Titanium screws will not only absorb and react strongly with 02, N2, H2, CO, CO2, H2O and NH3 in the ambient atmosphere in the melting state, but also act with most of the known crucible materials. Therefore, the melting of titanium screws needs to be carried out in the protective atmosphere or in the electric-arc furnace, which will be the most widely used in the future. Since the water-cooled steel is adopted in the self-consumption furnace, the metal solidifies quickly and the sequence of fabric can be guaranteed, so the density of the ingot is higher. Moreover, the melting under vacuum has a good effect of creating and removing gas, which can reduce the content of metal gas and improve the purity. However, on the other hand, because the melting period of the alloy is short and the composition is not uniform, the secondary melting process is generally adopted for small production, and even the tertiary remelting process is used in a few cases.
Forging quality of titanium screw is mainly to ensure purity, prevent inclusion and component 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. When smelting titanium screws with high melting point elements, metal element inclusions are easy to form, the most common is molybdenum inclusions, especially for titanium screws with high melting point elements. Another metallurgical defect of titanium screw manufacturing is component segregation. Aluminum segregation is easy to form in high-aluminum titanium screw, which causes local abnormal changes in phase composition.
The manufacturing defects mentioned above cannot or are difficult to eliminate in the middle of the following processing procedures. They affect the forming process and the final mechanical properties of titanium screws, so they are strictly controlled or eliminated in the smelting process.
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