JP2001279389A - Hydrophilic ferritic stainless steel product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferritic stainless steel product showing excellent hydrophilicity in a solid state. SOLUTION: This hydrophilic ferritic stainless steel product has a bright annealed surface, and the average concentration of Si+Mn in the surface layer part between the surface and a position at a depth of 100 nm from the surface is >=5.0 mass %. If necessary, surface roughening is applied, by means of polishing before bright annealing. As a steel stock, stainless steel, which has a composition containing by mass, <=0.15% C, 10.0-50.0% Cr, <=0.15% N, <=5.0% Si, <=10.0% Mn and >=0.3% of at least either of Si and Mn, or further containing one or more kinds among <=4.0%, by mass, Ni, <=4.0% Mo and <=4.0% Cu, or further containing <=1.0 mass %, in total, of one or more elements among Ti, Al, Nb, V, Zr, B and REM, can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a ferritic stainless steel having excellent surface hydrophilicity.

[0002]

2. Description of the Related Art Since stainless steel itself exhibits excellent corrosion resistance, most of the uses in which stainless steel is used without being subjected to surface treatments such as plating and painting without any treatment are used. In recent years, solid stainless steel materials have been actively used as exterior materials for buildings and vehicles. However, in the use of these exterior materials, "rust" is often seen, and the beautiful metal appearance which is a feature of stainless steel may be impaired. It is known that such "rust" seen in solid stainless steel is likely to occur when sea salt particles or dust adhere to the surface of the steel.

[0003] As means for improving the rust as described above,
Various attempts have been made on i) a method of improving the corrosion resistance level of the material by adjusting the chemical composition of the stainless steel, and ii) a method of performing a surface treatment such as plating or painting on the surface of the stainless steel material.

[0004]

However, even if the corrosion resistance level of the material is improved by the method i), rusting due to external factors such as sea salt particles and dust cannot always be prevented. Absent. If the level of corrosion resistance is greatly improved, the degree of rust is certainly reduced, but this requires the addition of expensive elements and causes a significant increase in material costs. There is a limit naturally. On the other hand, in the method of performing a surface treatment such as plating or painting as in the above ii), an increase in cost due to the surface treatment is inevitable,
The surface appearance also differs from the original metal appearance of stainless steel.

[0005] By the way, when the same solid stainless steel material is used for some parts of a building, for example, a part in an environment where deposits are easily washed away by rainwater, such as a roof upper surface or a lower part of a wall surface, is harder than other parts. Empirical facts also indicate that rust is unlikely to occur. If this is the case, if the surface properties such that the deposits such as sea salt particles can be easily washed away can be realized, the rust resistance of the stainless steel material surface can be drastically improved without using the above-mentioned means i) ii). Could be improved.

As a surface having such a property, a surface having good wettability with water droplets, that is, a surface having good hydrophilicity can be considered. On a surface with good hydrophilicity, water droplets such as rainwater tend to come into contact with the steel surface over a large area, so that they easily penetrate into the slight gap between the steel surface and the deposit particles.
The deposits are lifted and easily washed away. An object of the present invention is to provide a ferritic stainless steel material having excellent hydrophilicity in order to realize such a surface state.

[0007]

Means for Solving the Problems As a result of various studies, the inventors have found that pure ferritic stainless steel can be made of Si or Mn.
It has been found that hydrophilicity can be imparted by forming a surface layer portion which is appropriately concentrated. It was also confirmed that the surface layer portion can be formed by bright annealing, for example. The present invention has been completed based on these basic findings.

That is, in order to achieve the above object, the invention of claim 1 has a bright annealed surface, and the average concentration of Si + Mn in the surface layer from the surface to a depth of 100 nm is 5.0.
It is a hydrophilic ferritic stainless steel material having a mass percentage of not less than mass%.

Here, the “average concentration of Si + Mn in the surface layer from the surface to a depth of 100 nm” refers to a depth of 10 nm from the outermost surface.
It means the total value of the ratio (% by mass) of Si and the ratio (% by mass) of Mn to all elements constituting the surface layer portion up to 0 nm. Specifically, for example, GDS (glow discharge emission spectroscopy) , Elemental analysis is performed while digging in the depth direction from the surface, the average value of the Si concentration and the average value of the Mn concentration between the depths of 0 to 100 nm are determined, and the sum of the values is specified. be able to. Note that the average concentration of either Si or Mn may be zero.

[0010] The invention of claim 2 defines the point that the "bright annealed surface" in the invention of claim 1 is a surface that has been roughened by polishing and then annealed.

The invention according to claim 3 is characterized in that: C: 0.15% by mass or less;
Cr: 10.0 to 50.0 mass%, N: 0.15 mass% or less, Si: 5.0
Mass% or less, Mn: 10.0 mass% or less, and at least
One or two types of Si and Mn are concentrated on the surface of ferritic stainless steel containing 0.3% by mass or more of either Si or Mn, and the surface layer from the surface to a depth of 100nm Is a hydrophilic ferritic stainless steel material having an average Si + Mn concentration of 5.0% by mass or more.

Here, the “steel base surface” refers to a so-called solid (bare) stainless steel surface having no surface coating such as plating or painting. "Surface structure in which one or two of Si and Mn are enriched" means that at least one of Si and Mn has a higher concentration than the average concentration in steel in a region from the surface to a depth of 100 nm. Means that.

According to a fourth aspect of the present invention, in the third aspect, the steel material further comprises Ni: 4.0% by mass or less, and Mo: 4.0% by mass.
Hereinafter, Cu is defined as containing one or more kinds of 4.0% by mass or less. The invention according to claim 5 is the invention according to claim 3, wherein the steel material further comprises Ti, A
One or two of l, Nb, V, Zr, B, REM (rare earth element)
It is specified that a total of 1.0% by mass or less is contained.

[0014] The invention of claim 6 defines that the hydrophilic ferritic stainless steel material of claims 1 to 5 is, in particular, a steel plate for exterior of buildings or vehicles.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Ferritic stainless steel having the chemical composition shown in Table 1 was melted in a vacuum melting furnace, and was forged, hot rolled,
Intermediate annealing and cold rolling were performed to obtain a cold-rolled sheet with a thickness of 1 mm. The surface of each cold-rolled sheet was polished with # 600. Ra: 0.27 μm,
Rz: 1.47 μm, Rmax: 2.43 μm
Bright annealing was performed in a 0% hydrogen atmosphere at 880 ° C. for 300 seconds. In the bright annealing, the Si + Mn concentration on the sample surface was changed by changing the dew point variously. In Table 1, F11 to F13 are each 0.3% by mass of Si and Mn.
, Which does not fall within the scope of claims 3 to 5.

[0016]

[Table 1]

A sample for hydrophilicity test and a sample for surface analysis were collected from the bright annealed sample. The hydrophilicity test sample is exposed outdoors for 30 days to a location exposed to direct sunlight (a location where no shadow of surrounding buildings or obstacles occurs), and then subjected to the hydrophilicity test as it is without washing away dust etc. Was served. The hydrophilicity test is conducted in a room at a temperature of 20 ° C and a humidity of 60%, and the surface of the sample placed horizontally has 100 µL (microliter) of distilled water.
Was dropped, and after 60 seconds, a water drop on the sample surface was observed from right beside by a CCD camera, and the wetting angle was obtained from the enlarged image. The definition of the wetting angle is as shown in FIG. On the other hand, the surface analysis of the bright annealed sample was performed by GDS (glow discharge optical emission spectroscopy) by elemental analysis while digging in the depth direction from the surface. Then, the average value of the Si concentration and the average value of the Mn concentration between the depths of 0 to 100 nm are obtained, and the sum thereof is calculated as the value of “average concentration of Si + Mn in the surface layer from the surface to a depth of 100 nm (mass%)” And Table 2 shows the dew points during bright annealing and the above test results. FIG. 2 plots the relationship between the average concentration of Si + Mn and the wetting angle in the surface layer from the surface to a depth of 100 nm.

[0018]

[Table 2]

S in the surface layer from the surface to a depth of 100 nm
It can be seen that the steel material of the present invention example having an average concentration of i + Mn of 5% by mass or more has a small wetting angle of water droplet particles of 45 ° or less, and exhibits high hydrophilicity when exposed outdoors for 30 days. On the other hand, the average concentration of Si + Mn was 5% by mass.
The steel material of Comparative Example less than the above has a large wetting angle and is inferior in hydrophilicity. Among the comparative examples, Nos. 14 to 16 were Si and M
Although the content of n was less than 0.3% by mass, these were subjected to bright annealing under the same level of dew point conditions as those of the examples of the present invention, but the Si + Mn concentration in the surface layer was extremely low. , Good hydrophilicity is not provided. In other words, in order to increase the Si + Mn concentration in the surface layer, at least
It can be said that it is desirable to contain either Si or Mn at 0.3% by mass or more.

In the above experimental examples, the surface appearance of the sample immediately after being exposed outdoors for 30 days was also visually observed before performing the hydrophilicity test. As a result, it was found that the example of the present invention shown in Table 2 had a smaller amount of dust attached than the comparative example. This is thought to be due to the difference in how dust was washed away by the three rainfalls observed during the 30-day exposure period. That is, it was confirmed that in the case of the present invention having good hydrophilicity, the attached matter was easily washed away.

In the above experimental example, the surface was roughened by polishing with # 600 before bright annealing.
It has been confirmed that by further increasing the surface roughness, the wetting angle tends to be smaller.

Hereinafter, the main constituent elements in the steel material will be briefly described. C is inevitably mixed from scrap or the like at the time of smelting, but if the content is increased, moldability and corrosion resistance will be impaired. Therefore, C is desirably 0.15% by mass or less. In general, Si is added for the purpose of deoxidation in smelting stainless steel, but in the present invention, it plays a role of expressing hydrophilicity by being concentrated in the surface layer of the steel material. In order to relatively easily concentrate on the surface by heat treatment such as bright annealing, the content is preferably 0.3% by mass or more. However, excessive content degrades workability due to solid solution strengthening, so the Si content is preferably in the range of 0.3 to 5.0% by mass. In the present invention, Mn expresses hydrophilicity by being concentrated in the surface layer of the steel material along with Si. For this purpose, the content is preferably 0.3% by mass or more as in the case of Si. However, if the addition amount is large, Mn fumes are generated during melting and the productivity is deteriorated, so the Mn content is preferably set to 0.3 to 10.0% by mass. Note that Si and Mn do not always need to be contained in an amount of 0.3% by mass or more, and as a result, Si or Mn
However, it is sufficient to concentrate as described above.

[0023] Ni is effective in improving the toughness of ferritic stainless steel, but a large amount of Ni stabilizes the austenite phase at high and normal temperatures, so that 4.0% by mass.
It is desirable to do the following. Cr is an essential element for ensuring the corrosion resistance of stainless steel, and its content is
If it is less than 10.0% by mass, the corrosion resistance tends to be insufficient. On the other hand, if it exceeds 50.0% by mass, cold workability and toughness are deteriorated, so the Cr content is preferably set to 10.0 to 50.0% by mass.
Mo is an effective element for improving corrosion resistance, but excessive content causes solid solution strengthening at high temperature and delay of dynamic recrystallization,
Since the hot workability is deteriorated, the content is preferably set to 4.0% by mass or less. Although Cu may be unavoidably mixed depending on the raw material used, excessive content degrades hot workability and corrosion resistance.

N is inevitably mixed from scrap etc. like C, but excessive content detrimentally affects moldability and corrosion resistance. Therefore, N is desirably 0.15% by mass or less. Ti,
Nb and V improve workability by fixing solid solution C as carbides, Al and Zr improve workability and toughness by capturing oxygen in steel as oxides, and B and REM improve hot workability. It is an element that improves the properties. However, these are also elements that, when contained in large amounts, deteriorate the productivity. Therefore, it is desirable that each of these elements is 1.0% by mass or less, and the total content of these elements is also suppressed to 1.0% by mass or less.

[0025]

According to the present invention, it is possible to provide a pure ferritic stainless steel material stably exhibiting excellent hydrophilicity. This steel material is suitable for, for example, an exterior material of a building or a vehicle, since the attached matter on the surface is easily washed away by rainwater or washing water. Even when a relatively inexpensive steel composition is used for the material itself, rust resistance surpasses that of conventional steel using a very expensive high corrosion resistant steel due to simple daily maintenance (cleaning, etc.). It is also possible to maintain. Therefore, the present invention contributes to providing a very cost-effective material, particularly as an exterior stainless steel material.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a definition of a wetting angle of a water droplet on a steel material surface.

FIG. 2 Si + M in the surface layer from the surface to a depth of 100 nm
5 is a graph showing the relationship between the average concentration of n and the wetting angle.

Claims (6)

[Claims] 1. A hydrophilic ferritic stainless steel material having a bright annealed surface and having an average Si + Mn concentration of 5.0 mass% or more in a surface layer from the surface to a depth of 100 nm. 2. The method according to claim 1, wherein the surface has a bright annealed surface after being roughened by polishing, and has a surface layer from the surface to a depth of 100 nm.
A hydrophilic ferritic stainless steel material with an average concentration of + Mn of 5.0% by mass or more. 3. C: 0.15% by mass or less, Cr: 10.0 to 50.0% by mass, N: 0.15% by mass or less, Si: 5.0% by mass or less, Mn: 1
0.0% by mass or less, and a ferrite stainless steel material containing at least 0.3% by mass or more of either Si or Mn has a surface structure in which one or two types of Si and Mn are concentrated, A hydrophilic ferritic stainless steel material having an average Si + Mn concentration of 5.0 mass% or more in the surface layer from the surface to a depth of 100 nm. 4. The steel material further comprises Ni: 4.0% by mass or less,
o: One or more of 4.0 mass% or less, Cu: 4.0 mass% or less
The hydrophilic ferritic stainless steel material according to claim 3, which contains at least one kind. 5. The steel material further comprises Ti, Al, Nb, V, Zr,
The hydrophilic ferritic stainless steel material according to claim 3 or 4, which contains one or more of B and REM in a total amount of 1.0% by mass or less. 6. The hydrophilic ferritic stainless steel material according to claim 1, which is a steel plate for exterior of a building or a vehicle.