JPH11350084A - 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, 10 to 30% Cr, 0.1 to 10% Al, 0.0003 to 0.05% Mg, 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 base than that of the base material in an aq. soln. environment (aluminum, zinc, chromium, manganese or alloys essentially consisting of them) at a thickness of 0.5 to 500 μm. Furthermore, by incorporating at least one kind of Mn and In by 0.05 to 10% by individual content, more excellent corrosion resistance can be obtd.

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 particularly, for example, to (1) high-temperature wet corrosion of internal combustion engine exhaust systems of automobiles and ships, boiler exhaust systems, low-temperature heat exchangers, incinerator beds, etc. Environment, (2) bridges, columns, building interior and exterior materials,
Roofing materials, fittings, kitchen components, various handrails, guardrails,
Atmospheric corrosion environment such as various hooks, roof drains, railway vehicles, etc. (3) Soil corrosion environment such as various storage tanks, columns, piles, sheet piles, etc., (4) Can containers, various containers, low-temperature heat exchangers, bathroom members, automobile structures Dew condensation corrosion environment (freezing, wet,
(Including corrosive environment where drying is combined), (5) Corrosion environment of tap water such as water storage tank, water supply pipe, hot water supply pipe, can container, various containers, tableware, cooking equipment, bathtub, pool, vanity stand, etc., (6) Corrosive environment for drinking water such as cans, various containers, tableware, cooking equipment, etc.
(7) Steel having excellent corrosion resistance in various corrosive environments such as concrete corrosive environments such as various reinforcing steel structures and columns, and (8) seawater corrosive environments such as ships, bridges, piles, sheet piles and marine structures.

[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 the warranty period of vehicles in recent years, high-grade stainless steel further containing about 18% of Cr or further adding Mo 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. Further, as a result of various investigations on means for improving the corrosion resistance in the corrosive environment, it was found that Al was 0.1% to 1%.
It has been found that steel containing 10 to 30% of Cr to which 0% or less is added exhibits extremely excellent corrosion resistance in a corrosive environment including an exhaust system.

Further, the present inventors have continued to study the use of more excellent steel, and as a result, have found that Cr has a content of 10 to 30% and Al has a content of 0.1%.
When Nb, V, Ti, Zr, Ta, and Hf are added to satisfy specific conditions after reducing C and N of steel containing 1% to 10% or less, improvement in corrosion resistance and improvement in workability are achieved. It is effective, Si and Mn are suitable as deoxidizing and strengthening elements, and Cu, Mo, S
It has been found that more excellent corrosion resistance can be obtained by adding b, Ni, 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 was 10-30.
%, And a steel layer containing 0.1% or more of Al is used as a base material, and a metal layer having a potential lower than that of the base material in an aqueous solution environment is formed on the surface of the base material to provide excellent corrosion resistance, particularly excellent salt damage resistance. It has been found that corrosiveness can be obtained. In particular, the addition of Al to the substrate causes corrosion resistance after the metal layer whose potential applied to the substrate surface is lower than that of the substrate partially disappears and the substrate surface is slightly exposed to the corrosive environment. It has been found that the effect is remarkable for improvement.

The behavior of improving corrosion resistance by adding Al to a substrate is a phenomenon completely different from the corrosion resistance of the substrate described above. It is confirmed that this phenomenon is present only when the metal layer is partially disappeared.
At present, there are many unknown reasons for the remarkable improvement in corrosion resistance found, but by adding Al to the base material, the potential is applied to the remaining base material surface after the base material surface is exposed to the corrosive environment. The rate of disappearance of the layer of metal, which is more base than the material, was significantly reduced, and thus the rate of expansion of the area of the substrate surface exposed to the corrosive environment was significantly reduced. It has been confirmed that the corrosion resistance is improved by continuing the protective action on the exposed portion of the base material of the metal layer having a potential 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 substrate has a potential lower than that of the substrate and the metal layer partially disappears, the corrosion of the metal layer coated on the surface is reduced. 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.

[0014] Further studies have been conducted for the purpose of improving the corrosion resistance. With the addition of Al to such a base material, various elements which have been conventionally difficult to be added stably to steel are added. It is newly found that it becomes possible. In particular, it has been newly found that by adding Mg to steel containing 0.1 to 10% of Al, the corrosion resistance is significantly improved by the interaction between the base material and the coated metal.

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 improving the corrosion resistance by simultaneous addition of l and Mg, and Si, M
n, Nb, VTi, Zr, Ta, Hf, Cu, Mo, S
It has been clarified that the addition of b, Ni and W is effective.

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. As for these coated metals, as a result of various studies from the viewpoint of improving corrosion resistance due to interaction with the base material, aluminum, an alloy mainly composed of aluminum, zinc, an alloy mainly composed of zinc,
Any of metals such as chromium, chromium-based alloys, manganese, and manganese-based alloys,
It has been found that those containing at least 0.05% and not more than 10% by weight of any one or more of n realize more excellent corrosion resistance.

The present invention has been made mainly on the basis of the above findings, and the gist of the first invention of the present application is that, in terms of% by weight, S
i: 0.01 to 3.0%, Mn: 0.01 to 3.0%,
Cr: 10 to 30%, Al: 0.1 to 10%, Mg:
0.0003 to 0.05%, with the balance being Fe and unavoidable impurities, of which 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. The corrosion-resistant steel is characterized in that a coating layer of a base metal is formed to a thickness of 0.05 to 500 μm.

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
The corrosion-resistant steel according to any one of claims 1 to 3, wherein the steel contains 5 to 3.0% of one or more kinds.

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 in an amount of 0.001 to 0.1% of rare earth element by weight and 0.0001% of Ca.
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.
A steel having excellent corrosion resistance and workability, characterized in that it contains one or more elements selected from the group consisting of 0.01 to 1% in a single content and satisfies the following expression.

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 metal of the coating layer is aluminum or an alloy mainly composed of aluminum. In steel.

The gist of the sixth 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 zinc or an alloy mainly composed of zinc. is there. 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. The gist of the ninth invention is that, in the steel of the fifth invention, the sixth invention, the seventh invention, and the eighth invention, the metal of the coating layer further contains at least one of Mg and In in a single content by weight. Corrosion resistant steel characterized by containing 0.05 to 10%.

[0023]

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 Cr
By adding Si to steel containing 0% or more, it is effective to add Si as a deoxidizing agent and a strengthening element.
If it is less than 015%, its deoxidizing effect is not sufficient, and
%, The effect is no longer saturated and the processability is slightly reduced. Therefore, it is more desirable to add in the range of 0.015% or more and 1.5% or less.

Mn: Mn is formed on the surface of a substrate by forming a metal layer whose electric potential in an aqueous environment is lower than that of the substrate by 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 less than 3%. Furthermore, Mn is effective as a deoxidizing agent for steel, and it is necessary to contain Mn in an amount of 0.05% or more. , 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 0.1% or more of Al to form a metal layer whose electric potential in an aqueous solution environment is lower than that of the substrate by 0.5 to 5 on the surface of the substrate.
When formed to a thickness of 00 μm, the effect of improving the corrosion resistance is obtained, but if it is less than 10%, the effect is not sufficient.
On the other hand, even if it is added by 30% or more, the effect is saturated. Therefore, the content of Cr is limited to 10% or more and 30% or less. Further, in order to ensure the corrosion resistance of the base material alone against the exhaust gas environment and the like, it is necessary to contain 10% or more in steel containing 0.1% or more of Al. Workability decreases. Therefore, it is more desirable to add in the range of 10% or more and 25% or less.

Al: Al is the most important element for securing corrosion resistance in the present invention.
By adding Al to steel containing not less than 30% 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. However, if the content is less than 0.1%, the effect is not sufficient, and if the content exceeds 10%, the effect is saturated. Therefore, the content of Al is 0.1%.
It is limited to 10% or less. To obtain a more stable effect, the Al content is desirably 0.3% or more, but is desirably 4% or less so as not to lower workability. Therefore, the Al content is 0.3% or more and 4% or more.
It is desirable to make the following.

Mg: Mg is an important element after Al in order to secure corrosion resistance in the present invention. In a steel containing 0.1% to 10% of Al and 10% to 30% of Cr, By adding Mg, a metal layer whose electric potential in an aqueous solution environment is lower than that of the base material by 0.5 to 5
When formed to a thickness of 00 μm, the effect of improving the corrosion resistance is brought about. However, if it is less than 0.0003%, the effect is not sufficient, and even if added over 0.05%, the effect is saturated. , Mg content is limited to 0.0003% or more and 0.05% or less.

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.
%. 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, however, steel materials with further improved corrosion resistance by further adding the following elements as necessary are also included. And

Cu: Cu is formed on the surface of a steel substrate containing 0.1% or more of Al and 10% or more and 30% or less of Cr by forming a metal layer whose electric potential in an aqueous solution environment is lower than that of the substrate by 0.5%. When formed to a thickness of about 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 content exceeds 5%, the effect is saturated. Therefore, the range is limited to the range of 0.01% to 5%. Further, if 0.05% or more is added, there is an effect of improving the resistance to the overall corrosion of the base material alone, and if more than 2.5%, the effect is saturated.
Therefore, it is more desirable to add in the range of 0.05% or more and 2.5% or less.

Mo: Mo is a metal having a potential lower than that of a base material in an aqueous solution environment on the surface of a base material by being added to steel containing 0.1% or more of Al and 10% or more and 30% or less of Cr. When the 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 generation and growth of pitting corrosion in the base material alone. Lower. Therefore, 0.1
More preferably, it is added in the range of not less than 3% and not more than 3%.

Sb: Sb is 0.01% in steel containing 0.1% or more of Al and 10% or more and 30% or less of Cr.
When added as described above, 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 surface of the base material, an effect of improving corrosion resistance is obtained, but less than 0.01% Has no effect, while 0.5
%, The effect is saturated. Therefore, the range is limited to 0.01% or more and 0.5% or less. Further, when Sb is added in an amount of 0.015% or more, there is an effect of improving resistance to pitting corrosion and general corrosion of the base material alone, but when added in excess of 0.3%, hot workability is slightly reduced. . Therefore, it is more desirable to add in the range of 0.015% or more and 0.3% or less.

Ni: Ni is 0.01% in steel containing 0.1% or more of Al and 10% or more and 30% or less of Cr.
Addition of the above provides an effect of improving corrosion resistance when a metal layer having a potential lower than that of the base material in an aqueous environment is formed to a thickness of 0.5 to 500 μm on the base material surface, but on the other hand, exceeds 10% Even if added, the effect is saturated. Therefore, the range is limited to 0.01% or more and 10% or less. Further, the addition of 0.1% or more 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: W contains 0.1% or more of Al and C
When 0.05% or more is added to steel containing 10% or more and 30% or less of r, a metal layer whose electric potential in an aqueous environment is lower than that of the substrate is formed to a thickness of 0.5 to 500 μm on the surface of the substrate. In this case, the effect of improving the corrosion resistance is brought about, but 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 an 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, it is more desirable to add in the range of 0.1% or more and 2% or less.

Rare earth element (REM), Ca: Rare earth metal (REM) or Ca contains 0.1% or more of Al and 1% of Cr.
By adding to a steel containing 0% or more and 30% or less, corrosion resistance is improved when a metal layer whose electric potential in an aqueous solution environment is lower than that of the substrate is formed to a thickness of 0.5 to 500 μm on the surface of the substrate. , But with REM 0.00
No effect is observed at less than 1%, and 0.0001 for Ca.
%, No effect was observed, while in REM 0.1%
If Ca exceeds 0.05%, the effect is saturated. Therefore, the range of REM is 0.001%
The range of Ca is limited to at least 0.1% and the range of Ca is limited to at least 0.0001% and at most 0.05%. Further, REM and Ca are elements that are effective for improving hot workability and pitting corrosion resistance of the base material alone.
If the content is less than 1% and Ca is less than 0.005%, the effect is not sufficient, and 0.01% for Ca and 0.0% for REM.
If added in excess of 5%, coarse non-metallic inclusions are formed, respectively, deteriorating hot workability and pitting corrosion resistance. Therefore, the upper limit content is 0.1% in REM and 0.0% in Ca.
3%. Therefore, Ca is 0.005% or more and 0.01% or more.
%, And REM is more preferably added in the range of 0.01% to 0.05%. In the present invention, the rare earth element has an atomic number of 57 to 7
No. 1 and 89 to 103 elements and Y are indicated.

Nb, V, Ti, Zr, Ta, Hf: N
When b, V, Ti, Zr, Ta, and Hf are added to steel containing 0.1% or more of Al and 10% or more and 30% or less of Cr, the potential in an aqueous solution environment on the surface of the substrate is higher than that of the substrate. When the base metal layer is formed to a thickness of 0.5 to 500 μm, the effect of improving the corrosion resistance is obtained. However, if each element is less than 0.01%, the effect is not recognized, while about 1.0% The effect is saturated even if it is added in excess of. Therefore, the contents of Nb, V, Ti, Zr, Ta and Hf are 0.0
It is limited to 1% or more and 1.0% or less. 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 potential is lower than that of the substrate. At a thickness of 0.5 μm or less coated with a metal whose potential is lower than that of the base material, by adding Al to the base material,
After the surface of the substrate is exposed to the corrosive environment, the surface of the substrate exposed to the corrosive environment is reduced, with the decrease in the rate of disappearance of the layer of the metal whose potential is lower than that of the substrate coated on the remaining substrate surface. Significant reduction in the speed of expansion, and at the same time, the effect of protecting the exposed portion of the base material from the metal layer, which has a potential lower than that of the base material, covering the exposed base material portion over the exposed base material portion, is sufficiently exhibited. On the other hand, if the coating is performed to a thickness exceeding 500 μm, the effect is no longer saturated, but only the productivity is reduced and the cost is simply increased. 0.5-500 μm
And

Aluminum, zinc, chromium, manganese, and alloys based on 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 metal of the coating layer further comprises M
By containing at least one of g and In in a single content of 0.05 to 10%, more excellent corrosion resistance can be obtained.

The reasons for limiting the contents of Mg and In to the above ranges are as follows. That is, if the amount of each addition is less than 0.05%, the effect of improving the corrosion resistance is not seen. Conversely, if it exceeds 10%, the effect is only saturated, and the low content which is a feature of the steel of the present invention is low. Hurt costs. Therefore, each of Mg and In is added in the range of 0.05 to 10%.

The coating process is not limited as long as the metal is sufficiently fixed to the substrate. It should be selected after considering the application and cost, etc.
Hot-dip plating, electrodeposition plating, hot-dip salt electroplating, vacuum evaporation, sputtering, ion plating, thermal spraying, and the like can be used, and these can be used in combination. Further, any processing may be performed before and after the coating and the processing therefor.

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 and an impurity component contained in the zinc-based alloy 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 alloy mainly composed of chromium is an alloy in which the component that occupies the largest amount among 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. .

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

For the actual period of applying the above coating, coils,
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. 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. Any steel having a combination of composition and processing conditions limited by the present invention is an object of the present invention, and an optimal product manufacturing process can be selected according to cost, restrictions on existing product facilities, and the like. It would not be outside the scope of the present invention with a it even select process.

The steel proposed in the present invention can be used not only in a high-temperature wet corrosion environment such as an exhaust system of an internal combustion engine, but also in 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.

[0046]

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, 50 mm in width and 7 mm in length were obtained from these steel plates.
A test piece of 0 mm was sampled and subjected to various corrosion tests described below. High temperature wet corrosion test is 2000pp sulfate ion
m, chloride ion 2000ppm, bicarbonate ion 1000
The test piece was immersed in 50 cc of an aqueous solution to which 0 ppm was added in the form of an ammonium salt, halved, and the test solution was kept 100 ° C. and the test solution was completely evaporated and volatilized 100 times. 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 the maximum corrosion depth is less than 0.10 mm, ○ indicates less than 0.2 mm, and Δ indicates 0.3 mm.
Less than, and × show that it was 0.3 mm or more, respectively.

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.
% For 5 hours, followed by a further 1 hour of freezing, which was repeated 1500 times. The maximum pit depth of the test specimen after the test was measured and used as the test result. The obtained 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.
40,51-90) show good corrosion resistance even in a very severe corrosive environment called salt corrosion.
It can be seen that the comparative steels (Nos. 41 to 50, 100 to 109) have poor corrosion resistance.

In the soil corrosion test, the water content was 15% and the specific resistance was 2
A test piece was embedded in sand adjusted to a content of sodium chloride of 00 Ω · cm, kept at 60 ° C. and 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 the maximum corrosion depth was less than 0.05 mm, ○ indicates that the depth was less than 0.1 mm, Δ indicates that the depth was less than 0.5 mm, and x indicates that the depth was 0.5 mm 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 soil corrosive environment, while 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 using sea sand containing chloride, forming a sample, solidifying the sample, immersing the sample in half in artificial seawater, and placing it in a 60 ° C environment. The test was performed for standing for about 1500 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 ratio was less than 10%,
X shows that it was 10% or more, respectively.

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 (Nos. 50, 100 to 109) are inferior in corrosion resistance. The tap water environment corrosion test was a test in which a test piece was immersed in tap water and kept in an atmosphere at 60 ° C. for 30 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 a test piece was exposed to a shore splash zone for 36 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 (Nos. 1 to 40 and 51 to 90) show good corrosion resistance in a seawater corrosive environment, while the comparative steels (Nos.
0,100-109) are inferior in corrosion resistance. The dew condensation corrosion test was conducted at a humidity of 98 after being kept in an environment of -20 ° C for 2 hours.
%, The test was repeated 3000 times to maintain the environment at 50 ° C. for 4 hours. 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%, and △ indicates that the rusting area ratio was 1
Less than 0%, and x indicates 10% or more, respectively.

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 dew-condensation corrosion environment, whereas the comparative steels (Nos.
0,100-109) are inferior in corrosion resistance. In the atmospheric corrosion test, a test piece was placed at a position
The test was performed by exposing for 00 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%, and △ indicates that the rusting area ratio was 1
Less than 0%, and x indicates 10% or more, respectively.

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, while the comparative steels (Nos. 41 to 5).
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-0.5
6% test solution in 850 cc of a solution such as
It was immersed for 0 days, and the test was conducted 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 corrosion test results, ◎ indicates that the amount of iron ions eluted into the solution was 1 ppm or less, は indicates less than 3 ppm, Δ indicates less than 5 ppm, and × indicates 5 ppm 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 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 clear from Table 2, the steels of the present invention in which the workability was particularly improved (Nos. 51 to 90) show good corrosion resistance and good workability. That is, it shows good corrosion resistance in various corrosive environments such as high-temperature wet corrosive environment, dew condensation corrosive environment, atmospheric corrosive environment, tap water corrosive environment, soil corrosive environment, concrete corrosive environment, seawater corrosive environment, drinking water corrosive environment, and Excellent workability. On the other hand, it can be seen that the corrosion resistance and the workability of the comparative steel (numbers 100 to 109) cannot be simultaneously achieved.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

[0062]

[Table 5]

[0063]

[Table 6]

[0064]

[Table 7]

[0065]

[Table 8]

[0066]

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

Claims (9)

[Claims] 1. wt%: Si: 0.01 to 3.0%, Mn: 0.01 to 3.0%, Cr: 10 to 30%, Al: 0.1 to 10%, Mg: 0 .0003-0.05%, with the balance being Fe and unavoidable impurities, of which C is set to 0.
The base material is steel having a limit of 02% or less, P of 0.03% or less, S of 0.01% or less, and N of 0.02% or less. A steel excellent in corrosion resistance, characterized in that a coating layer of a metal that is more base than a base material 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,
3. The composition according to 3, wherein one or more selected from V, Ti, Zr, Ta, and Hf are contained in a single content of 0.01 to 1%, and the following formula is satisfied. Corrosion resistance and corrosion resistance steel. 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. 9. The coating of claim 1 wherein the metal of said coating layer further comprises M
6. At least one of g and In is contained alone in an amount of 0.05 to 10%.
The corrosion-resistant steel according to 6, 7, or 8.