Titanium screws in the melting state will not only have a strong absorption and reaction with the ambient atmosphere of 02, N2, H2, CO, CO2, H2O and NH3, but also will act with most of the known crucible materials, so the melting of titanium screws need to be carried out in the protective atmosphere or blank arc furnace, and the most widely used in the future. Since the self-consumption furnace adopts water-cooled steel volute, the metal solidification speed is fast, and the sequential fabric can be guaranteed, so the density of the ingot is higher, moreover, the smelting under vacuum has good effect of generating and degassing, which can reduce the metal gas content and improve the purity. But on the other hand, due to the short melting period of the alloy, the composition is not easy to be uniform, so the second melting process is generally adopted for small production, and even the third remelting process is used in a few cases.
The forging quality of titanium screw is mainly to ensure purity, prevent inclusion and composition segregation purity mainly refers to the content of oxygen, nitrogen, hydrogen and other elements in the alloy. Insufficient in the purity of raw materials, electrode preparation and mismanagement, and smelting under the condition of vacuum degree is not enough, increase oxygen, nitrogen and other gases containing exhibition, even HuiShan oxide and nitride inclusion. In melting titanium screws with high melting point elements, metal element inclusion is easy to form, the most common is molybdenum inclusion, especially for titanium screws with high melting point. Another metallurgical defect of titanium screw manufacturing is composition segregation. Aluminum segregation is easy to form in high-alumina titanium screw, and composition segregation causes local abnormal changes in phase composition ratio.
The above titanium screw manufacturing defects are impossible or difficult to eliminate in the middle of the following processing procedures. They have an impact on the forming process and the final mechanical properties of titanium screw, so they are strictly controlled or eliminated in the smelting process.
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