JP6447957B2 - Steel hydrogen embrittlement test solution, hydrogen charging method and hydrogen embrittlement test method - Google Patents
Steel hydrogen embrittlement test solution, hydrogen charging method and hydrogen embrittlement test method Download PDFInfo
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Description
本発明は、高強度の鋼材に対し、効率的に再現性よく、かつ刺激臭のある気体を発生させずに水素を添加することができる水素脆化試験溶液、それを用いた水素チャージ方法および水素脆化試験方法に関する。 The present invention relates to a hydrogen embrittlement test solution capable of adding hydrogen to a high-strength steel material with good reproducibility and without generating a gas with an irritating odor, a hydrogen charging method using the same, and The present invention relates to a hydrogen embrittlement test method.
電柱に使用されるコンクリート柱のようなプレストレスト構造物の内部鉄筋には、ＰＣ鋼材に代表される高強度鋼材が使用される。また、電力設備の保守保全を行うための高所作業車などは、偽装による重量化を避けるため、高強度鋼板を用いて軽量化し燃料費などの負荷を軽減することが求められている。 A high-strength steel material typified by a PC steel material is used as an internal reinforcing bar of a prestressed structure such as a concrete column used for a power pole. In addition, aerial work vehicles for maintenance and maintenance of electric power facilities are required to be lightened by using high-strength steel sheets to reduce the load such as fuel costs in order to avoid weight increase due to camouflage.
高強度鋼材を使用する時は、一般に水素脆化による鋼材損傷が懸念されることから、鋼材に溶液中で水素を促進添加する水素チャージや水素脆化試験が行われてきた。現状、鋼材に高濃度の水素を添加できる手法として、チオシアン酸アンモニウムを用いた溶液中での浸漬試験や水素チャージ方法が、もっとも高濃度の水素を鋼材に添加できることが報告されている（非特許文献１、非特許文献２）。 When using high-strength steel materials, there is a general concern about damage to steel materials due to hydrogen embrittlement, and therefore hydrogen charging and hydrogen embrittlement tests in which hydrogen is promoted and added to steel materials in solution have been performed. Currently, as a technique that can add high-concentration hydrogen to steel, it has been reported that immersion tests in solutions using ammonium thiocyanate and hydrogen charging methods can add the highest concentration of hydrogen to steel (non-patented). Document 1, Non-Patent Document 2).
上記の浸漬試験では、５０℃のチオシアン酸アンモニウム（ＮＨ４ＳＣＮ）２０ｍａｓｓ％水溶液中にＰＣ鋼材を浸漬し、水素を吸収して金属材料が脆化される現象（脆化特性）を測定する。チオシアン酸アンモニウムを用いた非特許文献１の浸漬試験では、鋼中水素量は２４ｈ程度で最大となり、その後、緩やかに低下することが報告されている。また、溶液ｐＨは短時間でｐＨ６．５程度になり２００ｈの試験期間中は安定していることが報告されている。 In the above immersion test, a PC steel material is immersed in a 20 mass% aqueous solution of ammonium thiocyanate (NH 4 SCN) at 50 ° C., and a phenomenon (embrittlement characteristic) in which the metal material is embrittled by absorbing hydrogen is measured. In the immersion test of Non-Patent Document 1 using ammonium thiocyanate, it has been reported that the amount of hydrogen in steel reaches a maximum at about 24 hours and then gradually decreases. Further, it has been reported that the solution pH becomes about pH 6.5 in a short time and is stable during the test period of 200 h.
チオシアン酸アンモニウムによる水素添加の作用については、アンモニウムイオンの緩衝作用によるｐＨの安定、およびチオシアン酸イオンの分解反応による水素侵入作用が報告されており、チオシアン酸アンモニウムは、緩衝作用によるｐＨの安定とチオシアン酸イオン（ＳＣＮ−）の分解反応による水素チャージ機能を兼ね備えた試薬であると報告されている（非特許文献３）。非特許文献３のＦｉｇ．５では鋼材浸漬後に、溶液ｐＨは緩衝機能により６．５に維持されることが示されている。また、アンモニウムイオンの緩衝機能を前提として、ＮＨ３＋Ｈ２Ｏ→ＮＨ４ＯＨ の解離定数（ＫＢ）を１０−４．７５、水の解離定数（ＫＷ）を１０−１４、２０％ＮＨ４ＳＣＮ溶液の濃度（ＣＮＨ４ＳＣＮ）を２．７３３ｍｏｌ／Ｌとしたときの試験前溶液ｐＨの計算値が、実際の実験結果と一致することが確認されている。 Regarding the action of hydrogenation with ammonium thiocyanate, it has been reported that the pH is stabilized by the buffering action of ammonium ions and the hydrogen invasion action by the decomposition reaction of thiocyanate ions. It has been reported that the reagent has a hydrogen charging function by the decomposition reaction of thiocyanate ion (SCN − ) (Non-patent Document 3). FIG. 5 shows that the solution pH is maintained at 6.5 by the buffering function after immersion in the steel material. Further, assuming the buffer function of ammonium ions, the dissociation constant (K B ) of NH 3 + H 2 O → NH 4 OH is 10 −4.75 , the dissociation constant of water (K W ) is 10 −14 , and 20% NH. It has been confirmed that the calculated value of the pre-test solution pH when the concentration of 4 SCN solution (C NH4SCN ) is 2.733 mol / L is consistent with the actual experimental results.
また、高濃度の水素をチャージする方法として、ｐＨ３．０以上の緩衝液と水素チャージ用触媒を併用した溶液に材料を浸漬する方法が開示されている（特許文献１）。高いｐＨで鋼材の腐食を抑制し、水素チャージ用触媒を用いて水素を大量に添加する方法である。緩衝液として、酢酸系、リン酸系、クエン酸系、酒石酸系、ほう酸系が開示され、水素チャージ用触媒として、チオシアン酸アンモニウム、チオ尿素、亜ヒ酸などが開示されている。 Further, as a method of charging high concentration hydrogen, a method of immersing a material in a solution using a buffer solution having a pH of 3.0 or higher and a hydrogen charging catalyst is disclosed (Patent Document 1). In this method, corrosion of a steel material is suppressed at a high pH, and a large amount of hydrogen is added using a hydrogen charging catalyst. As the buffer, acetic acid, phosphoric acid, citric acid, tartaric acid and boric acid are disclosed, and as a hydrogen charging catalyst, ammonium thiocyanate, thiourea, arsenous acid and the like are disclosed.
しかしながら、本発明者が、非特許文献１の試験済のチオシアン酸アンモニウム溶液（ｐＨ６．５）を再使用して、非特許文献１の条件で鋼材に２４ｈの水素チャージを行ったところ、アンモニウムイオンの緩衝作用により、試験期間中はｐＨが６．５で安定したものの、鋼中水素濃度は３ｐｐｍまでしか上がらなかった。また、さらに浸漬を継続したところｐＨは７を超えて上昇し、気相からアンモニアが検出された。 However, when the present inventors reused the tested ammonium thiocyanate solution (pH 6.5) of Non-Patent Document 1 and charged the steel material with hydrogen for 24 h under the conditions of Non-Patent Document 1, ammonium ions were obtained. Although the pH was stable at 6.5 during the test period, the hydrogen concentration in the steel increased only to 3 ppm. Further, when the immersion was further continued, the pH rose beyond 7 and ammonia was detected from the gas phase.
特許文献１の方法でも、鋼中水素濃度は、陰極チャージ試験（水素電解チャージ）で最大１．８ｐｐｍ、浸漬試験で最大２．５ｐｐｍであり、古くからある非特許文献１の方法の３ｐｐｍ程度の濃度の水素を鋼材に添加することも難しかった。 Even in the method of Patent Document 1, the hydrogen concentration in steel is 1.8 ppm at the maximum in the cathodic charge test (hydrogen electrolysis charge) and 2.5 ppm at the maximum in the immersion test, which is about 3 ppm of the method of the old Non-Patent Document 1. It was also difficult to add a concentration of hydrogen to the steel.
非特許文献２においても、チオシアン酸アンモニウムを添加した溶液中での水素電解チャージ、および非特許文献１の２０％チオシアン酸アンモニウムへの単純浸漬が、既存の方法で最も効率よく高い鋼中水素濃度を実現する方法とされており、チオシアン酸アンモニウムよりも高濃度の鋼中水素濃度を得ることが、如何に難しいことであるかわかった。 Also in Non-Patent Document 2, hydrogen electrolytic charge in a solution to which ammonium thiocyanate is added and simple immersion in 20% ammonium thiocyanate of Non-Patent Document 1 are the most efficient hydrogen concentrations in steel by existing methods. It has been found that it is difficult to obtain a hydrogen concentration in steel that is higher than that of ammonium thiocyanate.
以上の課題を解決するために、本発明は、チオシアン酸アンモニウムを用いた方法の鋼中水素濃度を超える、より高濃度の水素を鋼材に短時間で添加することが可能で、長期試験での水素添加の再現性向上や溶液のｐＨ変動を抑制することが可能な試験溶液、ならびに前記試験溶液を用いた水素チャージ方法および水素脆化試験方法を提供することを目的とする。 In order to solve the above problems, the present invention can add a higher concentration of hydrogen to the steel material in a short time, exceeding the hydrogen concentration in the steel of the method using ammonium thiocyanate. It is an object of the present invention to provide a test solution capable of improving reproducibility of hydrogenation and suppressing pH fluctuation of the solution, and a hydrogen charging method and a hydrogen embrittlement test method using the test solution.
本発明者は、非特許文献１の浸漬法による水素添加において、鋼中水素濃度が２４ｈ程度でピークを示す現象は、鉄酸化物と鉄硫化物による皮膜の生成にともない、チオシアン酸イオンが関与する水素侵入反応が抑制されることが原因であることを解明した。
即ち、鉄酸化物の生成は、溶存酸素が関与する反応であるため、必要であれば脱気により抑制できる。一方、鉄硫化物の生成は、ｐＨ上昇とともに析出が促進される。したがって、鉄硫化物の析出を抑制するには溶液ｐＨを少なくとも７以下、望ましくは５．５以下と低くして鉄硫化物の皮膜生成を抑制し、水素侵入を継続させることが望ましい。反対に試験溶液のｐＨを低くしすぎると、試験材となる鋼材の腐食を促進してしまい、試験材特有の形状などをかえてしまうおそれがあり、鋼材表面の腐食を抑制する必要がある浸漬試験では、試験溶液のｐＨは４以上にすることが望ましい。
In the hydrogenation by the dipping method of Non-Patent Document 1, the present inventor has found that the phenomenon in which the hydrogen concentration in the steel shows a peak at about 24 h is due to thiocyanate ions accompanying the formation of a film with iron oxide and iron sulfide. It was clarified that the cause is that the hydrogen invasion reaction is suppressed.
That is, since the production of iron oxide is a reaction involving dissolved oxygen, it can be suppressed by deaeration if necessary. On the other hand, precipitation of iron sulfide is promoted with an increase in pH. Therefore, in order to suppress the precipitation of iron sulfide, it is desirable to reduce the solution pH to at least 7 or less, preferably 5.5 or less to suppress the formation of iron sulfide film and to continue the hydrogen intrusion. On the other hand, if the pH of the test solution is too low, corrosion of the steel used as the test material may be accelerated and the shape unique to the test material may be changed. In the test, the pH of the test solution is desirably 4 or higher.
浸漬試験において、試験溶液のｐＨを４〜５．５に緩衝して制御するには、電離定数指数ｐＫａが５でｐＨ４〜６で有効に作用する酢酸が最適であることから、酢酸−酢酸ナトリウムが緩衝溶液として好ましい。酢酸アンモニウムのｐＫａは９と高く、目的とするｐＨでの緩衝作用には不適であり、ｐＨが不安定になる要因となる。チオシアン酸イオンは水素侵入に必須であることから、チオシアン酸イオンとしては緩衝機能を持たないチオシアン酸ナトリウムあるいはチオシアン酸カリウムが好ましく、コストや汎用性、緩衝液とのイオンの共通性を考えるとチオシアン酸ナトリウムがより好ましい。 In the immersion test, in order to buffer and control the pH of the test solution to 4 to 5.5, acetic acid that effectively works at an ionization constant index pKa of 5 and a pH of 4 to 6 is optimal. Is preferred as a buffer solution. Ammonium acetate has a high pKa of 9, which is unsuitable for buffering at the intended pH and causes the pH to become unstable. Since thiocyanate ion is essential for hydrogen penetration, sodium thiocyanate or potassium thiocyanate that does not have a buffer function is preferable as the thiocyanate ion. Sodium acid is more preferred.
また、浸漬試験において試験溶液のｐＨが上昇する原因を究明するため、チオシアン酸ナトリウムを添加した試験溶液のｐＨを試験開始前に酢酸緩衝溶液でｐＨ４．２に制御し、浸漬試験を行った後の溶液を分析した結果、アンモニウムイオンが検出された。
即ち、ｐＨの上昇は、水素侵入に関与する反応でアンモニウムが生成していることが原因と推察され、チオシアン酸イオンの反応量に合わせた適正量の緩衝液を用いることで、溶液のｐＨ変動を抑制できることを見出した。
In order to investigate the cause of the increase in pH of the test solution in the immersion test, the pH of the test solution to which sodium thiocyanate was added was controlled to pH 4.2 with an acetic acid buffer solution before the test was started, and the immersion test was performed. As a result of analyzing the solution, ammonium ions were detected.
In other words, the increase in pH is presumed to be caused by the formation of ammonium in the reaction involved in hydrogen invasion. By using an appropriate amount of buffer solution that matches the reaction amount of thiocyanate ion, the pH change of the solution It was found that can be suppressed.
以上の知見に基づき本発明を完成するに至った。すなわち、本発明は以下の通りである。 The present invention has been completed based on the above findings. That is, the present invention is as follows.
（１）酢酸緩衝溶液とチオシアン酸イオンを含み、かつアンモニウムイオンを含まないことを特徴とする鋼材に対する水素脆化試験溶液。
（２）酢酸と酢酸ナトリウムからなる酢酸緩衝溶液とチオシアン酸カリウムを含み、溶液調製時におけるチオシアン酸カリウムの濃度が０．０６ｍｏｌ／Ｌ以上３．０ｍｏｌ／Ｌ以下、かつ溶液調製時における酢酸ナトリウムの濃度がチオシアン酸カリウムの濃度の１／２００以上同濃度以下である、上記（１）に記載の鋼材に対する水素脆化試験溶液。
（３）酢酸と酢酸ナトリウムからなる酢酸緩衝溶液とチオシアン酸ナトリウムを含み、溶液調製時におけるチオシアン酸ナトリウムの濃度が０．０６ｍｏｌ／Ｌ以上３．０ｍｏｌ／Ｌ以下、かつ溶液調製時における酢酸ナトリウムの濃度がチオシアン酸ナトリウムの濃度の１／２００以上同濃度以下である、上記（１）に記載の鋼材に対する水素脆化試験溶液。
(1) A hydrogen embrittlement test solution for a steel material containing an acetate buffer solution and thiocyanate ions and not containing ammonium ions.
(2) An acetic acid buffer solution consisting of acetic acid and sodium acetate and potassium thiocyanate, the concentration of potassium thiocyanate at the time of solution preparation being 0.06 mol / L to 3.0 mol / L, and sodium acetate at the time of solution preparation The hydrogen embrittlement test solution for a steel material according to (1) above, wherein the concentration is 1/200 or more of the concentration of potassium thiocyanate to the same concentration or less.
(3) An acetic acid buffer solution composed of acetic acid and sodium acetate and sodium thiocyanate, wherein the concentration of sodium thiocyanate at the time of solution preparation is 0.06 mol / L or more and 3.0 mol / L or less, and sodium acetate at the time of solution preparation The hydrogen embrittlement test solution for a steel material according to (1), wherein the concentration is 1/200 or more of the concentration of sodium thiocyanate and the same or less.
（４）上記（１）〜（３）いずれかに記載の鋼材に対する水素脆化試験溶液を、試験材面積当り５ｍｌ／ｃｍ２以上の量で用い、試験開始前に酢酸を用いてｐＨ４．０〜５．５の範囲に調整した前記水素脆化試験溶液に、試験材を浸漬して、試験材中の水素濃度を高めることを特徴とする水素チャージ方法。
（５）浸漬試験中あるいは陰極チャージ試験中の水素脆化試験溶液内の溶存酸素濃度を、大気開放状態の１／１０以下に保持する、上記（４）に記載の水素チャージ方法。
（６）上記（４）または（５）に記載の水素チャージ方法で試験材に水素をチャージし、試験材の水素脆化特性を評価することを特徴とする水素脆化試験方法。
(4) The hydrogen embrittlement test solution for the steel material according to any one of (1) to (3) above is used in an amount of 5 ml / cm 2 or more per test material area, and the pH is 4.0 using acetic acid before the start of the test. A hydrogen charging method characterized by increasing the hydrogen concentration in the test material by immersing the test material in the hydrogen embrittlement test solution adjusted to a range of ˜5.5.
(5) The hydrogen charging method according to the above (4), wherein the dissolved oxygen concentration in the hydrogen embrittlement test solution during the immersion test or the cathode charge test is maintained at 1/10 or less of the atmospheric release state.
(6) A hydrogen embrittlement test method, wherein the test material is charged with hydrogen by the hydrogen charging method described in (4) or (5) above and the hydrogen embrittlement characteristics of the test material are evaluated.
本発明の水素脆化試験溶液およびそれを用いた水素チャージ法によれば、簡便な浸漬法でありながら、従来の浸漬法よりも高濃度の鋼中水素濃度を可能としたことにより、より低濃度の試薬で、短時間で、効率的に、精度の高い水素脆化試験を行うことができる。
本発明の水素脆化試験方法によれば、定荷重や定歪速度を付与する機械試験に供した試験材あるいは加工などの応力を付与した試験材に適用することにより、従来よりも高濃度の鋼中水素濃度を実現できるので、効率的により精度の高い水素脆化試験を行うことができる。
According to the hydrogen embrittlement test solution of the present invention and the hydrogen charging method using the same, the hydrogen concentration in the steel is higher than that of the conventional immersion method while being a simple immersion method. A highly accurate hydrogen embrittlement test can be performed efficiently in a short time with a reagent having a concentration.
According to the hydrogen embrittlement test method of the present invention, it can be applied to a test material subjected to a mechanical test that imparts a constant load or a constant strain rate or a test material that is subjected to stress such as processing. Since the hydrogen concentration in steel can be achieved, a more accurate hydrogen embrittlement test can be performed efficiently.
本発明の鋼材に対する水素脆化試験溶液は、酢酸緩衝溶液とチオシアン酸イオン（ＳＣＮ−）を含み、かつアンモニウムイオン（ＮＨ４ ＋）を含まないことを特徴とする。アンモニウムイオンが含まれることにより、試験溶液のｐＨが上昇し、水素濃度が上がらなくなるからである。酢酸緩衝溶液としては、酢酸−酢酸ナトリウム緩衝液が最適である。 The hydrogen embrittlement test solution for the steel material of the present invention is characterized by containing an acetate buffer solution and thiocyanate ions (SCN − ) and not containing ammonium ions (NH 4 + ). This is because inclusion of ammonium ions raises the pH of the test solution and prevents the hydrogen concentration from increasing. As the acetate buffer solution, an acetate-sodium acetate buffer is optimal.
水素脆化試験溶液における酢酸ナトリウムの濃度は、ｐＨ上昇によるアンモニウムの生成や水素濃度の低下を抑制するため、チオシアン酸イオン濃度の少なくとも１／２００以上にすることが好ましく、より好ましくは１／１００以上、特に好ましくは１／１０以上である。また、チオシアン酸イオン濃度を超えても効果がなく、試験溶液中で析出し易くなるため、同濃度以下とすることが好ましい。 The concentration of sodium acetate in the hydrogen embrittlement test solution is preferably at least 1/200 of the thiocyanate ion concentration, more preferably 1/100, in order to suppress the formation of ammonium and the decrease in hydrogen concentration due to pH increase. Above, especially preferably 1/10 or more. Moreover, even if it exceeds the thiocyanate ion concentration, there is no effect and it is easy to precipitate in the test solution.
水素脆化試験溶液におけるチオシアン酸イオンとしては、チオシアン酸カリウム（ＫＳＣＮ）、チオシアン酸ナトリウム（ＮａＳＣＮ）が好ましい。チオシアン酸イオンは、水素侵入反応により消費されるため、試験前溶液には反応量に対応する適正量（適正濃度）が必要とされる。適正量のチオシアン酸ＮａもしくはＫの溶液濃度は、対象とする試験鋼材の表面積、処理時間、処理条件での反応速度から推定することができる。
試験溶液調製時のチオシアン酸カリウムもしくはチオシアン酸ナトリウムの濃度は、一般的な条件下では、０．０６ｍｏｌ／Ｌ以上が好ましく、０．０６ｍｏｌ／Ｌ未満では、反応による濃度低下にともない試験溶液中での水素侵入速度が低下し、鋼材からの水素放出により水素濃度が低下する恐れがある。一方、３．０ｍｏｌ／Ｌを超えると、チオシアン酸カリウムやナトリウムの飽和溶解度を超える量の添加となり、効果が飽和する。水素侵入速度を高める観点より、試験溶液調製時のチオシアン酸カリウムもしくはチオシアン酸ナトリウムの濃度は、０．０６〜３．０ｍｏｌ／Ｌの範囲が好ましく、より好ましくは０．１〜３．０ｍｏｌ／Ｌ、特に好ましくは１．０〜３．０ｍｏｌ／Ｌの範囲である。
As thiocyanate ions in the hydrogen embrittlement test solution, potassium thiocyanate (KSCN) and sodium thiocyanate (NaSCN) are preferable. Since thiocyanate ions are consumed by the hydrogen intrusion reaction, an appropriate amount (appropriate concentration) corresponding to the reaction amount is required for the pre-test solution. The solution concentration of an appropriate amount of Na thiocyanate or K can be estimated from the surface area of the target test steel, the treatment time, and the reaction rate under the treatment conditions.
The concentration of potassium thiocyanate or sodium thiocyanate during preparation of the test solution is preferably 0.06 mol / L or more under general conditions, and less than 0.06 mol / L in the test solution as the concentration decreases due to the reaction. There is a risk that the hydrogen intrusion rate of the steel decreases and the hydrogen concentration decreases due to hydrogen release from the steel. On the other hand, if it exceeds 3.0 mol / L, the amount of addition exceeds the saturation solubility of potassium thiocyanate or sodium, and the effect is saturated. From the viewpoint of increasing the hydrogen penetration rate, the concentration of potassium thiocyanate or sodium thiocyanate during the test solution preparation is preferably in the range of 0.06 to 3.0 mol / L, more preferably 0.1 to 3.0 mol / L. Especially preferably, it is the range of 1.0-3.0 mol / L.
チオシアン酸イオン反応量には、試験時間と試験材の面積が影響する。試験時間は長いもので、非特許文献１に示される２００ｈである。そのため、水素脆化試験に供する水素脆化試験溶液量は、試験材の面積当り５ｍｌ／ｃｍ２以上必要であり、水素量で見る限り試験溶液量が少なくとも５ｍｌ／ｃｍ２以上ないと、試験期間中に水素濃度が低下してくるため、試験の再現性が乏しくなる。試験溶液量の上限値はなく、試験材の種類、形状などに応じて、適宜な容量を決定すれば良い。 The amount of thiocyanate ion reaction is affected by the test time and the area of the test material. The test time is long and is 200 h shown in Non-Patent Document 1. Therefore, the hydrogen embrittlement test solution volume subjected to hydrogen embrittlement test is required per area 5 ml / cm 2 or more test material, the at least 5 ml / cm 2 or more with no test solution amount as far as hydrogen amount, the test period Since the hydrogen concentration decreases, the reproducibility of the test becomes poor. There is no upper limit for the amount of the test solution, and an appropriate volume may be determined according to the type and shape of the test material.
試験装置および試験器具は、ＪＳＣＥ Ｓ １２０１：２０１２「２０％チオシアン酸アンモニウム溶液中でのＰＣ鋼材の水素脆化試験方法」に準ずるものを使用できる。試験溶液調製用器具はガラス製あるいは樹脂製とする。腐食する恐れがある金属製は好ましくない。 As the test apparatus and test equipment, those according to JSCE S 1201: 2012 “Method for testing hydrogen embrittlement of PC steel in 20% ammonium thiocyanate solution” can be used. The test solution preparation instrument is made of glass or resin. Metals that can corrode are not preferred.
また、本発明の水素脆化試験溶液は、調製から試験開始までの間に空気中の二酸化炭素を吸収してｐＨがアルカリ側にシフトしていることがあり得るため、試験開始前に酢酸を用いてｐＨ４．０以上〜５．５以下に調整することが好ましい。なお、ｐＨシフトを防止するためには、酢酸と酢酸ナトリウム１：１からなる１００ｍｍｏｌ酢酸緩衝溶液を作製すれば、緩衝液のｐＨは酢酸のｐＫａ付近の約４．７になり、緩衝作用を最大に利用することができ、さらに、酢酸（水溶液のｐＨ＝２．４）を用いてｐＨ４．０以上に調整することで、試験中の試験溶液ｐＨを安定的に保持し試験期間中のｐＨ変動を維持することで、アンモニウムの生成や水素濃度の低下を抑制する効果をより高めることができる。 In addition, since the hydrogen embrittlement test solution of the present invention may absorb carbon dioxide in the air between the preparation and the start of the test and the pH may be shifted to the alkali side, acetic acid is added before the start of the test. It is preferable to adjust the pH to 4.0 to 5.5. In order to prevent pH shift, if a 100 mmol acetic acid buffer solution composed of acetic acid and sodium acetate 1: 1 is prepared, the pH of the buffer solution is about 4.7 near the pKa of acetic acid, and the buffering action is maximized. Furthermore, by adjusting the pH to 4.0 or higher using acetic acid (aqueous solution pH = 2.4), the pH of the test solution during the test can be stably maintained, and the pH change during the test period. By maintaining the above, the effect of suppressing the generation of ammonium and the decrease in the hydrogen concentration can be further enhanced.
試験対象とする鋼材形状や試験目的によっては、鋼材の腐食による表面変形を抑制するため試験中の腐食を抑制する必要がある。チオシアン酸ナトリウムを酢酸緩衝溶液でｐＨ４．２に制御した溶液系で空気解放と窒素脱気の条件で試験を行った結果によれば、溶存酸素による腐食反応が、全体の腐食反応量の５０％程度である。溶存酸素濃度は、例えば液温２０℃の場合、約８ｐｐｍである。水素侵入を促進するにはチオシアン酸ナトリウムによる腐食反応は必須であり、コストが掛かるものの窒素やアルゴンで脱気した条件で試験を行えば、試験溶液中での腐食による試験材の損傷を低減することができる。溶存酸素濃度として、大気開放状態の１／１０以下に保持することが好ましく、例えば液温２０℃の場合、約０．８ｐｐｍ以下にすることが好ましい。 Depending on the shape of the steel material to be tested and the purpose of the test, it is necessary to suppress corrosion during the test in order to suppress surface deformation due to corrosion of the steel material. According to the results of testing in a solution system in which sodium thiocyanate was adjusted to pH 4.2 with an acetic acid buffer solution under conditions of air release and nitrogen deaeration, the corrosion reaction by dissolved oxygen was 50% of the total corrosion reaction amount. Degree. The dissolved oxygen concentration is, for example, about 8 ppm when the liquid temperature is 20 ° C. Corrosion reaction with sodium thiocyanate is indispensable for promoting hydrogen intrusion, and although it is costly, if the test is performed under a degassed condition with nitrogen or argon, damage to the test material due to corrosion in the test solution is reduced. be able to. The dissolved oxygen concentration is preferably maintained at 1/10 or less of the open air state. For example, when the liquid temperature is 20 ° C., it is preferably about 0.8 ppm or less.
本発明の水素チャージ方法あるいは水素脆化試験方法により、２．７ｍｏｌ／Ｌのチオシアン酸ナトリウムを酢酸緩衝溶液でｐＨ４．２に制御した溶液系で、鋼材面積に対する試験液量１０ｍｌ／ｃｍ２、窒素脱気、非特許文献１と同温度の５０℃、２４ｈの浸漬試験で、４．９ｐｐｍという高い鋼中水素量を確認できた。この濃度は、非特許文献２や特許文献１に報告されている鋼中水素濃度３ｐｐｍや２．８ｐｐｍよりも高い濃度である。 In a solution system in which 2.7 mol / L sodium thiocyanate is controlled to pH 4.2 with an acetic acid buffer solution by the hydrogen charging method or hydrogen embrittlement test method of the present invention, the amount of test solution is 10 ml / cm 2 with respect to the steel material area, nitrogen In the deaeration, the immersion test at 50 ° C. for 24 hours at the same temperature as in Non-Patent Document 1, a high hydrogen content in steel of 4.9 ppm was confirmed. This concentration is higher than the hydrogen concentration 3 ppm or 2.8 ppm in steel reported in Non-Patent Document 2 or Patent Document 1.
また、水素脆化試験溶液にチオシアン酸アンモニウムを用いた試験でのアンモニアの発生は、主として試験前の溶液に含まれるアンモニウムイオンが、溶液のｐＨ上昇により溶液中からアンモニアとして発生したものと考えられる。チオシアン酸ナトリウムやチオシアン酸カリウムでは溶液がｐＨ上昇してもアンモニアの発生は認められなかった。 In addition, the generation of ammonia in the test using ammonium thiocyanate as the hydrogen embrittlement test solution is thought to be mainly due to the ammonium ions contained in the solution before the test being generated as ammonia from the solution due to the pH increase of the solution. . With sodium thiocyanate and potassium thiocyanate, no ammonia was generated even when the pH of the solution was increased.
水素チャージを行う試験材としては、水素脆化感受性を有する高強度の鋼材で、高強度のＰＣ鋼材、高強度薄板、低合金鋼材、ステンレス鋼材等が挙げられる。試験材の形態は、特別な制限はなく、例えば、試験片、鋼材、それらより製造された成型部品など、いずれの形態でもよい。部品の場合は、大型で複雑な形状の成形品でもよい。 Examples of the test material that performs hydrogen charging include high-strength steel materials that are susceptible to hydrogen embrittlement, such as high-strength PC steel materials, high-strength thin plates, low-alloy steel materials, and stainless steel materials. There is no special restriction | limiting in the form of a test material, For example, any form, such as a test piece, steel materials, a molded part manufactured from them, may be sufficient. In the case of a part, it may be a molded product having a large and complicated shape.
以下、本発明を実施例および比較例を用いて具体的に説明するが、本発明は以下の実施例にのみ限定されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited only to a following example.
（実施例）
水素脆化試験溶液として、表１に示す組成、ｐＨの溶液を調製した。酢酸緩衝溶液を調製するため、酢酸と酢酸ナトリウムを同モル配合した。
試験開始前に酢酸（氷酢酸）を用いて、試験溶液のｐＨを表１に示すｐＨ（浸漬前）に調整した後、一部の試験溶液には窒素ガスをバブリングさせて脱気した。水素脆化試験溶液の試験材表面積当りの比液量（ｍｌ／ｃｍ２）は表１に示す量とした。
(Example)
As a hydrogen embrittlement test solution, a solution having the composition and pH shown in Table 1 was prepared. In order to prepare an acetate buffer solution, acetic acid and sodium acetate were mixed in the same molar amount.
Before starting the test, the pH of the test solution was adjusted to the pH shown in Table 1 (before immersion) using acetic acid (glacial acetic acid), and then a part of the test solution was deaerated by bubbling nitrogen gas. The specific liquid amount (ml / cm 2 ) per surface area of the test material in the hydrogen embrittlement test solution was the amount shown in Table 1.
試験材は、ＪＩＳ Ｇ ３１３７：２００８（細径異形ＰＣ鋼棒）Ｄ種１号に相当する直径７．１ｍｍ、引張り強さ１，４５５ＭＰａのマルテンサイト組織を有するＰＣ鋼棒を用いた。浸漬試験および水素侵入量の評価に供した試験材は、試験前に外周をエメリー＃４００研磨を施しアセトンで脱脂し、重量測定を行った。 As a test material, a PC steel rod having a martensite structure with a diameter of 7.1 mm and a tensile strength of 1,455 MPa corresponding to JIS G 3137: 2008 (small-diameter deformed PC steel rod) type D No. 1 was used. The test materials used for the immersion test and the evaluation of the hydrogen penetration amount were emery # 400 polished on the outer periphery before the test, degreased with acetone, and weighed.
鋼中水素量の測定は、浸漬後の試験材を溶液から取り出し、腐食生成物を機械的に除去し、アセトン洗浄後ただちに実施し、水素分析は昇温脱離分析法で行った。Ａｒ中に５０ｖｏｌｐｐｍの水素を含んだ標準ガスでキャリブレーションしたガストロマトグラフを検出計とし、室温から３００℃まで１００℃ｈ−１で昇温し、５ｍｉｎに１回の間隔で放出される水素をサンプリングした。積算水素量から、鋼中水素濃度を求めた。 The amount of hydrogen in the steel was measured by removing the test material after immersion from the solution, mechanically removing the corrosion products, and immediately after washing with acetone, and hydrogen analysis was performed by temperature programmed desorption analysis. A gastromatograph calibrated with a standard gas containing 50 volppm hydrogen in Ar is used as a detector, and the temperature is raised from room temperature to 300 ° C at 100 ° C h -1 and the hydrogen released at intervals of 5 min is sampled. did. The hydrogen concentration in the steel was determined from the accumulated hydrogen amount.
水素脆化試験溶液の評価は、下記Ａ〜Ｄの方法にて実施した。表１に、２４時間後および２００時間後の試験溶液のｐＨ、および評価結果をあわせて示す。 Evaluation of the hydrogen embrittlement test solution was carried out by the following methods A to D. Table 1 shows the pH of the test solution after 24 hours and 200 hours, and the evaluation results.
［評価Ａ：浸漬試験時の水素侵入量の評価］
既存の浸漬試験方法で高い水素濃度が報告されている非特許文献１のＦＩＰ試験を基準として、水素侵入の効率性を評価し、２４ｈ浸漬後の鋼中水素濃度を測定した。
試験溶液のチオシアン酸ナトリウムあるいはチオシアン酸カリウムの濃度と同一濃度の緩衝溶液を含まないチオシアン酸アンモニウム溶液に比較して、鋼中水素濃度が同等か高くなる溶液組成を効率的な水素侵入条件として「○」、鋼中水素濃度が低くなる溶液組成を優位性無しとして「×」と評価した。
[Evaluation A: Evaluation of hydrogen penetration amount during immersion test]
Based on the FIP test of Non-Patent Document 1 in which a high hydrogen concentration is reported in the existing immersion test method, the efficiency of hydrogen penetration was evaluated, and the hydrogen concentration in steel after 24 hours immersion was measured.
Compared to the ammonium thiocyanate solution that does not contain a buffer solution of the same concentration as sodium thiocyanate or potassium thiocyanate in the test solution, the solution composition in which the hydrogen concentration in the steel is equal or higher is regarded as an efficient hydrogen penetration condition. “O” was evaluated as “x”, assuming that the solution composition in which the hydrogen concentration in the steel was low was not superior.
［評価Ｂ：浸漬試験時の溶液ｐＨ安定性］
試験溶液のｐＨ安定性は、５０℃で２００ｈ浸漬した際の試験溶液ｐＨを、６ｈと２４ｈ浸漬時の試験溶液ｐＨと比較し、変動が±０．１以内に収まっているものを可として「○」、範囲を外れているものを不可として「×」と評価した。また、評価が○の試験条件で２００ｈ浸漬後のｐＨの上昇が２４ｈのｐＨに比較して０．５以内に留まっているものを非常にｐＨが安定しているとして「◎」と評価した。
[Evaluation B: Solution pH stability during immersion test]
The pH stability of the test solution was compared with the test solution pH when immersed for 200 h at 50 ° C. with the test solution pH when immersed for 6 h and 24 h. “○”, and “×” was evaluated as being out of range. In addition, a test in which the evaluation was evaluated as “good” and the increase in pH after immersion for 200 hours remained within 0.5 as compared with the pH of 24 hours was evaluated as “「 ”because the pH was very stable.
［評価Ｃ：浸漬試験時の鋼材腐食の評価］
２４ｈ浸漬試験後に試験材を水洗乾燥し、ＪＩＳ Ｚ ２３７１：２０００（塩水噴霧試験方法）に準拠して除錆処理を施し、試験前との重量差から腐食速度を算出した。
試験溶液のチオシアン酸ナトリウムあるいはチオシアン酸カリウムの濃度と同一濃度の緩衝溶液を含まないチオシアン酸アンモニウム溶液での腐食速度を基準として、腐食速度が同等か低くなる溶液組成を腐食が抑制される条件として「○」、腐食速度が高くなる溶液組成を優位性無しとして「×」と評価した。浸漬時間は２４ｈで比較した。また、本発明となる緩衝溶液を含む大気開放のチアシアン酸ソーダあるいはチオシアン酸カリウム溶液を基準として、同一濃度で腐食速度が更に抑制される条件を、より好ましい条件として「◎」と評価した。
[Evaluation C: Evaluation of steel corrosion during immersion test]
After the 24 h immersion test, the test material was washed with water and dried, subjected to rust removal according to JIS Z 2371: 2000 (salt spray test method), and the corrosion rate was calculated from the weight difference from the test.
Based on the corrosion rate of an ammonium thiocyanate solution that does not contain a buffer solution of the same concentration as the concentration of sodium thiocyanate or potassium thiocyanate in the test solution, the solution composition that makes the corrosion rate equal or lower is the condition for inhibiting corrosion. “○” was evaluated as “x”, assuming that the solution composition with a high corrosion rate had no superiority. The immersion time was compared at 24 hours. In addition, a condition where the corrosion rate is further suppressed at the same concentration based on the atmospheric open sodium thiocyanate or potassium thiocyanate solution containing the buffer solution according to the present invention was evaluated as “◎” as a more preferable condition.
［評価Ｄ：応力を付与した鋼材の水素脆化評価］
１５ｃｍ長さの試験の中央に油圧で曲げ応力を負荷し塑性変形した状態で、４０℃の試験溶液に浸漬し、脆化割れの有無を判断した。応力を付与した近傍で脆化割れを発生した溶液組成を水素脆化試験に適した溶液として「○」、脆化割れを示さない溶液組成を優位性無しとして「×」と評価した。「−」は評価しなかった。
[Evaluation D: Hydrogen embrittlement evaluation of stressed steel]
In the state where a bending stress was applied hydraulically at the center of a 15 cm long test and plastically deformed, it was immersed in a test solution at 40 ° C. to determine the presence or absence of embrittlement cracks. The solution composition in which embrittlement cracking occurred in the vicinity of the applied stress was evaluated as “◯” as a solution suitable for the hydrogen embrittlement test, and the solution composition not exhibiting embrittlement cracking was evaluated as “x” as having no superiority. "-" Was not evaluated.
表１より、チオシアン酸ナトリウム濃度が０．０６ｍｏｌ／Ｌ未満の場合は試験材の鋼中水素侵入量が低下した（比較例９）が、濃度０．０６ｍｏｌ／Ｌ以上にするとともに、酢酸ナトリウム濃度をその１／２００以上にすることで、鋼中水素濃度が増加し、試験溶液のｐＨも安定した（比較例４、５と本発明例の比較）。
水素侵入量は、試験溶液のｐＨが５．５を超える場合（比較例３、比較例６）と４．０未満の場合（比較例４）、および、比液量が５ｍｌ／ｃｍ２未満の場合（比較例８）は、低下する現象が見られた。
試験溶液のｐＨは、チオシアン酸ナトリウムのみで酢酸緩衝溶液を使用しない場合（比較例３）は不安定であった。チオシアン酸アンモニウムを使用した場合（比較例１、比較例２）は酢酸緩衝溶液の有無に拘わらず不安定であった。
試験材の腐蝕速度は、試験溶液のｐＨが４．０を下回る場合に大きくなる傾向があった（比較例４、比較例９）。
From Table 1, when the sodium thiocyanate concentration was less than 0.06 mol / L, the hydrogen penetration amount in the steel of the test material was reduced (Comparative Example 9), while the concentration was 0.06 mol / L or more and the sodium acetate concentration By setting the value to 1/200 or more, the hydrogen concentration in the steel increased and the pH of the test solution was also stabilized (Comparison between Comparative Examples 4 and 5 and Examples of the present invention).
The amount of hydrogen intrusion is when the pH of the test solution exceeds 5.5 (Comparative Example 3, Comparative Example 6) and less than 4.0 (Comparative Example 4), and the specific liquid amount is less than 5 ml / cm 2 . In the case (Comparative Example 8), a decreasing phenomenon was observed.
The pH of the test solution was unstable when only sodium thiocyanate was used and no acetate buffer solution was used (Comparative Example 3). When ammonium thiocyanate was used (Comparative Example 1 and Comparative Example 2), it was unstable regardless of the presence or absence of an acetate buffer solution.
The corrosion rate of the test material tended to increase when the pH of the test solution was below 4.0 (Comparative Example 4 and Comparative Example 9).
また、本発明例においては、試験溶液を脱気して溶存酸素を減少させることで、試験材の腐蝕が抑制される傾向が認められた（本発明例１、５と本発明例２の比較）。チオシアン酸ナトリウムに対する酢酸ナトリウムの濃度比を高くすることにより（本発明例７〜８、１０〜１２）、試験溶液のｐＨが安定する傾向が認められた。 Moreover, in this invention example, the tendency which the corrosion of a test material was suppressed by deaerating a test solution and reducing dissolved oxygen was recognized (Comparison of this invention example 1 and 5 and this invention example 2). ). By increasing the concentration ratio of sodium acetate to sodium thiocyanate (Invention Examples 7 to 8 and 10 to 12), a tendency for the pH of the test solution to stabilize was observed.
本発明の水素脆化試験溶液、それを用いた水素チャージ法および水素脆化試験方法は、従来法に比べて鋼中水素濃度が高く、再現性が良好であるため、鋼材試験方法に有用である。 The hydrogen embrittlement test solution of the present invention, the hydrogen charging method and the hydrogen embrittlement test method using the same are useful for steel testing methods because the hydrogen concentration in steel is higher and the reproducibility is better than the conventional method. is there.
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