JP6973193B2 - Hydrogen embrittlement resistance evaluation method - Google Patents
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Description
本発明は、耐水素脆化特性評価方法に関する。特に、遅れ破壊など水素脆化を発生する可能性のある金属材料（例えば、鋼）の耐水素脆化特性を評価する方法に関する。 The present invention relates to a method for evaluating hydrogen embrittlement resistance. In particular, the present invention relates to a method for evaluating hydrogen embrittlement resistance of a metal material (for example, steel) which may cause hydrogen embrittlement such as delayed fracture.
自動車、各種産業機械などには、軽量化、高性能化などが求められている。特に、機械構造用部品には、土木・建築構造物の建設費削減のため、高強度化が進められている。しかし、鋼などの金属材料は、高強度であるほど、遅れ破壊などの水素脆化を引き起こす可能性が高いという問題がある。 Automobiles, various industrial machines, etc. are required to be lighter and have higher performance. In particular, mechanical structural parts are being strengthened in order to reduce construction costs for civil engineering and building structures. However, there is a problem that the higher the strength of a metal material such as steel, the higher the possibility of causing hydrogen embrittlement such as delayed fracture.
「遅れ破壊」は、静的応力下に置かれた部品が、ある時間経過後に突然、脆性的に破壊する現象である。このような破壊が生じると、重大な事故につながる危険性が高いことから、使用環境において遅れ破壊が生じない材料を選択する必要がある。一般的に水素脆化抑制のためには高合金鋼を用いるのが有効であるが、経済性の観点からは安価な材料の選択が望まれる。したがって、耐遅れ破壊特性に優れ、かつ安価な材料を選択するためには、より詳細に耐水素脆化特性を評価できる方法が必要となる。 "Delayed fracture" is a phenomenon in which a part placed under static stress suddenly breaks brittlely after a certain period of time. If such destruction occurs, there is a high risk of serious accidents, so it is necessary to select a material that does not cause delayed destruction in the usage environment. Generally, it is effective to use high alloy steel to suppress hydrogen embrittlement, but from the economical point of view, it is desirable to select an inexpensive material. Therefore, in order to select an inexpensive material having excellent delayed fracture resistance, a method capable of evaluating hydrogen embrittlement resistance in more detail is required.
従来、遅れ破壊などの水素脆化特性を評価する方法が種々提案されている。特許文献１には、水素侵入した試験片で低歪み速度の引張試験における破断時伸びを測定し、その値から求めた水素脆化危険度指数（％）と鋼中に存在する拡散水素量との相関関係を求め、この相関関係から鋼材の水素脆化危険度を評価する方法が開示されている。また、非特許文献１には、限界拡散性水素量と侵入水素量を比較することによって耐水素脆化特性を評価する方法が開示されている。 Conventionally, various methods for evaluating hydrogen embrittlement characteristics such as delayed fracture have been proposed. Patent Document 1 describes the hydrogen embrittlement risk index (%) obtained by measuring the elongation at break in a low strain rate tensile test with a test piece infiltrated with hydrogen, and the amount of diffused hydrogen present in the steel. A method of determining the correlation between hydrogen embrittlement and evaluating the hydrogen embrittlement risk of steel materials from this correlation is disclosed. Further, Non-Patent Document 1 discloses a method for evaluating hydrogen embrittlement resistance by comparing the amount of critical diffusible hydrogen and the amount of invading hydrogen.
たとえば、自動車は、世界各地で販売され、利用されており、実際に、どのような環境で使用されるのかを知るのは難しく、また、その中で最も厳しい使用環境を正確に把握することも難しい。さらに、日本で使用される部品であっても、部品形状によっては構造上常時塩水がたまる可能性がある場合など、想定を超える厳しい環境となることもあり、その際に遅れ破壊などの水素脆化発生リスクがある。 For example, automobiles are sold and used all over the world, and it is difficult to know in what kind of environment they are actually used, and it is also possible to accurately grasp the harshest usage environment. difficult. Furthermore, even for parts used in Japan, depending on the shape of the part, there is a possibility that salt water will always accumulate due to the structure, and the environment may be harsher than expected. There is a risk of embrittlement.
特許文献１および非特許文献１に記載の水素脆化評価方法は、使用される環境が変化した際の水素侵入特性について明らかにできないため、想定範囲外の使用環境がどこまで許容できるかについて把握することができない。 Since the hydrogen embrittlement evaluation method described in Patent Document 1 and Non-Patent Document 1 cannot clarify the hydrogen embrittlement characteristics when the environment in which it is used changes, it is necessary to understand how much the usage environment outside the expected range can be tolerated. Can't.
本発明は、従来技術の問題を解決するためになされたものであり、任意の部材に関し、使用環境の許容範囲という指標によって、その部材の耐水素脆化特性を評価する方法を提供することを目的とする。 The present invention has been made to solve the problems of the prior art, and provides a method for evaluating the hydrogen embrittlement resistance property of any member by the index of the allowable range of the usage environment. The purpose.
本発明は、下記の耐水素脆化特性評価方法を要旨とする。
（Ａ）耐水素脆化特性を評価する方法であって、
（１）試験対象材の試験片を酸溶液に浸漬して水素をチャージし、侵入水素量ＨＥに対応する酸溶液濃度条件を求めるステップ、
（２）前記試験対象材の試験片に水素をチャージした後、遅れ破壊試験を行い、限界拡散性水素量ＨＣを測定するステップ、
（３）前記侵入水素量ＨＥが前記限界拡散性水素量ＨＣを下回る酸溶液濃度条件の広さによって耐水素脆化特性を判定するステップ、
を備える、耐水素脆化特性の評価方法。
The gist of the present invention is the following method for evaluating hydrogen embrittlement resistance.
(A) A method for evaluating hydrogen embrittlement resistance.
(1) A step of immersing a test piece of a test object in an acid solution to charge hydrogen and obtaining an acid solution concentration condition corresponding to the invading hydrogen amount HE.
(2) A step of charging the test piece of the test target material with hydrogen, performing a delayed fracture test, and measuring the critical diffusible hydrogen amount HC.
(3) A step of determining hydrogen embrittlement resistance by a wide range of acid solution concentration conditions in which the invading hydrogen amount HE is lower than the critical diffusible hydrogen amount HC.
A method for evaluating hydrogen embrittlement resistance.
（Ｂ）前記（１）のステップにおいて、
前記試験片の厚さが５ｍｍ以下であり、前記試験片の総質量が０．５ｇ以上である、上記（Ａ）の耐水素脆化特性の評価方法。
(B) In the step (1) above,
The method for evaluating hydrogen embrittlement resistance according to (A), wherein the test piece has a thickness of 5 mm or less and the total mass of the test piece is 0.5 g or more.
（Ｃ）前記（１）のステップにおいて、
予め行った水素透過試験により決定した所定の時間、前記試験片を酸溶液に浸漬する、
上記（Ａ）または（Ｂ）の耐水素脆化特性の評価方法。
(C) In the step (1) above,
Immerse the test piece in an acid solution for a predetermined time determined by a hydrogen permeation test performed in advance.
The method for evaluating the hydrogen embrittlement resistance of the above (A) or (B).
（Ｄ）前記（２）のステップにおいて、
前記試験片の応力集中係数が３以上である、
上記（Ａ）〜（Ｃ）のいずれかの耐水素脆化特性の評価方法。
(D) In the step (2) above,
The stress concentration coefficient of the test piece is 3 or more.
The method for evaluating hydrogen embrittlement resistance according to any one of (A) to (C) above.
（Ｅ）前記（１）のステップにおいて、
前記酸溶液が緩衝能力を有する、
（Ａ）〜（Ｄ）のいずれかの耐水素脆化特性の評価方法。
(E) In the step (1) above,
The acid solution has a buffering capacity.
A method for evaluating hydrogen embrittlement resistance according to any one of (A) to (D).
（Ｆ）前記（１）のステップにおいて、
前記試験片の表面積（ｃｍ２）に対する酸溶液量（ｍＬ）の比（酸溶液量／試験片表面積）が２０ｍＬ／ｃｍ２以上である、
（Ａ）〜（Ｅ）のいずれかの耐水素脆化特性の評価方法。
(F) In the step (1) above,
The ratio (acid solution amount / test piece surface area) of the acid solution amount (mL) to the surface area (cm 2 ) of the test piece is 20 mL / cm 2 or more.
A method for evaluating hydrogen embrittlement resistance according to any one of (A) to (E).
本発明によれば、任意の部材について使用することができる環境を把握するとともに、その際の侵入水素量を把握することができるので、水素脆化の観点から安全に使用できる材料を選択する際に有用な情報を提供することが可能である。さらに、使用可能な環境の範囲で評価することで材料の水素脆化特性優劣の判定を容易にする。このため、本発明は、産業上の貢献が極めて顕著である。 According to the present invention, it is possible to grasp the environment in which an arbitrary member can be used and the amount of invading hydrogen at that time, so that when selecting a material that can be safely used from the viewpoint of hydrogen embrittlement. It is possible to provide useful information to. Furthermore, it is easy to judge the superiority or inferiority of hydrogen embrittlement characteristics of the material by evaluating within the range of usable environment. Therefore, the present invention makes an extremely remarkable industrial contribution.
本実施形態に係る耐水素脆化特性評価方法は、下記のステップ（１）〜（３）を備える。
（１）試験対象材を酸溶液に浸漬して水素をチャージし、侵入水素量ＨＥに対応する酸溶液濃度条件を求めるステップ、
（２）前記試験対象材に水素をチャージした後、遅れ破壊試験を行い、限界拡散性水素量ＨＣを測定するステップ、
（３）前記侵入水素量ＨＥが前記限界拡散性水素量ＨＣを下回る酸溶液濃度条件の広さによって耐水素脆化特性を判定するステップ。
The hydrogen embrittlement resistant property evaluation method according to the present embodiment includes the following steps (1) to (3).
(1) A step of immersing the material to be tested in an acid solution, charging hydrogen, and obtaining an acid solution concentration condition corresponding to the invading hydrogen amount HE.
(2) A step of charging the material to be tested with hydrogen, performing a delayed fracture test, and measuring the critical diffusible hydrogen amount HC.
(3) A step of determining hydrogen embrittlement resistance characteristics based on a wide range of acid solution concentration conditions in which the invading hydrogen amount HE is lower than the critical diffusible hydrogen amount HC.
ステップ（１）について
このステップは、試験対象材の試験片についての侵入水素量ＨＥに対応する酸溶液濃度条件を把握する。なお、侵入水素量ＨＥとは、ある環境において試験片に侵入する最大の拡散性水素量である。このとき、酸溶液濃度条件は、任意の部材が実際の使用環境で用いられた場合の水素侵入の厳しさを示すことになる。酸溶液濃度条件として用いる物性値には制約がなく、ｐＨ、規定度、質量パーセント濃度などが挙げられるが、中でもｐＨを用いるのがよい。ｐＨは環境の酸濃度を表現する指標としてよく用いられ、使用環境との比較が容易に行えるためである。
About step (1) In this step, the acid solution concentration condition corresponding to the invading hydrogen amount HE for the test piece of the test target material is grasped. The invading hydrogen amount HE is the maximum amount of diffusible hydrogen that invades the test piece in a certain environment. At this time, the acid solution concentration condition indicates the severity of hydrogen intrusion when any member is used in an actual usage environment. There are no restrictions on the physical property values used as the acid solution concentration condition, and pH, normality, mass percent concentration, etc. can be mentioned, but it is preferable to use pH. This is because pH is often used as an index for expressing the acid concentration in the environment and can be easily compared with the environment in which it is used.
上記の試験片として、厚さ５ｍｍ以下の試験片を用いることが好ましい。ここで、厚さとは、試験片が板状の場合は板厚、管状の場合は肉厚、線状の場合は直径をいう。上記の試験片が厚すぎると、試験片中に水素が拡散し均一になるまでに時間がかかり、一方で酸溶液への浸漬中、試験時間の経過とともに試験片の表面が変質し、水素侵入量が減少するため、酸溶液濃度条件に対応する侵入水素量ＨＥを正確に求めることが困難となる恐れがある。したがって、試験片の厚さは５ｍｍ以下とすることが好ましい。試験片が軽すぎると、侵入水素量の定量が難しくなる恐れがある。したがって、試験片の総質量は０．５ｇ以上とするのが好ましい。試験片の厚さの下限は特に定めないが、試験片の総質量が上記の範囲内となる厚さであるのが好ましい。また、試験片の総重量の上限は特に定めないが、試験片の厚さが上記の範囲内となる重量であるのが好ましい。 As the above test piece, it is preferable to use a test piece having a thickness of 5 mm or less. Here, the thickness means the plate thickness when the test piece is plate-shaped, the wall thickness when it is tubular, and the diameter when it is linear. If the above test piece is too thick, it will take time for hydrogen to diffuse and become uniform in the test piece, while the surface of the test piece will deteriorate over time during immersion in an acid solution and hydrogen will enter. Since the amount is reduced, it may be difficult to accurately determine the amount of invading hydrogen HE corresponding to the acid solution concentration condition. Therefore, the thickness of the test piece is preferably 5 mm or less. If the test piece is too light, it may be difficult to quantify the amount of invading hydrogen. Therefore, the total mass of the test piece is preferably 0.5 g or more. The lower limit of the thickness of the test piece is not particularly specified, but it is preferable that the total mass of the test piece is within the above range. Further, although the upper limit of the total weight of the test piece is not particularly defined, it is preferable that the thickness of the test piece is within the above range.
まず、予備試験として水素透過試験を行い、酸溶液浸漬時間を決定する。水素透過試験とは、試験対象材から採取した試験片をカソード槽とアノード槽と間に挟みこみ、所定の電位を付与した状態で、カソード槽側で発生させた水素原子を試験片のカソード槽側の面から侵入させ、その反対面（アノード槽側の面）から引き抜く際の電流値から水素透過係数(μA/cm)を求めるものである。 First, a hydrogen permeation test is performed as a preliminary test to determine the acid solution immersion time. In the hydrogen permeation test, a test piece collected from the material to be tested is sandwiched between the cathode tank and the anode tank, and hydrogen atoms generated on the cathode tank side are used in the cathode tank of the test piece while a predetermined potential is applied. The hydrogen permeation coefficient (μA / cm) is obtained from the current value when the hydrogen is penetrated from the side surface and pulled out from the opposite surface (the surface on the anode tank side).
この試験により、試験片の酸溶液浸漬時間と水素侵入及び水素放出挙動との関係を調査し、試験片中に均一に水素が拡散し、拡散性水素量が最大となるまでの時間（酸溶液浸漬時間）を明らかにする。予備試験に用いる試験片は、侵入水素量ＨＥを測定する試験片と材質が同じであるだけでなく、厚さも同じものを使用することが望ましい。なぜならば、均一に水素がチャージされるまでの時間は、材質および厚さに影響されるからである。 In this test, the relationship between the acid solution immersion time of the test piece and the hydrogen intrusion and hydrogen release behavior was investigated, and the time until hydrogen diffused uniformly in the test piece and the amount of diffusible hydrogen became maximum (acid solution). Immersion time) is clarified. It is desirable that the test piece used for the preliminary test is not only made of the same material as the test piece for measuring the invading hydrogen amount HE, but also has the same thickness. This is because the time it takes for hydrogen to be charged uniformly is affected by the material and thickness.
ここで、拡散性水素量は、試験片中の水素濃度の平均値を表す。酸溶液浸漬時間が短い時は、試験片表面近くは水素濃度が高く、中心近くは水素濃度が低い状態となり、拡散性水素量は低い値を示す。また、酸溶液浸漬時間が長くなると、中心近くの水素濃度も高くなり、拡散性水素量が高くなる。しかし、酸溶液浸漬時間がある長さを超えると、表面にスマットと呼ばれる微粉末状の黒色物質が付着し、時間の経過に伴い水素侵入を抑制する。このように、酸溶液浸漬において最適な浸漬時間より短くても長くても、侵入水素量ＨＥは小さい値となってしまう。また、最適な浸漬時間は酸溶液と試験材の水素拡散係数の関係で決まるため、初めての組み合わせで試験をするときは、予備試験を行うことが望ましい。以上の予備試験結果より、拡散性水素量が最大となる最適な浸漬時間を求め、侵入水素量ＨＥの測定の際の酸溶液浸漬時間とする。 Here, the amount of diffusible hydrogen represents the average value of the hydrogen concentration in the test piece. When the acid solution immersion time is short, the hydrogen concentration is high near the surface of the test piece, the hydrogen concentration is low near the center, and the amount of diffusible hydrogen is low. Further, as the acid solution immersion time becomes longer, the hydrogen concentration near the center also increases, and the amount of diffusible hydrogen increases. However, when the acid solution immersion time exceeds a certain length, a fine powdery black substance called smut adheres to the surface and suppresses hydrogen invasion with the passage of time. As described above, the invaded hydrogen amount HE becomes a small value regardless of whether the immersion time is shorter or longer than the optimum immersion time in the acid solution immersion. In addition, since the optimum immersion time is determined by the relationship between the acid solution and the hydrogen diffusion coefficient of the test material, it is desirable to perform a preliminary test when testing with the first combination. From the above preliminary test results, the optimum immersion time at which the amount of diffusible hydrogen is maximized is determined, and is used as the acid solution immersion time when measuring the amount of invading hydrogen HE.
侵入水素量ＨＥを求める試験では、予備試験で決定した酸溶液浸漬時間において、酸浸漬により水素チャージを行い、昇温脱離分析（Ｔｈｅｒｍａｌ Ｄｅｓｏｒｐｔｉｏｎ Ａｎａｌｙｓｉｓ：ＴＤＡ）により試験片中の拡散性水素量を求めるのがよい。試験片中に侵入した微量な拡散性水素量を精度良く測定することが重要である。このため、試験片中の拡散性水素量は、ＴＤＡによって求めることとするのがよい。ＴＤＡは、ガスクロマトグラフまたは四重極質量分析計を用いた試験機にて行う。これらの装置を使うことにより微量な拡散性水素量を分析することができる。 In the test for determining the amount of penetrating hydrogen HE, hydrogen is charged by acid immersion during the acid solution immersion time determined in the preliminary test, and the amount of diffusible hydrogen in the test piece is determined by thermal desortion analysis (TDA). It is good to ask. It is important to accurately measure the amount of diffusible hydrogen that has penetrated into the test piece. Therefore, the amount of diffusible hydrogen in the test piece should be determined by TDA. TDA is performed on a testing machine using a gas chromatograph or a quadrupole mass spectrometer. By using these devices, it is possible to analyze a small amount of diffusible hydrogen.
ここで、ＴＤＡのグラフの例を図１に示す。試験片を室温から昇温すると水素放出量が増加し、１００℃から２００℃程度でピークとなり、その後減少する。この曲線の積分値
が試験片中に侵入した拡散性水素量（侵入水素量）となる。なお、素材によってはピークが２つとなることもあるが、室温から始まる第一ピークが水素脆化の原因となる拡散性水素であり、第二ピークに含まれる水素は水素脆化に関与しない非拡散性水素である。したがって、本発明では拡散性水素のみ対象とするため、第一ピークのみ積算し、第二ピークは積算しない。第一ピークの温度範囲は、測定開始温度からＴＤＡ曲線の傾きが正から負になった後、再度０となる温度までである。
Here, an example of a graph of TDA is shown in FIG. When the temperature of the test piece is raised from room temperature, the amount of hydrogen released increases, peaks at about 100 ° C to 200 ° C, and then decreases. The integrated value of this curve is the amount of diffusible hydrogen that has penetrated into the test piece (the amount of hydrogen that has penetrated). Depending on the material, there may be two peaks, but the first peak starting at room temperature is diffusible hydrogen that causes hydrogen embrittlement, and the hydrogen contained in the second peak is not involved in hydrogen embrittlement. It is diffusible hydrogen. Therefore, since only diffusible hydrogen is targeted in the present invention, only the first peak is integrated and the second peak is not integrated. The temperature range of the first peak is from the measurement start temperature to the temperature at which the slope of the TDA curve changes from positive to negative and then becomes 0 again.
様々な濃度の酸溶液において侵入水素量ＨＥを調査することで、酸溶液濃度と侵入水素量ＨＥとの関係を示す曲線が得られる。この際、酸溶液濃度は、ｐＨにおいて５．０以下の範囲に設定することが望ましい。なぜならば、ｐＨが５．０を超える条件では鋼に水素を侵入させることが難しいからである。また、ｐＨにおいて−０．５以上の範囲に設定することが望ましい。なぜならば、ｐＨが−０．５未満の場合は酸と金属の反応が激しくなり、水素侵入の前に金属が溶解しきってしまうからである。よって、酸溶液のｐＨは、−０．５〜５．０の範囲とするのがよく、特に、−０．５〜４．０の範囲とするのがよい。 By investigating the invading hydrogen amount HE in acid solutions of various concentrations, a curve showing the relationship between the acid solution concentration and the invading hydrogen amount HE can be obtained. At this time, it is desirable to set the acid solution concentration in the range of 5.0 or less in pH. This is because it is difficult for hydrogen to enter the steel under the condition that the pH exceeds 5.0. It is also desirable to set the pH in the range of -0.5 or higher. This is because when the pH is less than −0.5, the reaction between the acid and the metal becomes vigorous, and the metal is completely dissolved before hydrogen invades. Therefore, the pH of the acid solution is preferably in the range of −0.5 to 5.0, and particularly preferably in the range of −0.5 to 4.0.
酸溶液は、実環境に近い溶液を選ぶという観点からは、例えば塩化物イオンの多い環境を模擬するならば塩酸が適している。一方、試験片を酸溶液へ浸漬すると、酸溶液の水素イオンが消費されるため、ｐＨが上昇する恐れがあり、試験片への侵入水素量が安定しない可能性がある。このため、酸溶液として、緩衝能力を有する液（緩衝液）を用いるのが好ましい。ここで、緩衝液とは、水素イオンが消費されてもｐＨ変化が小さい液である。緩衝液は、酸解離定数（ｐＫａ）が酸溶液の目標とするｐＨに近い値である酸を含有することにより、緩衝能を有する。このような酸として好ましいのは、酸解離定数（ｐＫａ）が酸溶液の目標とするｐＨに対して−１〜＋１の範囲にある酸である。本発明では、ｐＨが−０．５〜５．０の範囲で試験を行うことを想定しているので、ｐＫａが６以下の酸が好ましい。このような酸は、例えば、酢酸、蟻酸、クエン酸、リン酸等である。酸のより好ましい酸解離定数（ｐＫａ）は４以下である。 As the acid solution, hydrochloric acid is suitable, for example, when simulating an environment containing a large amount of chloride ions from the viewpoint of selecting a solution close to the actual environment. On the other hand, when the test piece is immersed in the acid solution, the hydrogen ions of the acid solution are consumed, so that the pH may rise and the amount of hydrogen entering the test piece may not be stable. Therefore, it is preferable to use a liquid having a buffering capacity (buffer liquid) as the acid solution. Here, the buffer solution is a solution having a small pH change even when hydrogen ions are consumed. The buffer solution has a buffering ability by containing an acid whose acid dissociation constant (pKa) is close to the target pH of the acid solution. Preferred as such acids are acids whose acid dissociation constant (pKa) is in the range of -1 to +1 with respect to the target pH of the acid solution. In the present invention, since it is assumed that the test is carried out in the pH range of −0.5 to 5.0, an acid having a pKa of 6 or less is preferable. Such acids are, for example, acetic acid, formic acid, citric acid, phosphoric acid and the like. The more preferable acid dissociation constant (pKa) of the acid is 4 or less.
試験片の酸溶液への浸漬において、ｐＨを安定させ、試験片への侵入水素量を安定させるためには、酸溶液量を多くすることも有効である。すなわち、試験片の反応面積（試験片の表面積）に対する酸溶液量を多くすることで、ｐＨを安定させ、侵入水素量を安定させることができる。試験片表面積（ｃｍ２）に対する酸溶液量（ｍＬ）の比（酸溶液量／試験片表面積）が２０ｍＬ／ｃｍ２以上であることが望ましい。 It is also effective to increase the amount of the acid solution in order to stabilize the pH and the amount of hydrogen entering the test piece when the test piece is immersed in the acid solution. That is, by increasing the amount of the acid solution with respect to the reaction area (surface area of the test piece) of the test piece, the pH can be stabilized and the amount of invading hydrogen can be stabilized. It is desirable that the ratio (acid solution amount / test piece surface area) of the acid solution amount (mL) to the test piece surface area (cm 2 ) is 20 mL / cm 2 or more.
ステップ（２）について
このステップは、前記試験対象材の試験体に遅れ破壊試験を行い、限界拡散性水素量ＨＣを測定するステップである。ここで、遅れ破壊試験方法としては、公知の方法を採用すればよく、例えば、定荷重試験、低ひずみ速度試験（Ｓｌｏｗ Ｓｔｒａｉｎ Ｒａｔｅ
Ｔｅｓｔ：ＳＳＲＴ）、通常ひずみ速度試験（Ｃｏｎｖｅｎｔｉｏｎａｌ Ｓｔｒａｉｎ Ｒａｔｅ Ｔｅｓｔ：ＣＳＲＴ）によって求めることができる。ただし、ＣＳＲＴの場合は、水素の応力誘起拡散による局所水素量で評価する方法であるため、局所応力の計算を必要とする。また、ＳＳＲＴの場合は、破断応力と限界拡散性水素量ＨＣの関係が求まるので、本発明の評価においては想定される部品に負荷される応力値における限界拡散性水素量ＨＣを採用する。
About step (2) This step is a step of performing a delayed fracture test on the test piece of the test object and measuring the critical diffusible hydrogen amount HC. Here, as the delayed fracture test method, a known method may be adopted, for example, a constant load test and a low strain rate test (Slow Straight Rate).
Test: SSRT), can be determined by a conventional strain rate test (Conventional Strine Rate Test: CSRT). However, in the case of CSRT, since it is a method of evaluating by the amount of local hydrogen by stress-induced diffusion of hydrogen, it is necessary to calculate the local stress. Further, in the case of SSRT, since the relationship between the breaking stress and the critical diffusible hydrogen amount HC can be obtained, the critical diffusible hydrogen amount HC at the stress value applied to the assumed component is adopted in the evaluation of the present invention.
いずれの試験方法においても、基本的な試験手順は、水素チャージ、応力負荷、ＴＤＡからなる。これらの試験を侵入水素量が異なる複数の試験片について行うことにより、負荷応力と試験片中の限界水素量の関係、または試験片中の水素量と破断応力の関係を調査する。 In either test method, the basic test procedure consists of hydrogen charge, stress loading and TDA. By performing these tests on a plurality of test pieces having different amounts of penetrating hydrogen, the relationship between the load stress and the limit hydrogen amount in the test piece, or the relationship between the hydrogen amount in the test piece and the breaking stress is investigated.
試験片は、ボルトなどの実部品または切欠き付きのものを利用することが好ましい。その理由は、遅れ破壊などの水素脆化は応力集中部で発生する可能性が高いため、それを模擬するためである。 As the test piece, it is preferable to use an actual part such as a bolt or one with a notch. The reason is that hydrogen embrittlement such as delayed fracture is likely to occur in the stress concentration portion, and therefore it is simulated.
試験片に水素をチャージする方法については特に指定はなく、ステップ（１）と同様の酸浸漬法、または陰極水素チャージ法や高圧水素ガス曝露法などで行えばよい。なお、実際の使用環境での腐食ピットの応力集中係数は最大で３程度であるので、試験片には、この水準以上の応力集中係数、すなわち、３以上の応力集中係数のものを用いることが好ましい。 The method of charging the test piece with hydrogen is not particularly specified, and may be performed by the same acid immersion method as in step (1), the cathode hydrogen charging method, the high-pressure hydrogen gas exposure method, or the like. Since the stress concentration coefficient of the corrosion pit in the actual usage environment is about 3 at the maximum, a stress concentration coefficient of this level or higher, that is, a stress concentration coefficient of 3 or higher may be used for the test piece. preferable.
試験の際に注意すべき点は、定荷重試験やＳＳＲＴのように試験中に水素が拡散することを想定した試験方法では水素飛散防止処置をすることである。その方法は、Ｚｎ、Ｃｄなどの水素飛散防止めっきを水素チャージ後に施す、または応力負荷を水素チャージセル付帯で水素チャージさせながら行う、などの処置が必要である。水素飛散防止めっきを使用した場合は、ＴＤＡの前にそのめっきを除去する。 A point to be noted in the test is to take measures to prevent hydrogen scattering in a test method such as a constant load test or SSRT that assumes hydrogen diffusion during the test. The method requires measures such as applying hydrogen scattering prevention plating such as Zn and Cd after hydrogen charging, or applying a stress load while charging hydrogen with a hydrogen charge cell. If hydrogen shatterproof plating is used, remove the plating before TDA.
ステップ（３）について
このステップでは、前記侵入水素量ＨＥと前記限界拡散性水素量ＨＣとを比較し、ＨＥ＜ＨＣとなる酸溶液濃度条件の広さを調査する。この広さが水素脆化なく使用できる範囲を示し、その範囲が広い材料ほど耐水素脆化特性に優れていると評価することができる。
評価基準である、酸溶液濃度条件としては、ｐＨを用いるのが好ましい。環境の厳しさを一般的な基準で表現できるからである。
About step (3) In this step, the invading hydrogen amount HE and the critical diffusible hydrogen amount HC are compared, and the range of acid solution concentration conditions where HE <HC is investigated. This area indicates the range in which hydrogen embrittlement can be used, and it can be evaluated that the wider the range, the better the hydrogen embrittlement resistance.
It is preferable to use pH as the acid solution concentration condition, which is an evaluation standard. This is because the harshness of the environment can be expressed by general standards.
また、部品の抜き取り調査などによって実環境における侵入水素量ＨＥの値を採取できれば、各試験条件における侵入水素量ＨＥの変化と比較することにより、実環境においてその部品が遅れ破壊に対してどれぐらい余裕があるかを把握することができる。 In addition, if the value of the invading hydrogen amount HE in the actual environment can be collected by sampling the parts, how much the part will be delayed in the actual environment by comparing with the change in the invading hydrogen amount HE under each test condition. You can see if you can afford it.
以下、本発明に係る水素脆化特性の評価方法について実施例を挙げて更に具体的に説明するが、本発明は以下の実施例に限定されるものではない。 Hereinafter, the method for evaluating the hydrogen embrittlement property according to the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples.
表１に示す鋼を焼入れ焼戻しして引張強さ（Ｔｅｎｓｉｌｅ Ｓｔｒｅｎｇｔｈ：ＴＳ）を１２００〜１４００ＭＰａに調質した鋼材（鋼材Ａ〜Ｃ）を準備した。鋼材Ａ〜Ｃそれぞれについて、以下のとおり、ＨＥおよびＨＣの測定、ならびに、従来の評価試験を行った。 The steels shown in Table 1 were quenched and tempered to prepare steel materials (steel materials A to C) whose tensile strength (Tensile Strength: TS) was adjusted to 1200 to 1400 MPa. For each of the steel materials A to C, HE and HC were measured and conventional evaluation tests were performed as follows.
＜ＨＥ（侵入水素量）測定試験＞
まず、予備試験として、前記鋼材Ａ〜Ｃから、機械加工により切り出した円盤状の試験片（φ７０×１．５ｍｍｔ、質量１．２ｇ）について、水素透過試験を行い、それぞれの鋼材および酸溶液の条件に応じた浸漬時間を決定した。
<HE (Hydrogen Penetration) Measurement Test>
First, as a preliminary test, a hydrogen permeation test was conducted on a disk-shaped test piece (φ70 × 1.5 mmt, mass 1.2 g) cut out from the steel materials A to C by machining, and each steel material and acid solution were subjected to a hydrogen permeation test. The immersion time according to the conditions was determined.
図２には、鋼材Ｂの試験片をｐＨ＝１の塩酸に浸漬した予備試験の結果を示す。予備試験は、電気化学的水素透過試験にて試験時間と水素透過挙動の関係を調査した。図２に示す結果から、ｐＨ＝１の時のＨＥ測定試験で侵入水素量がピークとなる水素チャージ時間を４時間とすることとした。また、同様の調査を行った結果、ｐＨ＝２の時は６時間、ｐＨ＝３および４の時は２４時間が最適と求まった。このようにして求めた時間を、それぞれの鋼材および酸溶液の条件に応じた浸漬時間とする。 FIG. 2 shows the results of a preliminary test in which a test piece of steel material B was immersed in hydrochloric acid having a pH of 1. In the preliminary test, the relationship between the test time and hydrogen permeation behavior was investigated by the electrochemical hydrogen permeation test. From the results shown in FIG. 2, it was decided that the hydrogen charging time at which the amount of penetrating hydrogen peaked in the HE measurement test at pH = 1 was 4 hours. As a result of the same investigation, it was found that the optimum time was 6 hours when pH = 2 and 24 hours when pH = 3 and 4. The time thus determined is defined as the immersion time according to the conditions of each steel material and acid solution.
予備試験の後、ＨＥ測定試験を、前記鋼材Ａ〜Ｃの試験片について行った。すなわち、前記鋼材Ａ〜Ｃから機械加工により切り出した１０×１０×１．５ｍｍの試験片を様々な濃度条件（ｐＨ＝１，２，３または４）に調整した酸溶液に、予備試験で決定した時間、浸漬して水素チャージを行い、試験片中の侵入水素量（拡散性水素量）ＨＥを測定した。拡散性水素量の測定は、前述の昇温脱離分析（ＴＤＡ）により行った。 After the preliminary test, an HE measurement test was performed on the test pieces of the steel materials A to C. That is, a 10 × 10 × 1.5 mm test piece cut out from the steel materials A to C by machining is determined in a preliminary test as an acid solution adjusted to various concentration conditions (pH = 1, 2, 3 or 4). After soaking for a certain period of time, hydrogen charging was performed, and the amount of invading hydrogen (diffusible hydrogen amount) HE in the test piece was measured. The amount of diffusible hydrogen was measured by the above-mentioned thermal desorption analysis (TDA).
＜ＨＣ（限界拡散性水素量）測定試験＞
前記鋼材Ａ〜Ｃから、機械加工により試験片（φ７×７０ｍｍＬ）を切り出し、その中央部に応力集中係数が約３．５の環状切欠きを設けた。上記の試験片に、２４時間の陰極水素チャージにより拡散性水素を導入し、さらにＺｎめっきを施した。試験片内の拡散性水素量を均一にするため、試験片を室温に２４時間保持した。
<HC (Limited Diffusible Hydrogen Amount) Measurement Test>
A test piece (φ7 × 70 mmL) was cut out from the steel materials A to C by machining, and an annular notch having a stress concentration coefficient of about 3.5 was provided at the center thereof. Diffusible hydrogen was introduced into the above test piece by cathode hydrogen charging for 24 hours, and further Zn-plated. The test piece was kept at room temperature for 24 hours in order to make the amount of diffusible hydrogen in the test piece uniform.
室温保持後の試験片に、ＴＳの９０％の公称応力を負荷する定荷重試験を行い、破断直後または１００時間耐久後に試験片を回収した。回収した試験片について、めっきを逆電解により除去した後、ガスクロマトグラフを用いて試験片中の水素量を求めた。様々な拡散性水素量の水準において、以上の試験を行い、試験片が破断しない最大の水素量をＨＣ
とした。
A constant load test was performed in which a test piece kept at room temperature was loaded with a nominal stress of 90% of TS, and the test piece was recovered immediately after fracture or after durability for 100 hours. After removing the plating from the recovered test piece by reverse electrolysis, the amount of hydrogen in the test piece was determined using a gas chromatograph. The above tests were performed at various levels of diffusible hydrogen, and the maximum amount of hydrogen that did not break the test piece was HC.
And said.
＜従来の評価試験＞
非特許文献１に示される条件での評価を行った。すなわち、ＪＡＳＯ Ｍ ６０９（日本自動車技術協会規格）のＣＣＴを最大１８０サイクル行い、その条件での侵入水素量ＨＥ＿ＣＣＴも求めた。
<Conventional evaluation test>
Evaluation was performed under the conditions shown in Non-Patent Document 1. That is, the CCT of JASO M 609 (Japanese Automotive Standards Organization) was performed for a maximum of 180 cycles, and the amount of invading hydrogen HE_CCT under that condition was also obtained.
以上の結果を、表２に示す。また、図３には、鋼材Ｂについて、「酸溶液濃度とＨＥの関係」と「ＨＣ」とを比較した結果を示す。 The above results are shown in Table 2. Further, FIG. 3 shows the results of comparing "relationship between acid solution concentration and HE" and "HC" for steel material B.
図３において、鋼材ＢのＨＥ曲線とＨＣの交点が限界ｐＨとなり、それ以上の高いｐＨの環境においては遅れ破壊しないと判定できる。すなわち、鋼材Ｂについての限界ｐＨは、２．０である。鋼材Ａ、Ｃについても同様に限界ｐＨを求め、表２に示している。 In FIG. 3, it can be determined that the intersection of the HE curve of the steel material B and the HC becomes the limit pH, and the fracture is not delayed in an environment having a higher pH. That is, the critical pH of the steel material B is 2.0. For the steel materials A and C, the critical pH was similarly determined and shown in Table 2.
表２に示すように、比較法（非特許文献１に提案されている（ＨＣ−ＨＥ＿ＣＣＴ）／ＨＣを指標とする方法）は、ＣＣＴ環境において遅れ破壊するかどうかについては、その数値の正負で大まかに判定することはできるが、ＣＣＴ環境で遅れ破壊を生じないと判定される（ＨＣ−ＨＥ＿ＣＣＴ）／ＨＣ＞０を満たす試料においてどれぐらい厳しい環境まで使用できるかの判定は難しい。一方、本発明法は、ｐＨとＨＥの関係を示すことで、水素侵入環境の厳しい範囲についても評価可能であり、詳細な遅れ破壊特性の差を限界ｐＨという指標で評価可能である。 As shown in Table 2, the comparative method (method using (HC-HE_CCT) / HC as an index proposed in Non-Patent Document 1) determines whether or not the fracture is delayed in the CCT environment, depending on whether the numerical value is positive or negative. Although it can be roughly determined, it is difficult to determine how severe the environment can be used in a sample satisfying (HC-HE_CCT) / HC> 0, which is determined not to cause delayed fracture in the CCT environment. On the other hand, the method of the present invention can evaluate a severe range of hydrogen intrusion environment by showing the relationship between pH and HE, and can evaluate a detailed difference in delayed fracture characteristics by an index called a critical pH.
鋼材Ｂについて、ＨＥ（侵入水素量）測定試験を行った。ＨＥ測定試験は、試験片の形状、酸溶液の量、酸溶液の種類及びｐＨを表３に示す通りとした以外は、実施例１と同じ条件で行った。侵入水素量を表３に示す。 The HE (invaded hydrogen content) measurement test was performed on the steel material B. The HE measurement test was carried out under the same conditions as in Example 1 except that the shape of the test piece, the amount of the acid solution, the type of the acid solution and the pH were as shown in Table 3. The amount of invading hydrogen is shown in Table 3.
表３に示すように、試験Ｎｏ．１は、酸溶液として酢酸（ｐＫａ：４．７６）による緩衝液を用いた例である。具体的には、この緩衝液は、１Ｍ 酢酸１７０ｍｌと酢酸ナトリウム３ｇとを混合し、さらに蒸留水を足して１０００ｍｌとすることにより、作製した。試験Ｎｏ．１では、緩衝液を用いなかった試験Ｎｏ．２と比較して、侵入水素量が高くなった。また、試験Ｎｏ．３は、酸溶液量を増やし、比（酸溶液量／試験片面積）を２５．０に高めた例であるが、比（酸溶液量／試験片面積）が８．３である試験Ｎｏ．２と比較して、侵入水素量が高くなった。 As shown in Table 3, the test No. No. 1 is an example in which a buffer solution containing acetic acid (pKa: 4.76) is used as the acid solution. Specifically, this buffer solution was prepared by mixing 170 ml of 1M acetic acid and 3 g of sodium acetate, and further adding distilled water to make 1000 ml. Test No. In No. 1, the test No. 1 in which no buffer solution was used. Compared with 2, the amount of invading hydrogen was higher. In addition, the test No. No. 3 is an example in which the amount of acid solution is increased and the ratio (acid solution amount / test piece area) is increased to 25.0, but the ratio (acid solution amount / test piece area) is 8.3. Compared with 2, the amount of invading hydrogen was higher.
本発明によれば、任意の部材について使用することができる環境を把握するとともに、その際の侵入水素量を把握することができるので、水素脆化の観点から安全に使用できる材料を選択する際に有用な情報を提供することが可能である。さらに、使用可能な環境の範囲で評価することで材料の水素脆化特性優劣の判定を容易にする。このため、本発明は、産業上の貢献が極めて顕著である。 According to the present invention, it is possible to grasp the environment in which an arbitrary member can be used and the amount of invading hydrogen at that time, so that when selecting a material that can be safely used from the viewpoint of hydrogen embrittlement. It is possible to provide useful information to. Furthermore, it is easy to judge the superiority or inferiority of hydrogen embrittlement characteristics of the material by evaluating within the range of usable environment. Therefore, the present invention makes an extremely remarkable industrial contribution.
Claims (6)
（２）前記試験対象材の試験片に水素をチャージした後、遅れ破壊試験を行い、限界拡散性水素量ＨＣを測定するステップ、
（３）前記侵入水素量ＨＥが前記限界拡散性水素量ＨＣを下回る酸溶液濃度条件の広さによって耐水素脆化特性を判定するステップ、
を備える、耐水素脆化特性の評価方法。 (1) A step of immersing a test piece of a test object in an acid solution to charge hydrogen and obtaining an acid solution concentration condition corresponding to the invading hydrogen amount HE.
(2) A step of charging the test piece of the test target material with hydrogen, performing a delayed fracture test, and measuring the critical diffusible hydrogen amount HC.
(3) A step of determining hydrogen embrittlement resistance by a wide range of acid solution concentration conditions in which the invading hydrogen amount HE is lower than the critical diffusible hydrogen amount HC.
A method for evaluating hydrogen embrittlement resistance.
前記試験片の厚さが５ｍｍ以下であり、前記試験片の総質量が０．５ｇ以上である、
請求項１に記載の耐水素脆化特性の評価方法。 In step (1) above,
The thickness of the test piece is 5 mm or less, and the total mass of the test piece is 0.5 g or more.
The method for evaluating hydrogen embrittlement resistance according to claim 1.
予め行った水素透過試験により決定した所定の時間、前記試験片を酸溶液に浸漬する、請求項１または２に記載の耐水素脆化特性の評価方法。 In step (1) above,
The method for evaluating hydrogen embrittlement resistance according to claim 1 or 2, wherein the test piece is immersed in an acid solution for a predetermined time determined by a hydrogen permeation test performed in advance.
前記試験片の応力集中係数が３以上である、
請求項１から３までのいずれかに記載の耐水素脆化特性の評価方法。 In step (2) above,
The stress concentration coefficient of the test piece is 3 or more.
The method for evaluating hydrogen embrittlement resistance according to any one of claims 1 to 3.
前記酸溶液が緩衝能力を有する、
請求項１から４までのいずれかに記載の耐水素脆化特性の評価方法。 In step (1) above,
The acid solution has a buffering capacity.
The method for evaluating hydrogen embrittlement resistance according to any one of claims 1 to 4.
前記試験片の表面積面積（ｃｍ２）に対する酸溶液量（ｍＬ）の比（酸溶液量／試験片面積）が２０ｍＬ／ｃｍ２以上である、
請求項１から５までのいずれかに記載の耐水素脆化特性の評価方法。 In step (1) above,
The ratio (acid solution amount / test piece area) of the acid solution amount (mL) to the surface area area (cm 2 ) of the test piece is 20 mL / cm 2 or more.
The method for evaluating hydrogen embrittlement resistance according to any one of claims 1 to 5.
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