JP2001172773A - Method for producing weather resistant steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing weather resistant steel by which a rust layer enough in corrosion preventability is formed on the surface of steel in a short time. SOLUTION: In this method, a process in which the surface of steel is humidified with a solution of pH 2.5 to <7 by 0.10 to 5 mg/cm2 for 5 to 60 min and is next dried is repeated, as the above solution, the one containing Fe2+ by 0.05 to 2.5 g/l is preferable, and the one in which the combination of one or more kinds among Fe3+, Cu2+, Ni2+, Co2+, Cr3+, PO43-, Mo5+, Ti3+, W6+, Al3+, Mg2+, Sr2+, MoO42+, TiO32- and WO42- is contained by <=20 mass % of the above Fe2+ is more preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a weather-resistant steel material, and more particularly to a method for manufacturing a weather-resistant steel material in which a corrosion-resistant rust layer is formed on the surface of a steel material at an early stage to prevent generation of flow rust. . In the present invention, the steel material includes a thick steel plate,
Includes thin steel, bar and section steel.

[0002]

2. Description of the Related Art Weather-resistant steel, which has improved corrosion resistance in the atmosphere by adding alloying elements such as P, Cu, Cr, and Ni to the steel, is stable in that it does not allow oxygen and water, which cause corrosion, to be exposed in an exposed environment. A rust layer called rust is formed in a few years, and the corrosion of ground iron is suppressed. In addition, since the stable rust is dark brown in harmony with the scenery as compared with ordinary steel, it has recently been increasingly used for building exterior materials and steel structures such as bridges. Weather-resistant steel does not require the application of a rust-preventive paint, and is a so-called bare use highly corrosion-resistant material.

[0003] However, when used in the countryside, conventional weather-resistant steel takes several years to form stable rust, and during that time, it generates flowing rust called rust juice, which poses a problem in view. Was. In addition, peeling rust called floating rust was also generated during the period, which was a problem. Further, the weather-resistant steel has a problem in that stable rust is hardly formed due to the action of sea salt particles flying in the coastal zone, and the suppression of corrosion is not recognized.

[0004] To deal with such problems, various treatment methods have been studied for steel materials. First, it is widely practiced to apply a coating film on the surface of a weather-resistant steel to block a corrosive environment. Japanese Patent Application Laid-Open No. 49-11739 discloses a weather-resistant rust layer-forming steel material in which water, a corrosive liquid, or both are applied to the surface of the steel material to generate rust, and then a semipermeable coating is formed. I have.

On the other hand, as a method without using a coating film, a method of preventing flowing rust by forming a rust layer having an anticorrosion function in advance has been proposed. For example, Japanese Unexamined Patent Publication No.
Japanese Patent Publication No. 142088 discloses a method for treating a steel sheet surface with an acidic solution and then forming a phosphate film, and Japanese Patent Publication No. 7-37672 discloses a method for treating a steel sheet with a rust treatment liquid having a special composition. A rust-resistant weathering steel sheet is disclosed in Japanese Patent No. 2765425 as a rust layer having an average grain size of 200 nm or less or an average grain size of 2 nm.
A steel material covered with an α-FeOOH of 00 nm or less is disclosed, respectively.

[0006]

However, the method of forming a coating film on the surface of a weather-resistant steel has a problem that it takes a long time of several tens of years to form a stable rust layer because the coating film has high corrosion resistance. There is. During that period, peeling and the like were caused by deterioration of the coating film, and the appearance was sometimes unsightly. Also,
When the deterioration is particularly severe due to the environment, repainting must be performed, and the advantage of the weather-resistant steel material that can be used without maintenance is not necessarily utilized. Further, there is a problem that color unevenness occurs due to a difference in the degree of progress of corrosion under the coating film.

The steel material having a weather-resistant rust layer disclosed in JP-A-49-11739 is manufactured by coating a steel material with a semi-permeable film. In this way, the effect of suppressing flow rust and peeling rust is enhanced. However, as shown in FIG. 2 of the publication, the anticorrosion effect of the rust layer itself is insufficient, and the steps are complicated because two processes, a rust accelerating process and a coating application, are performed.

On the other hand, the techniques described in Japanese Patent Application Laid-Open No. 1-142088, Japanese Patent Publication No. Hei 7-37672, and Japanese Patent No. 2765425 form a rust layer having anticorrosion performance in advance without using a paint. To suppress the generation of flowing rust.
In these techniques, a focus has been placed on forming a rust layer having weather resistance, and studies have been made on a corrosion treatment solution and a method for forming a rust layer.

However, in the technique described in Japanese Patent Application Laid-Open No. 1-142088, an acidic corrosive solution having a pH of 2.3 or less is used.
The rust layer is formed by applying the coating several times and drying it, but it is essential to form a phosphate coating thereafter. But,
The phosphate coating is known as a rust stabilizing treatment for weathering steel. In this technique, the rusting and the rust stabilizing treatment are performed, so that the process is complicated.

In the technique described in Japanese Patent Publication No. 7-37672, the weathering rust layer is formed by reducing the concentration of ions contained in the corrosion treatment solution and reproducing corrosion close to the actual exposure environment. However, as shown in FIG. 1 of the publication, the effect of inhibiting corrosion at an early stage after exposure is not always sufficient, and there is a problem that rust is generated during this period. Further, there was a problem that the rusting treatment required a long period of three days.

A rust layer having an average crystal grain size of 200 nm or less or an average crystal grain size of 200 n disclosed in Japanese Patent No. 2765425.
m to obtain a steel material covered with α-FeOOH
The chromium sulfate solution may be applied to the bare steel material and exposed, or the chromium sulfate solution may be applied on rust generated by the exposure. However, simply applying the solution and exposing it is not effective enough because the chromium sulfate is washed away by rainfall in some places, and it is difficult to see the progress of rust etc. in the same building or bridge depending on the place There was a problem.

As a related technique, Japanese Patent No. 2,666,673 discloses a paint containing a substance effective in stabilizing rust such as chromium sulfate. There is a problem that it takes a long time to form a stable rust layer due to its high anticorrosion property. As described above, in the prior art, it has been studied to generate a rust layer rich in anticorrosion properties on a weather-resistant steel sheet in advance to reduce flow rust in subsequent exposure. No consideration has been given to the process of producing the above.

Accordingly, an object of the present invention is to provide a method for producing a weather-resistant steel material capable of forming a rust layer rich in corrosion protection on the surface of the steel material in a short time.

[0014]

Means for Solving the Problems The present inventors have conducted intensive studies on the process of forming a rust layer in order to achieve the above-mentioned object, and as a result, have found that the surface of a steel material can be adjusted to a solution having a pH of 2.5 or more and less than 7 with a solution of 0.10-5.
By repeating the step of wetting at mg / cm ² for 5 to 60 minutes and then drying, it was found that a weather-resistant rust layer having a high anticorrosive property was formed in a short period of time.

It has also been found that when the solution contains 0.05 to 2.5 g / l of Fe ²⁺ , the corrosion resistance of the weather-resistant rust layer is further improved. Also, 0.05 to 2.5 g / l of Fe ^{2+ in the} solution.
And further contain Fe ³⁺ , Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Cr ³⁺ , PO
₄ ^3- , Mo ⁵⁺ , Ti ³⁺ , W ⁶⁺ , Al ³⁺ , Mg ²⁺ , Sr ²⁺ , MoO ₄ ²⁺ ,
One or a combination of two or more of TiO ₃ ^2- and WO ₄ ^2-
It has been found that when the content is 2% by mass or less of ²⁺ , the corrosion resistance of the weather-resistant rust layer is further improved.

The present invention has been completed based on these findings, and the gist of the present invention is a method for producing a weather-resistant steel described below. (1) The surface of steel material is 0.10-5mg of a solution with pH 2.5 or more and less than 7.
A method for producing a weather-resistant steel material, comprising repeating a step of wetting at / cm ² for 5 to 60 minutes and then drying. (2) The steel surface has a pH of 2. 0 to 2.5 g / l containing Fe2 ⁺ .
A method for producing a weather-resistant steel material, comprising repeating a step of wetting with a solution of 5 to less than 7 and 0.10 to 5 mg / cm ² for 5 to 60 minutes and then drying.

(3) The surface of the steel material contains 0.05 to 2.5 g / l of Fe ²⁺ and further contains Fe ³⁺ , Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Cr ³⁺ , PO ₄ ^3- , Mo ₄
⁵⁺ , Ti ³⁺ , W ⁶⁺ , Al ³⁺ , Mg ²⁺ , Sr ²⁺ , MoO ₄ ²⁺ , TiO ₃ ^2- ,
WO ₄ ^{2 -} of one or pH2.5 less than 7 containing 20 wt% or less of two or more of the combination the Fe ²⁺ solution 0.10~5mg
A method for producing a weather-resistant steel material, comprising repeating a step of wetting at / cm ² for 5 to 60 minutes and then drying.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION In order to generate rust on a steel sheet, it is sufficient to supply water to the steel sheet. However, rust that adheres to the steel sheet is not generated in a state of being constantly wet with water (wet state). Requires a drying step. Corrosion-resistant rust of weathering steel is also gradually formed by repeated dry and wet in a natural exposure environment. Although the mechanism is not always clear, as for the point that a coherent rust layer having anticorrosion properties is generated by repeated drying and wetting, see, for example,
It has been known for a long time, as disclosed in Examples of JP-A-11739.

The point of the present invention is that the quality, quantity, and repetition cycle of the liquid to be applied in the repetition process of dry and wet are limited to a range in which an intimate rust layer having corrosion resistance can be formed in a short period of time. . Hereinafter, the reasons for limiting the requirements of the present invention will be described. Regarding the quality of the liquid for moistening the steel surface, the liquid must be a solution having a pH of 2.5 or more and less than 7. The solution is preferably an aqueous solution. The solution must be below pH 7, ie on the acidic side, in order to allow corrosion or electrochemical dissolution of the iron base to proceed at a sufficient rate. However, in a strongly acidic solution having a pH of less than 2.5, although the dissolution of the base iron proceeds at a sufficient rate, it is difficult to form a rust layer having high adhesion. Therefore, the solution to be applied is limited to a solution having a pH of 2.5 to less than 7.

As the solution having a pH of 2.5 or more and less than 7, an aqueous solution obtained by diluting sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, boric acid, or the like with water is preferable because the pH can be easily adjusted. In the present invention, an anticorrosive rust layer can be formed by using such a weakly acidic liquid. In the present invention, in order to further enhance the corrosion resistance of the rust layer, it is preferable that the solution contains 0.05 to 2.5 g / l of Fe2 ⁺ . Although the principle is not clear, Fe ²⁺ has the effect of accelerating corrosion, accelerating the formation of a rust layer, and improving the corrosion resistance of the rust layer. This effect is remarkable at 0.05 g / l or more.However, at more than 2.5 g / l, the corrosion resistance is too strong to form an adhesive rust layer.
The concentration of Fe ²⁺ is preferably in the range of 0.05 to 2.5 g / l.

In order to prepare an Fe ²⁺ -containing solution, one or more iron salts such as iron sulfate, iron chloride, iron nitrate and the like are added to a predetermined Fe
^It may be dissolved in water so as to have a ²⁺ concentration. Since these salts are acidic salts, a solution having a pH of 2.5 or more and less than 7 can be obtained without any need for pH adjustment. Of course, the pH may be adjusted by adding an acid as needed. In adjusting the Fe ²⁺ -containing solution, anions are inevitably added as described above. However, industrially, iron sulfate or iron chloride is inexpensively used. Of course, the present invention is not limited to these iron salts.

[0022] In the present invention, a further third component 0.05~2.5g / lFe ²⁺ containing ^{solution, Fe 3+, Cu 2+, Ni} 2+, Co 2+, C
r ³⁺ , PO ₄ ^3- , Mo ⁵⁺ , Ti ³⁺ , W ⁶⁺ , Al ³⁺ , Mg ²⁺ , Sr ²⁺ , M
When one or a combination of two or more of oO ₄ ²⁺ , TiO ₃ ^2- , and WO ₄ ^2- is added so that the content is within a range of 20% by mass or less of the Fe ²⁺ amount, rust is more reduced. It is preferable that a rust layer having finer corrosion resistance and better corrosion resistance is formed. The third component (Fe ³⁺ ,
Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Cr ³⁺ , PO ₄ ^3- , Mo ⁵⁺ , Ti ³⁺ , W ⁶⁺ ,
Content of one or more of Al ³⁺ , Mg ²⁺ , Sr ²⁺ , MoO ₄ ²⁺ , TiO ₃ ^2- , and WO ₄ ^2- ) exceeds 20% by mass of the Fe ²⁺ amount In addition, not only is the corrosion resistance of the rust layer deteriorated, but also the cost of the solution is increased. If the content of the third component is less than 2% by mass of the Fe ²⁺ amount, the effect is unlikely to be exhibited, so that the content is more preferably, and more preferably 4% by mass or more of the Fe ²⁺ amount.

Next, the amount of liquid for putting the steel material surface in the wet state, this fluid volume is required to be 0.10~5mg / cm ² (the steel surface 1 cm ² per 0.10~5mg). 0.10
If the amount is less than mg / cm ² , the progress of the corrosion is slowed down due to the lack of the liquid, and the control of the liquid amount is substantially difficult, and the liquid tends to evaporate immediately, which tends to cause unevenness. On the other hand, if the liquid amount exceeds 5 mg / cm ² , the supply of oxygen to the interface of the base iron becomes insufficient, and non-adhesive Fe ₃ O ₄ is generated as a corrosion product, so that a weather-resistant rust layer is not easily formed. As long as the liquid volume is within the range of 0.10 to 5 mg / cm ² , there is no problem even if it fluctuates in the holding time described later, but in a wet state, the atmosphere in the wet processing chamber where the steel material is set is kept at a high humidity. It is preferable to prevent evaporation of the liquid in contact with the surface of the steel material and make the liquid amount constant. In the method disclosed in JP-A-49-11739, since the means for creating a wet state is immersion in a corrosive liquid, the progress of corrosion is slow, and an adhesion rust layer is not easily formed.

Next, in a cycle of repeating wet and dry,
The holding time of the wet state per cycle needs to be 5 to 60 minutes. If the time is less than 5 minutes, the corrosion does not proceed so much and it takes time to form a weather-resistant rust layer. If the time exceeds 60 minutes, a large amount of Fe ₃ O ₄ is generated in the rust, and the weather resistance of the rust layer deteriorates. Also, the number of repetitions of wet and dry (number of dry and wet cycles)
Need not be repeated twice since it is not repeated once, but preferably 10 or more times. If the number of dry and wet cycles is less than 10, the thickness of the formed rust layer is too thin, and it is difficult to prevent the generation of flowing rust in an exposed environment. In the present invention, if the thickness of the rust layer is increased by increasing the number of times of the drying / wetting cycle and the treatment is performed 10 times or more, there is an effect of preventing flowing rust in an exposed environment. However, even if the number of drying and wet cycles is excessively increased, the anticorrosion property of the rust layer tends to be saturated, which is time-consuming and is not economically preferable. The number of times of dry and wet cycles in the present invention depends on the solution composition, etc.
A desirable range is up to 300 times, and a practical range is 30 to 150 times.

On the other hand, the time required for drying is not particularly limited, since the corrosion does not progress and the rust quality does not change in the dry state, and may be appropriately set depending on, for example, the size of the steel material and the specifications of the apparatus. However, in order to shorten the period of forming the rust layer, it is preferable to shift to the next cycle of wet treatment without delay after completion of one cycle of drying. In the methods (2) and (3) of the present invention, the additional components in the solution remain after drying and accumulate with each cycle, which may adversely affect the corrosion resistance of the rust layer. It is preferable that the surface of the steel material after drying and before wetting is washed with water and dried again in each cycle.

According to the present invention, in a weather-resistant steel material in which a weather-resistant rust layer having high corrosion resistance is formed on the surface of the steel material in a short period of time, the generation of flowing rust when unpainted is used is greatly reduced, and the appearance or environmental pollution is reduced. Problem is solved. This effect is also exerted in coastal areas where stable rust is not likely to be formed, and the occurrence of flowing rust of weather-resistant steel is significantly reduced even in areas near the coast.

The steel material on which a rust layer is formed by the methods (1) to (3) of the present invention is S steel specified in JIS G3114.
MA400AW, SMA400AP, SMA400B
W, SMA400BP, SMA400CW, SMA40
0CP, SMA490AW, SMA490AP, SMA
490BW, SMA490BP, SMA490CW, S
MA490CP, SMA570W, and SMA570P are preferable, and when used particularly in coastal areas, the following (S1) to (S1)
The high-shore weather-resistant steel material according to any of 4) is suitable.

(S1) In mass%, C: 0.001 to 0.025
%, Si: 0.60% or less, Mn: 0.10 to 3.00%, P: 0.005 to
0.030%, S: 0.01% or less, Al: 0.10% or less, Cu: 0.1
Weathering steel containing up to 1.5%, Ni: 0.1 to 6.0%, B: 0.0001 to 0.0050%, the balance being Fe and unavoidable impurities.

(S2) In S1, further in mass%,
Mo: A weathering steel containing 0.005 to 0.5% and satisfying the formula (1). (11P + 4.0 Cu + 3.1 Ni + 2.6 Mo) / (1−0.1 (10000 B) ^0.35 ) ≧ 1 + 13X (1) (where P, Cu, Ni, Mo, B: content of each element) Amount (% by mass), X: flying salt amount (mg / dm ² / day)) (S3) In S1, further in% by mass, Nb: 0.005 to
0.20%, V: 0.005 to 0.20%, Ti: 0.005 to 0.20%, RE
M: Weathering steel containing one or more selected from 0.02% or less.

(S4) In S1, further in mass%,
Mo: 0.005 to 0.5%, and satisfies the formula (1), and in mass%, Nb: 0.005 to 0.20%, V: 0.005 to 0.20
%, Ti: 0.005 to 0.20%, REM: 0.02% or less.

[0031]

EXAMPLE A rust accelerating test was conducted using the test apparatus shown in FIG. 1 in the following manner. A plurality of test pieces S were placed in the tank 1, and a solution was supplied to the surface of the test piece S by a spray type nozzle 4 installed on the upper part of the tank 1, and the surface of the test piece S was brought into a wet state. The arrangement of the nozzles 4 was set such that the same amount of solution was supplied to each test piece. The solution stored in the solution tank 2 was fed to the nozzle 4 by the pump 3. The amount of the solution on the surface of the test piece S was adjusted by changing the spray time. After the supply of the solution, the inside of the tank 1 was kept in a high humidity atmosphere (80% or more humidity) using the humidifier 5 to prevent the solution on the surface of the test piece S from evaporating and escaping. After maintaining this wet state for a predetermined holding time, air dried by the drying blower 6 was introduced into the tank 1 to forcibly dry the surface of the test piece S. Next, the surface of the test piece S was washed with a large amount of washing water, and was again forcedly dried. This wet (wet state) -dry cycle was repeated a predetermined number of times.

As test pieces, 100 × 50 × 10 mm ³ strip pieces obtained from two types of steel materials A and B having the chemical compositions shown in Table 1 were shot blasted. Steel A corresponds to the weather-resistant steel specified in JIS G3114, and steel B corresponds to the high shore weather-resistant steel.

[0033]

[Table 1]

The test pieces after the rust accelerating test were subjected to an exposure test for three months in a rural area and a coastal area for steel material A, and in a coastal area for steel material B, to investigate the occurrence of flow rust and floating rust. did. The flowing rust was collected every month by collecting rainwater flowing on the surface of the test piece in a polyethylene bottle, and measuring the amount of rust and iron ions in the collected liquid.
Evaluation was made based on the total amount of iron effluent for the months. The floating rust was peeled off again after the adhesive tape was stuck on the rust surface, and the amount of the rust adhered to the tape was visually evaluated.

(Case 1) In Case 1, the required items of the method (1), ie, the pH of the solution, the amount of the solution on the surface of the test piece, and the wet state holding time were variously changed as shown in Table 2 as test conditions. In addition, the acid for pH adjustment and the number of drying / wetting cycles were changed as shown in Table 2. Table 2 shows the results of the investigation on the occurrence of flowing rust and floating rust. Table 2 also shows the time required from the start to the end of the test (required rusting time) for each test condition.

[0036]

[Table 2]

[0037]

[Table 3]

Hereinafter, the test pieces of the steel materials A and B subjected to the rust accelerating treatment under the conditions of No. i are referred to as steel sheets Ai and Bi. Steel plate A5
0 and B50 are those exposed without treatment (bare) for comparison (bare exposed material), and steel plate A50 has much flow rust in the countryside,
Floating rust occurred, and more runoff and floating rust occurred in coastal areas. The steel plate B50 has reduced flow rust and floating rust in the coastal area compared to the steel material A, but the steel sheet A in the rural area
Occurred as much as 50.

The steel sheets A1 to A18 and B1 to B18 are p
H-adjusted solution was used, but method (1)
, Ie, steel plates A1 to A8, A15
-A18, B1-B8, B15-B18 are bare exposed materials (steel plate A
50, B50), the flow rust and floating rust are greatly reduced compared to the steel side. On the other hand, the comparative examples deviating from the range of the method (1), ie, the steel plates A9 to A10 and B9 to B10 deviating from the range of the method (1) in terms of the solution amount, and the steel plates A11 to A12 deviating in the period of the wet state holding time , B11-B12, steel plates A13 and B13 which deviate in terms of solution pH, and steel plates A which deviate in terms of the number of dry and wet cycles
In 14 and B14, run-off rust and floating rust were caused by bare exposed material (steel plate A5
0, B50) only slightly decreased as compared with the same steel material side.

In the examples, steel sheets A15 to A18 and B15 to B18 having different numbers of dry / wet cycles were used for steel sheets A15 to A16 and B15 to B16 having less than 10 dry / wet cycles. Steel plates A17-A18, B17-B18
The effect of reducing flowing rust and floating rust was smaller than that of The steel plates A19 to A31 and B19 to B31 use a solution whose pH has been adjusted with hydrochloric acid. Examples of the steel plates A19 to A23, A28 to A31, and B19 to B fall within the range of the method (1).
23, B28-B31 significantly reduced the flow rust and floating rust as compared with the bare exposed material (steel plates A50, B50) on the same steel side.

On the other hand, the comparative examples out of the range of the method (1), that is, the steel plates A24 and B24 out of the range of the method (1) in terms of the solution amount, and the steel plate A2 out of the range of the wet state holding time
5, B25, steel plates A26 and B26 that deviate in terms of solution pH, and steel plates A27 and B27 that deviate in terms of the number of dry and wet cycles, the flow rust and floating rust are lower than those of bare exposed materials (steel plates A50 and B50). Only a small reduction.

In the examples, the steel sheets A28-A31 and B28-B31 with the number of dry / wet cycles changed, and the steel sheets A28-A29 and B28-B29 with the number of dry / wet cycles less than 10 have the number of dry / wet cycles of 10 or more. Steel plates A30-A31, B30-B31
The effect of reducing flowing rust and floating rust was smaller than that of The steel plates A32 to A39 and B32 to B39 used the solutions whose pH was adjusted with nitric acid. Among them, the examples in the range of the method (1), that is, the steel plates A32 to A36 and B32 to B36 were exposed to naked. Rust and floating rust are greatly reduced as compared to the same material (steel plates A50 and B50).

On the other hand, the comparative examples deviating from the range of the method (1), ie, the steel plates A37 and B37 deviating from the range of the method (1) in terms of the amount of solution, and the steel plate A3 deviating in terms of the wet state holding time
8, B38, steel plates A39 and B39 which deviate in terms of solution pH,
Flow rust and floating rust were only slightly reduced as compared with the bare exposed materials (steel plates A50, B50) on the same steel side. Steel plate A40-A
43, B40-B43 are acid mixed with equal amounts of sulfuric acid and hydrochloric acid
Although the prepared solution was used, the examples within the range of the method (1), that is, the steel plates A40 to A42 and B40 to
In B42, the flow rust and floating rust were significantly reduced as compared to the bare exposed material (steel plates A50 and B50).

On the other hand, in the comparative examples out of the range of the method (1), that is, in the steel plates A43 and B43 out of the range of the method (1) in terms of the amount of the solution, the flowing rust and the floating rust are reduced by the bare exposed material (steel plate). A50, B50) only slightly decreased compared to the steel side. Steel plates A44-A46 and B44-B46 are pH adjusted with phosphoric acid.
Although the prepared solution was used, the examples within the range of the method (1), namely, steel plates A44 to A45 and B44 to
For B45, the flow rust and floating rust were significantly reduced as compared with the bare exposed material (steel plates A50 and B50).

On the other hand, in the comparative examples out of the range of the method (1), that is, in the steel plates A46 and B46 out of the range of the method (1) in terms of the wet state holding time, the flowing rust and the floating rust were not exposed to the bare exposed material. (Steel sheets A50, B50) showed only a slight reduction compared to the same steel material side. Steel plates A47-A49, B47-B49
Is a solution using a pH-adjusted solution with boric acid.
Examples of which are within the scope of the method (1), namely, the steel sheet A
47-A48, B47-B48 are bare exposed materials (steel plates A50, B50)
Rust and floating rust were greatly reduced compared to the same steel material side.

On the other hand, in the comparative examples out of the range of the method (1), that is, in the steel plates A49 and B49 out of the range of the method (1) in terms of the amount of the solution, the flowing rust and the floating rust are reduced by the bare exposed material (steel plate). A50, B50) only slightly decreased compared to the steel side. The required rusting time of the embodiment is 2.5 to 52.5
h, which is much shorter than the conventional 72 h (the method described in the above-mentioned Japanese Patent Application Laid-Open No. 7-37672).

(Case 2) In case 2, the test conditions include the requirements of method (2), ie, the solution pH and Fe ^2+.
The concentration, the amount of the solution on the test piece surface, and the wet state retention time were variously changed as shown in Table 3. An acid for pH adjustment, Fe ²⁺
The additive and the number of cycles of drying and wet were changed as shown in Table 3. The test conditions in Case 2 were all within the range of Method (1), and all were within the range of Method (2) except that some Fe ²⁺ concentrations were outside the range of Method (2). Table 3 shows the results of the investigation on the occurrence of flow rust and floating rust. Table 3
Shows the time required from the start to the end of the test (the time required for rusting) for each test condition.

[0048]

[Table 4]

The steel plates A51 to A60 and B51 to B60 are
Iron (II) sulfate was used as the Fe ²⁺ additive. Steel plates A51 to A58 and B51 to B58 which are applicable examples of method (2)
As a matter of course, the floating rust was remarkably reduced as compared with that of the same steel material of the example in the case 1 in addition to the fact that almost no floating rust was recognized. On the other hand, the flow rust and floating rust of the steel sheets A59 to A60 and B59 to B60 which are within the range of the method (1) but out of the range of the method (2) are the same as those of the same steel material of the embodiment in the case 1. It was about the same.

The steel plates A61 to A67 and B61 to B67 are
Iron (II) chloride was used as the Fe ²⁺ additive. Steel plates A61 to A65 and B61 to B65 which are applicable examples of method (2)
As a matter of course, the floating rust was remarkably reduced as compared with that of the same steel material of the example in the case 1 in addition to the fact that almost no floating rust was recognized. On the other hand, the flow rust and floating rust of the steel sheets A66 to A67 and B66 to B67 which are within the range of the method (1) but out of the range of the method (2) are the same as those of the same steel material of the embodiment in the case 1. It was about the same.

The steel plates A68 to A70 and B68 to B70 are
Fe2 ⁺ additive was prepared by mixing iron (II) sulfate and iron (II) chloride in equal amounts. Since all of them are compatible with method (2), there is almost no floating rust. Of course, the flow rust was remarkably reduced as compared with the case 1 of the same steel material of the embodiment. The time required for rusting in Case 2 was 16.6 to 33.3 h, and the anticorrosive rust layer was able to be formed in the same short period of time as the Example in Case 1.

(Case 3) In case 3, the test conditions
Requirements of method (3), ie, pH of solution, Fe ²⁺Dark
Degree, the third component (Fe³⁺, Cu²⁺, Ni²⁺, Co²⁺, Cr³⁺, P
O_Four ^3-, Mo⁵⁺, Ti³⁺, W⁶⁺, Al³⁺, Mg²⁺, Sr²⁺, Mo
O_Four ²⁺, TiO_Three ^2-, WO_Four ^2-One or a combination of two or more)
Amount (concentration) of the solution,
The state holding time was variously changed as shown in Table 4. In addition,
Acid for pH adjustment, Fe²⁺Additive, third component additive, dry
The number of wet cycles was changed as shown in Table 4. Case 3
Test conditions are all within the range of method (2).
Partly because the third component content was outside the range of method (3).
Everything else was within the range of method (3). Flow rust and floating rust
Table 4 shows the results of the survey on the occurrence status of the water. Table 4 shows the test results.
The time required from the start to the end of each test (rusting
Required time).

[0053]

[Table 5]

[0054]

[Table 6]

The steel plates A71 to A82 and B71 to B82 are
Iron (II) sulfate was used as the Fe ²⁺ additive. Steel plates A71 to A80 and B71 to B80 which are applicable examples of method (3)
As a matter of course, almost no floating rust was recognized, and the flowing rust was significantly reduced as compared with the case of the same steel material which is applicable to the method (2) in Case 2. On the other hand, steel plates A81 to A82, B which are within the range of method (2) but outside the range of method (3)
The flow rust of 81 to B82 was almost the same as that of the same steel of the method 2 in case 2 (2).

The steel plates A83 to A102 and B83 to B102 use iron (II) chloride as an Fe ²⁺ additive to the solution. Steel plates A83 to A87 and A90 which are applicable examples of method (3)
As for A102, B83 to B87 and B90 to B102, floating rust was hardly recognized, and the flowing rust was remarkably reduced as compared with the case of the same steel of the method (2) adapted in the case 2. On the other hand, the flow rust of the steel plates A88 to A89 and B88 to B89 that are within the range of the method (2) but out of the range of the method (3) is the same as that of the same steel material of the case 2 in the case of the method (2). Was about the same.

The time required for rusting in case 3 is 1
6.6 to 50 h, the case in Example 1 and Case 2
The anticorrosive rust layer could be formed in a short period of time.

[0058]

According to the present invention, a corrosion-resistant rust layer can be formed in a short time on the surface of a steel material such as a weather-resistant steel or a high-shore weather-resistant steel which is used without painting in a rural area or a coastal area. Can improve the productivity of weather-resistant steel that prevents run-off and floating rust during unpainted use, making it possible to solve environmental and landscape problems more economically and quickly. It has the effect.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a test device used for a rust acceleration test.

[Explanation of symbols]

 1 tank 2 solution tank 3 pump 4 nozzle 5 humidifier 6 drying blower S test piece

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiko Shioya 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. No. 1 Kawasaki Steel Research Institute, Inc. (72) Inventor Kawabata Fumimaru 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Pref. Mizushima Steel Works, Kawasaki Steel Corp. (72) Inventor Kenichi Amano Kurashiki, Okayama Pref. 1-chome, Kawasaki-dori, Mizushima-shi (No address) Kawasaki Steel Corporation Mizushima Works F-term (reference) 4K026 AA02 AA22 AA24 BA08 BB08 CA13 CA14 CA18 CA23 CA29 CA31 DA06 DA11

Claims (3)

[Claims] 1. A steel solution having a pH of 2.5 or more and less than 7
A method for producing a weather-resistant steel material, comprising repeating a step of wetting at 10 to 5 mg / cm ² for 5 to 60 minutes and then drying. 2. A process of wetting the surface of a steel material with 0.10 to 5 mg / cm ² of a solution containing 0.05 to 2.5 g / l of Fe ²⁺ and having a pH of 2.5 or more and less than 7 for 5 to 60 minutes, and then repeating the drying step. A method for producing weather-resistant steel. 3. The steel material surface contains 0.05 to 2.5 g / l of Fe ²⁺ and further contains Fe ³⁺ , Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Cr ³⁺ , PO ₄ ^3- , and Mo ^5+. ,
Ti ³⁺ , W ⁶⁺ , Al ³⁺ , Mg ²⁺ , Sr ²⁺ , MoO ₄ ²⁺ , TiO ₃ ^2- , WO ₄
0.10 to 5 mg / c, a solution having a pH of 2.5 or more and containing less than 20% by mass of Fe ²⁺ containing one or more combinations of ^2-
method for producing weather-resistant steel, characterized in that in m ² repeated step of 5 to 60 minutes wet and then dried.