JP5365153B2 - Surface-treated steel with excellent corrosion resistance - Google Patents
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Description
本発明は、耐食性に優れた表面処理鋼材に関し、特に、大気、水中、土中埋設環境での耐食性に優れ、これら環境での使用に適した耐食性に優れた表面処理鋼材、および該鋼材で形成された鋼構造物に関する。 The present invention relates to a surface-treated steel material having excellent corrosion resistance, and in particular, a surface-treated steel material having excellent corrosion resistance in an atmosphere, water, and underground environment, excellent in corrosion resistance suitable for use in these environments, and the steel material. Relates to a finished steel structure.
モリブデン、バナジウム、タングステンは、耐食性に優れた元素として知られており、鋼材中に添加することで耐食性を向上させることが知られている。またこれらの元素は、酸素酸塩を含む水溶液中に鋼板を浸漬することにより鋼材の表面に、厚みは薄いがこれら元素の酸化物を中心とした皮膜が形成されることも知られている。これら皮膜は、例えばモリブデンの場合は、リン酸と組み合わせて、鋼材の化成処理として商品化されてもいる。 Molybdenum, vanadium, and tungsten are known as elements excellent in corrosion resistance, and it is known to improve corrosion resistance by adding them to steel materials. It is also known that these elements are formed by immersing a steel sheet in an aqueous solution containing an oxyacid salt to form a thin film on the surface of the steel material, although the thickness is thin, centering on oxides of these elements. For example, in the case of molybdenum, these coatings are commercialized as a chemical conversion treatment of steel materials in combination with phosphoric acid.
一方で、拡散層や酸化物層を形成することにより表面特性を向上させる技術としては以下の特許文献に示されたものがある。
特許文献１には、Ｆｅ‐Ｎｉ拡散層、Ｎｉ層、Ｎｉ‐Ｓｎ合金層、Ｓｎ層からなる複層からなる缶用鋼板が示されている。また、特許文献２には、鋼材に窒化層を形成し、更に窒化層にＣｒの拡散層を形成することにより、塩浴内での耐食性を向上させる技術が開示されている。特許文献３には、鉄‐窒化物上に酸化物を形成する技術が開示され、特許文献４には、酸化物層、窒化物層とさらに窒素の拡散層を鋼材内部に作る耐摩耗性に優れた鋼材が開示されている。
Patent Document 1 discloses a steel plate for cans composed of a plurality of layers including a Fe—Ni diffusion layer, a Ni layer, a Ni—Sn alloy layer, and a Sn layer. Patent Document 2 discloses a technique for improving corrosion resistance in a salt bath by forming a nitride layer in a steel material and further forming a Cr diffusion layer in the nitride layer. Patent Document 3 discloses a technique for forming an oxide on iron-nitride. Patent Document 4 discloses an oxide layer, a nitride layer, and a nitrogen diffusion layer in the steel material for wear resistance. Excellent steel materials are disclosed.
鋼材の腐食は表面にかかる部分が主になるが、構造物用鋼材は板厚が大きく、重量に対する表面積が比較的小さい。そのため、構造物用鋼材のような表面積対重量比の比較的小さい鋼材を対象とする場合、鋼中に元素を添加して耐食性を向上させようとする従来方法では、添加元素全量のうち、鋼材内部に存在して鋼材表面の耐食性にはほとんど寄与しない元素量の割合が大きくなり、その分、添加元素のコストアップが大きくなるというところに課題があった。本発明は、この課題を解決しようとするものである。なお、前記特許文献１〜４には、かかる課題およびその解決策は何ら示されていない。 The corrosion of steel is mainly on the surface, but the structural steel has a large plate thickness and a relatively small surface area relative to the weight. Therefore, when a steel material having a relatively small surface area to weight ratio, such as a structural steel material, is targeted, the conventional method for improving the corrosion resistance by adding an element to the steel is a steel material out of the total amount of added elements. There is a problem in that the ratio of the element amount that exists inside and hardly contributes to the corrosion resistance of the steel material surface increases, and the cost increase of the additive element increases accordingly. The present invention is intended to solve this problem. In addition, the said patent documents 1-4 do not show such a subject and its solution at all.
発明者らは、前記課題を解決するための手段を検討し、次の知見を得た。
モリブデン、バナジウム、タングステンは、鋼中に含有された場合、以下の機構で鋼の耐食性を向上できると推定された。腐食反応に伴う鋼の溶解により溶解する上記元素が酸化され、鋼材表面に沈殿することにより鋼表面に蓄積される。これが鋼材表面の腐食反応を抑制するインヒビターとして作用し、耐食性を向上させるのである。
The inventors have studied means for solving the above-mentioned problems and have obtained the following knowledge.
When molybdenum, vanadium and tungsten were contained in steel, it was estimated that the corrosion resistance of the steel could be improved by the following mechanism. The element dissolved by the dissolution of the steel accompanying the corrosion reaction is oxidized and accumulated on the steel surface by being precipitated on the steel material surface. This acts as an inhibitor that suppresses the corrosion reaction on the steel surface and improves the corrosion resistance.
従って、これらの元素で構成された酸化物層が鋼材表面に予め存在することは耐食性向上に有効であり、しかも同種の元素が鋼材表面からさほど深くない鋼材内部位にかけて拡散層として存在することは、鋼が腐食した場合においても、これらの元素が表面に供給されることにつながって、耐食性の維持が図られる。
また拡散層を腐食として消費したとしても、表面にこれらの酸化物層が存在することで耐食性の継続が期待できる。
Therefore, the presence of an oxide layer composed of these elements in advance on the steel surface is effective for improving corrosion resistance, and that the same kind of element exists as a diffusion layer from the steel surface to a portion in the steel material that is not so deep. Even when the steel is corroded, these elements are supplied to the surface, and the corrosion resistance is maintained.
Even if the diffusion layer is consumed as corrosion, the presence of these oxide layers on the surface can be expected to continue corrosion resistance.
更に、これらの処理層は塗装などの下地処理としても有効であり、塗装下地処理の代替としても期待できる。即ち、裸で使用されても塗装を施す構造物であってもその耐久性を延命することができ、かつ合金として添加するよりも、比較的安価で経済的である。
本発明は、上記知見に基づいてなされたものであり、その要旨構成は次の通りである。
（請求項１） 黒皮を除去した鋼材の表面から外面側に、モリブデン、タングステンの内１種以上の元素を２０at.％以上含む厚さ１００ｎｍ〜１００μｍの酸化物層が形成され、同表面から内面側に、厚さ１００ｎｍ以上の前記元素の拡散層が形成されてなる耐食性に優れた鋼構造物用表面処理鋼材。
（請求項２） 黒皮を除去した鋼材の表面から外面側に、モリブデン、タングステンの内１種以上とバナジウムの元素を２０at.％以上含む厚さ１００ｎｍ〜１００μｍの酸化物層が形成され、同表面から内面側に、厚さ１００ｎｍ以上の前記元素の拡散層が形成されてなる耐食性に優れた鋼構造物用表面処理鋼材。
（請求項３） 請求項１または２に記載された鋼構造物用表面処理鋼材で形成されてなる鋼構造物。
（請求項４） 請求項１に記載された鋼構造物用表面処理鋼材を製造するにあたり、黒皮を除去した鋼材を、モリブデン、タングステンの内１種以上を含む溶液中に浸漬し、該溶液中にプラズマを発生させ、該プラズマを、前記鋼材の表面に所定の時間接触させ、次いでプラズマの発生を停止して所定の時間前記溶液中に保持した後、前記鋼材を前記溶液中から取り出すことを特徴とする、耐食性に優れた鋼構造物用表面処理鋼材の製造方法。
（請求項５） 請求項２に記載された鋼構造物用表面処理鋼材を製造するにあたり、黒皮を除去した鋼材を、モリブデン、タングステンの内１種以上とバナジウムを含む溶液中に浸漬し、該溶液中にプラズマを発生させ、該プラズマを、前記鋼材の表面に所定の時間接触させ、次いでプラズマの発生を停止して所定の時間前記溶液中に保持した後、前記鋼材を前記溶液中から取り出すことを特徴とする、耐食性に優れた鋼構造物用表面処理鋼材の製造方法。
Furthermore, these treatment layers are also effective as a ground treatment such as painting, and can be expected as an alternative to painting ground treatment. That is, even if it is used naked or a structure to be painted, its durability can be extended, and it is relatively inexpensive and economical than adding it as an alloy.
This invention is made | formed based on the said knowledge, The summary structure is as follows.
To (claim 1) outer surface from the surface of the steel to remove mill scale, molybdenum, one or more elements of tungsten 20at. Oxide layer having a thickness of 100nm~100μm containing more than% is formed from the surface A surface-treated steel material for steel structures having excellent corrosion resistance, wherein a diffusion layer of the element having a thickness of 100 nm or more is formed on the inner surface side.
(Claim 2) An oxide layer having a thickness of 100 nm to 100 μm containing one or more of molybdenum and tungsten and an element of vanadium of 20 at.% Or more is formed from the surface of the steel material from which the black skin is removed to the outer surface side. A surface-treated steel material for steel structures having excellent corrosion resistance, wherein a diffusion layer of the element having a thickness of 100 nm or more is formed from the surface to the inner surface side.
(Claim 3 ) A steel structure formed of the surface-treated steel material for a steel structure according to claim 1 or 2 .
In producing the (claim 4) steel structures for surface treatment steel according to claim 1, a steel material with a descaling, immersed molybdenum, in a solution comprising one or more of tungsten, the solution Plasma is generated, the plasma is brought into contact with the surface of the steel material for a predetermined time, and then the generation of the plasma is stopped and held in the solution for a predetermined time, and then the steel material is taken out from the solution. A method for producing a surface-treated steel material for steel structures having excellent corrosion resistance.
(Claim 5) In producing the surface-treated steel material for steel structures according to claim 2, the steel material from which the black skin has been removed is immersed in a solution containing one or more of molybdenum and tungsten and vanadium, Plasma is generated in the solution, the plasma is brought into contact with the surface of the steel material for a predetermined time, and then generation of the plasma is stopped and held in the solution for a predetermined time, and then the steel material is removed from the solution. A method for producing a surface-treated steel material for steel structures having excellent corrosion resistance, characterized by being taken out.
本発明の表面処理鋼材によれば、従来の土木建材用鋼材として使用される鋼材に比して腐食減量を７０％以下程度に抑制することが可能で、塗装を付与した場合には、その塗装寿命を３０％以上向上させることが可能である。また、従来の耐食鋼に対しても、防食コストを低く抑制することが可能である。
本発明の表面処理鋼材で形成された鋼構造物は、大気、水中、埋設土中環境において長期の耐久性を有する鋼構造物として使用することができる。
According to the surface-treated steel material of the present invention, it is possible to suppress the corrosion weight loss to about 70% or less as compared with steel materials used as conventional steel materials for civil engineering and building materials. It is possible to improve the lifetime by 30% or more. Moreover, it is possible to suppress the anticorrosion cost low as compared with the conventional corrosion resistant steel.
The steel structure formed of the surface-treated steel material of the present invention can be used as a steel structure having long-term durability in the atmosphere, water, and buried soil environment.
本発明の表面処理鋼材の製造方法によれば、前記拡散層と前記酸化物層とを同一装置内で形成することができる。 According to the method for producing a surface-treated steel material of the present invention, the diffusion layer and the oxide layer can be formed in the same apparatus.
以下、本発明の表面処理鋼材について、その製造方法（鋼材の表面処理方法）を交えながら詳細に説明する。
本発明の表面処理鋼材は、図１に示すように、鋼材表面1Sから外面側に酸化物層２、同表面1Sから内面側に拡散層1Dを有する。鋼材１から拡散層1Dを除いた残りを母材部1Bと称する。
Hereinafter, the surface-treated steel material of the present invention will be described in detail with reference to its production method (steel material surface treatment method).
As shown in FIG. 1, the surface-treated steel material of the present invention has an oxide layer 2 on the outer surface side from the steel material surface 1S and a diffusion layer 1D on the inner surface side from the surface 1S. The remainder obtained by removing the diffusion layer 1D from the steel material 1 is referred to as a base material portion 1B.
酸化物層２は酸素を１０at.％以上含有し、モリブデン、タングステンの内１種または２種の元素、または、モリブデン、タングステンの内１種または２種の元素とバナジウム元素、（これら３元素を以下、効能元素と総称する）を合計で２０at.％以上含み、その厚さは１００ｎｍ〜１００μｍとされる。
拡散層1Dは酸素含有量が１０at.％未満であり、効能元素を含有し、その含有量（at.％）は鋼材表面1S近傍では酸化物層２中のそれと同程度、母材部1Bとの境界近傍では母材部1B中のそれと同程度であり、鋼材表面1Sから母材部1Bとの境界に向かうにつれて概ね単調に減少する。拡散層1Dの厚さは１００ｎｍ以上とされる。
Oxide layer 2 contains oxygen 10at.% Or more of molybdenum, one or two elements of tungsten, or molybdenum, one or two elements and vanadium element of tungsten, (these 3 elements (Hereinafter collectively referred to as “effective element” ), the total thickness is 20 at.% Or more, and the thickness is 100 nm to 100 μm.
Diffusion layer 1D has an oxygen content of less than 10 at.% And contains active elements, and its content (at.%) Is about the same as that in oxide layer 2 in the vicinity of steel surface 1S. In the vicinity of the boundary, it is approximately the same as that in the base material part 1B, and decreases substantially monotonically from the steel material surface 1S toward the boundary with the base material part 1B. The thickness of the diffusion layer 1D is 100 nm or more.
母材部1Bの組成において、効能元素の合計の含有量が２０at.％以上であると、拡散層1Dの形成が難しくなるため、素材としての鋼材１は、効能元素の合計の含有量が０at.％、または０at.％超２０at.％未満である組成の鋼材とされる。なお、製鋼コスト削減の観点からすれば、効能元素の鋼中含有量を可及的に低めた鋼材を素材とすることが好ましい。
モリブデン、タングステン、バナジウムは、モリブデン酸塩、タングステン酸塩、バナジウム酸塩として水溶液中に溶解するが、いずれも安定に存在できるｐＨ領域が酸性側であり、中性領域では酸化物として沈殿する特性を有している。従ってこれらの酸化物層を形成するためには、これら塩類の水溶液に浸漬する方法が良い。鋼材表面では、その腐食反応のカソード領域では酸性溶液であっても、水素の発生反応が起きるので、局部的にはｐＨが低下しうる。この状態で各酸塩が沈殿し、皮膜を生成する。従って鋼材をカソード側に分極することにより、より多量で、かつ効能元素密度の高い沈殿層を形成することができる。浸漬処理を施した場合には、鋼材側もアノード反応で溶解するので、鉄酸化物と効能元素酸化物の混合体からなる酸化物層が形成される。この酸化物層を、鋼材の耐食性の確保に資するためには、該酸化物中の効能元素の合計の濃度を２０at.％以上とする必要がある。
In the composition of the base material part 1B, if the total content of the effect elements is 20 at.% Or more, it becomes difficult to form the diffusion layer 1D. Therefore, the steel material 1 as the material has a total content of the effect elements of 0 at. Or a steel material having a composition of more than 0 at.% And less than 20 at.%. From the viewpoint of reducing the steelmaking cost, it is preferable to use a steel material in which the content of the effective element in the steel is as low as possible.
Molybdenum, tungsten, and vanadium dissolve in an aqueous solution as molybdate, tungstate, and vanadate, but the pH range where any of them can exist stably is on the acidic side, and precipitates as an oxide in the neutral region. have. Therefore, in order to form these oxide layers, a method of immersing in an aqueous solution of these salts is preferable. On the surface of the steel material, even if it is an acidic solution in the cathode region of the corrosion reaction, a hydrogen generation reaction occurs, so that the pH can be locally reduced. In this state, each acid salt precipitates to form a film. Accordingly, by polarizing the steel material to the cathode side, it is possible to form a precipitated layer having a larger amount and a higher effective element density. When the immersion treatment is performed, the steel material side is also dissolved by the anodic reaction, so that an oxide layer composed of a mixture of iron oxide and effective element oxide is formed. In order for this oxide layer to contribute to ensuring the corrosion resistance of the steel material, the total concentration of the effect elements in the oxide needs to be 20 at.% Or more.
また酸化物層の厚みについては、１００ｎｍ未満では耐食性の発現にいたらず、１００ｎｍ以上の厚みが必要である。一方、酸化物層の厚みは厚い方が耐食性が向上するが１００μｍ以上では効果がほぼ飽和に達するため、処理にかかる費用が嵩むだけとなるので１００μｍを上限とした。
次に鋼材表面1Sから内面側の拡散層1Dであるが、この拡散層1Dは、鋼材表面1Sに、効能元素の純物質を塗布、あるいはめっきや溶射、コールドスプレーなどを行い、その後加熱することで形成することができる。
As for the thickness of the oxide layer, if it is less than 100 nm, the corrosion resistance is not exhibited, and a thickness of 100 nm or more is necessary. On the other hand, the thicker the oxide layer, the better the corrosion resistance. However, when the thickness is 100 μm or more, the effect is almost saturated, and the cost for the treatment only increases. Therefore, the upper limit is set to 100 μm.
Next, the diffusion layer 1D from the steel surface 1S to the inner surface side is applied to the steel surface 1S by applying a pure substance of the active element, plating, spraying, cold spraying, etc., and then heating. Can be formed.
例えばモリブデンについては、鋼材表面にめっき厚２〜３μｍのモリブデンめっきを施し、その後鋼材を８００℃〜１２００℃に加熱し、その温度で数分〜数十分保持することにより鋼材表面から内面側にモリブデンの拡散層を形成することができる。この拡散層については、その厚さが１００ｎｍ未満では耐食性に与える影響は小さく、拡散層に含まれる効能元素が少ないため耐食性の持続がない。１００ｎｍ以上とすることで拡散層に含まれる効能元素の濃度が高く耐食性の持続が期待できる。 For example, for molybdenum, the steel surface is plated with molybdenum having a plating thickness of 2 to 3 μm, and then the steel is heated to 800 ° C. to 1200 ° C. and held at that temperature for several minutes to several tens of minutes from the steel surface to the inner surface side. A diffusion layer of molybdenum can be formed. With respect to this diffusion layer, if the thickness is less than 100 nm, the influence on the corrosion resistance is small, and since there are few active elements contained in the diffusion layer, the corrosion resistance does not continue. By setting the thickness to 100 nm or more, the concentration of the effective element contained in the diffusion layer is high, and it is expected that the corrosion resistance is maintained.
上述の酸化物層の形成方法（便宜上、方法Ａという）と拡散層の形成方法（便宜上、方法Ｂという）とは、全く別の方法であり、これらを同一装置内で実行することはできない。
一方、発明者らの検討によれば、液中でプラズマを発生させる方法を応用することで、拡散層と酸化物層とを同一装置内で形成することができる。これを便宜上、方法Ｃという。
The method for forming the oxide layer (referred to as method A for convenience) and the method for forming the diffusion layer (referred to as method B for convenience) are completely different methods and cannot be executed in the same apparatus.
On the other hand, according to the study by the inventors, the diffusion layer and the oxide layer can be formed in the same apparatus by applying a method of generating plasma in the liquid. This is referred to as Method C for convenience.
方法Ｃでは、効能元素を含む溶液中にプラズマを発生させることにより、溶液中の例えばモリブデン酸などの溶質が分解されて効能元素イオンを含むプラズマ状態になり、これが鋼材表面に接すると表面温度が上昇し、効能元素が鋼材表面から内面側に拡散できるので、効能元素の拡散層が鋼材表面から内面側に形成され、プラズマから鋼材表面を離せば、溶液中の各酸素酸塩により鋼材表面から外面側に効能元素を含む酸化層が形成される。 In Method C, plasma is generated in a solution containing an effect element, so that a solute such as molybdic acid in the solution is decomposed into a plasma state containing an effect element ion. As the effect element can diffuse from the steel surface to the inner surface side, a diffusion layer of the effect element is formed from the steel surface to the inner surface side, and if the steel surface is separated from the plasma, each oxyacid salt in the solution will cause An oxide layer containing an effect element is formed on the outer surface side.
液中でプラズマを発生させる方法としては、外部で発生させたプラズマを液中に導入したり、鋼材表面を陰極として、対極との間の放電現象による方法、鋼材表面に高出力のレーザーを照射するなどの方法が挙げられる。 As a method of generating plasma in the liquid, plasma generated externally is introduced into the liquid, or the steel surface is used as a cathode and a discharge phenomenon occurs between the counter electrode, and the surface of the steel is irradiated with a high-power laser. The method of doing etc. is mentioned.
以下、実施例を挙げて本発明をより具体的に説明する。
＜表面処理鋼材の作製＞
表面処理に供する素材には、mass％でＣ：0.09％，Ｓｉ：0.25％，Ｍｎ：0.7％，Ｐ：0.015％，Ｓ：0.036％，Ａｌ：0.025％を含有し残部Ｆｅおよび不可避的不純物からなる組成を有する鋼材を使用した。この鋼材はサイズを１００ｍｍ×５０ｍｍ×６ｍｍ厚とし、表面の黒皮を酸洗処理で除去した。
Hereinafter, the present invention will be described more specifically with reference to examples.
<Production of surface-treated steel>
The material used for the surface treatment contains mass: C: 0.09%, Si: 0.25%, Mn: 0.7%, P: 0.015%, S: 0.036%, Al: 0.025%, and the remainder from Fe and inevitable impurities A steel material having the following composition was used. The steel material had a size of 100 mm × 50 mm × 6 mm and the surface black skin was removed by pickling.
表面処理は、前記方法Ｃを用いて次の要領で行った。イオン交換水に、モリブデン酸塩、タングステン酸塩、バナジウム酸塩を単独で、または複数組み合わせて、所定濃度（表１に示す）となるように溶解した溶液を作製した。これら溶液中に鋼材を浸漬し、対極に鋼材と同サイズのカーボン電極を使用した。鋼材と対極の間を５ｍｍに設定し、両電極間に直流で４００Ｖ印加し、両電極間で放電を起こさせた。この状態で０〜１０分間（表１に示す）保持した。その後電圧印加を停止し、この状態で０〜１０分間（表１に示す）保持した。この保持の終了をもって表面処理の終了とした。 The surface treatment was performed using the method C in the following manner. A solution in which the molybdate, tungstate, and vanadate were singly or in combination in ion-exchanged water so as to have a predetermined concentration (shown in Table 1) was prepared. A steel material was immersed in these solutions, and a carbon electrode having the same size as the steel material was used as the counter electrode. The distance between the steel material and the counter electrode was set to 5 mm, and a DC voltage of 400 V was applied between both electrodes to cause discharge between both electrodes. This state was maintained for 0 to 10 minutes (shown in Table 1). Thereafter, voltage application was stopped, and this state was maintained for 0 to 10 minutes (shown in Table 1). The end of the holding was regarded as the end of the surface treatment.
この表面処理後の鋼材すなわち表面処理鋼材を溶液から取り出し、これを対象材として以下の調査を行った。
<酸化物層の厚さおよび拡散層の厚さの同定>
オージェ電子分光装置を使用し、アルゴンスパッタにて対象材の表面から原子エッチングを行い、深さ方向の効能元素の割合(at.％)を求めた。酸化物層は、酸素が１０at.％以上検出される領域として同定し、該領域における効能元素の平均割合を、酸化物層中の効能元素量とした。また、酸化物層の厚さは、鉄に対するエッチング時間とエッチング深さ（厚さ）の関係を表す検量線（これは予め求めてある）に基づいて同定した。
The steel material after the surface treatment, that is, the surface-treated steel material was taken out from the solution, and the following investigation was performed using this as a target material.
<Identification of oxide layer thickness and diffusion layer thickness>
Using an Auger electron spectrometer, atomic etching was performed from the surface of the target material by argon sputtering, and the ratio of effective elements in the depth direction (at.%) Was determined. The oxide layer was identified as a region where oxygen was detected at 10 at.% Or more, and the average ratio of the effective element in the region was defined as the amount of the effective element in the oxide layer. Further, the thickness of the oxide layer was identified based on a calibration curve (which has been obtained in advance) representing the relationship between the etching time for iron and the etching depth (thickness).
拡散層は、酸素が１０at.％未満の層として同定し、効能元素が検出される最大深さ（前記検量線に基づき同定される）を拡散層の厚さとした。
<耐食性の調査>
まず、前記対象材の初期重量を計測した。重量はｍｇ単位で小数点以下１桁まで測定した。この対象材に対し、耐食性調査面分として面積が８０ｍｍ×４０ｍｍ（＝３２００ｍｍ２）の矩形部分を設定し、残りの面は、腐食しないよう、シールテープでマスキングを行い、これを試験材とした。
The diffusion layer was identified as a layer having oxygen of less than 10 at.%, And the maximum depth (identified based on the calibration curve) at which an effective element was detected was defined as the thickness of the diffusion layer.
<Investigation of corrosion resistance>
First, the initial weight of the target material was measured. The weight was measured to the first decimal place in mg. For this target material, a rectangular portion with an area of 80 mm × 40 mm (= 3200 mm 2 ) was set as a corrosion resistance investigation surface, and the remaining surface was masked with seal tape so as not to corrode, and this was used as a test material. .
この試験材を、関東ローム層から採取した土を入れたビーカー内の土中（土容積：２００ｍｍΦ×２００ｍｍ高さ）に埋め込み、０．５mass％のＮａＣｌ水溶液を土に対して２０mass％添加した。これを３０℃の一定温度に保持された恒温室に静置した。その後１週間毎に土に対して１０mass％のイオン交換水を継ぎ足した。１８０日後に試験材を取り出し、水洗後皮膜を塗膜剥離剤で剥離し、塩酸中にインヒビターを入れた溶液でさび層を取り除いた後、試験材の重量をｍｇ単位で小数点以下１桁まで測定した。 This test material was embedded in the soil (soil volume: 200 mmΦ × 200 mm height) in a beaker containing soil collected from the Kanto Loam layer, and 20 mass% of 0.5 mass% NaCl aqueous solution was added to the soil. This was left still in a temperature-controlled room maintained at a constant temperature of 30 ° C. Thereafter, 10 mass% of ion exchange water was added to the soil every week. After 180 days, the test material is taken out, washed with water, the film is peeled off with a coating film remover, the rust layer is removed with a solution containing an inhibitor in hydrochloric acid, and the weight of the test material is measured to the first decimal place in mg. did.
腐食した耐食性調査面分に対し、初期重量と腐食試験後重量の差から以下の式で平均腐食厚さを求め、これでもって耐食性を評価した。その結果を表１に示す。
平均腐食厚さ［ｍｍ/１８０日］＝(初期重量−腐食試験後重量)［ｍｇ/１８０日］/(３２００ｍｍ２×７．８ｍｇ/ｍｍ３)
The average corrosion thickness was calculated from the difference between the initial weight and the weight after the corrosion test for the corroded corrosion resistance investigation surface, and the corrosion resistance was evaluated with this. The results are shown in Table 1.
Average corrosion thickness [mm / 180 days] = (initial weight−weight after corrosion test) [mg / 180 days] / (3200 mm 2 × 7.8 mg / mm 3 )
表１より、比較例に比べ本発明例はいずれも耐食性が向上している。 As shown in Table 1, the corrosion resistance of each of the inventive examples is improved as compared with the comparative example.
１ 鋼材
1B 母材部
1D 拡散層（モリブデン、タングステンの内１種または２種の元素を含む拡散層、またはモリブデン、タングステンの内１種または２種の元素とバナジウム元素を含む拡散層）
1S 鋼材表面
２ 酸化物層（モリブデン、タングステンの内１種または２種の元素を含む酸化物層、またはモリブデン、タングステンの内１種または２種の元素とバナジウム元素を含む酸化物層）
1 Steel
1B Base material part
1D diffusion layer (Mo Ribuden, diffusion layer comprising one or two elements of tungsten, or molybdenum, a diffusion layer comprising one or two elements and vanadium element of tungsten)
1S steel surface 2 oxide layer (Mo Ribuden, oxide layer comprising one or two elements of tungsten, or molybdenum, an oxide layer comprising one or two elements and vanadium element of tungsten)
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