JPH02122064A - Stainless steel stock excellent in rust resistance and its production - Google Patents

Abstract

PURPOSE:To stably manufacture a stainless steel stock having superior rust resistance by treating a ferritic stainless steel stock with a specific composition with oxidizing acid and then forming a vapor plating phase of Al, etc., of a specific thickness on the surface of the above stock. CONSTITUTION:A ferritic stainless steel stock which has a composition consisting of, by weight, <=0.003% Al, 0.3-5% Si, 0.2-1% Mn, 8-25% Cr, and the balance essentially Fe and further containing, if necessary, one kind among 0.05-0.8% Cu, 0.05-0.8% Ni, 0.05-2.0% Nb, and 0.05-3.0% Mo is subjected to either of immersion treatment in a solution of oxidizing acid (e.g., about 30% aqueous solution of nitric acid) or peroxidizing acid and electrolytic treatment in an acid liquor. Subsequently, a coating layer in a state of single or double layer consisting of one or more kinds among Al, Ti, Si, Nb, Cr, Mo, Cu, Ni, and the nitrides and oxides thereof is formed to 200-30000Angstrom thickness on the surface of the above steel stock by means of vapor plating.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a ferritic stainless steel material (such as a steel plate) exhibiting excellent rust resistance, and a method for producing the same.

<Prior art and its challenges> In recent years, in a rapidly growing economic environment, there has been a remarkable diversification of lifestyles and values.
Although expensive, stainless steel has a beautiful, deep metallic luster and excellent corrosion resistance, giving it a unique sense of luxury, and has come to be widely used in building materials and other fields.

However, even with this kind of stainless steel, when used in harsh environments such as coastal areas or areas where volcanic ash has fallen, there are problems such as localized loss of gloss or red rust called "stains" on the surface. ``There are cases where the image of a high-quality product that is ``stainless steel,'' that is, ``rust-free'' may be damaged.

Of course, in order to solve the above-mentioned problems, measures have been taken up to now to improve the characteristics of stainless steel itself, such as d) adding alloying elements such as Cr and Mo, which have a large effect of improving corrosion resistance, as components of steel.

b) For bright annealing specification materials, a method of improving the corrosion resistance of the oxide film formed on the outermost surface by optimizing dew point control during bright annealing.

C) A method in which a material with bright annealing specifications is subjected to passivation strengthening treatment in an oxidizing acid solution after bright annealing.

Although such methods have been proposed and put into practical use, it cannot be said that they have produced sufficiently satisfactory results.

Therefore, based on consideration of the actual situation, [
The reason why conventional measures have not been sufficient to prevent stains is that the environment in which stains occur is a corrosive environment, although it is limited to a very small localized area called the stain formation area. This is because the scratches become unexpectedly harsh and severe, and in order to sufficiently suppress and prevent the occurrence of "stains" etc., it is necessary to provide a corrosion-resistant layer stronger than the conventional oxide film on the outermost surface of the stainless steel material. 8) A method of plating a highly corrosion-resistant metal such as Cr on the surface of stainless steel.

B) A method of coating the stainless steel surface with an organic resin film (painting method).

There was also a movement to implement measures to prevent stains and red rust.

However, among these measures, the method of providing a plating coating cannot be said to be a desirable industrial method, considering the regulations on the treatment of mebuki waste liquid, which are expected to become even more stringent in the future. The problem remains that the method of painting with organic resin loses the metallic luster and texture that characterize stainless steel, making it unsuitable for some applications.

<Means for Solving the Problems> From the above-mentioned viewpoints, the present inventors have devised a method that solves the problems of "stains" and "red rust" without losing the unique deep metallic luster, and that can be produced on an industrial scale. In order to provide a highly rust-resistant stainless steel material that can be stably manufactured, we have conducted intensive research while taking into account our own knowledge of corrosion-resistant coatings developed based on many years of experience.As a result, we have developed the following. We have obtained new knowledge, namely: (a) CVD, which has made remarkable progress in recent years;
Unlike ordinary plating methods, vapor phase plating methods such as (chemical vaporization method), ion blating method, and sputtering method can easily coat various metals, nitrides, oxides, etc. on stainless steel surfaces. However, by applying this vapor phase plating to provide a coating of a specific material with a specific thickness on the surface of stainless steel, the luster characteristic of stainless steel will not be lost (its rust resistance). The properties of the product are significantly improved, and the prevention of "stains" and "red rust" is achieved.

(bl) However, in this case, if conventional commercially available stainless steel materials were used as base materials, film defects would occur due to non-metallic inclusions exposed on the surface of the steel sheet, regardless of the type of plating substance or vapor phase plating method. 5 (C1) Furthermore, among the nonmetallic inclusions mentioned above, oxide-based nonmetallic inclusions, especially alumina-based nonmetallic inclusions, which are very commonly found, It has the greatest influence on the formation of defects in vapor phase plating films.

(dl) However, if a ferritic stainless steel material with appropriate components is used as a base material to reduce alumina-based nonmetallic inclusions in the steel, if necessary, it may be added to an oxidizing acid or peroxidizing acid solution. When the gas-phase meso-1- is applied after performing ``immersion treatment'' or ``electrolysis treatment in an acid solution'', a stainless steel material exhibiting excellent rust resistance can be obtained in an extremely stable manner.

The present invention has been made based on the above findings, etc. [8! = 0.003% or less or 0.1 to 4% (hereinafter, % representing the dividing table is weight %) Si: 0.3 to 5%, Mn: 0.2 to 1
%.

Contains Cr: 8 to 25% or less, and further contains Cu: 0.05 to 0.8% and Ni: 0.
05-0.8%.

Nb: 0.05-2.0%, Mo: 0.
05 to 3.0%, and the remainder is substantially Fe.
i','riSi, Nb, Cr, Mo, Cu,
It consists of Ni and one or more of these nitrides and oxides, and has a thickness of 200 to 30,000 layers. By forming the stainless steel material with a plating layer), it is characterized by extremely excellent rust resistance, and furthermore, rAf: 0.003% or less or 0.1 to 4%.

Si: 0.3-5%, Mn: 0.2-I
%.

Contains Cr: 8 to 25% or less, and further contains Cu: 0.05=0.8% and Ni: 0.0 as necessary.
5~0.8%Nb: 0.05~2.0%Mo
: A ferritic stainless steel material containing one or more of 0.05 to 3.0%, the remainder being substantially Fe, is immersed in an oxidizing acid or peroxidizing acid solution, or After electrolytic treatment in a solution, the surface of the steel is coated with 8ft of Ti, Si, Nb, Cr by vapor phase plating.
, +to, Cu, Ni, and one or more of these nitrides and oxides.
By forming the steel with a thickness of 0.00 to 30,000, it is possible to stably produce ferritic stainless steel material with excellent rust resistance.

In other words, the present invention applies a vapor phase plating method to artificially generate a highly corrosion-resistant film on the surface of a ferritic stainless steel material with a specific composition, which cannot be applied using normal plating methods, thereby retaining a unique luster. The aim is to create a stainless steel material that minimizes the formation of "stains" and the like even when the steel is in a state of being stained.

Below, the reason why the ferritic stainless steel +A and the method for producing the same according to the present invention are limited as described above, and the effect thereof will be explained.

8) Component Ml of stainless steel (2) 8. e In the present invention, the static content in the steel base material is set to 0.
．． It is extremely important to adjust the content to 0.003010 or less or within the range of 0.1 to 4%. Note that the amount is desirably adjusted to 0.002% or less or 0.1 to 4%. The reason is that -1 -Note A! This is because the inclusion of tail feathers is essential.

In other words, the formation of alumina-based nonmetallic inclusions can only be suppressed by suppressing the helium content in the steel base material to 0.003% or less or adjusting it to 0.1% or more, and alkaline earth metal inclusions. can be suppressed from being exposed to the surface of the steel material to an extent that does not cause any practical problems, and it is possible to prevent a decrease in the induction resistance of the steel material.

Note that when adjusting the Aβ content ■ to a range of 0.1% or more, it is necessary to suppress the upper limit to 4%. This is because even if AR is added in an amount exceeding 4%, not only the above effects are not further improved, but also the hot workability decreases significantly due to the addition of a large amount of Aβ.

Here, the fact that ``addition of Ai' at a high rate of ffi (0.1 to 4%) is effective in reducing alumina-based nonmetallic inclusions in steel materials'' feels strange, but This is based on the peculiarity of 8l, and 8! This is thought to be due to a phenomenon caused by a decrease in deoxidizing ability due to a change in the activity coefficient of .

By the way, in order to keep the amount of Al in steel to 0.003% or less, it is practical to not deoxidize Al or add A as an alloying element in the process from the end of refining to ingot formation. It is valid. In particular, not performing any Al deoxidation is a very characteristic and advantageous means in the production of this type of steel.

In addition, natural immersion in an oxidizing acid solution or peroxidizing acid solution or electrolytic treatment in an acid solution, which will be described later, are also extremely effective in reducing the negative effects of alumina-based nonmetallic inclusions exposed on the steel surface. .

(b) Si In the present invention, Si plays an important role as a very important deoxidizing element. In other words, when the steel material according to the present invention is melted, "8β", which is often used as a deoxidizing agent in the case of ordinary steel materials, cannot be effectively used. This is because it must depend on Si, although its effect is somewhat weaker than that of Si.

However, even if the Si content is added in excess of 5%, not only the effect as a deoxidizing agent is not further improved, but also the hot workability of the steel material is significantly reduced. On the other hand, Si
If the content is less than 0.3%, the steel will not be sufficiently deoxidized. Therefore, the Si content was determined to be 0.3 to 5%.

(Cl Mn The Mn component has the effect of fixing S in the steel and ensuring workability in hot fighting, but if its content is less than 0.2%, the desired effect due to the above effect cannot be obtained, and the Since Mn content exceeding 1% leads to deterioration of cold workability and formability, the Mn content is set at 0.2 to 1%.

(d) Cr Cr is the most important additive element that determines the corrosion resistance of the steel base material (steel base material) according to the present invention. The excellent rust resistance of the steel of the present invention is ensured by the large influence of the gas phase mesort layer provided on the surface, but the plating layer is very thin and the base metal may be exposed due to scratches etc. is often invited. Therefore, in order to prepare for such a situation, it is necessary to ensure sufficient corrosion resistance in the steel base material, and from this point of view, Cr plays an important role.

However, if the Cr content is less than 8%, the corrosion resistance of the scratched parts of the steel material and the end faces of the steel material cannot be sufficiently maintained.
On the other hand, in the steel materials of the present invention where rust resistance under atmospheric exposure is a problem, even if Cr is added in an amount exceeding 25%, further improvement of the effect is not clear, so the Cr content is 8 to 25%.
It was determined that

(“l Cu+Ni, Nb and MOCu+old,
Both Nb and Mo have the effect of improving the corrosion resistance of the steel base material (steel base material), so one type of Nb and Mo can be used as necessary from the viewpoint of preventing a decrease in corrosion resistance at scratched parts of the plating film, etc. Alternatively, two or more kinds of components are added, but the reason for limiting the content of each component will be explained in detail below.

Cu Cu is an effective component for improving the corrosion resistance of m-base materials, but in order to make its effect clear, it is necessary to add 0.05% or more, whereas if it is added in excess of 0.8%, Conversely, deterioration of corrosion resistance due to the formation of intermetallic compounds becomes apparent, so C
When u is added, the content is set at 0.05 to 0.8%.

Ni Like Cu, Ni is also an effective component for improving corrosion resistance, but in order to make its effect clear, it is necessary to add 0.05% or more; However, since the corrosion resistance improvement effect is not commensurate with that, the content when adding Ni is 0.05 to 0.8%.
It was determined that

Nb Nb has the effect of stabilizing C in the steel, and also has the effect of improving the corrosion resistance of the gH material. especially,
When it coexists with Cu or Ni, the effect of improving the corrosion resistance of the steel base material becomes even more remarkable due to their synergistic effect.

In order to ensure the desired C stabilizing effect in steel by Nb addition, it is necessary to include 0.05% or more, but even if it is added in excess of 2.0%, the C stabilizing effect and Not only does the effect of improving corrosion resistance not become more obvious, but conversely the corrosion resistance deteriorates due to the formation of Laves phase, so when adding Nb, the content should be 0.05 to 2.
．． It was set as 0%.

O Mo is an additive element that has a large effect on improving corrosion resistance along with Cr, but when its content is less than 0.05%, the effect on improving corrosion resistance is not clearly recognized. Since no further effect was observed in improving the weather resistance, which is the main objective of the steel material of the present invention, the content when adding Mo was determined to be 0.05 to 3.0.

(f) S mixed into steel materials as other impurity elements is
Not only does this generate n-based sulfides and promote coating defects during vapor phase plating, but it also causes deterioration of the corrosion resistance of the base material itself. Therefore, the lower the Sjl in the steel material, the better. In addition,
It becomes difficult to generate defects in the vapor phase plating film, and the value is 0.
, 0.005% or less, it is desirable to suppress the S content in the steel material to 0.005% or less.

B) Thickness of 7 layers of vapor phase plating Materials for vapor phase plating include Al, Ti, Si, and Nh.
, Cr.

One or more of the metals Mo, Cu, and Ni, as well as their nitrides and oxides, can be used, and these may be applied as a single layer coating or as a multilayer coating of two or more layers. It may be given as

In this case, if the thickness of the vapor phase plating layer is 200 mm or 2 B, a uniform plating surface (vapor deposition surface) cannot be obtained, and corrosion resistance from defective portions of the plating layer will deteriorate significantly.

On the other hand, if the thickness of the vapor phase plating layer exceeds 30,000 layers, problems such as cracking of the plating film and peeling of the coating film at the bending portion of the metal plate tend to occur. Therefore, the thickness of the vapor phase plating layer was determined to be 200 to 30,000 mm.

In order to stably form a vapor-phase metnide layer with almost no defects on the surface of ferritic stainless steel, it is necessary to naturally immerse it in an oxidizing acid solution or a peroxidizing acid electrolyte as a pretreatment, or to immerse it in an acid solution. It is better to incorporate an electrolytic treatment process. This pretreatment not only dissolves alumina-based nonmetallic inclusions exposed on the surface of the steel material and removes their negative effects, but also strongly passivates the area around the nonmetallic inclusions. The deterioration of gas-phase plated coated steel materials due to the presence of is reduced.

As mentioned above, as an oxidizing acid solution to reduce and render harmless alumina-based nonmetallic inclusions exposed on the surface of steel materials, for example, "30% nitric acid soluble in water" and a peroxidizing acid solution are used. As the solution, it is recommended to use a nitric acid aqueous solution to which hydrogen peroxide has been added, and as the acid solution for carrying out the electrolytic treatment, any acid solution that is applied to ordinary electrolytic pickling etc. may be adopted.

Next, the present invention will be explained in more detail with reference to Examples.

<Example> Example 1 First, as shown in Table 1, steels A-B and H~, which were not subjected to Al deoxidation treatment during the refining process, were subjected to nonmetallic inclusion flotation treatment and vacuum treatment in an R■1 furnace. Each of ferritic stainless steel plates consisting of ME-G containing a large amount of AI which had been subjected to deoxidation treatment and steels C to D which had been subjected to Al deoxidation treatment were prepared.

Then, these steel plates were electrolytically treated in a 30% nitric acid aqueous solution at 60°C to improve the surface quality. After conditioning (vapor phase plating pretreatment), 5iNx (x
#1.35) was played by 600 people with only 17 hits. Note that during the sputtering treatment, the steel plate substrate was heated and maintained at 300°C.

Subsequently, two test pieces were taken from each ferritic stainless steel sheet manufactured in this way, and the pitting corrosion potential was measured, and the induction resistance was evaluated. These results are summarized in Table 2. It was shown to.

The induction resistance was evaluated according to the standards shown in Table 3.
The corresponding scores are entered in Table 2.

As is clear from the results shown in Table 2, all of the ferritic stainless steel sheets according to the present invention exhibit excellent rust resistance, whereas the composition of the base steel sheet is under the conditions specified by the present invention. It can be seen that the rust resistance of Comparative Examples 3 and 4, which deviated from the above, was significantly inferior.

In addition, to! In Comparative Examples 3 and 4, in which deoxidized steel was applied, many alumina-based nonmetallic inclusions that were long in the rolling direction were observed in the base steel plate as "linear nonmetallic inclusion groups", and after sputtering, Multiple film defects caused by alumina-based nonmetallic inclusions were also observed in surface observation.

However, in Examples 5 to 7 of the present invention, the base copper plate was 0.
．． Although good results were obtained despite containing a large amount of Af (121 to 2.49%), this is due to the "8! deoxidizing power reduction phenomenon" that accompanies the addition of a large amount of Af. This is presumed to be due to a decrease in the formation of nonmetallic inclusions.

In fact, the alumina-based nonmetallic inclusions in the base steel sheet were removed by Al: Example 1 of the present invention, which was applied to steel that was not actively deoxidized.
-2 and 8-11 were at the same level.

In addition, these test results show that ``By adjusting the amount of Fe in the base steel sheet within a specific range, which is an industrially possible means, the rust resistance of the vapor-phase plated steel sheet can be maintained at a level that does not affect the rust resistance of the steel sheet. It is also confirmed that alumina-based nonmetallic inclusions can be controlled sufficiently.

Example 2 A ferritic stainless steel plate made of a steel not shown in Table 4 was prepared without β-deoxidation, but instead was subjected to levitation of nonmetallic inclusions using an RH furnace and vacuum deoxidation treatment.

Next, a plurality of test pieces were cut out from the steel plate, and after degreasing some of them as shown in Table 5, the surfaces were plated with Si OX (X #2) at various thicknesses by sputtering. Note that during the sputtering treatment, the steel plate substrate was heated and maintained at 300'C.

Regarding the vapor-phase plated ferritic stainless steel sheet manufactured in this manner, the pitting potential was measured and the rust resistance evaluated in the same manner as in Example 1, and the cracking of the vapor-phase plated film during 101 bending was investigated. However, the results are also shown in Table 5.

The results shown in Table 5 also show that all the ferritic stainless steel sheets according to the present invention exhibit excellent rust resistance, but the thickness of the vapor phase plating film deviates from the specified value in the present invention. It is clear that the products according to Comparative Examples 12 to 13 and 23 have significantly poor rust resistance, or are prone to film cracking during molding.

In addition, according to sputtering, 5i () on the base steel plate
The vapor deposition of When the plating film thickness (plated film j) was thin, there was a tendency for the level of improvement in induction resistance to decrease, which is presumed to be caused by defects in the deposited film. It was expected that this tendency would be improved to a certain degree by increasing the temperature of the deposition substrate (substrate steel plate), but in reality there was no significant improvement.
The rust resistance finally became stable and good when the film thickness reached approximately 200 people. This was not much different when other vapor phase plating substances (vapor deposition substances) were used.

Additionally, as the thickness of the deposited film (plated film 1γ) increases, cracks occur in the vapor-phase plating, which is thought to be due to the temperature difference between the time of vapor deposition and after cooling, as well as the internal stress of the vapor-phase plating material (deposited material). It was also confirmed that this tendency becomes remarkable especially when the film thickness exceeds 30,000 layers, and reaches a level that cannot be used in practical use.

It should be noted that the adhesion of the vapor phase plating film is greatly influenced by the degreasing treatment before sputtering (it was found that sufficient degreasing is necessary).

Example 3 As shown in Table 6, steel M was subjected to Af deoxidation treatment during the refining process, and steel N-P was not subjected to Af deoxidation treatment.
Each ferritic stainless steel net plate was prepared.

Next, these steel plates were immersed in a 30% nitric acid aqueous solution at 60°C to adjust the surface properties (vapor phase plating pretreatment), and then various coatings as shown in Table 7 were applied to the surface by sputtering. Plated. Note that during the sputtering treatment, the steel plate substrate was heated and maintained at 300° C. as in the previous examples.

Subsequently, each of the ferritic stainless steel sheets produced in this manner was subjected to pitting potential measurement and dielectric resistance evaluation in the same manner as in Example 1, and the results are summarized in Table 7.

As is clear from the results shown in Table 7, all of the ferritic stainless steel sheets according to the present invention exhibit excellent rust resistance, but the composition of the base steel sheet and the thickness of the plating film are Comparative example 24 that deviates from the conditions specified in the present invention
It can be seen that the rust resistance of those with grades 1 to 29 is significantly inferior.

It should be noted that the multilayer plating layer (vapor deposited material) not only has a synergistic effect on improving the corrosion resistance of the vapor-phase Menkhi ferrite stainless steel sheet, but also has an effect on improving the adhesion of the vapor deposited material. was confirmed, especially Ni or Cu
It was also found that it is effective to provide a lower layer of .

Furthermore, in each of the above examples, only sputtering was applied as the vapor phase plating method, but it is understood that similarly good results can be obtained when other vapor deposition methods such as CVD or ion blating are applied. Also confirmed.

Summary of Effects> As explained above, this invention has significantly superior rust resistance compared to conventional materials, and can be used in a wide range of fields such as automotive molding materials, exterior building materials, and interior building materials. Industrially, extremely useful effects are brought about, such as making it possible to stably provide highly rust-resistant ferritic stainless steel materials whose values and functions are expected to be significantly improved by application.

Claims (6)

[Claims] (1) Al: 0.003% or less, Si: 0.3 to 5% by weight. Contains Mn: 0.2 to 1%, Cr: 8 to 25% or less,
Al, Ti, Si, Nb, Cr, Mo, Cu
, Ni, and one or more of these nitrides and oxides, and has a single layer or multiple vapor phase plating layer with a thickness of 200 to 30,000 Å. Ferritic stainless steel material with excellent rust resistance. (2) Weight percentage: Al: 0.003% or less, Si: 0.3-5%, Mn:
0.2 to 1%, Cr: 8 to 25% or less, and further Cu: 0.05 to 0.8%, Ni: 0.05 to 0.8%
. Nb: 0.05-2.0%, Mo: 0.05-3.0%
The surface of the ferritic stainless steel base material containing one or more of the following, the remainder being substantially Fe,
i, Nb, Cr, Mo, Cu, Ni, and one or more of their nitrides and oxides, and has a thickness:
A ferritic stainless steel material with excellent rust resistance, characterized by having a single layer or multiple vapor phase plating layers of 200 to 30,000 Å. (3) Al: 0.1-4%, Si: 0.3-5%, Mn: 0.
2 to 1%, Cr: 8 to 25% or less, and the remainder is substantially Fe on the surface of the ferritic stainless steel base material,
Single-layer or multi-layer vapor phase plating consisting of one or more of Al, Ti, Si, Nb, Cr, Mo, Cu, Ni, and their nitrides and oxides, and having a thickness of 200 to 30,000 Å A ferritic stainless steel material with excellent rust resistance, characterized by having layers. (4) Weight percentage: Al: 0.1-4%, Si: 0.3-5%, Mn: 0.
2 to 1%, Cr: 8 to 25% or less, and further Cu: 0.05 to 0.8%, Ni: 0.05 to 0.8%
, Nb: 0.05-2.0%, Mo: 0.05-3.0
%, and the remainder is substantially Fe.
It is composed of one or more of Si, Nb, Cr, Mo, Cu, Ni, and their nitrides and oxides, and has a single or multiple vapor phase plating layer with a thickness of 200 to 30,000 Å. A ferritic stainless steel material with excellent rust resistance. (5) Weight percentage: Al: 0.003% or less, Si: 0.3-5%, Mn:
0.2-1%, Cr: 8-25% or less, or further Cu: 0.05-0.8%, Ni: 0.05-0.8%
, Nb: 0.05-2.0%, Mo: 0.05-3.0
%, and the remainder is substantially Fe, after being subjected to either immersion in an oxidizing acid or peroxidizing acid solution or electrolysis in an acid solution. , Al, Ti, S on the surface of the steel material by vapor phase plating.
It is characterized by forming a single or multilayer coating layer with a thickness of 200 to 30,000 Å consisting of one or more of i, Nb, Cr, Mo, Cu, Ni, and their nitrides and oxides. , a method for manufacturing ferritic stainless steel material with excellent rust resistance. (6) Weight percentage: Al: 0.1-4%, Si: 0.3-5%, Mn: 0.
2 to 1%, Cr: 8 to 25% or less, or further Cu: 0.05 to 0.8%, Ni: 0.05 to 0.8%
, Nb: 0.05-2.0%, Mo: 0.05-3.0
%, and the remainder is substantially Fe, after being subjected to either immersion in an oxidizing acid or peroxidizing acid solution or electrolysis in an acid solution. , Al, Ti, S on the surface of the steel material by vapor phase plating.
It is characterized by forming a single or multilayer coating layer with a thickness of 200 to 30,000 Å consisting of one or more of i, Nb, Cr, Mo, Cu, Ni, and their nitrides and oxides. , a method for manufacturing ferritic stainless steel material with excellent rust resistance.