JP5392779B2 - Simulated stress corrosion cracking specimen and its manufacturing method - Google Patents

Description

The present invention relates to a simulated stress corrosion cracking test body and a method for manufacturing the same, which are mainly used for skill training of an inspector and apparatus sensitivity calibration in nondestructive inspection.

In order to maintain the soundness of the plant, it is essential to carry out appropriate maintenance activities, particularly appropriate inspections for early and quantitative detection of deterioration. For this reason, appropriate specimens are indispensable for inspectors' skill training and equipment performance evaluation, but for `` flaws' 'that occur in actual machines, especially stress corrosion cracking, which is a serious problem in practice, It is widely known that detection is difficult because the signal at the time of inspection is weak.

However, there is a problem that the influencing factors and mechanisms for the response of the non-destructive signal are not sufficiently elucidated. Therefore, at present, various studies on stress corrosion cracking have been carried out using test specimens in which stress corrosion cracking has been artificially introduced by exposing the material to a corrosive environment for a long time.

In this way, artificially introducing stress corrosion cracking for a non-destructive test specimen uses a phenomenon called corrosion, so it is difficult to control the shape of the “flaw” to be introduced and a large amount of money. There is a problem that cost and long processing time are required.
In addition, it has been pointed out that artificially introduced stress corrosion cracks are not necessarily similar to the stress corrosion cracks that actually occur. For this reason, many studies have been conducted to simulate stress corrosion cracking from the viewpoint of nondestructive inspection.

For example, Patent Document 1 describes a method of providing an arbitrarily shaped intergranular stress corrosion cracking simulation region by cooling after applying a low melting point metal to the joint surface. However, in this technique, the shape control is described in units of mm, and in consideration of the “flaw” evaluation ability required in nondestructive inspection in an actual plant, the level of this Patent Document 1 is insufficient and more accurate. It is desirable to control the “flaw” shape high.

Attempts have been made to simulate stress corrosion cracking by using a fatigue crack whose shape is relatively easy to control, closing the crack by applying a compressive stress to the fatigue crack (Non-Patent Document 1 and Non-Patent Document). 2). However, the degree of opening of the crack does not necessarily affect the nondestructive inspection signal, and in the non-patent literature, it cannot be said that it is necessarily appropriate as a manufacturing technique for the simulated stress corrosion cracking.

In Non-Patent Document 3 and the cited reference (note), welding should be performed after processing a defect in one of the non-bonding materials or the insert material. Patent Document 2 describes a technique in which a void is formed inside a material by embedding a copper foil in a powder and press-molding it, and then melting the copper foil. However, these techniques still have the problem that it is difficult to simulate partial contact of the fracture surface, which is considered to be the main reason why the signal of stress corrosion cracking is weak.

Non-Patent Document 4 describes a method of manufacturing a simulated defect test body for nondestructive testing by diffusion bonding by forming a hollow portion corresponding to a cylindrical defect of φ6 mm × 0.2 mm. However, in this case, it may be effective as a specimen for welding defects, but the size of the processed defects is enormous, does not fit the “scratches” of simulated stress corrosion cracking, and is not suitable as a simulated defect specimen.

Japanese Patent No. 4055278 Registered Utility Model No. 3041280

R. Clark, et al., “The effect of crack closure on the reliability of NDT predictions of crack size” NDT INTERNATINAL, No. 20, 5 (October 1987) 269-275 Noritaka Yusa, 4 other authors, “Eddy current inspection of closed fatigue and stress corrosion cracks”, MEASUREMENT SCIENCE AND TECHNOLOGY IPO Publishing Ltd (2007 Printed in the UK), No. 18, pages 3403-3408 “Manufacture of simulated defect test specimen for ultrasonic flaw detection test”, Light Metal Welding No. 28 (1990) No. 10, pages 431-438 Matsui Shigeaki and five other authors, "Production of simulated defect specimens for nondestructive testing by diffusion bonding", National Welding Society Annual Performance, Vol. 42, ('88 -4), pages 108-102

The present invention was devised in view of such problems, and a test body that gives a nondestructive inspection signal equivalent to an actual stress corrosion cracking is manufactured at a low cost while quantitatively controlling its properties. It provides technology that makes things possible.

In order to solve the problems described above, the following inventions 1 to 8 are provided.
1. A test in which unevenness is formed in a part of the joining interface of two or more metal test pieces having a joining interface, and then these specimens are solid-phase joined to each other, and a joining part and a contact part region are provided in the joining interface. The contact part region of the metal test piece before joining is composed of irregularities having a roughness Ry of 50 μm or more, and the roughness Ra of the joint part other than the contact part region is 10 μm or less. Characteristic mockup for non-destructive inspection.
2. A test body in which a thin metal having a thickness of 50 μm or more having a through hole is sandwiched between two or more metal test pieces having a bonding interface and solid-phase bonded, and a bonding portion and a contact portion region are provided at the bonding interface. A non-destructive testing specimen for testing, wherein roughness Ra of the joint surface of the test piece and the surface of the metal thin film is 10 μm or less.
3. 3. The simulated specimen for nondestructive inspection as described in 1 or 2 above, which is used for a stress corrosion cracking test.

4). A test specimen for nondestructive inspection in which two or more metal test pieces having a bonding interface are prepared, and irregularities are formed on a part of the bonding interface of the test piece, and then these test pieces are solid-phase bonded to each other. The roughness Ry of the uneven | corrugated area | region which gave the said unevenness | corrugation of the metal test piece before joining shall be 50 micrometers or more, and the roughness Ra of junction parts other than this contact part area shall be 10 micrometers or less. A method for producing a simulated specimen for nondestructive inspection, comprising forming a joint portion and a contact portion region at a joint interface.
5. A method for producing a non-destructive test simulated test body in which a thin metal having a thickness of 50 μm or more having a through hole is sandwiched between two or more metal test pieces having a bonding interface, and the test A method for producing a simulated test specimen for nondestructive inspection, characterized in that a bonding portion and a contact portion region are formed at a bonding interface by setting the roughness Ra of the bonding surface of the piece and the surface of the metal thin film to 10 μm or less.
6). 6. The method for producing a simulated specimen for nondestructive inspection according to 4 or 5 above, wherein the pressure during solid phase bonding is 1 MPa or more, the temperature is 70% or more of the material melting point, and the holding time is 5 minutes or more.
7). 5. The method for producing a simulated specimen for nondestructive inspection according to the above 4, wherein a “flaw” having a predetermined shape is simulated by adjusting the roughness Ry of the region to be uneven and the region to be uneven.
8). 6. The method for producing a simulated specimen for nondestructive inspection according to 5 above, wherein a “flaw” having a predetermined shape is simulated by adjusting a three-dimensional position and a spatial density of the through hole of the metal foil.

The present invention makes it possible to easily, inexpensively and quickly obtain a simulated specimen for nondestructive inspection that has a response close to stress corrosion cracking that occurs in an actual machine, and accurately describes the properties of the intergranular stress corrosion cracking. It has an excellent effect that it can be controlled.

It is a manufacturing procedure of the simulated stress corrosion cracking test body which is embodiment of Claim 1 of this invention. It is a manufacture procedure of the simulation stress corrosion cracking test body which is embodiment of Claim 2 of this invention. It is a microscope picture showing the joining interface of the test body whose roughness Ry is 30 micrometers. It is a microscope picture which shows the joining interface of the test piece whose roughness Ry is 90 micrometers. It is a figure which shows the result represented as a signal on a two-dimensional plane as X signal = Acos ((phi)) and Y signal = Asin ((phi)) using the amplitude A of a sine wave, and the phase difference (phi) with respect to a reference signal.

The simulated specimen for nondestructive inspection according to the present invention comprises two or more metal test pieces having specific joint interfaces. Unevenness is formed in a part of the bonding interface of the test piece. The unevenness is an unevenness having a roughness Ry of 50 μm or more. The roughness Ry can be arbitrarily changed according to the material to be tested. This uneven portion becomes an incompletely bonded region at the bonding interface. When the roughness Ry has an unevenness of 50 μm or more, it can be formed by locally grinding the test piece, but Ry may be formed to an unevenness of 50 μm or more by other processing. The size of the flaw to be simulated is controlled by the width of the uneven region where Ry is 50 μm or more, and the degree of bonding can be controlled by the value of Ry, the smaller Ry is A flaw with a weak signal can be simulated.

On the other hand, the roughness Ra of the joined portion other than the region where the unevenness of the metal test piece before joining is set to 10 μm or less. This is formed by polishing so as to be clearly different from the region where the irregularities are formed. This joined portion is joined firmly during solid phase diffusion, and becomes a joined portion having no void. This simulated specimen for nondestructive inspection is usually suitable as a simulated specimen for stress corrosion cracking, but it goes without saying that it can be applied to a similar simulated specimen for nondestructive inspection.

The stress corrosion crack is a “flaw” generated in an actual machine and is a serious problem in practical use. However, the stress corrosion crack is difficult to detect because the signal at the time of inspection is weak. However, the inspection signal obtained from the region where the roughness Ry of the present invention has a roughness of 50 μm or more approximates to the stress corrosion cracking that occurs in the actual machine, as shown in the test described later, and for nondestructive inspection Ideal for mock specimens.

The test pieces thus prepared are brought into solid-phase bonding after the interfaces are brought into contact with each other so that the portions with roughness Ry of 50 μm or more and the portions with Ra of 10 μm or less face each other. In solid phase bonding, it is desirable that the pressure during bonding is 1 MPa or more, the temperature is 70% or more of the material melting point, and the holding time is 5 minutes or more. However, it goes without saying that the joining conditions can be changed according to the type of the non-destructive test specimen. However, many mock-up specimens for nondestructive inspection meet the above joining conditions.

In addition, a plurality of these test pieces can be simultaneously solid-phase bonded to form a non-destructive test specimen. In addition, it is possible to carry out a plurality of nondestructive inspections at the same time by shifting a part having roughness Ry of 50 μm or more and a part having Ra of 10 μm or less, and thus a small number of specimens. It will be readily appreciated that multiple simulation tests or simulation tests can be performed at

In the following, test examples will be described in detail. FIGS. 3 and 4 show the state of the bonding interface in that case. FIG. 3 shows the bonding interface of a test specimen having a roughness Ry of 30 μm. A thin line can be seen from left to right in the center of the test piece. This is the interface of the diffusion-bonded crystal of the material (test piece). As a result, the interface of this crystal appears as a fine streak.

On the other hand, FIG. 4 shows a bonding interface of a test piece having a roughness Ry of 90 μm. From left to right in the center of the test piece, black thick bar parts (two places) and thin line parts (parts sandwiching the two places) can be seen. The black thick bars are caused by the recesses in the region where Ry 90 μm is processed, and the thin line parts are caused by the projections. In the region of the black thick streaks, many of the interfaces are not joined, and are simply in contact or considered as non-contact portions.

It can be seen that the thickness (width in FIG. 4) of the black thick streak parts (two places) is smaller than the average crystal grain size. A test body in which the minute gaps are intermittently present is an optimum condition as a non-destructive testing simulated test body, particularly a stress corrosion cracking test body.
That is, by adjusting the roughness Ry between the unevenness area and the unevenness area, a “flaw” having a predetermined shape can be simulated.

About the above, although the example which produced the test specimen for a nondestructive inspection locally by the grinder process was shown for the test piece, the thickness which has a through-hole between two or more metal test pieces which have a joining interface It is also possible to produce a test specimen by sandwiching a thin metal having a thickness of 50 μm or more and solid-phase bonding and providing a bonded portion and an incompletely bonded region at the bonded interface. In this case, the roughness Ra of the joint surface of the test piece and the surface of the metal thin film needs to be 10 μm or less.

In this case as well, in the same manner as described above, it is desirable that the pressure during the solid phase bonding is 1 MPa or more, the temperature is 70% or more of the material melting point, and the holding time is 5 minutes or more. In this case, it is possible to simulate a “flaw” having a predetermined shape by adjusting the three-dimensional position and the spatial density of the through hole of the metal foil.

As for the above example, an example using a test piece of stainless steel (SUS316) was shown, but in addition to this, other stainless steel, nickel (including nickel base alloy), titanium (including titanium base alloy), these It can be a non-destructive inspection of a metal material such as a metal or alloy welding material, particularly a simulated specimen for testing stress corrosion cracking.
For nondestructive inspection such as stress corrosion cracking test, for example, ultrasonic nondestructive inspection method, eddy current flaw detection method and the like can be used.

Next, it demonstrates in detail based on an accompanying drawing. Parts common to the drawings use the same reference numerals. FIG. 1 shows an example of an embodiment of claim 1 in the present invention. 11 and 12 are materials constituting the simulated test body, and the simulated stress corrosion cracking test body is created by joining the surfaces 21 and 22 together.
Prior to the bonding, one or both of the surfaces 21 and 22 are provided with a region 31 in which irregularities such that Ry is 50 μm or more are artificially provided, and portions other than the region 31 on the surface 21 and the surface 22 are defined as Ra. Is smoothed so as to be 10 μm or less.

Thereafter, compressive stress is applied to the joint portions of 11 and 12, and the whole is kept under high temperature and high pressure to bond the portions 11 and 12 by solid phase joining. As a result, incomplete adhesion occurs in the region 31 with the unevenness, and complete adhesion occurs in the region 32 where the unevenness is not applied, and the characteristics of partial contact that the stress corrosion cracking has can be simulated. By arbitrarily setting the region 31, it is possible to simulate a “flaw” having a shape having a desired length, depth, and contour shape.

FIG. 2 shows an example of an embodiment of claim 2 in the present invention. 11 and 12 are materials constituting the mock specimen, and 13 is the same material as 11 and 12 having a thickness of 50 μm or more. Prior to bonding, the surfaces 21 and 22 and the surface where the material 13 is bonded to the surfaces 21 and 22 are smoothed so that the roughness Ra is 10 μm or less, and the material 13 has an arbitrary shape. The through hole 41 is processed. Thereafter, compressive stress is applied to the joints of 11, 12, and 13 and the whole is kept under high temperature and high pressure to be bonded by solid phase bonding.

Thereby, the non-contact area | region which has a three-dimensional shape according to the shape of the through-hole 41 is formed in the inside of a material, and the simulated test body of stress corrosion cracking can be manufactured. At that time, by arbitrarily setting the shape of the through hole 41 and the thickness of the material 13, it is possible to simulate a “flaw” having a shape having a desired length, depth, and contour shape.
In the figure, the number of the materials 13 is five, but this is not limited to five, and it goes without saying that the shape of the through-hole 41 to be processed does not have to be the same in all the materials 13.

In the present embodiment, the block material is used as the material for manufacturing the simulated test body. However, the material is not limited to the block material, and may be a flat plate or a tube. Needless to say.

In addition, a diagram assuming diffusion bonding was used for bonding, but this does not mean that the solid-phase bonding used is limited to diffusion bonding. For example, in the production of a test body having a large or complicated shape, HIP bonding is used. It is possible to apply other solid phase bonding, but the important point in the present embodiment is that the bonding surface is processed before the solid phase bonding. It follows technology. That is, for example, if HIP bonding is applied, it goes without saying that a procedure corresponding to each bonding method is added, such as encapsulating a material in a capsule.

Next, examples will be described. This embodiment facilitates understanding of the invention, and the present invention is not limited to this embodiment. The present invention is based on the technical idea described in the specification, and includes all contents described in the specification developed around this technical idea.

Example 1
The test piece shown in FIG. 1 was produced. That is, 11 and 12 are materials constituting the mock specimen, and are joined by the surfaces 21 and 22. A stainless steel (SUS316) is used as the test piece, and a simulated stress corrosion cracking specimen is produced.
Prior to the bonding, regions 31 on which surface irregularities having Ry of 90 μm were artificially formed were provided on both the surface 21 and the surface 22. The unevenness was roughened by a grinder, and Ry was 90 μm. The region 31 was provided such that the length of the incompletely joined portion after joining was 10 mm and the depth was 5 mm. On the other hand, on the surface 21 and the surface 22, the portions other than the region 31 were smoothed so that Ra becomes 1 μm or less by polishing with a buff.

Next, a compressive stress of about 10 M Pascal is applied to the joints of 11 and 12, and the whole is held at a high temperature (temperature: about 1000 ° C.) for about 60 minutes, so that the joint surfaces 11 and 12 are solid-phased. Bonded by bonding.
As a result, incomplete adhesion occurred in the region 31 with the unevenness, and complete adhesion occurred in the region 32 where the unevenness was not applied, and the characteristics of partial contact of stress corrosion cracking could be simulated. This is shown in FIG.

By joining under the above diffusion joining conditions, it was possible to see black thick streak portions (two places) and thin line portions (parts sandwiching the two places) from left to right in the center of the test piece. The thin line portion is the interface of the crystal (material) of the material (test piece) that is diffusion-bonded, and the black thick bars (two points) are non-bonded portions that are simply in contact or non-contact portions.
Under the above-described diffusion bonding conditions, because of the bonded portions, the contact portions of the black thick bars that are simply in contact or non-contact portions (two locations) did not progress further.

The thickness (width of FIG. 4) of the black thick streak portions (two locations) was smaller than the average crystal grain size. The test specimen in which the minute gaps intermittently exist became optimum conditions as a non-destructive test simulation specimen, particularly a stress corrosion cracking specimen.
In other words, by adjusting the roughness Ry between the uneven area and the uneven area, it was possible to simulate a “flaw” having a predetermined shape.
On the other hand, FIG. 3 shows a state in which the same test is performed with the roughness Ry of the region 31 being 30 μm. Compared with the result when Ry is 90 μm, the black thick streaks described above cannot be confirmed, and it can be confirmed that the entire interface is bonded.

Next, an eddy current flaw test was carried out using the simulated specimen for nondestructive inspection. The result is shown in FIG. FIG. 5 shows the result expressed as a signal on a two-dimensional plane using the amplitude A of the sine wave and the phase difference φ with respect to the reference signal as X signal = A cos (φ) and Y signal = Asin (φ). It is a figure (refer TEST PIECE).
For comparison, signals obtained by performing the same test on a rectangular artificial slit having a length of 10 mm, a depth of 5 mm, and a width of 0.3 mm processed by electric discharge machining are also shown in FIG. (See EDM, 5 mm).

As shown in FIG. 5, the phase angle of the flaw detection signal from the mock specimen and the flaw detection signal from the slit are substantially the same. Usually, in the eddy current flaw detection method, the phase angle of the signal represents the depth of the “scratch”, which means that the depth of the “scratch” contained in the simulated specimen is almost equal to the depth of the artificial slit. This shows that the “flaw” of the expected shape was introduced into the mock specimen.

However, although the size of the “flaw” contained in the fabricated test specimen is almost the same as that of the rectangular artificial slit, the signal amplitude is about one-tenth that of the artificial slit. It can be confirmed.
In general, since the flaw detection signal from stress corrosion cracking is about one-tenth to one-tenth of a slit having the same size, in this test, the X signal when an actual stress corrosion cracking test is performed = It can be said that a result consistent with Acos (φ), Y signal = Asin (φ) could be obtained.

However, the amplitude A depends on the amplitude of the input signal, the amplification factor of the flaw detector, etc., and φ also differs depending on what is used as the reference signal. Normally, these values are appropriately set so that the signal can be easily seen at the time of flaw detection. However, since it is difficult to give strict physical meaning to φ in the first place, the deviation from the reference signal is measured.
Therefore, in this test, it was possible to obtain a result consistent with X signal = A cos (φ) and Y signal = A sin (φ) in the actual stress corrosion cracking test. It can be said that it is proof that it is useful as a specimen.

In the above, a simulated stress corrosion cracking test specimen in which stainless steel (SUS316) is used as a test piece, and a region 31 in which irregularities having Ry of 90 μm are artificially provided on both the surface 21 and the surface 22 is provided. In the example shown in FIG. 2, similar results can be obtained.

That is, in this example, 11 and 12 are materials constituting the mock test specimen, and 13 is the same material as 11 and 12 having a thickness of 50 μm or more. The surfaces 21 and 22 and the surface where the material 13 is joined to the surfaces 21 and 22 are smoothed so that the roughness Ra is 10 μm or less. Further, the material 13 is processed with a through hole 41 having an arbitrary shape.

Thereafter, compressive stress is applied to the joints of 11, 12, and 13 and bonded by solid phase bonding under the same conditions as in Example 1 above.
Thereby, the non-contact area | region which has a three-dimensional shape according to the shape of the through-hole 41 is formed in the inside of a material, and the simulated test body of stress corrosion cracking can be manufactured.

According to the present invention, it is possible to easily and inexpensively obtain a non-destructive inspection simulated test body that has a response close to stress corrosion cracking occurring in an actual machine, and to accurately control the properties of the intergranular stress corrosion cracking. Therefore, it is possible to greatly contribute to improving the skills of non-destructive inspectors and evaluating the performance of non-destructive inspection devices.

11: Material constituting the simulated stress corrosion cracking specimen 12: Material constituting the simulated stress corrosion cracking specimen 13: Material constituting the simulated stress corrosion cracking specimen 21: Material 11 constituting the simulated stress corrosion cracking specimen One side 22: One side 31 of the material 12 constituting the simulated stress corrosion cracking specimen: A region 41 artificially provided with a roughness of Ry of 50 μm or more 41: A through-hole processed into the material 13

Claims (8)

A test in which unevenness is formed in a part of the joining interface of two or more metal test pieces having a joining interface, and then these specimens are solid-phase joined to each other, and a joining part and a contact part region are provided in the joining interface. The contact part region of the metal test piece before joining is composed of irregularities having a roughness Ry of 50 μm or more, and the roughness Ra of the joint part other than the contact part region is 10 μm or less. Characteristic mockup for non-destructive inspection. A test body in which a thin metal having a thickness of 50 μm or more having a through hole is sandwiched between two or more metal test pieces having a bonding interface and solid-phase bonded, and a bonding portion and a contact portion region are provided at the bonding interface. A non-destructive testing specimen for testing, wherein roughness Ra of the joint surface of the test piece and the surface of the metal thin film is 10 μm or less. The simulated specimen for nondestructive inspection according to claim 1 or 2, which is used for a stress corrosion cracking test. A test specimen for nondestructive inspection in which two or more metal test pieces having a bonding interface are prepared, and irregularities are formed on a part of the bonding interface of the test piece, and then these test pieces are solid-phase bonded to each other. The roughness Ry of the uneven | corrugated area | region which gave the said unevenness | corrugation of the metal test piece before joining shall be 50 micrometers or more, and the roughness Ra of junction parts other than this contact part area shall be 10 micrometers or less. A method for producing a simulated specimen for nondestructive inspection, comprising forming a joint portion and a contact portion region at a joint interface. A method for producing a non-destructive test simulated test body in which a thin metal having a thickness of 50 μm or more having a through hole is sandwiched between two or more metal test pieces having a bonding interface, and the test A method for producing a simulated test specimen for nondestructive inspection, characterized in that a bonding portion and a contact portion region are formed at a bonding interface by setting the roughness Ra of the bonding surface of the piece and the surface of the metal thin film to 10 μm or less. 6. The method for producing a simulated specimen for nondestructive inspection according to claim 4 or 5, wherein the pressure during solid-phase bonding is 1 MPa or more, the temperature is 70% or more of the material melting point, and the holding time is 5 minutes or more. The method for producing a simulated specimen for nondestructive inspection according to claim 4, wherein a “flaw” having a predetermined shape is simulated by adjusting the roughness Ry between the unevenness area and the unevenness area. 6. The method for producing a simulated specimen for nondestructive inspection according to claim 5, wherein a "flaw" having a predetermined shape is simulated by adjusting a three-dimensional position and a spatial density of the through hole of the metal foil.