JP2021139892A - Material evaluation device, and material observation method - Google Patents

Abstract

To provide a technology that enables on-site analysis of a generation process of corrosion and cracking of a metallic material.SOLUTION: A material evaluation device is provided, enabling observation a generation process of at least one of corrosion and cracking of a test piece 4 made of a metallic material under a stress environment, the material evaluation device comprises: a closed container 1 which has an observation window 5 enabling observation of the inside of the container, and in which the test piece 4 is arranged: a stress applying jig 3 applying stress to the test piece 4 arranged in the test container 1; an optical system probe 7 observing the test piece 4 arranged in the test container 1 through the observation window 5; and test solution 30 which immerses the test piece 4 introduced into and arranged in the test container 1, and can promote corrosion of the test piece 4.SELECTED DRAWING: Figure 1

Description

The present invention relates to a material evaluation device and a material observation method for observing and analyzing (evaluating) corrosion and cracking of a metal material in a corroded environment.

Metallic materials that are widely used for social infrastructure have problems such as shortening of life due to wall thinning due to corrosion phenomenon and accidents of cracking, and improvement of corrosion resistance is an extremely important issue. As a method for evaluating corrosion resistance, in addition to actually performing an exposure test in the usage environment, there is a method in which a test solution such as salt water is applied to the evaluation test piece by spraying or the like and the test is performed in a simulated environment. In particular, in the latter mock test, it is expected that environmental parameters such as temperature and humidity can be systematically controlled and their effects can be grasped, and that the morphology of corrosion can be directly observed at the same time to help clarify the mechanism of corrosion and corrosion resistance. .. For example, in Patent Document 1, as an in-situ analysis technique for the surface of a steel sheet, a solution is dropped onto a part of a metal material to partially form a hot and humid atmospheric corrosion environment, and a process of forming pitting corrosion on the surface of the steel sheet. Disclosed is a method of in-situ observation from the outside of a test chamber by an optical system device in a drying / wetting cycle.

Further, among the corrosion phenomena in metal materials, the cracking phenomenon caused by the action of tensile stress is called stress corrosion cracking. Stress corrosion cracking is said to occur under the condition that three factors, a material factor, a mechanical factor (stress), and an environmental factor, are present.
In general, stress corrosion cracking is likely to occur mainly in alloys such as stainless steel and copper alloys, which is a major safety issue for automobiles, plant equipment, nuclear power plants, etc., and alleviation of tensile residual stress by shot peening. In addition, measures such as preventive maintenance are being taken using predictive technology to detect the occurrence of stress corrosion cracking at an early stage.

The types of stress corrosion cracks are roughly classified according to the crack growth path and environment, and grain boundary type stress corrosion cracks that are likely to occur in the welding affected area and intragranular stress corrosion cracks that are likely to occur in the surface hardening part are known. There is. Furthermore, as environmental factors, irradiation-induced stress corrosion cracking that occurs in a neutron or gamma-ray irradiation environment, and flow-accelerated corrosion that accelerates corrosion due to the addition of flow velocity are superimposed. It wasn't easy to figure out.

As a method for investigating the generation process of stress corrosion cracking, for example, there is a method described in Patent Document 2. In Patent Document 2, in order to visualize the process of stress corrosion cracking and pitting corrosion of a metal material, a metal cation-reactive color former that reacts with cations, which are the main components of the metal material, is used to break the film. A method of utilizing the color-developing reaction by metal ions eluted from the above is disclosed.
Among the stress corrosion cracking, as the use environment, e.g., a phenomenon that cracking under sour environment containing hydrogen sulfide H _{2 S} is called the sulfide stress corrosion cracking. Sulfide stress corrosion cracking has become one of the important issues in the energy field such as oil country tubular goods for oil and natural gas, line pipes, etc., and optimum material design according to the usage environment such as each well is required.

Regarding the material suitability for each usage environment, sulfide stress corrosion cracking evaluation by a constant load test specified in NACE TM 0177 Method A is mainly known. This test, under each condition of pH and H _{2 S} concentration in the test solution simulating the formation water or condensed water, after 720 hours (approximately 1 month) test was carried out while applying a load stress to the test piece This is a method for evaluating sulfide stress corrosion cracking of a test piece based on the presence or absence of fracture or cracking of the test piece. In various environmental conditions with a large H _{2 S} equipment, and various stainless steel, a judgment was subjected to sulfide stress corrosion cracking test various variety materials such as strength grade, also in combination with other test and evaluation methods, Knowledge on each elemental process of sulfide stress corrosion cracking has been accumulated and reflected in material design.

At present, the essential elucidation of corrosion phenomena and cracking phenomena such as the stress corrosion cracking and sulfide stress corrosion cracking described above has not been sufficiently advanced. One of the biggest reasons for this is that the starting point of cracking disappears immediately with corrosion and crack growth, making it difficult to identify the starting point of cracking. Regarding the process of pitting corrosion, which is the starting point of cracking, pitting corrosion sprouting (initial corrosion that becomes pitting corrosion) occurs during corrosion of metal surface inclusions and microstructures, deterioration / destruction of passivation film, and re-passivation. Occurrence and growth are thought to occur in a transient and complex manner.

Therefore, if the actual conditions from the occurrence of corrosion and cracking to growth in the actual environment can be clarified by in-situ analysis technology, it will lead to the identification of the corrosion origin and the design of new materials based on the confirmatory data of cracking and material factors, and only corrosion resistance. However, it is expected that various cracking resistances caused by corrosion such as stress corrosion cracking resistance and sulfide stress corrosion cracking resistance can be dramatically improved.

JP-A-2019-178997 Japanese Unexamined Patent Publication No. 2008-216232

The in-situ observation device and observation method for atmospheric corrosion described in Patent Document 1 assume a composite cycle corrosion test (CCT) and flying sea salt, and stress corrosion cracking in a stress environment, especially stress corrosion in a sour environment. No mention is made of cracking. In addition, Patent Document 1 does not assume environmental control such as flow velocity, and has a problem that a microscale in-situ analysis technique for a stress-loaded steel sheet surface under each environmental control has not been established.

Further, in the method for detecting the generation process of stress corrosion cracking and pitting corrosion described in Patent Document 2, it can be expected that the generation process of stress corrosion cracking and pitting corrosion can be observed in real time. However, Patent Document 2 has a problem that it is difficult to simulate an actual corrosion environment because it is necessary to add a metal cation-reactive color former to an aqueous solution in a test environment. Further, in the method of Patent Document 2, although it is improved by using a thickener, the point where the colored part diffuses in the aqueous solution and the anode dissolution reaction are used, so that the detection is dissolved (corrosion) to some extent. There is a problem that it is difficult to detect minute microscale occurrence points such as initial corrosion of pitting corrosion sprouting because of the fact that

In general, if the crack test is temporarily stopped and taken out, the growth process in the middle can be inferred by analyzing those such as pitting corrosion and cracks at the bottom of the pitting corrosion at that time. It does not capture the initial process of the same part where cracks occur. Further, when the sample is taken out, observed with a stress load, and then subjected to the test again, the test becomes discontinuous and the actual phenomenon cannot be reproduced. In this way, it is difficult to track the same object, and it is extremely difficult to obtain information on the conditions under which pitting corrosion that leads to cracking occurs in the end. In addition, the actual situation is that the cracking phenomenon is inferred by conducting verification tests and analyzes focusing on each elementary process of cracking (pitting corrosion / growth, cracking / propagation, etc.), and corrosion. The actual state of continuous stress corrosion cracking from occurrence to cracking has not been fully grasped. In addition, on the material factor side, there are various materials and parts including low carbon steel, stainless steel, welding affected parts, and dissimilar composite materials. As a result, it has become a big problem that a huge amount of time and cost are spent on investigating the cause of cracks that occur under various conditions for various materials and parts.

Here, in order to improve the stress corrosion cracking resistance (corrosion resistance) of metal materials and to provide better materials to society toward the construction of a safe and secure social infrastructure, cracking should occur from the starting point of pitting corrosion. In-situ cracking analysis technology that includes stress corrosion cracking morphology that occurs in various environments and combinations of various materials is indispensable by continuously identifying detailed phenomena up to this point on a microscale and establishing drastic measures. ..
The present invention has been made in view of the above points, and an object of the present invention is to provide a technique capable of analyzing the process of corrosion and cracking of a metal material on the spot.

In order to solve the above problems, the present inventors have conducted intensive research on devices and methods that can be grasped from the very early stage of corrosion, pitting corrosion, and cracking that lead to stress corrosion cracking. Then, the present inventors have completed the present invention by further studying based on the findings obtained from such diligent research.
Then, in order to solve the problem, one aspect of the present invention is a material evaluation device capable of observing at least one generation process of corrosion and cracking of a test piece made of a metal material under a stress environment, and observes the inside of the container. A closed container having a possible observation window, the test container in which the test piece is arranged in the container, the stress loading jig for applying stress to the test piece arranged in the test container, and the observation window. The optical system probe for observing the test piece placed in the test container and the test piece introduced in the test container and placed in the container can be immersed in the test piece to promote corrosion of the test piece. It is characterized in that it is provided with a new test solution.

Further, one aspect of the present invention is a material evaluation device capable of observing at least one generation process of corrosion and cracking of a test piece made of a metal material, and is a closed container having an observation window capable of observing the inside of the container. A test container for arranging the test piece in the container, an optical probe for observing the test piece arranged in the test container through the observation window, and an optical probe introduced into the test container and placed in the container. It is characterized by immersing the arranged test piece and providing a test solution capable of accelerating the corrosion of the test piece.

One aspect of the present invention may be characterized in that the test solution is filled in the test container.
Further, in one aspect of the present invention, the observation surface of the test piece arranged in the test container is arranged to face the observation window, and the test solution existing between the observation surface and the observation window. On the other hand, a flow forming device for forming a flow along the observation surface may be provided.
Further, in one aspect of the present invention, the flow forming apparatus includes an introduction pipe for pouring the test liquid into the test container and a discharge pipe for discharging the test liquid from the test container. , And the direction of at least one of the introduction pipe and the discharge pipe facing into the test container may be directed between the observation surface and the observation window.

Further, one aspect of the present invention may be characterized in that the observation surface of the test piece is provided with an irradiator that irradiates the observation surface of the test piece with light or radiation that affects the corrosion of the test piece through the observation window.
Another embodiment of the present invention, the test liquid may be characterized in that it comprises sulfide as solute hydrogen H _{2 S,} carbon dioxide CO _2, and any one or more of chloride ions.
Further, one aspect of the present invention may be characterized in that the observation surface of the test piece arranged in the test container and the observation window are arranged so as to face each other in the lateral direction.
Further, in one aspect of the present invention, except for the light receiving portion of the optical system probe, the covering material that covers the circumference of the optical system probe in a sealed state and the sealed space between the optical system probe and the coating material are positive. It may be characterized by including a positive pressure forming device as a pressure.

Further, one aspect of the present invention may be characterized by including a vibration isolation table that supports the test container and the optical system probe.
Further, one aspect of the present invention may be characterized in that the test container is provided with a sample electrode, a reference electrode, and a counter electrode for performing an electrochemical measurement of the test piece.
Further, one aspect of the present invention may be characterized in that the metal material forming the test piece is a steel material.
Another aspect of the present invention is a material observation method for observing the generation process of at least one of corrosion and cracking in a stress environment of a test piece made of a metal material, wherein the test piece is corroded. It is characterized in that it is immersed in a test solution capable of accelerating the above-mentioned test under a stressed state, and the corrosion and cracking process of the observation surface of the test piece is observed with an optical system probe arranged outside the test solution. ..

Further, another aspect of the present invention is a material observation method for observing at least one generation process of corrosion and cracking of a test piece made of a metal material, and the test piece can promote corrosion of the test piece. It is characterized in that at least one process of corrosion and cracking on the observation surface of the test piece is observed with an optical system probe immersed in the test solution and placed outside the test solution.
Another aspect of the present invention is also characterized in that the test piece and the test solution are housed in a test container made of a closed container, and the optical system probe observes the test piece from outside the test container. good.

In addition, another aspect of the present invention may be characterized in that a flow along the observation surface is continuously or intermittently formed with respect to the test liquid located on the observation surface of the test piece.
In addition, another aspect of the present invention may be characterized in that the observation surface of the test piece is irradiated with light or radiation that affects the corrosion of the test piece.
Another aspect of the present invention, the test liquid may be characterized in that it comprises sulfide as solute hydrogen H _{2 S,} carbon dioxide CO _2, and any one or more of chloride ions.
Another aspect of the present invention is characterized in that the test piece is observed with the optical system probe in a state where the light receiving portion of the optical system probe and the observation surface of the test piece are opposed to each other in the lateral direction. May be good.

According to the aspect of the present invention, it is possible to provide an apparatus and an analysis method capable of in-situ analysis of the origin and growth process of corrosion and cracking on a microscale.
As a result, by adopting the aspect of the present invention, the root cause of stress corrosion cracking according to various environments such as automobiles, plants, nuclear power plants, mobile media such as line pipes, structures, and infrastructure equipment can be found. It will be possible to identify the actual situation and essence, and it will greatly contribute to the formulation of material development guidelines with improved corrosion resistance and stress corrosion cracking resistance, and will contribute to the construction of a safe and secure social infrastructure.

It is the schematic which shows the apparatus structure which concerns on 1st Embodiment based on this invention. It is the schematic which shows another apparatus configuration which concerns on 1st Embodiment based on this invention. It is the schematic which shows the apparatus structure which concerns on 2nd Embodiment based on this invention. It is a figure which shows the result of the real-time observation of the microcrack growth on the surface of the test piece made of martensitic steel in Example 2. FIG.

Next, an embodiment of the present invention will be described with reference to the drawings.
The apparatus of this embodiment relates to a material evaluation apparatus capable of observing at least one generation process of corrosion and cracking of a test piece made of a metal material. The device of the present embodiment is a device for observing, for example, the process of progressing to cracking due to corrosion and the cracking progress behavior due to stress after cracking occurs.

"First embodiment"
First, the first embodiment will be described.
As shown in FIGS. 1 and 2, the material evaluation device of the present embodiment includes a test container 1, a stress load jig 3, an optical system probe 7 of an optical system measuring device, a flow forming device 20, an irradiator 11, and an excluding device. A shaking table 12 is provided. The stress load jig 3 may be omitted.

(Test piece 4)
The test piece 4 to be evaluated is made of a metal material. The metal material to be evaluated is not particularly limited. That is, the test piece 4 is not particularly limited as long as it is a material that may be corroded or cracked due to use over time. Examples of the metal material include high alloys such as stainless steel, low alloy steel materials such as carbon steel, and alloys such as copper alloys. In this embodiment, the metal material is a steel material.
The shape of the test piece 4 is not particularly limited. In this embodiment, a rectangular flat plate (strip shape) is used.

(Test container 1)
The test container 1 is a closed container having an observation window 5 capable of observing the inside of the container. In the test container 1, the test piece 4 can be arranged in the container. The test container 1 is installed on the vibration isolation table 12.
When the observation surface 4a is directed to the side, for example, as shown in FIG. 2, the observation surface 4a is supported by the vibration isolation table 12 via the container fixing table 13. The container fixing base 13 only needs to have strength to support the test container 1, and more preferably has corrosion resistance. Examples of the material of the container fixing base 13 include stainless steel.
The test container 1 may be of a size such that the airtightness is maintained, the observation window 5 is provided on one or more side surfaces, and the test piece 4 can be arranged. The shape of the test container 1 is not particularly limited, and the test container 1 may be a cube, a cylinder, or the like. The material other than the observation window 5 is not particularly limited as long as it has liquid resistance to the test liquid 30, but transparent acrylic is preferable from the viewpoint of operability and price.

<Observation window 5>
The observation window 5 is made of a material having sufficient light transmittance, for example, glass, so that the test piece 4 can be observed by the optical system probe 7.
The observation window 5 is preferably made of a material having high transparency and excellent light transmission from the viewpoint of microscale observation and analysis at high magnification by the optical system probe 7. The wall thickness of the observation window 5 is not limited in order to reduce the influence of refraction and attenuation, but it is preferable that the observation window 5 is thin as long as strength and durability can be obtained. More preferably, the observation window 5 is made of quartz glass having a thickness of 2 mm or more and less than 4 mm.
The position (orientation) of the observation window 5 is not particularly limited as long as the inside of the container can be observed. The observation window 5 is formed on, for example, the upper surface or the side surface of the test container 1.

FIG. 1 illustrates a case where the observation window 5 is formed on the upper surface of the test container 1.
However, if a gas phase space is created in the container by bubbling the test solution 30 to saturate it, the gas phase space hinders observation or the influence of air bubbles in the test solution 30 is as much as possible. Make it smaller. From the viewpoint of suppressing such an adverse effect, it is preferable that the observation window 5 is provided on the side surface as shown in FIG.
That is, under the condition that the CO ₂ gas or the like is saturated and becomes a gas and bubbles are likely to be generated, or the condition that the test is performed while bubbling the test liquid 30 to the saturated state, the bubbles or the gas phase is contained in the test container 1. Space is created and obstructs observation. Therefore, from the viewpoint of avoiding the influence of air bubbles in the test liquid 30 as small as possible, the observation window 5 is provided on the side surface, and the observation surface 4a of the test piece 4 attached to the stress load jig 3 is tilted left and right from the horizontal plane. For example, it is preferable to install it in the vertical direction and observe it from the side surface of the container with the optical system probe 7.

(Stress load jig 3)
The stress loading jig 3 is a jig that supports the test piece 4 arranged in the test container 1 and loads the test piece 4 with stress. The stress loading jig 3 may have any shape as long as it can apply tensile stress to the test piece 4 and can be introduced into the test container 1.
As the stress load jig 3, a strip-shaped test piece 4 is given by a small three-point bending or four-point bending jig, or a flaky test piece 4 is given by a small tension jig. More preferred.
In FIG. 1, a case where the center of the test piece 4 in the longitudinal direction is warped so as to be convex upward by four-point bending is illustrated, and the upper surface of the test piece 4 becomes the observation surface 4a.
The material of the stress load jig 3 may be corrosion resistance and rigidity, and SUS316L or the like can be used. Further, when the test piece 4 is installed, it is more desirable to keep the size of the jig to a minimum so that the tension surface is not too far from the observation window 5 by 30 mm or more. In addition, by changing the stress conditions in three large patterns (no load, elastic region, plastic region), it is possible to investigate the presence or absence of stress and the effect of stress in detail.

Further, a stress load jig 3 is used to apply stress to the strip-shaped test piece 4, and a transparent material such as glass is adhered to one side surface of the test piece 4, and one side surface of the test piece 4 is observed. The stress load jig 3 may be arranged so as to be on the surface 4a. In this case, not only the surface change of the test piece 4 but also the dynamic behavior such as corrosion and crack generation / growth process in the depth direction can be continuously visualized through the transparent material.

(Sample stand 2)
The sample table 2 is installed in the test container 1. In the present embodiment, as shown in FIGS. 1 and 2, the test piece 4 to which the tensile stress is applied by the stress load jig 3 can be installed on the sample table 2 installed in the test container 1. ing.
The material and shape of the sample table 2 are not particularly limited as long as it has corrosion resistance to the corrosive test liquid 30 used and is structurally stable, and examples thereof include polyvinyl chloride. ..
By installing the test piece 4 to which the tensile stress is applied by the stress loading jig 3 on the sample table 2, the observation surface 4a formed on the upper surface of the test piece 4 is opened at a predetermined distance, and the optical system probe 7 is opened. It is set so as to face the light receiving portion 7a of the above and below.
The shape and structure of the sample table 2 are not particularly limited as long as the test piece 4 and the observation surface 4a can be arranged so as to face each other with a predetermined distance.
The distance between the observation surface 4a and the light receiving portion 7a of the optical system probe 7 is, for example, less than 30 mm, preferably 15 mm.
The observation surface 4a of the test piece 4 is arranged in a non-contact state with the observation window 5.

(Optical system probe 7)
The optical system probe 7 is a measuring unit of an optical system measuring instrument for observing the test piece 4 arranged in the test container 1 through the observation window 5. The optical system probe 7 is arranged outside the test container 1 and is supported by the vibration isolation table 12 via the probe fixing table 6. The probe fixing base 6 is preferably made of metal from the viewpoint of stability, and more preferably stainless steel from the viewpoint of corrosion resistance.
The optical system probe 7 is preferably a long working distance optical system probe capable of microscale observation of corrosion and cracks that occur under the corrosive environment and stress of the test piece 4.
The light receiving portion 7a of the optical system probe 7 is arranged close to the observation window 5 at a position facing the observation surface 4a of the test piece 4.
When the observation window 5 is arranged sideways, as shown in FIG. 2, the light receiving portion 7a of the optical system probe 7 may also be arranged so as to face the observation window 5 from the lateral direction.

When the probe 7 is a long working distance optical system probe, a digital microscope system (microscope) can be used as the probe 7, and examples thereof include KEYENCE, HiROX, and OLYMPUS. The distance between the tension surface of the stressed test piece 4 installed in the test container 1 and the lens (light receiving portion 7a) installed on the outside is adjusted according to various long working distance lenses. The distance between the tip of the lens and the tensile surface (observation surface 4a) of the test piece 4 via the observation window 5 is preferably 5 mm or more and 60 mm or less, and more preferably 10 mm or more and 20 mm or less from the viewpoint of the effects of refraction and attenuation. ..
Further, by utilizing the long working distance optical system of the digital microscope as the probe 7, it is possible to freely switch from low magnification observation to high magnification observation as needed without causing disturbance in the measurement environment even during real-time observation. .. Therefore, one of the major features of this configuration is that it is possible to select a specific corrosion occurrence site and trace the micro phenomenon further while capturing the macro phenomenon by low-magnification observation at the beginning, and seamlessly perform multi-scale analysis. It is one.

(Test solution 30)
The test liquid 30 is introduced into the test container 1. The test liquid 30 immerses the test piece 4 arranged in the test container 1. The test liquid 30 is preferably in a state of being filled in the test container 1. By being filled, it is possible to suppress a decrease in accuracy due to shaking of the interface of the test liquid 30.
Even when the test liquid 30 is filled in the test container 1, a gas phase gas space is formed in the upper part of the container.
The test liquid 30 is composed of a liquid capable of accelerating the corrosion of the test piece 4.
When reproducing the under sour environment as the test environment, test liquid 30, for example, sulfide as a solute hydrogen H _{2 S,} carbon dioxide CO _2, and employing a liquid containing any one or more of chloride ions. When this test solution 30 is used, bubbles are generated.
However, the test liquid 30 is not particularly limited as long as it is under stress corrosion cracking occurrence conditions or verification conditions.
The temperature of the test solution 30 is maintained in the range of −10 to 90 ° C. using, for example, a constant temperature bath or the like. In the presence of chloride ions, depending on the concentration, on the low temperature side, an antifreeze solution such as dimethyl sulfoxide DMSO may be added to prevent freezing.

(Flow forming device 20)
The flow forming device 20 is a device that forms a flow of liquid along the observation surface 4a with respect to the test liquid 30 existing between the observation surface 4a of the test piece 4 and the observation window 5. The flow forming device 20 includes, for example, an introduction pipe 8 for flowing the test liquid 30 into the test container 1 and pouring the test liquid 30 into the test container 1, and a discharge pipe 9 for discharging the test liquid 30 from the test container 1. It is preferable that the direction of at least one of the introduction pipe 8 and the discharge pipe 9 facing into the test container 1 is directed between the observation surface 4a and the observation window 5.
Here, the observation surface 4a and the observation window 5 are arranged so as to face each other. It is preferable that the observation surface 4a and the observation window 5 are arranged in parallel with each other.

The flow forming device 20 of the present embodiment has an introduction pipe 8 and a discharge pipe 9 that form an outflow port that communicates with the test container 1. The introduction pipe 8 and the discharge pipe 9 communicate with a liquid tank (not shown) to form a circulation path. The test liquid 30 is housed in the liquid tank, and the test liquid 30 can be circulated and supplied to the test container 1. A flow rate control system 10 is connected to the introduction pipe 8 so that the flow rate of the test liquid 30 to be introduced into the test container 1 can be adjusted. As the flow rate control system 10, a liquid feed pump or a liquid flow meter may be provided in the circulation path, and it is preferable that an inverter control or the like for flow rate control is provided.

According to this configuration, the test liquid 30 is supplied from the introduction pipe 8 and discharged from the discharge pipe 9, so that convection of the test liquid 30 is generated in the test container 1, so that the observation surface 4a of the test piece 4 and the test liquid 30 are formed. A flow of liquid is formed along the observation surface 4a with respect to the test liquid 30 existing between the observation window 5.
More effectively, in order for the liquid to flow along the observation surface 4a with respect to the test liquid 30 existing between the observation surface 4a and the observation window 5 of the test piece 4, the introduction pipe 8 and the discharge pipe 9 are used. It is preferable that the direction of at least one tube facing the test container 1 is directed between the observation surface 4a and the observation window 5. In this case, for example, the test liquid 30 is injected from the introduction pipe 8 toward the observation surface 4a and the observation window 5, or the test liquid 30 between the observation surface 4a and the observation window 5 is discharged from the discharge pipe 9. The liquid flow along the observation surface 4a is efficiently formed by being discharged from the observation surface 4a.
The configuration of the flow forming device 20 is not limited to the above configuration.

(Irradiator 11)
The irradiator 11 is composed of a light source or a radiation source that irradiates the observation surface 4a of the test piece 4 with light or radiation that affects the corrosion of the test piece 4 through the observation window 5. “Affecting corrosion” may, for example, promote corrosion or suppress the progress of corrosion.
Although the irradiator 11 is not shown in FIG. 2, the irradiator 11 may be provided. On the contrary, in the configuration of FIG. 1, the irradiator 11 may be omitted.
The light source / radiation source is irradiated from an oblique direction of the test piece 4 observation surface 4a so that it can be used at the same time as the optical system probe 7. Alternatively, the optical system probe 7 may be placed close to the observation window 5 only when observing, and the light source / radiation source may be installed in front of the observation window 5, and the arrangement may be freely determined.
The types of light sources and radiation sources are not limited as long as the corrosive environment due to irradiation can be simulated. For example, examples of the light source to be irradiated include a light source having an ultraviolet region on the short wavelength side from the visible light region, and examples of the radiation source include X-rays, γ-rays, and neutron rays.

(Vibration isolation table 12)
The vibration isolation table 12 is a device that supports the test container 1 and the optical system probe 7 and alleviates vibration input from the surroundings such as mechanical vibration to the test container 1 and the optical system probe 7. That is, the vibration isolation table 12 is installed as a frame for the optical system probe 7 and the test container 1.
Since the influence of mechanical vibration becomes remarkable especially at high magnification observation, the vibration isolation table 12 is installed as a stand of the test container 1 in order to mitigate the influence of vibration. Examples of the vibration isolator 12 include a rubber type, a spring type, and a pneumatic type.

(Coating material 21, positive pressure forming device 22)
Here, as shown in FIG. 2, the optical system probe 7 may be covered with a covering material 21 in a sealed state around the optical system probe 7 except for the light receiving portion 7a.
The covering material 21 may have any shape and material as long as the optical system probe 7 can be sealed, but it is desirable that the covering material 21 is transparent from the viewpoint of operability. For example, a bag-shaped sheet body such as an acrylic box or a vinyl glove bag with gloves can be mentioned.
At this time, it is preferable to provide a positive pressure forming device 22 having a positive pressure in a closed space between the optical system probe 7 and the covering material 21 (see FIG. 2).

The positive pressure forming apparatus 22 is particularly required in the case of a test using a corrosive gas such as hydrogen sulfide. In recent years, the miniaturization of electronic circuits has progressed, and even a very small amount of corrosive gas on the order of ppb affects Cu wiring and causes a failure of measuring equipment. Therefore, the positive pressure forming device 22 is one of the essential requirements for introducing the measuring instruments into the corrosive gas test environment, and supplies the gas to the closed space between the optical system probe 7 and the covering material 21. Any device that can be used may be used, for example, an air circulation pump may be used. The air circulation pump is not particularly limited as long as it can introduce outside air into the closed space of the covering material 21 to create a positive pressure.
When the corrosion test condition is performed on the high temperature side, the temperature of the air supplied by connecting the constant temperature control device may be appropriately controlled from the viewpoint of avoiding the temperature rise of the optical system probe 7. That is, it may be configured to supply a gas having a temperature lower than that of the test environment to the enclosed space.

"Second embodiment"
Next, the second embodiment will be described with reference to FIG.
The basic configuration of the material evaluation device of this embodiment is the same as that of the first embodiment, but as shown in FIG. 3, a sample electrode for performing an electrochemical measurement of the test piece 4 in the test container 1 is referred to. It differs from the first embodiment in that an electrode and a counter electrode are provided. FIG. 3 shows an example in which a jig for electrochemical measurement is provided in the configuration of FIG. 2, but the basic configuration of the material evaluation device is not limited to the configuration of FIG. You may.
The sample electrode for electrochemical measurement is installed in the vicinity of the observation window 5 by connecting the covered lead wiring to the test piece 4 stress-loaded by the stress loading jig 3. As the reference electrode and the counter electrode, a commercially available electrode may be used. For example, a silver-silver chloride reference electrode (Ag / AgCl), a platinum (Pt) counter electrode can be mentioned, and general electrochemical measurements can be applied using a potentiostat device.

Further, a specific description will be given.
As the device for electrochemical measurement, a general-purpose electrochemical measuring device can be applied. Examples of the electrochemical measurement include anode / cathode polarization measurement, immersion potential measurement, and impedance measurement, which correspond to oxidation and reduction reactions of corrosion. In the sample electrode composed of the test piece 4, the coated lead wire 15 is connected to the test piece 4 stress-loaded by the stress loading jig 3, and the sample electrode port 16 is located near the observation window 5 in the test container 1. The reference electrode 17 and the counter electrode 18 are also inserted into the test container 1 in the same manner, and the voltage / current signal is controlled / acquired using the potentiostat 19. As the reference electrode and the counter electrode, a commercially available product may be used, and examples thereof include a silver-silver chloride reference electrode (Ag / AgCl) and a platinum (Pt) counter electrode.

Further, as a crack evaluation due to hydrogen embrittlement, if hydrogen is introduced into the material by using the material evaluation device of the present embodiment and a generally known electrochemical hydrogenation method, a high-strength material such as in the automobile field can be used. It can be applied to crack evaluation and analysis of hydrogen embrittlement resistant materials.
Here, the present embodiment is not limited to the embodiment shown above. For example, the optical system probe 7 can be extended to various analyzes such as fine shape analysis by a laser microscope and structural analysis by Raman instead of a long working distance optical system. Further, when the crack in-situ analyzer of the present invention is used on the higher temperature and higher pressure side, the test container 1 may be made of metal and the observation window 5 may be replaced with heat-resistant and pressure-resistant glass. Just do it.

"effect"
Next, the effects and the like of the embodiment (embodiment) based on the present invention will be described.
By using the embodiment based on the present invention for the above-mentioned problems, it is possible to continuously observe the generation process of pitting corrosion, which is the starting point of cracking, in real time on the spot. That is, according to the aspect of the present invention, it is possible to provide an apparatus and an analysis method capable of in-situ analysis of various forms of stress corrosion cracking occurrence starting points and growth processes on a microscale.
As a result, by adopting the aspect of the present invention, it is possible to identify the root cause of stress corrosion cracking according to various environments such as automobiles, plants, mobile media such as nuclear power plants, structures, and infrastructure equipment. It will be possible. As the actual situation and essence are elucidated, it will greatly contribute to the formulation of material development guidelines with improved corrosion resistance and stress corrosion cracking resistance, and will contribute to the construction of a safe and secure social infrastructure.

That is, this embodiment has the following effects.
(1) The present embodiment is a material observation method for observing the generation process of at least one of corrosion and cracking of a test piece made of a metal material under a stress environment, in which the test piece 4 is corroded. At least one process of corrosion and cracking of the observation surface of the test piece 4 with the optical system probe 7 placed outside the test solution 30 after being immersed in the test solution 30 under stress. Observe.
For example, the present embodiment is a material evaluation device capable of observing at least one generation process of corrosion and cracking of a test piece 4 made of a metal material under a stress environment, and has an observation window 5 capable of observing the inside of the container. A closed container, a test container 1 in which the test piece 4 is arranged in the container, a stress loading jig 3 for applying stress to the test piece 4 arranged in the test container 1, and an observation window 5. The optical system probe 7 for observing the test piece 4 arranged in the test container 1 and the test piece 4 introduced into the test container 1 and arranged in the container are immersed in the test piece 4. The configuration includes the test liquid 30 capable of accelerating the corrosion of No. 4.
According to this configuration, it is possible to continuously observe the generation process of pitting corrosion, which is the starting point of cracking, in real time in a stress-corroded environment. That is, according to the aspect of the present invention, it is possible to provide an apparatus and an analysis method that enable in-situ analysis of the generation starting point and growth process of stress corrosion cracking on a microscale.

(2) Further, the present embodiment is a material observation method for observing the corrosion generation process of the test piece 4 made of a metal material, and the test piece 4 is a test solution capable of accelerating the corrosion of the test piece 4. With an optical system probe 7 immersed in the test liquid 30 and placed outside the test solution 30, at least one process of corrosion and cracking of the observation surface 4a of the test piece 4 is observed.
For example, the present embodiment is a material evaluation device capable of observing at least one generation process of corrosion and cracking of a test piece 4 made of a metal material, and is a closed container having an observation window 5 capable of observing the inside of the container. The test container 1 in which the test piece 4 is arranged in the container, the optical system probe 7 for observing the test piece 4 arranged in the test container 1 through the observation window 5, and the inside of the test container 1 The test piece 4 introduced into the container and arranged in the container is immersed in the test piece 4, and the test liquid 30 capable of accelerating the corrosion of the test piece 4 is provided.
According to this configuration, it is possible to continuously observe the generation process of pitting corrosion, which is the starting point of cracking, in real time in a corrosive environment. That is, according to the aspect of the present invention, it is possible to provide an apparatus and an analysis method that enable in-situ analysis of the origin and growth process of corrosion on a microscale.

(3) Further, in the present embodiment, it is preferable that the test liquid 30 is filled in the test container 1.
In this configuration, for example, an air layer having a predetermined volume or more is not formed at the interface between the observation surface 4a and the test liquid 30, and the test liquid 30 in the test container 1 is stabilized, so that the observation accuracy is further improved. Even when the test liquid 30 is filled, a gas phase gas space is formed in the upper part of the container due to the generated gas or the like.
(4) Further, in the present embodiment, the test piece 4 and the test liquid 30 are housed in a test container 1 composed of a closed container, and the optical system probe 7 is the test piece 4 from the outside of the test container 1. Observe.
According to this configuration, it is possible to suppress the influence of the optical system probe 7 on the corrosive environment.

(5) Further, in the present embodiment, a flow along the observation surface 4a is continuously or intermittently formed with respect to the test liquid 30 located on the observation surface 4a of the test piece 4.
For example, in this embodiment, the observation surface 4a of the test piece 4 arranged in the test container 1 is arranged to face the observation window 5 and exists between the observation surface 4a and the observation window 5. The test liquid 30 is provided with a flow forming device 20 for forming a flow along the observation surface 4a.
At this time, the flow forming device 20 has an introduction pipe 8 for pouring the test liquid 30 into the test container 1 and a discharge pipe for discharging the test liquid 30 from the test container 1. It is preferable that the direction of at least one of the introduction pipe 8 and the discharge pipe 9 facing the inside of the test container 1 is directed between the observation surface 4a and the observation window 5.
This configuration is particularly effective in tests that reproduce a sour environment in which bubbles are generated.
According to this configuration, even if bubbles may be generated in the test container 1 due to the reaction of the test liquid 30, the test existing between the observation surface 4a and the observation window 5 due to the flow of the liquid. Bubbles contained in the liquid 30 can be suppressed. It also has the effect of removing air bubbles adhering to the inner surface of the observation window 5. As a result, the observation accuracy is improved.

(6) Further, in the present embodiment, the observation surface 4a of the test piece 4 is irradiated with light or radiation that affects the corrosion of the test piece 4.
For example, the present embodiment includes an irradiator 11 that irradiates the observation surface 4a of the test piece 4 with light or radiation that affects the corrosion of the test piece 4 through the observation window 5.
According to this configuration, the setting conditions of the corrosive environment can be set more finely, and it becomes possible to get closer to the environment in which the metal material is used. As a result, the observation accuracy is improved.

(7) Further, this embodiment, the test solution 30 includes sulfide as a solute hydrogen _H 2 S, carbon dioxide CO _2, and any one or more of chloride ions.
By using the test solution 30 containing such a solute, it is possible to reproduce a sour sweet environment or the like.
Here, the sour-sweet environment is an environment in which air bubbles are likely to be generated.

(8) Further, in the present embodiment, the test piece 4 is held by the optical system probe 7 in a state where the light receiving portion 7a of the optical system probe 7 and the observation surface 4a of the test piece 4 are opposed to each other in the lateral direction. Observe.
For example, in this embodiment, the observation surface 4a of the test piece 4 arranged in the test container 1 and the observation window 5 are arranged so as to face each other in the lateral direction.
According to this configuration, even if bubbles are generated in the test liquid 30, it is possible to reduce that the bubbles move upward and are located between the observation window 5 and the observation surface 4a. This configuration is particularly effective in tests that reproduce the above sour environment.

(9) Further, in the present embodiment, except for the light receiving portion 7a of the optical system probe 7, the coating material 21 that covers the periphery of the optical system probe 7 in a sealed state, and the optical system probe 7 and the coating material are provided. A positive pressure forming device 22 having a positive pressure in a closed space between them is provided.
Even in a closed container, a small amount of vaporized gas of the test solution 30 may be unavoidably contained outside the container from the closed container, etc., even when the container is opened or closed by exchanging the test solution or sample, or even during the test. be. On the other hand, the coating material 21 can protect the optical system probe 7.
In particular, by setting the closed space to a positive pressure, the coating material 21 can more reliably protect the optical system probe 7.
At this time, it is also possible to protect the optical system probe 7 from heat by setting the temperature of the atmosphere to be positive pressure to be lower than the temperature of the test liquid 30 such as room temperature.

(10) Further, the present embodiment includes a vibration isolation table 12 that supports the test container 1 and the optical system probe 7.
According to this configuration, the vibration input during observation is suppressed, and observation on a microscale can be performed with high accuracy.
(11) Further, in the present embodiment, the test container 1 is provided with a sample electrode, a reference electrode, and a counter electrode for performing the electrochemical measurement of the test piece 4.
According to this configuration, observation by electrochemical measurement is possible as well as optical observation.
(12) Further, in the present embodiment, the test piece 4 generated in the test liquid 30 by continuously observing the test piece 4 with the optical system probe 7 using the material evaluation device of the above embodiment. Observe the process leading to cracking due to corrosion.
According to this configuration, it is possible to analyze the origin and growth process of corrosion and cracks on the spot.

Hereinafter, the present invention will be specifically described with reference to examples. The present invention is not limited to the following examples.
"Example 1"
In Example 1, the apparatus configuration shown in FIG. 1 was adopted.
The test piece 4 was formed into a strip shape made of SUS304 austenitic stainless steel. The test piece 4 was placed in the test container 1 in a state where stress was applied by a small four-point bending jig. A test solution 30 having a chloride ion concentration of 10000 ppm was prepared. Then, the test liquid 30 having a temperature of 80 ° C. was introduced into the test container 1 and the test piece 4 was completely immersed.
For the observation of the test piece 4, a long working distance optical system manufactured by KEYENCE is used, and the stress corrosion cracking in-situ observation is performed on the tensile surface (observation surface 4a) of the test piece 4 from a low magnification to a high magnification (field of view 200 μm square). carried out.
In the observation of stress corrosion cracking in Example 1, it was possible to continuously observe from the very initial occurrence of corrosion on the surface of the steel sheet to the growth process of microcracks on the order of several μm.

"Example 2"
In Example 2, the apparatus configuration shown in FIG. 2 was adopted.
As the test piece 4, a strip-shaped shape made of high Cr stainless steel having a martensite phase as a main phase and a mass% of Cr: 13% was adopted.
A long working distance optical system manufactured by KEYENCE is used for observing the test piece 4, and the tensile surface (observation surface 4a) of the test piece 4 is subjected to sulfide stress corrosion cracking in-situ from low magnification to high magnification (field of view 200 μm square). Observations were carried out. Then, by continuously observing, the microcrack growth generated in the test piece 4 was tracked in real time.

Here, the test conditions are as follows.
That is, the observation surface of the test piece 4 to be observed was mirror-polished. A load stress of 90% actual YS was applied to the test piece 4 using a 4-point bending jig. Further, the test piece 4 was completely immersed using Formation water (geological water simulation environment: 20% NaCl + 0.5% CH ₃ COOH + CH ₃ COONa, pH 3.5, H ₂ S 0.15 atm) as the test solution 30.
As a result of observation, it was possible to clearly grasp the appearance of pitting corrosion occurring from the surface of the steel sheet through the long working distance lens. In addition, it was possible to observe in real time how microcracks grow in the vertical direction with respect to the tensile stress direction in the pitting corrosion generating part.

FIG. 4 shows an example of the observation result. FIG. 4 shows images cut out at 10-minute intervals at the tip of a minute crack at a position about 1 mm away from the pitting corrosion portion.
As can be seen from FIG. 4, the time when the crack generated from the pitting corrosion portion reaches 1 mm is defined as zero, and an image cut out from there every 10 minutes is shown. Further, the arrow (→) in FIG. 4 indicates the position of the crack tip in each image. As described above, based on the present invention, minute cracks of several μm were clearly captured, and the surface of the steel sheet under a sour stress environment could be observed on a microscale. Furthermore, the dynamic behavior of the growth of minute cracks can be captured, and not only the occurrence point of sulfide stress corrosion cracking can be elucidated, but also the events leading to pitting corrosion growth and crack growth process can be grasped seamlessly from the same viewpoint. , It was found that these findings can greatly contribute to the elucidation of the actual condition of sulfide stress corrosion cracking.

1 Test container 2 Sample stand 3 Stress load jig 4 Test piece 4a Observation surface 5 Observation window 6 Probe fixing base 7 Optical system probe 7a Light receiving part 8 Introduction pipe 9 Discharge pipe 10 Flow control system 11 Irradiator 12 Vibration isolation table 13 Container Fixed base 15 Lead wire 16 Sample electrode port 17 Reference electrode 18 Counter electrode 19 Potential stat 20 Flow forming device 21 Coating material 22 Positive pressure forming device 30 Test solution

Claims (19)

A material evaluation device capable of observing at least one of the processes of corrosion and cracking of a test piece made of a metallic material under a stress environment.
A closed container having an observation window for observing the inside of the container, and a test container in which the test piece is placed in the container, and a test container.
A stress loading jig that applies stress to the test piece placed in the test container,
An optical system probe for observing the test piece placed in the test container through the observation window, and
A test solution that can accelerate the corrosion of the test piece by immersing the test piece that has been introduced into the test container and placed in the container.
A material evaluation device characterized by comprising. A material evaluation device capable of observing the generation process of at least one of corrosion and cracking of a test piece made of a metal material.
A closed container having an observation window for observing the inside of the container, and a test container in which the test piece is placed in the container, and a test container.
An optical system probe for observing the test piece placed in the test container through the observation window, and
A test solution that can accelerate the corrosion of the test piece by immersing the test piece that has been introduced into the test container and placed in the container.
A material evaluation device characterized by comprising. The material evaluation device according to claim 1 or 2, wherein the test solution is filled in the test container. The observation surface of the test piece arranged in the test container is arranged so as to face the observation window.
Any one of claims 1 to 3, wherein a flow forming device for forming a flow along the observation surface is provided with respect to the test liquid existing between the observation surface and the observation window. The material evaluation device described in the section. The flow forming device includes an introduction pipe for flowing the test liquid into the test container and pouring the test liquid into the test container, and a discharge pipe for discharging the test liquid from the test container.
The material evaluation according to claim 4, wherein the direction of at least one of the introduction pipe and the discharge pipe facing the test container is directed between the observation surface and the observation window. Device. Any one of claims 1 to 5, wherein the observation surface of the test piece is provided with an irradiator that irradiates light or radiation that affects the corrosion of the test piece through the observation window. Material evaluation device described in. The test solution, as described in any one of claims 1 to 6, characterized in that it comprises sulfide as solute hydrogen H _{2 S,} carbon dioxide CO _2, and any one or more of chloride ions Material evaluation device. The material according to any one of claims 1 to 7, wherein the observation surface of the test piece and the observation window arranged in the test container are arranged so as to face each other in the lateral direction. Evaluation device. Except for the light receiving part of the optical system probe, the covering material that covers the optical system probe in a sealed state and
A positive pressure forming device having a positive pressure in a closed space between the optical system probe and the covering material,
The material evaluation apparatus according to any one of claims 1 to 8, further comprising. The material evaluation apparatus according to any one of claims 1 to 9, further comprising a vibration isolator that supports the test container and the optical system probe. The material evaluation apparatus according to any one of claims 1 to 10, wherein the test container is provided with a sample electrode, a reference electrode, and a counter electrode for performing an electrochemical measurement of the test piece. The material evaluation apparatus according to any one of claims 1 to 11, wherein the metal material forming the test piece is a steel material. A material observation method for observing at least one of the processes of corrosion and cracking of a test piece made of a metallic material under a stress environment.
The test piece is immersed in a test solution capable of accelerating the corrosion of the test piece under stress, and the optical system probe placed outside the test solution is used to corrode the observation surface of the test piece and to prevent the test piece from being corroded. A material observation method characterized by observing at least one process of cracking. A material observation method for observing the generation process of at least one of corrosion and cracking of a test piece made of a metal material.
The test piece is immersed in a test solution capable of promoting corrosion of the test piece, and an optical probe placed outside the test solution is used to perform at least one process of corrosion and cracking of the observation surface of the test piece. The described material observation method, which comprises observing. The test piece and test solution are housed in a test container composed of a closed container.
The material observation method according to claim 13 or 14, wherein the optical system probe observes the test piece from the outside of the test container. The invention according to any one of claims 13 to 15, wherein a flow along the observation surface is continuously or intermittently formed with respect to the test liquid located on the observation surface of the test piece. The material observation method described. The material observation method according to any one of claims 13 to 16, wherein the observation surface of the test piece is irradiated with light or radiation that affects the corrosion of the test piece. The test solution, as described in any one of claims 13 17, characterized in that it comprises sulfide as solute hydrogen H _{2 S,} carbon dioxide CO _2, and any one or more of chloride ions Material observation method. 13. The material observation method according to item 1.

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