JPH01208484A - Polished stainless steel having superior corrosion resistance and production thereof - Google Patents

Abstract

PURPOSE:To obtain polished stainless steel having superior corrosion resistance by immersing surface-polished stainless steel in a nitric acid-based aq. soln. to regulate the ratio of Cr to Fe in the surface layer of a prescribed thickness to a prescribed value. CONSTITUTION:Surface-polished stainless steel is immersed in nitric acid or a nitric acid-based aq. soln. to regulate the ratio of the number of Cr atoms to that of Fe atoms in the surface layer of 20Angstrom thickness to >=0.5. Thus, polished stainless steel having superior corrosion resistance is obtd.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides polished stainless steel materials that have good corrosion resistance and hardly rust even in severe corrosive environments.
The present invention also relates to a method for producing the stainless steel polished material.

<Prior art and its challenges> In recent years, the uses of stainless steel materials have become extremely diversified, and accordingly, products with various surface specifications have come to be manufactured. Among them, BA specification materials and 2B specification materials, which take advantage of the surface gloss unique to stainless steel, are in the widest demand, but depending on the application, matte materials with less surface gloss are often preferred, and recently they are used in construction materials. Interior Material 3 Demand for "stainless steel materials with intentionally scratched surfaces (polished materials)" used for home appliances, kitchen products, etc. is rapidly increasing.

Conventionally, the industrial production of the stainless steel polishing specifications mentioned above involves
Generally, a method of mechanically scratching a stainless steel material to be processed such as a continuously running copper strip by bringing a rotary grinding belt into contact with the stainless steel material to be processed has been generally adopted. The following two methods, which are broadly classified according to the "contact mode" and "surface pattern of the resulting product," were the mainstream.

A) As shown in Fig. 2, a method in which the stainless steel material 2 to be processed is run at a speed faster than the rotational movement speed of the grinding heald 1 causes scratches that are parallel to each other on the entire surface of the resulting product. This method is called HL (Hair Line) specification.

B) As shown in Fig. 3, this is a method in which the rotation speed of the grinding belt 1 is made faster than the traveling speed of the stainless steel material 2 to be processed, and relatively short scratches are intermittent in the longitudinal direction of the stainless steel material to be processed. A pattern is generated, and B
This method is called the G (Belt Grinded) specification.

Depending on the size of the abrasive grains in the belt used, a variety of abrasive materials with surface roughness ranging from coarse to fine were obtained using both methods, but both methods were used to improve the surface roughness of the stainless steel material due to processing heat. To prevent oxidation coloring and increase grinding efficiency, apply grinding oil (
It was essential to sprinkle some cutting oil and grind it.

Note that in BG polishing, the belt speed is usually 1000 m/
Performed at an extremely high speed of min or more, 1160~#3
A belt with an abrasive grain count of 20 is often used.In contrast, in the case of HL grinding, the relative speed between the belt and the stainless steel surface is about several tens of m/ff1in, but it is quite fast because the pressure pressing the belt is large. It is thought that there is a localized temperature rise.

However, it has been reported that the ``stainless steel polished material that exudes a unique style'' manufactured as described above ``occasionally rusts when used outdoors near the coast.'' BA specification materials and 2B used under similar conditions
Polished specification materials are generally graded B because specification materials do not rust.
It is said to have lower corrosion resistance than A specification material and 2B specification material,
Although the HL specification materials have somewhat better corrosion resistance than the BG specification materials, their applications are currently limited to some extent.

Therefore, in the course of research aimed at investigating and overcoming the causes of poor corrosion resistance of polished stainless steel materials as described above, the inventors discovered that the cause of the deterioration in corrosion resistance of stainless steel polished materials was during polishing. We have come to believe that the S (sulfur) in the cutting fluid used reacts with the stainless steel surface to create chromium sulfide. Based on this,
``When manufacturing stainless steel polishing specification materials, the S content in the cutting fluid must be 0.35% or less (hereinafter referred to as %, which represents the component ratio).
(% by weight) or C instead of S.
He proposed a measure to prevent deterioration of corrosion resistance of abrasive materials by using a cutting fluid containing T-compounds and P-compounds (Japanese Patent Application No. 1983).
-178956, Japanese Patent Application No. 62-278851).

However, as the inventors continued their research on this problem, they discovered that one of the major factors behind the poor corrosion resistance of stainless steel polished materials is that the surface We must also point out that the chemical composition of the oxide film has a high Fe content.''This new finding was reached.

That is, the surface of stainless steel is coated with Cr oxides (Cr203, etc.), Fe oxides (Fez O3+ Fe:+ Oa, etc.), l'In oxides (MnO, etc.), or Si oxides (S
iOz, etc.), of which Cr
The oxidation of Fe and Si forms a dense film with good corrosion resistance, but the oxidation of Fe
It is said that oxide films of Mn and Mn have poor corrosion resistance. When industrially mass producing stainless steel polished materials,
Although mechanical polishing is performed while being cooled with a large amount of grinding oil, it is estimated that the temperature of the polished stainless steel surface locally increases to several hundred degrees (probably 600 to 800 degrees Celsius). . Therefore, the oxidation of the stainless steel surface is promoted, and an oxide film made of various oxides as described above is formed on the surface of the stainless steel polished material. The present inventors analyzed the chemical composition of the surface layer (from the surface to a depth of about 20 mm) using XPS (X-ray photoelectron spectroscopy) and found that oxides of Fe, Cr, and Mn were present. It has been confirmed that the main component is
Moreover, as shown in Table 1, compared to BA specification material, Cr vs. F
It was discovered that the ratio of e (Cr/Fe) was extremely small.

Moreover, this (Cr/Fe) ratio is
It was also found that the larger the content, the smaller the content.

(Note) Stainless steel is 16.5χCr-0,4χCu-
0.6χNb material.

In other words, stainless steel polished materials have poor corrosion resistance due to the high Fe ratio in the surface oxide film, and in particular, products using grinding oil containing a large amount of S have a high Cr ratio in the oxide film. It was assumed that the corrosion resistance would become even lower and the deterioration of corrosion resistance would become more noticeable. However, when examining the [sulfide/Fe) ratio in the surface film of the "polishing material using S-containing grinding oil" shown in the middle row of Table 1, it was found to be 0.05, which is shown in the upper row. Since the value is one order of magnitude higher than 0.004, which is the value for "abrasive specification material using S-free grinding oil," it cannot be denied that the presence of sulfides is the cause of the deterioration of corrosion resistance.

<Major findings that formed the basis for the completion of the invention> In any case, based on the above speculation, the present inventors improved the corrosion resistance by changing the surface film composition (increasing the Cr content) of the polished stainless steel material. In order to achieve this, we conducted further research using effective methods, and as a result, we were able to obtain the following knowledge.

(al) After mechanically polishing the surface of a stainless steel material to obtain a polished material, if the material is immersed or electrolyzed in nitric acid or an aqueous solution containing nitric acid as its main component, special changes in appearance such as luster may occur. Its corrosion resistance is noticeably improved without causing corrosion.

fbl The above corrosion resistance improvement effect is presumed to be due to the nitric acid treatment dissolving Fe on the surface of the polished stainless steel material and relatively increasing the Cr concentration.
The atomic ratio of Cr and Fe in the extremely superficial layer (Cr/Fe
) is 0.5 or more, it stably exhibits excellent corrosion resistance not seen in conventional polished materials.

(C) Furthermore, based on the research results explained so far, he further inferred that ``If stainless steel polishing specification material is lightly etched chemically or electrochemically to dissolve and remove the layer with poor corrosion resistance on the surface, However, when chemical polishing and/or electrolytic polishing is actually performed, although changes in gloss and appearance are observed before and after the treatment, corrosion resistance is certainly improved. Moreover, a unique surface with excellent design can sometimes be obtained due to light etching.

(C) Furthermore, if a treatment of immersion in a nitric acid-based aqueous solution or a treatment of electrolysis in the aqueous solution is added after the chemical polishing or electrolytic polishing described in Section C1 above, the chemical polishing or electrolytic polishing It becomes possible to stably secure a (Cr/Pe) ratio of 0.5 or more in the surface layer of the surface-polished material, and further reliability is added to its corrosion resistance.

The present invention was made based on the above findings, and [the atomic ratio of Cr and Fe from the surface to a depth of 20 mm] Cr/Fe) is 0
．． It is characterized by the fact that it has a structure with a surface layer adjusted to 5 or more, which gives it excellent corrosion resistance. A method of immersing the stainless steel material in an aqueous solution containing the main component or electrolytically treating it in the aqueous solution, or a method of mechanically polishing the surface of the stainless steel material and then subjecting it to either or both of chemical polishing and electrolytic polishing. Alternatively, after mechanically polishing the surface of the stainless steel material, chemical polishing and/or electrolytic polishing are performed, and then immersion in nitric acid or an aqueous solution containing nitric acid as a main component or electrolytic polishing in the aqueous solution. Depending on the treatment method, the atomic ratio of Cr and Pe (Cr
/Fe) is adjusted to 0.5 or more, thereby making it possible to stably manufacture stainless steel polishing specification materials with excellent corrosion resistance.''

By the way, in the present invention, the reason why the atomic ratio of Cr and Fe (Cr/Fe) is adjusted to 0.5 or more from the surface of the polished stainless steel material to a depth of 20 mm is that (Cr/Fe) in the surface layer of the steel material is If the /Fe) ratio is lower than 0.5, the desired corrosion resistance cannot be obtained, and it is sufficient if the (Cr/Fe) ratio is at least 0.5 in the surface layer from the surface to a depth of 20 mm. This is because satisfactory corrosion resistance is ensured.

The type of stainless steel applied to the present invention is not particularly limited, but if a highly corrosion-resistant stainless steel with a high content of Cr, Ni, or MO is used, a product with better rust resistance can be obtained. Needless to say, it can be done.

Furthermore, the finer the abrasive grains of the abrasive material (endless belt, etc.) used in mechanical polishing, the more advantageous it is to obtaining a product with excellent rust resistance. From the viewpoint of improving the resistance to induction of the product, it is preferable that the relative speed between the abrasive material and the stainless steel material during polishing is slow, and that the pressure and time of pressing the abrasive material are small. In other words, roughening of the abrasive material, increase in the polishing speed, and increase in the pressure and time of pressing the abrasive material, etc. all cause local increases in the temperature of the stainless steel material, which promotes rusting. It is from.

Nitric acid treatment after surface polishing (either after mechanical polishing or after further chemical polishing and/or electrolytic polishing after mechanical polishing) is performed using nitric acid or nitric acid as the main component. Electrolysis in an aqueous solution has higher industrial value than simply immersion in an aqueous solution because the desired effect can be achieved in a shorter time.

Possible means of electrolytic treatment include anodic electrolysis, which applies a positive potential to the material to be treated, and alternating electrolysis, which applies alternately negative and positive potentials, but the latter is often more effective. Therefore, it is preferable.

Furthermore, in the case of alternating electrolysis, as shown in FIG. 4, for example, the stainless steel polished steel strip 3 is passed continuously near the cathode 4 and the anode 5 in a nitric acid-based aqueous solution to indirectly energize. It is also possible to adopt the method of
This method is suitable for mass production due to its high efficiency, and is advantageous in industrially providing polished stainless steel materials with good corrosion resistance at a lower cost.

The concentration of nitric acid used in the nitric acid-based aqueous solution treatment can range from 1 to 60% in both immersion treatment and electrolytic treatment, but is desirably adjusted to 5 to 30%.

As additives for the nitric acid-based aqueous solution, in addition to nitric acid, nitrates, chromates, and the like are allowed.

The nitric acid-based aqueous solution treatment described above only dissolves the very surface layer (probably several dozen) of polished stainless steel materials, and there is almost no difference in appearance before and after the treatment, and there is almost no change in gloss. It's not easy.

Chemical polishing uses hydrochloric acid, sulfuric acid, and phosphoric acid as usual.

Electrolytic polishing can be carried out in an aqueous solution such as nitric, hydrofluoric acid, aqua regia, or organic acid; electrolytic polishing can be carried out in a sulfate or mineral acid solution.

It is sufficient to carry out the reaction in an aqueous solution of an organic acid or the like.

By implementing the above-mentioned "corrosion resistance improvement treatment after polishing stainless steel materials", the degree of freedom in BG and HL polishing conditions is greatly increased. It is also possible to freely add additives such as and S-based compounds, so its industrial value is extremely large.

Now, FIG. 1 shows the manufacturing process of the stainless steel polishing specification material according to the present invention [FIG. 1(a)] compared to the conventional manufacturing process [FIG.
Figure (b)] is shown in comparison.

From Figure 1, it can be seen that the process of the present invention requires more man-hours than the conventional process, and may be viewed as disadvantageous.
Considering that the work efficiency in manufacturing stainless steel polished materials is rate-limited after mechanical polishing, selecting the process of the present invention that can increase the mechanical polishing rate will lead to increased production speed in the entire process, It is clear that cost reductions can be achieved.

In other words, in the conventional process, in order not to deteriorate corrosion resistance, it is necessary to use a grinding fluid with few additives (in other words, poor grinding properties), so the grinding speed (speed of movement of the steel strip) must be reduced or Polishing must be repeated. Furthermore, the abrasive belt suffers a lot of wear and tear and needs to be replaced frequently, resulting in poor work efficiency and increased material costs.

On the other hand, in the process of the present invention, grinding oil with good abrasiveness (added oil such as S) can be used, so the grinding speed is faster, and the wear and tear on the abrasive belt is less. Because the particles sharply scrape the stainless steel surface (if you use oil with poor abrasive properties, the surface will look like it's been ripped off, it will have a jagged surface), and you can also obtain a polished surface with a good gloss. Furthermore, the nitric acid-based aqueous solution treatment, chemical polishing, or electropolishing treatment according to the present invention can be performed as an integrated process that is continuous with the mechanical polishing treatment, and in this case, the manufacturing speed can be increased and the cost can be significantly reduced. .

In addition, "degreasing" in the process of the present invention in Figure 1 ta) is as follows:
An organic solvent such as trichlorethylene may be used, or
It goes without saying that alkaline degreasing, which is applied as a pretreatment for plating, is also effective.

Next, the effects of the present invention will be specifically explained using examples and comparing with comparative examples.

<Example> 5US304 equivalent stainless steel (A steel) and C: 0.0
15%, Si: 0.49%, Mn: 0.4
5%, P: 0.026%.

S: 0.003%, Cr: 16.5%, Nb
A thin plate of stainless steel (B steel) containing: 0.6%, Cu: 0.4%, and the remainder substantially consisting of Fe (both
A 2B specification material with a plate thickness of 0.7 dragon was prepared and polished to No., 4 specification (BG specification) and HL specification using existing continuous polishing equipment.

In addition, for the examples of the present invention, following the mechanical polishing described above, post-treatment was further performed under the conditions shown in Table 2 to obtain polished stainless steel strip products.

Here, as the polishing oil, use Daphne Polishing Oil F-1 (product name: Idemitsu Kosan Co., Ltd.) for No. 4 specifications, and Subinosox 5-2 (product name: Nippon Oil Co., Ltd.) for HL specifications. ) were used, all of which had S added to improve grindability.

Next, test pieces were cut out from each of these polished stainless steel strip products, and after being thoroughly degreased with trichlorethylene and thinner, the chemical composition of the surface was analyzed using the XPS, and a corrosion resistance test was also conducted.

These results are also shown in Table 2.

The "feroxyl test" is a test in which 3 g of potassium ferricyanide, 3 g of potassium ferrocyanide, 4 g of sodium chloride, and 31 dl of 3.3% hydrochloric acid are dissolved in water to make a total of 100 mN, and a filter paper wetted with this solution is tested. This is a method in which local corrosion is caused by pasting it on a piece of paper and holding it at 22°C for 10 minutes, and the corrosion resistance is determined from the density and size of the spots of blue compound attached to the filter paper in the corroded area. The test results are JIS
Evaluation was made using the rating number H8502-1982 (the larger the number, the better the corrosion resistance).

In addition, the salt spray test is a test specified in JIS Z2371, and "16 hours of spraying - 8 hours of stopping the spraying" was repeated three times.

In the salt water spray test after heating, the test piece was heated to 260°C for 9
After heating for 0 seconds, the same repeated salt water spraying as above was performed.

As is clear from the results shown in Table 2, the surface layer (C
It can be seen that all of the stainless steel polishing specification materials whose r/Fe ratio satisfies the conditions specified in the present invention have superior corrosion resistance compared to conventional materials manufactured by conventional methods.

<Summary of Effects> As explained above, according to the present invention, it is possible to produce polished stainless steel material with excellent corrosion resistance, which hardly causes rust even in a relatively severe corrosive environment, with sufficiently high production efficiency. It brings about extremely useful effects industrially, such as being able to manufacture at low operating costs.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing the manufacturing process of the stainless steel polishing specification material according to the present invention in comparison with the conventional process.
Figure 1 shows the process of the present invention, and Figure 1(b) shows the conventional process. FIG. 2 is a conceptual diagram illustrating the polishing situation of HL specification material. FIG. 3 is a conceptual diagram illustrating the polishing situation of BG specification material. FIG. 4 is a conceptual diagram showing an example of the alternating electrolysis method. In the drawings, l... Grinding belt 2... Stainless steel material to be processed. 3... Stainless steel polished steel strip. 4...Cathode, 5...Positive pole. Applicant Nippon Stainless Co., Ltd.

Claims (4)

[Claims] (1) Polished stainless steel with excellent corrosion resistance, characterized by having a surface layer with an atomic ratio of Cr and Fe (Cr/Fe) adjusted to 0.5 or more from the surface to a depth of 20 Å Specification material. (2) Production of a polished stainless steel material with excellent corrosion resistance according to claim 1, which is characterized by being immersed in nitric acid or an aqueous solution containing nitric acid as a main component after surface polishing. Method. (3) Manufacturing a polished stainless steel material with excellent corrosion resistance as set forth in claim 1, which is characterized by electrolyzing in nitric acid or an aqueous solution containing nitric acid as a main component after surface polishing. Method. (4) Stainless steel polishing specification with excellent corrosion resistance as set forth in claim 1, characterized in that after mechanical surface polishing, one or both of chemical polishing and electrolytic polishing is applied. Method of manufacturing wood.