A method and device for improving the accuracy of ndt test results

Abstract

The present invention relates to a method and its device for NDT testing of metallic materials, in particular to a method and device for improving the accuracy of NDT test results. Processing crack source, test piece cooling and drop weight test, in the step of surfacing welding crack source weld bead, the present invention is to let each side and the bottom surface of the test piece on the test piece groove directly contact with the cooling liquid, and then put it on the test piece The crack source weld bead is surfacing on the upper part; the device includes a cooling liquid, a cooling box, and a test piece tank, and the cooling liquid outlet and the cooling liquid inlet are respectively arranged on the cooling box for the cooling liquid to enter and exit. The cooling box is a non-closed structure. There are through holes on the side wall and / or bottom of the tank body of the test piece, and the through holes communicate with the cooling box through the cooling liquid; the device has high cooling efficiency, strong stability, and minimizes the area affected by welding temperature rise .

Description

technical field [0001] The invention relates to a method and a device for NDT testing of metal materials, in particular to a method and a device for improving the accuracy of NDT test results. Background technique [0002] According to the applicant's understanding, the toughness of ferritic structural steel decreases with the decrease of temperature. When the temperature drops to a certain value, it reaches a critical point. At this time, the fracture is completely crystalline and brittle. This temperature is called no plastic transition. The nil-ductility transition temperature (NDT) is the highest temperature that characterizes the brittle fracture of steel containing small cracks under dynamic loading yield stress; the non-plastic transition temperature of the material can be determined by the drop weight test method. Use the temperature to obtain the maximum crack size allowed to prevent brittle fracture under the design stress, or obtain the minimum stress for brittle ...

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Problems solved by technology

[0002] According to the applicant's understanding, the toughness of ferritic structural steel decreases with the decrease of temperature. When the temperature drops to a certain value, it reaches a critical point. At this time, the fracture is completely crystalline and brittle. This temperature is called no plastic transition. The nil-ductility transition temperature (NDT) is the highest temperature that characterizes the brittle fracture of steel containing small cracks under dynamic loading yield stress; the non-plastic transition temperature of the material can be determined by the drop weight test method. Use the temperature to obtain the maximum crack size allowed to prevent brittle fracture under the design stress, or obtain the minimum stress for brittle fracture from the crack size; the drop weight test is to surfacing the weld bead on the tensile surface of the sample and Open a notch, the brittle weld bead causes several microcracks in the base metal as the source of crack initiation; during the test, brittle cracks are generated under loading at a certain temperature, if the cracks do not extend to one side of the sample, it is considered that the sample is not cracked, continue Cool down until such a temperature is found, at which the crack spreads to one or both sides of the sample, it is considered "fracture"; therefore, the non-plastic transition temperature belongs to the crack arrest temperature, and its essence is that the material is brittle under dynamic load conditions. The highest breaking temperature is a parameter to evaluate the crack arrest characteristics of materials; usually, materials with different structures have different NDT temperatures, so ensuring that the structure of the test piece is consistent with the product body is a necessary prerequisite for accurate NDT temperature measurement; however, When surfacing the crack source weld bead, due to the high temperature generated by welding, the vicinity of the weld bead reaches a temperature close to melting, and the structure of the specimen will inevitably grow

If the welding parameters are not properly controlled, the range of the welding heat-affected zone will be very large, resulting in coarsening of the structure in a large range and deteriorating NDT performance

In addition, if the cooling rate of the test piece is not controlled during surfacing welding, due to the influence of human factors and environmental factors, the size and cooling rate of the heat affected zone of the test piece will be different each time surfacing welding, and the obtained tissue type And the grain size is also different, so the measured NDT temperature is also different, resulting in unstable NDT test results

These factors will affect the accuracy of the test results, resulting in misjudgment of the performance of the steel

[0003] Patent No. CN101017124A discloses a method and device for measuring the non-plastic transition temperature. The device provided by this patent is the cooling device commonly used at present. The device uses an indirect cooling method to indirectly cool the specimen placed on the base plate by cooling the base plate. This cooling method has the following disadvantages: 1. The cooling efficiency of this cooling method is low, and it takes a long time to reach the expected cooling temperature; 2. Due to Most of the specimens are exposed to the ambient temperature and are easily affected by the ambient temperature; 3. The local high temperature diffuses quickly during welding, and this cooling method cannot suppress the increase in temperature, and the range of microstructure coarsening inevitably increases

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