JP6309826B2 - Fracture stress estimation method and fracture stress estimation device for oxide film fracture - Google Patents
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- 238000002791 soaking Methods 0.000 claims 1
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- 238000007254 oxidation reaction Methods 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000004626 scanning electron microscopy Methods 0.000 description 2
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 2
- 229910000975 Carbon steel Inorganic materials 0.000 description 1
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- 239000000075 oxide glass Substances 0.000 description 1
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Description
本発明は、特に鋼材の表面に形成される酸化被膜（いわゆる黒皮）が破壊され、当該鋼材の金属素地が露出するときの破壊応力を推定する酸化被膜破壊時の破壊応力推定方法および破壊応力推定装置に関する。 In particular, the present invention relates to a method for estimating a fracture stress and a fracture stress at the time of fracture of an oxide film for estimating a fracture stress when an oxide film (so-called black skin) formed on a surface of a steel material is broken and a metal substrate of the steel material is exposed. The present invention relates to an estimation device.
従来、メーカーで製造される鋼材は熱処理を経る際、その表面に黒皮と呼ばれる酸化被膜が形成される。このように熱処理後に形成される黒皮などの金属表面に形成される酸化皮膜は金属素地を覆うことになるため、この酸化被膜によって周囲環境から金属素地への物質付着を防ぎ、防食効果等を有することが期待されている（例えば、非特許文献１を参照。） Conventionally, when steel materials manufactured by manufacturers are subjected to heat treatment, an oxide film called a black skin is formed on the surface thereof. Since the oxide film formed on the metal surface such as black skin formed after heat treatment covers the metal substrate in this way, this oxide film prevents substances from adhering to the metal substrate from the surrounding environment, and has an anticorrosive effect, etc. (For example, refer nonpatent literature 1.)
この酸化被膜（黒皮）は金属素地に比べて延性が低いため、当該酸化被膜に対して外部から所定の応力が負荷されると優先的に破壊されてしまう（例えば、非特許文献２を参照。）。この酸化被膜が破壊されるときの鋼材の応力については、当該応力の負荷および除荷後、金属表面を目視、顕微鏡観察あるいはＳＥＭ( Search Engine Optimization)による走査型電子顕微鏡法を用いた表面観察を行い、酸化被膜の破壊が確認されたとき応力を破壊応力をとして決定する方法が用いられている（例えば、非特許文献３を参照。）。 Since this oxide film (black skin) has a lower ductility than a metal substrate, it is preferentially destroyed when a predetermined stress is applied to the oxide film from the outside (for example, see Non-Patent Document 2). .) Regarding the stress of the steel material when this oxide film is broken, after loading and unloading of the stress, visually observe the metal surface, observe the microscope, or observe the surface using scanning electron microscopy by SEM (Search Engine Optimization). When the destruction of the oxide film is confirmed, a method is used in which the stress is determined as the fracture stress (see, for example, Non-Patent Document 3).
ここで、この破壊応力を測定する必要性について簡単に説明する。鋼材表面に形成される酸化被膜（黒皮）は、金属素地の防食に有効であるが、当該酸化被膜が破壊されると鋼材の耐久性が急激に低下することが知られている。 Here, the necessity to measure the fracture stress will be briefly described. Although the oxide film (black skin) formed on the steel material surface is effective for preventing corrosion of the metal substrate, it is known that the durability of the steel material is drastically reduced when the oxide film is destroyed.
そのため、使用される環境において、鋼材に負荷された応力に耐え得る酸化被膜を形成することが望まれている。鋼材の酸化被膜の破壊応力が分かれば、その破壊応力に基づいて、使用環境下において鋼材の強度特性を満足する酸化被膜の選定および開発に活用することができるのである。 Therefore, it is desired to form an oxide film that can withstand the stress applied to the steel material in the environment in which it is used. If the fracture stress of the oxide film of the steel material is known, it can be used for selection and development of an oxide film that satisfies the strength characteristics of the steel material under the usage environment based on the fracture stress.
ところで、表面観察によって推定される酸化被膜の破壊応力が、鋼材の金属素地が露出した時の応力として妥当であるとは限らない。なぜなら、表面観察では、金属素地と酸化被膜との判別が難しいため、酸化被膜に生じた亀裂が当該酸化被膜の内部で止まっているのか、金属素地が露出するところまで達しているのかを正確に判断することが困難であるからである。したがって、表面観察では金属素地が露出した時の破壊応力を正確に検出できないという問題があった。 By the way, the fracture stress of the oxide film estimated by surface observation is not necessarily valid as the stress when the metal base of the steel material is exposed. This is because it is difficult to distinguish between the metal substrate and the oxide film in the surface observation, so it is accurate whether the crack generated in the oxide film has stopped inside the oxide film or the metal substrate has been exposed. This is because it is difficult to judge. Therefore, the surface observation has a problem that the fracture stress when the metal substrate is exposed cannot be detected accurately.
また、ＳＥＭによる走査型電子顕微鏡法を用いて表面観察に伴う表面成分分析を行えば、酸化被膜と金属素地との判別は可能であるが、観察環境に制約があり、応力が負荷されたままの状態や酸化被膜が破壊した瞬間を観察することは困難であるため、この場合も、酸化被膜が破壊して金属素地が露出した時の破壊応力を正確に検出できないという問題があった。 Moreover, if surface component analysis accompanying surface observation is performed using scanning electron microscopy with SEM, it is possible to discriminate between an oxide film and a metal substrate, but there are restrictions on the observation environment, and stress is still applied. Since it is difficult to observe the state and the moment when the oxide film is broken, there is also a problem in this case that the fracture stress when the oxide film is broken and the metal substrate is exposed cannot be detected accurately.
本発明は、以上のような問題点を解消するためになされたものであり、鋼材に対して所定の応力を負荷したままの状態で鋼材の表面に形成された酸化被膜が破壊されたときの破壊応力を正確に推定し得る酸化被膜破壊時の破壊応力推定方法および破壊応力推定装置を提案することを目的とする。 The present invention has been made to solve the above-described problems, and when an oxide film formed on the surface of a steel material is destroyed while a predetermined stress is applied to the steel material. The purpose is to propose a fracture stress estimation method and fracture stress estimation device at the time of oxide film fracture that can accurately estimate the fracture stress.
本発明に係る酸化被膜破壊時の破壊応力推定方法は、導電性を有しかつ鋼材（１０）が溶出することのないアルカリ性水溶液（３）に対し、その表面に酸化被膜が形成された前記鋼材（１０）を浸漬する浸漬ステップと、前記アルカリ性水溶液（３）に浸漬された前記鋼材（１０）に対し試験機（９）により所定の応力（Ｔｓ）を負荷することによって破壊試験を実施しながら、前記鋼材（１０）の自然電位（Ｐ１）を測定する自然電位測定ステップと、前記鋼材（１０）に前記応力（Ｔｓ）を負荷している状態で、前記自然電位測定ステップで測定される前記鋼材（１０）の自然電位（Ｐ１）の変曲点（Ｑ１）を特定する変曲点特定ステップと、前記変曲点（Ｑ１）に対応した前記応力（Ｔｓ）を前記酸化被膜が破壊されたときの破壊応力として推定する推定ステップとを有するようにする。 Breaking stress estimation method when the oxide film breakdown according to the present invention has a conductivity and relative steel alkaline water solution (10) is not to elute (3), the oxide film formed on its surface an immersion step of immersing the steel material (10), carried out destructive tests by loading a predetermined stress (Ts) by the alkaline water solution (3) the steel material is immersed in (10) relative to tester (9) However, the natural potential measurement step of measuring the natural potential (P1) of the steel material (10) and the natural potential measurement step in the state where the stress (Ts) is loaded on the steel material (10). The inflection point identifying step for identifying the inflection point (Q1) of the natural potential (P1) of the steel material (10), and the oxide film destroys the stress (Ts) corresponding to the inflection point (Q1). Fracture stress when applied To have the estimated estimating by.
上記破壊応力推定方法において、前記変曲点特定ステップでは、前記鋼材（１０）の自然電位（Ｐ１）の変化を表すプロットを近似する高次多項式を用いて前記自然電位（Ｐ１）の変化の傾きが最初に正から負になる極大点を前記変曲点（Ｑ１）として特定するようにする。 In the fracture stress estimation method, in the inflection point specifying step, the slope of the change in the natural potential (P1) using a high-order polynomial approximating a plot representing the change in the natural potential (P1) of the steel material (10). Is first specified as the inflection point (Q1).
上記破壊応力推定方法において、前記変曲点特定ステップでは、前記高次多項式を微分することによって得られる導関数が０となる点を前記変曲点（Ｑ１）として特定するようにする。 In the fracture stress estimation method, in the inflection point specifying step, a point at which a derivative obtained by differentiating the high-order polynomial is 0 is specified as the inflection point (Q1).
上記破壊応力推定方法において、前記推定ステップでは、前記変曲点（Ｑ１）に対応した前記応力（Ｔｓ）を前記酸化被膜が破壊されて前記鋼材（１０）の金属素地が露出したときの前記破壊応力として推定するようにする。 In the fracture stress estimation method, in the estimation step, the stress (Ts) corresponding to the inflection point (Q1) is broken when the oxide film is broken and the metal substrate of the steel material (10) is exposed. Try to estimate it as stress.
本発明に係る酸化被膜破壊時の破壊応力推定装置は、その表面に酸化被膜が形成された鋼材（１０）を、導電性を有しかつ当該鋼材（１０）が溶出することのないアルカリ性水溶液（３）に浸漬する容器（２）と、
前記アルカリ性水溶液（３）に浸漬された前記鋼材（１０）に対し試験機（９）により所定の応力（Ｔｓ）を負荷することによって破壊試験を実施しながら、前記鋼材（１０）の自然電位（Ｐ１）を測定する自然電位測定部（４、５、６）と、前記鋼材（１０）に対し前記応力（Ｔｓ）を負荷している状態で、前記自然電位測定部（４、５、６）により測定される前記鋼材（１０）の自然電位（Ｐ１）の変曲点（Ｑ１）を特定する変曲点特定部（７ａ）と、前記変曲点（Ｑ１）に対応した前記応力（Ｔｓ）を前記酸化被膜が破壊されたときの破壊応力として推定する推定部（７ｂ）とを備えるようにする。
Breaking stress estimation apparatus when the oxide film breakdown according to the present invention, the alkaline aqueous solution without steel (10) an oxide film formed on its surface, which has conductivity and the steel (10) is eluted A container (2) immersed in (3);
While performing destructive testing by loading a predetermined stress (Ts) by the test machine (9) with respect to the dipped the steel (10) to said alkaline water solution (3), the self-potential of steel (10) The natural potential measuring unit (4, 5, 6) for measuring (P1) and the natural potential measuring unit (4, 5, 6) in a state where the stress (Ts) is applied to the steel material (10). ) And the inflection point specifying part (7a) for specifying the inflection point (Q1) of the natural potential (P1) of the steel material (10), and the stress (Ts) corresponding to the inflection point (Q1). ) Is estimated as a fracture stress when the oxide film is broken.
本発明によれば、試験機（９）により鋼材（１０）に所定の応力（Ｔｓ）を負荷しながら、鋼材（１０）の自然電位（Ｐ１）の変曲点（Ｑ１）に対応した鋼材（１０）の応力（Ｔｓ）を酸化被膜が破壊されたときの破壊応力として推定することにより、表面観察によることなく、かつ、酸化被膜が破壊した瞬間を観察することもなく、鋼材（１０）に応力（Ｔｓ）を負荷したままの状態であっても、鋼材（１０）の表面に形成された酸化被膜が破壊されたときの破壊応力を正確に推定することができる。 According to the present invention, a steel material corresponding to the inflection point (Q1) of the natural potential (P1) of the steel material (10) while applying a predetermined stress (Ts) to the steel material (10) by the testing machine (9). By estimating the stress (Ts) of 10) as the fracture stress when the oxide film is destroyed, the steel material (10) can be obtained without observing the surface and without observing the moment when the oxide film is destroyed. Even when the stress (Ts) is still applied, the fracture stress when the oxide film formed on the surface of the steel material (10) is broken can be accurately estimated.
＜破壊応力推定装置の構成＞
図１に示すように、酸化皮膜破壊時の破壊応力推定装置１は、その表面に酸化被膜（黒皮）が形成された試験片である鋼材１０に対して、引っ張り試験機９により矢印ＡＢ方向へ引張力を付与し、その引張力を次第に増加させている最中に、当該酸化被膜が破壊されて当該鋼材１０の金属素地が露出したときの鋼材１０の引張応力を酸化被膜の破壊応力として推定するものである。以下、破壊応力推定装置１の具体的構成を説明する。
<Configuration of fracture stress estimation device>
As shown in FIG. 1, the fracture stress estimation device 1 at the time of destruction of an oxide film is applied to a steel material 10 which is a test piece having an oxide film (black skin) formed on the surface thereof by a tensile tester 9 in the direction of arrow AB. The tensile stress of the steel material 10 when the oxide film is destroyed and the metal substrate of the steel material 10 is exposed while the tensile force is gradually increased and applied to the steel substrate 10 as the fracture stress of the oxide film. To be estimated. Hereinafter, a specific configuration of the fracture stress estimation apparatus 1 will be described.
この破壊応力推定装置１は、導電性を有し鋼材１０が酸化反応等により溶出しないアルカリ性水溶液３の入った容器２と、当該アルカリ性水溶液３に浸漬された対極４、参照極５および鋼材１０（作用極）と、対極４、参照極５および鋼材１０と接続された状態で当該鋼材１０の自然電位を測定するポテンショスタット６と、酸化被膜が破壊されて鋼材１０の金属素地が露出したときの当該鋼材１０の応力（破壊応力）をポテンショスタット６からの出力である自然電位に基づいて推定する制御部７と、当該応力（破壊応力）の値を制御部７からの出力結果として受け取り表示する表示部８とによって構成されている。 The fracture stress estimation apparatus 1 includes a container 2 containing an alkaline aqueous solution 3 that has conductivity and does not elute the steel material 10 due to an oxidation reaction or the like, a counter electrode 4 that is immersed in the alkaline aqueous solution 3, a reference electrode 5, and a steel material 10 ( Working electrode), a potentiostat 6 for measuring the natural potential of the steel material 10 in a state of being connected to the counter electrode 4, the reference electrode 5 and the steel material 10, and when the metal film of the steel material 10 is exposed due to destruction of the oxide film. A control unit 7 that estimates the stress (fracture stress) of the steel material 10 based on a natural potential that is an output from the potentiostat 6, and receives and displays the value of the stress (fracture stress) as an output result from the control unit 7. And a display unit 8.
ここで、試験片または試料として用いられる鋼材１０は、例えば円柱状の直径９ｍｍの鉄筋である。引張試験機９は、鋼材１０の両端を互いに離反する矢印ＡＢ方向へ引っ張る試験機であり、制御部７によって引張力の値が制御される。 Here, the steel material 10 used as a test piece or a sample is, for example, a cylindrical rebar having a diameter of 9 mm. The tensile testing machine 9 is a testing machine that pulls both ends of the steel material 10 in the directions of arrows AB that are separated from each other, and the value of the tensile force is controlled by the control unit 7.
引張試験機９では、鋼材１０を単位時間当たり一定長伸ばす条件として例えば０．００２７mm／min に設定する。アルカリ性水溶液３は、鋼材１０（作用極）が溶出することなく、かつ、その表面に形成された酸化被膜（黒皮）を破壊しない例えばｐｈ１０以上の１００ｍＭ（m mol/L）の水酸化ナトリウム水溶液である。 In the tensile tester 9, for example, 0.0027 mm / min is set as a condition for extending the steel material 10 by a certain length per unit time. The alkaline aqueous solution 3 is, for example, a 100 mM (m mol / L) aqueous solution of sodium hydroxide having a pH of 10 or more that does not cause the steel material 10 (working electrode) to elute and does not destroy the oxide film (black skin) formed on the surface. It is.
なお、破壊応力推定装置１では、作用極として鋼材１０を用いるとともに、対極４として例えば白金電極、参照極５として例えば銀塩化銀(Ag/AgCl)電極を用いる。この場合、対極４、参照極５および鋼材１０がそれぞれ電気的に接続されたポテンショスタット６により、作用極である鋼材１０の自然電位を測定する自然電位測定部としての電気化学測定系（三電極法）が構成される。 In the fracture stress estimation apparatus 1, the steel material 10 is used as the working electrode, and for example, a platinum electrode is used as the counter electrode 4, and a silver / silver chloride (Ag / AgCl) electrode is used as the reference electrode 5. In this case, an electrochemical measurement system (three electrodes) as a natural potential measuring unit for measuring a natural potential of the steel material 10 as a working electrode by a potentiostat 6 to which the counter electrode 4, the reference electrode 5 and the steel material 10 are electrically connected. Law).
ポテンショスタット６は、鋼材１０に電圧もしくは電流を印加していない状態で、参照極５を基準にした当該参照極５と鋼材１０との電位差を自然電位Ｐとして測定し、これを制御部７へ出力するものである。 The potentiostat 6 measures the potential difference between the reference electrode 5 with respect to the reference electrode 5 and the steel material 10 as a natural potential P in a state where no voltage or current is applied to the steel material 10, and supplies this to the control unit 7. Output.
制御部７は、ＣＰＵ、メモリおよびインタフェース等からなるコンピュータ（ハードウェア）であり、当該コンピュータ（ソフトウェア）にプログラムがインストールされ、当該ハードウェアと当該ソフトウェアとが協働することにより変曲点特定部７ａおよび破壊応力推定部７ｂを構成する。 The control unit 7 is a computer (hardware) including a CPU, a memory, an interface, and the like. A program is installed in the computer (software), and the hardware and the software cooperate with each other so that the inflection point specifying unit 7a and the fracture stress estimation part 7b are comprised.
制御部７の変曲点特定部７ａは、図３に示すような鋼材１０の自然電位Ｐ１の変曲点（極大点）Ｑ１を特定し、制御部７の破壊応力推定部７ｂは当該変曲点（極大点）Ｑ１に対応した鋼材１０の引張応力Ｔｓを破壊応力として推定し、これを表示部８へ出力するものであるが、その詳細については後述する。 The inflection point specifying unit 7a of the control unit 7 specifies the inflection point (maximum point) Q1 of the natural potential P1 of the steel material 10 as shown in FIG. 3, and the fracture stress estimation unit 7b of the control unit 7 is the inflection point. The tensile stress Ts of the steel material 10 corresponding to the point (maximum point) Q1 is estimated as a fracture stress, and this is output to the display unit 8. The details will be described later.
なお、制御部７は、引張試験機９の引張力の値を制御したり、ポテンショスタット６により鋼材１０の自然電位の測定を行わせたり、当該引張力および鋼材１０の断面積に基づいて当該鋼材１０に負荷される引張応力Ｔｓ（後述する）を計算する種々の機能についても有している。 The control unit 7 controls the value of the tensile force of the tensile tester 9, causes the potentiostat 6 to measure the natural potential of the steel material 10, or based on the tensile force and the cross-sectional area of the steel material 10. It also has various functions for calculating a tensile stress Ts (described later) applied to the steel material 10.
＜自然電位の測定＞
ところで、この応力推定装置１では、鋼材１０の酸化被膜（黒皮）の破壊応力を推定する前に、その表面に酸化被膜の形成された黒皮有りの鋼材の自然電位Ｐ１と、その表面に酸化被膜の形成されていない黒皮無しの鋼材の自然電位Ｐ２とをポテンショスタット６により測定する。
<Measurement of natural potential>
By the way, in this stress estimation apparatus 1, before estimating the fracture stress of the oxide film (black skin) of the steel material 10, the natural potential P1 of the steel material with the black skin on which the oxide film is formed and the surface The natural potential P2 of the steel material having no black skin without an oxide film is measured by a potentiostat 6.
図２に示すように、ポテンショスタット６により黒皮有りの鋼材の自然電位Ｐ１と、黒皮無しの鋼材の自然電位Ｐ２とを測定すると、自然電位Ｐ１と自然電位Ｐ２との間にはそもそも電位差が生じている。 As shown in FIG. 2, when the potentiostat 6 is used to measure the natural potential P1 of the steel material with black skin and the natural potential P2 of the steel material without black skin, a potential difference is originally between the natural potential P1 and the natural potential P2. Has occurred.
ポテンショスタット６による測定開始から６０時間経過した時点においても、黒皮有りの鋼材の自然電位Ｐ１の方が、黒皮無しの鋼材の自然電位Ｐ２よりも高くなっており、常に次の（式１）の関係が成立する。 Even when 60 hours have elapsed from the start of measurement by the potentiostat 6, the natural potential P1 of the steel material with black skin is higher than the natural potential P2 of the steel material without black skin. ) Is established.
Ｐ１＞Ｐ２…………………………………………………………………………………（式１） P1> P2 …………………………………………………………………………………… (Formula 1)
この（式１）が成立するのは、黒皮有りの鋼材よりも黒皮無しの鋼材の電気的抵抗が常に低いため、黒皮有りの鋼材の自然電位Ｐ１よりも、黒皮無しの鋼材の自然電位Ｐ２の方が低くなると考えられるからである。 This (Equation 1) is established because the steel sheet without black skin is always lower in electrical resistance than the steel with black skin, so that the steel plate without black skin has a natural potential P1 lower than the natural potential P1 of the steel with black skin. This is because the natural potential P2 is considered to be lower.
したがって、酸化被膜の形成された黒皮有りの鋼材１０に引張試験機９による引張応力が負荷され、当該鋼材１０の表面に形成された酸化被膜が破壊された場合には、当該鋼材１０の金属素地が露出されるため、その時点から自然電位Ｐ１が自然電位Ｐ２まで低下すると考えられる。 Therefore, when the steel material 10 with a black skin on which the oxide film is formed is loaded with a tensile stress by the tensile testing machine 9 and the oxide film formed on the surface of the steel material 10 is destroyed, the metal of the steel material 10 is broken. Since the substrate is exposed, it is considered that the natural potential P1 decreases to the natural potential P2 from that point.
図３には引張試験機９による鋼材１０の引張試験前の表面状態を示し、図４には引張試験機９による鋼材１０の引張試験中（自然電位Ｐ１の低下前）の表面状態を示し、図５には引張試験機９による鋼材１０の引張試験中（自然電位Ｐ１の低下後）の表面状態を示し、図６には引張試験機９による鋼材１０の引張試験後の表面状態を示す。 FIG. 3 shows the surface state of the steel material 10 before the tensile test by the tensile tester 9, and FIG. 4 shows the surface state of the steel material 10 by the tensile tester 9 during the tensile test (before the decrease of the natural potential P1). FIG. 5 shows the surface state of the steel material 10 during the tensile test (after the reduction of the natural potential P1) by the tensile tester 9, and FIG. 6 shows the surface state of the steel material 10 after the tensile test by the tensile tester 9.
図３の引張試験前の鋼材１０の表面状態および図４の引張試験中（自然電位Ｐ１の低下前）の鋼材１０の表面状態では、双方ともに酸化被膜（黒皮）に破壊が生じていない様子が分かる。 In both the surface state of the steel material 10 before the tensile test of FIG. 3 and the surface state of the steel material 10 during the tensile test of FIG. 4 (before the decrease of the natural potential P1), neither oxide film (black skin) is broken. I understand.
しかし、図４における引張試験中（自然電位Ｐ１の低下前）の鋼材１０の表面状態と、図５における引張試験中（自然電位Ｐ１の低下後）の鋼材１０の表面状態とを比較すると、図４に比較して図５では酸化被膜（黒皮）内に細かい剥離部分（白色部）が多数出現しており、当該酸化被膜（黒皮）に破壊が生じている様子が分かる。図６における引張試験後では、更に剥離部分が増えて酸化皮膜の破壊が進んでいる様子が分かる。 However, when the surface state of the steel material 10 during the tensile test in FIG. 4 (before the decrease of the natural potential P1) is compared with the surface state of the steel material 10 during the tensile test (after the decrease of the natural potential P1) in FIG. Compared to FIG. 4, in FIG. 5, a large number of fine peeled portions (white portions) appear in the oxide film (black skin), and it can be seen that the oxide film (black skin) is broken. After the tensile test in FIG. 6, it can be seen that the number of peeled portions further increases and the destruction of the oxide film proceeds.
＜破壊応力推定原理＞
次に、鋼材１０の酸化被膜（黒皮）が破壊される前の自然電位Ｐ１が、酸化被膜（黒皮）が破壊された後の金属素地の露出時に自然電位Ｐ２まで低下する現象を利用した破壊応力推定原理について説明する。
<Fracture stress estimation principle>
Next, a phenomenon is used in which the natural potential P1 before the oxide film (black skin) of the steel material 10 is destroyed is reduced to the natural potential P2 when the metal substrate is exposed after the oxide film (black skin) is destroyed. The principle of fracture stress estimation will be described.
制御部７は、上述したアルカリ性水溶液３に黒皮有りの鋼材１０が浸漬された状態で、当該鋼材１０の自然電位Ｐ１をポテンショスタット６により測定開始する。因みに、ここで用いられる黒皮有りの鋼材１０は、予め、黒皮有りの鋼材に対する自然電位Ｐ１、および黒皮無しの鋼材に対する自然電位Ｐ２を測定したときのサンプルであってもよいし、それとは異なる新たな黒皮有りの鋼材であってもよい。 The control unit 7 starts measuring the natural potential P1 of the steel material 10 with the potentiostat 6 in a state where the steel material 10 with black skin is immersed in the alkaline aqueous solution 3 described above. Incidentally, the steel material 10 with the black skin used here may be a sample when the natural potential P1 for the steel material with the black skin and the natural potential P2 for the steel material without the black skin are measured in advance. May be a different new steel with black skin.
そして制御部７は、鋼材１０の単位時間当たりの伸び量が０．００２７mm／min になるように引張試験機９により引張力を次第に増加させながら当該鋼材１０に付与し、その間もポテンショスタット６により当該鋼材１０（作用極）の自然電位Ｐ１を１分毎に測定し続ける。 And the control part 7 is given to the said steel material 10 while increasing the tensile force gradually by the tensile tester 9 so that the elongation amount per unit time of the steel material 10 may become 0.0027 mm / min, and during that time, the potentiostat 6 is used. The natural potential P1 of the steel material 10 (working electrode) is continuously measured every minute.
黒皮有りの鋼材１０には、引張試験機９による引張力が増加しながら付与されるため、時間の経過に連れて酸化被膜が徐々に破壊され、いずれ当該鋼材１０の金属素地が露出することになる。図７には、鋼材１０に負荷された引張応力Ｔｓおよび黒皮有りの鋼材１０の自然電位Ｐ１との関係を示す。この図７では、横軸が時間であり、左縦軸が引張応力Ｔｓであり、右縦軸が鋼材１０の自然電位Ｐ１である。 The steel material 10 with black skin is applied while the tensile force by the tensile tester 9 is increased, so that the oxide film is gradually destroyed over time, and the metal substrate of the steel material 10 is eventually exposed. become. FIG. 7 shows the relationship between the tensile stress Ts loaded on the steel material 10 and the natural potential P1 of the steel material 10 with black skin. In FIG. 7, the horizontal axis represents time, the left vertical axis represents the tensile stress Ts, and the right vertical axis represents the natural potential P1 of the steel material 10.
この場合、鋼材１０の自然電位Ｐ１を測定開始してからの経緯を参照すると、約３０分経過した時点において当該自然電位Ｐ１が単調増加から単調減少へ転じている。この変曲点（極大点）Ｑ１の時点における鋼材１０の引張応力Ｔｓは１２６０[MPa]となっている。この引張応力Ｔｓは、制御部７が引張試験機９の引張力を鋼材１０の断面積で除算することにより算出することができる。 In this case, referring to the history of starting the measurement of the natural potential P1 of the steel material 10, the natural potential P1 has changed from monotonically increasing to monotonically decreasing after about 30 minutes. The tensile stress Ts of the steel material 10 at the time of the inflection point (maximum point) Q1 is 1260 [MPa]. The tensile stress Ts can be calculated by the control unit 7 dividing the tensile force of the tensile testing machine 9 by the cross-sectional area of the steel material 10.
制御部７の変曲点特定部７ａにおいては、鋼材１０の自然電位Ｐ１の変曲点（極大点）Ｑ１を特定する。具体的には、変曲点特定部７ａは、図３における自然電位Ｐ１のプロットを近似する高次多項式の係数を最小二乗法により算出し、その高次多項式に基づいて当該自然電位Ｐ１の変化の傾きを求め、その傾きが最初に正から負になる変曲点（極大点）Ｑ１を特定する。 In the inflection point specifying unit 7a of the control unit 7, the inflection point (maximum point) Q1 of the natural potential P1 of the steel material 10 is specified. Specifically, the inflection point specifying unit 7a calculates a coefficient of a high-order polynomial that approximates the plot of the natural potential P1 in FIG. 3 by the least square method, and changes the natural potential P1 based on the high-order polynomial. The inflection point (maximum point) Q1 at which the inclination first becomes negative from the positive is specified.
制御部７の破壊応力推定部７ｂは、変極点特定部７ａにより特定された変曲点（極大点）Ｑ１の時点において当該制御部７が制御していた引張試験機９により鋼材１０に負荷された引張応力Ｔｓ（この場合は１２６０[MPa]）を酸化被膜の破壊応力であると推定し、当該破壊応力の値を表示部８に出力する。 The fracture stress estimating unit 7b of the control unit 7 is loaded on the steel material 10 by the tensile testing machine 9 controlled by the control unit 7 at the time of the inflection point (maximum point) Q1 specified by the inflection point specifying unit 7a. The tensile stress Ts (in this case, 1260 [MPa]) is estimated as the fracture stress of the oxide film, and the value of the fracture stress is output to the display unit 8.
＜破壊応力推定装置の動作＞
このような破壊応力推定装置１の動作について、図８のフローチャートを用いて説明する。
<Operation of fracture stress estimation device>
The operation of the fracture stress estimation apparatus 1 will be described with reference to the flowchart of FIG.
破壊応力推定装置１では、ステップＳＰ１において、黒皮有りの鋼材１０（作用極）を容器２のアルカリ性水溶液３に浸漬させ、次のステップＳＰ２へ移る。 In the fracture stress estimating apparatus 1, in step SP1, the steel material 10 (working electrode) with black skin is immersed in the alkaline aqueous solution 3 in the container 2, and the process proceeds to the next step SP2.
ステップＳＰ２において破壊応力推定装置１の制御部７は、ポテンショスタット６により鋼材１０の自然電位Ｐ１の測定を開始し、次のステップＳＰ３へ移る。 In step SP2, the control unit 7 of the fracture stress estimation apparatus 1 starts measuring the natural potential P1 of the steel material 10 with the potentiostat 6, and proceeds to the next step SP3.
ステップＳＰ３において制御部７は、鋼材１０の自然電位Ｐ１の測定を実施したままの状態で、引張試験機９を制御し、図７に示すように、鋼材１０の単位時間当たりの伸び量が０．００２７mm／min になるように鋼材１０に負荷させる引張応力Ｔｓを増大させ、次のステップＳＰ４へ移る。すなわち制御部７は、引張試験機９により鋼材１０の破壊試験を実施しながら、当該鋼材１０の自然電位を測定する。 In step SP3, the control unit 7 controls the tensile tester 9 in a state where the measurement of the natural potential P1 of the steel material 10 is performed, and the elongation amount per unit time of the steel material 10 is 0 as shown in FIG. The tensile stress Ts applied to the steel material 10 is increased so as to be .0027 mm / min, and the process proceeds to the next step SP4. That is, the control unit 7 measures the natural potential of the steel material 10 while performing a destructive test of the steel material 10 with the tensile tester 9.
ステップＳＰ４において制御部７は、鋼材１０の自然電位Ｐ１の測定が終了すると、変曲点特定部７ａにより鋼材１０の自然電位Ｐ１が単調増加から単調減少に転じる変曲点（極大点）Ｑ１を高次多項式に基づいて特定し、次のステップＳＰ５へ移る。 In step SP4, when the measurement of the natural potential P1 of the steel material 10 is completed, the control unit 7 sets an inflection point (maximum point) Q1 at which the natural potential P1 of the steel material 10 changes from monotonically increasing to monotonically decreasing by the inflection point specifying unit 7a. Based on the high-order polynomial, the process proceeds to the next step SP5.
ステップＳＰ５において制御部７は、破壊応力推定部７ｂにより変曲点（極大点）Ｑ１の時点で鋼材１０に負荷されていた引張応力Ｔｓを求め、これを鋼材１０の酸化被膜の破壊応力として推定した後、これを表示部８へ出力し、次のステップＳＰ６へ移る。 In step SP5, the control unit 7 obtains the tensile stress Ts applied to the steel material 10 at the time of the inflection point (maximum point) Q1 by the fracture stress estimation unit 7b, and estimates this as the fracture stress of the oxide film of the steel material 10. After that, this is output to the display unit 8, and the process proceeds to the next step SP6.
ステップＳＰ６において制御部７は、表示部８に対して鋼材１０の酸化被膜の破壊応力の値を表示することにより、使用環境下において鋼材１０の強度特性を満足する酸化被膜の選定および開発に活用するための情報として当該破壊応力の値を提供し、この一連の処理を全て終了する。 In step SP6, the control unit 7 displays the value of the fracture stress of the oxide film of the steel material 10 on the display unit 8, so that it is utilized for selection and development of the oxide film that satisfies the strength characteristics of the steel material 10 in the use environment. The value of the fracture stress is provided as information for performing the processing, and all the series of processing is completed.
＜効果＞
この破壊応力推定装置１では、黒皮有りの鋼材１０の自然電位Ｐ１の測定結果に基づき当該鋼材１０の酸化被膜が破壊されて金属素地が露出するときの破壊応力を推定することができるので、従来のような目視により表面観察や顕微鏡観察等の煩雑な観察作業を作業者に強いることなく、かつ、引張試験機９により鋼材１０に引張応力Ｔｓが負荷されたままの状態で鋼材１０の酸化被膜が破壊されるときの破壊応力を容易かつ正確に推定することができる。
<Effect>
In this fracture stress estimation device 1, since the oxide film of the steel material 10 is destroyed and the metal substrate is exposed based on the measurement result of the natural potential P1 of the steel material 10 with black skin, the fracture stress can be estimated. Oxidation of the steel material 10 with the tensile stress Ts being applied to the steel material 10 by the tensile testing machine 9 without forcing the operator to perform complicated observation work such as surface observation and microscopic observation by conventional visual observation. It is possible to easily and accurately estimate the breaking stress when the coating is broken.
また破壊応力推定装置１では、鋼材１０の酸化被膜が破壊される前の自然電位Ｐ１が、酸化被膜が破壊された後の金属素地の露出時には自然電位Ｐ２まで低下する現象を利用して破壊応力を推定するようにしたことにより、酸化被膜が破壊されただけではなく、金属素地が露出するという鋼材１０の耐久性が急激に低下するときの破壊応力を正確に推定することができる。 Further, the fracture stress estimation apparatus 1 utilizes the phenomenon that the natural potential P1 before the oxide film of the steel material 10 is destroyed is reduced to the natural potential P2 when the metal substrate is exposed after the oxide film is destroyed. Thus, not only the oxide film is destroyed, but also the fracture stress when the durability of the steel material 10 that the metal substrate is exposed rapidly decreases can be estimated accurately.
＜他の実施の形態＞
なお上述した実施の形態においては、鋼材１０に対して引張試験機９により引張力を付与し、当該鋼材１０の酸化被膜が破壊されて金属素地が露出したときの引張応力Ｔｓを酸化被膜の破壊応力として推定するようにした場合について述べたが、本発明はこれに限るものではなく、鋼材１０に対して圧縮試験機（図示せず）により圧縮力を付与し、当該圧縮力により酸化被膜が破壊されたときの当該鋼材１０の圧縮応力を酸化被膜の破壊応力として推定するようにしても良い。
<Other embodiments>
In the embodiment described above, a tensile force is applied to the steel material 10 by the tensile tester 9, and the tensile stress Ts when the oxide film of the steel material 10 is broken and the metal substrate is exposed is determined as the destruction of the oxide film. Although the case where the stress is estimated is described, the present invention is not limited to this, and a compressive force is applied to the steel material 10 by a compression tester (not shown), and the oxide film is formed by the compressive force. You may make it estimate the compressive stress of the said steel material 10 when it destroys as a fracture stress of an oxide film.
また上述した実施の形態においては、制御部７の変曲点特定部７ａが自然電位Ｐ１のプロットを近似する高次多項式を用いて当該自然電位Ｐ１の変化の傾きを求め、その傾きが最初に正から負になる変曲点（極大点）Ｑ１を特定するようにした場合について述べたが、本発明はこれに限らず、自然電位Ｐ１のプロットを近似する高次多項式を微分することにより得られる導関数が０になる点、つまり接線の傾きが０となる点すなわち変曲点（極大点）Ｑ１を求めるようにしても良い。 In the above-described embodiment, the inflection point specifying unit 7a of the control unit 7 obtains the slope of the change in the natural potential P1 using a high-order polynomial that approximates the plot of the natural potential P1, and the slope is the first. Although the case where the inflection point (maximum point) Q1 from positive to negative is specified has been described, the present invention is not limited to this, and is obtained by differentiating a higher-order polynomial that approximates the plot of the natural potential P1. The point at which the derived function becomes 0, that is, the point at which the slope of the tangent becomes 0, that is, the inflection point (maximum point) Q1 may be obtained.
さらに上述した実施の形態においては、鋼材１０の自然電位Ｐ１の測定が終了した後に、制御部７の変曲点特定部７ａが自然電位Ｐ１のプロットを近似する高次多項式を用いて当該自然電位Ｐ１の変曲点（極大点）Ｑ１を特定するようにした場合について述べたが、本発明はこれに限らず、鋼材１０の自然電位Ｐ１の測定中、高次多項式を用いてリアルタイムに変曲点（極大点）Ｑ１を特定し、その変曲点Ｑ１に基づいて破壊応力を推定するようにしても良い。 Furthermore, in embodiment mentioned above, after the measurement of the natural potential P1 of the steel material 10 is complete | finished, the inflexion point specific | specification part 7a of the control part 7 uses the said natural potential using the high order polynomial which approximates the plot of the natural potential P1. Although the case where the inflection point (maximum point) Q1 of P1 is specified has been described, the present invention is not limited to this, and during the measurement of the natural potential P1 of the steel material 10, inflection is performed in real time using a high-order polynomial. A point (maximum point) Q1 may be specified, and the fracture stress may be estimated based on the inflection point Q1.
１…応力推定装置、２…容器、３…アリカリ性水溶液、４…対極、５…参照極、６…ポテンショスタット、７…制御部、７ａ…変曲点特定部、７ｂ…破壊応力推定部、８…表示部、９…引張試験機。 DESCRIPTION OF SYMBOLS 1 ... Stress estimation apparatus, 2 ... Container, 3 ... Alikari aqueous solution, 4 ... Counter electrode, 5 ... Reference electrode, 6 ... Potentiostat, 7 ... Control part, 7a ... Inflection point specific | specification part, 7b ... Fracture stress estimation part, 8: Display unit, 9: Tensile tester.
Claims (5)
前記アルカリ性水溶液に浸漬された前記鋼材に対し試験機により所定の応力を負荷することによって破壊試験を実施しながら、前記鋼材の自然電位を測定する自然電位測定ステップと、
前記鋼材に前記応力を負荷している状態で、前記自然電位測定ステップで測定される前記鋼材の自然電位の変曲点を特定する変曲点特定ステップと、
前記変曲点に対応した前記応力を前記酸化被膜が破壊されたときの破壊応力として推定する推定ステップと
を有することを特徴とする酸化被膜破壊時の破壊応力推定方法。 Has conductivity and to alkaline water solution without the steel is eluted, an immersion step of immersing the steel oxide film is formed on the surface thereof,
While performing destructive testing by loading a predetermined stress by the test machine to said steel immersed in the alkaline aqueous solution, a self-potential measuring step of measuring the natural potential of the steel,
An inflection point identifying step for identifying an inflection point of the natural potential of the steel material measured in the natural potential measurement step in a state where the stress is applied to the steel material;
An estimation step of estimating the stress corresponding to the inflection point as a fracture stress when the oxide film is destroyed.
前記変曲点特定ステップでは、前記鋼材の自然電位の変化を表すプロットを近似する高次多項式を用いて前記自然電位の変化の傾きが最初に正から負になる極大点を前記変曲点として特定する
ことを特徴とする酸化被膜破壊時の破壊応力推定方法。 In the fracture stress estimation method at the time of oxide film fracture according to claim 1,
In the inflection point specifying step, a local maximum point at which the slope of the change in the natural potential first becomes negative from the positive using a high-order polynomial that approximates a plot representing the change in the natural potential of the steel material is used as the inflection point. A method for estimating the fracture stress when an oxide film breaks, characterized by specifying.
前記変曲点特定ステップでは、前記高次多項式を微分することによって得られる導関数が０となる点を前記変曲点として特定する
ことを特徴とする酸化被膜破壊時の破壊応力推定方法。 In the fracture stress estimation method at the time of oxide film fracture according to claim 2,
In the inflection point specifying step, a point at which a derivative obtained by differentiating the higher-order polynomial is 0 is specified as the inflection point.
前記推定ステップでは、前記変曲点に対応した前記応力を前記酸化被膜が破壊されて前記鋼材の金属素地が露出したときの前記破壊応力として推定する
ことを特徴とする酸化被膜破壊時の破壊応力推定方法。 In the fracture stress estimation method at the time of oxide film fracture according to claim 1,
In the estimating step, the stress corresponding to the inflection point is estimated as the fracture stress when the oxide film is broken and the metal base of the steel material is exposed. Estimation method.
前記アルカリ性水溶液に浸漬された前記鋼材に対し試験機により所定の応力を負荷することによって破壊試験を実施しながら、前記鋼材の自然電位を測定する自然電位測定部と、
前記鋼材に対し前記応力を負荷している状態で、前記自然電位測定部により測定される前記鋼材の自然電位の変曲点を特定する変曲点特定部と、
前記変曲点に対応した前記応力を前記酸化被膜が破壊されたときの破壊応力として推定する推定部と
を備えることを特徴とする酸化被膜破壊時の破壊応力推定装置。 A container for soaking the steel oxide film is formed on the surface thereof has conductivity and the alkaline water solution not to the steel is eluted,
While performing destructive testing by loading a predetermined stress by the test machine to said steel immersed in the alkaline aqueous solution, and the natural potential measuring unit for measuring the natural potential of the steel,
An inflection point identifying unit that identifies an inflection point of the natural potential of the steel material measured by the natural potential measurement unit in a state in which the stress is applied to the steel material;
An estimation unit for estimating the stress corresponding to the inflection point as a fracture stress when the oxide film is destroyed.
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