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Machinability of Niobium

Niobium can have different microstructures in different states (such as as cast, processed, annealed, sintered, etc.), so its mechanical properties are significantly different. For example, at room temperature, the tensile strength of the cold worked state is 550~689MPa, and the elongation rate is 5%~15%; after heat treatment, the tensile strength of the annealed state is 310~379MPa, and the elongation rate is 15%~40%. The mechanical properties change greatly before and after heat treatment, and the machinability of the material will inevitably vary greatly. Among the three experimental methods for testing sheet metal forming performance, one of the metallurgical laboratories, the crystalline orientation and grain size of the material are important experimental contents. In terms of the characteristic values of the material that reflect the refurbishment performance, the structure performance of the material is the main One aspect to consider.

Under normal circumstances, three experimental methods can obtain the thermal denaturation parameters of the material, so as to evaluate the processing possibility of the material. (1) High temperature tensile test. High temperature tensile test is easy to complete, and the strength and ductility (elongation and reduction of area) of the material at different temperatures can be obtained. In the tensile test, it is difficult to control the strain rate. After the necking occurs, the sample has an uneven shape, which limits the amount of strain to be achieved, resulting in uncertainty in the amount of strain before fracture. Therefore, the evaluation of the tensile test data is limited in the workability.

(2) Torsion experiment, the deformation in torsion is pure shear, and there is no shrinkage problem at large strains. The strain rate directly corresponds to the rotation speed and is easy to control, and there is no friction contribution. During the torsion process, especially when the strain is large, the material will have excessive reorientation, which is inconsistent with the plastic processing process. Therefore, the torsion experiment data evaluates the workability of the material is also limited.

(3) If a specific lubrication is used in the hot compression test, the uniform deformation can be maintained to a large strain, and the compression stress state is closest to the conditions of the forging, extrusion, and rolling process. In the hot compression experiment, the "constant strain rate compression" can be used to obtain the flow stress data and the deep processability data required by the "finite element" method to establish the processing map. The hot compression experiment is used in evaluating the processability of the material. Priority is adopted.

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