JP2016045158A - Pretreatment method for material evaluation - Google Patents
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Description
本発明は、材料評価のための前処理方法に関する。 The present invention relates to a pretreatment method for material evaluation.
金属材料は、応力を負荷した状態で水素を吸収すると水素脆化と呼ばれる現象を生じることが知られている（非特許文献１参照）。水素脆化とは、原子状水素が金属中に吸蔵されて材料が脆くなる現象である。亀裂等の現象が現れるまでに時間がかかるため、遅れ破壊とも呼ばれる。 It is known that a metal material causes a phenomenon called hydrogen embrittlement when it absorbs hydrogen in a stressed state (see Non-Patent Document 1). Hydrogen embrittlement is a phenomenon in which atomic hydrogen is occluded in a metal and the material becomes brittle. Since it takes time until a phenomenon such as a crack appears, it is also called delayed fracture.
水素脆化は、同じ量の水素が侵入しても金属種によって感受性が異なる。また、金属材料の硬さや金属組織の違いによっても水素脆化に対する感受性が変わると考えられている。 Hydrogen embrittlement varies depending on the metal species even if the same amount of hydrogen enters. In addition, it is considered that the sensitivity to hydrogen embrittlement varies depending on the hardness of the metal material and the difference in metal structure.
水素脆化のメカニズムについてはいくつかの説明が提示されている。一説によれば、水素と転位との相互作用により原子空孔が生成され、材料が脆くなると言われている（非特許文献２参照）。また、原子空孔は、水素のトラップサイトとなることが知られており、材料中に水素を強制的に吸収させ、そのときの水素量を調べることで原子空孔などの格子欠陥量を間接的に知ることができる。この手法を用いて、水素をトレーサーとして格子欠陥量の増加を調べ、水素脆化の進行を実験的に調べた報告がある（非特許文献２参照）。 Several explanations have been presented for the mechanism of hydrogen embrittlement. According to one theory, it is said that atomic vacancies are generated by the interaction between hydrogen and dislocation, and the material becomes brittle (see Non-Patent Document 2). In addition, atomic vacancies are known to be hydrogen trap sites, and the amount of lattice defects such as atomic vacancies is indirectly measured by forcibly absorbing hydrogen into the material and examining the amount of hydrogen at that time. Can know. There is a report using this technique to investigate the increase in the amount of lattice defects using hydrogen as a tracer and experimentally investigate the progress of hydrogen embrittlement (see Non-Patent Document 2).
また、各材料には固有の限界水素濃度と呼ばれる閾値がある。水素脆化は、限界水素濃度を超える水素量が材料中に吸収された状態になることで進行することが知られている（非特許文献３参照）。また、応力集中部等、水素濃度が局所的に高まる領域において特に水素脆化が進行すると言われている（非特許文献４参照）。 In addition, each material has a threshold value called a specific critical hydrogen concentration. It is known that hydrogen embrittlement proceeds when a hydrogen amount exceeding the critical hydrogen concentration is absorbed in the material (see Non-Patent Document 3). Further, it is said that hydrogen embrittlement progresses particularly in a region where the hydrogen concentration is locally increased, such as a stress concentration portion (see Non-Patent Document 4).
ところで、実際の使用環境下での材料の水素濃度分布は表面において高くなる。そのため、水素脆化の進行も材料の表面の方が内部よりも高いと考えられる。しかし、従来の材料評価手法では、材料の各部分における水素脆化の進行度合いの違いを考慮せずに、材料全体に対して材料評価を行っていた。このため、材料内部の水素脆化の進行状態を正確に評価することができなかった。 By the way, the hydrogen concentration distribution of the material in the actual use environment becomes high on the surface. Therefore, the progress of hydrogen embrittlement is considered to be higher on the surface of the material than on the inside. However, in the conventional material evaluation method, the material evaluation is performed on the entire material without considering the difference in the degree of progress of hydrogen embrittlement in each part of the material. For this reason, it was not possible to accurately evaluate the progress of hydrogen embrittlement inside the material.
また、水素脆化の進行が速いと考えられる表面部分を除去して材料を評価することを考えた場合も、除去する厚みを材料や試料に応じて適切に決定することが困難であった。 In addition, even when considering the evaluation of a material by removing a surface portion that is considered to progress rapidly in hydrogen embrittlement, it is difficult to appropriately determine the thickness to be removed depending on the material and the sample.
また、実際の使用環境下で材料に負荷される応力や温度も、金属組織中の原子空孔等の存在状況に影響する。そのため、応力や温度によって、材料の大部分の面積を占める内部の耐水素脆化特性に変化が生じる可能性がある。しかし、耐水素脆化特性の変化は、水素脆化の進行速度よりも遅く、従来の材料評価手法では、材料内部の耐水素脆化感受性の変化を調べることができなかった。 In addition, the stress and temperature applied to the material in the actual use environment also affect the presence of atomic vacancies in the metal structure. Therefore, the internal hydrogen embrittlement resistance, which occupies most of the area of the material, may change depending on stress and temperature. However, the change in hydrogen embrittlement resistance is slower than the progress rate of hydrogen embrittlement, and the conventional material evaluation method cannot examine the change in hydrogen embrittlement susceptibility inside the material.
開示の実施形態は、上記に鑑みてなされたものであって、材料内部の水素脆化の進行状況や耐水素脆化感受性の変化を評価することができる、材料評価のための前処理方法を提供することを目的とする。 An embodiment of the disclosure has been made in view of the above, and provides a pretreatment method for material evaluation that can evaluate the progress of hydrogen embrittlement inside the material and the change in resistance to hydrogen embrittlement. The purpose is to provide.
開示する材料評価のための前処理方法は、評価対象材料の限界水素量を決定する第１の決定工程と、評価対象材料の応力集中係数を算出する第１の算出工程と、応力集中係数に基づき評価対象材料の水素濃度分布を算出する第２の算出工程と、第２の算出工程で算出した水素濃度分布に基づき、第１の決定工程で決定した限界水素量を超える水素濃度の領域を、研磨対象とする水素脆化進行領域と決定する第２の決定工程と、を含む。 The disclosed pre-processing method for material evaluation includes a first determination step of determining a critical hydrogen amount of an evaluation target material, a first calculation step of calculating a stress concentration factor of the evaluation target material, and a stress concentration factor. Based on the second calculation step of calculating the hydrogen concentration distribution of the material to be evaluated based on the hydrogen concentration distribution calculated in the second calculation step, a hydrogen concentration region exceeding the limit hydrogen amount determined in the first determination step is determined. And a second determination step of determining a hydrogen embrittlement progression region to be polished.
開示する材料評価のための前処理方法は、材料内部の水素脆化の進行状況や耐水素脆化感受性の変化を評価することができる、という効果を奏する。 The disclosed pretreatment method for evaluating a material has an effect that the progress of hydrogen embrittlement inside the material and the change in resistance to hydrogen embrittlement can be evaluated.
以下に、開示する材料評価のための前処理方法の実施形態を図面に基づいて詳細に説明する。なお、この実施形態によりこの発明が限定されるものではない。 Hereinafter, embodiments of a pre-processing method for material evaluation disclosed will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.
（第１の実施形態）
図１は、第１の実施形態に係る前処理方法の処理の流れの一例を示すフローチャートである。図１を参照し、第１の実施形態に係る前処理方法の処理の流れの一例を説明する。
(First embodiment)
FIG. 1 is a flowchart illustrating an example of a processing flow of the preprocessing method according to the first embodiment. With reference to FIG. 1, an example of the flow of the preprocessing method according to the first embodiment will be described.
（第１の実施形態に係る前処理方法の流れの一例）
図１に示すように、まず評価対象とする材料の限界水素量を決定する（ステップＳ１０１）。ここでは、限界水素量とは、所定量の水素を材料にチャージして定荷重を負荷した場合に、材料に破断が生じなかった水素量の最大値とする。
(Example of flow of pre-processing method according to the first embodiment)
As shown in FIG. 1, first, the critical hydrogen amount of the material to be evaluated is determined (step S101). Here, the critical hydrogen amount is the maximum value of the amount of hydrogen that does not cause breakage in the material when a predetermined amount of hydrogen is charged to the material and a constant load is applied.
次に、評価対象とする材料の応力集中係数を算出する（ステップＳ１０２）。次に、評価対象とする材料の水素濃度分布を算出する（ステップＳ１０３）。そして、ステップＳ１０１で決定した限界水素量を超える水素濃度となる部分を、ステップＳ１０３で算出した水素濃度分布に基づいて求め、水素脆化進行領域とする（ステップＳ１０４）。そして、水素脆化進行領域に該当する厚みを研磨対象として決定する（ステップＳ１０５）。次に、決定した厚みを、評価対象とする材料の表面から研磨して除去する（ステップＳ１０６）。これによって、第１の実施形態に係る前処理方法の処理は終了する。 Next, the stress concentration coefficient of the material to be evaluated is calculated (step S102). Next, the hydrogen concentration distribution of the material to be evaluated is calculated (step S103). Then, a portion having a hydrogen concentration exceeding the limit hydrogen amount determined in step S101 is obtained based on the hydrogen concentration distribution calculated in step S103, and is set as a hydrogen embrittlement progression region (step S104). Then, the thickness corresponding to the hydrogen embrittlement progression region is determined as a polishing target (step S105). Next, the determined thickness is polished and removed from the surface of the material to be evaluated (step S106). Thereby, the processing of the preprocessing method according to the first embodiment is completed.
第１の実施形態に係る前処理方法においては、特に水素脆化が進んだと考えられる表面領域を水素脆化進行領域として特定し、当該水素脆化進行領域に該当する厚みを材料の表面から除去する。このため、特に水素脆化の進行が速い領域を除外して、材料内部の水素脆化の状態や、耐水素脆化感受性の変化を調べることができる。 In the pretreatment method according to the first embodiment, the surface region where hydrogen embrittlement is considered to have progressed in particular is identified as the hydrogen embrittlement progression region, and the thickness corresponding to the hydrogen embrittlement progression region is determined from the surface of the material. Remove. For this reason, it is possible to investigate the state of hydrogen embrittlement inside the material and the change in resistance to hydrogen embrittlement, excluding the region where the progress of hydrogen embrittlement is particularly fast.
また、第１の実施形態に係る前処理方法においては、個々の材料固有の限界水素量や、応力集中係数を考慮して算出した水素濃度分布に基づいて水素脆化進行領域を決定している。このため、材料や試料に応じて、水素脆化が特に進行していると考えられる領域を正確に決定して除去することができ、材料内部の水素脆化の状態や、耐水素脆化感受性の変化を正確に評価することができる。 In the pretreatment method according to the first embodiment, the hydrogen embrittlement progress region is determined based on the hydrogen concentration distribution calculated in consideration of the critical hydrogen amount specific to each material and the stress concentration factor. . For this reason, it is possible to accurately determine and remove the region where hydrogen embrittlement is considered to be particularly advanced depending on the material and sample, and the state of hydrogen embrittlement inside the material and the resistance to hydrogen embrittlement resistance. Can be accurately evaluated.
次に、図１に示した各ステップにおける処理の例をさらに詳細に説明する。 Next, an example of processing in each step shown in FIG. 1 will be described in more detail.
（評価対象とする材料の準備）
まず、評価対象とする材料を準備する。たとえば、経年劣化した材料であって、内部で耐水素脆化感受性に変化が生じていると予測される材料を準備する。たとえば、実際に建造物に使用した鋼材を評価対象として準備する。または所定の条件下で負荷を与えた後の材料を準備する。たとえば、所定量の水素をチャージしつつ定荷重試験を行った材料であってまだ破断が生じていない材料等を準備する。材料の種類は特に限定されず、水素脆化が生じる金属材料等であればよい。
(Preparation of materials to be evaluated)
First, a material to be evaluated is prepared. For example, a material that is aged and that is predicted to have a change in hydrogen embrittlement susceptibility is prepared. For example, a steel material actually used for a building is prepared as an evaluation target. Or the material after applying a load under predetermined conditions is prepared. For example, a material that has been subjected to a constant load test while being charged with a predetermined amount of hydrogen and has not yet broken is prepared. The kind of material is not particularly limited, and may be a metal material that causes hydrogen embrittlement.
（限界水素量の決定）
第１の実施形態における限界水素量は、たとえば図２に示す手順で決定する。図２は、第１の実施形態に係る前処理方法において、限界水素量を算出するための処理の流れの一例を示すフローチャートである。
(Determination of critical hydrogen amount)
The limit hydrogen amount in the first embodiment is determined by, for example, the procedure shown in FIG. FIG. 2 is a flowchart illustrating an example of a process flow for calculating the critical hydrogen amount in the pretreatment method according to the first embodiment.
図２に示すように、複数の水素量レベルＮ（Ｎ＝１〜ｎ）を設定する（ステップＳ２０１）。まず、水素量レベルＮ＝１とする（ステップＳ２０２）。そして、準備した評価対象とする材料に所定の応力を負荷して水素量レベルＮとなるよう水素チャージを行う（ステップＳ２０３）。次に、所定の条件下で、定荷重試験をおこなって材料に生じた破断の有無を確認する（ステップＳ２０４）。次に設定した水素量レベルＮがｎか否かを判定し（ステップＳ２０５）、Ｎ＝ｎでない場合（ステップＳ２０５、否定）、Ｎ＝Ｎ＋１（ステップＳ２０６）と設定し直して、ステップＳ２０３からの処理を繰り返す。Ｎ＝ｎである場合（ステップＳ２０５、肯定）、すなわち、設定したすべての水素量レベルでの破断の有無の確認が終了した場合、破断が生じなかった水素量の最大値を限界水素量として設定する（ステップＳ２０７）。これで限界水素量の決定処理が終了する。 As shown in FIG. 2, a plurality of hydrogen amount levels N (N = 1 to n) are set (step S201). First, the hydrogen amount level N = 1 is set (step S202). Then, hydrogen is charged so that a predetermined stress is applied to the prepared material to be evaluated and the hydrogen amount level N is reached (step S203). Next, under a predetermined condition, a constant load test is performed to confirm the presence or absence of breakage in the material (step S204). Next, it is determined whether or not the set hydrogen amount level N is n (step S205). When N = n is not satisfied (step S205, negative), N = N + 1 (step S206) is set again. Repeat the process. When N = n (step S205, affirmative), that is, when the confirmation of the presence or absence of breakage at all the set hydrogen amount levels is completed, the maximum value of the hydrogen amount that did not break is set as the limit hydrogen amount. (Step S207). This completes the process for determining the critical hydrogen amount.
ここで、限界水素量とは、非特許文献３に記載の、遅れ破壊試験で破断しない水素量の上限値である限界拡散性水素量（critical hydrogen content for delayed fracture, [Hc]）であってよい。また、図２に示す各ステップは順次行うのではなく、複数の試料に対して時間や電流密度等の条件を変えて平行して水素チャージを行って実行してもよい。 Here, the critical hydrogen content is the critical hydrogen content for delayed fracture (Hc), which is the upper limit of the hydrogen content that does not break in the delayed fracture test described in Non-Patent Document 3. Good. In addition, the steps shown in FIG. 2 are not sequentially performed, and may be performed by performing hydrogen charging in parallel on a plurality of samples by changing conditions such as time and current density.
また、限界水素量を求める際に使用する材料は、評価対象とする試料、たとえば鋼材とは別に、腐食を生じていない同様の材料とすればよい。 Moreover, the material used when calculating | requiring the amount of limit hydrogen should just be taken as the same material which has not produced corrosion apart from the sample made into evaluation object, for example, steel materials.
（応力集中係数の算出）
次に、図１のステップＳ１０２における応力集中係数は以下のように算出する。
(Calculation of stress concentration factor)
Next, the stress concentration coefficient in step S102 of FIG. 1 is calculated as follows.
上述のように、水素脆化は応力集中部等、水素濃度が局所的に高まる領域において特に進行が早まると言われている（非特許文献４参照）。そこで、第１の実施形態では、材料表面に生じた凹凸等を加味して水素濃度分布を計算するため、材料の形状に基づき、応力集中係数を算出する。 As described above, hydrogen embrittlement is said to progress particularly rapidly in a region where the hydrogen concentration locally increases, such as a stress concentration portion (see Non-Patent Document 4). Therefore, in the first embodiment, the stress concentration coefficient is calculated based on the shape of the material in order to calculate the hydrogen concentration distribution in consideration of the irregularities generated on the material surface.
応力集中係数の算出手法は特に限定はされない。たとえば、材料表面が腐食して形状が不規則な場合等は、有限要素法（Finite Element Method; FEM）などの計算的方法を利用すればよい。また、たとえば以下に示す、非特許文献６に記載の式（１）に基づいて算出すればよい。 The method for calculating the stress concentration factor is not particularly limited. For example, when the material surface corrodes and the shape is irregular, a computational method such as a finite element method (FEM) may be used. Moreover, what is necessary is just to calculate based on Formula (1) described in the nonpatent literature 6 shown below, for example.
上記式（１）は、略円柱形状の材料の外周上にノッチを形成して応力集中部とした試験片について、ノッチ底の応力集中係数を算出するための式である。式（１）中、θはノッチ開き角の２分の１、Ｂはノッチのない部分の試験片半径、ｄはノッチ深さ、Ｋｔ（０）は、ノッチ開き角が０°のときの応力集中係数である。 The above equation (1) is an equation for calculating the stress concentration factor at the bottom of the notch for a test piece formed as a stress concentration portion by forming a notch on the outer periphery of a substantially cylindrical material. In equation (1), θ is half the notch opening angle, B is the test piece radius of the unnotched portion, d is the notch depth, and Kt (0) is the stress when the notch opening angle is 0 °. Concentration factor.
たとえば、非特許文献６、７は、図３Ａに示す試験片を用いた応力集中係数の算出について記載している。図３Ａは、第１の実施形態に係る前処理方法において、応力集中係数を算出するための処理で用いる試験片の一例の寸法を示す図である。図３Ｂは、第１の実施形態に係る前処理方法において、応力集中係数を算出するための処理で用いる試験片の一例の細部を示す図である。図３Ｃは、第１の実施形態に係る前処理方法において、応力集中係数を算出するための処理で用いる試験片の他の例の細部を示す図である。 For example, Non-Patent Documents 6 and 7 describe the calculation of the stress concentration coefficient using the test piece shown in FIG. 3A. FIG. 3A is a diagram illustrating dimensions of an example of a test piece used in a process for calculating a stress concentration coefficient in the pretreatment method according to the first embodiment. FIG. 3B is a diagram illustrating details of an example of a test piece used in a process for calculating a stress concentration coefficient in the pretreatment method according to the first embodiment. FIG. 3C is a diagram illustrating details of another example of the test piece used in the process for calculating the stress concentration coefficient in the pretreatment method according to the first embodiment.
非特許文献６、７の記載によれば、ノッチ底半径ρが０．１ｍｍの試験片（図３Ｂ）については、応力集中係数は４．９、ノッチ底半径ρが０．８ｍｍの試験片（図３Ｃ）については、応力集中係数は２．１である。なお、図３Ａから図３Ｃ中、寸法の単位はミリメートル（ｍｍ）である。 According to the description of Non-Patent Documents 6 and 7, for a test piece having a notch bottom radius ρ of 0.1 mm (FIG. 3B), a test piece having a stress concentration factor of 4.9 and a notch bottom radius ρ of 0.8 mm ( For FIG. 3C), the stress concentration factor is 2.1. In FIGS. 3A to 3C, the unit of dimension is millimeter (mm).
（水素濃度分布の計算）
図１のステップ１０３における水素濃度分布の算出はたとえば次のように行う。まず、腐食の生じた評価対象材料を、恒温恒湿槽中に保持する。相対湿度は９８％、温度は３０℃とする。その後、表面の錆をブラストで除去する。そして、錆が除去された材料を昇温脱離分析することで水素量を求める。たとえば非特許文献８に記載の水素分析の手法を用いて、評価対象材料の水素量を算出すればよい。
(Calculation of hydrogen concentration distribution)
The calculation of the hydrogen concentration distribution in step 103 of FIG. 1 is performed as follows, for example. First, the evaluation target material in which corrosion has occurred is held in a constant temperature and humidity chamber. The relative humidity is 98% and the temperature is 30 ° C. Thereafter, rust on the surface is removed by blasting. And the amount of hydrogen is calculated | required by temperature-programmed desorption analysis of the material from which rust was removed. For example, the hydrogen amount of the evaluation target material may be calculated using the hydrogen analysis technique described in Non-Patent Document 8.
このようにして求めた水素量が材料内部まで分布すると仮定して、ステップＳ１０２で求めた応力集中係数をパラメータとして、材料の表面近傍における水素濃度分布を計算する。 Assuming that the amount of hydrogen obtained in this way is distributed to the inside of the material, the hydrogen concentration distribution in the vicinity of the surface of the material is calculated using the stress concentration coefficient obtained in step S102 as a parameter.
たとえば、非特許文献７には、図３Ａ乃至図３Ｃに示す試験片を用いて求めたデータが記載されている。非特許文献７に記載のデータを図４および図５に示す。図４は、図３Ａ乃至図３Ｃに示す試験片を用いて求めた、静水圧応力とノッチ底からの距離との関係を示すグラフである。静水圧応力は水素濃度を律するパラメータであると考えられる。 For example, Non-Patent Document 7 describes data obtained using the test pieces shown in FIGS. 3A to 3C. The data described in Non-Patent Document 7 are shown in FIGS. FIG. 4 is a graph showing the relationship between the hydrostatic stress and the distance from the notch bottom, obtained using the test pieces shown in FIGS. 3A to 3C. Hydrostatic stress is considered to be a parameter governing the hydrogen concentration.
なお、図４中、Ｂ１５とは６３３Ｋで１．５時間焼き戻した試験片を意味し、Ｂ１３とは、７３３Ｋで１．５時間焼き戻した試験片を意味する。Ｋｔは、各試験片のノッチ底の応力集中係数を意味する。 In FIG. 4, B15 means a test piece tempered at 633K for 1.5 hours, and B13 means a test piece tempered at 733K for 1.5 hours. Kt means the stress concentration factor of the notch bottom of each test piece.
図５は、図４に示す応力分布に基づき算出された水素濃度分布を示すグラフである。図５は、図４のグラフに示す３つの試験片のうち、１点鎖線で示される試験片（Ｂ１３−Ｋｔ４．９）に対応するデータを示す。また、図５中、４つの線は下からそれぞれ、０．９σＢの応力を１分、１０分、１００分、１０００分負荷したのちのノッチ底近傍の水素濃度分布を示す（非特許文献７参照）。 FIG. 5 is a graph showing the hydrogen concentration distribution calculated based on the stress distribution shown in FIG. FIG. 5 shows data corresponding to a test piece (B13-Kt4.9) indicated by a one-dot chain line among the three test pieces shown in the graph of FIG. Further, in FIG. 5, the four lines show the hydrogen concentration distribution in the vicinity of the notch bottom after applying a stress of 0.9 σB from the bottom for 1, 10, 100, and 1000 minutes, respectively (see Non-Patent Document 7). ).
（水素脆化進行領域の算出）
上記のように、限界水素量および水素濃度分布を計算したのちに、図６に示すように、水素濃度分布のうち、限界水素量を超える範囲を水素脆化進行領域とする。図６は、第１の実施形態に係る前処理方法において、限界水素量に基づき水素脆化進行領域を決定するための処理を説明するためのグラフである。
(Calculation of hydrogen embrittlement progress region)
As described above, after calculating the limit hydrogen amount and the hydrogen concentration distribution, the range exceeding the limit hydrogen amount in the hydrogen concentration distribution is set as the hydrogen embrittlement progress region as shown in FIG. FIG. 6 is a graph for explaining a process for determining a hydrogen embrittlement progress region based on the critical hydrogen amount in the pretreatment method according to the first embodiment.
（材料の研磨）
図５、６に示すように、ノッチ底からの水素濃度分布を算出して、さらに材料表面からの距離に基づき水素脆化進行領域を決定することで、水素脆化進行領域に対応する領域を、材料表面から除去する層の厚みとして決定できる。そして、評価対象材料の表面から決定した厚みの層を研磨により除去する。なお、評価内容や材料の実使用環境等、条件に応じて、決定した厚みよりも厚い層を研磨してもよい。
(Polishing materials)
As shown in FIGS. 5 and 6, by calculating the hydrogen concentration distribution from the notch bottom and determining the hydrogen embrittlement progress region based on the distance from the material surface, the region corresponding to the hydrogen embrittlement progress region is determined. The thickness of the layer to be removed from the material surface can be determined. Then, the layer having the thickness determined from the surface of the evaluation target material is removed by polishing. A layer thicker than the determined thickness may be polished according to conditions such as evaluation contents and actual use environment of the material.
これによって、表面の水素脆化進行領域の影響を受けずに、評価対象材料の内部の水素脆化の状態や、耐水素脆化感受性等を調べることができる。 Thus, the state of hydrogen embrittlement inside the evaluation target material, the resistance to hydrogen embrittlement, and the like can be examined without being affected by the surface hydrogen embrittlement progress region.
（評価手法）
上記のように第１の実施形態に係る前処理方法を実施して前処理を施した評価対象材料を評価する手法としては、たとえば、予め決めた水素量を吸収させた材料に応力を負荷して、破断するまでの時間を比較する等である。
(Evaluation method)
As a technique for evaluating the evaluation target material that has been subjected to the pretreatment by performing the pretreatment method according to the first embodiment as described above, for example, stress is applied to a material that has absorbed a predetermined amount of hydrogen. For example, the time until breakage is compared.
（応力集中係数の算出と使用材料）
なお、第１の実施形態では、ノッチのある材料を前提として応力集中係数を算出している。このような計算を行うのは、実際の使用環境にあった試料は表面に傷や腐食などによる多数の凹凸があると予想されるからである。表面が滑らかな試料の場合、材料の拡散係数に基づいて表面から内部への水素濃度分布を比較的容易に算出することができる。これに対して、凹凸が多数存在する試料の場合、水素濃度分布がより深い方向で大きな値となると予想される。このため、表面が滑らかな状態に基づいて水素濃度分布を予測したのでは、実際の評価対象材料の実体を反映できず、除去する厚みが不十分になる可能性があると考えられる。そこで、第１の実施形態では、ノッチが形成された試験片に基づいて応力集中係数を算出した上で、当該応力集中係数をパラメータとした水素濃度分布を算出して、除去する厚みを決定している。
(Calculation of stress concentration factor and materials used)
In the first embodiment, the stress concentration coefficient is calculated on the assumption of a material having a notch. The reason why such calculation is performed is that a sample in an actual use environment is expected to have a large number of irregularities on the surface due to scratches or corrosion. In the case of a sample having a smooth surface, the hydrogen concentration distribution from the surface to the inside can be calculated relatively easily based on the diffusion coefficient of the material. On the other hand, in the case of a sample having a large number of irregularities, it is expected that the hydrogen concentration distribution becomes a large value in a deeper direction. For this reason, if the hydrogen concentration distribution is predicted based on a smooth surface, the actual substance to be evaluated cannot be reflected, and the thickness to be removed may be insufficient. Therefore, in the first embodiment, after calculating the stress concentration factor based on the test piece in which the notch is formed, the hydrogen concentration distribution using the stress concentration factor as a parameter is calculated to determine the thickness to be removed. ing.
このようにノッチのある試験片に基づく応力集中係数をパラメータとして利用することで、実際の評価対象材料の実体に即した水素脆化進行領域の決定を実現できる。したがって、評価対象とする材料表面の凹凸の状態に応じて、応力集中係数を算出すればよく、図３Ａ乃至図３Ｃに示す試験片は一例にすぎない。たとえば、実際に評価対象とする材料の一部を切り取って、表面の凹凸を調べて応力集中係数を算出すればよい。これによって、材料の状態に即した応力集中係数を算出した上で水素濃度分布を算出でき、当該材料の水素脆化進行領域を正確に求めることができる。 In this way, by using the stress concentration factor based on the notched specimen as a parameter, it is possible to determine the hydrogen embrittlement progress region in accordance with the actual material to be evaluated. Therefore, the stress concentration coefficient may be calculated according to the unevenness state of the material surface to be evaluated, and the test pieces shown in FIGS. 3A to 3C are merely examples. For example, the stress concentration coefficient may be calculated by cutting out a part of the material to be actually evaluated and examining the surface irregularities. Accordingly, the hydrogen concentration distribution can be calculated after calculating the stress concentration factor in accordance with the state of the material, and the hydrogen embrittlement progression region of the material can be accurately obtained.
（第１の実施形態の効果）
上記のように、第１の実施形態に係る材料評価のための前処理方法は、評価対象材料の限界水素量を決定する第１の決定工程と、評価対象材料の応力集中係数を算出する第１の算出工程と、応力集中係数に基づき評価対象材料の水素濃度分布を算出する第２の算出工程と、第２の算出工程で算出した水素濃度分布に基づき、第１の決定工程で決定した限界水素量を超える水素濃度の領域を、研磨対象とする水素脆化進行領域と決定する第２の決定工程と、を含む。このため、評価対象材料のうち、特に水素脆化の進行が速い部分の厚みを決定して除去することが可能となり、評価対象材料の内部の水素脆化の状態や耐水素脆化感受性等の特性を正確に評価することができる。
(Effects of the first embodiment)
As described above, the pretreatment method for material evaluation according to the first embodiment includes the first determination step of determining the critical hydrogen amount of the evaluation target material, and the first calculation of the stress concentration coefficient of the evaluation target material. 1 determination step, a second calculation step for calculating the hydrogen concentration distribution of the evaluation target material based on the stress concentration factor, and a first determination step based on the hydrogen concentration distribution calculated in the second calculation step. A second determination step of determining a region having a hydrogen concentration exceeding the limit hydrogen amount as a hydrogen embrittlement progression region to be polished. For this reason, it becomes possible to determine and remove the thickness of the portion of the evaluation target material where hydrogen embrittlement is particularly rapid, such as the state of hydrogen embrittlement inside the evaluation target material and the resistance to hydrogen embrittlement resistance. Properties can be accurately evaluated.
また、上記第１の実施形態に係る前処理方法は、第２の決定工程において水素脆化進行領域として決定した領域内を含む部分を評価対象材料から除去する除去工程を、さらに含む。これによって、後続する材料評価をスムーズに実行することができる。 The pretreatment method according to the first embodiment further includes a removal step of removing a portion including the inside of the region determined as the hydrogen embrittlement progression region in the second determination step from the evaluation target material. Thereby, subsequent material evaluation can be performed smoothly.
また、上記第１の実施形態に係る前処理方法において、第１の決定工程は、評価対象材料と同等の材料であって腐食や凹凸がない材料に所定の応力を負荷しつつ吸収させる水素量を変化させ、破断が生じない水素量の最大値を限界水素量と決定する。これにより、限界水素量を適切に決定して、水素脆化進行領域を決定することができる。 In the pretreatment method according to the first embodiment, the first determination step includes the amount of hydrogen absorbed while applying a predetermined stress to a material that is equivalent to the evaluation target material and has no corrosion or unevenness. The maximum value of the amount of hydrogen that does not cause breakage is determined as the critical hydrogen amount. Thereby, the critical hydrogen amount can be determined appropriately, and the hydrogen embrittlement progress region can be determined.
また、上記第１の実施形態に係る前処理方法において、第１の算出工程は、所定の凹凸を有する評価対象材料を用いて応力集中係数を算出する。このため、実際の使用環境において腐食や傷が生じた評価対象材料について、かかる腐食や傷により生じる応力集中の状態を加味して水素濃度分布を決定することができ、水素脆化進行領域を適切に決定することができる。 In the pretreatment method according to the first embodiment, the first calculation step calculates a stress concentration coefficient using an evaluation target material having predetermined unevenness. For this reason, it is possible to determine the hydrogen concentration distribution for the evaluation target material that has been corroded or scratched in the actual usage environment, taking into account the state of stress concentration caused by such corrosion or scratching. Can be determined.
また、上記第１の実施形態に係る前処理方法において、第２の算出工程は、所定の凹凸を有する前記評価対象材料を用いて水素濃度分布を算出する。このため、実際の使用環境において腐食や傷が生じた評価対象材料について、かかる腐食や傷により生じる応力集中の状態を加味して水素濃度分布を決定することができ、水素脆化進行領域を適切に決定することができる。 In the pretreatment method according to the first embodiment, the second calculation step calculates a hydrogen concentration distribution using the evaluation target material having predetermined irregularities. For this reason, it is possible to determine the hydrogen concentration distribution for the evaluation target material that has been corroded or scratched in the actual usage environment, taking into account the state of stress concentration caused by such corrosion or scratching. Can be determined.
Claims (5)
前記評価対象材料の応力集中係数を算出する第１の算出工程と、
前記応力集中係数に基づき前記評価対象材料の水素濃度分布を算出する第２の算出工程と、
前記第２の算出工程で算出した前記水素濃度分布に基づき、前記第１の決定工程で決定した限界水素量を超える水素濃度の領域を、研磨対象とする水素脆化進行領域と決定する第２の決定工程と、
を含むことを特徴とする材料評価のための前処理方法。 A first determination step for determining a critical hydrogen amount of the material to be evaluated;
A first calculation step of calculating a stress concentration factor of the material to be evaluated;
A second calculation step of calculating a hydrogen concentration distribution of the material to be evaluated based on the stress concentration factor;
Based on the hydrogen concentration distribution calculated in the second calculation step, a region having a hydrogen concentration exceeding the limit hydrogen amount determined in the first determination step is determined as a hydrogen embrittlement progression region to be polished. And the determination process of
A pretreatment method for evaluating a material, comprising:
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