Welding is an important process in the equipment manufacturing process. There are many welding methods, and it is necessary to choose the appropriate welding method according to the product and equipment. The principle followed in the selection of welding methods is to ensure the quality of welded joints, high production efficiency, easy operation, low cost, etc. Among them, ensuring the quality of the weld should be the first priority.
Titanium has high chemical properties and has a high affinity for oxygen and nitrogen in the air. At lower temperatures, titanium interacts with oxygen to form a dense oxide film, which thickens as the temperature increases, and after exceeding 600 degrees Celsius, titanium begins to absorb oxygen and dissolve it into titanium. When the temperature rises again, the activity of titanium increases dramatically, and it reacts violently with oxygen to form titanium oxides. Titanium begins to absorb hydrogen above 300°C and nitrogen above 700°C. As a result of the contamination of titanium by oxygen and nitrogen, titanium increases its strength and hardness while its plasticity decreases. Oxygen is more affected than nitrogen.
When the mass fraction of hydrogen in titanium is 0.01%~0.05%, the impact toughness of the weld metal will decrease sharply, but the plasticity will decrease less. This indicates that the brittleness (hydrogen embrittlement) caused by hydrides is indicated. In the process of fusion welding, the molten pool acts like a small metallurgical furnace, and the molten metal is exposed to the atmosphere. If the corresponding protective measures are not taken to isolate the molten metal from the air, the gaseous elements such as oxygen, nitrogen, and hydrogen will be integrated into the titanium to form brittle oxides or nitrides, resulting in the reduction of weld metal plasticity, the increase of tensile strength, and in severe cases, brittle fracture will occur, and the plasticity is equal to 0. When titanium welding, try to use a softer welding specification, that is, use less welding line energy and faster cooling rate.
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