JP2012047629A - Method for evaluating embrittlement sensitivity in high-pressure hydrogen environment of high-strength low-alloy steel - Google Patents
Method for evaluating embrittlement sensitivity in high-pressure hydrogen environment of high-strength low-alloy steel Download PDFInfo
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この発明は、高圧水素環境下における高強度低合金鋼の脆化感受性を評価する評価方法に関するものである。 The present invention relates to an evaluation method for evaluating the embrittlement susceptibility of a high-strength low-alloy steel under a high-pressure hydrogen environment.
水素社会構築のための水素インフラ整備において、高圧水素を貯蔵、供給する水素スタンドの普及は重要である。高信頼性を有する水素スタンドの構成には高圧水素ガス蓄圧器の開発が必須であり、優れた蓄圧器用材料の開発が望まれている。ここで、金属材料、特に鉄鋼材料はコストやリサイクル性の観点から蓄圧器材料として有望である。
技術的な趨勢として、水素自動車の航続距離延伸のため貯蔵ガスの圧力はより高圧化することが望まれており、水素スタンドの蓄圧器には３５ＭＰａ以上の高圧水素ガスを貯蔵することが考えられている。しかしながら、炭素鋼や高強度低合金鋼においては高圧水素ガス環境下において水素環境脆化が生じるとされており、現在まででは３５ＭＰａ以上の高圧水素環境で使用できる鉄鋼材料はオーステナイト系ステンレス鋼にほぼ限定されていた。オーステナイト系ステンレス鋼は一般的に低合金鋼よりも高価であり、また室温まで安定なオーステナイト相を有することから熱処理による強度調整ができない。そのため、より高圧の水素ガスを貯蔵するための蓄圧器材料として高強度低合金鋼が望まれている。
In the development of a hydrogen infrastructure for building a hydrogen society, the spread of hydrogen stations that store and supply high-pressure hydrogen is important. Development of a high-pressure hydrogen gas accumulator is indispensable for the construction of a highly reliable hydrogen stand, and the development of an excellent accumulator material is desired. Here, metal materials, particularly steel materials are promising as pressure accumulator materials from the viewpoint of cost and recyclability.
As a technical trend, it is desired to increase the pressure of the storage gas to extend the cruising range of hydrogen vehicles, and it is conceivable to store high-pressure hydrogen gas of 35 MPa or more in the hydrogen stand pressure accumulator. ing. However, carbon steel and high-strength low-alloy steel are considered to cause hydrogen environment embrittlement in a high-pressure hydrogen gas environment. To date, steel materials that can be used in a high-pressure hydrogen environment of 35 MPa or more are almost equivalent to austenitic stainless steels. It was limited. Austenitic stainless steels are generally more expensive than low alloy steels and have an austenitic phase that is stable up to room temperature, so that the strength cannot be adjusted by heat treatment. Therefore, high strength low alloy steel is desired as a pressure accumulator material for storing higher pressure hydrogen gas.
該高強度低合金鋼は、通常は、大気中引張強度として８５０〜１０５０ＭＰａの強度を有し、ベイナイトまたはマルテンサイトもしくはこれらの混合組織を有している。さらに、組織中にフェライト、残留オーステナイトを含むこともある。
この高強度低合金を高圧水素環境下で使用した場合の耐高圧水素環境脆化感受性を簡便に評価する方法が求められている。
The high-strength low-alloy steel usually has a strength of 850 to 1050 MPa as an atmospheric tensile strength, and has bainite, martensite, or a mixed structure thereof. Further, the structure may contain ferrite and retained austenite.
There is a need for a method for simply evaluating the high-pressure hydrogen environment embrittlement susceptibility when this high-strength low-alloy is used in a high-pressure hydrogen environment.
従来、水素脆化感受性の評価法に関する技術はいくつか開発されている。特許文献１には、地中埋設管などに用いる炭素鋼に関する水素脆化評価法が開示されており、試験材の水素濃度を基に脆化感受性を評価するものとしている。具体的には、試験材中の水素濃度が１０ｐｐｂを越えると断面収縮率が顕著に低下することから、水素濃度が１０ｐｐｂ以上で脆化感受性が高くなると判断している。
特許文献２には、引張強度７８０ＭＰａ以上のめっき鋼板を含む各種鋼材について、拡散性水素量と評価鋼の伸びを基に水素脆化感受性を評価する技術が開示されている。
特許文献３には、ボルト用鋼について、電解質水溶液の電解で発生した水素を利用して試験材を水素脆化させ、耐遅れ破壊特性を評価する技術が開示されている。
特許文献４および特許文献５には、それぞれ薄鋼板および高強度鋼板について、試験片を特定形状に加工した後で電解チャージにより水素を導入し、割れが発生するまでの時間を基に水素脆化感受性もしくは遅れ破壊特性を評価する技術が開示されている。
Conventionally, several techniques related to a method for evaluating hydrogen embrittlement sensitivity have been developed. Patent Document 1 discloses a hydrogen embrittlement evaluation method for carbon steel used for underground pipes and the like, and evaluates the embrittlement sensitivity based on the hydrogen concentration of the test material. Specifically, when the hydrogen concentration in the test material exceeds 10 ppb, the cross-sectional shrinkage ratio is remarkably reduced. Therefore, it is determined that the embrittlement susceptibility increases when the hydrogen concentration is 10 ppb or more.
Patent Document 3 discloses a technique for evaluating the delayed fracture resistance of a steel for bolts by hydrogen embrittlement of a test material using hydrogen generated by electrolysis of an aqueous electrolyte solution.
In
しかしながら、水素環境脆化に着目すれば、上記のような脆化評価技術は開発されていない。一方で、高強度鋼の高圧水素環境脆化特性に関する最近の研究から、脆化特性に影響を及ぼす因子が明らかになりつつある。非特許文献１では結晶粒径を小さくすることにより外部環境からの水素侵入を抑制して高圧水素環境脆化感受性が低減されること、あるいは合金元素が水素中での変形における結晶粒内での格子欠陥形成に影響を与えうることを報告している。 However, if attention is focused on hydrogen environment embrittlement, no such embrittlement evaluation technology has been developed. On the other hand, factors affecting the embrittlement characteristics are becoming clear from recent studies on the high-pressure hydrogen environment embrittlement characteristics of high-strength steels. In Non-Patent Document 1, by reducing the crystal grain size, hydrogen penetration from the external environment is suppressed and the high-pressure hydrogen environment embrittlement susceptibility is reduced, or the alloy element is deformed in hydrogen in the crystal grains. It has been reported that it can affect the formation of lattice defects.
ところで、高圧水素環境脆化の場合、試験材の変形と同時に水素が侵入して脆化に寄与するため、上述した従来の水素脆化感受性評価法のうち、変形前の鋼中の水素量を基にした手法は、高圧水素環境脆化に対しては有効とは言いがたい。また、電解水素チャージを利用した評価法は必ずしも高圧水素環境を再現しているとは言えず、高圧水素環境下で使用する鋼材の脆化感受性を評価するには適当ではない。
一方で、高圧水素環境下における材料の機械的特性評価には、特殊な試験装置やそれらを扱う上での技術、経験が必要であり、設備的、コスト的な観点から容易に実行できるものではない。極めて多種にわたる高強度低合金鋼の中から高圧水素環境中での使用に適した材料を選択するためには、実際に高圧水素環境下で特性評価試験を行う前に、簡易的に材料の耐高圧水素環境脆化感受性を評価して候補材を絞り込める方法の確立が望まれる。
さらに、特許文献１のように、図面を用いた評価法であれば、視覚的にも理解しやすく便利である。
By the way, in the case of high-pressure hydrogen environment embrittlement, hydrogen penetrates simultaneously with deformation of the test material and contributes to embrittlement. Therefore, among the conventional hydrogen embrittlement susceptibility evaluation methods described above, the amount of hydrogen in the steel before deformation is determined as follows. It is difficult to say that the method based on the high-pressure hydrogen environment embrittlement is effective. Moreover, it cannot be said that the evaluation method using the electrolytic hydrogen charge necessarily reproduces the high-pressure hydrogen environment, and is not suitable for evaluating the embrittlement susceptibility of the steel material used in the high-pressure hydrogen environment.
On the other hand, the mechanical property evaluation of materials under high-pressure hydrogen environment requires special test equipment, techniques and experience in handling them, and can not be easily executed from the viewpoint of equipment and cost. Absent. In order to select a material suitable for use in a high-pressure hydrogen environment from among a wide variety of high-strength low-alloy steels, the material resistance must be simplified before actually performing a characterization test in a high-pressure hydrogen environment. It is desirable to establish a method to narrow down candidate materials by evaluating the susceptibility to high-pressure hydrogen environment embrittlement.
Furthermore, if it is an evaluation method using drawing like patent document 1, it is easy to understand visually and is convenient.
本発明はこれらの状況を解決するためになされたものであり、比較的容易に測定でき、かつ水素環境脆化特性に影響を与えると考えられる化学組成、結晶粒径および転位密度と、高強度鋼の高圧水素環境下での機械的特性との関連を整理し、簡便な水素脆化感受性評価法を提供することを目的としている。 The present invention has been made to solve these situations, and can be measured relatively easily and has a chemical composition, a crystal grain size and a dislocation density, which are considered to affect the hydrogen environment embrittlement characteristics, and high strength. The purpose of this study is to provide a simple method for assessing the susceptibility to hydrogen embrittlement by organizing the relationship between the mechanical properties of steel under high-pressure hydrogen environment.
本願発明者は鋼中への水素侵入に対し転位密度が関係することを見出している。水素中での変形に伴う水素侵入は水素環境脆化機構における特徴的な、かつ重要な素過程であり、これに影響を及ぼす因子は脆化感受性も左右することが予想される。また化学組成や結晶粒径、転位密度は特殊な装置を用いずとも比較的容易に測定できる量であり、これらと脆化感受性の間に相関が見出せれば、水素環境脆化感受性を評価する簡便な方法に応用できる可能性がある。
本願発明者は、上記課題に基づいて、大気中引張強度が８５０〜１０５０ＭＰａであり、フェライト、ベイナイト、マルテンサイト、残留オーステナイトおよびそれらの混合組織を有する高強度低合金鋼である種々のＮｉＣｒＭｏ鋼、高降伏点鋼および高Ｃｒ鋼を試験材として用いて、試験材の化学組成分析、結晶粒径測定、転位密度測定および４５ＭＰａ水素雰囲気における引張試験を行い、これらの諸量間の関係を詳細に検討した。その結果、試験材の炭素ならびにニッケル当量、結晶粒径、転位密度および後述する脆化指数ＥＩとの間に、高強度低合金鋼の水素環境脆化感受性を簡便に評価できる方法に応用できる相関を見出し、本発明に至った。
The present inventor has found that dislocation density is related to hydrogen penetration into steel. Hydrogen intrusion due to deformation in hydrogen is a characteristic and important elementary process in the hydrogen environment embrittlement mechanism, and factors affecting this are expected to influence the embrittlement susceptibility. Chemical composition, crystal grain size, and dislocation density are quantities that can be measured relatively easily without using special equipment. If a correlation is found between these and embrittlement susceptibility, the hydrogen environment embrittlement susceptibility is evaluated. There is a possibility that it can be applied to a simple method.
Based on the above problems, the inventor of the present application has various NiCrMo steels that are high strength low alloy steels having a tensile strength in the air of 850 to 1050 MPa, and having ferrite, bainite, martensite, retained austenite, and a mixed structure thereof. Using high yield point steel and high Cr steel as test materials, chemical composition analysis, crystal grain size measurement, dislocation density measurement and tensile test in a 45MPa hydrogen atmosphere were conducted, and the relationship between these quantities was detailed. investigated. As a result, there is a correlation that can be applied to a method that can easily evaluate the hydrogen environment embrittlement susceptibility of high-strength low-alloy steel among the carbon and nickel equivalent of the test material, crystal grain size, dislocation density, and embrittlement index EI described later. And found the present invention.
すなわち、本発明の高強度低合金鋼の高圧水素環境脆化感受性の評価方法のうち、第１の本発明は、大気中引張強度が８５０〜１０５０ＭＰａで、焼入れ組織を有する高強度低合金について、ＪＩＳＧ０５５２（鋼のフェライト結晶粒度試験方法）の比較法により測定した結晶粒度番号から換算した平均結晶粒径ｄと、Ｘ線回折法によって測定した局所ひずみから得た転位密度ρと、炭素当量Ｃｅｑおよびニッケル当量Ｎｉｅｑと、から下記式（１）によって算出されるＺパラメータに基づいて高圧水素環境下における脆化感受性を評価することを特徴とする。
Ｚ＝２／（ｄ√ρ）×（Ｎｉｅｑ／Ｃｅｑ） … （１）
That is, among the methods for evaluating the high-pressure hydrogen environment embrittlement susceptibility of the high-strength low-alloy steel of the present invention, the first present invention relates to a high-strength low-alloy having a quenching structure with an atmospheric tensile strength of 850 to 1050 MPa. The average grain size d converted from the grain size number measured by the comparative method of JIS G 0552 (steel ferrite grain size test method), the dislocation density ρ obtained from the local strain measured by the X-ray diffraction method, and the carbon equivalent C eq In addition, the susceptibility to embrittlement in a high-pressure hydrogen environment is evaluated based on the Z parameter calculated by the following formula (1) from the nickel equivalent Ni eq .
Z = 2 / (d√ρ) × (Ni eq / C eq ) (1)
第２の本発明の高強度低合金鋼の高圧水素環境脆化感受性の評価方法は、前記第１の本発明において、大気中および高圧水素環境下における引張試験の測定値から下記式（２）によって算出される下記脆化指数ＥＩと、前記Ｚパラメータとを関連付けて予め相関関係を求めておき、該相関関係に基づいて前記脆化感受性を評価することを特徴とする。
脆化指数ＥＩ＝（ＬＨ−Ｌａｉｒ−ＴＳ）／Ｌａｉｒ−ＴＳ … （２）
ただし、ＬＨ：４５ＭＰａ水素中における破断伸び，Ｌａｉｒ−ＴＳ：大気中の引張強度σＵＴＳにおける伸び
The method for evaluating the high-pressure hydrogen environment embrittlement susceptibility of the high-strength low-alloy steel according to the second aspect of the present invention is the following formula (2) from the measured values of the tensile test in the atmosphere and under the high-pressure hydrogen environment in the first aspect of the present invention. A correlation is obtained in advance by associating the following embrittlement index EI calculated by the above and the Z parameter, and the embrittlement susceptibility is evaluated based on the correlation.
Brittleness index EI = (L H −L air−TS ) / L air−TS (2)
However, L H: 45 MPa elongation at break in the hydrogen, L air-TS: elongation in a tensile strength in the air sigma UTS
第３の本発明の高強度低合金鋼の高圧水素環境脆化感受性の評価方法は、前記第１または第２の本発明において、前記高圧水素環境が、４５ＭＰａ水素環境下であることを特徴とする。 The method for evaluating the high-pressure hydrogen environment embrittlement susceptibility of the high-strength low-alloy steel of the third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the high-pressure hydrogen environment is a 45 MPa hydrogen environment. To do.
第４の本発明の高強度低合金鋼の高圧水素環境脆化感受性の評価方法は、前記第１〜第３の本発明のいずれかにおいて、前記焼入れ組織がベイナイトまたはマルテンサイトもしくはこれらの混合組織であることを特徴とする。 The method for evaluating the high-pressure hydrogen environment embrittlement susceptibility of the high-strength low-alloy steel according to the fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein the quenched structure is bainite, martensite, or a mixed structure thereof. It is characterized by being.
第５の本発明の高強度低合金鋼の高圧水素環境脆化感受性の評価方法は、前記第１〜第４の本発明のいずれかにおいて、前記Ｚパラメータが１０−２以上である場合、水素環境下での脆化感受性が小さい材料であると判定することを特徴とする。 The evaluation method for high-pressure hydrogen environment embrittlement susceptibility of the high-strength low-alloy steel according to the fifth aspect of the present invention is the hydrogenation method according to any one of the first to fourth aspects, wherein the Z parameter is 10 −2 or more. It is determined that the material is less susceptible to embrittlement under the environment.
すなわち、本発明によれば、大気中引張強度が８５０〜１０５０ＭＰａで、焼入れ組織を有する高強度低合金について、ＪＩＳＧ０５５２（鋼のフェライト結晶粒度試験方法）の比較法により測定した結晶粒度番号から換算した平均結晶粒径ｄと、Ｘ線回折法によって測定した局所ひずみから得た転位密度ρと、炭素当量Ｃｅｑおよびニッケル当量Ｎｉｅｑと、から下記式（１）によって算出されるＺパラメータに基づいて高圧水素環境下における脆化感受性を評価するので、
Ｚ＝２／（ｄ√ρ）×（Ｎｉｅｑ／Ｃｅｑ） … （１）
高強度低合金鋼の高圧水素環境脆化感受性を簡易的に把握することが可能となる。
さらに従たる効果として、実際に高圧水素環境下で行う試験の回数を最小限に抑えることができ、研究開発に要する時間と費用を大幅に削減することが可能となる。
That is, according to the present invention, a high strength low alloy having a quenching structure with an atmospheric tensile strength of 850 to 1050 MPa, converted from the grain size number measured by the comparison method of JISG 0552 (steel ferrite grain size test method). Based on the Z parameter calculated by the following formula (1) from the average crystal grain size d, the dislocation density ρ obtained from the local strain measured by the X-ray diffraction method, the carbon equivalent C eq and the nickel equivalent Ni eq. Because we evaluate the susceptibility to embrittlement under high pressure hydrogen environment,
Z = 2 / (d√ρ) × (Ni eq / C eq ) (1)
It is possible to easily grasp the high-pressure hydrogen environment embrittlement susceptibility of high-strength low-alloy steel.
As a secondary effect, the number of tests actually performed under a high-pressure hydrogen environment can be minimized, and the time and cost required for research and development can be greatly reduced.
以下に、本発明の一実施形態を説明する。
本発明では、焼入れ組織を有し、大気中引張強度が８５０〜１０５０ＭＰａである高強度低合金鋼が対象になる。低合金鋼としては、種々のＮｉＣｒＭｏ鋼、高降伏点鋼および高Ｃｒ鋼などが挙げられる。
上記低合金鋼は、焼ならし、焼入れあるいは焼戻しなどの熱処理によって大気中引張強度が８５０〜１０５０ＭＰａに調整される。具体的な熱処理条件については特に限定されるものではなく、低合金鋼の組成、目標強度などに従って適宜の条件を選定することができる。
上記熱処理によって、上記高強度低合金鋼は、ベイナイトまたはマルテンサイトもしくはこれらの混合組織からなる焼入れ組織を有している。該組織には、その他に、フェライトや残留オーステナイトが含まれるものであってもよい。ただし、高強度低合金鋼はベイナイトまたはマルテンサイトもしくはこれらの混合組織を主相とするものが例示される。
Hereinafter, an embodiment of the present invention will be described.
In the present invention, a high strength low alloy steel having a quenched structure and an atmospheric tensile strength of 850 to 1050 MPa is an object. Examples of the low alloy steel include various NiCrMo steels, high yield point steels, and high Cr steels.
The low alloy steel is adjusted to an atmospheric tensile strength of 850 to 1050 MPa by heat treatment such as normalizing, quenching or tempering. Specific heat treatment conditions are not particularly limited, and appropriate conditions can be selected according to the composition of the low alloy steel, the target strength, and the like.
By the heat treatment, the high-strength low-alloy steel has a quenched structure composed of bainite, martensite, or a mixed structure thereof. In addition, the structure may contain ferrite and retained austenite. However, examples of the high-strength low-alloy steel include bainite, martensite, or a mixed structure thereof having a main phase.
該低合金鋼は、大気中および４５ＭＰａ水素中で引張試験を行う。引張試験後、得られた応力−クロスヘッド変位線図から、大気中引張強度σＵＴＳにおける伸びＬａｉｒ−ＴＳと４５ＭＰａ水素中での破断伸びＬＨを求め、次式で定義する脆化指数ＥＩを算出する。
ＥＩ＝（ＬＨ−Ｌａｉｒ−ＴＳ）／Ｌａｉｒ−ＴＳ
前記脆化指数ＥＩの定義から明らかなように、ＥＩ＜０はＬＨ＜Ｌａｉｒ−ＴＳであり、σＵＴＳを与える伸びに達する前に水素中では破断したことを示す。図２にＥＩ＜０ならびにＥＩ＞０を示す応力−クロスヘッド変位線図の例を示す。
供試材の平均結晶粒ｄは、ＪＩＳＧ０５５２に規定された比較法に基づき測定した結晶粒度番号Ｇを次式で換算して得ることができる。
ｄ＝（８×２Ｇ）−１／２
The low alloy steel is subjected to a tensile test in air and in 45 MPa hydrogen. After the tensile test, from the obtained stress-crosshead displacement diagram, the elongation L air-TS in the atmospheric tensile strength σ UTS and the breaking elongation L H in 45 MPa hydrogen were obtained, and the embrittlement index EI defined by the following equation: Is calculated.
EI = (L H -L air - TS) / L air - TS
Wherein As is apparent from the definition of embrittlement index EI, EI <0 is L H <L air - a TS, indicating that the fracture in hydrogen before reaching the elongation giving sigma UTS. FIG. 2 shows an example of a stress-crosshead displacement diagram showing EI <0 and EI> 0.
The average crystal grain d of the test material can be obtained by converting the crystal grain size number G measured based on the comparison method defined in JISG0552 by the following formula.
d = (8 × 2 G ) −1/2
転位密度ρはＸ線回折法により測定する。先ず後記非特許文献３で示された次式を用いて局所ひずみεｌｏｃａｌを求める。 The dislocation density ρ is measured by an X-ray diffraction method. First, the local strain ε local is obtained using the following equation shown in Non-Patent Document 3 described later.
βは回折ピークの半価幅、θは回折角、λはＸ線の波長である。またＫはＳｃｈｅｒｒｅｒ定数であり、０．８９に等しい。Ｄは結晶子の大きさである。続いて、非特許文献４で示される次式を用いてρを得る。
β is the half width of the diffraction peak, θ is the diffraction angle, and λ is the X-ray wavelength. K is a Scherrer constant and is equal to 0.89. D is the size of the crystallite. Subsequently, ρ is obtained using the following equation shown in
ｂはＢｕｒｇｅｒｓ ｖｅｃｔｏｒであり、本発明では２．５×１０−１０ｍとした。 “b” is a Burgers vector, which is 2.5 × 10 −10 m in the present invention.
［非特許文献３］Ｗ．Ｈ．Ｈａｌｌ：Ｐｒｏｃ．Ｐｈｙｓ．Ｓｏｃ．Ａ，６２（１９４９），７４１．
［非特許文献４］Ｇ．Ｋ．Ｗｉｌｌｉａｍｓｏｎ ａｎｄ Ｒ．Ｅ．Ｓｍａｌｌｍａｎ：Ｐｈｉｌｏｓ．Ｍａｇ．，８（１９５６），３４．
[Non-Patent Document 3] H. Hall: Proc. Phys. Soc. A, 62 (1949), 741.
[Non-Patent Document 4] K. Williamson and R.W. E. Smallman: Philos. Mag. , 8 (1956), 34.
炭素当量Ｃｅｑとニッケル当量Ｎｉｅｑではそれぞれ以下の式を用いて算出する。
Ｃｅｑ／％＝Ｃ＋Ｓｉ／２４＋Ｍｎ／６＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４
Ｎｉｅｑ／％＝Ｎｉ＋１２．６Ｃ＋０．６５Ｃｒ＋０．９８Ｍｏ＋１．０５Ｍｎ＋０．３５Ｓｉ
ただし各元素記号はｍａｓｓ％表示での含有量を示す。
The carbon equivalent C eq and the nickel equivalent Ni eq are calculated using the following equations, respectively.
C eq /% = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
Ni eq /%=Ni+12.6C+0.65Cr+0.98Mo+1.05Mn+0.35Si
However, each element symbol indicates the content in mass%.
次に、Ｚパラメータは以下の式で定義する。 Next, the Z parameter is defined by the following equation.
Ｚパラメータの右辺第一項は平均転位間隔を平均結晶粒径の１／２倍で除した値であり、変形による転位同士の反応と粒界での転位堆積に伴う格子欠陥形成挙動を反映する。右辺第二項は炭素とニッケルが格子欠陥形成に及ぼす影響を表す。 The first term on the right side of the Z parameter is a value obtained by dividing the average dislocation interval by 1/2 of the average crystal grain size, and reflects the reaction between dislocations due to deformation and the behavior of lattice defect formation accompanying dislocation deposition at the grain boundary. . The second term on the right side represents the effect of carbon and nickel on the formation of lattice defects.
上記Ｚパラメータによって４５ＭＰａ水素環境下における脆化感受性を評価することができる。Ｚが１０−２以上、望ましくは２×１０−２以上であれば、該試験材の４５ＭＰａ水素環境脆化感受性は小さいと判定できる。なお、Ｚと脆化指数との間には相関関係があり、上記Ｚの数値を満たすことでＥＩが０よりも大きくなる。 The embrittlement susceptibility in a 45 MPa hydrogen environment can be evaluated by the Z parameter. If Z is 10 −2 or more, preferably 2 × 10 −2 or more, it can be determined that the 45 MPa hydrogen environment embrittlement sensitivity of the test material is small. Note that there is a correlation between Z and the embrittlement index, and the EI becomes larger than 0 when the value of Z is satisfied.
表１に示す組成の低合金鋼（残部がＦｅおよび不可避不純物）について、焼ならし、焼入れあるいは焼戻しなどの熱処理によって大気中引張強度を８５０〜１０５０ＭＰａに調整した。なお、各供試材の組織を顕微鏡観察し、その観察結果を表１に示した。なお、表中で主相がベイナイトであるものはＢ、主相がマルテンサイトであるものはＭ、ベイナイトとマルテンサイトの混合組織であるものはＢ＋Ｍで表した。 About the low alloy steel of the composition shown in Table 1 (the balance is Fe and inevitable impurities), the tensile strength in the atmosphere was adjusted to 850 to 1050 MPa by heat treatment such as normalizing, quenching or tempering. The structure of each specimen was observed with a microscope, and the observation results are shown in Table 1. In the table, B indicates that the main phase is bainite, M indicates that the main phase is martensite, and B + M indicates a mixed structure of bainite and martensite.
また、各供試材は、ＪＩＳＺ２２０１で規定された１４号平滑引張試験片に加工し、大気中および４５ＭＰａ水素中で引張試験を行い、引張試験後、得られた応力−クロスヘッド変位線図から、大気中引張強度σＵＴＳにおける伸びＬａｉｒ−ＴＳと４５ＭＰａ水素中での破断伸びＬＨを求め、下記式に基づいて脆化指数ＥＩを算出した。なお、本発明における伸びとは、σＵＴＳに到達もしくは４５ＭＰａ水素中で破断した時点でのクロスヘッド変位を引張試験片の標点間距離で除した値を指す。
ＥＩ＝（ＬＨ−Ｌａｉｒ−ＴＳ）／Ｌａｉｒ−ＴＳ
In addition, each specimen is processed into a No. 14 smooth tensile test piece defined in JISZ2201, subjected to a tensile test in air and 45 MPa hydrogen, and after the tensile test, from the obtained stress-crosshead displacement diagram. The elongation L air-TS in the atmospheric tensile strength σ UTS and the breaking elongation L H in 45 MPa hydrogen were determined, and the embrittlement index EI was calculated based on the following formula. In addition, the elongation in the present invention refers to a value obtained by dividing the crosshead displacement at the time of reaching σ UTS or breaking in 45 MPa hydrogen by the distance between the gauge points of the tensile test piece.
EI = (L H -L air - TS) / L air - TS
これら供試材について、前記実施形態の説明に基づいて、炭素当量Ｃｅｑ（％）、ニッケル当量Ｎｉｅｑ（％）、平均結晶粒径ｄ（μｍ）、転位密度ρ（１０１５ｍ−２）を算出し、これら算出結果から、前記したＺパラメータを算出した。
これらの結果を表１に示すとともに、図１に脆化指数ＥＩとＺパラメータとを相関させて図示した。
前記相関図より、４５ＭＰａ水素環境下における引張特性が未評価であって、大気中引張強度が８５０〜１０５０ＭＰａで、フェライト、ベイナイト、マルテンサイト、残留オーステナイトおよびそれらの混合組織を有する高強度低合金鋼の試験材について、該試験材のＺパラメータが１０−２以上、望ましくは２×１０−２以上の値であれば、該試験材は４５ＭＰａ水素中における水素環境脆化感受性が小さい材料と判定できる。
したがって、各材料について、Ｚパラメータを用いて水素環境下での脆化感受性を簡易に評価することができる。また、図１を用いて脆化指数に従って適切なＺパラメータを視覚的に容易に選定することができる。
For these specimens, based on the description of the above embodiment, carbon equivalent C eq (%), nickel equivalent Ni eq (%), average crystal grain size d (μm), dislocation density ρ (10 15 m −2 ). And the above-described Z parameter was calculated from these calculation results.
These results are shown in Table 1, and are shown in FIG. 1 by correlating the embrittlement index EI and the Z parameter.
From the above correlation diagram, the tensile properties in a 45 MPa hydrogen environment have not been evaluated, the tensile strength in the atmosphere is 850 to 1050 MPa, high strength low alloy steel having ferrite, bainite, martensite, retained austenite and a mixed structure thereof. If the Z parameter of the test material is 10 −2 or more, preferably 2 × 10 −2 or more, the test material can be determined as a material having a low hydrogen environment embrittlement sensitivity in 45 MPa hydrogen. .
Therefore, for each material, the embrittlement susceptibility in a hydrogen environment can be easily evaluated using the Z parameter. In addition, an appropriate Z parameter can be easily selected visually according to the embrittlement index using FIG.
Claims (5)
Ｚ＝２／（ｄ√ρ）×（Ｎｉｅｑ／Ｃｅｑ） … （１） The average crystal grain size d converted from the grain size number measured by the comparative method of JISG 0552 (steel ferrite grain size test method) for a high strength low alloy having a quenching structure with an atmospheric tensile strength of 850 to 1050 MPa, and X Susceptibility to embrittlement in a high-pressure hydrogen environment based on the Z parameter calculated by the following formula (1) from the dislocation density ρ obtained from the local strain measured by the line diffraction method, the carbon equivalent C eq and the nickel equivalent Ni eq. A method for evaluating the high-pressure hydrogen environment embrittlement susceptibility of a high-strength low-alloy steel characterized by
Z = 2 / (d√ρ) × (Ni eq / C eq ) (1)
脆化指数ＥＩ＝（ＬＨ−Ｌａｉｒ−ＴＳ）／Ｌａｉｒ−ＴＳ … （２）
ただし、ＬＨ：４５ＭＰａ水素中における破断伸び，Ｌａｉｒ−ＴＳ：大気中の引張強度における伸び A correlation is obtained in advance by associating the following embrittlement index EI calculated by the following formula (2) from the measured value of the tensile test in the atmosphere and in a high-pressure hydrogen environment with the Z parameter, and based on the correlation. The method for evaluating the susceptibility to high-pressure hydrogen environment embrittlement of a high-strength low-alloy steel according to claim 1, wherein the susceptibility to embrittlement is evaluated.
Brittleness index EI = (L H −L air−TS ) / L air−TS (2)
Where L H : elongation at break in 45 MPa hydrogen, L air-TS : elongation in tensile strength in the atmosphere
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| CN118090792A (en) * | 2024-04-23 | 2024-05-28 | 合肥通用机械研究院有限公司 | Non-contact nondestructive evaluation method for metal hydrogen embrittlement |
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