Titanium and titanium alloys are new metal materials with great development prospects. It has been widely used in more than ten light industries such as aviation, aerospace, petroleum, chemical industry, pharmacy and so on. After more than 30 years of efforts, China's titanium industry has formed a certain scale, whether from raw materials - processing - remanufacturing, or from scientific research - production - application. The amount of titanium used in a country indicates a country's scientific and technological level and military strength, which has become a consensus. In China, vigorously promote the application of titanium and drive the large-scale development of titanium processing and sponge titanium production; Based on the civilian use of titanium and adhering to the development direction of military industry and high and new technology, it is considered to be the development direction of China's titanium industry in the 21st century. It plays an important role in promoting national defense and national economic development.
1. Titanium is a very active metal. When the temperature exceeds 400 ° C, it begins to react chemically with nitrogen and oxygen in the air. When 600 ° C is reached, the reaction becomes more intense. After titanium reacts with hydrogen, oxygen and carbon, the resulting compounds deteriorate the properties of titanium, increase its hardness and strength, and significantly reduce its plasticity. For example, in the welding process of titanium, if the inert gas protection is not good, the content of oxygen, nitrogen and carbon in the weld will be increased, resulting in the increase of the strength and hardness of the weld metal and the sharp decrease of plasticity. Therefore, when designing titanium equipment, its structure must be simple, reduce the stress concentration of the weld, facilitate the cleaning of the surface near the weld, and provide the use of inert gas. In order to protect the conditions of the back and front of the weld, for the equipment made of industrial pure titanium and some titanium alloys, the long-term service temperature shall not exceed 350 ℃, and the short-term and intermittent service temperature shall also be lower than 400 ° C.
2. Industrial pure titanium and most titanium alloys can be welded separately or mutually. According to different titanium manufacturing equipment, some parts can be repaired with corresponding corrosion-resistant alloy. Make the application and service life of the equipment more reasonable. For example, corrosion-resistant alloys such as titanium target alloy and titanium molybdenum alloy are welded on the sealing surface of pure titanium flange. It not only reduces the cost, but also plays a good role in preventing crevice corrosion. However, titanium cannot be welded with other metals, otherwise it is easy to form brittle intermetallic compounds and cause brittle fracture of welds. Therefore, when it is necessary to connect with other metals, only welding, brazing, explosive welding or threaded connection can be used.
3. The elastic modulus of titanium is low, about 1 / 2 of that of carbon steel and stainless steel, so it is easy to deform under low stress. Therefore, the design of bending structure or the size of steel parts that need to check the stiffness cannot be applied to members. For example, when making tray support with titanium, it should be calculated according to the elastic modulus of titanium at the service temperature. The required section shape is larger than stainless steel or carbon steel. For titanium shell and tube heat exchangers, in order to prevent vibration damage, the spacing between baffles or support plates should be much smaller than that of steel heat exchangers.
