Method for producing test material, method for measuring amount of diffusible hydrogen, method for evaluating delayed fracture characteristics, method for selecting metal material, and method for producing member

Abstract

Provided is a method for producing a test material capable of measuring the amount of diffusible hydrogen in a metal material having a welded portion with high accuracy. A method for producing a test material for measuring the amount of diffusible hydrogen in a metal material provided with a welded part, the method comprising: a step for specifying a pore position in a test material, which is a metal material provided with a welded part; and a processing step in which processing is performed or the pores are removed so that the pores determined in the pore position determination step are not changed into a closed structure.

Description

Technical Field

[0001] This invention relates to methods for preparing test materials, methods for determining diffusible hydrogen content, methods for evaluating delayed fracture characteristics, methods for selecting metallic materials, and methods for manufacturing components. Background Technology

[0002] In recent years, from the perspective of preventing global warming, there has been a demand to improve energy efficiency by reducing the weight of mobile vehicles such as cars, ships, and railway vehicles. For example, in the case of cars, there is a demand to improve the fuel efficiency of gasoline. As for steel, which is one of the constituent materials of mobile vehicles, even when the thickness of the plate is reduced for the purpose of reducing weight, high strength is required to ensure the same level of safety as before.

[0003] On the other hand, automotive steel is plastically formed into the desired shape through stamping and assembled onto the car body through welding, such as spot welding. Therefore, automotive steel not only requires stamping formability but also the ability to be properly welded in various sheet metal assemblies.

[0004] However, with the increasing strength of steel, there is a problem of delayed fracture. Delayed fracture refers to the phenomenon where a metallic material, under static load, suddenly fractures after a certain period of time with almost no plastic deformation. In this case, it refers to hydrogen embrittlement caused by hydrogen entering the metallic material.

[0005] Factors influencing delayed fracture include the hydrogen embrittlement susceptibility of metallic materials, load (e.g., residual stress), and the amount of hydrogen penetrating the metallic material. For example, in the case of steel, the hydrogen embrittlement susceptibility increases significantly with increasing strength, and fracture (cracking) can occur even with trace amounts of hydrogen penetrating the steel. In particular, the hydrogen embrittlement susceptibility is significantly increased in steels with a tensile strength of 1180 MPa or higher (Non-Patent Literature 1).

[0006] Therefore, even with increased strength requirements for steel, it is necessary to ensure that the steel does not experience delayed fracture, i.e., excellent resistance to delayed fracture is required. In particular, because the welded portion of steel has higher strength compared to the base metal, its susceptibility to hydrogen embrittlement is more likely to increase. Furthermore, delayed fracture has been reported to occur in metallic materials other than steel.

[0007] Therefore, a method for evaluating the delayed fracture characteristics of welded parts of metallic materials is required. For example, in an embodiment of Patent Document 1, a method for evaluating the hydrogen embrittlement characteristics of spot welded parts of steel plates is disclosed as follows: a test piece is made by clamping plates with a thickness of 2 mm or 4 mm at both ends of a plate as spacers, and then spot welding the spacers together to form a central joint. The test piece is then immersed in 0.5 mol / L sulfuric acid, hydrogen is introduced by passing an electric current, and the presence or absence of cracking is evaluated after 2 hours.

[0008] Furthermore, delayed fracture is considered to be affected by hydrogen (diffuse hydrogen) penetrating the steel. Therefore, it is believed that the delayed fracture characteristics of the weld can be evaluated by measuring the amount of diffuse hydrogen that does not cause delayed fracture at the upper limit of the weld (limiting diffuse hydrogen amount).

[0009] For example, Patent Document 2 discloses a method for measuring the amount of diffusible hydrogen, which is a cause of delayed fracture, from the welded joints of an actual structure with high precision.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2007-231373

[0013] Patent Document 2: Japanese Patent Application Publication No. 2008-261821

[0014] Non-patent literature

[0015] Non-patent literature 1: Shinsaku Matsuyama: Delayed fracture, Nikkan Kogyo Shimbun, Tokyo, (1989). Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] When evaluating the delayed fracture characteristics of welded parts of metallic materials using the method disclosed in Patent Document 1, a test of a specified time is required to determine whether fracture has occurred at the welded part. However, since the determination of whether fracture has occurred at the welded part is made within a specified time, test pieces that fractured before the specified time and test pieces that fractured within the specified time are evaluated to the same degree, resulting in the problem that the occurrence of fracture in each test piece cannot be evaluated with high precision.

[0018] In addition, using the method for measuring the diffusive hydrogen content of welded joints disclosed in Patent Document 2, the diffusive hydrogen content (intrusion hydrogen content) of welded parts that were introduced with hydrogen under the same conditions was measured. The results showed that the measured values ​​of hydrogen content were sometimes quite different.

[0019] The present invention was made in view of the above circumstances, and its object is to provide a method for preparing a test material capable of measuring the diffusible hydrogen content of a metallic material having a welded portion with high precision.

[0020] Furthermore, the present invention aims to provide a method for determining the diffusive hydrogen content of test materials prepared by the above-described test material preparation method, a method for evaluating delayed fracture characteristics, a method for selecting metallic materials, and a method for manufacturing components.

[0021] Methods for solving problems

[0022] The inventors conducted in-depth research and found that the above-mentioned objectives can be achieved by adopting the following configuration, thus completing the present invention.

[0023] [1] A method for manufacturing a test material for determining the diffusive hydrogen content of a metal material having a welded portion, comprising: a step of determining the pore position, wherein the pore position of the test material being the metal material having a welded portion is determined; and a processing step, wherein the processing is performed in such a way that the pores determined in the step of determining the pore position do not become closed structures, or the pores are removed.

[0024] [2] According to the method for preparing the test material described in [1], wherein the volume ratio of the welding metal in the test material is 50% or more.

[0025] [3] A method for determining the diffusivity of hydrogen, which is a method for determining the diffusivity of hydrogen in a metal material having a welded part, comprising: a hydrogen introduction step, wherein hydrogen is introduced into a test material prepared by the test material preparation method described in [1] or [2] above; and a hydrogen content determination step, wherein the hydrogen content of the test material in which hydrogen was introduced in the above hydrogen introduction step is determined.

[0026] [4] An evaluation method for delayed fracture characteristics, which is an evaluation method for delayed fracture characteristics of a metallic material having a welded part, comprising: an evaluation step, wherein the delayed fracture characteristics are evaluated based on the diffusive hydrogen content obtained by the diffusive hydrogen content determination method described above [3].

[0027] [5] A method for selecting a metallic material, comprising: The selection step involves selecting a metallic material based on the delayed fracture characteristics obtained by the evaluation method for delayed fracture characteristics described above [4].

[0028] [6] A method for manufacturing a component, comprising: a welding step, wherein the component is manufactured by welding at least a metal material selected by the metal material selection method described above [5].

[0029] Invention Effects

[0030] According to the present invention, a method for preparing a test material capable of accurately measuring the diffusible hydrogen content of a metallic material having a welded portion is provided.

[0031] Furthermore, according to the present invention, it is possible to provide a method for determining the diffusive hydrogen content of test materials prepared by the above-described test material preparation method, a method for evaluating delayed fracture characteristics, a method for selecting metallic materials, and a method for manufacturing components. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating an example of a cutting method for cutting test materials from metal materials with weldable parts.

[0033] Figure 2 This is a schematic diagram illustrating an example of the processing method in the processing steps. Detailed Implementation

[0034] In response to the problem mentioned above regarding the inability to reproducibly obtain the diffusible hydrogen content in metal materials with welded portions, the inventors conducted repeated studies using spot-welded steel and found that the above method has the following problems.

[0035] The spot weld contains pores, which are internal defects. Furthermore, when the spot weld is exposed to a hydrogen-infiltrating environment (hydrogen intrusion environment), a large amount of hydrogen accumulates within the pores. It is presumed that the hydrogen within the pores has vaporized. Additionally, the hydrogen accumulated within the pores is stable hydrogen, i.e., non-diffusive hydrogen. According to Non-Patent Literature 1, this non-diffusive hydrogen does not predominantly affect the delayed fracture characteristics. However, the hydrogen accumulated within the pores undergoes forced desorption during hydrogen heating desorption analysis, and may be detected as diffusive hydrogen, thus increasing the apparent amount of infiltrated hydrogen (diffusive hydrogen content) into the weld. Furthermore, the amount of hydrogen accumulated within the pores varies depending on the pore size; therefore, the measured hydrogen content of the spot weld also yields different results depending on the volume and number of pores. However, controlling the size, shape, and number of pores is difficult in existing welding techniques.

[0036] Therefore, the inventors investigated the relationship between porosity and hydrogen content in the weld and discovered that by eliminating porosity in the closed structure, the amount of intrusive hydrogen (diffuse hydrogen content) that enters the weld from the environment and affects delayed fracture can be evaluated with high precision.

[0037] This invention is based on the above-described understanding. Hereinafter, a method for preparing a test material for measuring the diffusible hydrogen content of a metallic material having a welded portion, a method for measuring the diffusible hydrogen content, a method for evaluating delayed fracture, a method for selecting the metallic material, and a method for manufacturing a component according to one embodiment of the present invention will be described. It should be noted that the present invention is not limited to the following embodiments. Furthermore, the constituent elements in the following embodiments include elements that can and are easily substituted by those skilled in the art, or substantially the same elements.

[0038] <Preparation Method of Experimental Materials>

[0039] An embodiment of the present invention provides a method for manufacturing a test material for measuring the diffusive hydrogen content of a metallic material having a welded portion, comprising: a step of determining the pore positions, wherein the pore positions of the test material being used as a metallic material having a welded portion are determined; and a processing step, wherein the processing is performed in a manner that does not cause the pores determined in the step of determining the pore positions to become closed structures, or the pores are removed.

[0040] (Metallic materials)

[0041] First, the metallic material will be explained. There are no particular limitations on the metallic material as long as it is weldable and exhibits hydrogen-induced delayed fracture. As mentioned above, in the case of steel, the hydrogen embrittlement susceptibility increases significantly when the tensile strength of the steel is 1180 MPa or higher. Therefore, high-strength steel plates, especially those with a tensile strength of 1180 MPa or higher, are preferred as the metallic material. The metallic material can be a coated steel plate based on the aforementioned high-strength steel plate.

[0042] The metal material for the welded section can be any metal material that has been welded. Here, the welded section consists of the weld metal and the heat-affected zone.

[0043] Welding can be any of the following methods: fusion welding (electric arc welding, laser welding, electron beam welding, plasma arc welding, etc.) and pressure welding (spot welding, projection welding, seam welding, etc.). For example, when spot welding is used, the weld metal becomes the weld nugget.

[0044] The test material is preferably prepared in such a manner that the volume ratio of weld metal is 50% or more. Therefore, a method for preparing the test material according to one embodiment of the present invention may include a preparation step of preparing a test material containing weld metal at a desired volume ratio. Compared to the base material and the heat-affected zone, more hydrogen (diffuse hydrogen) that influences delayed fracture enters the weld metal. Therefore, in order to properly evaluate the quality of the delayed fracture characteristics of the metal material having the weld, it is preferable that the volume ratio of weld metal in the test material is 50% or more. More preferably, the volume ratio of weld metal is 70% or more, even more preferably 80% or more, and can be 100%.

[0045] It should be noted that the volume ratio of the weld metal in the test material can be adjusted, for example, when cutting the test material from the welded metal material (the metal material with the welded part). Figure 1 This is a schematic diagram illustrating an example of a cutting method for cutting test material from a metal material with weldable parts. In the preparation steps, for example, as... Figure 1As shown, test material 3 can be cut from metal material 1 having a welding portion, including welding metal (weld nugget) 2. At this time, as described above, it is preferable to cut test material 3 such that the volume ratio of welding metal 2 is 50% or more. Examples of cutting methods include cutting using a micro-cutting machine or wire cutting. Furthermore, during the preparation step, the volume ratio of welding metal contained in the test material can be adjusted by adjusting the welding current, etc.

[0046] Furthermore, in appropriately evaluating the quality of delayed fracture characteristics of metallic materials with welded portions, it is preferable to ensure that the volume ratio of weld metal is consistent among the test materials. When evaluating the quality of delayed fracture characteristics among test materials, it is preferable to use test materials with a weld metal volume ratio within ±10%, and more preferably, test materials with a weld metal volume ratio within ±5%.

[0047] (Steps for determining the location of stomata)

[0048] In the step of determining the location of pores, the locations of pores present in the weld portion of the test material are identified. The method for determining the location of pores requires identifying the pores inside the weld portion, then introducing hydrogen into the test material and measuring the amount of hydrogen introduced; therefore, this is performed using non-destructive testing. Examples of such non-destructive testing include X-ray CT examination and ultrasonic testing. Furthermore, by using the images obtained from these examinations, the volume ratio of the weld metal in the test material can also be evaluated.

[0049] (Processing steps)

[0050] In the processing step, the processing is performed in a manner that prevents the pores determined in the above-mentioned pore location determination step from becoming closed structures, or the processing is performed to remove the above-mentioned pores. Examples of methods for processing in a manner that prevents the above-mentioned pores from becoming closed structures include: Figure 2 (a) shows the machining of the through hole T connecting the test material surface to the pore B; as shown Figure 2(b) shows the process of grinding or lapping the surface of the test material until the pores B are connected to the external environment. This allows for processing in a way that connects the pores to the external environment without making them a closed structure. There are no particular limitations on the processing method for creating the aforementioned through-holes; for example, methods using micro-drills to form through-holes from the surface of the test material to the pores can be listed. Furthermore, there are no particular limitations on the processing method for performing the aforementioned grinding or lapping; for example, methods for grinding or lapping the surface of the test material by mechanical or chemical means can be listed. Additionally, if pores exist near the surface of the test material, grinding or lapping can be performed to remove the pores. It should be noted that when the test material has a cut surface, mechanical defects are generated, such as work-hardened portions due to dislocations or increased lattice defects. Hydrogen may be trapped in these mechanical defects; therefore, chemical lapping is preferable to remove these surfaces.

[0051] Following the steps described above, a test material for measuring the diffusible hydrogen content of a metallic material having a welded portion is prepared. The test material prepared by the method for preparing the test material according to one embodiment of the present invention is suitable as a test material for measuring the diffusible hydrogen content, and particularly suitable as a test material for evaluating delayed fracture characteristics.

[0052] <Method for Determination of Diffuse Hydrogen Content>

[0053] An embodiment of the present invention provides a method for determining the diffusible hydrogen content of a metallic material having a welded portion, comprising: a hydrogen introduction step, wherein hydrogen is introduced into a test material prepared by the above-described test material preparation method; and a hydrogen content determination step, wherein the hydrogen content of the test material introduced in the above-described hydrogen introduction step is determined.

[0054] (Hydrogen introduction steps)

[0055] In the hydrogen introduction step, hydrogen is introduced into the test material prepared as described above. The hydrogen introduction method can be appropriately selected according to the purpose. Specifically, examples of hydrogen introduction methods include: electrolyzing the electrolyte by using the test material as the cathode and platinum or the like as the anode in an electrolyte solution, and introducing the generated hydrogen into the cathode of the test material; or immersing the test material in a hydrochloric acid solution, etc. Furthermore, if it is desired to evaluate the amount of hydrogen introduced into an environment where the metal material is actually used (the actual environment), the test material can be placed in the actual environment. It should be noted that the test material after hydrogen introduction in the hydrogen introduction step is preferably stored by immersion in liquid nitrogen. By immersing the test material in liquid nitrogen, the hydrogen introduced into the test material cannot be desorbed.

[0056] (Hydrogen content determination procedure)

[0057] In the hydrogen content determination step, the hydrogen content (diffuse hydrogen content) of the test material to which hydrogen was introduced in the aforementioned hydrogen introduction step is measured. There is no limitation on the method for determining the hydrogen content, as long as it is capable of measuring hydrogen. For example, temperature-induced desorption analysis can be used. Temperature-induced desorption analysis can analyze extremely small amounts of hydrogen, therefore it is preferred as an analytical method for determining the diffusible hydrogen content used to evaluate the delayed fracture characteristics of metallic materials. It should be noted that when the test material after hydrogen introduction in the hydrogen introduction step is stored in liquid nitrogen, it is preferable to quickly measure the hydrogen content after removing the test material from the liquid nitrogen.

[0058] <Evaluation Methods for Delayed Fracture Characteristics>

[0059] One embodiment of the present invention provides a method for evaluating delayed fracture characteristics, comprising an evaluation step that evaluates the delayed fracture characteristics based on the hydrogen content (diffuse hydrogen content) obtained by the aforementioned method for measuring diffusible hydrogen content. In the evaluation step, for example, when judging the quality of the delayed fracture characteristics of welds between different test materials of metallic materials, each test material is evaluated as follows: For each test material, in the aforementioned method for measuring diffusible hydrogen content, in the hydrogen introduction step, the diffusible hydrogen content is measured when the hydrogen introduction environment (hydrogen introduction conditions) are consistent, and their values ​​are compared to evaluate the results. This is because it is generally believed that metallic materials with higher diffusible hydrogen content are more prone to delayed fracture. For more accurate evaluation, it is preferable to measure the diffusible hydrogen content under hydrogen introduction conditions where the weld of the test material cracks, and then determine the delayed fracture characteristics of the test material.

[0060] <Methods for Selecting Metallic Materials>

[0061] One embodiment of the present invention provides a method for selecting metallic materials, comprising a selection step based on delayed fracture characteristics obtained through the aforementioned evaluation method for delayed fracture characteristics. By performing the aforementioned evaluation step on metallic materials having weldable portions, the relationship between welding conditions and delayed fracture characteristics, such as the amount of diffusible hydrogen when the hydrogen introduction environment is consistent during the hydrogen introduction step, is obtained. Furthermore, this relationship can also be obtained by changing the type of metallic material. Moreover, these relationships can be used to classify metallic materials. Furthermore, in the selection step, for example, by evaluating the amount of diffusible hydrogen in the environment in which the metallic material is used, metallic materials suitable for use in the aforementioned environment can be selected from the aforementioned classifications. Furthermore, the selected metallic materials can be shipped, etc.

[0062] <Methods for manufacturing components>

[0063] One embodiment of the present invention provides a method for manufacturing a component, comprising a welding step of at least welding a metal material selected by the aforementioned metal material selection method to manufacture the component. When manufacturing the component, for example, the component can be manufactured by welding after processing the metal material, or by processing after welding. The welding method in the welding step is not particularly limited; for example, known welding methods can be used. Furthermore, the processing is not particularly limited; various metal processing methods such as forming can be listed. Moreover, the component is preferably an automotive component.

[0064] Example

[0065] The present invention will now be specifically described by way of examples. However, the present invention is not limited to the examples described below.

[0066] First, fabricate the metal material with weldable parts according to the following steps. Prepare steel plates of grades A to C with a thickness of 1.6 mm and a tensile strength of 1200 to 1500 MPa, having the representative composition shown in Table 1.

[0067]

[0068] First, spot welding was performed on the central area of ​​three test pieces obtained by cutting steel plates A, B, and C into 120mm × 30mm sections. During spot welding, the electrodes were kept in a water-cooled state. Both the lower and upper electrodes were set with a front diameter of 6mm and a radius of curvature of 40mm, and DR-shaped electrodes made of chromium copper were used. The welding was performed at room temperature. At this time, a current was applied so that the diameter of the weld nugget was 3√t (t: plate thickness), and a metal material (test body) with a welded part was produced.

[0069] The obtained test specimens were cut into test materials using a micro-cutting machine. The cutting size of the test materials was adjusted according to the volume ratio of the target weld metal. Then, chemical grinding was performed by immersion in a mixed solution of hydrogen peroxide and oxalic acid.

[0070] (Steps for determining the location of stomata)

[0071] For the obtained test material, the location of pores was determined three-dimensionally using X-ray CT. Furthermore, the volume ratio of weld metal in the test material was calculated using the images obtained from X-ray CT. The number of pores determined above and the calculated volume ratio of weld metal in the test material are shown in Tables 2 and 3.

[0072] (Processing steps)

[0073] Next, for the pores determined in the pore position determination step, machining is performed in such a way that the pores do not become a closed structure. Specifically, a through-hole is provided in the pore from the surface of the test material using a micro drill. However, for No.1 and No.2 in Table 2, the above machining is not performed, and for No.3 in Table 2, the above machining is performed on a part of the determined pores. It should be noted that for No.6 in Table 2, there are no pores in the welded part of the test material, so the above machining is not performed (reference example). In addition, after the above machining, X-ray CT is used for the machined test material to confirm whether the pores have become a closed structure. The number of pores with a closed structure present in the test material is shown in Table 2 and Table 3. In Table 2 and Table 3, if the number of pores with a closed structure is 0, it is determined that the machining has been performed in such a way that the pores do not become a closed structure, and it is considered qualified.

[0074] (Hydrogen introduction step)

[0075] Hydrogen is introduced into the test material produced as described above under the hydrogen introduction conditions described in Table 2 and Table 3. In order to prevent the introduced hydrogen from desorbing, the test material after hydrogen introduction is immediately immersed in liquid nitrogen and stored frozen.

[0076] (Hydrogen amount measurement step)

[0077] Before measuring the hydrogen amount, the above test material is quickly taken out of liquid nitrogen, and a low-temperature type temperature-rising hydrogen analysis device is used to measure the hydrogen amount (diffusive hydrogen amount) by temperature-programmed desorption analysis. The temperature-programmed desorption analysis is performed at a heating rate of 200 °C / hour in the temperature range from -50 °C to 800 °C. The diffusive hydrogen amount is the cumulative value of the hydrogen amount measured from -50 °C to 200 °C, and the obtained cumulative value of the hydrogen amount is divided by the mass of the test material to obtain the mass fraction (mass ppm). The values of the hydrogen amount (diffusive hydrogen amount) obtained for each test material are shown in Table 2 and Table 3.

[0078]

[0079] According to Table 2, when there are pores with a closed structure in the test material (No.1 to No.3), the diffusive hydrogen amount is from 3.8 to 4.5 mass ppm. In contrast, when the pores with a closed structure are eliminated by machining (No.4 and No.5), the diffusive hydrogen amount is from 2.3 to 3.2 mass ppm. In addition, the diffusive hydrogen amount of the test material without pores (No.6) is 2.7 mass ppm. It can be seen from this that by eliminating the pores with a closed structure, the diffusive hydrogen amount is significantly reduced, and due to the presence of the pores with a closed structure, the diffusive hydrogen amount is estimated to be larger. It can also be seen that by using the test material with the pores having a closed structure eliminated, the diffusive hydrogen amount can be evaluated with high precision.

[0080] Furthermore, according to Table 3, in the test materials with eliminated closed-structure pores, if the volume ratio of weld metal in the test materials is approximately equal, the obtained diffusible hydrogen values ​​show the order of steel plate A > steel plate B > steel plate C. It can also be seen that when the volume ratio of weld metal in the test materials is above 50%, the differences caused by the steel grade become more pronounced.

[0081] On the other hand, the delayed fracture characteristics of the welded parts of steel plates A, B, and C were evaluated using existing methods (Patent Document 1). The results showed that the delayed fracture resistance characteristics were in the order of (superior) steel plate C > steel plate B > steel plate A (inferior).

[0082] Based on the above, it is believed that steel plates with a higher diffusibility of hydrogen obtained by the method of the present invention are more prone to delayed fracture.

[0083] As can be seen from the above, the method of the present invention can be used to determine the diffusible hydrogen content of metallic materials with welded portions with high precision and reproducibility. Furthermore, the method of the present invention can be used as an indicator for evaluating the delayed fracture resistance of the aforementioned metallic materials, and can be said to be able to quantitatively and accurately evaluate delayed fracture characteristics.

[0084] Symbol Explanation

[0085] 1. Metal materials with weldable parts

[0086] 2 Welding metal

[0087] 3. Experimental Materials

[0088] B. Stomata

[0089] T-hole

Claims

1. A method for preparing a test material, which is used to determine the diffusive hydrogen content of a metallic material having a welded portion, comprising: The steps for determining the location of stomata, among which, Determine the pore locations of the test material, which is a metallic material with weldable parts; and The processing steps include processing in a manner that does not cause the pores determined in the step of determining the pore location to become closed structures, or removing the pores.

2. The method for preparing the test material according to claim 1, wherein, The volume ratio of welding metal in the test material is more than 50%.

3. A method for determining the diffusible hydrogen content, which is a method for determining the diffusible hydrogen content of a metallic material having a welded portion, comprising: The hydrogen introduction step, in which, Introducing hydrogen into the test material prepared by the method for preparing the test material according to claim 1 or 2; and The hydrogen content determination step includes determining the hydrogen content of the test material in which hydrogen was introduced during the hydrogen introduction step.

4. A method for evaluating delayed fracture characteristics, which is a method for evaluating the delayed fracture characteristics of metallic materials with welded parts, comprising: Evaluation steps, among which, The delayed fracture characteristics are evaluated based on the diffusivity of hydrogen obtained by the method for determining diffusivity of hydrogen as described in claim 3.

5. A method for selecting a metallic material, comprising: Select the steps, among which, Metallic materials are selected based on the delayed fracture characteristics obtained by the evaluation method of delayed fracture characteristics as described in claim 4.

6. A method for manufacturing a component, comprising: Welding steps, among which, The component is manufactured by welding the metal material selected by the metal material selection method of claim 5.

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