CN102692373A - Stress corrosion sensitivity evaluation device based on small punch rod test technology - Google Patents

Abstract

The invention relates to a stress corrosion susceptibility evaluation device based on a small punch test technology, which comprises a cylinder, a fixture arranged in the cylinder to clamp a sample to be tested, and placed on the sample There is a cavity inside the clamp, one end of the internal cavity of the clamp communicates with the inner cavity of the cylinder, and the other end communicates with the sample to be tested. By using this device, combined with a specific sampling device, a nearly non-destructive and rapid stress corrosion resistance evaluation can be performed on in-service equipment, which can effectively solve the difficult problem of stress corrosion sensitivity evaluation of small samples and single-sided processed samples. . The present invention has been tested by a large number of experiments, the data is stable and reliable, the test period is short (ranging from several hours to tens of hours), and it is faster and more reliable than the slow stretching method. The device is simple, easy to manufacture and process, convenient to store and install, convenient to operate and good in controllability.

Description

Stress Corrosion Sensitivity Evaluation Device Based on Small Punch Test Technology

technical field

The invention relates to a stress corrosion sensitivity evaluation device, in particular to a stress corrosion sensitivity evaluation device based on a small punch test technology.

technical background

There are a large number of long-term service stainless steel components in the chemical and nuclear power industries. After long-term operation in harsh environments such as high temperature, high pressure and radiation, stainless steel components will inevitably experience various failures, of which stress corrosion cracking accounts for a large proportion. Therefore, how to correctly and quickly evaluate the stress corrosion cracking resistance of in-service components has become a topic of widespread concern. Because it is necessary to ensure that service components can be sampled and tested without stopping the vehicle, a new testing technology is needed to quickly evaluate the performance of stress corrosion cracking (Stress Corrosion Cracking, hereinafter referred to as SCC) on tiny samples. Small Punch Test (SPT) Technique is a new effective and economical safety detection method gradually developed in the early 1980s. It is a kind of "non-destructive sampling" and accurate reliability. new test method. SPT uses the punch to stamp the sample sheet at a certain speed, records the load-displacement (deformation deflection) data of the test piece from deformation to failure, and analyzes and obtains various performance parameters of the material. Today, this technology has been widely used to evaluate the conventional mechanical properties and creep properties of materials. However, it is still rare to be used to evaluate the stress corrosion resistance of materials. A large number of experiments have proved that with special sampling devices, it is completely possible to evaluate its stress corrosion resistance without stopping production.

Since the stress corrosion cracking research was carried out in the last century, a wide variety of sample types and corresponding testing machines have emerged, as well as various standard test methods. Different samples have different test purposes, some are only for testing the susceptibility of stress corrosion cracking; some require measuring the stress corrosion crack growth rate da/dt; some also require measuring the critical stress of stress corrosion cracking σ _c , while some require the initial value of stress intensity factor K _ISCC (also a critical value) of stress corrosion. The existing test methods for stress corrosion cracking generally fall into the following categories:

(1) Stress corrosion cracking test under constant displacement. The processed sample first obtains a certain amount of pre-deformation (displacement), and then the strain (displacement) is fixed with a clamp, and placed in a corrosive environment for any It cracks and expands, and the deformation (displacement) of the specimen is fixed throughout the test. This stress generation test method does not need any testing machine, not only can be used in the laboratory, but also can be used for hanging piece test on site, and it is convenient for both parties. There are many types of samples for this kind of constant displacement stress corrosion cracking test, such as C-shaped ring, U-shaped, three-point bending, four-point bending (pure bending), stress ring and other samples. The current status of the samples is shown in Figure 1.

(2) WOL sample This is evolved from the compact tensile sample (CT sample) of fracture mechanics and is used to test the stress corrosion crack growth rate da/dt and the critical stress intensity factor K _ISCC value of stress corrosion cracking in a corrosive environment of samples. See Figure 2.

(3) Stress corrosion cracking test under constant load The tensile sample is suspended on a tensile testing machine loaded with weights, and the tensile sample must be immersed in a sealed corrosive medium environment box. Or use a cantilever beam sample, one end of which is horizontally clamped on the chuck of the fixed frame, the tested part of the sample is immersed in a sealed corrosive medium environment box, and the other end of the cantilever is hung with a weight to load. Generally, there is a notch in the center of the cantilever beam sample. Figure 3a, 3b.

(4) Constant strain rate slow tensile test method This method uses a special round bar-shaped tensile sample or plate-shaped sample, both ends of which are clamped on a special tensile testing machine, and an environmental chamber with a corrosive medium on the sample coat , maintaining a constant and slow strain rate while loading. If the material to be tested has a tendency of stress corrosion in this medium, stress corrosion cracks will be initiated and expanded during the continuous plastic strain deformation process, and it is best to promote the fracture of the sample. The characteristic of this test method is mainly to artificially apply continuous slow plastic strain to the sample, and keep the strain rate constant. If stress corrosion cracking occurs, the fracture of the final sample is a macroscopic brittle fracture. If stress corrosion cracking does not occur, a plastic fracture with obvious necking is finally formed after a considerable plastic strain. This test is also referred to as the "slow tension" test, and is considered to be a reliable rapid test method for stress corrosion cracking. The results are accurate and reliable, and it has high sensitivity to stress corrosion tests. quick filter. A standard test method has now been established. See Figure 4.

Contents of the invention

In order to overcome the problem of quickly evaluating the SCC resistance of in-service equipment without stopping production, the present invention provides a device for quickly evaluating the SCC sensitivity of materials based on the small punch test method. The specific technical solution is as follows:

A stress corrosion susceptibility assessment device based on small punch test technology, comprising a cylinder, a fixture arranged in the cylinder to hold a sample to be tested, and a pressure device placed on the sample, There is a cavity inside the clamp, one end of the internal cavity of the clamp communicates with the inner cavity of the cylinder, and the other end communicates with the sample to be tested.

Further, the clamp includes an upper clamp disposed above the sample to be tested and a lower clamp disposed below the sample to be tested, and the inner cavity of the clamp is disposed in the lower clamp.

Further, the inner cavity of the lower clamp body includes a horizontal through hole penetrating through the lower clamp, and a vertical hole communicating with the horizontal through hole and penetrating the upper surface of the lower clamp.

Further, the outlet of the vertical hole is designed with rounded corners, the diameter of the horizontal through hole is 8-12mm, the vertical hole is 4mm and has a rounded corner of R=1 or 0.5mm. In fact, the bigger the better, that is In order to allow the solution to contact the sample, the transverse through hole is designed so that the corrosion solution can always be filled around the test surface of the sample to be tested and fully contact with the sample to be tested.

Further, the pressure applying device is in contact with the sample to be tested through the clamp, and the pressure applying device includes a load pressure head and a pressure rod extending therefrom so as to apply pressure to the sample to be tested, and the pressure rod is the same as A steel ball is arranged between the samples to be tested, and its diameter is adapted to that of the pressing bar. Both the diameter of the steel ball and the pressure rod are 2.5mm and their hardness value shall not be lower than HRC55. The material selection should consider that it has better corrosion resistance.

Further, the device is provided with a top cover, which is provided with a through hole leading to the load pressure head and a hole for connecting a thermometer and a condensation pipe, and a heating control device is provided outside the device to control the temperature in the inner cylinder. temperature.

Further, the size of the sample to be tested is a small disc with a diameter of 10mm and a thickness of 0.5±0.01mm.

The beneficial effects of the present invention are:

This device uses the principle of small punch test technology to develop a device for evaluating the performance of SCC. The device is equipped with a small punch fixture in the cylinder, which is connected with the cylinder cavity and the sample to be tested, and supplemented by The pressure applying device realizes the rapid detection of SCC performance, and because it requires a small sample, it solves the problem of testing the in-service components without stopping production.

Specifically, the present invention designs a reasonable device and technical solution, which can be used in conjunction with a specific sampling device to perform nearly non-destructive and rapid stress corrosion resistance evaluation on in-service equipment. It can effectively solve the difficult problem of stress corrosion susceptibility assessment of tiny samples and single-sided treated samples.

Moreover, the technical solution has been tested by a large number of experiments, the data is stable and reliable, and the test period is short (ranging from several hours to tens of hours), which is faster and more reliable than the slow stretching method. The device is simple, easy to manufacture and process, convenient to store and install, convenient to operate and good in controllability.

Description of drawings

Figure 1 is a schematic diagram of a constant displacement stress corrosion cracking test specimen, Figure 1a is a C-ring specimen, Figure 1b is a U-ring specimen, Figure 1c is a stress ring specimen, Figure 1d is a three-point bending specimen, and Figure 1e A four-point bending specimen.

Figure 2 is a schematic diagram of the WOL sample.

Figure 3a is a schematic diagram of a round bar tensile stress corrosion cracking specimen.

Figure 3b is a schematic diagram of the stress corrosion cracking test of a rectangular cross-section cantilever beam.

Figure 4 is a schematic diagram of a constant strain rate slow tensile sample.

Fig. 5 is the general assembly drawing of the small punch method stress corrosion test device.

Fig. 6 is an enlarged view of the assembly of the small punch clamp in Fig. 5 .

Figure 7 is a schematic diagram of a small punch sample.

Fig. 8 is a sectional view of the clamp on the small punch.

Fig. 9 is a section and a top view of the lower jig of the small punch.

Fig. 10 is a top view of the top cover and a schematic sectional view of A-A.

Fig. 11 is the load-displacement curve of the small punch obtained by applying the device of the present invention.

Description of reference symbols

In Fig. 2, l is the gap opening displacement measurement point.

In Figure 3a/Figure 3b, 01 is the environmental chamber, 02 is the cantilever beam test/tensile sample, and 03 is the weight.

In Figure 4, 01 is the environmental chamber, 02 is the tensile sample, 04 is the upper chuck of the tensile testing machine, and 05 is the lower chuck of the tensile testing machine.

In Figure 5, 1 is the load pressure head, 2 is the temperature measuring hole, 3 is the condensation hole, 4 is the top cover, 5 is the pressure rod, 6 is the upper fixture, 7 is the heating temperature control device, 8 is the steel ball, and 9 is the waiting For the test sample, 10 is the lower clamp, 11 is the cylinder, 12 is the boss of the base, 13 is the vertical hole, and 14 is the horizontal through hole.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention should not be limited thereby.

Please refer to Figures 5 to 6, which are schematic diagrams of the principle of this embodiment. The evaluation device includes a cylinder body 11, a top cover 4, and a clamp arranged in the cylinder body for clamping the sample 9 to be tested, specifically including An upper clamp 6 and a lower clamp 10, and a pressure applying device placed on the sample 9 to be tested. The sample 9 to be tested is clamped between the upper jig 6 and the lower jig 10 . The pressure applying device includes a load pressure head 1 passing through the top cover 4 and an extended pressure rod 5 , and a steel ball 8 is arranged between the pressure rod 5 and the sample 9 to be tested. There is a cavity inside the fixture. In this embodiment, the cavity is arranged inside the lower fixture 10 and consists of a transverse through hole 14 penetrating through the lower fixture 10 and a vertical hole 13 passing through the upper surface of the lower fixture 10. The transverse through hole The outlets at both ends of 14 communicate with the inner cavity of the cylinder 11, and the outlets of the vertical holes 13 communicate with the sample 9 to be tested, so that the corrosion solution can always be filled around the test surface of the sample. The exit of the vertical hole 13 is also designed with a chamfer in order to obtain stable experimental results and optimize the stressed state of the sample. The top cover 4 of the device is provided with a through hole leading to the load pressure head 1 and a hole 3 for connecting the thermometer hole 2 and the condensation pipe, and a heating control device 7 can be provided outside the device to control the temperature in the inner cylinder. temperature. In this embodiment, the fixture is embedded and fixed through a base protrusion 12 fixed at the bottom of the cylinder 11 .

Please refer to Figures 7 to 10, which are schematic diagrams of the optimal specific size and structure of sample 9, fixture and top cover 4 in this embodiment. Sample 9 to be tested is a small disc with a diameter of 10 mm and a thickness of 0.5 ± 0.01 mm. , the diameter of the steel ball and the pressure rod is 2.5mm and its hardness value shall not be lower than HRC55. The horizontal through hole of the lower fixture 10 is designed to be 10mm in diameter, and the central vertical hole 14 is selected to be 4mm and rounded with a radius of 1mm. After testing , A fillet with a radius of 0.5mm can also achieve the same good process effect.

The small punch method stress corrosion test device of the present invention can be installed on an existing universal testing machine (that is, a tensile testing machine) to realize loading.

During specific implementation, the cylindrical body 11 is first fixed on the lower chuck of the universal testing machine. To further assemble the small punch mold, first place the sample 9 on the base boss 12 of the lower fixture 10, then cover the upper fixture 6 and fasten it with bolts, and then put in the steel ball 8 and the pressure rod in sequence from the center through hole of the upper fixture 5. Further, the assembled small punch mold is placed on the base boss 12 of the fixed cylinder. The corrosive medium is further injected, and the height of the medium should be higher than the lower clamp 10 of the small punch to ensure that the sample is always immersed in the environmental medium during the experiment. Further, the top cover 4 and the cylinder body 11 are fixed with bolts. Further install the load indenter 1 on the upper fixture of the universal testing machine and approach the small punch bar through the center hole of the top cover in a clearance fit manner. If the corrosive liquid has a temperature requirement, a heating and temperature control device 7 can also be connected to the outside of the cylinder 11. At the same time, a temperature measuring hole 2 can be opened on the top cover as needed, and the thermometer is embedded in the cork and the latter is wrapped with a sealing tape. Then plug it into the hole for temperature measurement to prevent the solution from volatilizing in large quantities in the temperature measurement hole. The condensation tube is wrapped with polytetrafluoroethylene tape and then plugged into the condensation hole 3 for condensation and reflux to ensure that the concentration of the solution in the cylinder remains constant. If the solution has no temperature requirements and is not volatile, it is not necessary to install a top cover and a heating temperature control device.

The loading process is achieved by clamping the load head of the universal tensile testing machine and pressing it downward. For the assessment of the stress corrosion susceptibility of the small punch method, the drop rate of the load head should be controlled at 10 ^-2 ~ 10 ^-5 mm/min , which has a faster test speed than the traditional slow stretching method.

Please refer to Figure 11, which is the load-displacement curve of the small punch obtained under the premise of using the device of the present invention and the aforementioned experimental method. The specific experimental conditions are: the sample to be tested is 304L stainless steel in air and 1mol/L NaCl+0.5mol/L HCl solution The conventional mechanical property test and the SCC sensitivity test were respectively carried out in the test at a rate of 3×10 ^-3 mm/min, and the test temperature was room temperature. It can be clearly found that the device and technical scheme can effectively and quickly evaluate the anti-SCC performance of the material, and has good data repeatability.

In summary, the above are only preferred embodiments of the invention, and are not intended to limit the implementation scope of the invention. That is, all equivalent changes and modifications made according to the content of the patent scope of the present invention shall be within the technical scope of the present invention.

Claims (10)

1. A stress corrosion susceptibility assessment device based on small punch test technology, comprising a cylinder, a fixture arranged in the cylinder for clamping the sample to be tested, and placed on the sample to be tested The pressure applying device is characterized in that there is a cavity inside the clamp, one end of the internal cavity of the clamp communicates with the inner cavity of the cylinder, and the other end communicates with the sample to be tested. 2. The stress corrosion sensitivity evaluation device according to claim 1, wherein the clamps include an upper clamp arranged above the sample to be tested and a lower clamp below the sample to be tested respectively, and the internal cavity of the clamp is The body is set in the lower fixture. 3. The stress corrosion susceptibility assessment device according to claim 2, characterized in that, the inner cavity of the lower fixture comprises a transverse through hole passing through the lower fixture, and communicates with the transverse through hole to pass through the upper surface of the lower fixture vertical holes. 4 . The stress corrosion sensitivity assessment device according to claim 3 , wherein the diameter of the horizontal through hole is 8-12 mm, and the diameter of the vertical hole is 4 mm. 5. The stress corrosion susceptibility assessment device according to claim 3, characterized in that the outlet of the vertical hole is designed with rounded corners. 6 . The stress corrosion sensitivity assessment device according to claim 4 , wherein the fillet is a fillet with a radius of 1 or 0.5 mm. 7. The stress corrosion susceptibility evaluation device according to claim 1, characterized in that, the pressure applying device passes through the clamp and is in contact with the sample to be tested, and the pressure applying device comprises a load indenter and its extension , In order to apply pressure to the sample to be tested, a steel ball is arranged between the pressure rod and the sample to be tested. 8. The stress corrosion sensitivity evaluation device according to claim 7, characterized in that the diameters of the pressure rod and the steel ball are 2.5mm. 9. The stress corrosion sensitivity assessment device according to claim 1, wherein the device is provided with a top cover, the top cover is provided with condensation holes and temperature measuring holes, and a heating control device is provided outside the device To control the temperature inside the cylinder. 10 . The stress corrosion sensitivity evaluation device according to claim 1 , wherein the size of the sample to be tested is a small disc with a diameter of 10 mm and a thickness of 0.5±0.01 mm. 11 .

Images