JPH11350082A - Corrosion resistant steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel having excellent corrosion resistance at a low cost on the surface of a steel base material having a specified componental compsn., by forming a coating layer of a metal whose potential is baser than that of the base material in an aq. soln. environment at a specified thickness. SOLUTION: A steel having a compsn. contg., by weight, 0.01 to 3.0% Si, 0.01 to 3.0% Mn, 0.1 to 9.9% Cr, >3 to 10% Al, and the balance Fe with inevitable impurities in which the content of C is limited to <=0.02%, P to <=0.03%, S to <=0.01% and N to <=0.02% is prepd. The steel is used as a base material, and, on the surface of the base material, a coating layer of a metal whose potential is baser than that of the base material in an aq. soln. environment (aluminum, zinc, chromium, manganese or an alloy essentially consisting of them) is formed at a thickness of 0.5 to 500 μm. In this way, the corrosion- resistant steel useful for various corrosive environments including high temp. wet corrosive environment such as the exhaust system of the internal combustion engine of an automobile or the like and a dewing corrosive environment is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to corrosion-resistant steel, and more specifically, for example, to (1) high-temperature wetness of an exhaust system of an internal combustion engine of a car or a ship, a boiler exhaust system, a low-temperature heat exchanger, an incinerator floor, and the like. Corrosive environment, (2) bridges, columns, building interior and exterior materials, roofing materials, fittings, kitchen members, various handrails, guardrails, various hooks, roof drains, atmospheric corrosion environments such as railway vehicles, (3) various storage tanks, columns , Piles, sheet piles, etc., soil corrosion environment, (4) can containers, various containers, low-temperature heat exchangers,
Dew condensation corrosive environment (including corrosive environment where freezing, humidification and drying are combined) of bathroom members, automobile structural members, etc., (5) water storage tank,
Water supply pipe, hot water supply pipe, can container, various containers, tableware, cooking equipment,
Corrosion environment of tap water such as bathtub, pool, vanity, etc. (6)
Corrosion environment of drinking water for canned containers, various containers, tableware, cooking equipment, etc., (7) Corrosion environment for concrete such as various reinforced structures and columns, (8) Seawater corrosion for ships, bridges, piles, sheet piles, marine structures, etc. The present invention relates to a corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as environments.

[0002]

2. Description of the Related Art Conventionally, in an exhaust system of an internal combustion engine mainly for an automobile, steel in which ordinary steel is plated with aluminum or zinc to suppress corrosion from the inside or outside has been used. Since a catalyst or the like is provided in the exhaust system for the purpose of purifying exhaust gas to suppress environmental pollution, such a plated steel material does not have sufficient corrosion resistance, and contains 5 to 10% Cr for the purpose of improving the corrosion resistance of the steel base. Steel is disclosed in JP-A-63-143240 and JP-A-6-143240.
It is disclosed in JP-A-3-143241. However, with the extension of the service period and warranty period of vehicles in recent years,
Further, Cr is contained up to about 18%, or
The high-grade stainless steel to which is added is widely used in exhaust systems.

[0003] However, even such a high-grade stainless steel does not always have sufficient corrosion resistance, for example, pitting-like local corrosion may occur. In addition, such high-grade stainless steel has poor workability because it contains a large amount of Cr and Mo, and in order to form a complicated shape such as an exhaust system member, production is extremely difficult, and the production process is extremely difficult. There is a disadvantage that the processing cost increases due to the complexity. Also, the material cost is high.

[0004] As a representative of the above exhaust system, Cr
In steels containing a certain amount of iron, local corrosion is likely to occur when the use corrosion environment becomes severe. In order to improve resistance to corrosion as a measure against this, Cr or M
Increasing the content of o has been a very common technical measure. When Cr and Mo are used to maintain corrosion resistance, even if they have sufficient corrosion resistance to the exhaust gas environment, they can be used to prevent freezing of road surfaces in winter, such as in the cold regions of the United States and Canada. When spraying a large amount of salt, there is a problem that the exhaust system member is eroded from the outer surface by the salt.

In recent years, Japanese Patent Application Laid-Open Nos. Hei 5-279791, Hei 6-179949, Hei 6-179950
JP, JP-A-6-179951, JP-A-6-2
JP-A-12256, JP-A-6-212257 and JP-A-7-3388 disclose steels in which Al is added to Cr for the purpose of improving corrosion resistance or improving corrosion resistance and workability. Although these steels are recognized to be effective to some extent in improving the exhaust system inner corrosion resistance or the exhaust system inner surface corrosion resistance and workability, there is still room for improvement in wet corrosion resistance, especially salt corrosion resistance. .

[0006]

SUMMARY OF THE INVENTION In view of these circumstances, the present invention provides a high-temperature wet corrosion environment including an exhaust system of an internal combustion engine, a condensation corrosion environment, an atmospheric corrosion environment, a tap water corrosion environment, and a soil corrosion. It is an object of the present invention to provide a low-cost corrosion-resistant steel having excellent corrosion resistance in various corrosive environments such as an environment, a concrete corrosive environment, a seawater corrosive environment, and a drinking water corrosive environment.

[0007]

Means for Solving the Problems In order to achieve the above object, the present inventors have set a high temperature wet corrosion environment including an exhaust system of an internal combustion engine, a dew condensation corrosion environment, an atmospheric corrosion environment, and a tap water corrosion environment. , Soil corrosion environment, concrete corrosion environment,
In order to develop a steel having excellent corrosion resistance in various corrosive environments such as a seawater corrosive environment and a drinking water corrosive environment, studies have been made from various viewpoints.

First, the present inventors examined the internal corrosion environment of the exhaust system, which is the most susceptible to corrosion. Found to occur in a heated environment. Furthermore, as a result of various investigations on means for improving the corrosion resistance in the corrosive environment, Al was found to exceed 3% to 10%.
It has been found that a steel containing 0.5 to 9.9% of Cr added in an amount of 0.5% or less exhibits extremely excellent corrosion resistance in a corrosive environment including an exhaust system.

Further, the present inventors have continued their studies as a better steel, and have found that C and N of steel containing 0.5 to 9.9% of Cr and more than 3% to 10% or less of Al are used. When Nb, V, Ti, Zr, Ta, and Hf are added so as to satisfy specific conditions after the reduction, it is effective in improving corrosion resistance and workability.
And Mn are appropriate, and Cu, Mo,
It has been found that more excellent corrosion resistance can be obtained by adding Sb, Ni, and W alone or in combination.

On the other hand, the present inventors separately studied in parallel the means for obtaining a steel material having enhanced corrosion resistance against salt damage corrosion, which is a severe corrosive environment next to the exhaust gas inner surface corrosive environment, and repeated wet and dry conditions such as salt water. As a result, Cr
When a coating layer of a metal whose electric potential in an aqueous environment is lower than that of the base material is formed on the surface of a base material made of steel containing 9.9% and more than 3% of Al, excellent corrosion resistance, particularly excellent It has been found that salt corrosion resistance is obtained.

Particularly, when Al is added to the substrate, the metal layer coated on the surface of the substrate and having a potential lower than that of the substrate partially disappears, and the surface of the substrate is slightly exposed to the corrosive environment. It has been found that the effect of improving the corrosion resistance later is remarkable. This A
The behavior of improving the corrosion resistance by adding 1 to the substrate is a phenomenon completely different from the corrosion resistance of the above-described substrate, and there is a metal layer whose potential coated on the surface of the substrate is lower than that of the substrate, and It has been confirmed that this phenomenon is only observed when the metal layer partially disappears.

At present, there are many unknown reasons for the remarkable improvement in corrosion resistance found, but by adding Al to the substrate, the surface of the substrate was coated on the remaining substrate surface after being exposed to the corrosive environment. The rate of disappearance of the layer of metal whose potential is lower than that of the substrate is significantly reduced, and thus the rate of expansion of the area of the substrate surface exposed to the corrosive environment is significantly reduced, and at the same time, the surface of the substrate relative to the exposed substrate portion It has been confirmed that the corrosion resistance is improved by protecting the exposed portion of the base material of the metal layer whose potential is lower than that of the base material over a long period of time.

The exposed portion of the substrate surface to the corrosive environment where such an effect is recognized can be confirmed for the first time by microscopic observation, and has a small area of about 0.05 mm ² or less in absolute value and a ratio to the total corroded area. Is less than 0.2%, and it is judged that there is no occurrence of red rust at all on the macroscopic appearance assuming actual use, and that generally no corrosion of the substrate is observed. It has an external appearance.
Moreover, it is a feature that such a state is maintained for a long time.

According to conventional knowledge, when a metal layer coated on the surface of a base material has a potential lower than that of the base material, and when this metal layer partially disappears, corrosion of the metal layer coated on the surface is caused. The speed is increased to control the corrosion of the base metal,
Therefore, considering that it is generally considered that the exposed area of the base metal to the corrosive environment rapidly expands, and that it is generally considered that the base metal quickly shifts to the corrosion of the base metal. The improvement of the corrosion resistance is a means of improving the corrosion resistance, which has not been known at all, and is the basis of the present invention, and the present invention has been made based on such a new discovery.

The inventors of the present invention have proposed that A is added to a base metal in which a metal layer having a potential lower than that of the base coated on the surface of the base exists.
Various studies have been made on means for further increasing the corrosion resistance improving effect by the addition of l, and Si, Mn, Ti,
It is clear that the addition of Zr, Ta, Hf, Cu, Mo, Sb, Ni, and W is effective, and that Nb and V, which are effective in improving the base material corrosion resistance and workability, do not inhibit the corrosion resistance improvement effect. I made it.

Further, the present inventors have continued their studies and have found that aluminum, an alloy mainly composed of aluminum, zinc, an alloy mainly composed of zinc, chromium, and chromium are metals whose electric potential in an aqueous solution environment is lower than that of a substrate. It has also been found that an alloy mainly composed of manganese and an alloy mainly composed of manganese are metals suitable for the purpose of the present invention. The present invention has been mainly made based on the above findings, and the gist of the first invention of the present application is that, by weight%, Si: 0.01 to 3.0%, Mn:
0.01-3.0%, Cr: 0.1-9.9%, Al:
More than 3% to 10% or less, with the balance being Fe and unavoidable impurities, of which C is 0.02% or less;
P is 0.03% or less, S is 0.01% or less, and N is 0.0% or less.
A steel substrate limited to 2% or less is used as a base material, and a metal coating layer whose potential in an aqueous environment is lower than that of the base material is formed on the base material surface to a thickness of 0.05 to 500 μm. In corrosion resistant steel.

The gist of the second invention is that, in the steel of the first invention, the base material further contains Cu: 0.
01-5.0%, Mo: 0.05-10%, Sb: 0.
01 to 0.5%, Ni: 0.01 to 10%, W: 0.0
Corrosion resistant steel containing one or more of 5 to 3.0%.

The gist of the third invention is that, in the steel of the first invention and the second invention, the base material is further added as an additional component by weight, rare earth element: 0.001 to 0.1%, Ca: 0.0001.
Corrosion-resistant steel characterized by containing one or more of 0.05% or more. The gist of the fourth invention is the first invention,
In the steels of the second and third inventions, the base material may further contain Nb, V, Ti, Zr, Ta, and Hf by weight as an additional component.
Wherein each of one or more elements selected from the group consisting of 0.01 to 1% is contained, and the following formula is satisfied.

Nb / 93 + V / 51 + Ti / 48 + Zr
/91+Ta/181+Hf/179≧0.8×(C/
12 + N / 14) The gist of the fifth invention is that in the first invention, the second invention, the third invention, and the fourth invention, the corrosion-resistant steel in which the metal of the coating layer is either aluminum or an alloy mainly containing aluminum. is there.

The gist of the sixth invention is that the first invention, the second invention,
In the third invention and the fourth invention, there is provided the corrosion-resistant steel in which the metal of the coating layer is either zinc or an alloy mainly containing zinc. The gist of the seventh invention resides in the corrosion-resistant steel according to the first, second, third, and fourth inventions, wherein the metal of the coating layer is either chromium or an alloy mainly composed of chromium.

The gist of the eighth invention is that the first invention, the second invention,
In the third invention and the fourth invention, there is provided the corrosion-resistant steel in which the metal of the coating layer is either manganese or an alloy mainly containing manganese.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the range of each component of a substrate in the present invention will be described below. Si: Si has an effect of improving the corrosion resistance when a metal layer having a potential lower than that of the base material in an aqueous solution environment is formed to a thickness of 0.05 to 500 μm on the base material surface, but 0.01%. %, The effect is not recognized, and even if added over 3%, the effect is saturated. Therefore, the content range is limited to 0.01% or more and 3% or less. Further, the addition of Si as a deoxidizing agent and a strengthening element is effective by adding Si to steel containing 0.1% or more of Cr, but if the content is less than 0.015%, the deoxidizing effect is not sufficient. ,
When the content is 1.5% or more, the effect is no longer saturated and the processability is slightly reduced. Therefore, 0.015%
More preferably, it is added in the range of 1.5% or less.

Mn: Mn is formed on the surface of a base material by forming a metal layer having a potential lower than that of the base material in an aqueous solution environment from 0.5 to 50%.
When formed to a thickness of 0 μm, the effect of improving the corrosion resistance is obtained, but if less than 0.01%, the effect is not recognized,
Even if it exceeds 3%, the effect is saturated. Therefore,
The content range is limited to 0.01% or more and 3% or less. Further, Mn is effective as a deoxidizing agent for steel, and is effective when contained at 0.05% or more. However, even when it is contained more than 1.2%, the effect is not only saturated but also excessive. If Mn is contained in the steel, the workability is reduced. Therefore,
It is more desirable to add in the range of 0.05% or more and 1.2% or less.

Cr: Cr is added to steel containing more than 3% of Al to form a metal layer whose electric potential in an aqueous solution environment is lower than that of the substrate on the surface of the substrate by 0.5 to 500 μm.
When formed to a thickness of m, the effect of improving corrosion resistance is brought about. However, if it is less than 0.1%, the effect is not sufficient, while if it exceeds 9.9%, the effect is saturated. Therefore, the content of Cr is limited to 0.1% or more and 9.9% or less. Further, in order to ensure the corrosion resistance of the base material alone against the exhaust gas environment, etc., it is necessary that steel containing more than 3% of Al contain 0.5% or more, but more than 9.9% is contained. However, since the workability is reduced, the upper limit content is 9.
9%. Therefore, it is more desirable to add in the range of 0.5% or more and 9.9% or less.

Al: Al is the most important element for ensuring corrosion resistance in the present invention.
% To 9.9% or less by adding Al to form a 0.5 to 500 μm thick metal layer whose potential in an aqueous environment is lower than that of the substrate on the surface of the substrate. Although the effect of improving the corrosion resistance is brought about, the effect is not sufficient at 3% or less, and the effect is saturated even if added over 10%. Therefore, the Al content is more than 3% and 10% or less. limit.

C, N: C and N reduce the workability of the steel sheet, and also, C forms carbides with Cr to lower the corrosion resistance, and N lowers the toughness. The smaller the content, the better. The upper limit of the content is set to 0.02%, and the smaller the content, the better. Furthermore,
In order to ensure excellent workability, it is necessary to reduce the total amount of C + N. In a steel according to a preferred embodiment of the present invention, C + N is set to 0.03% or less.

P: Since a large amount of P lowers the toughness if it is present in a large amount, it is desirable that P is small, and the upper limit content is 0.03.
%. S: Since the presence of a large amount of S lowers the pitting corrosion resistance, the smaller the amount, the better. The upper limit content is 0.01%. The above are the basic components of the steel substrate excellent in corrosion resistance targeted by the present invention.In the present invention, steel materials with further improved corrosion resistance by further adding the following elements as necessary are also included. And

Cu: Cu contains more than 3% of Al and contains
0.1% or more and 9.9% or less of a metal layer having a potential lower than that of the base material in the aqueous solution environment on the surface of the steel base material containing 0.1% or more.
When formed to a thickness of 5 to 500 μm, the effect of improving the corrosion resistance is obtained. However, if the content is less than 0.01%, the effect is not recognized. On the other hand, if the addition exceeds 5%, the effect is saturated. Therefore, the range is limited to the range of 0.01% to 5%. Further, when added in an amount of 0.05% or more, there is an effect of improving resistance to general corrosion of the substrate alone,
If added over 2.5%, the effect saturates. Therefore, it is more desirable to add in the range of 0.05% or more and 2.5% or less.

Mo: Mo is added to steel containing more than 3% of Al and 0.1% or more and 9.9% or less of Cr, so that the potential in an aqueous solution environment on the surface of the substrate becomes lower than that of the substrate. When the metal layer is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained.
If the amount is less than 10%, the effect is not recognized. Therefore, the range is 0.05
% To 10% or less. Further, when Mo is added in an amount of 0.1% or more, there is an effect of suppressing the occurrence and growth of pitting corrosion in the base material alone. Lower. Therefore, 0.
More preferably, it is added in the range of 1% to 3%.

Sb: Sb contains more than 3% of Al and contains
Is added to steel containing 0.1% or more and 9.9% or less, a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material on the base material surface to a thickness of 0.5 to 500 μm. When formed, it has the effect of improving corrosion resistance,
If it is less than 0.01%, no effect is observed, while if it exceeds 0.5%, the effect is saturated. Therefore, the range is limited to 0.01% or more and 0.5% or less. Further S
Addition of b has the effect of improving resistance to pitting corrosion and general corrosion of the substrate alone, but adding more than 0.3% slightly reduces hot workability. Therefore,
It is more desirable to add in the range of 0.015% or more and 0.3% or less.

Ni: Ni contains more than 3% of Al and contains Cr
Is added to steel containing 0.1% or more and 9.9% or less, a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material on the base material surface to a thickness of 0.5 to 500 μm. When formed, it has the effect of improving corrosion resistance,
On the other hand, even if it exceeds 10%, the effect is saturated. Therefore, the range is limited to 0.01% or more and 10% or less. Further, the addition of Ni has an effect of suppressing pitting corrosion of the base material alone, but the effect is saturated even if it exceeds 6%. Therefore, it is more desirable to add in the range of 0.1% or more and 6% or less.

W: When W is added to steel containing more than 3% of Al and 0.1% or more and 9.9% or less of Cr, 0.05% or more is added to the surface of the substrate to cause a potential in an aqueous solution environment on the substrate The effect of improving the corrosion resistance is obtained when a metal layer that is more base than that is formed to a thickness of 0.5 to 500 μm. On the other hand, the effect is saturated even if it exceeds 3%. Therefore, the range is limited to 0.05% or more and 3% or less. Further, the addition of W has the effect of suppressing the occurrence and growth of pitting corrosion in the base material alone, but the effect is not sufficient if the addition is less than 0.1%, while adding more than 2.0%. This not only saturates the effect but also lowers the workability. Therefore, 0.1%
More preferably, it is added in the range of 2% or less.

Rare earth element (REM), Ca: Rare earth element (REM) or Ca contains more than 3% of Al and 0.1% of Cr
By adding to a steel containing at least 9.9% or less, the corrosion resistance is improved when a metal layer having a potential lower than that of the base material in an aqueous solution environment is formed to a thickness of 0.5 to 500 μm on the base material surface. But with REM 0.001
%, No effect is recognized, and Ca is 0.0001%.
Is less than 0.1%, whereas rare earth elements have no effect.
%, And even if Ca is added exceeding 0.05%, the effect is saturated. Therefore, the range of REM is 0.001.
% To 0.1% and the range of Ca is limited to 0.0001% to 0.05%. REM and Ca are elements that are effective in improving hot workability and pitting corrosion resistance of the base material alone.
If the content is less than 0.01% and Ca is less than 0.005%, the effect is not enough. 0.01% for Ca and 0.1% for REM.
When added in excess of 05%, coarse nonmetallic inclusions are respectively formed, and conversely, hot workability and pitting corrosion resistance are deteriorated.
Therefore, it is more preferable that Ca is added in the range of 0.005% to 0.01%, and REM is added in the range of 0.01% to 0.05%. In the present invention, the rare earth element (REM) refers to an element having an atomic number of 57 to 71 or 89 to 103 and Y.

The steel of the present invention imparts excellent corrosion resistance to the above-described components, and can further improve the workability, in addition to the corrosion resistance, by further adding the following components. Nb, V, Ti, Zr, Ta, Hf: Nb,
V, Ti, Zr, Ta and Hf contain more than 3% Al and contain Cr
Is added to steel containing 0.1% or more and 9.9% or less to form a metal layer having a potential lower than that of the base material in the aqueous solution environment at a thickness of 0.5 to 500 μm on the base material surface. In this case, the effect of improving the corrosion resistance is obtained. However, if the content of each element is less than 0.01%, the effect is not recognized. On the other hand, if the content exceeds 1.0%, the effect is saturated. Therefore Nb,
The contents of V, Ti, Zr, Ta, and Hf are each 0.01%.
It is limited to not less than 1.0%. Further, Nb, V, T
i, Zr, Ta, and Hf have remarkable effects on the improvement of corrosion resistance and workability of the base material alone by fixing C and N in the Cr-containing steel as carbides. More than one kind of element can be added in combination. However, if the amount of addition alone is less than 0.05%, there is no effect. Cause. Therefore, N
b, V, Ti, Zr, Ta, and Hf are 0.05% or more.
It is more desirable to add in the range of 8% or less. And,
In order to effectively improve the workability, Nb, V, Ti, Z
It is necessary that the total amount of added r, Ta, and Hf satisfies the following expression.

Nb / 93 + V / 51 + Ti / 48 + Zr
/91+Ta/181+Hf/179≧0.8×(C/
12 + N / 14) In the present invention, the surface of the steel substrate, particularly at least the surface exposed to the corrosive environment, is coated with a metal whose electric potential is lower than that of the substrate. At a thickness of 0.5 μm or less, which is coated with a metal whose potential is lower than that of the base material, by adding Al to the base material, the base material surface was coated on the remaining base material surface after being exposed to the corrosive environment. , The rate of disappearance of the metal layer whose potential is lower than that of the base material, and the rate of expansion of the area exposed to the corrosive environment on the base material surface are significantly reduced, and at the same time, the base material surface is coated on the exposed base part The effect of protecting the exposed portion of the base material of the metal layer having a base potential lower than that of the base material over a long period of time is not sufficient, and even when coating is performed to a thickness exceeding 500 μm, the effect is no longer saturated. On the other hand, the thickness of the coating layer is 0.5 to 500 because it only lowers the productivity and increases the cost.
μm.

Aluminum, zinc, chromium, manganese, and alloys mainly containing these can be used as the metal forming the coating layer and having a lower potential in an aqueous solution environment than the base material. The coating process is not limited as long as the metal is sufficiently fixed to the substrate. It should be selected in consideration of the application and cost, etc., and hot-dip plating, electrodeposition plating, molten salt electrolytic plating, vacuum evaporation, sputtering, ion plating, thermal spraying, etc. can be used, and they can be used together It is possible. In addition, any processing may be performed before and after the coating and the processing therefor as necessary.

The alloy mainly composed of zinc is an alloy in which the component occupying the largest amount among the alloy components is zinc, that is, a zinc-based alloy. Generally, an alloy component such as aluminum contained in the zinc-based alloy and an impurity component are removed. May include. An alloy mainly composed of aluminum is an alloy in which the component occupying the largest amount among the alloy components is aluminum, that is, an aluminum-based alloy, and generally includes an alloy component such as silicon and zinc and an impurity component contained in the aluminum-based alloy. Is fine.

The chromium-based alloy is an alloy in which the component that accounts for the largest amount of the alloy components is chromium, that is, a chromium-based alloy. Generally, an alloy component such as silicon and an impurity component contained in the chromium-based alloy are removed. May include. A manganese-based alloy is an alloy in which the component occupying the largest amount among the alloy components is manganese, that is, a manganese-based alloy, and may generally include an alloy component such as aluminum and an impurity component contained in the manganese-based alloy. .

If only one surface of a material having front and back surfaces, such as a steel pipe or a plate material, needs to be coated for the purpose of use, only one surface is coated from the process of coating a base metal. May be used. In such a case, whether to use coating on one side or steel coated on both sides may be selected in consideration of other factors such as cost and weldability.

The time for applying the coating is as follows:
After making the steel, such as a plate, a rod, a cable, or a perforated steel pipe into a general shape, the coating of the present invention or a treatment therefor may be performed, or the steel of the present invention after coating and processing may be pressed or roll-formed. It may be formed into a predetermined shape, and further processed and welded to produce a product. It is also possible to apply the surface coating treatment of the present invention after forming the steel material into the target shape by the above-described process before performing the coating / treatment of the present invention. Steels having a combination of composition and processing conditions limited by the present invention are all objects of the present invention, and an optimal product manufacturing process can be selected according to costs, restrictions on existing manufacturing facilities, and the like. It is not intended to depart from the scope of the present invention with a it as the selected manufacturing process.

The steel proposed in the present invention described above can be used not only in an exhaust system of an internal combustion engine, but also in a high-temperature wet-corrosion environment, a condensation corrosion environment, an atmospheric corrosion environment, a tap water corrosion environment, and the like.
Soil corrosion environment, concrete corrosion environment, seawater corrosion environment,
The present invention can be applied to various corrosive environments such as a drinking water corrosive environment.

[0042]

Embodiments of the present invention will be described below. [Evaluation of Corrosion Resistance] Steel having the components shown in Tables 1 and 2 was melted, made into a steel plate having a thickness of 1 mm by a normal steel plate manufacturing process such as hot rolling or cold rolling, and then annealed at 900 ° C. Each was coated under the condition of 15 ± 2 μm per side. In Tables 1 and 2, coating 1 indicates aluminum coating, coating 2 indicates zinc coating, coating 3 indicates manganese coating, and coating 4 indicates chromium coating.

Next, from these steel plates, a width of 50 mm and a length of 7 mm were used.
A test piece of 0 mm was sampled and subjected to various corrosion tests described below. High-temperature wet corrosion test: Sulfate ion 500ppm
, Chloride ion 500ppm, bicarbonate ion 500ppm
The test specimen was immersed in 50 cc of an aqueous solution to which the test solution was added in the form of an ammonium salt, and the test solution was repeated 70 times in which the test solution was completely evaporated and volatilized while keeping the test container in an atmosphere at 130 ° C. This test is a corrosion test corresponding to the internal environment of an automobile exhaust system, and is a strict test method corresponding to the running of an actual vehicle for about four years or more. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the maximum corrosion depth was 0.
Less than 10 mm, ○ is less than 0.2 mm, Δ is less than 0.3 mm, ×
Indicates that it was 0.3 mm or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance even in a very severe corrosive environment of high temperature wet containing chloride. In contrast, comparative steels (numbers 41 to 50, 10
0-109) are inferior in corrosion resistance. In addition, as a test assuming salt damage caused by the atmospheric environment and the outer surface of an automobile exhaust system, after spraying salt water at 50 ° C. for one hour, a humidity of 96 ° C. and a humidity of 96 ° C.
% Holding for 5 hours, followed by 1 hour of freezing and holding was repeated 200 times. The maximum pit depth of the test specimen after the test was measured and used as the test result. The obtained test results are also shown in Tables 1 and 2.
If the maximum pit depth is 0.2mm or less, ◎, if the maximum pit depth is more than 0.2mm and 0.4mm or less, ○, the maximum pit depth is more than 0.4mm and 0.8mm or less , And those having a maximum pit depth exceeding 0.8 mm are indicated by XX.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance even in a very severe corrosive environment such as salt damage corrosion. , Comparative steel (Nos. 41 to 50, 100 to 109)
Indicates that the corrosion resistance is inferior. The soil corrosion test was a test in which a test piece was embedded in sand adjusted to have a water content of 15% and a specific resistance of 350 Ω · cm with a sodium chloride content, and was kept at 40 ° C. for about 700 days. The test results are also shown in Tables 1 and 2. ◎ in the corrosion test result indicates that the maximum corrosion depth is 0.0
Less than 5 mm, ○ indicates less than 0.1 mm, Δ indicates less than 0.5 mm, and X indicates 0.5 mm or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in a soil corrosion environment, whereas the comparative steels (Nos.
0,100-109) are inferior in corrosion resistance. The corrosion test in concrete is performed by embedding a test piece in Portland cement kneaded with sea sand containing chloride to form a sample, solidifying it, immersing the sample in artificial seawater by half, and placing it in a 50 ° C environment. It was a test that was left for about 900 days. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, Δ indicates that the rusting area rate was less than 10%, and ×.
Indicates that it was 10% or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in a corrosive environment in concrete, whereas the comparative steels (No. 41 to No. 41). 50, 100 to 109) are inferior in corrosion resistance. The tap water environmental corrosion test was a test in which a test piece was immersed in tap water and kept in a 50 ° C. atmosphere for 18 months. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, △ indicates that the rusting area ratio was less than 10%, and × indicates that the rusting area ratio was less than 10%.
0% or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in tap water corrosive environments, while the comparative steels (Nos.
50, 100 to 109) are inferior in corrosion resistance.
The seawater environment corrosion test was a test in which the test piece was exposed to the shore splash zone for 18 months. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the corrosion depth was less than 0.05 mm, O indicates less than 0.1 mm, Δ indicates less than 0.3 mm, and X indicates 0.
3 mm or more. As is clear from Tables 1 and 2, the steels of the present invention (numbers 1 to 40, 51 to 90)
Shows good corrosion resistance in a seawater corrosive environment, whereas the comparative steels (Nos. 41 to 50, 100 to 109) are inferior in corrosion resistance.

The dew condensation corrosion test was a test in which the device was kept in an environment of -20 ° C. for 2 hours, and then kept in an environment of 95% humidity and 30 ° C. for 4 hours, repeated 1800 times. Tables 1 and 2 show the test results.
Are also shown. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 5%, Δ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more. .

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in a dew-condensation corrosion environment, while the comparative steels (Nos. 41 to 5) have good corrosion resistance.
0,100-109) are inferior in corrosion resistance. The atmospheric corrosion test was a test in which a test piece was exposed to a position about 250 m from the coast for about 700 days. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that no corrosion was observed, は indicates that the rusting area ratio was less than 3%, △ indicates that the rusting area ratio was less than 10%, and X indicates that the rusting area ratio was 10% or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in an atmospheric corrosion environment, whereas the comparative steels (Nos.
0,100-109) are inferior in corrosion resistance. In the drinking water environmental corrosion test, the pH was adjusted to 2.3 using sodium hydroxide, and high-purity nitrogen gas was ventilated to remove the gas.
(A) 0.5% phosphoric acid solution maintained at 7 ° C., (b)
0.5% citric acid solution, (c) 0.5% citric acid-0.
The test pieces were immersed in 850 cc of a solution such as a 5% sodium chloride solution for 35 days to analyze the amount of iron ions eluted in the solution. In addition, only this test performed the test about the aluminum coating of the coating 1, and the chromium coating of the coating 4. The test results are also shown in Tables 1 and 2. In the results of the corrosion test, ◎ indicates that the elution amount of iron ions into the solution was 1 ppm or less, and ○ indicates 3 ppm.
, △ indicates less than 5 ppm, and X indicates 5 ppm or more.

As is clear from Tables 1 and 2, the steels of the present invention (Nos. 1 to 40, 51 to 90) show good corrosion resistance in a drinking water corrosive environment, whereas the comparative steels (Nos.
50, 100 to 109) are inferior in corrosion resistance.
That is, the steel of the present invention (Nos. 1 to 40, 51 to 90) is a high-temperature wet corrosion environment, dew condensation corrosion environment, atmospheric corrosion environment, tap water corrosion environment, soil corrosion environment, concrete corrosion environment, seawater corrosion environment, drinking water corrosion environment, and the like. Of the comparative steels (Nos. 41 to 5)
0,100-109) are inferior in corrosion resistance. [Evaluation of workability] Steel having the components shown in Table 2 was melted, hot rolled,
By a normal steel plate manufacturing process such as cold rolling, a steel plate having a thickness of 1.0 mm was annealed at 850 ° C. Test pieces having a width of 100 mm and a length of 100 mm were sampled from these steel sheets, and subjected to a cylindrical drawing test with a drawing ratio of 1.8 to determine whether or not cracks were present. The test results are also shown in Table 2. In the workability in Table 2, ○ indicates that the cylindrical drawing test result was good,
X indicates that a crack occurred in the cylindrical drawing test.
In addition, the X value in Table 2 described what was calculated by the following formula.

X = Nb / 93 + V / 51 + Ti / 48 +
Zr / 91 + Ta / 181 + Hf / 179-0.8 ×
(C / 12 + N / 14) As is evident from Table 2, the steels of the present invention in which workability is particularly enhanced (Nos. 51 to 90) show good corrosion resistance and good workability. That is, high temperature wet corrosion environment, dew condensation corrosion environment, atmospheric corrosion environment, tap water corrosion environment,
Soil corrosion environment, concrete corrosion environment, seawater corrosion environment,
It shows good corrosion resistance in various corrosive environments such as drinking water corrosive environment and also has excellent workability. On the other hand, it can be seen that the comparative steels (Nos. 100 to 109) cannot simultaneously achieve corrosion resistance and workability.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

[0058]

[Table 5]

[0059]

[Table 6]

[0060]

[Table 7]

[0061]

[Table 8]

[0062]

As described above, according to the present invention, in addition to a high-temperature wet-corrosion environment and a dew-corrosion environment such as an exhaust system of an internal combustion engine of an automobile, etc., an atmospheric corrosion environment, tap water corrosion environment, soil Steel having excellent corrosion resistance in various corrosive environments such as a corrosive environment, a concrete corrosive environment, a seawater corrosive environment, and a drinking water corrosive environment is provided at low cost.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidetoshi Shintoka 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Works

Claims (8)

[Claims] 1. In weight%, Si: 0.01 to 3.0%, Mn: 0.01 to 3.0%, Cr: 0.1 to 9.9%, Al: more than 3% to 10% Hereinafter, the balance consists of Fe and unavoidable impurities. Of the unavoidable impurities, C is 0.02%
Hereinafter, steel having a P content of 0.03% or less, an S content of 0.01% or less, and a N content of 0.02% or less is used as a base material, and the potential in an aqueous solution environment is applied to the surface of the base material. A corrosion-resistant steel, wherein a coating layer of a base metal is formed to a thickness of 0.5 to 500 μm. 2. The steel of the base material further contains, by weight%, Cu: 0.01 to 5.0%, Mo: 0.05 to 10%, Sb: 0.01 to 0.5%, Ni: The corrosion-resistant steel according to claim 1, comprising one or more of 0.01 to 10%, and W: 0.05 to 3.0%. 3. The steel of the base material further contains, by weight%, a rare earth element: 0.001 to 0.1%, and Ca: 0.000.
The corrosion-resistant steel according to claim 1, wherein the steel contains 1 to 0.05% of one or more kinds. 4. The steel of the base material further comprises Nb,
4. The method according to claim 1, wherein one or more selected from V, Ti, Zr, Ta and Hf are each contained in an amount of 0.01 to 1% and satisfy the following formula. 3. The corrosion-resistant steel according to 3. Nb / 93 + V / 51 + Ti / 48 + Zr / 91 + Ta
/181+Hf/179≧0.8×(C/12+N/1
4) 5. The corrosion-resistant steel according to claim 1, wherein the metal of the coating layer is one of aluminum and an alloy mainly containing aluminum. 6. The corrosion-resistant steel according to claim 1, wherein the metal of the coating layer is one of zinc and an alloy mainly containing zinc. 7. The corrosion-resistant steel according to claim 1, wherein the metal of the coating layer is one of chromium and an alloy mainly composed of chromium. 8. The corrosion-resistant steel according to claim 1, wherein the metal of the coating layer is one of manganese and an alloy mainly containing manganese.