Titanium Welding

Titanium, an extremely active metal chemically, has a strong affinity for gases such as oxygen, hydrogen and nitrogen at high temperatures. Especially in the titanium welding process, this characteristic is more and more significant as the welding temperature rises. If the absorption and dissolution of titanium and these gases are not strictly controlled, it will undoubtedly bring great challenges to the processing of titanium welded joints.
The significance of titanium welding process
In recent years, with the rapid development of China's economy, especially under the continuous promotion of reform and opening up, China's economic construction has made remarkable achievements. At the same time, China's welding processing technology in pipelines and other projects has also made great progress. Titanium welding as a common welding method, the quality control of its processing has a crucial impact on the formation of weld color. The intuitive nature of weld color, in turn, provides an important basis for us to study the relationship between weld color and weld quality in titanium welding processing.
The influence of titanium properties on titanium welding processing
The effect of oxygen and nitrogen: oxygen and nitrogen will be interstitial solid fusion in titanium, resulting in titanium lattice distortion, increase deformation resistance, improve strength and hardness, but will reduce plasticity and toughness. Oxygen and nitrogen in the weld is unfavorable and should be avoided as much as possible.
The effect of hydrogen: the increase of hydrogen will make the titanium weld metal impact toughness decreased sharply, plasticity will also be reduced, while hydride will also cause joint brittleness.
The effect of carbon: at room temperature, carbon in the form of interstitial solid dissolved in titanium, will increase strength but reduce plasticity. When the amount of carbon exceeds the solubility, it will generate hard and brittle TiC, network distribution, easy to produce cracks. Therefore, the national standard stipulates that the carbon content in titanium and its titanium alloys shall not exceed 0.1%. During welding processing, it is necessary to ensure that the workpiece and the welding wire are cleaned of oil to avoid increasing the carbon content.
Titanium weldability analysis and processing points
Titanium has good weldability, its thermal conductivity is small, so that the titanium metal is only melted in the arc burning range, and has good fluidity. At the same time, the coefficient of thermal expansion of titanium is also small, which greatly improves the weldability of titanium metal. When performing titanium welding processing, the following points need to be noted:
Protection of the welding area and the high temperature area after welding: In order to avoid the influence of air on the welding and high temperature areas, these areas must be strictly protected. The use of 99.99% pure argon and post-trailing protective cover are necessary measures.
Welding bevel processing method: Welding bevel should be processed by mechanical processing method, and shall not be processed by grinding method.
Avoidance of spot welding and application of high-frequency arc starting: Spot welding should be avoided as much as possible in the welding process, and high-frequency arc starting should be used.
Control of post-welding heat treatment: avoid post-welding heat treatment as much as possible; if it is necessary, the heat treatment temperature should be controlled below 650℃.

The weld color and quality relationship of titanium welding processing
Weld color changes and its defects Generation mechanism: in the titanium tube welding process, due to argon arc welding gun formed by the argon gas protective layer can only protect the welded molten pool from the harmful effects of the air, and has solidified and is in the vicinity of the high temperature state of the weld and its adjacent areas have no protective effect. These areas still have a high capacity to absorb nitrogen and oxygen from the air. With the gradual increase in the level of oxidation, titanium tube weld color will change, while the plasticity of the weld will also be reduced. The color changes in the following order: silver-white (no oxidation), golden-yellow (slightly oxidized), blue (slightly oxidized), gray (heavily oxidized).
Discriminate the welding quality through the weld color: experiments have proved that, with the deepening of the weld color, that is, the degree of oxidation of the weld increases, the hardness of the weld will also increase. At the same time, the weld such as oxygen, nitrogen and other harmful substances will also increase, thus greatly reducing the quality of the weld.
In summary, titanium welding processing is a complex and delicate process that requires strict control of various factors to ensure the quality of welding. Through in-depth study of titanium characteristics and weldability, as well as mastering the correct processing points and precautions, we can better realize the high quality and high efficiency of titanium welding processing.