Causes of defects in titanium tube welding
Oxidation and contamination: Titanium is sensitive to oxygen and easily reacts with oxygen at high temperatures to form oxides. During the welding process, if appropriate protective measures are not taken, the oxygen in the air may cause the titanium surface to oxidize and form an oxide film, thus affecting the welding quality. Furthermore, the welding area may become contaminated, for example, due to the presence of impurities in the welding material or the environment.
Temperature gradient: Titanium has high thermal conductivity and will form a large temperature gradient during welding. Temperature gradients can lead to stress concentrations and the formation of thermal cracks, especially in rapidly cooling areas.
Hydrogen Capture: Titanium is a material that readily absorbs hydrogen. During the welding process, if hydrogen is absorbed into titanium, it may lead to hydrogen embrittlement caused by hydrogen capture. Hydrogen embrittlement may lead to the formation of cracks.
Structural changes: Titanium is prone to grain growth and structural changes at high temperatures. This can result in a reduction in strength in the weld area, affecting overall weld performance.
Residual stress: Residual stress generated during the welding process may cause deformation and cracks of the titanium tube. This may be caused by rapid cooling, different thermal expansion coefficients of the materials, and non-uniform shrinkage during welding.
The welding defects of titanium tubes are caused by the argon gas protective layer formed by the argon arc welding gun during welding of titanium tubes. The surrounding area has no protective effect, but the titanium pipe weld and its surrounding area in this state still have a strong ability to absorb nitrogen and oxygen in the air. Oxygen begins to be absorbed at 400°C, and nitrogen begins to be absorbed at 600°C. The air contains a large amount of nitrogen and oxygen.
As the degree of oxidation gradually increases, the color of the titanium pipe weld changes and the plasticity of the weld decreases. Silvery white (not oxidized) Golden yellow (TiO, titanium begins to absorb hydrogen at around 250°C. Slightly oxidized) Blue (Ti2O3 slightly oxidized) Gray (TiO2 severely oxidized).
The uniformity of the chemical composition of titanium alloy ingots is the basic guarantee for the reliability of processed materials and titanium alloy cutting parts with good performance.
As far as existing titanium alloys are concerned, the main alloy elements are Al, Mo, Sn, Si, Zr, Cr, Cu, V, and Fe. It is very necessary to understand and master the distribution rules of these alloy elements in the ingot under vacuum consumable arc melting and crystallization conditions, and to take appropriate process measures to ensure their uniform distribution in the ingot.
Anatomical tests were conducted on five titanium species: Ti-6Al-4V, Ti-2.5Cu, Ti-6.5Al-3.5Mo-2.5Sn-0.3Si, Ti-2.5Al-11Sn-5Zr-1Mo-0.25Si and Ti-6.5 Al-2.5Mo-1.5Cr-0.5Fe-6.3Si alloy ingot, investigate the distribution of alloy elements under different smelting conditions, and explore the segregation and elimination methods of aluminum alloy element Cu.
The titanium tube alloy elements are divided into several parts and added to the titanium sponge when pressing the unit electrode block. Consumable electrodes with a diagonal of 450 mm are welded from internal unit electrode blocks. The consumable electrodes were smelted once and remelted twice in a vacuum white consumable arc furnace, and three remelting tests were conducted. According to the crystal structure characteristics of vacuum consumable electric arc furnace steel ingots, a typical steel ingot mold was dissected. Truncated. On the top of the profile, drill holes every 30-50 mm in diameter with a φ1.5 mm drill bit to analyze the maximum content of alloy elements. Vacuum (1×10^(-3) mmHg) and argon filling (pressure 80-120 mmHg) melting, high and low melting power, and comparative tests of φ220 mm and φ622 mm ingots were conducted on Ti-2.5Cu alloy.
In order to reduce the occurrence of these defects, some measures need to be taken, such as using inert gas for protection during the welding process, controlling the welding speed and temperature gradient, preheating the workpiece to reduce the temperature gradient, using appropriate welding materials, adopting appropriate welding processes, etc. . In addition, strict control of hydrogen content during welding and appropriate heat treatment after welding are also important means to reduce defects.
