JPH10140324A - Building material made of weather resistant stainless steel and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a building material free from the generation of rust or the like even if being left alone in the outdoor over a long period and capable of maintaining its beautiful appearance by subjecting the surface of a stainless steel to cleaning treatment and then executing heating in an oxidizing atmosphere to form a film of metallic oxide. SOLUTION: The surface of a stainless steel is subjected to electrolytic polishing or buffing to remove a working altered layer as an external layer, and the surface is cleaned. The electrolytic polishing is executed thereto preferably by treatment for about 1 to 10min, e.g. in a phosphoric acid-sulfuric acid based electrolyte. The stainless steel whose surface has been subjected to the cleaning treatment is subjected to heating treatment in an oxidizing atmosphere to form a film of metallic oxide. This heat treatment is executed preferably in the range of 300 to 500 deg.C for about 1 to 3hr. In the case the treating temp. is low, the formation of the oxidized film is made insufficient to increase the possibility of the generation of rust, and in the case the treating temp. is high, the oxidized coating is often made excessively thick and is simultaneously made brittle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stainless steel building material having weather resistance and a method for producing the same. More specifically, it is suitably used for a monument installed outdoors, a building material constituting an exterior of a building or the like, and is not corroded even if it is continuously exposed to the wind and rain or direct sunlight for a long time, and rust is generated. TECHNICAL FIELD The present invention relates to a stainless steel building material capable of maintaining a beautiful appearance without any problem and a method for manufacturing the same.

[0002]

2. Description of the Related Art As many monuments and buildings with high artistic arts are installed, these materials maintain their aesthetic appearance without being changed even under severe conditions where they are exposed to wind, rain and direct sunlight for a long period of time outdoors. There is a growing demand for building materials. In particular, in recent years, since there are many opportunities to be exposed to acid rain and various exhaust gases outdoors, a material having more weather resistance is required, and a variety of appearances can be obtained as desired. There is a need for a material which can be colored and easily formed into various shapes.

[0003] Stainless steel, such as SUS304 or SU, which is generally widely used as a material which hardly generates rust.
S304L also cannot escape corrosion under the above-mentioned conditions and cannot meet the requirements.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a weather-resistant stainless steel having a surface capable of maintaining an aesthetic appearance without rusting even when installed outdoors for a long period of time. It is an object to provide a building material and a method for manufacturing the same.

[0005]

Means for Solving the Problems In view of the above prior art, the present inventors have intensively studied to solve this problem, and as a result, after cleaning the surface of stainless steel, heat treatment was performed in an oxidizing atmosphere. The present inventors have found that a stainless steel building material having weather resistance is provided by a manufacturing method characterized by including a step of forming a metal oxide film by performing the process, thereby completing the present invention.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The cleaning treatment step in the above-mentioned manufacturing method is a step carried out with the intention of removing a work-affected layer (Bailby layer, crushed crystal zone) of the outer layer of stainless steel. As this cleaning step, buff polishing, electrolytic polishing, or the like can be performed, but in view of the fact that the work-affected layer can be substantially removed, it is particularly preferable to carry out the electrolytic polishing method. This electropolishing method essentially follows the method disclosed in Japanese Patent Application Laid-Open No. Hei 7-266134 by the present applicant. For example, it can be carried out in a phosphoric acid / sulfuric acid-based electrolytic solution for 1 to 10 minutes. preferable. If the treatment time is too short, cleaning of the surface is insufficient, and then it is difficult to obtain the desired weather resistance even if a film is formed by oxidation treatment, and if the treatment time is long, it is further removed to the lower layer. There is a fear that it will be done.

The second step of the method of the present invention, ie, the step of forming a metal oxide film, involves performing a heat treatment in an oxidizing atmosphere. This heat treatment is preferably performed for 300 to 5
It is good to carry out in the range of 00 ° C. for 1 to 3 hours, preferably for about 2 hours. If the treatment temperature is low, the possibility of rusting is increased due to insufficient formation of an oxide film, and if the treatment temperature is high, the oxide film may become excessively thick and weak at the same time. On the other hand, if the heating time is too short, the formation of an oxide film will also be insufficient, and if the treatment is performed for a long time, the oxide film may become too thick.

As the stainless steel, various stainless steels can be used. For example, SUS316, S
US316L, SUS304 or SUS304L are preferably used. SUS304 or SUS304L
When using, the cleaning treatment should be performed by electropolishing. This is because the affected layer (Bailby layer, crushed crystal zone) is completely removed by performing the electrolytic polishing, and therefore, if an oxidation treatment is performed thereafter, a uniform and dense iron oxide (FeO, Fe ₃ O _{4) is obtained.} , Fe ₂ O _3, etc.), and the release of iron is suppressed. On the other hand, in the case of buff polishing, the film obtained by the oxidation treatment may become non-uniform due to incomplete removal of the affected layer, so that a heat treatment for applying an oxide film from above is performed. Even if it goes, only an unstable film is formed,
Tends to be susceptible to corrosion. However, in the case where a material whose surface potential is lowered, such as SUS316L, is used as the material, oxidation by heat treatment may be performed after buffing. This means that even if a non-uniform passivation film is formed, neutral p
This is because rusting can be suppressed because the H region has a potential lower than the corrosion prevention potential of iron. That is, SUS
In the iron corrosion diagram shown in FIG. 1, 316L indicates the potential belonging to the iron stable region, which is lower than the corrosion prevention potential of iron in the neutral region, −0.62 V, and below the corrosion region (shaded portion). It is thought to have.

[0009]

[Example] SUS304L stainless steel (2 mm thick,
30mm width, 50mm length) or SUS316L stainless steel (2mm thickness, 50mm width, 100mm length)
As shown in Table 1 below, the sample was subjected to buffing or electrolytic polishing as a cleaning treatment, and then subjected to a heating treatment in an oxidizing atmosphere at various temperature ranges for 2 hours to form a metal oxide film. I let it.

The buff polishing was performed using a # 400 buff. Electropolishing was performed using a phosphoric acid / sulfuric acid-based electrolyte for 8 minutes while circulating the electrolyte.

The heat treatment is performed at each temperature shown in Table 1 for 2 hours.
The operation was carried out at normal pressure for a time.

During the above steps, the operation was performed in an inert gas (nitrogen) except for the holding time in an oxidizing atmosphere gas.

A stainless steel sample obtained according to this method was subjected to the following outdoor exposure test to examine weather resistance. The outdoor exposure test was carried out outdoors on a hill in winter (January to February; temperature 0 to 15 ° C, and humidity 20 to 70).
%) For one month, it was suspended at a height of 1.5 m above the ground and left standing. One month later, the presence or absence of rust was confirmed by visual inspection as described below, and the weather resistance of each sample was evaluated.

The results obtained are shown in Table 1 below.

[0015]

[Table 1]

As is apparent from Table 1, SUS304L
If oxidization is performed after buffing, rust is generated in a short period of time, especially when oxidization is performed at 410 ° C. or more,
Heavy brown rusting was observed over 90% of the total area. When the oxidation treatment was performed at 350 ° C., the gold color due to the oxide film was maintained. On the other hand, SUS31
When oxidation treatment was similarly performed after buffing on 6 L, no rusting or discoloration was observed at any temperature,
The anticorrosion property accompanying the above-mentioned potential drop was suggested. Regardless of the type of stainless steel used, it was suggested that if oxidation treatment was performed after electrolytic polishing, a stainless steel having excellent weather resistance without rusting or discoloration was obtained.

[0017]

According to the present invention, it is possible to provide a stainless steel building material which has excellent weather resistance and is suitably used for materials such as outdoor monuments and building materials.

[Brief description of the drawings]

FIG. 1 is a diagram showing a correlation between pH and potential for iron corrosion.

Claims (5)

[Claims] 1. A method for producing a stainless steel building material having weather resistance, comprising a step of cleaning a surface of a stainless steel and then performing a heat treatment in an oxidizing atmosphere to form a metal oxide film. A method for producing a weather-resistant stainless steel building material, characterized in that: 2. The method for producing a weather-resistant stainless steel building material according to claim 1, wherein the cleaning treatment is performed by electrolytic polishing. 3. The method for producing a weather-resistant stainless steel building material according to claim 1, wherein the heat treatment is performed in a range of 300 to 500 ° C. 4. The stainless steel as SUS304
4. The method for producing a weather-resistant stainless steel building material according to claim 2, wherein SUS304L is used. 5. A weather-resistant stainless steel comprising a step of cleaning a stainless steel surface by electrolytic polishing, and then performing a heat treatment in an oxidizing atmosphere at a temperature of 300 to 500 ° C. to form a metal oxide film. A stainless steel building material having weather resistance, which is manufactured by a manufacturing method.