JP6565665B2 - Corrosion resistance evaluation method for electrical steel sheets - Google Patents
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本発明は、絶縁皮膜の施された電磁鋼板の耐食性評価方法に関する。本発明の耐食性評価方法は、電磁鋼板の保管環境、輸送環境、使用環境を模擬した試験環境で、耐食性を評価することができる評価方法である。 The present invention relates to a method for evaluating corrosion resistance of an electromagnetic steel sheet provided with an insulating film. The corrosion resistance evaluation method of the present invention is an evaluation method capable of evaluating corrosion resistance in a test environment that simulates the storage environment, transport environment, and use environment of an electromagnetic steel sheet.
電磁鋼板には、通常、絶縁皮膜が施されている。絶縁皮膜の最大の機能は、電磁鋼板の間を絶縁することにより、積層鉄心（電磁鋼板）の磁気特性を確保することにあるが、電磁鋼板の保管、輸送、使用に際しての防食機能も有している。したがって、このような観点から、電磁鋼板の絶縁皮膜の耐食性を評価することは重要である。 An electromagnetic steel sheet is usually provided with an insulating film. The greatest function of the insulation film is to secure the magnetic properties of the laminated iron core (electromagnetic steel sheet) by insulating between the magnetic steel sheets, but it also has anti-corrosion functions when storing, transporting and using the electromagnetic steel sheets. ing. Therefore, from such a viewpoint, it is important to evaluate the corrosion resistance of the insulating coating of the electrical steel sheet.
近年、需要者が、腐食環境の厳しい東南アジア・中国南部へ移転したことに伴い、該地域へ輸出される電磁鋼板の絶縁皮膜には、海上輸送時の高飛来塩分環境や、現地の高温多湿環境に耐える耐食性が求められるので、特に、輸送時の防食機能が重要となり、電磁鋼板の絶縁皮膜の耐食性、特に、耐錆性を適切に評価することが重要となっている。 In recent years, as customers have moved to Southeast Asia and southern China, where corrosive environments are severe, the insulation coatings of electrical steel sheets exported to these regions include high-flying salinity environments during marine transportation and local high-temperature and high-humidity environments. Therefore, it is important to properly evaluate the corrosion resistance, especially the rust resistance of the insulating film of the electrical steel sheet.
絶縁被膜を施した電磁鋼板の耐食性の評価には、一般に、湿潤試験（ＪＩＳ Ｋ ２２４６）が用いられる場合が多い。この湿潤試験は、温度と湿度を一定条件に保ち、所定の時間の経過後、発錆状態を観察して評価する試験である。例えば、特許文献１には、５０℃、９８％ＲＨ、４８時間という条件での試験例が記載されている。 In general, a wet test (JIS K 2246) is often used to evaluate the corrosion resistance of an electrical steel sheet provided with an insulating coating. This wet test is a test in which the temperature and humidity are maintained under constant conditions, and the rusting state is observed and evaluated after a lapse of a predetermined time. For example, Patent Document 1 describes a test example under the conditions of 50 ° C., 98% RH, and 48 hours.
塩水噴霧試験（ＪＩＳ Ｚ ２３７１）も、一般的な耐食性評価試験である。この塩水噴霧試験は、３５℃に保った恒温槽中で、５％ＮａＣｌ水溶液を、一定期間噴霧し、その後、発錆状態を観察して評価する試験である。試験環境を、実際の腐食環境に近づけるため、塩水噴霧後に、乾燥と湿潤を、所定の時間で繰り返す試験がサイクル試験である。 The salt spray test (JIS Z 2371) is also a general corrosion resistance evaluation test. This salt spray test is a test in which a 5% NaCl aqueous solution is sprayed for a certain period in a thermostatic chamber maintained at 35 ° C., and then the rusting state is observed and evaluated. In order to bring the test environment closer to the actual corrosive environment, the cycle test is a test in which drying and wetting are repeated at a predetermined time after spraying with salt water.
特許文献２では、主として自動車用表面処理鋼板の耐食性を評価する目的で、表面に塩水を接触させ塩分を付着させる工程と湿潤乾燥繰り返しを行う工程を、１回以上繰り返す方法が記載されている。この方法は自動車の使用される環境を想定した試験条件を作ることができる。 Patent Document 2 describes a method in which a step of bringing salt water into contact with the surface and depositing salt and a step of repeating wet and dry are repeated one or more times, mainly for the purpose of evaluating the corrosion resistance of the surface-treated steel sheet for automobiles. This method can create test conditions assuming the environment in which the automobile is used.
これまで提案されてきた各種耐食性試験法においては、それぞれの手法による発錆条件・環境中に試験片をさらしたのち、試験片全体の発錆状況をもって錆びやすさを判定、評価する。例えば、湿潤試験や塩水噴霧試験では、ＪＩＳ Ｚ ２３７１付属書に記載されているように、試験片に発生した錆びの頻度等によりレーティングする。また、特許文献２では、塗膜の膨れ幅等、試験片全体の「腐食量」によって耐食性を評価している。 In the various corrosion resistance test methods that have been proposed so far, the test piece is exposed to the rusting conditions and environment by the respective methods, and then the rustability is judged and evaluated based on the rusting state of the entire test piece. For example, in the wet test and the salt spray test, as described in the JIS Z 2371 appendix, the rating is based on the frequency of rust generated on the test piece. Moreover, in patent document 2, corrosion resistance is evaluated by the "corrosion amount" of the whole test piece, such as the swelling width of a coating film.
しかしながら、絶縁皮膜が施された電磁鋼板（以下、単に「電磁鋼板」ということがある。）に対し、単純な湿潤試験を適用しても、多くの場合、腐食は認められない。したがって、湿潤試験のみでは、絶縁皮膜の耐食性の優劣を判断するのは難しい。 However, even when a simple wet test is applied to an electromagnetic steel sheet provided with an insulating film (hereinafter sometimes simply referred to as “magnetic steel sheet”), corrosion is not recognized in many cases. Therefore, it is difficult to judge the superiority or inferiority of the corrosion resistance of the insulating film only by the wet test.
他方、絶縁皮膜が施された電磁鋼板に対し、塩水噴霧試験を適用すると、激しい腐食が生じるが、塩水噴霧試験や、それを改良したサイクル試験の試験環境は、海浜屋外環境に近いとされ、電磁鋼板の保管環境、輸送環境、使用環境に比べて、極めて厳しい試験環境になっている。 On the other hand, when a salt spray test is applied to an electrical steel sheet with an insulating coating, severe corrosion occurs, but the test environment of the salt spray test and improved cycle test is said to be close to the beach outdoor environment, Compared to the storage environment, transportation environment, and usage environment of electrical steel sheets, the test environment is extremely severe.
電磁鋼板の保管、輸送、使用に際し、塩水に浸されたり、噴霧されたりすることは、通常、あり得ない。また、塩水を噴霧しての腐食と、陸上の屋内倉庫での腐食、又は、輸出時の船倉での腐食（塩分を含み、乾燥と湿潤が繰り返される環境での腐食）では、腐食時の鋼板表面の環境が異なり、それに伴い腐食機構も異なっている。それ故、塩水噴霧を含む試験は、電磁鋼板の耐食性、特に、耐錆性の評価には適切でない。 When storing, transporting, and using electrical steel sheets, it is usually impossible to immerse or spray them in salt water. Corrosion caused by spraying salt water, corrosion in indoor warehouses on land, or corrosion in cargo hold during export (corrosion in an environment that includes salt and is repeatedly dried and moistened) The surface environment is different and the corrosion mechanism is also different. Therefore, the test including salt spray is not appropriate for evaluating the corrosion resistance, particularly rust resistance, of the electrical steel sheet.
上記の観点から、絶縁皮膜が施された電磁鋼板の保管環境、輸送環境、使用環境を模擬した環境にて、電磁鋼板の、耐錆性を含む耐食性を定量的にかつ再現性良く評価できる耐食性評価方法が要望されている。 From the above viewpoint, corrosion resistance that enables quantitative and reproducible evaluation of corrosion resistance, including rust resistance, of electrical steel sheets in an environment that simulates the storage environment, transport environment, and usage environment of electrical steel sheets with insulating coatings An evaluation method is desired.
本発明は、上記要望を踏まえ、電磁鋼板の保管環境、輸送環境、使用環境を模擬した環境にて、電磁鋼板の耐食性、特に、耐錆性を定量的にかつ再現性良く評価することができる電磁鋼板の耐食性評価方法を提供することを目的とする。 In light of the above requirements, the present invention can quantitatively and reproducibly evaluate the corrosion resistance, in particular, rust resistance, of an electromagnetic steel sheet in an environment simulating the storage environment, transportation environment, and use environment of the electromagnetic steel sheet. It aims at providing the corrosion-resistance evaluation method of an electromagnetic steel plate.
本発明者らは、上記課題を解決する手法について鋭意研究した。その結果、電磁鋼板の表面に、濃度の異なる塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥し、電磁鋼板を特定の環境においた後、電磁鋼板の表面（絶縁皮膜）における発錆状態を観察することにより、電磁鋼板の耐食性を定量的にかつ再現性良く評価できることを見いだした。 The inventors of the present invention have intensively studied a method for solving the above-described problems. As a result, the surface of the electrical steel sheet (insulating film) is obtained after a certain size droplet of salt solution of different concentration is locally attached to the surface of the electrical steel sheet and dried, and the electrical steel sheet is placed in a specific environment. It was found that the corrosion resistance of the electrical steel sheet can be evaluated quantitatively and with good reproducibility by observing the rusting state at.
本発明は、上記知見に基づいてなされたもので、その要旨は、以下のとおりである。 This invention was made | formed based on the said knowledge, The summary is as follows.
（１）絶縁皮膜が施された電磁鋼板の表面に、濃度の異なる複数の塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥する工程と、
上記電磁鋼板を、恒温恒湿状態に所定時間保持する工程と、
その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、及び、錆発生の原因となる物質のいずれか一つ又は二つを評価する工程と、
を有することを特徴とする電磁鋼板の耐食性評価方法。
(1) A step of locally attaching and drying droplets of a certain size of a plurality of salt aqueous solutions having different concentrations on the surface of an electrical steel sheet provided with an insulating film;
Holding the electromagnetic steel sheet in a constant temperature and humidity state for a predetermined time;
Then, observe the rusting state of the drying marks of the individual droplets on the surface of the magnetic steel sheet, the concentration of the salt aqueous solution that does not generate rust, and any one or two of the substances that cause rust generation A process of evaluating;
A method for evaluating the corrosion resistance of an electrical steel sheet, comprising:
（２）絶縁皮膜が施された電磁鋼板の表面に、濃度の異なる複数の塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥する工程と、
上記電磁鋼板を、乾燥状態と湿潤状態に、交互に、所定時間保持する工程と、
その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、錆発生の原因となる物質、及び、錆が発生しない環境の露点のいずれか一つ又は二つ以上を評価する工程と、
を有することを特徴とする電磁鋼板の耐食性評価方法。
(2) A step of locally attaching and drying droplets of a certain size of a plurality of salt aqueous solutions having different concentrations on the surface of a magnetic steel sheet provided with an insulating film;
Holding the electromagnetic steel sheet alternately in a dry state and a wet state for a predetermined time; and
Then, observe the rusting state of the drying traces of the individual droplets on the surface of the magnetic steel sheet, the concentration of the salt aqueous solution that does not generate rust, the substances that cause rusting, and the dew point of the environment that does not generate rusting Evaluating any one or more, and
A method for evaluating the corrosion resistance of an electrical steel sheet, comprising:
（３）前記液滴の大きさを０．５ｍｍ〜２０ｍｍとすることを特徴とする（１）又は（２）に記載の電磁鋼板の耐食性評価方法。 (3) The method for evaluating corrosion resistance of an electrical steel sheet according to (1) or (2), wherein the size of the droplet is 0.5 mm to 20 mm.
（４）マイロピペットを用いて前記液滴の付着位置と大きさを制御することを特徴とする（１）〜（３）のいずれかに記載の電磁鋼板の耐食性評価方法。 (4) The method for evaluating corrosion resistance of an electrical steel sheet according to any one of (1) to (3), wherein the adhesion position and size of the droplets are controlled using a micropipette.
（５）前記塩水溶液の濃度を０.００３質量％〜３質量％とすることを特徴とする（１）〜（４）のいずれかに記載の電磁鋼板の耐食性評価方法。 (5) The method for evaluating corrosion resistance of an electrical steel sheet according to any one of (1) to (4), wherein the concentration of the aqueous salt solution is 0.003 to 3% by mass.
（６）前記複数の液滴の間の距離を、前記液滴の大きさの２倍以上とすることを特徴とする（１）〜（５）のいずれかに記載の電磁鋼板の耐食性評価方法。 (6) The method for evaluating corrosion resistance of an electrical steel sheet according to any one of (1) to (5), wherein a distance between the plurality of droplets is at least twice the size of the droplets. .
本発明によれば、電磁鋼板の保管、使用環境（付着物種類、付着量、保管温度と湿度、使用温度と湿度等）を定量的に模擬した状態で錆の発生有無を再現性良く評価することができる。更に、本発明によれば、定量的でかつ再現性が良い耐食性評価に基づいて、適切な錆防止対策又は錆抑制対策を容易に立案することができる。 According to the present invention, the presence / absence of rust is evaluated with good reproducibility in a state of quantitatively simulating the storage and use environment of magnetic steel sheets (attachment type, adhesion amount, storage temperature and humidity, use temperature and humidity, etc.). be able to. Furthermore, according to the present invention, it is possible to easily devise an appropriate rust prevention measure or rust suppression measure based on quantitative and reproducible corrosion resistance evaluation.
以下、添付の図面を参照しながら、本発明の実施形態について詳細に説明する。 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
本発明の第１の実施形態に係る電磁鋼板の耐食性評価方法では、絶縁被膜が施された電磁鋼板の表面に、濃度の異なる複数の塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥し、上記電磁鋼板を、恒温恒湿状態に所定時間保持し、その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、及び、錆発生の原因となる物質のいずれか一つ又は二つを評価する。 In the corrosion resistance evaluation method for an electrical steel sheet according to the first embodiment of the present invention, a predetermined size droplet of a plurality of salt aqueous solutions having different concentrations is locally attached to the surface of the electrical steel sheet provided with an insulating coating. The magnetic steel sheet is kept in a constant temperature and humidity state for a predetermined time, and then the rusting state of the drying marks of individual droplets on the surface of the magnetic steel sheet is observed, and a salt aqueous solution that does not generate rust is obtained. Evaluate any one or two of the substances that cause concentration and rusting.
本発明の第２の実施形態に係る電磁鋼板の耐食性評価方法では、絶縁皮膜が施された電磁鋼板の表面に、濃度の異なる複数の塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥し、上記電磁鋼板を、乾燥状態と湿潤状態に、交互に、所定時間保持し、その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、錆発生の原因となる物質、及び、錆が発生しない環境の露点のいずれか一つ又は二つ以上を評価する。 In the method for evaluating corrosion resistance of an electrical steel sheet according to the second embodiment of the present invention, droplets of a certain size of a plurality of salt aqueous solutions having different concentrations are locally attached to the surface of the electrical steel sheet provided with an insulating film. The magnetic steel sheet is kept in a dry state and a wet state alternately for a predetermined time, and then the rusting state of the drying marks of individual droplets on the surface of the magnetic steel sheet is observed, and the rust is removed. Evaluate one or more of the concentration of salt solution that does not occur, substances that cause rust generation, and the dew point of the environment where rust does not occur.
ここで、本発明に想到した経緯について説明する。 Here, the background of the present invention will be described.
本発明者らは、電磁鋼板コイルの保管中に錆が生じた場合において、発錆状態を調査した。その結果、電磁鋼板の表面に生ずる錆は、ほとんどの場合、数百μｍ（ミクロン）乃至数ｍｍの「点状錆」であり、全面腐食は、ほとんどないことが判明した。従って、塩水噴霧のような試験方法では、電磁鋼板の保管中に発生する錆の発生条件を定量的に評価することは困難である。 The inventors investigated the rusting state when rust was generated during storage of the magnetic steel sheet coil. As a result, it has been found that the rust generated on the surface of the electrical steel sheet is “spot rust” of several hundred μm (microns) to several mm in most cases, and there is almost no overall corrosion. Therefore, it is difficult to quantitatively evaluate the conditions for generating rust generated during storage of the electromagnetic steel sheet by a test method such as salt spray.
後述する図１（ａ）〜（ｃ）で示す発錆状態は、「点状錆」の一例であり、Ｘ線微小分析（electron probe micro-analysis：ＥＰＭＡ）により、発錆領域元素分布を調べたものである。図１（ａ）〜（ｃ）から、絶縁皮膜の表面に、塩化ナトリウムが局所的に付着したことにより、錆が発生したことが解る。 The rusting state shown in FIGS. 1A to 1C, which will be described later, is an example of “spot-like rust”, and the element distribution of the rusting region is examined by X-ray microanalysis (EPMA). It is a thing. 1 (a) to 1 (c), it can be seen that rust is generated by sodium chloride locally adhering to the surface of the insulating film.
本発明者らは、更に、保管中に錆が生じた複数の電磁鋼板コイルにおいて、以下の要領で、電磁鋼板コイルの表面の水溶性付着物調査を行った。 The present inventors further conducted a water-soluble deposit investigation on the surface of the electromagnetic steel sheet coil in the following manner in the plurality of electromagnetic steel sheet coils in which rust was generated during storage.
純水で湿らせた脱塩ガーゼで電磁鋼板コイルの表面を拭き、該ガーゼを純水に浸漬して水溶性の表面付着物を抽出し、イオンクロマトグラフィーで、イオン種と付着量を測定した。その結果、錆が生じた電磁鋼板コイルの表面から、しばしば、数十ｍｇ／ｍ2の塩化物イオン、硝酸イオン、硫酸イオン等が検出された。 The surface of the magnetic steel sheet coil was wiped with demineralized gauze moistened with pure water, the gauze was immersed in pure water to extract water-soluble surface deposits, and ion species and adhesion amount were measured by ion chromatography. . As a result, tens of mg / m 2 of chloride ion, nitrate ion, sulfate ion, etc. were often detected from the surface of the electromagnetic steel sheet coil in which rust occurred.
以上の検出結果から、何らかの理由により、電磁鋼板の表面に、上記イオンを含む水溶性塩が付着して、「錆」が発生したと推定される。 From the above detection results, it is presumed that for some reason, a water-soluble salt containing the ions adheres to the surface of the electrical steel sheet and “rust” is generated.
以上の研究結果に基づき、本発明者らは、絶縁皮膜を有する電磁鋼板における発錆機構を、以下のように結論づけた。
（ａ）電磁鋼板の表面に、何らかの原因により、塩化ナトリウム等の塩が局所的に付着する（局所的な塩付着）。
（ｂ）付着した塩が潮解性の塩であると、塩付着箇所では結露が生じ易い。
（ｃ）電磁鋼板の保管、輸送、及び／又は、使用中、温度変化や乾湿繰返により、塩付着箇所に結露が生じて錆が発生する（温度変化や乾湿繰返による発錆）。
Based on the above research results, the present inventors have concluded the rusting mechanism in an electrical steel sheet having an insulating film as follows.
(A) A salt such as sodium chloride locally adheres to the surface of the electrical steel sheet for some reason (local salt adhesion).
(B) If the adhering salt is a deliquescent salt, dew condensation is likely to occur at the salt adhering site.
(C) During storage, transportation, and / or use of electrical steel sheets, dew formation occurs at the salt adhesion site due to temperature changes and repeated wet and dry processes, and rust is generated (rust generated by repeated temperature changes and wet and dry processes).
そして、第１、第２の実施形態における、「電磁鋼板の表面に、濃度の異なる複数の塩水溶液の一定の大きさの液滴を局所的に付着させて乾燥し」が、上記発生機構（ａ）の「局所的な塩付着」に対応し、その後の「上記電磁鋼板を、恒温恒湿状態に所定時間保持し」、及び、「上記電磁鋼板を、乾燥状態と湿潤状態に、交互に、所定時間保持し」が、上記発生機構（ｃ）の「温度変化や乾湿繰返」に対応する。 Then, in the first and second embodiments, “the droplets of a certain size of a plurality of salt aqueous solutions having different concentrations are locally attached and dried on the surface of the electromagnetic steel sheet” Corresponding to “local salt adhesion” in a), and thereafter “holding the electrical steel sheet in a constant temperature and humidity state for a predetermined time” and “alternating the electrical steel sheet in a dry state and a wet state alternately. , “Hold for a predetermined time” corresponds to “temperature change and repeated wet and dry” of the generating mechanism (c).
したがって、第１、第２の実施形態は、絶縁皮膜を有する電磁鋼板の保管環境、輸送環境、及び、使用環境における錆発生条件を定量的に再現性良く模擬し得る評価方法であり、第１、第２の実施形態による“腐食状態の観察”結果は、電磁鋼板が置かれる実環境における錆発生条件を定量的にかつ再現性良く評価し得るものである。塩水噴霧試験に代表される従来の方法では、電磁鋼板の保管・使用環境のうち、雰囲気温度条件はさておき、付着する塩の種類と付着量を定量的に模擬することはできない。 Therefore, the first and second embodiments are evaluation methods that can simulate the rust generation conditions in the storage environment, the transport environment, and the use environment of the electrical steel sheet having the insulating film quantitatively with good reproducibility. The result of “observation of corrosion state” according to the second embodiment can quantitatively and reproducibly evaluate the rust generation conditions in the actual environment where the electromagnetic steel sheet is placed. In the conventional method typified by the salt spray test, it is not possible to quantitatively simulate the type and amount of the adhering salt, apart from the ambient temperature condition in the storage / use environment of the magnetic steel sheet.
第１、第２の実施形態において、重要なことの一つは、制御された状態で、再現性良く、電磁鋼板（以下「鋼板」ということがある。）への局所的な塩付着を行うことである。以下、その重要性について述べる。 In the first and second embodiments, one important thing is to perform local salt adhesion to an electromagnetic steel sheet (hereinafter also referred to as “steel sheet”) in a controlled state with good reproducibility. That is. The importance is described below.
鉄をはじめ、金属の腐食は、鉄の電子放出・溶解によるアノード反応（１）と酸素が電子を受容するカソード反応（２）が対となって進行する。
２Ｆｅ→２Ｆｅ2+＋４ｅ- （１）
Ｏ2＋Ｈ2Ｏ＋４ｅ-→４ＯＨ- （２）
Corrosion of metals, including iron, proceeds in pairs by an anodic reaction (1) due to electron emission and dissolution of iron and a cathodic reaction (2) in which oxygen accepts electrons.
2Fe → 2Fe 2+ + 4e - ( 1)
O 2 + H 2 O + 4e − → 4OH − (2)
塩が付着した状態で湿潤雰囲気中におかれると潮解作用により結露し、酸素の供給が可能な液滴周辺部で（２）の反応が進行し、液滴中央部では（１）の反応が進行する。したがって、液滴の大きさはアノード反応部とカソード反応部の距離に影響する。 When placed in a humid atmosphere with salt attached, dew condensation occurs due to deliquescent action, and the reaction (2) proceeds at the periphery of the droplet where oxygen can be supplied, and the reaction (1) occurs at the center of the droplet. proceed. Therefore, the size of the droplet affects the distance between the anode reaction part and the cathode reaction part.
液滴の大きさが０．５ｍｍ未満ではアノード反応とカソード反応が近接し、腐食現象は皮膜の局所的変動を受けるため、再現性が低くなることがある。一方、液滴の大きさが２０ｍｍを超えると、アノード反応部とカソード反応部の距離が大きくなるため、金属の電気抵抗により腐食電流が低下し、腐食反応が遅くなる。したがって、付着させる塩水溶液の直径は０．５〜２０ｍｍが望ましい。 When the droplet size is less than 0.5 mm, the anodic reaction and the cathodic reaction are close to each other, and the corrosion phenomenon is subject to local fluctuations of the film, so that the reproducibility may be lowered. On the other hand, when the size of the droplet exceeds 20 mm, the distance between the anode reaction part and the cathode reaction part becomes large, so that the corrosion current decreases due to the electrical resistance of the metal, and the corrosion reaction becomes slow. Therefore, the diameter of the salt aqueous solution to be adhered is desirably 0.5 to 20 mm.
液滴間の距離も重要である。液滴間の距離が小さくなると、異なる液滴間でのアノード反応とカソード反応の結合が生じ、腐食反応が複雑化する。この現象を回避するためには、液滴間の距離を液滴の大きさの２倍以上確保することが望ましい。 The distance between the droplets is also important. As the distance between the droplets decreases, the anodic reaction and the cathodic reaction between different droplets are combined, complicating the corrosion reaction. In order to avoid this phenomenon, it is desirable to secure the distance between the droplets at least twice the size of the droplet.
以上のように、第１、第２の実施形態においては、液滴の大きさと液滴間の距離を制御することが望まれる。液滴の大きさと液滴間の距離を制御しつつ表面に液滴を付着させるためには、マイクロピペットが好適である。直径０．５ｍｍ〜２０ｍｍの液滴サイズは、液滴量０．０５μｌ〜２ｍｌに相当する。この液量範囲の液滴付着は、マイクロピペットを用いることにより、精密にかつ再現性良く実現できる。特許文献２で例示されている方法、すなわち、スプレーノズルなど噴霧による方法では、液滴同士の合体は避けがたく液滴の大きさを再現性良く制御すること、また液滴間の距離を確保することは困難である。液滴サイズが０．５ｍｍ〜２０ｍｍの場合、液滴間の距離は１ｍｍ以上とすることが望ましい。 As described above, in the first and second embodiments, it is desired to control the size of the droplet and the distance between the droplets. A micropipette is suitable for attaching droplets to the surface while controlling the size of the droplets and the distance between the droplets. A droplet size of 0.5 mm to 20 mm in diameter corresponds to a droplet amount of 0.05 μl to 2 ml. Droplet adhesion in this liquid amount range can be realized precisely and with good reproducibility by using a micropipette. In the method exemplified in Patent Document 2, that is, a method using spraying such as a spray nozzle, it is inevitable to combine the droplets, and the size of the droplets is controlled with good reproducibility, and the distance between the droplets is ensured. It is difficult to do. When the droplet size is 0.5 mm to 20 mm, the distance between the droplets is desirably 1 mm or more.
また、マイクロピペットを用いることにより、同一の評価試験片の表面に、複数の塩濃度の液滴や複数の塩種の液滴を付着させることが可能になる。すなわち、数の錆発生条件を評価することができる。 Further, by using a micropipette, it is possible to attach a plurality of salt concentration droplets or a plurality of salt species droplets to the surface of the same evaluation test piece. That is, the number of rust generation conditions can be evaluated.
第１、第２の実施形態で用いる水溶性塩は、塩化物、硝酸塩、及び、硫酸塩のなかで、潮解性を有するものが好適である。塩化物イオン、硝酸イオン、及び、硫酸イオンは、鋼板表面の不動態膜を破壊し、錆を誘引・促進し易い。具体例としては、Ｌｉ、Ｎａ、Ｋ、Ｍｇ、Ｃａ、ＮＨ4の塩化物、硝酸、硫酸を挙げることができる。 The water-soluble salt used in the first and second embodiments is preferably a salt having deliquescence among chloride, nitrate, and sulfate. Chloride ions, nitrate ions, and sulfate ions easily destroy the passive film on the surface of the steel sheet and attract and promote rust. Specific examples include Li, Na, K, Mg, Ca, NH 4 chloride, nitric acid, and sulfuric acid.
往々にして、錆の原因となる海塩粒子は、ＮａＣｌとＭｇＣｌ2から構成されており、各種耐食試験に用いられる塩であるが、第１、第２の実施形態においても好適である。非特許文献２には、大気腐食の原因となる汚染物質として、各種の塩があげられているが、これらの塩も、第１、第２の実施形態に用いることができる。 Often, the sea salt particles that cause rust are composed of NaCl and MgCl 2 and are salts used in various corrosion resistance tests, but are also suitable in the first and second embodiments. Non-Patent Document 2 lists various salts as pollutants that cause atmospheric corrosion. These salts can also be used in the first and second embodiments.
なお、塩酸や硝酸のような揮発性の酸は、乾燥により蒸発してしまので、通常、第１、第２の実施形態では用いない。 Note that volatile acids such as hydrochloric acid and nitric acid are not used in the first and second embodiments because they evaporate by drying.
より具体的には、下記の「各種の塩」が好適に使用可能である（非特許文献２のＴａｂｌｅＩＸを参照）。
Ｎａ2ＳＯ4、ＮＨ4Ｃｌ、（ＮＨ4）2ＳＯ4、ＮａＣｌ、ＮａＮＯ3、（ＮＨ4）3Ｈ（ＳＯ4）2、ＮＨ4ＮＯ3、ＮａＨＳＯ4、（ＮＨ4）ＨＳＯ4、ＭｇＣｌ2
More specifically, the following “various salts” can be preferably used (see Table IX of Non-Patent Document 2).
Na 2 SO 4 , NH 4 Cl, (NH 4 ) 2 SO 4 , NaCl, NaNO 3 , (NH 4 ) 3 H (SO 4 ) 2 , NH 4 NO 3 , NaHSO 4 , (NH 4 ) HSO 4 , MgCl 2
第１、第２の実施形態において、液滴の付着後に、一旦乾燥させる工程は、塩が付着した領域を限定するために必須のことである。乾燥に時間を要すると、乾燥中に腐食が始まる可能性がある。液滴を形成した後の乾燥は、迅速（５分以内）に行うことが望ましく、１００℃以下の加熱又は真空乾燥が好適である。 In the first and second embodiments, the step of once drying after the droplets are attached is essential for limiting the region where the salt is attached. If drying takes time, corrosion may begin during drying. Desirably, the drying after forming the droplets is performed quickly (within 5 minutes), and heating at 100 ° C. or lower or vacuum drying is preferable.
上記手順により、液滴の付着領域、付着量が制御され、再現性良く局所的な塩付着を行うことができる。その後、第１の実施形態では恒温恒湿試験を、第２の実施形態では乾湿繰返試験を実施する。 By the above procedure, the adhesion area and the adhesion amount of the droplet are controlled, and local salt adhesion can be performed with good reproducibility. Thereafter, a constant temperature and humidity test is performed in the first embodiment, and a dry and wet repeated test is performed in the second embodiment.
恒温恒湿試験は、一定の保管環境における発錆状態を観察するのに適しており、乾湿繰返試験は、乾湿が繰り返される保管環境、輸送環境、使用環境における発錆状態を観察するのに適している。乾湿繰返試験を行う場合、非特許文献３に記載の、露点一定条件下での乾湿繰返が、実際の保管環境を再現していると考えられる。 The constant temperature and humidity test is suitable for observing the rusting state in a certain storage environment, and the repeated drying and wetting test is for observing the rusting state in a storage environment where transporting and drying is repeated, transportation environment, and use environment. Is suitable. When performing a dry and wet test, it is considered that the dry and wet process described in Non-Patent Document 3 under the condition of constant dew point reproduces the actual storage environment.
露点一定条件下での乾湿繰返試験は、例えば、以下のようにして行う。試験槽内の露点を３８℃にし、試験片温度を６０℃に４時間保定した後、１時間の移行時間を設けて、試験片温度を４０℃にして４時間保定し、再び、１時間の移行時間を設けて、再び、試験片温度を６０℃にして４時間保定する。このサイクルを所定回数繰り返す。 For example, the wet and dry repeated test under the constant dew point condition is performed as follows. The dew point in the test tank was set to 38 ° C., the test piece temperature was held at 60 ° C. for 4 hours, a transition time of 1 hour was provided, the test piece temperature was set to 40 ° C., held for 4 hours, and again for 1 hour. A transition time is provided, and the test piece temperature is again set to 60 ° C. and held for 4 hours. This cycle is repeated a predetermined number of times.
このサイクル条件においては、６０℃保定が、湿度３３％の乾燥に相当し、４０℃保定が、湿度９０％の湿潤に相当する。ここに、「保定時間」とは、一定の状態に維持する時間であり、「移行時間」とは、「ある条件」から「他の条件」への移行に要する時間である。第２の実施形態において、上記「乾湿繰返」条件は、使用者における保管環境や使用環境に応じて適宜決めることができる。 In this cycle condition, holding at 60 ° C. corresponds to drying at a humidity of 33%, and holding at 40 ° C. corresponds to wetting at a humidity of 90%. Here, “holding time” is the time for maintaining a certain state, and “transition time” is the time required for transition from “a certain condition” to “another condition”. In the second embodiment, the “wet and dry repeat” condition can be appropriately determined according to the storage environment and use environment of the user.
電磁鋼板表面の観察は、個々の液滴乾燥痕に対して実施する。ＥＰＭＡ、目視または顕微鏡観察により発錆の有無を確認し、錆が発生しない塩水溶液の濃度、錆発生の原因となる物質、及び、錆が発生しない環境の露点を特定する。 Observation of the surface of the electrical steel sheet is carried out on individual droplet drying marks. The presence or absence of rusting is confirmed by EPMA, visual observation or microscopic observation, and the concentration of the salt aqueous solution that does not generate rust, the substance that causes rusting, and the dew point of the environment that does not generate rusting are specified.
塩水溶液の濃度の低下とともに、塩の付着量が減少するので、発錆程度が軽度になり、最終的には錆が発生しなくなる。この錆が発生しなくなる限界の塩濃度をもって、電磁鋼板の耐錆性を定量的にかつ再現性良く評価することができる。 As the concentration of the aqueous salt solution decreases, the amount of salt attached decreases, so the degree of rusting becomes mild and eventually rust does not occur. The rust resistance of the electrical steel sheet can be evaluated quantitatively and with good reproducibility with the salt concentration at which the rust is not generated.
なお、上記実施形態は、何れも本発明を実施するにあたっての具体化の例を示したものに過ぎず、これらによって本発明の技術的範囲が限定的に解釈されてはならないものである。すなわち、本発明はその技術思想、又はその主要な特徴から逸脱することなく、様々な形で実施することができる。 The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.
次に、本発明の実施例について説明する。実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。 Next, examples of the present invention will be described. The conditions in the examples are one condition example adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one condition example. 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.
（実施例１）
クロム酸マグネシウム、ほう酸、アクリル樹脂エマルション、グリセリンから構成される液を、電磁鋼板に塗布し乾燥して、絶縁皮膜を形成した（特公昭５０−１５０１３号公報、参照）。皮膜形成量は１ｇ／ｍ2とした。
Example 1
A liquid composed of magnesium chromate, boric acid, acrylic resin emulsion, and glycerin was applied to a magnetic steel sheet and dried to form an insulating film (see Japanese Patent Publication No. 50-15013). The film formation amount was 1 g / m 2 .
塩化ナトリウム０．３質量％の水溶液を用意し、試験片として採取した電磁鋼板の絶縁皮膜に、マイクロピペットにより、０．５μｌの水溶液を滴下し、電磁鋼板の表面に液滴を付着させた。液滴の態様を図２（ａ）に示す。試験片を、真空デシケータを用いて真空乾燥し、試験片の液滴付着領域に塩の付着を行った。液滴乾燥は２分間行った。 An aqueous solution of 0.3% by mass of sodium chloride was prepared, and 0.5 μl of an aqueous solution was dropped onto the insulating film of the magnetic steel sheet collected as a test piece with a micropipette, and a droplet was adhered to the surface of the magnetic steel sheet. The mode of the droplet is shown in FIG. The test piece was vacuum-dried using a vacuum desiccator, and salt was attached to the droplet adhesion region of the test piece. Droplet drying was performed for 2 minutes.
乾燥後、相対湿度９５％、５０℃の恒温恒湿槽内に４８時間保定した。その結果を図２（ｂ）に示す。図２（ａ）に示す液滴サイズに対応して錆が発生していることが解る。液滴付着領域以外の領域では発錆していない。塩の局所付着による発錆を再現できたことになる。 After drying, it was kept for 48 hours in a constant temperature and humidity chamber of 95% relative humidity and 50 ° C. The result is shown in FIG. It can be seen that rust is generated corresponding to the droplet size shown in FIG. There is no rusting in areas other than the droplet adhesion area. It was possible to reproduce rusting due to local adhesion of salt.
（実施例２）
塩化ナトリウム及び塩化カルシウムの３質量％、１質量％、０．３質量％、０．１質量％、０．０３質量％、０．０１質量％、０．００３質量％の水溶液を用意した。これらの水溶液の１０μｌの液滴を、実施例１で用いた試験片と同じ電磁鋼板コイルから採取した１枚の試験片の表面に付着させ、真空乾燥により乾燥した。
(Example 2)
An aqueous solution of 3% by mass, 1% by mass, 0.3% by mass, 0.1% by mass, 0.03% by mass, 0.01% by mass, and 0.003% by mass of sodium chloride and calcium chloride was prepared. 10 μl droplets of these aqueous solutions were attached to the surface of one test piece taken from the same magnetic steel sheet coil as the test piece used in Example 1, and dried by vacuum drying.
この試験片を、相対湿度９５％、５０℃の恒温恒湿槽内に９６時間保定し、錆発生の有無を確認した。その結果を表１に示す。０．０３質量％以上の塩濃度の水溶液で錆が発生したことが解る。 This test piece was kept in a constant temperature and humidity chamber with a relative humidity of 95% and 50 ° C. for 96 hours to confirm whether or not rust was generated. The results are shown in Table 1. It can be seen that rust was generated in an aqueous solution having a salt concentration of 0.03% by mass or more.
（実施例３）
Ｎａ、Ｍｇ、Ｃａ、の塩化物、硝酸塩、硫酸塩、炭酸塩、及び、水酸化物を用いて、０．１質量％の水溶液を用意した（ただし、炭酸マグネシウム、炭酸カルシウム、水酸化マグネシウムは、水に対する溶解度が０．１％に満たないので、除いた）。
(Example 3)
A 0.1 mass% aqueous solution was prepared using Na, Mg, Ca chloride, nitrate, sulfate, carbonate, and hydroxide (however, magnesium carbonate, calcium carbonate, and magnesium hydroxide are This was excluded because the solubility in water was less than 0.1%).
これらの水溶液の２μｌの液滴を、実施例１で用いた試験片と同じ電磁鋼板コイルから採取した１枚の試験片の表面に付着させ、真空乾燥により乾燥した。この試験片を、相対湿度９５％、５０℃の恒温恒湿槽内に４８時間保定し、錆発生の有無を確認した。その結果を表２に示す。表２より、どのような塩の付着が錆の原因となるかを判定することができる。 2 μl droplets of these aqueous solutions were attached to the surface of one test piece taken from the same magnetic steel sheet coil as the test piece used in Example 1, and dried by vacuum drying. This test piece was kept in a constant temperature and humidity chamber of 95% relative humidity and 50 ° C. for 48 hours to confirm the presence or absence of rust generation. The results are shown in Table 2. From Table 2, it can be determined what kind of salt adhesion causes rust.
（実施例４）
実施例１で用いた試験片と同じ電磁鋼板コイルから５枚の試験片を採取した。塩化ナトリウム、塩化マグネシウム、及び、塩化カルシウムの０．１％の水溶液を用意した。各試験片にこれらの水溶液の２μｌの液滴を付着させ、真空乾燥により乾燥した。
Example 4
Five test pieces were collected from the same magnetic steel sheet coil as the test piece used in Example 1. A 0.1% aqueous solution of sodium chloride, magnesium chloride, and calcium chloride was prepared. 2 μl droplets of these aqueous solutions were attached to each test piece and dried by vacuum drying.
これらの試験片に対し、表３に示す５種類の露点の条件下で、試験片温度６０℃と４０℃で乾湿繰返試験を行った。乾燥及び湿潤での保定時間は、いずれも４時間とし、両者の移行時間は１時間、繰返回数は８０サイクル（３０日間）とした。 These test pieces were subjected to a wet and dry repeated test at the test piece temperatures of 60 ° C. and 40 ° C. under the conditions of five types of dew points shown in Table 3. The retention time in dry and wet conditions was 4 hours for both, the transition time for both was 1 hour, and the number of repetitions was 80 cycles (30 days).
試験完了後の発錆状況を表３に示す。表３より、付着物質により、発錆が起こる保管条件（湿度）が異なることが解る。結露し易い塩化マグネシウムや塩化カルシウムは、低い露点でも錆を誘引し易いことが解る。 Table 3 shows the rusting situation after the test is completed. From Table 3, it can be seen that the storage conditions (humidity) at which rusting occurs differ depending on the adhered substances. It can be seen that magnesium chloride and calcium chloride, which are easy to condense, tend to attract rust even at a low dew point.
前述したように、本発明によれば、電磁鋼板の保管、使用中における錆発生の可能性（付着物種類、付着量、保管温度と湿度、使用温度と湿度等による錆発生の可能性）を定量的にかつ再現性良く評価することができる。更に、本発明によれば、定量的でかつ再現性が良い耐食性評価に基づいて、適切な錆防止対策又は錆抑制対策を容易に立案することができる。よって、本発明は、電磁鋼板製造及び利用産業において利用可能性が高いものである。 As described above, according to the present invention, the possibility of rust generation during storage and use of electrical steel sheets (adhesive matter type, amount attached, storage temperature and humidity, possibility of rust generation due to use temperature and humidity, etc.) It can be evaluated quantitatively and with good reproducibility. Furthermore, according to the present invention, it is possible to easily devise an appropriate rust prevention measure or rust suppression measure based on quantitative and reproducible corrosion resistance evaluation. Therefore, the present invention has high applicability in the manufacture and use industries of electrical steel sheets.
Claims (6)
上記電磁鋼板を、恒温恒湿状態に所定時間保持する工程と、
その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、及び、錆発生の原因となる物質のいずれか一つ又は二つを評価する工程と、
を有することを特徴とする電磁鋼板の耐食性評価方法。 A step of locally attaching and drying droplets of a certain size of a plurality of salt aqueous solutions having different concentrations on the surface of an electrical steel sheet to which an insulating coating has been applied; and
Holding the electromagnetic steel sheet in a constant temperature and humidity state for a predetermined time;
Then, observe the rusting state of the drying marks of the individual droplets on the surface of the magnetic steel sheet, the concentration of the salt aqueous solution that does not generate rust, and any one or two of the substances that cause rust generation A process of evaluating;
A method for evaluating the corrosion resistance of an electrical steel sheet, comprising:
上記電磁鋼板を、乾燥状態と湿潤状態に、交互に、所定時間保持する工程と、
その後、上記電磁鋼板の表面における個々の液滴の乾燥痕の発錆状態を観察し、錆が発生しない塩水溶液の濃度、錆発生の原因となる物質、及び、錆が発生しない環境の露点のいずれか一つ又は二つ以上を評価する工程と、
を有することを特徴とする電磁鋼板の耐食性評価方法。 A step of locally attaching and drying droplets of a certain size of a plurality of salt aqueous solutions having different concentrations on the surface of an electrical steel sheet to which an insulating film has been applied; and
Holding the electromagnetic steel sheet alternately in a dry state and a wet state for a predetermined time; and
Then, observe the rusting state of the drying traces of the individual droplets on the surface of the magnetic steel sheet, the concentration of the salt aqueous solution that does not generate rust, the substances that cause rusting, and the dew point of the environment that does not generate rusting Evaluating any one or more, and
A method for evaluating the corrosion resistance of an electrical steel sheet, comprising:
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