JP2001234353A - Steel excellent in weather resistance and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel having an oxide layer stable in an atmospheric corrosive environment on the surface of steel and excellent in weather resistance and to provide a producing method therefor. SOLUTION: This steel has a magnetite layer and/or a hematite layer containing either or both of chromium and nickel by >=0.3 mass % in total on the surface. The steel can be produced by coating the surface of base material steel (carbon steel, low alloy steel or alloy steel) with an aqueous solution containing 0.3 to 5 mass % chromium (III) ions and/or 0.3 to 6 mass % nickel (II) ions and thereafter performing heating at 450 to 720 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material having a stable surface in an atmospheric corrosive environment and covered with an oxide having a high anticorrosion property and having excellent weather resistance, and a method for producing the same.

[0002]

2. Description of the Related Art In general, when steel contains elements such as phosphorus (P), copper (Cu), chromium (Cr), and nickel (Ni), the corrosion resistance of the steel in the atmosphere (that is, weather resistance). Can be improved. These low-alloy steels are called weather-resistant steels and have a rust that protects their surface against corrosion in a few years outdoors (hereinafter referred to as “weather-resistant rust”).
This is a so-called maintenance-free steel in which no anticorrosion treatment such as painting is required thereafter. However, it takes several years before weather-resistant rust is formed. During that time, floating rust such as red rust and yellow rust and flowing rust occur, which is not only unfavorable in appearance but also pollutes the surrounding environment. The problem remains that it also causes.
Regarding this problem, for example, the steel surface with Fe ions,
A surface treatment method has been proposed in which a phosphate film is formed after treatment with an acidic aqueous solution containing one or more of P, Cu, Cr, Ni, and Mn ions (Japanese Patent Laid-Open No. 1-142088).
Reference). However, there has been a problem that the processing content is complicated, for example, pretreatment with an acidic aqueous solution is required before forming a phosphate film. Also,
In order to prevent the formation of floating rust and flowing rust, surface treatment methods such as a method of applying a coating on the surface of weather-resistant steel and a method of applying a coating after forming a phosphate film have been used. In addition, there is a problem that the formation of weather-resistant rust is delayed by coating, and the coating film itself is deteriorated to significantly impair the appearance. Furthermore, there are many environments in which formation of weather-resistant rust is difficult even in weather-resistant steel such as coastal areas, and in such an area, weather-resistant rust is not formed even if the treatment described in the above-mentioned publication is performed. is there.

[0003]

An object of the present invention is to provide an oxide layer on a steel surface which is stable in an atmospheric corrosive environment, has a high corrosion resistance, and suppresses the generation of floating rust such as red rust and yellow rust and flow rust. Steel material as a material for construction and the like having excellent weather resistance, and to generate such an oxide layer by a simple treatment,
An object of the present invention is to provide a method for producing a steel material having excellent weather resistance.

[0004]

The gist of the present invention resides in the following (1) a steel material excellent in weather resistance and (2) a method for producing the same. (1) A magnetite layer and / or a hematite layer (hereinafter, referred to as “oxide”) containing 0.3% by mass or more of either or both of chromium as an oxide and nickel as an oxide on the surface. Layer)
Steel material with excellent weather resistance. (2) After applying an aqueous solution containing 0.3 to 5% by mass of chromium (III) ions and / or 0.3 to 6% by mass of nickel (II) ions on the surface of the base steel, heating to 450 to 720 ° C. The method for producing a steel material having excellent weather resistance according to (1). The above-mentioned "base steel" is a steel as a base material of the steel material excellent in weather resistance of the present invention, and is a carbon steel or a low alloy such as a so-called weather-resistant steel containing Cr, Cu, P, Ni, etc. Steel and even alloy steel (in which steel that produces so-called "rust" described later)
And does not include steel that does not generate "rust", such as stainless steel and Ni-based alloys. In addition, "carbon steel" as used herein means a specific chemical composition, for example, C: 0.1 to 0.4.
%, Si: 0.1 to 0.4%, Mn: 0.2 to 0.6%, P: 0.03%
Hereinafter, S: steel containing 0.03% or less. "Low alloy steel" refers to C, Si, Mn, P, Cr, Ni, Mo, C
A steel containing alloy elements such as u, Ti, etc. in a total content of about 5% or less. An “alloy steel” is a steel having a total alloy content exceeding 5%, for example, Cr: 10% Below, Ni: 10%
Hereinafter, steel containing 10% or less of Ti is also included in the alloy steel as the base steel.

[0005] Further, the base steel may have "rust" formed on the surface. Further, the base steel includes not only a material in a state before being used for a building or the like but also a material already used for a building or the like. If the rust formed on the steel surface is chemically stable, the elution of Fe ions from the steel surface is suppressed, and if the chemically stable rust is physically dense, it breaks into rust. It is difficult to generate structural defects such as pores and voids, and prevents oxygen, water, and corrosive substances from penetrating into the surface of the base steel. Elution of Fe ions, which is the cause of the formation of, is more remarkably suppressed or prevented. The present inventors have developed a product (α-FeOOH, generally referred to as “rust”) formed on a steel surface in the presence of water.
γ-FeOOH, amorphous rust, etc.)
When the steel surface is covered with an oxide layer made of stable magnetite or hematite, and the oxide contains Cr and Ni, the weather resistance of the steel is found to be extremely good. The present invention has been accomplished.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a steel material excellent in weather resistance according to the present invention and a method for producing the same will be described in detail. The so-called “rust”, “%” of Cr and Ni contained in the magnetite layer and the hematite layer, and Cr and Ni in the aqueous solution
"%" Means "% by mass". The steel material of the present invention is a steel material having a magnetite layer and / or a hematite layer containing 0.3% or more in total of one or both of Cr as an oxide and Ni as an oxide on the surface.

[0007] Cr and Ni present in the oxide layer are present as their oxides.
r "," Ni as oxide ", not just" Cr ",
Write "Ni".

The reason for having a magnetite layer and / or a hematite layer on the surface is that these layers are very stable in the air, do not undergo phase transformation, and do not dissolve even in the presence of moisture.

Furthermore, if one or both of Cr and Ni are contained in these oxide layers, the structure of magnetite and hematite is dense and has few cracks and pores. Alternatively, when Ni is contained alone, the content of each is 0.3% or more, and when both Cr and Ni are contained, the total content of both is 0.3%.
%. If the content of Cr and / or Ni is too large, the layer of magnetite or hematite becomes poor in adhesion to the base steel and collapses and peels off from the interface with the base steel. Alternatively, the upper limit of the Ni content is preferably set to 50%. The thickness of the oxide layer is desirably 0.1 to 50 μm.

[0010] The steel material of the present invention having such a structure is as follows.
The base steel surface is shielded from the atmospheric corrosion environment, preventing oxygen, water, and even corrosive substances from entering the base steel surface, making it difficult for Fe ions to elute and preventing the formation of floating rust and flowing rust. Or be suppressed. The steel material of the present invention is applied with an aqueous solution containing 0.3 to 5% chromium (III) ions and / or 0.3 to 6% nickel (II) ions on the surface of the base steel, and then heated to 450 to 720 ° C. Can be manufactured. An aqueous solution containing 0.3 to 5% Cr (III) ions and / or 0.3 to 6% Ni (II) ions is applied to the surface of the base steel during the heating process after application. The magnetite and hematite formed in
This is because a structure with few cracks and pores is formed. When an aqueous solution containing Cr (III) ions and Ni (II) ions is applied to the surface of the base steel, these ions are mixed with Fe ions eluted from the base steel, and when dried in this state,
So-called “rust” containing Cr and Ni in Fe is formed on the surface of the base steel, and when this is further heated to a high temperature, the “rust” transforms into magnetite or hematite. At this time, when Cr and Ni are contained, when the above-mentioned “rust” is formed, the “rust” becomes finer, and the structure of the interface between “rust” and the base steel becomes dense, and as a result, , Magnetite and hematite are dense and have a structure with few cracks and pores. Alternatively, after an aqueous solution containing Cr (III) ions and Ni (II) ions is applied, it may be directly heated to a high temperature without drying. In the process of heating, drying first produces so-called `` rust '' containing Cr and Ni in Fe, then transforms `` rust '' into dense magnetite and hematite similar to the above containing Cr and Ni. Become. This effect is due to the effect of Cr (III)
It is also seen when an aqueous solution containing each of the ions alone and Ni (II) ions is applied. The lower limit of the concentration of each of Cr (III) ions and Ni (II) ions in the aqueous solution applied to the surface of the base steel is set to 0.3%, respectively.
0.3% for both ions and Ni (II) ions
If it is less than the above, the effect of making the above magnetite or hematite dense and has a structure with few cracks and pores is not sufficiently exhibited. Also, the upper limits of the concentrations of Cr (III) ions and Ni (II) ions are set to 5% and 6%, respectively, if the upper limits are exceeded, the magnetite layer and the hematite layer formed in the heating process described below. This is because the (oxide layer) becomes too thick and collapses and separates from the interface between the oxide layer and the base steel. This is presumably because the internal stress acting on the oxide layer exceeds the adhesion between the oxide layer and the base steel. The application of the aqueous solution containing Cr (III) ions or Ni (II) ions to the surface of the base steel is performed by any method such as air spraying, airless spraying, and brushing as in the case of ordinary coating. You may. The amount (or thickness) of the aqueous solution to be applied is not particularly limited. However, if the coating amount is too small, it may not be possible to coat the entire surface of the base steel, and if the coating amount is too large, it does not contribute to the interface reaction, and is economically unsuitable. Therefore, the coating amount is preferably 2 to 50 μm. Thus, Cr (III) ions and Ni (II)
The application of the aqueous solution containing ions can be easily performed at any place, and is economical because it is effective only once. After applying an aqueous solution containing Cr (III) ions and / or Ni (II) ions to the surface of the base steel, heat treatment is performed. After the application, the drying process is naturally incorporated between heating and heating. . That is, when the application area is large and the application requires time, the result is that the coating is naturally dried in the air before the drying treatment is performed, and after the application, the coating is directly heated to a high temperature without drying in the air. Even in this case, drying is performed in the course of heating as described above.
In addition, the elution rate of Fe ions from the base steel, Cr ions,
At least 5 at room temperature in terms of Ni ion mass transfer
Min, at a higher temperature, for example at 50 ° C, at least
It is desirable that the surface of the base steel is in a wet state for one minute. However, if the wet state is too long, the elution amount of Fe ions increases and the amounts of Cr and Ni in the oxide layer formed on the surface of the base steel decrease, so that at room temperature, the maximum is 6 Time is desirable. When forming a dense magnetite or hematite oxide layer on the surface of the base steel, the advantage of using an aqueous solution containing Cr (III) ions or Ni (II) ions is that, as described above, construction is simple, In addition to being excellent in economical efficiency, it has a role of improving the adhesion of the oxide layer generated on the surface of the base steel. Since the mobility of ions in solution is much higher than that in solids, the first rust generated on the steel surface contains a large amount of Fe ions eluted from the base steel, The “rust” generated later contains only Fe ions that have passed through the layer of “rust” generated first, and the content of Cr (III) ions and Ni (II) ions increases. As a result, the oxide layer formed on the surface of the base steel,
This is because, as it goes to the outer surface side, the layer becomes richer in Cr or Ni, whereas the base steel side becomes richer in Fe, and the adhesion becomes better.

Heating to 450 to 720 ° C. after applying an aqueous solution containing Cr (III) ions or Ni (II) ions is because the so-called “rust” generated after coating is very stable in an atmospheric corrosion environment. It is for transforming into magnetite or hematite. If the heating temperature is lower than 450 ° C, dense magnetite or hematite which is sufficiently adhered to the base steel will not be formed, and defective parts will be formed. On the other hand, when the temperature exceeds 720 ° C, oxidation into the inside of the base steel proceeds, and the oxide layer easily peels off during cooling, exposing the base steel at that part and significantly reducing the weather resistance. In some cases, the mechanical properties near the surface of the steel deteriorate. Heating methods include Cr (III) ion and Ni (II)
It is possible to heat the entire steel material after applying the aqueous solution containing ions.However, in the high-temperature range of 450 ° C or higher, when low-alloy steel is used as a normal structural steel, It may be in a heat-treated state, and properties such as strength may be significantly deteriorated. Therefore, it is preferable to adopt a method of heating only the surface of the steel material by using an induction heating device or a gas burner. The reaction to transform so-called “rust” into magnetite or hematite generated by applying an aqueous solution containing Cr (III) ions or Ni (II) ions is relatively fast. It is preferable that the heating time is not less than 5 minutes at 600 ° C and not less than 1 second at 720 ° C. Note that the effect of maintaining the high temperature for a long time does not change even if it is extended.
In this case, it is desirable to set 10 minutes, 30 seconds at 600 ° C, and 10 seconds at 720 ° C.

After the heat treatment, the substrate may be allowed to cool in the air.
During cooling, a porous (porous) oxide layer in the vicinity of the surface of the oxide layer formed on the surface of the base steel may be peeled off. Since an oxide layer having strong adhesion is formed at the interface of the base steel, there is no problem with respect to weather resistance. However, when aesthetics are important, the porous oxide layer on the surface may be removed with a brush, a nylon brush, or the like. According to the method of the present invention described above, a chemically stable and dense oxide layer is formed on the surface of the base steel by a simple treatment, and a steel material having excellent weather resistance can be obtained.

[0013]

EXAMPLE A steel material (specimen) having an oxide layer formed on the surface by the method of the present invention using weather-resistant steel and ordinary steel having the chemical compositions shown in Table 1 as a base steel was exposed to the air. And
The surface condition and the thickness reduction of the test piece after the exposure were investigated.

[0014]

[Table 1] Table 2 shows an aqueous solution containing Cr (III) ions and / or Ni (II) ions applied to the surface of the base steel (hereinafter referred to as “treatment liquid”).
) And heat treatment conditions. In addition,
The reference numerals in the column “base steel” correspond to the reference numerals in the column “base steel” in Table 1.

[0015]

[Table 2] First, a test piece with a size of 150 mm × 60 mm × 3 mm was cut out from the above base steel, and its surface was polished with emery paper.
After buffing, the treatment liquid was applied by spraying, and the surface was wet-dried in a wet state. Thereafter, the test piece was heated by an induction heating device so that the surface temperature of the test piece became the temperature shown in Table 2, and allowed to cool in the air to form a test piece having an oxide layer formed on the surface. The surface of each test piece is black or black-brown, and if you touch the surface by hand, the porous powdery material on the surface layer can be easily removed, but an oxide layer that cannot be removed by hand at the interface with the base steel. Had been formed. Each of the above test pieces was exposed for 365 days (1 year) or 730 days (2 years) under the same conditions in an industrial area at a distance of 4 km from the coast. With regard to the test specimen one year and two years after the exposure, the appearance and the concentration of Cr and Ni in the surface oxide layer were examined.
The thickness reduction was determined. The appearance was examined by visual observation, and the concentrations of Cr and Ni were examined by EDX (energy dispersive microanalyzer). In addition, the amount of reduction in the thickness is measured in advance by measuring the mass of the test piece before applying the treatment liquid using the blank material, applying the treatment liquid and performing heat treatment, and then removing the oxide layer on the surface. The thickness of the test piece was measured and the thickness reduced by the application of the treatment liquid and the heat treatment (that is, the blank value) was determined from the measured values. By subtraction, the amount of thickness reduction due to exposure was determined.
As a result of the appearance investigation, the present invention examples 1 to 3 and 5 shown in Table 2
The appearance of the test pieces used in 6, 8, and 9 was not much different from that before the exposure, and was black or black-brown. On the other hand, in the appearance of the test pieces used in Examples 4, 7, 10 and 11 of the present invention, flowing rust was partially observed, and when the surface after removing the flowing rust and the oxide layer was observed, some corrosion was observed. However, the depth was slight.

On the other hand, in the test pieces of Comparative Examples 1 and 2, the appearance before the exposure was black-brown, which was indistinguishable from the test piece of the present invention. After one year, almost half of the exposed surface had no black-brown portion after 2 years, and after 2 years the entire surface was covered with rust, giving a completely different appearance than before exposure. Further, as a result of analysis of the oxide layer on the surface of the test piece before EDX exposure, in each of the test pieces used in the present invention, Cr and / or Ni contained 0.3% in the entire area of the test piece.
As described above, concentration of Cr and Ni was recognized. However, despite the use of weathering steel as the base steel, the test pieces used in the comparative examples had very low Cr and Ni contents overall, and the portion of 0.3% or more was locally localized. But less than 0.3%.

Table 3 shows the results of examination of the amount of reduction in the thickness of the test piece after exposure. From these results, in the test piece of the present invention example,
It can be seen that the amount of reduction in the thickness of the test piece is much smaller than that of the test piece used in the comparative example. The reduction in thickness of 1 to 2 μm, in other words, means that corrosion has hardly occurred during the two-year exposure period.

[0018]

[Table 3]

According to the steel material of the present invention, the base steel surface is shielded from the atmospheric corrosion environment, and oxygen, water, and even corrosive substances are prevented from penetrating into the base steel surface. Difficult and has excellent weather resistance. This steel material can be easily manufactured by the method of the present invention in which a chemically stable and dense oxide layer is formed on the surface of the base steel by a simple treatment.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takeshi Chikan 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. F-term (reference) 4K026 AA02 BA08 BB08 CA11 CA17 CA19 DA02 DA06 DA11 DA16

Claims (2)

[Claims] 1. A method according to claim 1, wherein one or both of chromium as an oxide and nickel as an oxide are combined on the surface.
A steel material excellent in weather resistance characterized by having a magnetite layer and / or a hematite layer containing 0.3% by mass or more. 2. The method according to claim 1, wherein 0.3 to 5 mass% of chromium (I
II) ions and / or 0.3-6% by mass of nickel (I
2. The method for producing a steel material having excellent weather resistance according to claim 1, wherein the coating is heated to 450 to 720 ° C. after applying an aqueous solution containing ions.