JP6749872B2 - Method for measuring hydrogen embrittlement resistance characteristic value - Google Patents

Description

The present invention relates to a method for measuring a hydrogen embrittlement resistance characteristic value of a steel material for obtaining a characteristic value for evaluating hydrogen embrittlement resistance of a steel material.

High-strength steel materials such as high-strength steel lose their ductility when hydrogen is contained, resulting in a marked decrease in strength. This phenomenon is called hydrogen embrittlement (see Non-Patent Document 1). Regarding hydrogen embrittlement of such a steel material, there is a hydrogen embrittlement characteristic evaluation method for evaluating this state. For example, a method is widely used in which a steel material is hydrogen-charged while a constant tensile stress is applied to the steel material (constant load test), and the fracture time of the steel material is measured for evaluation (see Non-Patent Document 2).

There is an idea that fracture due to hydrogen embrittlement occurs when the amount of hydrogen invading the steel material exceeds the limit amount of hydrogen (see Non-Patent Document 3). Based on this idea, it can be said that the rate of hydrogen penetration and the limit amount of hydrogen are the hydrogen embrittlement resistance characteristic values that determine the fracture time of steel materials. Since the hydrogen penetration rate is a function of time, in order to compare the easiness of hydrogen penetration for each steel material, it is sufficient to compare the time coefficient (which will be referred to as the hydrogen penetration rate coefficient). The higher the hydrogen penetration rate coefficient, the easier hydrogen will penetrate into the steel material.

Conventionally, the hydrogen penetration rate has been obtained by using an electrochemical hydrogen permeation method (see Non-Patent Document 4). For the critical hydrogen content, a constant load test is performed on steel materials that have been hydrogen-charged under predetermined conditions in advance, and the hydrogen content when the fracture does not occur by changing the hydrogen-charge conditions is determined by the temperature programmed desorption method ( It is obtained by measurement by TDS (see Non-Patent Document 5).

Tetsuo Shirakami, "Hydrogen Embrittlement in Steel Materials", Materials and Environment, vol. 60, No. 5, 236-240, 2011. Hydrogen embrittlement test method for PC steel in 20% ammonium thiocyanate solution, Japan Corrosion Protection Association, JSCE S 1201, 2012. Shinichi Suzuki, Nobuyuki Ishii, Toshio Miyagawa, Hiroaki Harada, "Test Method for Delayed Fracture Characteristic Evaluation of Steel", Iron and Steel, vol. 79, no. 2, 227-232, 1992. Takahiro Kushida, “Research on hydrogen embrittlement using electrochemical hydrogen permeation method”, Materials and environment, vol. 49, No. 4, pp. 195-200, 2000. Shusaku Takagi, Tadanobu Inoue, Tohru Hara, Masao Hayakawa, Kaneaki Tsuzaki, Toshihiko Takahashi, “Evaluation Parameters of Hydrogen Cracking Susceptibility in High Strength Steel”, Iron and Steel, vol. 86, no. 10, pp. 689-696, 2000.

However, in the above-mentioned method, in order to obtain the critical hydrogen content and the hydrogen intrusion rate coefficient, which are the hydrogen embrittlement resistance characteristic values of high-strength steel, it is necessary to perform each test separately from the measurement of the rupture time. A great deal of effort is required to obtain the data of. Further, in the conventional method, it was necessary to obtain the breaking time, the limit hydrogen amount, and the hydrogen intrusion rate coefficient using different samples, but each value may vary greatly from sample to sample, and the breaking time in the same sample, It was not possible to know the interrelationship between the critical hydrogen content and the hydrogen entry rate coefficient. As described above, conventionally, there has been a problem that it is not easy to measure the hydrogen embrittlement resistance characteristic value, and the correlation between different hydrogen embrittlement resistance characteristic values cannot be known.

The present invention has been made in order to solve the above problems, the hydrogen embrittlement resistance characteristic value can be more easily measured, also know the correlation between different hydrogen embrittlement resistance characteristic value The purpose is to be able to.

A method for measuring a hydrogen embrittlement resistance characteristic value according to the present invention comprises a first step of performing a constant load test on a sample made of a steel material in a state where hydrogen is charged, and obtaining a break time until the sample breaks, Immediately after the sample is broken by the constant load test, the second step of measuring the hydrogen amount in the broken portion of the sample to obtain the limiting hydrogen amount, and the third step of obtaining the hydrogen intrusion rate coefficient for the sample from the breaking time and the limiting hydrogen amount And a process.

In the method for measuring the hydrogen embrittlement resistance characteristic value, a tensile test may be performed as a constant load test in the first step.

In the above method for measuring the hydrogen embrittlement resistance characteristic value, in the first step, the sample may be charged with hydrogen by the cathode charging method.

In the method for measuring the hydrogen embrittlement resistance characteristic value, in the third step, the hydrogen penetration rate coefficient is determined by (limit hydrogen amount)/{2×(breaking time) ^1/2 }.

As described above, according to the present invention, an excellent effect that the hydrogen embrittlement resistance characteristic value can be more easily measured and the correlation between different hydrogen embrittlement resistance characteristic values can be known can be obtained. To be

FIG. 1 is a flowchart for explaining a method for measuring a hydrogen embrittlement resistance characteristic value according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of an experimental device used to carry out the measuring method according to the embodiment. FIG. 3 is an explanatory diagram for explaining the production of the sample piece for obtaining the limit hydrogen amount. FIG. 4 is a characteristic diagram showing the relationship between the breaking time and the limit hydrogen amount.

Hereinafter, a method for measuring the hydrogen embrittlement resistance characteristic value according to the embodiment of the present invention will be described with reference to FIG.

First, in a first step S101, a constant load test is performed on a sample made of a steel material while hydrogen is being charged, and a fracture time until the sample fractures is obtained. For example, a sample is charged with hydrogen by a cathode charging method, and then a tensile test is performed with the sample being charged with hydrogen. For example, for the constant load of the tensile test, a stress 0.7 times the tensile strength of the steel material is used.

For example, the above-described first step (measurement) may be performed using the device shown in FIG. This apparatus includes a container 201 made of acrylic resin or the like, a lid 202 also made of acrylic resin, and an electrolyte solution 203 contained in the container 201. The electrolyte solution 203 is, for example, a 1 mol/L sodium hydrogen carbonate aqueous solution. The device also includes a reference electrode 204 and a counter electrode 205 arranged in an electrolyte solution 203. The reference electrode 204 is, for example, an Ag/AgCl (silver silver chloride) electrode, and the counter electrode 205 is a Pt electrode.

The sample 206 is a rod-shaped smooth material (SBPDN 1275/1420) having a diameter of 7 mm and a length of 500 mm, which is circular in cross section. The sample 206 is in a state of penetrating the lid 202 from the bottom of the container 201 and coming into contact with the electrolyte solution 203. The length of the region where the sample 206 is in contact with the electrolyte solution 203 is 150 mm. The portion of the bottom of the container 201 where the sample 206 penetrates is sealed so that the electrolyte solution 203 does not leak.

In this state, a potentiostat (not shown) is used, the sample 206 is used as a working electrode, and the reference electrode 204 and the counter electrode 205 are used as a three-electrode configuration. .SSE) is applied. It should be noted that this condition is an electrochemical condition in which the surface of the sample 206 in contact with the electrolyte solution 203 does not corrode. By thus performing the cathode charge, hydrogen is generated on the surface of the sample 206. As a result, hydrogen is absorbed (absorbed) in the sample 206. Thus, by the cathode charging method, hydrogen is generated on the surface of the steel material to be a sample, and the hydrogen is absorbed in the steel material, the tensile test of the sample is performed, and the fracture time at which the sample fractures is obtained.

Next, in the second step S102, the hydrogen content in the fractured part of the sample is measured immediately after the sample is fractured by the constant load test to obtain the critical hydrogen content. For example, immediately after the sample is broken, the vicinity of the broken part is cut out and the amount of hydrogen in the cut out sample piece is measured. When cutting out the vicinity of the fractured part of the sample, it is desirable to cut out only the region as close as possible to the fractured part as shown in FIG. For example, the sample piece may be cut out so that the maximum thickness is 1 mm so as to include the fracture surface.

The amount of hydrogen in the sample piece may be measured by the thermal desorption analysis method. As is well known, the temperature programmed desorption analysis method is a method of analyzing a gas component and a component desorbed as a gas at a high temperature among components existing in a solid sample. In the temperature programmed desorption analysis method, a temperature programmed desorption analyzer is used, for example, a sample is heated in vacuum, and the substance desorbed from the sample is ionized by this heating and detected by a mass spectrometer. The measurement conditions in this case are, for example, measurement at a temperature rising rate of 10° C./min up to 500° C. Based on the idea that the amount of hydrogen in steel increases with time due to hydrogen charging, and a fracture occurs when the amount of hydrogen in the steel reaches the limit amount of hydrogen, the fracture part measured immediately after fracture by this method The amount of hydrogen can be regarded as the limit amount of hydrogen.

Next, in the third step S103, the hydrogen penetration rate coefficient for the sample is obtained from the fracture time and the limit hydrogen amount obtained as described above. In the third step S103, the hydrogen penetration rate coefficient is calculated by (limit hydrogen amount)/{2×(breaking time) ^1/2 }.

Here, hydrogen is considered to enter the steel by diffusion, so when the diffusion coefficient is constant regardless of time and the hydrogen content in the steel is 1/2 or less of the saturated hydrogen content, the hydrogen content in the steel is , As shown in FIG. 4, it can be approximated as being proportional to the 1/2 power of time. Therefore, the amount of hydrogen in the steel material is expressed as (limit hydrogen amount)/(breaking time) ^1/2 ×t ^1/2 as a function of time t. Since the hydrogen penetration rate is obtained by the time derivative of the hydrogen content, it is represented by (limit hydrogen content)/{(breaking time) ^1/2 ×2t ^1/2 }, and the hydrogen penetration rate coefficient is (limit hydrogen content)/ It becomes {2×(breaking time) ^1/2 }.

When the breaking time and the limiting hydrogen amount were actually measured in the first step S101 and the second step S102, the breaking time was 1.52 hours and the limiting hydrogen amount was 1.85 ppm. After the sample was broken by the tensile test, 40 minutes later, the amount of hydrogen in the broken part of the sample was measured. Using these values, the hydrogen entry rate coefficient is calculated to be 0.75.

As described above, in the present invention, the breaking time after carrying out the constant load test on the sample charged with hydrogen is determined, and the hydrogen amount in the broken portion of the sample is measured to determine the limit hydrogen amount. Then, the hydrogen penetration rate coefficient for the sample was calculated from the breaking time and the limit hydrogen amount. As a result, according to the present invention, the hydrogen embrittlement resistance characteristic value can be more easily measured, and the correlation between different hydrogen embrittlement resistance characteristic values can be known.

Conventionally, in order to obtain the breaking time, the limit hydrogen amount, and the hydrogen intrusion rate coefficient, it was necessary to perform three different tests. However, according to the present invention, the rupture time, the limit hydrogen amount, and the hydrogen intrusion rate coefficient can be obtained by two types of tests, that is, the rupture time measurement and the limit hydrogen amount measurement, and a simpler measurement is possible. This is because the fracture time and the limit hydrogen amount are measured using the same sample, and the measurement of the limit hydrogen amount is not a method of using a sample that was previously charged with hydrogen as in the conventional method, but hydrogen charging is performed until the fracture. This is because it is possible to calculate the hydrogen penetration rate coefficient from the relationship between the breaking time and the limit hydrogen amount by using the method that is continuously performed. In addition, since the breaking time, the limit hydrogen amount, and the hydrogen intrusion rate coefficient vary greatly from sample to sample, it was not possible to know the interrelationship of each value by the conventional method of measuring each sample using different samples. In the invention, since the same sample is used for measurement, it has become possible to clarify the mutual relation of each value.

As described above, according to the present invention, the critical hydrogen amount and hydrogen intrusion rate coefficient, which are the hydrogen embrittlement resistance characteristic values of high strength steel materials, which have required a great deal of labor until now, can be easily determined by a series of tests. Can be measured. In this way, if the critical hydrogen content and hydrogen entry rate coefficient of high-strength steel can be easily measured, for example, when developing new steel products, application of certain hydrogen embrittlement countermeasures will increase the critical hydrogen content and hydrogen entry rate coefficient. It is easy to get a guideline for product development by clarifying how effective and how effective it is. Further, if the critical hydrogen amount and hydrogen penetration rate coefficient in a certain usage environment are clarified, it is possible to study what measures can be taken to prevent hydrogen embrittlement fracture in the future.

Further, in the present invention, unlike the conventional method, the breaking time and the limit hydrogen amount in the same sample are obtained, and the hydrogen intrusion rate coefficient is obtained from these, so that the mutually unclear mutual relations have been clarified. More detailed examination is possible in development and countermeasure planning. For example, if there is a correlation between the limit hydrogen amount and the hydrogen penetration rate coefficient, only one of them needs to be focused, and if there is an inverse correlation, it is necessary to take measures to optimize the balance between the two. For example, the way of measures can be changed by mutual relation.

The present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by a person having ordinary knowledge in the field within the technical idea of the present invention. That is clear.

201... Container, 202... Lid, 203... Electrolyte solution, 204... Reference electrode, 205... Counter electrode, 206... Sample.

Claims (4)

A first step in which a constant load test is performed on the sample made of a steel material while hydrogen is charged on the sample to obtain a fracture time until the sample fractures;
A second step of measuring the amount of hydrogen in the broken portion of the sample immediately after the sample is broken by the constant load test to obtain a limit hydrogen amount;
A third step of obtaining a hydrogen intrusion rate coefficient for the sample from the breaking time and the limit hydrogen amount, the method for measuring a hydrogen embrittlement resistance characteristic value. The method for measuring a hydrogen embrittlement resistance characteristic value according to claim 1,
In the first step, a tensile test is performed as the constant load test, and a method for measuring a hydrogen embrittlement resistance characteristic value. The method for measuring the hydrogen embrittlement resistance characteristic value according to claim 1,
In the first step, a method for measuring a hydrogen embrittlement resistance characteristic value is characterized in that the sample is charged with hydrogen by a cathode charging method. The method for measuring a hydrogen embrittlement resistance characteristic value according to any one of claims 1 to 3,
In the third step, the hydrogen embrittlement resistance characteristic value measuring method is characterized in that the hydrogen penetration rate coefficient is obtained by (limit hydrogen amount)/{2×(breaking time) ^1/2 }.

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