JP6042772B2 - Method of evaluating hydrogen penetration characteristics for metal members - Google Patents

Description

The present invention relates to a hydrogen penetration property evaluation method for a metal member that evaluates hydrogen penetration property for a metal member made of metal .

  For example, high-strength carbon steel is widely used as a member for prestressed concrete structures and automobiles. When hydrogen intrudes into a metal member in a state where stress is applied, such as high strength steel, a hydrogen embrittlement phenomenon may occur in which the toughness, which is a characteristic of the original metal, is reduced. In a metal member in which hydrogen embrittlement has occurred, a predetermined strength in design is lost, which may lead to destruction of the metal member itself and further destruction of a structure composed of the metal member. This hydrogen embrittlement phenomenon can occur not only in steels such as carbon steel but also in metals such as titanium and aluminum.

  On the other hand, as a metal member that hardly causes hydrogen embrittlement, for example, a metal member mainly composed of iron includes stainless steel SUS316L. However, this material is more expensive than general carbon steel, and cannot be substituted for carbon steel in terms of productivity. For this reason, it is necessary to select a type of steel material that has high resistance to hydrogen embrittlement among low-cost carbon steels, in other words, low steel steel susceptibility to hydrogen embrittlement. Or it is necessary to use cheap carbon steel on the use conditions in which hydrogen embrittlement does not become a problem. In order to realize this, it is important to evaluate the hydrogen embrittlement susceptibility.

  One of the assessments of hydrogen embrittlement susceptibility is the assessment of hydrogen penetration. The amount of hydrogen intrusion can be determined by, for example, processing several kinds of metal members to a predetermined size, immersing each processed metal member in a solution, and voluntarily or electrochemically adding hydrogen into the metal member. A test for intruding hydrogen is performed, and the amount of hydrogen intrusion is measured and evaluated. As a result, it is possible to grasp the hydrogen penetration amount in each metal member under a certain hydrogen penetration test condition. Therefore, the mechanical characteristics of each metal member in the hydrogen penetration amount can be determined by using another mechanical test such as a tensile test. By grasping, hydrogen embrittlement susceptibility can be evaluated.

  In addition, in the case of an assessment of hydrogen embrittlement susceptibility for a certain type of steel material, with the exception of general, the greater the amount of hydrogen penetration, the poorer the mechanical properties. Under these experimental conditions, it can be estimated without performing a mechanical test that hydrogen embrittlement is more likely to occur in the use environment corresponding to the experimental condition that gives a result of a large amount of hydrogen intrusion. As an analysis method used for measuring the hydrogen penetration amount, for example, there is a temperature programmed desorption analysis method (see Non-Patent Document 1).

Michihiko Nagumo, “Basics of Hydrogen Embrittlement: Hydrogen Behavior and Embrittlement Mechanism”, Uchida Otsukuru, 1st Edition, pp. 55-67, 2008.

  By the way, generally, the evaluation of the hydrogen intrusion amount of a metal member is generally performed by analysis using the whole metal member processed into a predetermined size. In this analysis, the total amount of hydrogen that has intruded into the metal member is grasped, and it is possible to grasp which metal member has a certain degree of ease of hydrogen intrusion. A thin oxide film is formed on the surface of the metal member actually used in comparison with the internal metal structure at the manufacturing stage or after the manufacturing stage. At the time of processing, the oxide film is previously removed by a method such as polishing. This is because the evaluation of the hydrogen intrusion amount of the metal member is performed for the internal metal structure.

  However, when evaluating the penetration characteristics of hydrogen into a metal member in a state where it is actually used, it is necessary to evaluate the ease of hydrogen penetration into the internal metal structure including the influence of the oxide film described above. On the other hand, in the analysis using the whole metal member such as the temperature programmed desorption analysis, the measurement is performed by removing the oxide film as described above, so that the amount of hydrogen that has entered the oxide film and the oxide film The amount of hydrogen that has penetrated into the internal metallographic structure underneath cannot be evaluated separately. Thus, in the conventional analysis method, there is a problem that it is difficult to evaluate the invasion characteristics of hydrogen into a metal member in a state where it is actually used.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to make it possible to evaluate the hydrogen penetration characteristics with respect to a metal member such as a steel material in an actually used state. .

The method for evaluating hydrogen penetration characteristics for a metal member according to the present invention includes a hydrogen accumulation step for accumulating hydrogen in a target metal member, and measuring a hydrogen distribution in a depth direction from the surface of the metal member that accumulates hydrogen. A distribution measuring step.

In the method for evaluating hydrogen penetration characteristics with respect to the metal member, a depth determining step for determining a diffusion depth of hydrogen from the surface of the metal member from the measured hydrogen distribution, and an oxide film formed on the surface of the metal member by comparing the thickness of the diffusion depth Ru and a evaluation step of evaluating the penetration characteristics of the hydrogen in the metal member.

In the method for evaluating hydrogen penetration characteristics with respect to the metal member , the distribution measurement step may measure the hydrogen distribution in the depth direction from the surface of the metal member in which hydrogen is accumulated by glow discharge optical emission spectrometry. In the distribution measurement step, the hydrogen distribution in the depth direction from the surface of the metal member storing hydrogen may be measured by glow discharge mass spectrometry. In the distribution measurement step, the hydrogen distribution in the depth direction from the surface of the metal member storing hydrogen may be measured by secondary ion mass spectrometry. In the hydrogen accumulation step, hydrogen may be accumulated on the metal member by an electrochemical method.

  As described above, according to the present invention, it is possible to obtain an excellent effect that the invasion characteristics of hydrogen into a metal member such as a steel material in an actually used state can be evaluated.

FIG. 1 is a flowchart for explaining a method for evaluating hydrogen penetration characteristics with respect to a metal member according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a configuration of an apparatus for injecting hydrogen into a metal member by an electrochemical method. FIG. 3 is a characteristic diagram showing an example of a measurement result of a concentration distribution in the depth direction of hydrogen in a hydrogen charging process for a certain steel material A. FIG. 4 is a characteristic diagram showing an example of the measurement result of the concentration distribution in the depth direction of hydrogen in the hydrogen charging step for a certain steel material B.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining a method for evaluating hydrogen penetration characteristics with respect to a metal member according to an embodiment of the present invention. In this hydrogen intrusion characteristic evaluation method for a metal member , first, in step S101, hydrogen is accumulated (invaded) into the target metal member. For example, hydrogen can be stored in the metal member by an electrochemical method. Alternatively, hydrogen may be allowed to enter the metal member by placing the metal member in a high-pressure hydrogen atmosphere.

  Next, in step S102, the hydrogen distribution (concentration distribution) in the depth direction from the surface of the metal member that has accumulated hydrogen is measured. The distribution of hydrogen in the depth direction from the surface of the metal member storing hydrogen can be measured by glow discharge optical emission spectrometry, glow discharge mass spectrometry, or secondary ion mass spectrometry.

  In this way, the hydrogen distribution in the depth direction in the oxide film and metal structure of the metal member is measured in the state where hydrogen is newly accumulated, so the hydrogen penetration characteristics into the metal structure through the oxide film are measured. It can be grasped, and the hydrogen penetration characteristics in the metal member can be evaluated by the following.

  In step S103, the diffusion depth of hydrogen from the surface of the metal member is determined from the hydrogen distribution measured as described above. Next, in step S104, the hydrogen penetration characteristics in the metal member are evaluated by comparing the thickness of the oxide film formed on the surface of the metal member with the diffusion depth. Here, the thickness of the oxide film can be determined by simultaneously measuring the oxygen distribution (concentration distribution) in the hydrogen distribution measurement. As is well known, such a hydrogen distribution measurement technique in the depth direction can measure the distribution in the depth direction of oxygen simultaneously with the hydrogen distribution. From the result of the oxygen distribution measurement, information on the thickness of the oxide film can be obtained using a certain standard. Information on the thickness of the oxide film can be obtained by other analysis methods.

  As described above, by measuring the distribution of hydrogen in the oxide film and metal structure in the metal member, it is possible to grasp the state of diffusion to the metal structure corresponding to the ease of hydrogen penetration through the oxide film. become. Thereby, for example, in a certain steel material, it can be determined that a part of hydrogen has penetrated into the underlying metal structure through the oxide film. Thus, if the diffusion state of hydrogen through the oxide film can be grasped, the invasion characteristics of hydrogen in a state in which it is actually used can be grasped.

  Hereinafter, it demonstrates in detail using an Example.

[Example]
First, an apparatus for causing hydrogen to enter (accumulate) a target metal member will be described with reference to FIG. FIG. 2 is a configuration diagram showing a configuration of an apparatus for injecting hydrogen into a metal member by an electrochemical method.

  This apparatus includes an alkaline aqueous solution 202 accommodated in a container 201 and a galvano potentiostat 203. A working electrode wiring 204, a counter electrode wiring 205, and a reference electrode wiring 206 are connected to the galvano potentiostat 203. A counter electrode 207 is connected to the counter electrode wiring 205, and a reference electrode 208 is connected to the reference electrode wiring 206. The working electrode wiring 204 is connected to a sample piece 211 of a target metal member. The connected sample piece 211, counter electrode 207, and reference electrode 208 are used by being immersed in the alkaline aqueous solution 202.

  In this example, first, a steel rod made of carbon steel is used as a metal member, and a sample taken from the vicinity of the surface of the steel rod is formed into a flat plate shape as a sample piece 211. Further, in the sample piece 211, a sealing film (not shown) is formed except for the surface region where the oxide film (natural oxide film) is formed so as not to contact the alkaline aqueous solution 202. Moreover, in the present Example, the alkaline aqueous solution 202 was used supposing the steel material in concrete as an environment actually used.

  The alkaline aqueous solution 202 was a sodium hydroxide 0.1 M aqueous solution (corresponding to pH 13). In addition, this pH is good as conditions of the range which the experimenter or the person who instruct | indicates an experiment intends between 8-14. Further, in this embodiment, the alkaline aqueous solution 202 is added so that ammonium thiocyanate is 1 weight percent as a catalyst for suppressing the generation of hydrogen gas and promoting the penetration of hydrogen. Other chemicals that promote hydrogen penetration may be added under conditions intended by the experimenter or the person directing the experiment.

  In this example, in order to promote the penetration of hydrogen, the potential between the sample piece 211 as the working electrode and the mercury-mercury oxide electrode as the reference electrode 208 was maintained at minus 1100 mV. This value may be a potential that promotes the entry of hydrogen under conditions within the range intended by the experimenter or the person who directs the experiment. Further, a reference electrode other than the mercury-mercury oxide electrode may be used. For example, a silver-silver chloride electrode may be used as the reference electrode 208, and the potential between the sample piece 211 and the reference electrode 208 may be a constant potential between minus 500 mV and minus 1500 mV. Further, in this embodiment, the galvano potentiostat 203 is used to make the potential constant. However, even if the current is made constant using the same galvano potentiostat under conditions within the range intended by the experimenter or the person who instructs the experiment. Good.

  In this example, the immersion time in the state where the potential was maintained was set to 50 hours. This time may be determined under conditions within the range intended by the experimenter or the person who instructs the experiment.

  The above hydrogen accumulation conditions are made uniform for all sample pieces as long as the hydrogen penetration characteristics of a plurality of sample pieces using members made of different steel materials are compared. In addition, if you want to compare the hydrogen penetration characteristics of multiple specimens using a member made of a certain kind of steel material, you should set up several experimental conditions assuming several usage environments. What is necessary is just to set in the range which the instructor intends.

  FIG. 3 is a characteristic diagram showing an example of a measurement result of a concentration distribution in the depth direction of hydrogen in a hydrogen charging process for a certain steel material A. The depth direction elemental analysis method is a glow discharge emission analysis method. The concentration distribution of oxygen in the depth direction is also shown. In FIG. 3, the solid line occupies the concentration distribution in the depth direction of hydrogen, and the dotted line indicates the concentration distribution in the depth direction of oxygen.

  The horizontal axis given by the glow discharge optical emission spectrometry is the sputter time, but the horizontal axis can be converted from the sputter time to the corresponding depth by a method using a standard sample of an equivalent steel material. The vertical axis given by glow discharge emission spectrometry is the emission intensity at a specific wavelength for each element, but the vertical axis shows the emission intensity by a method using a standard sample containing a known amount of the target element such as hydrogen. To the corresponding concentration. The vertical axis given by glow discharge mass spectrometry or secondary ion mass spectrometry is the ionic strength of the specific mass of each element, but a method using a standard sample containing a known amount of the target element such as hydrogen The vertical axis can be converted from the ionic strength to the corresponding concentration.

  Information on the thickness of the oxide film formed on the surface of the sample piece 211 may be obtained by another analysis method. In this embodiment, the concentration distribution of the measured oxygen in the depth direction in FIG. In this example, with reference to a concentration of 0.01 weight percent, the depth from the surface showing a concentration higher than the reference is defined as the substantial thickness of the oxide film that affects the penetration characteristics of the metal member for convenience. As can be seen from the change in the dotted line in FIG. 3, in the example, the substantial thickness of the oxide film of the sample piece made of the steel material A is about 4 μm. Similarly, in the concentration distribution of hydrogen in the depth direction of FIG. 3, the depth from the surface showing a concentration higher than this reference is defined as the hydrogen diffusion depth for convenience, with a concentration of 0.0001 weight percent as a reference. From the change of the solid line in FIG. 3, the hydrogen diffusion depth is approximately 5.5 μm.

  Since the thickness of the oxide film varies depending on the steel material or the portion of the steel material sampled as the sample piece, the substantial thickness of the oxide film varies depending on the sample piece. Therefore, by using the relative relationship between the substantial thickness of the oxide film and the hydrogen diffusion depth, the hydrogen penetration characteristics into the metal structure through the oxide film are evaluated. In the present embodiment, even if the hydrogen diffusion depth exceeds the substantial thickness of the oxide film, it remains up to twice the substantial thickness of the oxide film, that is, the oxidation of the hydrogen diffusion depth. If the ratio to the substantial thickness of the film is 2 or less, it is evaluated that the penetration of hydrogen into the metal structure is small due to the influence of the oxide film. In the result shown in FIG. 3, since the ratio of the diffusion depth of hydrogen to the substantial thickness of the oxide film is 2 or less, it is evaluated that the penetration of hydrogen into the metal structure is small. This ratio may be set under conditions within the range intended by the experimenter or the person who instructs the experiment.

  FIG. 4 is a characteristic diagram showing an example of the measurement result of the concentration distribution in the depth direction of hydrogen in the hydrogen charging step for a certain steel material B. The depth direction elemental analysis method is a glow discharge emission analysis method. The concentration distribution of oxygen in the depth direction is also shown. In FIG. 4, the solid line shows the concentration distribution in the depth direction of hydrogen, and the dotted line shows the concentration distribution in the depth direction of oxygen.

  According to the convention used in the description with reference to FIG. 3, the result shown in FIG. 4 indicates that the substantial thickness of the oxide film of the sample piece made of steel B is approximately 2 μm. Similarly, the results shown in FIG. 4 indicate that the hydrogen diffusion depth is 10 μm or more. In the result of FIG. 4, since the ratio of the diffusion depth of hydrogen to the substantial thickness of the oxide film is 5 or more and not 2 or less, it is evaluated that the penetration of hydrogen into the metal structure is large.

  Thus, according to the present invention, the diffusion state of hydrogen through the oxide film can be grasped. For this reason, about the steel material A and the steel material B, the penetration | invasion characteristic of the hydrogen in the state actually used can be grasped | ascertained and it can compare. In this example, it can be evaluated that the steel material B is more easily penetrated by hydrogen than the steel material A.

  As described above, according to the present invention, after hydrogen is accumulated in the target metal member, the hydrogen distribution in the depth direction is measured from the surface of the metal member in which hydrogen is accumulated. Further, the hydrogen diffusion depth from the surface of the metal member was determined from the measured hydrogen distribution, and the hydrogen penetration characteristics in the metal member were evaluated by comparing the thickness of the oxide film with the diffusion depth. As a result, it is possible to evaluate the hydrogen penetration characteristics with respect to a metal member such as a steel material in a state where it is actually used.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above-described embodiment, the steel member is used as the metal member. However, the present invention is not limited to this, and the same applies to a metal member made of titanium, aluminum, or the like.

  DESCRIPTION OF SYMBOLS 201 ... Container, 202 ... Alkaline aqueous solution, 203 ... Galvano potentiostat, 204 ... Working electrode wiring, 205 ... Counter electrode wiring, 206 ... Reference electrode wiring, 207 ... Counter electrode, 208 ... Reference electrode, 211 ... Sample piece.

Claims (5)

A hydrogen accumulation step for accumulating hydrogen on the target metal member;
A distribution measuring step for measuring the distribution of hydrogen in the depth direction from the surface of the metal member storing hydrogen ;
A depth determination step for determining a diffusion depth of hydrogen from the surface of the metal member from the measured hydrogen distribution;
Hydrogen penetration characterization to the metal member, characterized in that it comprises an evaluation step of evaluating the penetration characteristics of the hydrogen in the metal member by the thickness and comparison with the diffusion depth of the oxide film formed on the surface of the metal member Method. In the hydrogen penetration characteristic evaluation method according to aspect 1 Symbol mounting metal member,
The method for evaluating hydrogen penetration characteristics with respect to a metal member , wherein the distribution measuring step measures the hydrogen distribution in the depth direction from the surface of the metal member in which hydrogen is accumulated by glow discharge optical emission spectrometry. In the hydrogen penetration characteristic evaluation method according to aspect 1 Symbol mounting metal member,
The method for evaluating hydrogen penetration characteristics for a metal member , wherein the distribution measuring step measures the distribution of hydrogen in the depth direction from the surface of the metal member in which hydrogen is accumulated by glow discharge mass spectrometry. In the hydrogen penetration characteristic evaluation method according to aspect 1 Symbol mounting metal member,
The method of evaluating hydrogen penetration characteristics for a metal member , wherein the distribution measuring step measures the distribution of hydrogen in the depth direction from the surface of the metal member in which hydrogen is accumulated by secondary ion mass spectrometry. In the hydrogen penetration characteristic evaluation method with respect to the metal member of any one of Claims 1-4 ,
The method for evaluating hydrogen penetration characteristics for a metal member , wherein the hydrogen accumulation step accumulates hydrogen in the metal member by an electrochemical method.

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