applied to the cross-cut section and the coating was peeled off. I went about paying the meeting fees.

The results are shown in the attached table, and the steel sheets manufactured by the method of the present invention exhibit superior coating film adhesion compared to those manufactured by the conventional method. In particular, it can be seen that the products that were subjected to recrystallization competitive hammering showed much better coating adhesion than the conventional products. Note 1) a Shot blasting method uses particle size #8
o glass beads were sprayed at a pressure of 6&.

b The nitric-fluoric acid solution corrosion method involves heating a silicic acid solution containing 5 volumes of nitric acid* and 5 volumes of hydrofluoric acid* to 50 to 60°C,
It was soaked for 8 minutes.

In the ferric chloride solution corrosion method, a mixed solution containing 30% by weight of ferric chloride and 5% by volume of hydrochloric acid was heated to 50-0°C and immersed in it for 8 minutes.

Note 2) Evaluation of paint film adhesion ×Painting of Go number part is peeled off by more than 40 years △ ″ 40-10% peeling ○ 〃 10% or less ◎The desert part of the grid remains

[Brief explanation of drawings]

Figure 1 shows the surface roughness measured by a roughness meter of a satin-textured austenitic stainless steel sheet manufactured by the conventional manufacturing method, Figure 2A shows the metallographic structure of the austenitic stainless steel sheet after sensitization heat treatment, and Figure 2B shows the metallographic structure of the austenitic stainless steel sheet after sensitization heat treatment. The metal structures of austenitic stainless steel sheets obtained by solution heat treatment after sensitization heat treatment are shown. FIG. 3 shows the surface grain size of the satin-textured austenitic stainless steel sheets of Examples 1 to 4 measured by a roughness meter. Figure l Figure 2 Figure 3

Claims (1)

[Scope of Claims] 1. A method for producing a satin-textured austenitic stainless steel material, which comprises subjecting the stainless steel material to a sensitizing heat treatment, and then corroding the surface by applying a corrosive liquid to the surface to make the surface matte-like. 2. A method for producing a satin-textured austenitic stainless steel material, which comprises subjecting the stainless steel material to sensitization heat treatment, corroding the surface by applying a corrosive solution to make the surface matte, and then subjecting it to solution heat treatment. 3 After cold working the stainless steel material, recrystallization annealing is performed to coarsen the crystals, followed by sensitization heat treatment, and then a corrosive liquid is applied to the surface to corrode it and make the surface matte. A method for producing a characteristic satin-textured austenitic stainless steel material. 4. After cold working the stainless steel material, recrystallization annealing is performed to coarsen the crystals, then sensitization heat treatment is performed, and then a corrosive liquid is applied to the surface to corrode it, making the surface matte. A method for producing a satin-textured austenitic stainless steel material, characterized by subjecting it to solution heat treatment.