Method for evaluating hydrogen embrittlement resistant characteristic of metal test piece

Abstract

To provide a method capable of introducing a lot of hydrogen into a metal test piece for a short period of time compared with the conventional techniques to evaluate the hydrogen embrittlement resistant characteristics of the metal test piece.SOLUTION: A method for evaluating the hydrogen embrittlement resistant characteristics of a metal test piece comprises steps of: putting a chloride ion solution having chloride ion concentration of 0.001 mol / L or more and a metal test piece into a vessel to immerse at least a part of the metal test piece into the chloride ion solution so as to have a part that a distance at which the chloride ion solution between the surface of the at least the part of the metal test piece and the inner wall of the vessel intervenes is 0.001-0.900 cm; and evaluating the hydrogen embrittlement resistant characteristics of at least the part of the metal test piece.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece.

Background Art

[0002] In recent years, from the viewpoints of reducing the fuel consumption of automobiles and ensuring the cruising range of electric vehicles, further weight reduction has been demanded for automotive materials. As a main means of weight reduction, there is strengthening of the material, and thereby it is possible to reduce the diameter of metal parts such as bolts, for example.

[0003] On the other hand, it is generally known that metal materials such as steel materials have increased susceptibility to delayed fracture with increasing strength. In the environment in which an automobile travels, some of the hydrogen generated mainly in the process of the corrosion reaction penetrates and diffuses into metal materials such as steel materials, which can cause delayed fracture.

[0004] In order to improve the delayed fracture resistance of metal materials, it is important to reproduce the amount of hydrogen that can penetrate in the actual environment. Non-Patent Document 1 analyzes the amount of hydrogen in bolts exposed to the atmospheric corrosion environment for 9 years, and it is described that the amount of hydrogen in the part without plastic strain (Body part) was 0.05 ppm or less.

Prior Art Documents

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the prior art as disclosed in Non-Patent Document 1, in addition to the long-term test, it has been found that the hydrogen intrusion can be further promoted by the alignment of certain conditions in the actual environment also for the amount of hydrogen.

[0007] The present invention has been made in view of such a situation, and one of its objects is to provide a method capable of introducing a large amount of hydrogen into a metal test piece in a short period of time and evaluating the hydrogen embrittlement resistance characteristics of the metal test piece as compared with the prior art.

Means for Solving the Problems

[0008] Aspect 1 of the present invention is a step of placing a chloride ion solution having a chloride ion concentration of 0.001 mol / L or more and a metal test piece in a container and immersing at least a part of the metal test piece in the chloride ion solution, wherein the distance between the surface of at least a part of the metal test piece and the inner wall of the container is such that the chloride ion solution intervenes, and the distance is 0.001 cm to 0.900 cm, and the immersing step; a step of evaluating the hydrogen embrittlement resistance characteristics of at least a part of the metal test piece; A method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece, comprising:

[0009] Aspect 2 of the present invention is The evaluation step includes evaluating the hydrogen embrittlement resistance characteristics of at least a part of the metal test piece, excluding a portion where the separation distance from the liquid surface of the chloride ion solution in the immersion step is less than 0.001 cm. The method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece according to Aspect 1.

[0010] Aspect 3 of the present invention is In the immersion step, the portion where the distance is 0.001 cm to 0.900 cm includes a portion where stress is applied, The evaluation step includes evaluating the hydrogen embrittlement resistance characteristics of the stress-applied portion. The method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece according to Aspect 1 or 2.

[0011] Aspect 4 of the present invention is The method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece according to any one of Aspects 1 to 3, wherein in the immersion step, the distance is 0.001 cm to 0.400 cm.

[0012] Aspect 5 of the present invention is The method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece according to any one of Aspects 1 to 4, wherein the chloride ion solution has not been subjected to nitrogen bubbling treatment.

Advantages of the Invention

[0013] According to an embodiment of the present invention, compared with the prior art, it is possible to provide a method capable of introducing a large amount of hydrogen into a metal test piece in a short period of time and evaluating the hydrogen embrittlement resistance characteristics of the metal test piece.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0015] The inventors of the present invention have studied from various angles in order to realize a method capable of introducing a large amount of hydrogen into a metal test piece in a short period of time and evaluating the hydrogen embrittlement resistance characteristics of the metal test piece, as compared with the prior art.

[0016] As a result of the study by the inventors of the present invention, it has been found that metal parts used in automobiles and the like are corroded mainly by the influence of chloride ions contained in sea salt and antifreeze agents (such as NaCl, CaCl 2 etc.) in the actual environment, and a large amount of hydrogen can be introduced. Further, for example, in the case of a bolt, when the lower part of the male screw head can be sealed during tightening, if a solution containing the above chloride ions invades such a sealed space, corrosion is promoted, and a large amount of hydrogen can be introduced into the lower part of the male screw head and the like. In view of the above situation, as a result of further intensive studies, the inventors of the present invention have found that when a metal test piece is immersed in a chloride ion solution having a predetermined chloride ion concentration, a large amount of hydrogen is introduced into the metal test piece by setting the distance between the metal test piece and the inner wall of the container containing the chloride ion solution, in which chloride ions are interposed, to a predetermined distance. Although the detailed mechanism thereof is not clear, by adjusting the distance between the immersed portion of the metal test piece in the solution and the inner wall of the container, in which chloride ions are interposed, to a predetermined distance, the anode and cathode reaction sites are separated, the liquid property is likely to change, corrosion is promoted, and it is considered that hydrogen is likely to be introduced into the metal test piece. Details of each requirement defined in the embodiments of the present invention are shown below.

[0017] A method for evaluating the hydrogen embrittlement resistance characteristics of a metal test piece according to an embodiment of the present invention is (A) A step of placing a chloride ion solution having a chloride ion concentration of 0.001 mol / L or more and a metal test piece in a container and immersing at least a part (hereinafter also referred to as an "immersed portion") of the metal test piece in the chloride ion solution, wherein the distance between the surface of at least a part of the metal test piece and the inner wall of the container, in which the chloride ion solution is interposed, is 0.001 cm to 0.900 cm (hereinafter also referred to as a "corrosion promoting portion"), and immersing; (B) A step of evaluating the hydrogen embrittlement resistance characteristics of at least a part of the metal test piece; and includes. Thereby, compared with the prior art, a large amount of hydrogen can be introduced into the metal test piece in a short period of time, and the hydrogen embrittlement resistance characteristics of the metal test piece can be evaluated. Hereinafter, each step will be described in detail.

[0018] (A) A step of immersing at least a part of a metal test piece in a chloride ion solution FIG. 1 is a schematic cross-sectional view parallel to the height (depth) direction of the container when at least a part of the metal test piece is immersed in the chloride ion solution. As shown in FIG. 1, at least a part (immersed part 1a) of the metal test piece 1 is immersed in the chloride ion solution 3 in the container 2. If the distance (shortest distance) D1 between an arbitrary point P1 on the surface 1b of the immersed part 1a and the inner wall 2a of the container, with the chloride ion solution 3 intervening, is between 0.001 cm and 0.900 cm, then P1 is defined as a corrosion-promoting part. In an embodiment of the present invention, it is sufficient if there is even one point (part) like P1. In FIG. 1, an example is shown where the surface 1b of the metal test piece 1 and the inner wall 2a of the container are parallel, but they do not necessarily have to be parallel as long as the requirements of the embodiment of the present invention are met. Also, in FIG. 1, an example is shown where the surface 1b of the metal test piece 1 and the inner wall 2a of the container have flat surfaces, but they may have irregularities as long as the requirements of the embodiment of the present invention are met.

[0019] The container 2 is not particularly limited as long as it can accommodate the metal test piece 1 and the chloride ion solution 3. Examples of the material of the container 2 include metal materials typified by acrylic resin, glass, and steel.

[0020] The order of putting the chloride ion solution 3 and the metal test piece 1 into the container 2 is not particularly limited. When putting the metal test piece 1 into the container 2, the metal test piece 1 is preferably fixed within the container 2. Thereby, the distance D1 during the test can be made constant, and the corrosion of the metal test piece 1 can be promoted more reliably. The fixing method is not particularly limited. For example, a convex part (or concave part) may be provided on the metal test piece 1 and fitted into a concave part (or convex part) provided within the container 2 to fix the metal test piece 1 within the container 2.

[0021] The material of the metal test piece 1 can be a metal material or an alloy material, and can be, for example, steel, aluminum alloy, titanium alloy, etc. The dimensions and shape of the metal test piece 1 are not particularly limited and can be those of a general test piece. The shape of the metal test piece 1 may be, for example, a prismatic shape, a cylindrical shape, a plate shape, etc. The shape of the metal test piece 1 has the same shape as, or a shape along the inner wall 2a (or a part thereof) of the container 2 of the space inside the container 2 on the surface 1b (however, with respect to the dimensions, the metal test piece 1 is smaller than the space inside the container 2 so that the metal test piece 1 fits into the space inside the container 2). For example, if the shape of the space inside the container 2 is cylindrical, the shape of the metal test piece 1 is preferably a cylindrical shape, a semi-cylindrical shape, etc. Also, in a top view from the height (depth) direction (Z-axis direction), the surface 1b and the inner wall 2a of the container are in a substantially similar relationship deformed with substantially equal magnification in the vertical and horizontal directions (for example, without changing the ratio of the length in the X-axis direction to the length in the Y-axis direction, the lengths in the X-axis direction and the Y-axis direction are different). Also, in the top view, it is preferable that the surface 1b of the metal test piece 1 and the inner wall 2a of the container are substantially parallel (for example, the angle formed by them is, for example, within ±5°). By these, the ratio of the corrosion-promoting portion P1 in the immersed portion 1a of the metal test piece 1 can be increased.

[0022] By selecting the chloride ion solution 3 as the test solution, the corrosion of the metal material by sea salt and antifreeze agents (such as NaCl, CaCl 2 etc.) in the actual environment can be simulated. Chloride ions can destroy the passive film of the metal material at a concentration of at least 0.001 mol / L. The chloride ion concentration is preferably 0.01 mol / L or more, and more preferably 0.1 mol / L or more. Thereby, the metal test piece 1 can be corroded in a shorter period, and a large amount of hydrogen can be introduced into the metal test piece 1. The upper limit of the chloride ion concentration is not particularly limited, but in order to avoid the precipitation of chloride and its influence on the test, it is preferably, for example, 8 mol / L or less.

[0023] There are no particular restrictions on the counter ions of chloride ions in the initial stage (i.e., at the start of immersion) of the chloride ion solution 3, but it is preferably a metal ion from the perspective of simulating corrosion in the actual environment. It is more preferably any one or more selected from the group consisting of alkali metals, alkaline earth metals, and Al, and even more preferably any one or more selected from the group consisting of Na, Mg, K, and Ca (i.e., the chloride ion solution 3 is more preferably any one or more solutions selected from the group consisting of sodium chloride, magnesium chloride, potassium chloride, and calcium chloride). Note that during the immersion, as a result of the progress of corrosion of the metal test piece 1, other ions may be generated due to this.

[0024] The chloride ion solution 3 may contain other substances as long as it contains chloride ions at the above concentration. For example, 2 SO 4 such sulfate compounds as 3 KNO 2 such nitrate compounds as Na 3 CO 3 such carbonate compounds as Mg(CH 2 COO)

[0025] The solvent of the chloride ion solution 3 is not particularly limited as long as it is a liquid capable of dissolving chloride ions at the above concentration, but it is preferably a polar solvent such as water or ethanol, and more preferably water from the perspectives of cost and simulating a general corrosion environment.

[0026] The initial pH of the chloride ion solution 3 is preferably from 1 to 12, more preferably from 3 to 10 in terms of being able to reproduce corrosion in the actual environment, even more preferably from 5 to 9, and even more preferably from 6 to 8. However, during the immersion, as a result of the progress of corrosion of the metal test piece 1, the pH may vary from the initial stage of immersion, and as a result, it may deviate from the above preferred pH range.

[0027] The chloride ion solution 3 is preferably not subjected to nitrogen bubbling treatment. That is, in the immersion step, it is preferable to use the chloride ion solution 3 that has not been subjected to nitrogen bubbling treatment. Thereby, the corrosion reaction can be promoted. Although the detailed reason is not clear, it is considered that the chloride ion solution 3 that has not been subjected to nitrogen bubbling treatment has a relatively large amount of dissolved oxygen and the like, which promotes the oxidation of the metal and the reduction reaction of hydrogen.

[0028] By setting the distance D1 to 0.001 cm or more, the amount of the chloride ion solution 3 intervening between the immersion portion 1a and the inner wall 2a of the container can be sufficiently ensured, and the corrosion reaction can be promoted. More preferably, it is 0.010 cm or more, and still more preferably, it is 0.050 cm or more. On the other hand, by setting the distance D1 to 0.900 cm or less, the anode and cathode reaction sites are separated and the liquid property is likely to change, and the corrosion of the metal test piece 1 progresses and hydrogen is likely to be introduced. The distance D1 for obtaining this effect is more preferably 0.600 cm or less, still more preferably 0.400 cm or less, even more preferably 0.300 cm or less, and even more preferably 0.200 cm or less. A large amount of hydrogen can be introduced from the corrosion promotion portion P1 into the metal test piece 1, and the introduced hydrogen can be diffused in the metal test piece 1.

[0029] Among the immersion portions 1a, it is preferable that the ratio of the corrosion promotion portion P1 is larger. The ratio of the corrosion promotion portion P1 to the entire surface of the immersion portion 1a of the metal test piece 1 is preferably, for example, 1 area% or more, more preferably 10 area% or more, still more preferably 30 area% or more, and even more preferably 50 area% or more.

[0030] At the time of immersion, the corrosion promotion portion can include a portion where stress is applied (not shown; hereinafter also referred to as a "stress application portion"). Further, the stress to be applied can be arbitrarily set assuming the environment in which the metal material to be evaluated is actually used.

[0031] In an embodiment of the present invention, the test time can be shortened compared with the prior art. Specifically, even if the immersion time is shortened to less than 9 years, a large amount of hydrogen can be introduced into the metal test piece 1. The immersion time may be appropriately adjusted according to the amount of hydrogen to be introduced, the amount and / or state of corrosion products, the environment to be simulated, etc., and may be adjusted to the time when the amount of hydrogen to be introduced is large (for example, 0.05 ppm or more). For example, the immersion time can be 10 minutes or more, 1 hour or more, 24 hours or more, etc. Considering productivity, the immersion time can be 365 days or less, 30 days or less, 10 days or less, 5 days or less, etc. Also, the temperature of the chloride ion solution 3 can be appropriately adjusted within a range where the solution does not freeze or boil. For example, when water is selected as the solvent of the chloride ion solution 3, the temperature can be -50°C to 105°C, 20°C to 80°C, 50°C to 80°C, etc.

[0032] (B) Step of evaluating hydrogen embrittlement resistance In an embodiment of the present invention, the means for evaluating hydrogen embrittlement resistance is not particularly limited. For example, the amount of hydrogen (for example, diffusible hydrogen amount) in the immersed portion 1a of the metal test piece 1 can be measured, and the hydrogen embrittlement resistance can be evaluated based on the amount of hydrogen. Alternatively, without measuring the amount of hydrogen, the hydrogen embrittlement resistance can be evaluated by performing a known slow fracture test on the immersed portion 1a. Preferably, it is to measure the amount of hydrogen and / or the breaking stress in the immersed portion 1a of the metal test piece 1, whereby quantitative evaluation is easy.

[0033] When evaluating, it is preferable to evaluate the hydrogen embrittlement resistance characteristics of the immersed portion 1a of the metal test piece 1, excluding the portion where the distance from the liquid surface 3a of the chloride ion solution 3 during immersion is less than 0.001 cm. The portion where the distance from the liquid surface 3a of the chloride ion solution 3 is less than 0.001 cm is a portion where the introduced hydrogen is likely to be released again, and in addition, the pH rises due to the hydroxide ions generated by the cathodic reaction, and hydrogen intrusion can be suppressed. By excluding this portion, a more appropriate evaluation becomes possible. Preferably, it is to exclude the portion where the distance from the liquid surface 3a of the chloride ion solution 3 is less than 0.010 cm, more preferably, it is to exclude the portion where the distance from the liquid surface 3a of the chloride ion solution 3 is less than 0.050 cm, and still more preferably, it is to exclude the portion where the distance from the liquid surface 3a of the chloride ion solution 3 is less than 0.100 cm. Also, if there is the stress loading portion described above, it is preferable to evaluate including that portion.

Example

[0034] Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate modifications within the range that can conform to the gist described above and below, and all of them are included in the technical scope of the embodiments of the present invention.

[0035] As a test container, a container made of acrylic resin was prepared. The container has a cylindrical space with a diameter of 1.5 cm and a height of 4 cm inside, and further, a cylindrical space (recess) with a diameter of 1 cm and a height of 0.5 cm is provided at the center of the bottom surface to fix the metal test piece.

[0036] As the metal test piece, commercially available SCM440 was used. The metal test piece was cylindrical with a diameter of 1.45 cm and a height of 2 cm. Further, at the center of the bottom surface of the cylinder, a cylinder (protrusion) having the same shape as the recess was provided so as to be fitted into the recess in the container. By fitting the protrusion into the recess in the container, the metal test piece can be fixed in the container. The distance between the side surface of the metal test piece (excluding the protrusion) and the inner wall of the container (excluding the recess) when the protrusion was fitted into the recess was 0.03 cm over the entire circumference in a top view seen from the height direction (Test Nos. 1 and 5).

[0037] Test Nos. 2 and 6 were the same as Test No. 1, except that a metal test piece having a cylindrical shape with a diameter of 1.3 cm and a height of 2 cm was used, and a protrusion similar to that of Test No. 1 was provided at the center of the bottom surface of the cylinder. The distance between the side surface of the metal test piece (excluding the protrusion) and the inner wall of the container (excluding the recess) when the protrusion was fitted into the recess was 0.1 cm over the entire circumference in a top view seen from the height direction.

[0038] As the test container for Test No. 3, a container made of acrylic resin was prepared. The container had a cylindrical space with a diameter of 2 cm and a height of 4 cm inside, and further, at the center of the bottom surface, a cylindrical space (recess) with a diameter of 1 cm and a height of 0.5 cm was provided to fix the metal test piece. As the metal test piece for Test No. 3, commercially available SCM440 was used. The metal test piece was cylindrical with a diameter of 1 cm and a height of 2.5 cm. The distance between the side surface of the metal test piece (excluding the protrusion) and the inner wall of the container (excluding the recess) when the lower part of the test piece was fitted into the recess in the container was 0.5 cm over the entire circumference in a top view seen from the height direction.

[0039] As a test container for Test No. 4, a glass container was prepared. The container had a cylindrical space with a diameter of 3.4 cm and a height of 3 cm inside, and further, a cylindrical space (recess) with a diameter of 1 cm and a height of 0.5 cm was provided at the center of the bottom surface to fix the metal test piece. The test was conducted in the same manner as Test No. 2 except for using this glass container. The distance between the side surface of the metal test piece (excluding the convex part) and the inner wall of the container (excluding the recess) was 1 cm over the entire circumference in a top view seen from the height direction.

[0040] As the chloride ion solution, a 10 wt% aqueous NaCl solution (initially, the pH was adjusted to 7 and the chloride ion concentration was 1.9 mol / L) was prepared. For the chloride ion solutions in Test No. 1 to 4, nitrogen gas bubbling treatment (nitrogen gas flow rate of about 0.1 L / min) was performed for 24 hours. For the chloride ion solutions in Test No. 5 to 6, nitrogen gas bubbling treatment was not performed. These chloride ion solutions were placed in the respective containers of Test No. 1 to 6, and then the convex parts of the metal test pieces were fitted into the recesses in the containers. At this time, the liquid volume was adjusted so that the liquid level in the container of the chloride ion solution and the upper surface of the metal test piece were the same. Thereafter, with the opening of the container blocked with silicone rubber to suppress the evaporation of the solution, it was left standing at 80 °C for 3 days.

[0041] After standing, each metal test piece was taken out from each container and immediately cooled with liquid nitrogen so as to suppress the release of hydrogen from the metal test piece. After cooling, the hydrogen introduction amount of each metal test piece was evaluated to evaluate the hydrogen embrittlement resistance characteristics of each metal test piece. When evaluating the hydrogen introduction amount, the convex part provided at the center of the bottom surface of the metal test piece in Test No. 1 was removed, and the remaining cylinder was cut parallel to the height direction, and it was made into a bow shape (maximum length in the radial direction: 0.4 to 0.5 cm) in a plan view seen from the height direction. The test piece made into the bow-shaped column was divided into three equal parts in the height direction, and was designated as Test No. 1-1, 1-2, and 1-3 from the upper side (that is, the side closer to the liquid surface) during immersion. In Test No. 2 to 6, it was also divided into three equal parts in the same manner as Test No. 1.

[0042] The hydrogen content was measured by the temperature-programmed desorption method using gas chromatography. The temperature was raised from room temperature to 600 °C at a heating rate of 100 °C / h, and the hydrogen detected up to 200 °C was regarded as diffusible hydrogen, which is considered to mainly affect delayed fracture, and the amount of this hydrogen was described in Table 1. Here, in Non-Patent Document 1, the amount of hydrogen introduced into the bolt by the exposure test is 0.05 ppm or less in the range without plastic strain. In this example, it was assumed that a large amount of hydrogen could be introduced (judgment B) when it was more than that (i.e., 0.05 ppm or more), that more hydrogen could be introduced (judgment A) when it was 0.06 ppm or more, and that even more hydrogen could be introduced (judgment AA) when it was 0.07 ppm or more. Also, when the hydrogen content was less than 0.05 ppm, it was judged as insufficient (judgment C). The results were summarized in Table 1. Here, the "distance" is the distance between the immersed part of the metal test piece and the inner wall of the container with the chloride ion solution intervening, and the "average hydrogen content" is the arithmetic mean value of the hydrogen content of the test piece divided into three equal parts in the height direction.

[0043]

Table 1

[0044] It can be seen from Table 1 that Test Nos. 1 to 3 and 5 to 6, which satisfy all the requirements of the embodiments of the present invention, have an average hydrogen content of 0.05 ppm or more, and a large amount of hydrogen can be introduced in a shorter period than before. On the other hand, Test No. 4, in which the "distance" shown in Table 1 is outside the range of "0.001 cm to 0.900 cm" and does not satisfy the requirements of the embodiments of the present invention, has an average hydrogen content of less than 0.05 ppm, and a large amount of hydrogen could not be introduced. When comparing the case where the chloride ion solution was subjected to nitrogen bubbling treatment, Test Nos. 1 to 2 had a higher average hydrogen content than Test No. 3. This is considered to be because Test Nos. 1 to 2 satisfied the favorable requirement of having a portion where the distance between the anode and cathode reaction sites between the immersed part of the metal test piece and the inner wall of the container is 0.400 cm or less, making it easier for the liquid properties to change due to separation. Furthermore, when comparing with the case where the chloride ion solution was subjected to nitrogen bubbling treatment, Test No. 2 had a larger average hydrogen amount than Test No. 1. This is considered to be because Test No. 2 satisfied the more preferable requirement of having a portion where the distance with the chloride ion solution intervening between the immersed portion of the metal test piece and the inner wall of the container is 0.050 cm or more, and having a portion where the distance at which the anode and cathode reaction sites are separated and the liquid property is likely to change is 0.400 cm or less.

[0045] Test No. 5 had a larger average hydrogen amount than Test No. 1. Also, Test No. 6 had a larger average hydrogen amount than Test No. 2. This is considered to be because Test Nos. 5 and 6 satisfied the preferable requirement of not being subjected to nitrogen bubbling treatment for the chloride ion solution.

[0046] Test Nos. 1-2 to 1-3 (or Test Nos. 2-2 to 2-3, or Test Nos. 3-2 to 3-3, or Test Nos. 5-2 to 5-3, or Test Nos. 6-2 to 6-3) had a larger hydrogen amount than Test No. 1-1 (or Test No. 2-1, or Test No. 3-1, or Test No. 5-1, or Test No. 6-1). This is considered to be because Test Nos. 1-2 to 1-3 (or Test Nos. 2-2 to 2-3, or Test Nos. 3-2 to 3-3, or Test Nos. 5-2 to 5-3, or Test Nos. 6-2 to 6-3) satisfied the preferable requirement of being evaluated excluding the portion where the separation distance from the liquid level of the chloride ion solution during immersion is less than 0.001 cm.

[0047] The results in Table 1 are summarized in Figure 2. Figure 2 shows the relationship between the average hydrogen amount and the distance with chloride ions intervening between the immersed portion of the metal test piece and the inner wall of the container in Test Nos. 1 to 4 of the examples. The broken line is the logarithmic approximation curve of all the plots. As shown in Figure 2, it is considered that the average hydrogen amount can be made 0.05 ppm or more when the above distance is 0.001 cm to 0.900 cm.

Explanation of Signs

[0048] 1 Metal test piece 1a Immersion part 1b Surface of the immersion part 2 Container 2a Inner wall of the container 3 Chloride ion solution 3a Liquid level

Claims

1. A step of placing a chloride ion solution having a chloride ion concentration of 0.001 mol / L or more and a metal test piece in a container, and immersing at least a portion of the metal test piece in the chloride ion solution, so that the distance between the surface of the at least a portion of the metal test piece and an inner wall of the container, which is separated by the chloride ion solution, is 0.001 cm to 0.900 cm; evaluating the hydrogen embrittlement resistance of said at least a portion of said metal specimen; A method for evaluating hydrogen embrittlement resistance of a metal test piece, comprising:

2. 2. The method for evaluating hydrogen embrittlement resistance of a metal test piece according to claim 1, wherein the evaluation step includes evaluating the hydrogen embrittlement resistance of at least a portion of the metal test piece, excluding a portion that is separated from the liquid surface of the chloride ion solution by a distance of less than 0.001 cm in the immersion step.

3. In the immersion step, the portion where the distance is 0.001 cm to 0.900 cm includes a portion to which stress is applied, 3. The method for evaluating hydrogen embrittlement resistance of a metal test piece according to claim 1, wherein the evaluation step includes evaluating the hydrogen embrittlement resistance of the stress-applied portion.

4. 3. The method for evaluating hydrogen embrittlement resistance of a metal test piece according to claim 1, wherein in the immersion step, the distance is 0.001 cm to 0.400 cm.

5. 3. The method for evaluating hydrogen embrittlement resistance of a metal test piece according to claim 1, wherein the chloride ion solution is not subjected to nitrogen bubbling treatment.

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