JPH11264079A - Early formation of weather resistant stabile rust and production of weather resistant steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of flow rust and to early produce corrosion resistant stabilized rust improving corrosion resistance by holding an environment of a specified oxygen gas composition while forming a water film of a specified thickness on a steel surface. SOLUTION: While forming a water film of <=500 μm thickness on a steel plate surface, an environment of 15-50 vol% gaseous oxygen thereon. A steel 1 is held in a rust forming bath 2, voltage of a humidifying pump 12 is continuously changed so that an output value of a water film thickness detection sensor 13 set to a dummy test piece 1D surface is coincide to an objective value, a water film thickness is maintained fixed by feed-back control changing a water spray quantity to a water content adjustment chamber 3 communicating to a rust forming bath 2. The atmosphere in the rust forming bath 2 is a mixed one between a gaseous nitrogen 7 and gaseous oxygen 8, by changing a partial pressure of the gaseous oxygen 8 with using a gas supply device 6, the gaseous oxygen in the atmosphere is adjusted. Pure water is used for spraying in order to produce efficiently obtain stabilized rust.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rapidly forming weather-resistant stable rust and a method for producing a weather-resistant steel material.
The present invention relates to a method for rapidly growing weather-resistant stable rust, which rapidly grows weather-resistant stable rust on the surface of a steel material, and a method for manufacturing a weather-resistant steel material in which flow rust is prevented by the method. In the "steel material",
Includes steel plates, steel plates, bars and sections.

[0002]

2. Description of the Related Art Weather-resistant steel in which alloy elements such as P, Cu, Cr and Ni are added to steel to improve corrosion resistance in the atmosphere is used for steel structures such as ships and tanks and steel buildings such as bridges. Widely used for Weatherproof steel forms rust called stable rust, which is hard to pass oxygen and water that cause corrosion outdoors in a few years, and suppresses subsequent corrosion. For this reason, the weather-resistant steel does not need to be coated with a rust-preventive paint, and is a so-called inexpensive and highly corrosion-resistant material that can be used naked.

[0003] However, in weather-resistant steel, it takes several years until stable rust is formed, and during that time, flowing rust called rust juice is generated, which causes a problem of deteriorating aesthetic appearance and polluting the environment. there were. Further, the weather-resistant steel has a problem that stable rust is hardly formed due to the action of the sea salt particles flying in the coastal zone, and the suppression of corrosion is not recognized.

To solve such a problem, see, for example,
No. 1739 discloses a steel material having a weather-resistant rust layer in which a semipermeable coating is formed on a steel material having rust formed by the action of water, a corrosive liquid or both on the surface of a base metal. -3767
No. 2 discloses a rust-resistant weather-resistant steel sheet treated with a rust-treating solution having a special composition. In addition,
Japanese Patent Application Laid-Open No. 6-136557 proposes a surface treatment method for a steel material in which an aqueous solution of chromium sulfate or an aqueous solution of copper sulfate is applied, and after moisture drying, an organic resin coating is performed. In addition,
Japanese Patent Application No. 8-13158 proposes a surface treatment method for a steel material in which an aqueous solution containing aluminum ions is applied, and after moisture drying, an organic resin film is further formed.

Further, Japanese Patent No. 2572447 discloses that extremely low Si and extremely low S, Ni, Al and Nb are added in combination, and a composite oxide of Al and Ca is further contained. A steel material having a property has been proposed.

[0006]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open
With the technology described in JP-A-49-11739 and JP-B-7-37672, corrosion during exposure to the atmosphere is suppressed at an early stage,
Both use a treatment liquid containing a chemical, so there remains a problem in handling.In addition, in the technology described in JP-A-6-136557 and JP-A-8-13158, weather-resistant rust is short-term. However, there are problems such as complicated processes and expensive surface treatment materials. Further, in the technology described in Patent No. 2572447,
Adjustment of the composite oxide has been a problem, for example, it takes a great deal of effort to uniformly disperse the composite oxide in the steel.

The present invention advantageously solves the above problems,
Prevention of run-off rust, weather-resistant stable rust that improves weather resistance even in use in the coastal zone, weather-resistant stable rust that can be easily and early grown, and flow rust generation was prevented by the method. An object of the present invention is to provide a method for manufacturing a weather-resistant steel material.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors first analyzed stable rust.
The present inventors observed under a polarizing microscope the cross section of rust generated on the steel sheet surface exposed for more than 25 years in the countryside and the coastal zone, and the rust generated in the countryside had many quenched parts. On the other hand, it was found that the rust generated in the coastal zone could hardly find polarized and quenched parts. Also,
The corrosion rate of the steel sheet exposed in the rural area was almost zero, while the corrosion rate of the steel sheet exposed in the coastal area was not as large as the initial exposure, but was about 1/3 of the initial corrosion rate. Corrosion was progressing. From these facts,
The present inventors believe that the essence of stable rust is rust observed as a quenched portion under a polarizing microscope, and that this portion is a corrosion factor, oxygen, which suppresses the penetration of water to the surface of the base steel. I guessed.

Further, the present inventors conducted an experiment in which a steel sheet which had been exposed in a rural area for 15 years and had a large amount of quenching under a polarizing microscope and had rust formed was further exposed in a coastal area for more than 3 years. No generation of flowing rust and no increase in corrosion rate were observed. This suggests that once formed stable rust is stable even in the presence of sea salt particles,
The present inventors have found that if stable rust is formed on the surface of a steel sheet before it is used in the atmosphere, it is possible to prevent the occurrence of flowing rust and to obtain a steel sheet that can sufficiently withstand use in coastal areas. I came to my mind.

Therefore, the present inventors diligently studied a method for growing stable rust in a short period of time in the production process of steel, and the rust quenched under a polarizing microscope has a strong correlation with the water film thickness on the surface of the steel. Newly obtained by maintaining the water film thickness at 500 μm or less. The present invention has been completed by further study based on the above findings.

That is, according to the present invention, a steel material is treated with an oxygen gas 15 to 50 with a water film having a thickness of 500 μm or less formed on its surface.
A method for rapidly producing weather-resistant stable rust, characterized in that the method is maintained in an environment of at least volume%, and the method for producing weather-resistant steel is carried out during the production of weather-resistant steel. Is the way.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a water film is formed on a steel surface.
It is uniformly formed with a thickness of 0 μm or less. Water film thickness of 500 μ
If it exceeds m, the amount of rust quenched under a polarizing microscope becomes extremely small, so the water film thickness was limited to 500 μm or less. To adjust the water film thickness, put the steel material in a room where the atmosphere can be adjusted,
It is preferable to perform this by spraying water into the room. The type of water used for this purpose may be ordinary water such as tap water, but pure water is preferred for more efficiently obtaining stable rust.

The interior of the room must be kept at an atmosphere of 15 to 50% by volume of oxygen gas. If the oxygen gas content in the atmosphere is less than 15% by volume, the rate of progress of corrosion is slow, and it takes a long time to form stable rust, and the production efficiency is reduced. Also, oxygen gas in the atmosphere
If it exceeds 50% by volume, corrosion does not progress. Therefore, the oxygen gas in the atmosphere is limited to 15 to 50% by volume or more. The atmosphere is preferably composed of a mixed gas of nitrogen gas and oxygen gas, and the adjustment of the oxygen gas in the mixed gas is preferably performed by changing the partial pressure of the oxygen gas. The oxygen gas to be mixed is preferably as pure as possible to obtain a predetermined stable rust.

The steel material used in the present invention may be any of a thick steel plate, a thin steel plate and a shaped steel. The composition is not particularly limited, and either ordinary steel or weather-resistant steel can be suitably used. However, from the viewpoint of increasing corrosion resistance, it is preferable to use weather-resistant steel to which P, Cu, Cr, Ni, or the like is added. In order to implement the present invention in the production of a weather-resistant steel material, a combination of a device that holds the steel material in an atmosphere-adjustable manner, a device that can adjust the moisture in the atmosphere, and a device that can adjust the oxygen gas in the atmosphere is used for weather resistance. It is only necessary to add it to the steel material manufacturing process. By such a simple means, it is possible to form stable rust which can effectively prevent rust from flowing on the steel material surface within a very short period of about one month or less. .

[0015]

EXAMPLE A test piece (5 mmt × 50 mmw ×) cut out from a steel plate having the composition shown in Table 1 (steel A is ordinary steel, steel B is weather-resistant steel)
100mml), using the model stable rust forming equipment shown in Fig. 1,
Rust was formed under the conditions shown in Tables 2 and 3. Three test pieces were prepared for each condition. The treatment period was 20 days. During this period, the test piece 1 was held in the rust forming tank 2 and the dummy test piece 1 was kept.
The voltage of the pump 12 of the humidifier 4 is continuously changed so that the output value of the water film thickness detection sensor 13 set on the surface D coincides with the target value, and the water 4 is supplied to the moisture adjusting chamber 3 communicating with the inside of the tank. The water film thickness was kept constant by feedback control to change the spray amount. The atmosphere in the tank is nitrogen gas 7 and oxygen gas 8
, A temperature of 40 ° C. and a pressure of 1
The oxygen gas in the atmosphere was adjusted by changing the partial pressure of the oxygen gas 8 using the gas supply device 6 to the atmospheric pressure. In FIG. 1, 5 is a humidifying heater, 9 is a heater for controlling the temperature in the tank, and 10 is an exhaust gas treatment device. In addition, as the water film thickness detection sensor 13, a non-contact vibration electrode was used.
It is preferable to use the application of the Kelvin method (Kelvin probe: manufactured by Hokuto Denko).

[0016]

[Table 1]

After the treatment, one of the three test pieces, each of which was covered with rust, was cut at five places, and the section was observed with a polarizing microscope. The thickness ratio was measured. Further, the remaining two test pieces, including those whose entire surfaces were not covered with rust, were exposed for 3 months in the countryside and coastal areas, and the occurrence of flow rust was investigated. Tables 2 and 3 show the results.

[0018]

[Table 2]

[0019]

[Table 3]

From Tables 2 and 3, it can be seen that the ratio of the quenched rust thickness to the total rust thickness of the test piece treated under the conditions within the range of the present invention was 0.36 to 0.46 for ordinary steel (Table 2). It is as high as 0.55 to 0.67 in the weathering steel (Table 3), which indicates that stable rust is sufficiently formed. In addition, the test pieces treated under the conditions within the scope of the present invention did not show any flow rust even after exposure to any of the countryside and coastal areas. On the other hand, in the test pieces treated under the conditions out of the range of the present invention, the ratio of the quenched rust thickness to the total rust thickness is as low as 0.22 or less, and the amount of rust is small and the entire test piece is not covered. After the exposure in the countryside and coastal areas, run-off rust was observed.

[0021]

As described above, according to the present invention, stable rust can be easily grown in a short period of time, and generation of flowing rust can be prevented.
This has an excellent effect that a weather-resistant steel material that can withstand use in a coastal zone can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a model stable rust forming facility suitable for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test piece (steel material) 1D dummy test piece 2 Rust forming tank 3 Moisture adjustment chamber 4 Humidifier 5 Humidifier heater 6 Gas supply device 7 Nitrogen gas 8 Oxygen gas 9 Temperature control heater 10 Exhaust gas treatment device 11 Water 12 Pump 13 Water Film thickness detection sensor

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Fumimaru Kawabata 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Pref. 1-chome (without address) Inside Mizushima Steel Works, Kawasaki Steel Corp. (72) Inventor Kenichi Amano 1-chome, with Kawasaki-dori Mizushima, Kurashiki City, Okayama Prefecture (without address) Inside Mizushima Works, Kawasaki Steel Corporation

Claims (2)

[Claims] 1. A method for rapidly forming a weather-resistant stable rust, comprising maintaining a steel material in an environment of oxygen gas of 15 to 50% by volume or more while forming a water film having a thickness of 500 μm or less on its surface. 2. A method for producing a weather-resistant steel material, wherein the method according to claim 1 is carried out during the production of the weather-resistant steel material.