JP2016089245A - Corrosion resistant steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion resistant steel material excellent in local corrosion resistance when exposed to an extremely severe corrosion environment where a chloride ion is concentrated or the like.SOLUTION: There is provided a corrosion resistant steel material having a composition containing, by mass%, Cr:4.0 to 9.0%, Al:0.10 to 0.70%, Ti:0.005 to 0.100%, N:0.0020 to 0.0080% and further one or both of Mo and W of 0.050 to 1.0% in total. It may contain one or more kinds of Cu, Ni, V, Nb, Ta, Sb, Sn, B, Ca, Mg and REM. Preferably the contents of Ti and N satisfy Ti/N≥3.5, an inorganic zinc-rich primer layer having a thickness of 5 to 100 μm and containing metal zinc or zinc alloy of 30 mass% or more can be arranged on a surface, and an epoxy-based resin layer or a silicon-based resin layer having a thickness of 20 to 400 μm can be arranged on an outer surface side of the inorganic zinc-rich primer layer.SELECTED DRAWING: None

Description

  The present invention relates to a corrosion-resistant steel material.

  Corrosion due to chloride is a problem in steel materials used in steel structures in the beach area and the marine environment, steel structural members of ships, and the like. In particular, when seawater droplets or particles containing salt are attached to a steel material and further exposed to an environment in which drying and wetting are repeated (dry and wet repeated environment), corrosion of the steel material is promoted. In addition, even in the inland area, there is a concern about corrosion due to chloride in structures such as bridges in areas where antifreeze containing chloride is sprayed in winter.

  Cr is an element that improves the corrosion resistance of steel. Various stainless steels containing a large amount of Cr and other alloy elements have been developed to suppress corrosion caused by chlorides, and exposed to the above-mentioned corrosive environment. Applied to structural members. However, since stainless steel is expensive, steel materials in which the addition amount of Cr is suppressed and the corrosion resistance is improved by adding Al to reduce costs have been proposed (for example, Patent Documents 1 to 5). .

  The invention proposed by Patent Documents 1 to 3 attempts to improve the mechanical properties of the base material and the welded portion by controlling the addition amount of alloy components and the metal structure. In addition, the inventions proposed by Patent Documents 4 and 5 attempt to suppress the occurrence of crevice corrosion by appropriately controlling the ratio of Cr and Al contents (Cr / Al).

JP 2004-162121 A JP 2005-256135 A JP 2006-161125 A Japanese Patent Laid-Open No. 2006-37201 JP 2008-7860 A

Corrosion is particularly a problem in areas where the chloride ion concentration is high, such as tidal and splashing parts of marine structures and ballast tanks of tankers. In addition, in steel materials whose overall corrosion resistance has been improved by adding alloying elements such as Cr, Al, Cu, and Ni, local corrosion such as pitting corrosion tends to be promoted if there is a site where corrosion resistance has locally deteriorated. is there. Therefore, the corrosion resistant steel material whose overall corrosivity is improved by the addition of alloying elements is likely to accelerate local corrosion when exposed to a very severe corrosive environment.
However, until now, steel materials that can achieve both general corrosion resistance and local corrosion resistance have not been studied, and their development has been desired.

  The present invention has been devised in view of such circumstances, and is particularly excellent in local corrosion resistance when exposed to a very severe corrosive environment in which chloride ions are concentrated. It provides corrosion resistant steel.

The present inventor has found that a corrosion resistance steel material containing Cr and Al causes a partial decrease in corrosion resistance due to the Al deficient layer resulting from the formation of AlN, and studied the countermeasures. As a result, it was newly found that by forming Ti at a temperature higher than that of Al and adding Ti which does not contribute to the improvement of the corrosion resistance of steel in the solid solution state, the formation of AlN can be suppressed and local corrosion can be suppressed. It was. Furthermore, new knowledge was obtained that local corrosion resistance is remarkably improved by adding one or both of Mo and W, which are harder to form nitrides than Al and improve corrosion resistance in a solid solution state.
This invention is made | formed based on such knowledge, The summary is as follows.

[1] By mass%
C: 0.005 to 0.20%,
Mn: 0.30 to 3.00%,
Cr: 4.0-9.0%,
Al: 0.10 to 0.70%,
Ti: 0.005 to 0.100%,
N: 0.0020 to 0.0080%
Further,
Contains one or both of Mo and W in total, 0.050 to 1.0%,
Si: 1.00% or less,
P: 0.030% or less,
S: limited to 0.0050% or less,
A corrosion-resistant steel material characterized in that the balance consists of Fe and inevitable impurities.
[2] By mass%,
Cu: 0.50% or less,
Ni: The corrosion resistant steel material according to [1] above, containing one or both of 0.50% or less.
[3] By mass%,
V: 0.50% or less,
Nb: 0.150% or less,
Ta: 0.040% or less,
Sb: 1.00% or less,
Sn: 1.00% or less,
B: The corrosion-resistant steel material according to [1] or [2] above, containing one or more of 0.010% or less.
[4] By mass%,
Ca: 0.010% or less,
Mg: 0.010% or less,
REM: The corrosion-resistant steel material according to any one of the above [1] to [3], containing one or more of 0.010% or less.
[5] The content of Ti and N is
Ti / N ≧ 3.5
The corrosion resistant steel material according to any one of the above [1] to [4], wherein:
[6] An inorganic zinc-rich primer layer having a thickness of 5 to 100 μm containing 30% by mass or more of metallic zinc or a zinc alloy on the surface of the corrosion-resistant steel material according to any one of [1] to [5]. Corrosion-resistant steel characterized by being provided.
[7] The corrosion-resistant steel according to [6], wherein an epoxy resin layer or a silicon resin layer having a thickness of 20 to 400 μm is provided on the surface of the inorganic zinc rich primer layer.

  According to the present invention, it is possible to provide a corrosion-resistant steel material that is also excellent in local corrosion resistance when exposed to a very severe corrosive environment where chloride ions are concentrated. Has an extremely significant industrial contribution.

  In the present invention, an appropriate amount of Cr and Al are added at the same time to further add Ti and one or both of Mo and W to the corrosion resistant steel material whose overall corrosion resistance is improved. It is a corrosion resistant steel with improved local corrosion resistance when exposed to extremely severe corrosive environments. In other words, the addition of Ti suppresses the formation of AlN that is the starting point of local corrosion and the surrounding Al deficient layer, and further, the addition of one or both of Mo and W, which are harder to form nitrides than Al, can cause local corrosion. The progress can be remarkably suppressed.

Furthermore, by applying an inorganic zinc rich primer on the surface of the steel material, it becomes possible to prevent rusting over a long period of time while having a low alloy composition compared to commercially available stainless steel. Furthermore, in the present invention, in order to improve durability, an epoxy resin layer or a silicon resin layer may be formed on the surface of the inorganic zinc rich primer layer.
In addition, the shape of the corrosion-resistant steel material of the present invention is not particularly limited, and may be a steel plate, a steel pipe, or a shape steel.

  Hereinafter, the reason which limited the component of the corrosion-resistant steel material of this invention is demonstrated. In addition, the description of% means the mass% unless there is particular notice.

(C: 0.005-0.20%)
C is an element that improves the strength, and in order to obtain this effect, it is necessary to contain 0.005% or more. Preferably, the C content is 0.01% or more. On the other hand, if the C content exceeds 0.20%, the corrosion resistance deteriorates due to the formation of Cr-based carbides, so the C content is 0.20% or less. Preferably, the C content is 0.10% or less, more preferably 0.05% or less.

(Mn: 0.30 to 3.00%)
Mn is an element that stabilizes austenite and is added to suppress the formation of coarse ferrite. In the present invention, since a large amount of Cr and Al for stabilizing ferrite is contained, if the amount of Mn is less than 0.30%, coarse ferrite crystal grains are formed, which impairs manufacturability and mechanical properties. Therefore, the Mn content is 0.30% or more. Preferably, the amount of Mn is 0.50% or more, more preferably 1.00% or more, and still more preferably 1.50% or more. On the other hand, if the amount of Mn exceeds 3.00%, coarse MnS is generated and the corrosion resistance and mechanical properties deteriorate, so the amount of Mn is made 3.00% or less. The amount of Mn is preferably 2.75% or less, more preferably 2.50% or less.

(Cr: 4.0-9.0%)
Cr is an element that forms a passivating film and improves the corrosion resistance of the steel material. By containing it simultaneously with Al, this effect is remarkably exhibited. In the present invention, the Cr content is 4.0% or more in order to obtain excellent corrosion resistance. Preferably it is 5.0% or more, more preferably 5.5% or more. On the other hand, if the Cr content exceeds 9.0%, coarse ferrite crystal grains are formed, which impairs manufacturability and mechanical properties. Therefore, the Cr content is 9.0% or less, preferably 8.0% or less, more preferably 7.5% or less.

(Al: 0.10 to 0.70%)
Al is a useful element that remarkably improves corrosion resistance by interaction with Cr. In order to obtain this effect, an Al amount of 0.10% or more is necessary, and the Al amount is preferably 0.20% or more. On the other hand, excessive addition of Al may promote the formation of AlN which is the starting point of local corrosion. Therefore, in order to suppress the formation of AlN and suppress the occurrence of local corrosion, the Al amount needs to be 0.70% or less. Preferably, the Al content is 0.50% or less.

(Ti: 0.005-0.100%)
Ti is an element that forms a nitride at a higher temperature than AlN, and suppresses the generation of AlN and contributes to the suppression of local corrosion. In the present invention, Ti is one of important elements, and 0.005% or more is added to improve local corrosion resistance. Preferably, 0.010% or more is added. On the other hand, if more than 0.100% Ti is added, the mechanical properties deteriorate, so the upper limit of the Ti amount is made 0.100% or less. Preferably, the Ti content is 0.050% or less, more preferably 0.030% or less.

(N: 0.0020 to 0.0080%)
N forms an element that contributes to the refinement of crystal grains by forming Ti and nitrides, while forming AlN together with Al impairs local corrosion resistance. In the present invention, in order to suppress the formation of coarse ferrite, the N content is set to 0.0020% or more. On the other hand, if the N content exceeds 0.0080%, the mechanical properties deteriorate due to the nitride, so the upper limit is made 0.0080% or less. The N amount is preferably 0.0070% or less, more preferably 0.0060% or less.

(Total of one or both of Mo and W: 0.050 to 1.0%)
Mo and W are important elements that are less likely to form nitrides than Al and that can suppress the occurrence and growth of local corrosion in a solid solution state. In the present invention, only one or both of Mo and W may be added. In order to improve local corrosion resistance, it is necessary to add 0.050% or more of one or both of Mo and W in total. Preferably, it is 0.05% or more. If one or both of Mo and W are contained in total exceeding 1.0%, coarse ferrite crystal grains are formed, and the manufacturability and mechanical properties are impaired. Therefore, the total content of one or both of Mo and W is 1.0% or less, preferably 0.8% or less, more preferably 0.5% or less.

(Si: 1.00% or less)
Si is an element that contributes to deoxidation and improvement of strength, but if contained over 1.00%, the toughness decreases, so the amount of Si is limited to 1.00% or less. Preferably, the Si amount is 0.50% or less. The lower limit of the amount of Si is not limited and may be 0%. However, in order to suppress the formation of oxides of Al and to dissolve Al in steel and improve the corrosion resistance, the amount of Si is 0.05%. It is preferable to make it above. More preferably, the Si amount is 0.10% or more.

(P: 0.030% or less)
P is an impurity, and limits the amount of P to 0.030% or less in order to reduce the mechanical properties and manufacturability of the steel material. Preferably, the P content is 0.020% or less. The lower limit of the amount of P is not limited and may be 0%, but is preferably 0.001% or more from the viewpoint of manufacturing cost.

(S: 0.0050% or less)
Since S is an impurity and forms a sulfide that is a starting point of local corrosion, the amount of S is limited to 0.0050% or less. Preferably, the S amount is 0.0020% or less, more preferably 0.0010% or less. The lower limit of the amount of S is not limited and may be 0%, but is preferably 0.0001% or more from the viewpoint of manufacturing cost.

(Ti / N ≧ 3.5)
Ti is an element added to fix N in the steel as a nitride and suppress the formation of AlN. Therefore, it is preferable to determine the amount of Ti according to the amount of N. The nitride of Ti is mainly TiN, and in order to secure Ti equal to or more than the number of N atoms, the Ti / N content ratio Ti / N represented by mass% is set to 3.5 or more. It is preferable. The upper limit of Ti / N is not particularly limited, but is 50 or less from the upper limit of Ti amount (0.10%) and the lower limit of N amount (0.0020%). The upper limit with preferable Ti / N is 25 or less from the preferable upper limit of Ti amount, More preferably, it is 15 or less.

  The steel components used in the steel sheet of the present invention are composed of the above elements, impurities, and the balance Fe, but the following elements may be further added.

  In the present invention, in addition to the above elements, one or both of Cu: 0.50% or less and Ni: 0.50% or less can be added.

(Cu: 0.50% or less)
Cu is an element that improves the corrosion resistance, and preferably 0.05% or more is added. More preferably, the amount of Cu is 0.10% or more. On the other hand, since addition of Cu exceeding 0.50% may cause embrittlement, the amount of Cu is preferably 0.50% or less. More preferably, the amount of Cu is set to 0.30% or less.

(Ni: 0.50% or less)
Ni is an element that improves the corrosion resistance, and preferably 0.05% or more is added. More preferably, the Ni content is 0.10% or more. On the other hand, since Ni is an expensive element, the upper limit of the amount of Ni is preferably 0.50% or less. More preferably, the Ni content is 0.30% or less.

  Cu and Ni are preferably added at the same time. Cu has a greater effect of improving the corrosion resistance than Ni, but is easily segregated, and if added alone, it may promote cracking after casting. In contrast, Ni has the effect of reducing the segregation of Cu, and when both Cu and Ni are added simultaneously, in addition to suppressing cracking of the slab caused by Cu segregation, local corrosion caused by segregation also occurs. Since it is suppressed, the effect of improving the corrosion resistance is remarkably exhibited.

  In the present invention, in addition to the above elements, V: 0.50% or less, Nb: 0.150% or less, Ta: 0.040% or less, Sb: 1.00% or less, Sn: 1.00 % Or any one kind or two kinds or more can be contained.

(V: 0.50% or less)
V, like Ti, is an element that forms a nitride, but can be added mainly to improve the strength by precipitation strengthening. In order to obtain this effect, the V amount is preferably set to 0.005% or more. On the other hand, if adding more than 0.50% V, the mechanical properties may deteriorate, so the V content is preferably 0.50% or less. The amount of V is more preferably 0.20% or less, and further preferably 0.30% or less.

(Nb: 0.150% or less)
Nb, like Ti, is an element that forms nitrides, and contributes to the suppression of the formation of AlN and coarse ferrite. In order to obtain this effect, the Nb content is preferably 0.005% or more. On the other hand, when Nb exceeding 0.150% is added, the mechanical properties may be deteriorated, so the Nb content is preferably 0.150% or less. The Nb amount is more preferably 0.10% or less, and further preferably 0.050% or less.

(Ta: 0.040% or less)
Ta is an element effective for improving corrosion resistance. Although the mechanism is not necessarily clear, it is considered that the oxide of Ta ₂ O ₅ acts on the stability and denseness of the protective film formed on the surface. In order to obtain this effect, the Ta content is preferably 0.001% or more. On the other hand, even if Ta is added in excess of 0.040%, a significant improvement in corrosion resistance cannot be expected, and the manufacturing cost increases. Therefore, the Ta content is preferably 0.040% or less. More preferably, the Ta amount is 0.020% or less.

(Sb: 1.00% or less)
(Sn: 1.00% or less)
Sn and Sb are effective elements for improving the corrosion resistance. The amount of Sn and Sb added is preferably 0.01% or more, more preferably 0.03% or more, and still more preferably 0.10% or more. On the other hand, if the amount of each of Sn and Sb exceeds 1.00%, the hot workability tends to deteriorate, so 1.00% or less is preferable. More preferably, each is 0.50% or less, and more preferably 0.30% or less.

(B: 0.010% or less)
B is an element that improves hardenability and increases strength. In order to obtain the effect, 0.0003% or more of B is preferably contained. However, even if B is added in excess of 0.010%, the effect is saturated, and the toughness of the base material and HAZ may be lowered. Therefore, 0.010% or less is preferable. A more preferable upper limit of the amount of B is 0.0050% or less.

  In the present invention, in addition to the above elements, one or more of Ca: 0.010% or less, Mg: 0.010% or less, REM: 0.010% or less should be added. Can do.

(Ca: 0.010% or less)
(Mg: 0.010% or less)
Ca and Mg are generally used to control oxides and sulfides, but steel containing Cr and Al is selectively dissolved in the environment to form an alkaline environment on the steel sheet surface, thereby improving corrosion resistance. Contribute. In order to obtain this effect, it is preferable to add 0.0005% or more of each of Ca and Mg. On the other hand, even if Ca and Mg are added in an amount exceeding 0.010%, the effect of improving the corrosion resistance is saturated and the mechanical properties may be impaired. Therefore, the addition amount of Ca and Mg is 0.010% or less. Is preferred. More preferably, it is 0.005% or less, respectively.

(REM: 0.010% or less)
In the present invention, a rare earth element (REM) may be appropriately added for the purpose of controlling oxides and sulfides. In order to obtain this effect, it is preferable to add 0.001% or more of REM. On the other hand, even if REM is added over 0.010%, the effect of improving the corrosion resistance is saturated and mechanical properties may be impaired. Therefore, the amount of REM added is preferably 0.010% or less. More preferably, it is 0.005% or less.

  In the present invention, the balance other than the above elements is composed of Fe and unavoidable impurities, but other elements can be added in minute amounts within a range that does not impair the effects of the present invention.

(Inorganic zinc rich primer layer)
Although the steel material of the present invention exhibits good corrosion resistance even when used as it is, the corrosion resistance can be further improved by coating the surface with an anticorrosion film.
The corrosion-resistant steel material of the present invention may be provided with an inorganic zinc rich primer layer on the surface of the base steel material having the above composition as the above-described anticorrosion film.

  The inorganic zinc rich primer layer is a film formed by applying an inorganic zinc rich primer and drying it. Zinc (metal zinc or zinc alloy) contained in the inorganic zinc rich primer layer contributes to sacrificial corrosion protection of the corrosion resistant steel material. Zinc contained in the inorganic zinc rich primer layer is in the form of powder (sometimes called zinc dust).

  Furthermore, after the zinc of the inorganic zinc rich primer layer is consumed and the sacrificial anti-corrosion effect is lost, the progress of corrosion of the corrosion-resistant steel material is suppressed by the interaction between the corrosion product and Cr, etc. Thus, it is possible to obtain an anticorrosion effect.

  The inorganic zinc-rich primer layer is preferably 5 μm or more because the anticorrosion effect may be lost early if the thickness is less than 5 μm. More preferably, it is 10 μm or more. On the other hand, if the thickness of the inorganic zinc rich primer layer exceeds 100 μm, cracks and sagging are likely to occur, and therefore it is preferably 100 μm or less. Furthermore, when the thickness of the inorganic zinc rich primer layer increases, fumes and blowholes are likely to occur during fusing and welding. In consideration of the balance of processability, corrosion resistance, and economic efficiency, the thickness of the inorganic zinc rich primer layer is more preferably 80 μm or less, and further preferably 50 μm or less.

As the inorganic zinc rich primer layer, it is preferable to use a layer containing 30% by mass or more of metallic zinc or zinc alloy in the dry coating film.
As the composition of the inorganic zinc-rich primer applied to the surface of the corrosion-resistant steel material, a composition using a silicate condensate such as an alkyl silicate or ethyl silicate as a vehicle is often used. Further, the metal zinc or zinc alloy in the heating residue is not particularly specified as long as it is 30% by mass or more, but it is preferable in terms of reliability that it is a JIS K5552 type 1 equivalent product. As the zinc alloy, for example, a Zn—Al alloy, a Zn—Mg alloy, or a Zn—Al—Mg alloy can be used.

  Moreover, in the corrosion-resistant steel material of the present invention, it is possible to further improve the durability by forming an epoxy resin layer or a silicon resin layer on the surface of the inorganic zinc rich primer layer. In addition, it is not preferable to form an epoxy resin layer or a silicon resin layer directly on the surface of the corrosion resistant steel material of the present invention.

  As the epoxy resin coating, a two-pack type containing a main agent and a curing agent, for example, Eponics (registered trademark) or Marine Ballaster (registered trademark) can be used. Marine Ballaster (registered trademark) is an epoxy resin coating composed of a main agent containing an epoxy resin and a curing agent containing a modified aliphatic polyamine. As the silicon-based resin paint, those obtained by mixing a main agent containing silicon resin and a curing agent containing toluene, for example, Pyrogin Stack ACT # 250 or Pyrogin (registered trademark) B # 1000 can be used. .

  When the thickness of the epoxy resin layer or the silicon resin layer is less than 20 μm, the resin layer may be damaged or peeled at an early stage and the effect may be lost, and is preferably 20 μm or more. In the case of an epoxy resin layer, 40 μm or more is more preferable. On the other hand, when the thickness of the epoxy resin layer or the silicon resin layer exceeds 400 μm, the effect is saturated, which may be disadvantageous for economy, and is preferably 400 μm or less. From the viewpoints of paintability and economy, the epoxy resin layer is more preferably 100 μm or less, and the silicon resin layer is more preferably 75 μm or less. Moreover, even if the thickness is the same, it is preferable to apply multiple layers such as applying twice.

  Note that the inorganic zinc rich primer layer and the epoxy resin layer or silicon resin layer described above do not necessarily have to be formed on the entire surface of the corrosion-resistant steel material, but one surface of the steel material (which may be a steel pipe) as a surface exposed to the corrosive environment. For example, only the outer surface or the inner surface), that is, at least a part of the steel surface may be subjected to anticorrosion treatment.

  About the manufacturing method of the corrosion-resistant steel material of this invention, it does not specifically limit, A conventional method may be sufficient. For example, the steel slab is heated and manufactured through a hot rolling process and, if necessary, a heat treatment process. The steel slab is manufactured by a process such as a continuous casting method and an ingot-making / bundling method after the components are adjusted by a converter or an electric furnace and melted. The steel slab may be subjected to a heat treatment such as quenching, tempering, normalizing, annealing, etc. according to the purpose after heating, as a steel plate, shape steel, steel pipe or the like by hot rolling.

  The method for forming the inorganic zinc rich primer layer is not particularly limited. For example, an inorganic zinc rich primer layer can be formed on the steel material surface by applying an inorganic zinc rich primer to the steel material with a brush or a spray. Before applying or spraying the inorganic zinc rich primer, it is preferable in terms of adhesion to remove rust on the surface of the steel material by shot blasting or sand blasting. In the case of performing the blasting process, it is preferably set to Sa2 · 1/2 or more shown in ISO 8501-1. Moreover, when spraying an inorganic zinc rich primer on the blasted steel material surface, it is preferable from the point of work efficiency to spray by airless spray.

  The construction method of the epoxy resin layer or the silicon resin layer is not particularly limited. For example, an epoxy resin paint or a silicon resin paint is applied to the surface of a steel material or the surface of an inorganic zinc rich primer layer by brush, airless or air spray so that the thickness of the dry coating film becomes a desired thickness. It can be cured by curing at room temperature.

  The technical contents of the present invention will be further described below with reference to examples of the present invention. In addition, the conditions in the Example shown below are one example of conditions used in order to confirm the feasibility and effect of this invention, and this invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  Steels having the composition shown in Table 1 were melted and cast, and the obtained steel pieces were heated to 1100 ° C, hot-rolled to a thickness of 5 mm at a finishing temperature of 740 ° C, and air-cooled to room temperature. Thereafter, the mixture was heated to 950 ° C., held for 15 minutes, and then cooled in the furnace.

A test piece having a length of 150 mm, a width of 60 mm, and a thickness of 4 mm was collected from the obtained steel plate. The surface of the test piece was subjected to blasting so as to be Sa2.5 (ISO 8501-1) or more. In some test pieces, an inorganic zinc rich primer layer was formed, and in some test pieces, an epoxy resin layer or a silicon resin layer was further formed on the inorganic zinc rich primer layer.
Next, two straight lines having a width of 0.6 mm and a length of 300 mm are formed on the test piece on which the inorganic zinc-rich primer layer is formed and on the test piece on which the epoxy resin layer or the silicon resin layer is further formed. The X-cuts intersecting each other at 30 ° as viewed from above the test piece at the center of the test surface were put with a cutter to expose the ground iron surface. The X cut simulates an inevitable defect.

The inorganic zinc rich primer was prepared with a JIS K 5552 type 1 equivalent product (trade name: NIPPE ZINKI 1000P manufactured by Nippon Paint Co., Ltd.), and applied to the surface of the test piece with a thickness of 15 μm by air spray. .
After forming the inorganic zinc rich primer layer, in some test pieces, a silicon-based resin paint (manufactured by Oshima Kogyo Co., Ltd., trade name: Pyrozine B # 1000) is aimed at a thickness of 100 μm on the inorganic zinc rich primer layer. Was applied to form a silicon-based resin layer. Moreover, in some test pieces, an epoxy resin coating (trade name: Epomarin SHB, manufactured by Kansai Paint Co., Ltd.) was applied to the inorganic zinc rich primer layer with a target of 100 μm to form an epoxy resin layer. .

Actual seawater immersion test in which the test specimen is immersed in seawater for 3 years, and actual exposure for 2 years in which the test specimen is exposed horizontally in a shade-exposed environment that is affected by the splash of seawater and is about 5 meters away from the coast and without rain. And the test.
By measuring the corrosion depth using a point micrometer before and after the test, three points having the deepest corrosion in each test piece were selected, and the average depth was defined as the maximum local depth. The maximum local depth was 0.05 mm or less as “「 ”, more than 0.05 mm, 0.1 mm or less as“ ◯ ”, and those exceeding 0.1 mm as“ × ”.
The results are shown in Table 2.

In Table 2, a test piece (only bare) subjected to blast treatment on the surface, a test piece (inorganic Zn layer) on which an inorganic zinc rich primer layer was formed, an epoxy resin layer or a silicon resin layer were formed. The evaluation result of the maximum local depth of the test piece (inorganic Zn layer + resin layer) is indicated by “◯”, “◎”, or “×”.
As shown in Table 2, steel no. Nos. 1-21 (examples of the present invention) have good corrosion resistance, but steel No. 1 containing both Mo and W is not included. No. 22, steel No. in which Cr amount and Ti amount are insufficient. 23, 24, and No. with excessive Al content. No. 25 has low corrosion resistance (particularly local corrosion resistance). In addition, the steel No. in which the C amount is excessive is used. No. 26 and the amount of Al is insufficient. 27 also has reduced corrosion resistance (particularly local corrosion resistance).

Claims (7)

% By mass
C: 0.005 to 0.20%,
Mn: 0.30 to 3.00%,
Cr: 4.0-9.0%,
Al: 0.10 to 0.70%,
Ti: 0.005 to 0.100%,
N: 0.0020 to 0.0080%
Further,
Contains one or both of Mo and W in total, 0.050 to 1.0%,
Si: 1.00% or less,
P: 0.030% or less,
S: limited to 0.0050% or less,
A corrosion-resistant steel material characterized in that the balance consists of Fe and inevitable impurities. In mass%,
Cu: 0.50% or less,
The corrosion-resistant steel material according to claim 1, wherein one or both of Ni: 0.50% or less are contained. In mass%,
V: 0.50% or less,
Nb: 0.150% or less,
Ta: 0.040% or less,
Sb: 1.00% or less,
Sn: 1.00% or less,
B: 0.010% or less of 1 type or 2 types or more are contained, The corrosion-resistant steel materials of Claim 1 or 2 characterized by the above-mentioned. In mass%,
Ca: 0.010% or less,
Mg: 0.010% or less,
REM: 0.010% or less of 1 type or 2 types or more are contained, The corrosion-resistant steel materials of any one of Claims 1-3 characterized by the above-mentioned. Ti and N content is
Ti / N ≧ 3.5
The corrosion-resistant steel material according to any one of claims 1 to 4, wherein:   An inorganic zinc rich primer layer having a thickness of 5 to 100 μm containing 30% by mass or more of metal zinc or a zinc alloy is provided on the surface of the corrosion-resistant steel material according to claim 1. Corrosion resistant steel.   The corrosion-resistant steel material according to claim 6, wherein an epoxy resin layer or a silicon resin layer having a thickness of 20 to 400 μm is provided on a surface of the inorganic zinc rich primer layer.