JP2008163374A - Steel for bridge - Google Patents
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本発明は、海浜地域や融雪塩が散布される地域等で飛来塩分量が多い環境下でもミニマムメンテナンス材料として使用することができる、耐候性および耐塗装剥離性に優れた橋梁用鋼材と、この鋼材からなる橋梁に関する。 The present invention provides a steel material for bridges having excellent weather resistance and paint peeling resistance, which can be used as a minimum maintenance material even in an environment where the amount of incoming salt is large, such as in a beach area or an area where snow melting salt is sprayed. It relates to bridges made of steel.
一般に、耐候性鋼材は、それを大気腐食環境中に暴露すると、保護性のあるさび層が表面に形成され、それ以降の鋼材腐食が抑制されることにより耐候性を発揮する。そのため、耐候性鋼材は、塗装せずに裸のまま使用できるミニマムメンテナンス鋼材として、橋梁等の構造物に用いられている。 In general, when weathering steel is exposed to an atmospheric corrosive environment, a protective rust layer is formed on the surface, and the subsequent corrosion of steel is suppressed, thereby exhibiting weather resistance. Therefore, the weather-resistant steel is used for structures such as bridges as a minimum maintenance steel that can be used as it is without being painted.
ところが、海浜地域はもちろん、内陸部でも融雪塩や凍結防止剤が散布される地域のように飛来塩分量が多い環境下では、耐候性鋼材の表面に保護性のあるさび層が形成されにくく、腐食を抑制する効果が発揮されにくい。そのため、これらの地域では、裸のままの耐候性鋼材を用いることができず、塗装をして用いる必要があった。 However, not only in the beach area, but also in inland areas where snow melting salt and anti-freezing agents are sprayed, in environments where the amount of incoming salt is high, it is difficult to form a protective rust layer on the surface of weathering steel, It is difficult to exert the effect of suppressing corrosion. Therefore, in these areas, it is not possible to use the weather-resistant steel material as it is, and it is necessary to use it after painting.
日本工業規格（ＪＩＳ）で規格化された耐候性鋼（ＪＩＳ Ｇ３１１４：溶接構造用耐候性熱間圧延鋼材）においても、海浜地域のように飛来塩分量がＮａＣｌとして０.０５ｍｇ／ｄｍ2／ｄａｙ（０.０５ｍｄｄ）以上の地域では、ウロコ状錆や層状錆等の発生による腐食減量が大きいため、無塗装では使用できないことになっている（建設省土木研究所、（社）鋼材倶楽部、（社）日本橋梁建設協会：耐候性鋼の橋梁への適用に関する共同研究報告書（ＸＸ）−無塗耐候性橋梁の設計・施工要領（改訂版−１９９３.３）参照）。 Even in weathering steel standardized by Japanese Industrial Standards (JIS) (JIS G3114: weathering hot rolled steel for welded structures), the amount of incoming salt as NaCl is 0.05 mg / dm 2 / day as in the beach area. (0.05mdd) and higher areas have a large weight loss due to the occurrence of scale-like rust, layered rust, etc., so they cannot be used without painting (Ministry of Construction, Civil Engineering Research Institute, Steel Club, ( Japan Association for Bridge Construction: Joint Research Report on the Application of Weatherproof Steel to Bridges (XX)-Design and Construction Guidelines for Uncoated Weatherproof Bridges (Ref. Rev. 1993.3)).
このため、海浜地域などの塩分の多い環境下では、普通鋼材に塗装を施して使用する普通鋼の塗装使用が一般的である。しかし、河口付近の海浜地域に建設される橋梁や、融雪塩や凍結防止剤を撒く山間部等の道路に建設される橋梁では腐食が著しく、腐食による塗膜劣化のため、約１０年毎に再塗装する必要がある。これらの再塗装には多大な工数がかかり、維持管理に莫大な費用がかかることから、海浜地域においても無塗装で使用できる海浜耐候性に優れた鋼材への要望が強い。 For this reason, in a salty environment such as a beach area, it is common to use ordinary steel that is coated with ordinary steel. However, bridges constructed in the coastal area near the estuary, and bridges constructed in roads such as mountainous areas where snowmelt salt and anti-freezing agents are sprayed are extremely corroded, and the coating film deteriorates due to corrosion. It is necessary to repaint. Since these repaints require a great amount of man-hours and enormous costs for maintenance, there is a strong demand for steel materials with excellent beach weather resistance that can be used without painting even in beach areas.
最近、Ｎｉを１〜３％程度添加したＮｉ系高耐候性鋼が開発され、実用化されてきているが、このようなＮｉ添加だけでは、飛来塩分量が０.３〜０.４ｍｄｄを越える地域では適用が難しいことが判明している。 Recently, Ni-based high weathering steel with about 1 to 3% Ni added has been developed and put to practical use. However, the amount of incoming salt exceeds 0.3 to 0.4 mdd only with such addition of Ni. It has proven difficult to apply locally.
鋼材の腐食は、飛来塩分量が多くなるにつれて激しくなるため、耐食性と経済性の観点からは、飛来塩分量に応じた耐候性鋼材が必要になる。また、橋梁といっても、使用される場所や部位により、鋼材の腐食環境は異なる。例えば、桁外部では、降雨、結露水および日照に曝される。一方、桁内部では、結露水に曝されるが、雨掛かりはない。一般に、飛来塩分量が多い環境では、雨で洗われる桁外部より、雨掛かりのない桁内部の方が、腐食が激しいと言われている。 Since corrosion of steel materials becomes more severe as the amount of flying salt increases, a weather-resistant steel material corresponding to the amount of flying salt is required from the viewpoint of corrosion resistance and economy. Moreover, even if it is called a bridge, the corrosive environment of steel materials changes with places and parts used. For example, outside the girder, it is exposed to rainfall, condensed water and sunlight. On the other hand, inside the girders, they are exposed to condensed water, but there is no rain. In general, in an environment with a large amount of incoming salt, it is said that the inside of a girder without rain is more corrosive than the outside of the girder washed with rain.
また、融雪塩や凍結防止剤を道路に撒く環境では、その塩が走行中の車に巻き上げられ、道路を支える橋梁に付着し、厳しい腐食環境となる。さらに、海岸から少し離れた軒下等も厳しい塩害環境に曝され、このような地域では、飛来塩分量が１ｍｄｄ以上の厳しい腐食環境になる。 In addition, in an environment where snow melting salt or an antifreezing agent is sprayed on the road, the salt is wound up on a running car and adheres to a bridge that supports the road, resulting in a severe corrosive environment. Furthermore, the eaves under the eaves a little away from the coast are also exposed to severe salt damage environments, and in such areas, the amount of incoming salt becomes a severe corrosive environment with 1 mdd or more.
飛来塩分量が多い環境での腐食を防止する鋼材も従来から開発が進められてきた。 Steel materials that prevent corrosion in environments with a high amount of incoming salt have also been developed.
例えば、特許文献１ではクロム（Ｃｒ）の含有量を増加させた耐候性鋼材が、そして特許文献２ではニッケル（Ｎｉ）含有量を増加させた耐候性鋼材が、それぞれ提案されている。 For example, Patent Document 1 proposes a weather-resistant steel material having an increased chromium (Cr) content, and Patent Document 2 proposes a weather-resistant steel material having an increased nickel (Ni) content.
また、本発明者らは、先に特許文献３で、Ｃｕ、ＮｉおよびＣｒを複合して含有させた海浜耐候性を有する鋼材を提案している。 In addition, the present inventors have previously proposed a steel material having beach weather resistance in which Cu, Ni, and Cr are combined and contained in Patent Document 3.
そして、特許文献４には、Ｐ、Ｎｉ、Ｍｏ、ＳｂおよびＳｎ等を含有する溶接構造用鋼が、そして特許文献５にはＣｕ、ＮｉおよびＳｂを含有させた高耐候性鋼材が、それぞれ提案されている。 Patent Document 4 proposes a welded structural steel containing P, Ni, Mo, Sb and Sn, and Patent Document 5 proposes a highly weather-resistant steel material containing Cu, Ni and Sb, respectively. Has been.
さらに、特許文献６にはＣｕ、Ｎｉ、Ｃｒ、ＳｎおよびＳｂ等を含有することにより耐食性を向上させた耐酸露点腐食鋼が提案されており、煙突や熱交換器等における酸露点腐食に対し優れた耐食性を発揮している。 Furthermore, Patent Document 6 proposes an acid dew-point corrosion steel having improved corrosion resistance by containing Cu, Ni, Cr, Sn, Sb, etc., and is excellent against acid dew point corrosion in a chimney or a heat exchanger. Exhibits high corrosion resistance.
上記特許文献１で提案されたクロム（Ｃｒ）の含有量を増加させた耐候性鋼材は、ある程度以下の飛来塩分量の領域においては耐候性を改善することができるものの、それを超える厳しい塩分環境においては逆に耐候性を劣化させる。 The weather-resistant steel material with an increased chromium (Cr) content proposed in Patent Document 1 can improve the weather resistance in a region where the amount of incoming salt content is below a certain level, but it is a severe salt environment that exceeds that. In contrast, the weather resistance is deteriorated.
上記特許文献２で提案されたニッケル（Ｎｉ）含有量を増加させた耐候性鋼材の場合、耐候性はある程度改善されるが、鋼材自体のコストが高くなり、橋梁等の用途に使用される材料としては高価なものになる。これを避けるため、Ｎｉ含有量を少なくすると、耐候性はさほど改善されず、飛来塩分量が多い場合には、鋼材の表面に層状の剥離さびが生成し、腐食が著しく、長期間の使用に耐えられないという問題が生じる。 In the case of the weathering steel material with the increased nickel (Ni) content proposed in Patent Document 2, the weather resistance is improved to some extent, but the cost of the steel material itself increases, and the material is used for applications such as bridges. As an expensive thing. In order to avoid this, if the Ni content is reduced, the weather resistance will not be improved so much, and if the amount of incoming salt is high, layered peeling rust will form on the surface of the steel material, corrosion will be remarkable, and it will be used for a long time. The problem of being unbearable arises.
上記特許文献３で提案された、Ｃｕ、ＮｉおよびＣｒを複合して含有させた海浜耐候性を有する鋼材では、これらの元素を数％程度含有させることによって、ＪＩＳ耐候性鋼に比べれば耐候性を改善することができるものの、飛来塩分量が１ｍｄｄを超えるような非常に厳しい環境では十分な耐候性を発揮することができず、さらなる改善が必要である。 In the steel material having a beach weather resistance compounded with Cu, Ni and Cr, proposed in Patent Document 3, the weather resistance is higher than that of JIS weathering steel by containing about several percent of these elements. However, in a very severe environment where the amount of incoming salt exceeds 1 mdd, sufficient weather resistance cannot be exhibited, and further improvement is necessary.
上記特許文献４で提案された、Ｐ、Ｎｉ、Ｍｏ、ＳｂおよびＳｎ等を含有する溶接構造用鋼については、飛来塩分量の多い環境における耐候性を得るためにＰの含有量を多くしているため、溶接性が十分でない。 About the steel for welded structures containing P, Ni, Mo, Sb, Sn etc. proposed by the said patent document 4, in order to obtain the weather resistance in an environment with many amounts of incoming salt, P content is increased. Therefore, weldability is not sufficient.
上記特許文献５で提案された、Ｃｕ、ＮｉおよびＳｂを含有させた高耐候性鋼材は、飛来塩分量０.８ｍｄｄの環境において耐候性が良好であるとしているが、１ｍｄｄを超えるような厳しい腐食環境においては耐候性が十分でない。 The high weather resistance steel material containing Cu, Ni and Sb proposed in Patent Document 5 is said to have good weather resistance in an environment with an incoming salt content of 0.8 mdd, but severe corrosion exceeding 1 mdd. The weather resistance is not sufficient in the environment.
上記特許文献６で提案された、Ｃｕ、Ｎｉ、Ｃｒ、ＳｎおよびＳｂ等を含有することにより耐食性を向上させた耐酸露点腐食鋼は、煙突や熱交換器等における酸露点腐食に対し優れた耐食性を発揮するものの、飛来塩分量が１ｍｄｄを超えるような大気腐食環境において、耐候性は十分でない。 The acid dew-point corrosion steel proposed in Patent Document 6 and improved in corrosion resistance by containing Cu, Ni, Cr, Sn, Sb, etc. has excellent corrosion resistance against acid dew point corrosion in chimneys and heat exchangers. However, the weather resistance is not sufficient in an atmospheric corrosive environment where the amount of incoming salt exceeds 1 mdd.
さらに、橋梁分野における耐塗装剥離性が大きな問題である。すなわち上記示したように、多量の塩化物が飛来する海岸環境や、融雪剤や凍結防止剤を散布する環境においては、塗装を施しても塗装が早期に剥離し、且つ腐食が進行するという問題があり、数年から十数年毎に塗装の塗り替えを実施する必要がある。しかしながら、塗装の塗り替えを実施するためには、一度腐食した橋梁に足場を組んで再ブラスト処理を施す必要があるので多大なコストがかかる。そして、再ブラスト処理を施してもさびを完全に除去できるわけではなく、さびを完全には除去しきれていない鋼材上に再度、塗装しても、塗装寿命が著しく短くなる。 Furthermore, paint peeling resistance in the bridge field is a major problem. That is, as shown above, in coastal environments where a large amount of chlorides come in, or in environments where snow melting agents and antifreeze agents are sprayed, the problem is that the coating peels off early and corrosion proceeds. There is a need to repaint every few to a dozen years. However, in order to repaint the paint, it is necessary to assemble a scaffold on the once corroded bridge and perform a reblast treatment, which is very expensive. And even if it re-blasts, a rust cannot be removed completely, and even if it repaints on the steel material which has not removed rust completely, a coating life will become remarkably short.
したがって、塗装の寿命を延長し、補修塗装間隔を大きく延ばすことが強く望まれていた。すなわち、塗装が必要とされる橋梁においても、ライフサイクルコストのミニマム化の要求が高く、塗装寿命を延長することは橋梁のライフサイクルマネジメントを考える上で非常に重要となる。 Therefore, it has been strongly desired to extend the service life of the coating and greatly extend the interval between repair coatings. In other words, even for bridges that require painting, there is a high demand for minimizing the life cycle cost, and extending the life of painting is very important in considering bridge life cycle management.
本発明は、従来の鋼材が内包する上述のような問題を解決すべく、高塩化物環境において、耐候性および耐塗装剥離性に優れた橋梁用鋼材を提供することを目的とする。 An object of the present invention is to provide a steel material for bridges which is excellent in weather resistance and paint peeling resistance in a high chloride environment in order to solve the above-described problems included in conventional steel materials.
本発明者らの一人が既に報告しているように（「材料と環境」第４３巻（１９９４）第１号２６頁参照）、耐候性鋼材においてさび層が保護性を有するのは、Ｆｅの一部がＣｒで置換された微細なα−(Ｆｅ１−ｘＣｒｘ)ＯＯＨ からなるさび層が生成することによる。 As already reported by one of the present inventors (see “Materials and Environment”, Vol. 43 (1994), No. 1, p. 26), the rust layer has a protective property in the weathering steel. This is because a rust layer made of fine α- (Fe 1-x Cr x ) OOH partially substituted with Cr is formed.
しかし、前述したように、Ｃｒの添加は飛来塩分量が比較的少ない環境では耐候性の向上に有効であるが、飛来塩分量が多い環境では、逆に耐候性を劣化させる。一方、Ｎｉの添加は、飛来塩分量の多い地域での耐候性の向上に有効であるとされてきた。 However, as described above, the addition of Cr is effective in improving the weather resistance in an environment where the amount of incoming salt is relatively small, but in the environment where the amount of incoming salt is large, the weather resistance is deteriorated conversely. On the other hand, it has been considered that the addition of Ni is effective for improving the weather resistance in an area where the amount of incoming salt is large.
本発明者らは、これらの知見を踏まえて、飛来塩分量の多い環境での腐食について検討した結果、このような環境下では、ＦｅＣｌ３溶液の乾湿繰り返しが腐食の本質的な条件となり、Ｆｅ３＋の加水分解によりｐＨが低下した状態で、かつＦｅ３＋が酸化剤として作用することによって腐食が加速されることを見出した。 Based on these findings, the inventors of the present invention have studied corrosion in an environment with a large amount of incoming salt. As a result, in such an environment, repeated drying and wetting of the FeCl 3 solution becomes an essential condition for corrosion. It has been found that corrosion is accelerated when pH decreases due to hydrolysis of 3+ and Fe 3+ acts as an oxidizing agent.
このときの腐食反応は、以下に示すとおりである。 The corrosion reaction at this time is as follows.
カソード反応としては、主として、次の反応が起こる。
Ｆｅ３＋＋ｅ−→Ｆｅ２＋ (Ｆｅ３＋の還元反応)
そして、この反応以外にも、次のカソード反応も併発する。
２Ｈ２Ｏ＋Ｏ２＋２ｅ−→４ＯＨ−、
２Ｈ＋＋２ｅ−→Ｈ２
一方、上記のＦｅ３＋の還元反応に対して、次のアノード反応が起こる。
アノード反応：Ｆｅ→Ｆｅ２＋＋２ｅ− (Ｆｅの溶解反応)
As the cathode reaction, the following reaction mainly occurs.
Fe 3+ + e − → Fe 2+ (reduction reaction of Fe 3+ )
In addition to this reaction, the following cathode reaction also occurs.
2H 2 O + O 2 + 2e − → 4OH − ,
2H + + 2e − → H 2
On the other hand, the following anodic reaction occurs with respect to the above Fe 3+ reduction reaction.
Anode reaction: Fe → Fe 2+ + 2e − (Fe dissolution reaction)
従って、腐食の総括反応は、次の(1)式のとおりである。
２Ｆｅ３＋＋Ｆｅ→３Ｆｅ２＋ ・・・・・・(1)式
上記(1)式の反応により生成したＦｅ２＋は、空気酸化によってＦｅ３＋に酸化され、生成したＦｅ３＋は再び酸化剤として作用し、腐食を加速する。この際、Ｆｅ２＋の空気酸化の反応速度は低ｐＨ環境では一般に遅いが、濃厚塩化物溶液中では加速され、Ｆｅ３＋が生成され易くなる。このようなサイクリックな反応のため、飛来塩分量が非常に多い環境では、Ｆｅ３＋が常に供給され続け、鋼の腐食が加速され、耐食性が著しく劣化することになることが判明した。
Therefore, the overall reaction of corrosion is as shown in the following equation (1).
2Fe 3+ + Fe → 3Fe 2+ (1) Formula Fe 2+ generated by the reaction of the above formula (1) is oxidized to Fe 3+ by air oxidation, and the generated Fe 3+ acts as an oxidizing agent again. Accelerate corrosion. At this time, the reaction rate of air oxidation of Fe 2+ is generally slow in a low pH environment, but is accelerated in a concentrated chloride solution, and Fe 3+ is easily generated. It has been found that due to such a cyclic reaction, in an environment where the amount of incoming salt is very large, Fe 3+ is always supplied, corrosion of steel is accelerated, and corrosion resistance is significantly deteriorated.
このように、飛来塩分量が非常に多い環境では、さび層による保護は期待できないため、鋼自身のアノード溶解反応を遅くすることによって、鋼の腐食を遅らせるのが有効である。すなわち、飛来塩分量が非常に多い環境では、Ｃｒを含有する鋼はアノード溶解反応が促進されるため、耐候性が劣化すると推測されるのに対して、Ｎｉを含有する鋼はアノード溶解反応を遅延させるので耐候性が向上することが期待できる。 Thus, in an environment where the amount of incoming salt is very high, protection by the rust layer cannot be expected. Therefore, it is effective to delay the corrosion of the steel by slowing the anodic dissolution reaction of the steel itself. That is, in an environment where the amount of flying salt is very large, it is presumed that the steel containing Cr accelerates the anodic dissolution reaction, so that the weather resistance deteriorates, whereas the steel containing Ni does not perform the anodic dissolution reaction. Since it is delayed, it can be expected that the weather resistance is improved.
上述の塩分環境における腐食のメカニズムを基に、種々の合金元素の耐候性への影響について検討した結果、下記の（ａ）〜（ｉ）に示す知見を得た。 As a result of examining the influence of various alloy elements on the weather resistance on the basis of the mechanism of corrosion in the above-described salinity environment, the following findings (a) to (i) were obtained.
（ａ）Ｓｎは、Ｓｎ２＋として溶解し、２Ｆｅ３＋＋Ｓｎ２＋→２Ｆｅ２＋＋Ｓｎ４＋なる反応によりＦｅ３＋の濃度を低下させることで、(1)式の反応を抑制する。Ｓｎには、さらにアノード溶解を抑制するという作用もある。 (A) Sn dissolves as Sn 2+, by lowering the concentration of Fe 3+ by 2Fe 3+ + Sn 2+ → 2Fe 2+ + Sn 4+ becomes reactions, (1) inhibit the reaction of formula. Sn also has an effect of suppressing anodic dissolution.
（ｂ）Ｃｕは、従来から飛来塩分の多い環境において耐食性改善効果の基本とされていた元素であり、比較的濡れ時間が長い環境において耐食性改善効果は見られる。しかしながら、塩化物濃度がさらに大きくなり、局部的にｐＨが下がるような環境、例えば塩分が付着し、湿度が変化することにより乾湿が繰り返され、β−ＦｅＯＯＨが生成するような比較的ドライな環境では、Ｃｕはむしろ腐食を促進することを知見した。 (B) Cu is an element that has conventionally been regarded as the basis for the effect of improving the corrosion resistance in an environment where the amount of flying salt is high, and the effect of improving the corrosion resistance is seen in an environment having a relatively long wet time. However, an environment where the chloride concentration is further increased and the pH is locally lowered, for example, a relatively dry environment in which salt is attached and the humidity is changed, resulting in repeated drying and wetting to produce β-FeOOH. Then, it was found that Cu rather promotes corrosion.
図１は、塩分付着乾湿試験結果例である。本実験は、Ｆｅ−０．０５Ｃ鋼の表面に、予め塩分付着量が１０ｍｇ／ｃｍ２になるように塩水を塗布し、４０℃ 恒温高湿槽内において、４時間４０％ＲＨ（相対湿度４０％）、４時間８０％ＲＨ（相対湿度８０％）を１サイクルとして繰り返し、３０サイクル後に再度１０ｍｇ／ｃｍ２になるように塩水を塗布し、さらに３０サイクル、合計６０サイクル実施した後のＦｅ−０．０５Ｃ鋼の腐食量の変化を鋼中のＣｕ含有量で整理したものである。 FIG. 1 is an example of a result of a salt adhesion drying / wetting test. In this experiment, salt water was applied to the surface of Fe-0.05C steel in advance so that the amount of salt adhered was 10 mg / cm 2, and 40% RH (relative humidity 40 %) 4 hours 80% RH (relative humidity 80%) was repeated as one cycle, and after 30 cycles, salt water was applied again to 10 mg / cm 2 , and after 30 cycles, a total of 60 cycles, Fe- The change in the corrosion amount of 0.05C steel is organized by the Cu content in the steel.
（ｃ）さらに、ＮｉはＳｎと複合添加した場合には、飛来塩分の多い環境における耐食性改善効果が無く、多量に添加すると、逆に耐候性を劣化させることが判明した。このＮｉの挙動は、Ｎｉ添加量が増すほど耐候性が向上するという従来の知見とは相反するものである。 (C) Furthermore, when Ni is added in combination with Sn, it has been found that there is no effect of improving the corrosion resistance in an environment with a large amount of incoming salt, and if it is added in a large amount, the weather resistance is deteriorated. This behavior of Ni is contrary to the conventional knowledge that weather resistance improves as the amount of Ni added increases.
（ｄ）Ｃｒは、単独添加した場合には、飛来塩分量の多い環境において耐候性を劣化させるが、Ｓｎと複合添加した場合には、飛来塩分量の多い環境での耐候性を向上させる効果を発揮する。 (D) When Cr is added alone, it degrades the weather resistance in an environment with a large amount of incoming salt, but when combined with Sn, Cr improves the weather resistance in an environment with a large amount of incoming salt. Demonstrate.
（ｅ）Ａｌを含有させると海浜耐候性が向上する。 (E) When Al is contained, the beach weather resistance is improved.
（ｆ）Ｎはアンモニアとして溶解し、腐食界面のｐＨを上昇させる作用を有する。飛来塩分量の多い環境では、上記Ｆｅ３＋の加水分解によりｐＨが低下するが、Ｎを含有させることにより、腐食界面のｐＨ低下が抑制され、耐候性および塗膜剥離性が向上する。 (F) N dissolves as ammonia and has the effect of raising the pH of the corrosion interface. In an environment with a large amount of incoming salt, the pH decreases due to the hydrolysis of the Fe 3+ , but the inclusion of N suppresses the pH decrease at the corrosion interface and improves the weather resistance and the coating film peelability.
（ｇ）上記（ａ）〜（ｆ）で述べた合金元素を含有させた材料に、さらに、Ｔｉ、Ｎｂ、Ｍｏ、Ｗ、Ｖ、ＣａおよびＭｇから選んだ１種または２種以上を含有させても、海浜耐候性の改善に効果がある。 (G) The material containing the alloy elements described in the above (a) to (f) further contains one or more selected from Ti, Nb, Mo, W, V, Ca and Mg. However, it is effective in improving beach weather resistance.
（ｈ）さらに、ＲＥＭを含有させると、鋼材の溶接性が改善される。 (H) Furthermore, when REM is contained, the weldability of the steel material is improved.
（ｉ）これらの海浜耐候性に優れた橋梁用鋼材は、表面を防食皮膜で被覆してもよく、塗装寿命延長化に効果が大きい。 (I) These steel materials for bridges excellent in beach weather resistance may be coated on the surface with an anticorrosive film, and are highly effective in extending the coating life.
本発明は、上記の知見に基づきなされたもので、その要旨は、次の(1)〜(6)の橋梁用鋼材と、(7)の橋梁にある。以下、総称して、本発明ということがある。 The present invention has been made on the basis of the above findings, and the gist thereof is the following steel materials for bridges (1) to (6) and the bridge (7). Hereinafter, the present invention may be collectively referred to as the present invention.
本発明の橋梁用鋼材は、飛来塩分量が多い環境下においても十分な耐候性を有している。海浜耐候性に優れた材料として最適であり、海浜地域における橋梁等の構造物や、融雪塩や凍結防止剤が散布される地域における橋梁等の構造物に使用するミニマムメンテナンス材料として、土木および建築分野等において広く適用することができる。さらに、塗装を施して、船舶や橋梁等の鋼構造物に使用した場合に、欠陥部等からの腐食を著しく抑制するためメンテナンスミニマム化に寄与する材料として広く適用することができる。 The steel for bridges of the present invention has sufficient weather resistance even in an environment with a large amount of incoming salt. Civil engineering and construction as a minimum maintenance material that is ideal as a material with excellent beach weather resistance and used for structures such as bridges in beach areas and structures such as bridges in areas where snowmelt salt and antifreezing agents are applied. It can be widely applied in fields. Furthermore, when coated and used for steel structures such as ships and bridges, it can be widely applied as a material that contributes to maintenance minimization because it significantly suppresses corrosion from defects and the like.
以下に、本発明の橋梁用鋼材に含まれる合金元素の作用効果を、その含有量の限定理由とともに、説明する。なお、合金元素の含有量「％」は、いずれも「質量％」を意味する。 Below, the effect of the alloy element contained in the steel material for bridges of this invention is demonstrated with the reason for limitation of the content. The alloy element content “%” means “mass%”.
Ｃ：０.００１〜０.１５％
Ｃは、鋼の強度を確保するために必要な合金元素であるが、多量に含有させると鋼材の溶接性が劣化する。したがって、Ｃ含有量は０.１５％を上限とする。また、０.００１％未満になると所定の強度が確保できないので、下限は０.００１％とする。望ましい範囲は、０.００５％〜０.１５％である。
C: 0.001 to 0.15%
C is an alloying element necessary for ensuring the strength of steel, but if contained in a large amount, the weldability of the steel material deteriorates. Therefore, the upper limit of the C content is 0.15%. Further, if the content is less than 0.001%, a predetermined strength cannot be secured, so the lower limit is made 0.001%. A desirable range is 0.005% to 0.15%.
Ｓｉ：２.５％以下
Ｓｉは、製鋼時の脱酸に必要な合金元素である。同じく脱酸剤としての働きをするＡｌを含有する場合には、特に添加をしなくてもよいが、Ａｌ含有量が０．００５％未満の場合には、０.４％以上含有させるのが望ましい。一方、Ｓｉを２.５％を超えて含有させると、鋼の靱性が損なわれる。したがって、Ｓｉの含有量は２.５％以下とする。また、Ｓｉには耐候性を向上させる効果もある。この効果を得たい場合には、０．１％以上添加するのが好ましい。
Si: 2.5% or less Si is an alloy element necessary for deoxidation during steelmaking. Similarly, when Al is included which acts as a deoxidizer, it is not particularly necessary to add it. However, when the Al content is less than 0.005%, it is necessary to contain 0.4% or more. desirable. On the other hand, if the Si content exceeds 2.5%, the toughness of the steel is impaired. Therefore, the Si content is 2.5% or less. Si also has the effect of improving weather resistance. In order to obtain this effect, it is preferable to add 0.1% or more.
Ｍｎ：０.５％を超え２.５％以下
Ｍｎは、低コストで鋼の強度を高める作用効果を有する元素であり、鋼中のＳの含有量が低い場合には、一般に高飛来塩分環境における耐候性を向上させる作用を有する。しかしながら、鋼中のＳと結合してＭｎＳを形成し、このＭｎＳが腐食の起点となり、耐食性、ひいては耐候性を劣化させる。また、機構は不明であるが、Ｎｉと共存する場合にはＭｎの含有量が２.５％を超えると耐候性が劣化する。したがって、Ｍｎの含有量は２.５％以下とする。望ましくは１.５％以下とする。なお、構造用鋼としての強度を維持するためには、Ｍｎを０.５％を超えて含有させる必要がある。
Mn: more than 0.5% and not more than 2.5% Mn is an element that has the effect of increasing the strength of steel at low cost. When the content of S in steel is low, it is generally a high-flying salinity environment. Has the effect of improving the weather resistance. However, it combines with S in steel to form MnS, and this MnS becomes a starting point of corrosion, which deteriorates the corrosion resistance and consequently the weather resistance. Further, the mechanism is unknown, but when it coexists with Ni, the weather resistance deteriorates when the Mn content exceeds 2.5%. Therefore, the Mn content is 2.5% or less. Desirably, it is 1.5% or less. In addition, in order to maintain the strength as structural steel, it is necessary to contain Mn exceeding 0.5%.
Ｐ：０.０３％未満
Ｐは、不純物として含有されるが、濃厚塩化物環境での過度のＰの含有は耐候性を劣化させるため、できるだけ少なくする必要がある。したがって、その含有量は０.０３％未満とする。
P: Less than 0.03% P is contained as an impurity, but excessive P content in a concentrated chloride environment deteriorates the weather resistance, so it is necessary to reduce it as much as possible. Therefore, the content is made less than 0.03%.
Ｓ：０.００５％以下
Ｓは、不純物として含有されるが、Ｍｎと結合すると非金属介在物のＭｎＳを形成して腐食の起点となり易く、耐候性を劣化させる。したがって、Ｓの含有はできるだけ少なくする必要があるので、その上限は０.００５％とする。
S: 0.005% or less Although S is contained as an impurity, when it is combined with Mn, it forms MnS of non-metallic inclusions, which tends to be a starting point of corrosion, and deteriorates weather resistance. Accordingly, the S content needs to be as small as possible, so the upper limit is made 0.005%.
Ｃｕ：０.０５％未満
Ｃｕは、一般的に耐候性を向上させる基本元素とされ、全ての海浜耐候性鋼や耐食鋼に添加されているが、高飛来塩分下の比較的ドライな環境においては、むしろ耐食性を低下させる。したがって、Ｃｕの含有はできるだけ少なくする必要があり、不純物として含有されるとしても、Ｃｕ含有量は０.０５％未満とする必要がある。
Cu: Less than 0.05% Cu is generally regarded as a basic element for improving weather resistance, and is added to all beach weather resistant steels and corrosion resistant steels. However, in a relatively dry environment under high flying salt content. Rather, it reduces the corrosion resistance. Therefore, it is necessary to reduce the Cu content as much as possible, and even if it is contained as an impurity, the Cu content needs to be less than 0.05%.
Ｎｉ：０.０５％未満
Ｎｉは、一般的に飛来塩分量の多い環境下での海浜耐候性を著しく向上させる元素として従来から鋼中に添加され、Ｎｉ系耐候性鋼として開発・実用化されてきている。しかし、理由は定かではないが、Ｓｎと複合添加した場合には、耐食性の改善効果がないばかりか、Ｓｎによる耐候性改善効果を低下させるという悪影響が現れる。したがって、Ｎｉの含有はできるだけ少なくする必要があり、不純物として含有されるとしても、Ｎｉ含有量は０.０５％未満とする必要がある。
Ni: Less than 0.05% Ni is conventionally added to steel as an element that significantly improves beach weather resistance in environments with a large amount of incoming salt, and has been developed and put into practical use as Ni-based weather-resistant steel. It is coming. However, although the reason is not clear, when it is added in combination with Sn, there is not only an effect of improving the corrosion resistance but also an adverse effect of reducing the effect of improving the weather resistance by Sn. Therefore, it is necessary to reduce the Ni content as much as possible, and even if it is contained as an impurity, the Ni content needs to be less than 0.05%.
Ｃｒ：０.０１〜３.０％
Ｃｒは、飛来塩分量がそれほど多くない環境では保護性さびの形成による耐食性の向上が期待できるが、飛来塩分量が多い環境において鋼のアノード溶解反応を促進し耐候性を劣化させる。
Cr: 0.01 to 3.0%
Cr can be expected to improve the corrosion resistance due to the formation of protective rust in an environment where the amount of flying salt is not so large, but it promotes the anodic dissolution reaction of steel and degrades the weather resistance in an environment where the amount of flying salt is large.
ところが、Ｓｎを含有する場合には、飛来塩分量が多い環境においても、Ｃｒ含有による耐候性の向上効果が発揮される。この効果は含有量０.０１％以上で発揮されるが、３.０％を超えると局部腐食感受性が高まるとともに、溶接性が劣化する。したがって、Ｃｒ含有量は０.０１〜３.０％とする必要がある。なお、Ｃｒの含有量の望ましい範囲は０.０５〜１.０％である。 However, when Sn is contained, the effect of improving weather resistance due to the Cr content is exhibited even in an environment with a large amount of incoming salt. This effect is exhibited when the content is 0.01% or more. However, if the content exceeds 3.0%, the local corrosion susceptibility increases and weldability deteriorates. Therefore, the Cr content needs to be 0.01 to 3.0%. In addition, the desirable range of Cr content is 0.05 to 1.0%.
Ａｌ：０.００３〜０．１％
Ａｌは、０.００３％以上含有させると耐候性が向上するが、含有量が０．１％を超えると鋼が脆化し易くなる。したがって、Ａｌの含有量の上限は０．１％とする。
Al: 0.003-0.1%
When Al is contained in an amount of 0.003% or more, the weather resistance is improved. However, if the content exceeds 0.1%, the steel is easily embrittled. Therefore, the upper limit of the Al content is 0.1%.
Ｎ：０.００１〜０.１％
Ｎは、アンモニアとなって溶解し、飛来塩分量の多い環境におけるＦｅ３＋の加水分解によるｐＨ低下を抑制することで、塩分環境における耐候性を向上させる効果を有する。この効果はＮを０.００１％以上含有させることにより得られ、０.１％を超えると飽和する。したがって、Ｎの含有量は０.００１〜０.１％とする。含有量の望ましい範囲は０.００２〜０.０８％である。
N: 0.001 to 0.1%
N dissolves as ammonia and has an effect of improving the weather resistance in a salt environment by suppressing the pH drop due to the hydrolysis of Fe 3+ in an environment with a large amount of incoming salt. This effect is obtained by containing 0.001% or more of N, and is saturated when it exceeds 0.1%. Therefore, the N content is set to 0.001 to 0.1%. A desirable range of the content is 0.002 to 0.08%.
Ｓｎ：０.０３〜０.５０％
Ｓｎは、Ｓｎ２＋となって溶解し、酸性塩化物溶液中でのインヒビター作用により腐食を抑制する作用を有する。また、Ｆｅ３＋を速やかに還元させ、酸化剤としてのＦｅ３＋濃度を低減する作用を有することにより、Ｆｅ３＋の腐食促進作用を抑制するので、高飛来塩分環境における耐候性を向上させる。
Sn: 0.03 to 0.50%
Sn dissolves as Sn 2+ and has an action of inhibiting corrosion by an inhibitor action in an acidic chloride solution. Further, rapidly to reduce the Fe 3+, by have the effect of reducing the Fe 3+ concentration of the oxidizing agent, since inhibit corrosion promoting effect of Fe 3+, thereby improving the weather resistance in high airborne salt environments.
また、Ｓｎには鋼のアノード溶解反応を抑制し耐食性を向上させる作用がある。さらに、Ｓｎを含有することにより、飛来塩分が多い環境においてもＣｒの耐候性を向上させる効果が発揮される。 Moreover, Sn has the effect | action which suppresses the anodic dissolution reaction of steel and improves corrosion resistance. Furthermore, by containing Sn, the effect of improving the weather resistance of Cr is exhibited even in an environment with a large amount of incoming salt.
これらの作用は、Ｓｎを０．０３％以上含有させることにより得られ、０.５０％を超えると飽和する。したがって、Ｓｎの含有量は０.０３〜０.５０％とする。Ｓｎの含有量の望ましい範囲は０．０３〜０．２０％である。 These effects are obtained by containing 0.03% or more of Sn, and saturate when it exceeds 0.50%. Therefore, the Sn content is set to 0.03 to 0.50%. A desirable range of the Sn content is 0.03 to 0.20%.
Ｃｕ／Ｓｎ比：１以下
本願発明のようにＳｎを含有する鋼の場合には、Ｃｕの含有による耐食性の低下が著しい。また、鋼材を製造する際、Ｃｕの含有による圧延割れの原因ともなる。このため、Ｃｕ／Ｓｎ比、すなわち、Ｓｉ含有量に対するＣｕ含有量の比を１以下とする必要がある。
Cu / Sn ratio: 1 or less In the case of steel containing Sn as in the present invention, the deterioration of corrosion resistance due to the inclusion of Cu is remarkable. Moreover, when manufacturing steel materials, it becomes a cause of the rolling crack by inclusion of Cu. For this reason, it is necessary to make Cu / Sn ratio, ie, ratio of Cu content with respect to Si content 1 or less.
本発明の橋梁用鋼材は、上記の合金元素の他に、さらにＴｉ、Ｎｂ、Ｍｏ、Ｗ、Ｖ、ＣａおよびＭｇよりなる群から選ばれた１種または２種以上を含有してもよいし、また、ＲＥＭを含有してもよい。これらの元素の含有させてもよい理由とそのときの含有量は、次の通りである。 The steel for bridges of the present invention may further contain one or more selected from the group consisting of Ti, Nb, Mo, W, V, Ca and Mg in addition to the above alloy elements. Moreover, you may contain REM. The reason why these elements may be contained and the contents at that time are as follows.
Ｔｉ：０.３％以下
Ｔｉは、ＴｉＣを形成してＣを固定することによって、クロム炭化物の形成を抑制して耐候性を向上させる。また、ＴｉＳの形成によりＳを固定することによって、腐食の起点となるＭｎＳの形成を抑える。
Ti: 0.3% or less Ti forms TiC and fixes C, thereby suppressing the formation of chromium carbide and improving weather resistance. Further, by fixing S by forming TiS, formation of MnS that becomes a starting point of corrosion is suppressed.
しかしながら、Ｔｉの含有量が０.３％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は０．３％とする。なお、この効果を確実に発現させるために、Ｔｉを０.０１％以上含有させるのが好ましい。 However, if the Ti content exceeds 0.3%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 0.3%. In addition, in order to express this effect reliably, it is preferable to contain Ti 0.01% or more.
Ｎｂ：０.１％以下
Ｎｂには、Ｔｉと同様、ＮｂＣを形成することによって、クロム炭化物の形成を抑制して耐候性を向上させる効果がある。
Nb: 0.1% or less Nb, like Ti, has the effect of suppressing the formation of chromium carbide and improving the weather resistance by forming NbC.
しかしながら、Ｎｂの含有量が０.１％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は０．１％とする。なお、この効果を確実に発現させるために、Ｎｂを０.０１％以上含有させるのが好ましい。 However, if the Nb content exceeds 0.1%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is 0.1%. In addition, in order to express this effect reliably, it is preferable to contain Nb 0.01% or more.
Ｍｏ：１.０％以下
Ｍｏは、溶解して酸素酸イオンＭｏＯ４ ２−の形でさびに吸着し、さび層中の塩化物イオンの透過を抑制し、耐食性を向上させる効果がある。
Mo: 1.0% or less Mo dissolves and is adsorbed on rust in the form of oxyacid ions MoO 4 2− , and suppresses transmission of chloride ions in the rust layer, thereby improving the corrosion resistance.
しかしながら、Ｍｏの含有量が１．０％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は１．０％とする。なお、この効果を確実に発現させるために、Ｍｏを０.０１％以上含有させるのが好ましい。 However, if the Mo content exceeds 1.0%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to express this effect reliably, it is preferable to contain Mo 0.01% or more.
Ｗ：１.０％以下
Ｗは、Ｍｏと同様、溶解して酸素酸イオンＭｏＯ４ ２−の形でさびに吸着し、さび層中の塩化物イオンの透過を抑制し、耐食性を向上させる効果がある。
W: 1.0% or less W, like Mo, dissolves and adsorbs to rust in the form of oxygenate ion MoO 4 2− , suppresses permeation of chloride ions in the rust layer, and improves corrosion resistance. There is.
しかしながら、Ｗの含有量が１．０％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は１．０％とする。なお、この効果を確実に発現させるために、Ｗを０.０１％以上含有させるのが好ましい。 However, if the W content exceeds 1.0%, this effect is saturated, and the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to express this effect reliably, it is preferable to contain 0.01% or more of W.
Ｖ：１.０％以下
Ｖは、ＭｏやＷと同様、溶解して酸素酸イオンＭｏＯ４ ２−の形でさびに吸着し、さび層中の塩化物イオンの透過を抑制し、耐食性を向上させる効果がある。
V: 1.0% or less V, like Mo and W, dissolves and adsorbs to rust in the form of oxyacid ion MoO 4 2- , suppresses the permeation of chloride ions in the rust layer, and improves corrosion resistance. There is an effect to make.
しかしながら、Ｖの含有量が１．０％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は１．０％とする。なお、この効果を確実に発現させるために、Ｖを０.０１％以上含有させるのが好ましい。 However, if the V content exceeds 1.0%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is 1.0%. In addition, in order to express this effect reliably, it is preferable to contain V 0.01% or more.
Ｃａ：０.１％以下
Ｃａは、鋼中に酸化物の形で存在し、腐食反応部における界面のｐＨの低下を抑制して、腐食の促進を抑える効果がある。
Ca: 0.1% or less Ca is present in the form of oxide in steel, and has an effect of suppressing the promotion of corrosion by suppressing the decrease in pH at the interface in the corrosion reaction part.
しかしながら、Ｃａの含有量が０．１％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は０．１％とする。なお、この効果を確実に発現させるために、Ｃａを０.０００１％以上含有させるのが好ましい。 However, when the Ca content exceeds 0.1%, not only this effect is saturated, but also the cost of the steel material increases, so the upper limit of the content is set to 0.1%. In addition, in order to express this effect reliably, it is preferable to contain 0.0001% or more of Ca.
Ｍｇ：０.１％以下
Ｍｇは、Ｃａと同様、腐食反応部における界面のｐＨの低下を抑制し、耐食性を向上させる効果がある。
Mg: 0.1% or less Mg, like Ca, has the effect of suppressing the decrease in pH at the interface in the corrosion reaction part and improving the corrosion resistance.
しかしながら、Ｍｂの含有量が０．１％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は０．１％とする。なお、この効果を確実に発現させるために、Ｍｇを０.０００１％以上含有させるのが好ましい。 However, if the Mb content exceeds 0.1%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is set to 0.1%. In addition, in order to express this effect reliably, it is preferable to contain 0.0001% or more of Mg.
ＲＥＭ：０.０２％以下
ＲＥＭは、鋼の溶接性を向上させる目的で含有させることができる。
REM: 0.02% or less REM can be contained for the purpose of improving the weldability of steel.
しかしながら、ＲＥＭの含有量が０．０２％を超えると、この効果が飽和するだけでなく、鋼材のコストが上昇するので、その含有量の上限は０．０２％とする。なお、この効果を確実に発現させるために、ＲＥＭを０.０００１％以上含有させるのが好ましい。なお、ＲＥＭとは、ランタニドの１５元素にＹおよびＳｃを合わせた１７元素を意味する。 本発明の橋梁用鋼材は、上記の必須元素あるいはさらに上記の任意元素を含有し、残部がＦｅおよび不純物からなる鋼材である。なお、鋼中にオキサイド等の介在物が微細分散されている鋼も本発明の橋梁用鋼材に含まれる。 However, if the content of REM exceeds 0.02%, this effect is not only saturated, but the cost of the steel material increases, so the upper limit of the content is 0.02%. In addition, in order to express this effect reliably, it is preferable to contain 0.0001% or more of REM. Note that REM means 17 elements in which Y and Sc are combined with 15 elements of lanthanide. The steel material for bridges of the present invention is a steel material that contains the above essential elements or further the above optional elements, and the balance being Fe and impurities. Note that steel in which inclusions such as oxide are finely dispersed in steel is also included in the steel for bridges of the present invention.
本発明の橋梁用鋼材は、板材、管材、棒材、Ｈ型鋼などの異形材を含む多様な形状とすることができる。厚みは一般に３ｍｍ以上とすることが好ましい。耐候性鋼材は一般に熱間圧延材であるが、本発明の橋梁用鋼材を製造する際の熱間圧延条件は特に制限されず、通常と同様でよい。 The steel material for bridges of the present invention can have various shapes including deformed materials such as plate materials, pipe materials, bar materials, and H-shaped steel. In general, the thickness is preferably 3 mm or more. The weathering steel is generally a hot rolled material, but the hot rolling conditions for producing the bridge steel of the present invention are not particularly limited, and may be the same as usual.
本発明の橋梁用鋼材は、さらに耐候性を高める場合には、その表面を防食皮膜で覆うのが望ましい。本発明において用いる防食皮膜とは、鋼材の防食目的で施される皮膜を意味する。具体的には、耐候性鋼材において周知の各種のさび安定化処理皮膜（化成処理系と塗装系とを含む）；Ｚｎめっき、Ａｌめっき、Ｚｎ−Ａｌめっき等の防食めっき皮膜；Ｚｎ溶射、Ａｌ溶射等の金属溶射皮膜；ビニルブチラール系、エポキシ系、ウレタン系、フタル酸系などの一般の防食塗装皮膜、さらにいわゆるＣ系塗装系、I系塗装系等を包含する。いずれの防食皮膜を施した場合であっても、優れた耐候性と高い防食性能を発揮することができる。これらの防食皮膜の膜厚または付着量は特に制限されず、通常の範囲内でよい。さらに本橋梁用鋼材は、さび付き鋼材、すなわち補修時に表面さびが除去しきれない状況で、特に塗装部耐食性を発揮するので、ケレン等でさびを完全に除去出来ない場合、例えば電動工具、ワイヤーブラシによるケレン程度で上記塗装を施しても著しく寿命を延長することができる。これは、塗装した場合に、キズ部がアノードと成りやすく、特にさび付き状態で塗装する場合に、局部的にｐＨが低下する現象が顕著になるために、本橋梁用鋼材の性能が発揮されるものと考えられる。 When further improving the weather resistance, it is desirable to cover the surface of the steel material for bridges of the present invention with an anticorrosive film. The anticorrosion film used in the present invention means a film applied for the purpose of anticorrosion of steel materials. Specifically, various types of rust stabilization coatings (including a chemical conversion treatment system and a coating system) well-known in weathering steel materials; anticorrosion plating coatings such as Zn plating, Al plating, Zn-Al plating; Zn spraying, Al Metal spray coatings such as thermal spraying; general anticorrosion coatings such as vinyl butyral, epoxy, urethane, and phthalic acid, and so-called C coating and I coating systems. Even when any anticorrosion film is applied, excellent weather resistance and high anticorrosion performance can be exhibited. The film thickness or adhesion amount of these anticorrosion films is not particularly limited, and may be within a normal range. Furthermore, the steel for this bridge is rusted steel, that is, the surface rust cannot be completely removed during repair, and especially exhibits the corrosion resistance of the painted part. Even if the above-mentioned coating is applied with a degree of cleansing with a brush, the service life can be extended significantly. This is because when scratches are applied, the scratches tend to become anodes, and particularly when painting in a rusted state, the phenomenon of local drop in pH becomes prominent, so the performance of this steel for bridges is demonstrated. It is thought that.
上述の通り、本発明の橋梁用鋼材は、飛来塩分量が多い環境下において優れた海浜耐候性を発揮するので、海浜地域における橋梁等、そして融雪塩や凍結防止剤が散布される地域における橋梁等の構造物に、塗装を必要としないミニマムメンテナンス材料として使用することができる。さらに、塗装を施す場合には、塗装部の耐剥離性・キズ部耐食性を著しく向上させることができ、ライフサイクルコスト低減に寄与する。この種の構造物は、一般に切断、曲げ加工等の成形加工、および溶接により作製されるが、本発明の橋梁用鋼材は加工性および溶接性にも優れている。 As described above, the steel for bridges of the present invention exhibits excellent beach weather resistance in an environment with a large amount of incoming salt, so bridges in beach areas, and bridges in areas where snowmelt salt and antifreeze are sprayed It can be used as a minimum maintenance material that does not require painting. Furthermore, when coating is performed, the peel resistance and scratch resistance of the coated portion can be significantly improved, which contributes to a reduction in life cycle cost. This type of structure is generally produced by forming, such as cutting and bending, and welding, but the steel for bridges of the present invention is excellent in workability and weldability.
表１に示した化学組成を有するＮｏ.１〜Ｎｏ.２２の鋼について、１５０Ｋｇ真空溶解炉で溶製し、インゴットに鍛造した後、１１００℃に加熱後、圧延を行って、厚さ４ｍｍ×幅１５０ｍｍ×長さ１０００ｍｍの寸法の鋼材を作製した。次いで、この鋼材の表裏面を機械研削し、厚さ３ｍｍ×幅６０ｍｍ×長さ１００ｍｍの試験片を切り出した。なお、本実施例で作製した鋼材の酸素含有量は０.０００１〜０.００５％の範囲であった。 No.1 to No.22 steels having the chemical compositions shown in Table 1 were melted in a 150 kg vacuum melting furnace, forged into an ingot, heated to 1100 ° C., rolled, and 4 mm thick. A steel material having a size of 150 mm width × 1000 mm length was produced. Next, the front and back surfaces of the steel material were mechanically ground, and a test piece having a thickness of 3 mm × width of 60 mm × length of 100 mm was cut out. The oxygen content of the steel material produced in this example was in the range of 0.0001 to 0.005%.
得られた試験片をＳＡＥ（Society of Automotive Engineers）Ｊ２３３４試験により評価した。ＳＡＥ Ｊ２３３４試験は、次の条件で行う加速試験であり、腐食形態が大気暴露試験に類似しているとされている（長野博夫、山下正人、内田仁著：環境材料学、共立出版（２００４）、ｐ.７４参照）。本試験は、飛来塩分量が１ｍｄｄを超えるような厳しい腐食環境を模擬する試験である。
湿潤：５０℃、１００％ＲＨ、６時間、
塩分付着：０.５質量％ＮａＣｌ、０.１質量％ＣａＣｌ２、０.０７５質量％ＮａＨＣＯ３水溶液浸漬、０.２５時間、
乾燥：６０℃、５０％ＲＨ、
１７.７５時間を１サイクル（合計２４時間）とした。
The obtained test piece was evaluated by SAE (Society of Automotive Engineers) J2334 test. The SAE J2334 test is an accelerated test conducted under the following conditions, and the corrosion form is said to be similar to the atmospheric exposure test (Hiroo Nagano, Masato Yamashita, Hitoshi Uchida: Environmental Materials Science, Kyoritsu Shuppan (2004) , P.74). This test simulates a severe corrosive environment in which the amount of incoming salt exceeds 1 mdd.
Wet: 50 ° C., 100% RH, 6 hours,
Adherence of salt: 0.5 mass% NaCl, 0.1 mass% CaCl 2 , 0.075 mass% NaHCO 3 aqueous solution immersion, 0.25 hours,
Drying: 60 ° C., 50% RH,
17.75 hours was defined as one cycle (24 hours in total).
ＳＡＥ Ｊ２３３４試験１６０サイクル終了後、各試験片の表面のさび層を除去し、板厚減少量を測定した。試験結果を表１に示す。同表における「腐食減量」は、試験片の平均の板厚減少量であり、試験前後の重量減少と試験片の表面積を用いて算出したものである。 After 160 cycles of SAE J2334 test, the rust layer on the surface of each test piece was removed, and the thickness reduction amount was measured. The test results are shown in Table 1. “Corrosion weight loss” in the table is an average reduction in the thickness of the test piece, and is calculated using the weight reduction before and after the test and the surface area of the test piece.
さらに、β−ＦｅＯＯＨが生成する塩分付着乾湿繰り返し試験を行った。鋼材を厚さ３ｍｍ×幅５０ｍｍ×長さ５０ｍｍに切り出し、予め塩分付着量が１ｍｇ／ｃｍ２になるように塩水を塗布し、４０℃の恒温高湿槽にいれ、４時間４０％ＲＨ、４時間８０％ＲＨを１サイクルとして繰り返し、３０サイクル毎に、さらに１ｍｇ／ｃｍ２になるように塩水を塗布する試験である。本実施例では、０．１７１mol/L ＮａＣｌ水溶液３ｍＬを鋼材表面全面に塗布して塩分を付着させた。本試験は１５０サイクル実施し、各試験片の表面のさび層を除去し、板厚減少量を測定した。試験結果を表１に示す。 Furthermore, a salt adhesion dry / wet repetition test in which β-FeOOH was produced was performed. The steel material is cut into a thickness of 3 mm, a width of 50 mm, and a length of 50 mm, and salt water is applied in advance so that the amount of salt is 1 mg / cm 2, and is placed in a constant temperature and high humidity bath at 40 ° C. for 4 hours 40% RH. In this test, 80% RH is repeated as one cycle, and salt water is further applied every 30 cycles to 1 mg / cm 2 . In this example, 3 mL of a 0.171 mol / L NaCl aqueous solution was applied to the entire surface of the steel material to deposit salt. This test was carried out for 150 cycles, the rust layer on the surface of each test piece was removed, and the thickness reduction was measured. The test results are shown in Table 1.
次に、表１に示した化学組成を有する鋼Ｎｏ.１〜Ｎｏ.２２に対して、汎用エポキシ樹脂塗料（バンノー２００：中国塗料製）を塗膜厚さ１５０μｍになるようにスプレー塗装し、鋼面にキズがつくまで塩化ビニルカッターによりクロスにカットを入れて、クロスカット試験評価を行った。さらに、予めＳＡＥ Ｊ２３３４試験を１０サイクル実施し、表面にさびを形成させた後、ワイヤーブラシにてケレンしたさび付き鋼材に、同様に、汎用エポキシ樹脂塗料（バンノー２００：中国塗料製）を塗膜厚さ１５０μｍになるようにスプレー塗装し、鋼面にキズがつくまで塩化ビニルカッターによりクロスにカットを入れて、クロスカット試験評価を行った。クロスカット試験後の表面状態を図２に示す。これら試験後、ポイントマイクロメーターを用いて、最大腐食深さを測定した。 Next, the steel No. 1 to No. 22 having the chemical composition shown in Table 1 was spray-coated with a general-purpose epoxy resin paint (Banno 200: made in China) to a coating thickness of 150 μm, A cross cut test was performed by cutting the cross with a vinyl chloride cutter until the steel surface was scratched. In addition, after 10 SAE J2334 tests were conducted in advance and rust was formed on the surface, a general-purpose epoxy resin paint (Banno 200: made in China) was applied to the rusted steel material with a wire brush. The coating was sprayed to a thickness of 150 μm, and the cloth was cut with a vinyl chloride cutter until the steel surface was scratched. The surface state after the cross-cut test is shown in FIG. After these tests, the maximum corrosion depth was measured using a point micrometer.
表１の結果から明らかなように、本発明例に係る鋼材では、いずれも本発明で規定する化学組成の含有量を満足しているので、腐食減量濡れ環境であるＳＡＥ Ｊ２３３４試験の結果、裸耐食性及び塗装部耐食性に優れており、また、塩分付着乾湿環境においても優れた耐食性を示している。 As is clear from the results in Table 1, since the steel materials according to the examples of the present invention all satisfy the chemical composition content specified in the present invention, the results of the SAE J2334 test, which is a corrosion weight loss wet environment, Excellent corrosion resistance and painted part corrosion resistance, and also shows excellent corrosion resistance in a salt-attached dry and wet environment.
これに対して、比較例の鋼Ｎｏ．２３及び２６の鋼材においてはＳｎの量が不足するために、塩分付着乾湿試験で腐食減量が増大する傾向が明瞭に観察される。そして、比較例の鋼Ｎｏ．２４及び２５の鋼材においては、Ｓｎが規定範囲に添加されているものの、Ｃｕ量が多すぎるため、Ｃｕ／Ｓｎが１を超えてしまっており、塩分付着乾湿試験で腐食減量が増大する傾向が明瞭に観察される。なお、比較例の鋼Ｎｏ．２４及び２５の鋼材は、圧延後に微小の割れが観察された。 On the other hand, steel No. of the comparative example. In the steel materials 23 and 26, since the amount of Sn is insufficient, the tendency to increase the weight loss of corrosion is clearly observed in the salt adhesion wet and dry test. And steel No. of a comparative example. In the steel materials of 24 and 25, although Sn is added in the specified range, Cu / Sn exceeds 1 because the amount of Cu is too much, and the corrosion weight loss tends to increase in the salt adhesion wet and dry test. Observed clearly. In addition, steel No. of the comparative example. In the steel materials 24 and 25, minute cracks were observed after rolling.
また、比較例の鋼Ｎｏ．２７の鋼材は、Ｓｎ、Ｃｕともに規定範囲に添加されているものの、Ｃｕ／Ｓｎが１を超えてしまっており、塩分付着乾湿試験で腐食減量が増大する。また、クロスカット試験の結果も良好ではない。比較例の鋼Ｎｏ．２８および２９の鋼材は、ＣｕまたはＮｉのいずれかが規定範囲を超えており、塩分付着乾湿試験で腐食減量が増大する。比較例の鋼Ｎｏ．３０の鋼材は、Ｓｎの量が不足するために、腐食減量が増大すると共に、クロスカット試験でも、最大腐食深さは増大し、良好な結果は得られなかった。 In addition, steel No. of the comparative example. In Steel No. 27, both Sn and Cu are added within the specified range, but Cu / Sn exceeds 1 and the corrosion weight loss increases in the salt adhesion wet and dry test. Moreover, the result of the crosscut test is not good. Steel No. of Comparative Example In the steel materials 28 and 29, either Cu or Ni exceeds the specified range, and the corrosion weight loss increases in the salt adhesion wet / dry test. Steel No. of Comparative Example In the steel No. 30, the amount of Sn was insufficient, so that the corrosion weight loss increased, and the maximum corrosion depth also increased in the cross-cut test, and good results were not obtained.
本発明の橋梁用鋼材は、飛来塩分量が多い環境下においても十分な耐候性を有する。海浜耐候性に優れた材料として最適であり、海浜地域における橋梁等の構造物や、融雪塩や凍結防止剤が散布される地域における橋梁等の構造物に使用するミニマムメンテナンス材料として、土木および建築分野等において広く適用することができる。さらに、塗装を施して、船舶や橋梁等の鋼構造物に使用した場合に、欠陥部等からの腐食を著しく抑制するためメンテナンスミニマム化に寄与する材料として広く適用することができる。 The steel for bridges of the present invention has sufficient weather resistance even in an environment with a large amount of incoming salt. Civil engineering and construction as a minimum maintenance material that is ideal as a material with excellent beach weather resistance and used for structures such as bridges in beach areas and structures such as bridges in areas where snowmelt salt and antifreezing agents are applied. It can be widely applied in fields. Furthermore, when coated and used for steel structures such as ships and bridges, it can be widely applied as a material that contributes to maintenance minimization because it significantly suppresses corrosion from defects and the like.
Claims (7)
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| JP2006352255A JP4656054B2 (en) | 2006-12-27 | 2006-12-27 | Steel for bridge |
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| JP2006352255A JP4656054B2 (en) | 2006-12-27 | 2006-12-27 | Steel for bridge |
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| JP2009046750A (en) * | 2007-08-22 | 2009-03-05 | Jfe Steel Kk | Corrosion-resistant steel material for ship and manufacturing method therefor |
| JP2009046751A (en) * | 2007-08-22 | 2009-03-05 | Jfe Steel Kk | Corrosion-resistant steel material for ship and manufacturing method therefor |
| JP2010144207A (en) * | 2008-12-18 | 2010-07-01 | Sumitomo Metal Ind Ltd | Steel pipe sheet pile and steel pipe sheet pile wall |
| JP2010144209A (en) * | 2008-12-18 | 2010-07-01 | Sumitomo Metal Ind Ltd | Steel, steel sheet pile, steel pipe sheet pile, steel pipe stake, steel sheet pile wall, and steel pipe sheet pile wall |
| JP2010248567A (en) * | 2009-04-15 | 2010-11-04 | Sumitomo Metal Ind Ltd | Surface-treated steel material excellent in corrosion resistance |
| WO2011087116A1 (en) * | 2010-01-18 | 2011-07-21 | 住友金属工業株式会社 | Steel sheet with small welding deformation and excellent corrosion resistance |
| JP2011208200A (en) * | 2010-03-29 | 2011-10-20 | Sumitomo Metal Ind Ltd | Surface-treated corrosion-resistant steel material having excellent weather resistance |
| JP2012140710A (en) * | 2012-02-22 | 2012-07-26 | Jfe Steel Corp | Corrosion-resistant steel material for ship, and method of manufacturing the same |
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| JP2012144799A (en) * | 2011-01-14 | 2012-08-02 | Sumitomo Metal Ind Ltd | Thick steel plate for marine structure, and method for producing the same |
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| WO2019186797A1 (en) | 2018-03-28 | 2019-10-03 | 日本製鉄株式会社 | Method for manufacturing flux-cored wire, flux-cored wire and method for manufacturing welded joint |
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| JPS4834018A (en) * | 1971-09-04 | 1973-05-15 | ||
| JP2001214236A (en) * | 2000-01-31 | 2001-08-07 | Nippon Steel Corp | Corrosion resistant steel for crude oil and heavy oil storage speed |
| JP2005220394A (en) * | 2004-02-04 | 2005-08-18 | Sumitomo Metal Ind Ltd | Seawater corrosion resisting steel |
| JP2006118011A (en) * | 2004-10-22 | 2006-05-11 | Sumitomo Metal Ind Ltd | Steel having excellent seaside weather resistance and structure |
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| JP2001214236A (en) * | 2000-01-31 | 2001-08-07 | Nippon Steel Corp | Corrosion resistant steel for crude oil and heavy oil storage speed |
| JP2005220394A (en) * | 2004-02-04 | 2005-08-18 | Sumitomo Metal Ind Ltd | Seawater corrosion resisting steel |
| JP2006118011A (en) * | 2004-10-22 | 2006-05-11 | Sumitomo Metal Ind Ltd | Steel having excellent seaside weather resistance and structure |
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| JP2009046750A (en) * | 2007-08-22 | 2009-03-05 | Jfe Steel Kk | Corrosion-resistant steel material for ship and manufacturing method therefor |
| JP2010144207A (en) * | 2008-12-18 | 2010-07-01 | Sumitomo Metal Ind Ltd | Steel pipe sheet pile and steel pipe sheet pile wall |
| JP2010144209A (en) * | 2008-12-18 | 2010-07-01 | Sumitomo Metal Ind Ltd | Steel, steel sheet pile, steel pipe sheet pile, steel pipe stake, steel sheet pile wall, and steel pipe sheet pile wall |
| JP2010248567A (en) * | 2009-04-15 | 2010-11-04 | Sumitomo Metal Ind Ltd | Surface-treated steel material excellent in corrosion resistance |
| WO2011087116A1 (en) * | 2010-01-18 | 2011-07-21 | 住友金属工業株式会社 | Steel sheet with small welding deformation and excellent corrosion resistance |
| JP4924775B2 (en) * | 2010-01-18 | 2012-04-25 | 住友金属工業株式会社 | Steel sheet with small welding deformation and excellent corrosion resistance |
| CN102652181A (en) * | 2010-01-18 | 2012-08-29 | 住友金属工业株式会社 | Steel sheet with small welding deformation and excellent corrosion resistance |
| JP2011208200A (en) * | 2010-03-29 | 2011-10-20 | Sumitomo Metal Ind Ltd | Surface-treated corrosion-resistant steel material having excellent weather resistance |
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| WO2019186811A1 (en) | 2018-03-28 | 2019-10-03 | 日本製鉄株式会社 | Method for manufacturing flux-cored wire, flux-cored wire and method for manufacturing welded joint |
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