In the molten state, titanium screws will not only absorb and react with 02, N2, H2, CO, CO2, H2O, and NH3 in the ambient atmosphere, but also interact with most known crucible materials. Therefore, titanium screws The smelting needs to be carried out in a protective atmosphere or a blank electric arc furnace, and it is the most widely used in the future. Since the consumable furnace uses a water-cooled steel snail, the metal solidification speed is fast, and the sequential fabric can be guaranteed, so the density of the ingot is higher. Furthermore, smelting under vacuum has a good invasive degassing effect and can reduce the metal gas content To increase purity. But on the other hand, due to the short melting period of the alloy, the composition is not easy to be uniform. For this reason, the secondary melting process is generally used for small production, and the remelting process is even used in a few cases.
The forging quality of titanium screws is mainly to ensure purity, to prevent the occurrence of inclusions and composition segregation. Purity mainly refers to the content of oxygen, nitrogen, hydrogen and other elements in the alloy. In the case of insufficient raw material purity, improper electrode preparation and management, and insufficient vacuum during smelting, the content of oxygen, nitrogen and other gases will increase, and even oxides and nitrides will appear. When smelting titanium screws containing high melting point elements, it is easy to form metal element inclusions, the most common is molybdenum inclusions, especially for high molybdenum titanium screws. Another metallurgical defect in the manufacture of titanium screws is composition segregation. Aluminum segregation is easily formed in high-aluminum titanium screws. The composition segregation causes local abnormal changes in the phase composition ratio.
The manufacturing defects of titanium screws mentioned above are impossible or difficult to eliminate in the middle of subsequent processing steps. They have an impact on the forming process and final mechanical properties of titanium screws, so they are very strictly controlled or eliminated in the melting process.