Titanium, a metal with extremely active chemical properties, is strongly associated with gases such as oxygen, hydrogen, and nitrogen at high temperatures. This characteristic becomes increasingly significant in the titanium welding process as the welding temperature increases. 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 processing
In recent years, with the rapid development of the economy, especially under the continuous promotion of reform and opening up, economic construction has achieved remarkable achievements. At the same time, great progress has been made in the welding processing technology of pipelines and other projects. Titanium welding is a common welding method, and the quality control during its processing has a vital influence on the formation of weld color. The intuitiveness of weld color provides an important basis for us to study the relationship between weld color and welding quality in titanium welding processing.
The influence of titanium characteristics on titanium welding processing
The influence of oxygen and nitrogen: oxygen and nitrogen will interstitially dissolve in titanium, resulting in titanium lattice distortion, increasing deformation resistance, improving strength and hardness, but reducing plasticity and toughness. Oxygen and nitrogen in the weld are unfavorable and should be avoided as much as possible.
Effect of hydrogen: The increase of hydrogen will cause the impact toughness of titanium weld metal to drop sharply, and the plasticity will also be reduced. At the same time, hydrides will also cause the brittleness of the joint.
Effect of carbon: At room temperature, carbon is solid-dissolved in titanium in the form of gaps, which will increase strength but reduce plasticity. When the amount of carbon exceeds the solubility, hard and brittle TiC will be generated, which is distributed in a network and prone to cracks. Therefore, the national standard stipulates that the carbon content in titanium and its titanium alloys shall not exceed 0.1%. During welding, it is necessary to ensure that the oil stains on the workpiece and welding wire are cleaned to avoid increasing the carbon content.
Analysis and processing points of titanium weldability
Titanium has good weldability and its thermal conductivity is small, so titanium metal only melts within the arc-burning range and has good fluidity. At the same time, the thermal expansion coefficient of titanium is also small, which greatly improves the weldability of titanium metal. When performing the titanium welding process, the following points should be noted:
Protection of welding area and high-temperature area after welding: To avoid the influence of air on welding and high-temperature areas, these areas must be strictly protected. Using 99.99% pure argon and a rear drag shield is a necessary measure.
Processing method of weld groove: The weld groove should be processed by mechanical processing, and the grinding method should not be used.
Avoidance of spot welding and application of high-frequency arcing: Spot welding should be avoided as much as possible during welding, and high-frequency arcing should be used.
Control of post-weld heat treatment: Try to avoid post-weld heat treatment; if it must be performed, the heat treatment temperature should be controlled below 650℃.
Relationship between weld color and quality in titanium welding
Mechanism of weld color change and its defects: During the titanium tube welding process, the argon gas protective layer formed by the argon arc welding gun can only protect the welding pool from the harmful effects of air, but has no protective effect on the weld and its surrounding areas near the solidified and high-temperature state. These areas still have a strong ability to absorb nitrogen and oxygen in the air. As the oxidation level gradually increases, the color of the titanium tube weld will change, and the plasticity of the weld will also decrease. The color changes are silvery white (no oxidation), golden yellow (slightly oxidized), blue (slightly oxidized), and gray (severely oxidized).
Judging the welding quality by the color of the weld: Experiments have shown that as the color of the weld deepens, that is, the degree of oxidation of the weld increases, the hardness of the weld will also increase. At the same time, harmful substances such as oxygen and nitrogen in the weld will also increase, greatly reducing the quality of the weld.
In summary, titanium welding is a complex and delicate process that requires strict control of various factors to ensure welding quality. By deeply studying the characteristics and weldability of titanium, as well as mastering the correct processing points and precautions, we can better achieve high quality and high efficiency in titanium welding.
