What are the methods for improving titanium tube welding that titanium tube manufacturers can explain to you?
There are many welding methods available for titanium tubes. At present, inert gas shielded arc welding (group arc welding) is widely used, and other welding methods such as plasma welding, vacuum electron beam welding, spot welding, brazing and vacuum Diffusion welding are also used. However, the commonly used oxygen acetylene welding, manual arc welding, carbon dioxide gas shielding and hydrogen atom welding methods are not suitable. Because titanium reacts with oxygen and chlorine at high temperatures. Gases such as hydrogen can undergo strong reactions, and fusion welding in air can cause complete embrittlement of the weld seam. Only in a vacuum or protective atmosphere can the weld metal have weldability.
In order to improve the weldability of titanium pipes and ensure the quality of the weld zone, the following two factors need to be paid special attention to.
（1） The influence of gap elements
During welding, oxidation, nitridation, and hydrogenation caused by good protection techniques; The moisture absorbed by the workpiece and welding wire, as well as the oxygen and hydrogen absorption caused by processes such as acid washing; Oil stains and residual cleaning agents, cotton yarn, and other factors at the weld seam can cause an increase in the content of interstitial elements in the weld seam area, resulting in an increase in strength, a decrease in plasticity, and a loss of plasticity.
The pores in the titanium pipe weld are caused by the gas generated in the welding pool and the flow of protective gas being drawn in, which cannot be discharged during the condensation process. It is generally believed that hydrogen is the main cause of porosity.
The cold cracks in titanium welds are caused by excessive hydrogen forming hydrides, which sometimes occur after a period of time after welding, known as delayed fracture.
（2） Formation of coarse grains and metastable structures
Titanium and titanium tubes have high melting points and poor thermal conductivity. The weld and Heat-affected zone stay at the temperature higher than the critical point T for a long time, resulting in coarse grains in these two parts of the region. Because titanium can not refine grains through phase transformation, the plasticity of welded joints is often reduced. In addition, the post weld cooling rate of the anti Heat-affected zone of the weld is generally very fast, so the performance of the weld zone will also be affected if the proper post weld heat treatment is not carried out.
In view of the above situation, it is necessary to strictly control the harmful impurities in the base metal and welding materials (including filler materials and oxygen free flux), especially the content of interstitial elements such as hydrogen, oxygen, nitrogen, and carbon, in the welding of titanium pipes. Before welding, the workpiece, filler wire, fixture, and equipment should be strictly cleaned to prevent contamination during welding and reduce the harm of gap elements. Furthermore, welding specifications with low linear energy should be used as much as possible to reduce the tendency of metal overheating; Appropriate post weld heat treatment system shall be selected for different alloys to adjust the microstructure and mechanical properties of weld and Heat-affected zone.