Research on simulation technology and internal qua

Research on simulation technology and internal quality control of large forgings

before leaving the factory, large forgings are required to be inspected not only for mechanical properties and grain size, but also for ultrasonic flaw detection, especially for nuclear power forgings, tndt (non ductile transition temperature) analysis is also required. Although the steel smelting technology has developed rapidly, its smelting and solidification characteristics determine that there are inevitably inclusions and grains with different sizes and orientations in the ingot, and with the increase of the ingot, the inclusions and coarse grains will be more obvious. Therefore, the change of inclusions and grain boundaries is still an important reason for the scrapping of large forgings. In-depth study of its change and influence law plays an important role in improving product quality

therefore, the high temperature, three-dimensional and dynamic simulation technology represented by moire method was explored to save auxiliary experimental time, and the deformation law of large forgings, the damage and repair mechanism of internal defects, the grain structure control process were studied, and the prototype of the control forging theory was put forward. Many production problems have been solved, especially the nuclear power heavy forgings with international advanced level

1 simulation technology and analysis and testing methods

large forgings are mostly single piece production, with complex production process, long cycle and high cost, so they are not suitable for physical research to obtain quality control theory, basic laws, etc. Using simulation technology to study the quality control law of large forgings is currently recognized as one of the most effective methods [1]

high temperature moire method can be used to simulate the production process of large forgings. Using the ion bombardment method, the moire grating plate is made directly on the surface of steel specimens, with a resolution of 0.05mm and a high temperature resistance of 1250 ℃. In the thermal simulation furnace, the specimen deforms according to the needs, and the image analysis system dynamically collects the field data, which solves the technical problems of high temperature and micro analysis deformation. In the process of plastic deformation, the change process of nondestructive testing internal defects of materials with acoustic microscope is discussed, and satisfactory results are obtained. Through computer numerical analysis technology to simulate the change process parameters of defects, the three-dimensional dynamic change law of internal defects of materials can be obtained

at present, he has mastered the high-temperature moire simulation technology, the problem of using acoustic microscope to detect and computer to limit the dimensionality of chromatographic peaks, the development and change process of non-destructive detection and analysis of internal defects of materials, and the numerical simulation research method of ingot solidification, forging and heat treatment. Integrating the above research methods can be used to study the development and change process of internal defects of materials under high temperature, three-dimensional and dynamic deformation conditions, and obtain quality control forging rules

2 the deformation distribution law of forgings

the deformation distribution law in cake, can body and shaft forgings is systematically studied by physical simulation method [2]. It is found that during the deformation process, due to the effect of boundary friction, there is no obvious transition zone between the large deformation zone and the rigid zone, and a severe shear deformation zone is formed between the two zones; With the increase of deformation, the internal stress of the material will change after large deformation in the deformation area. When the deformation continues to increase, the shear band begins to move and causes the rigid zone to enter the plastic state layer by layer. Under the above conditions, combined with the existence of inclusions and coarse grain boundaries, cracks are very easy to occur at inclusions and grain boundaries. For example, in the process of upsetting, the deformation in the shear band between the rigid area in contact with the anvil surface and the large deformation area in the middle part is very intense. When the deformation reaches a certain value, the original rigid area begins to deform, resulting in a sharp increase in load, which often leads to defect expansion. Similar phenomena also exist in the deformation process of module, can body and shaft forgings. The distribution of micro deformation at defects such as inclusions and cavities is studied by moire method. It is proved that the morphology of defects directly affects the degree of stress concentration. The combined action of shear deformation and local stress of defects leads to the fracture of metal matrix between defects. Small inclusions are connected through cracks, and then inclusions squeeze into cracks until larger inclusion cracks are formed, which is one of the important reasons for exceeding the standard of flaw detection. With this method, the cause of the formation of the defects in the central entrapment layer of cake forgings can be satisfactorily explained, and the theoretical basis for eliminating such defects is laid

inclusion morphology and grain boundary condition directly affect the usability of large forgings. The operation of each machine is based on technical parameters. Unreasonable defect distribution is likely to become a major hidden danger of sudden failure of large forgings in the process of use. Although the current inspection standards can not make a scientific evaluation, the deformation characteristics should be fully used to ensure the reasonable distribution of defects in the forging process. Studying the deformation distribution law can effectively solve the problem of cavity compaction, and provide process parameters for deformation control of grain size and production of composite forgings

3 damage and repair law of internal defects in materials

in the forging process, the inclusions and coarse grain boundaries in large forgings are the causes of material damage. The study on the deformation behavior of inclusions and its influence on the deformation of metal matrix shows that there are three forms of crack generation with the increase of temperature in the temperature range of 800 ℃ ~ 1200 ℃: ① voids are formed in the matrix at the inclusion, and the voids grow until they converge; ② The inclusion separates from the matrix to form a cavity, and then extends to the matrix along the interface until fracture; ③ The crack initiated at the grain boundary and propagated along the grain boundary to fracture. Based on this, the physical model of inclusion crack aggregation is proposed, and the meso damage mechanics model and criterion are proposed in combination with the deformation law. The coarse grain boundary is very easy to cause cracks and damage in the deformation process, and its law and mechanism need to be further studied. The energy used accounts for about 12% of the total energy consumption of the national economy

high temperature repair is a new phenomenon found in production practice. When the mechanism is not clear, the forgings such as large tubesheets, modules and rotors that have been proved to be scrapped by flaw detection have been repaired, and remarkable economic benefits have been achieved

above the recrystallization temperature, the repair process mainly consists of the diffusion and migration of atoms in the matrix metal at the crack interface to the crack cavity and grain growth