Titanium Bar Rod

The welding performance of titanium is relatively poor. How to ensure that there are no defects such as cracks and pores during the welding of titanium round bars? Are appropriate welding methods and process parameters used?

Titanium has a high melting point (1668℃), low thermal conductivity, and small linear expansion coefficient and elastic modulus. These characteristics cause titanium to easily produce large welding stress and deformation during welding, thereby increasing the risk of cracks. In addition, titanium is very easy to react with elements such as oxygen, nitrogen, and hydrogen at high temperatures to produce brittle compounds, reducing the plasticity and toughness of the welded joint.
Weldability characteristics of titanium
Crack sensitivity: Titanium is prone to hot cracks and cold cracks during welding. Hot cracks are mainly caused by the tensile stress of low-melting-point eutectics in the molten pool during solidification; cold cracks are caused by the diffusion and aggregation of hydrogen and the action of welding stress during the cooling of the welded joint.
Porosity sensitivity: Porosity is easy to occur during titanium welding, which is mainly due to the failure of gases (such as hydrogen, oxygen, nitrogen, etc.) in the molten pool to escape in time during welding. The presence of pores will reduce the mechanical properties and corrosion resistance of the welded joint.
Causes of cracks
Welding stress: During the welding process of titanium round bars rod, due to uneven local heating and cooling, large welding stress will be generated. When the welding stress exceeds the strength limit of the material, cracks will occur.
Impurity elements: Impurity elements in titanium materials (such as iron, carbon, hydrogen, etc.) will increase the tendency of cracks. These elements are prone to segregation at the grain boundaries during welding, forming low-melting point eutectics or promoting the diffusion and aggregation of hydrogen, thereby causing cracks.
Improper welding process: If the welding speed is too fast, the welding current is too large or too small, the arc length is too long or too short, etc., cracks may occur in the welded joint.
Causes of pores
Gas dissolution and precipitation: Titanium materials can dissolve a large amount of hydrogen, oxygen, nitrogen and other gases at high temperatures. During the welding process, the solubility of these gases in the molten pool decreases with the decrease in temperature. When the molten pool solidifies, pores will be formed if the gas fails to escape in time.
Welding material contamination: If the welding wire, welding rod or flux contains more moisture, oil or impurities, it will also introduce gas during the welding process, resulting in the formation of pores.
Poor welding protection: Inert gas (such as argon) is required for protection when titanium is welded to prevent the molten pool from reacting with oxygen, nitrogen and other elements in the air. If the flow rate of the shielding gas is insufficient or the protection effect is poor, pores will also be generated.
Choose a suitable welding method
Tungsten inert gas welding (TIG): TIG welding has the advantages of stable arc, good protection effect and high welding quality, and is the preferred method for titanium welding. During the welding process, by adjusting parameters such as welding current, arc length and welding speed, the temperature and shape of the molten pool can be controlled, thereby reducing the generation of cracks and pores.
Plasma arc welding: Plasma arc welding has high energy density, stable arc length and good protection effect, which is suitable for welding thick-walled titanium materials. During the welding process, the quality of the welded joint can be further improved by controlling the flow and pressure of the plasma gas.
Optimize welding process parameters
Welding current: The size of the welding current directly affects the temperature and depth of the molten pool. Too large a current can easily cause the molten pool to overheat, increasing the risk of cracks; too small a current may cause the molten pool to not be completely melted, resulting in unfused defects. Therefore, it is necessary to select a suitable welding current according to the diameter and wall thickness of the titanium round bar.
Arc length: If the arc length is too long, the molten pool temperature will decrease and the quality of the welded joint will decrease; if the arc length is too short, the tungsten electrode may be damaged, affecting the stability of the welding process. Therefore, it is necessary to control the arc length within a suitable range.
Welding speed: If the welding speed is too fast, the molten pool will cool too fast, increasing the risk of cracks; if the welding speed is too slow, the molten pool may overheat and reduce the mechanical properties of the welded joint. Therefore, it is necessary to select a suitable welding speed according to the characteristics of the titanium material and the welding method.
Strengthen the preparation work before welding
Clean the surface of the weldment: Before welding, the surface of the titanium round bar needs to be thoroughly cleaned to remove impurities such as oil, dust and oxide film to reduce the dissolution and precipitation of gas during welding.
Preheat the weldment: By preheating the weldment, the temperature gradient during welding can be reduced, welding stress and deformation can be reduced, and the risk of cracks can be reduced. The preheating temperature is generally controlled between 150-300℃.
Choose the right welding material: The choice of welding material has a vital impact on the quality of the welded joint. It is necessary to select welding materials with similar composition and reliable quality to the parent material for welding.
Strengthen the protective measures during welding
Use inert gas protection: During the welding process, inert gases such as argon need to be used to protect the molten pool to prevent the molten pool from reacting with oxygen, nitrogen and other elements in the air. The flow rate and pressure of the shielding gas need to be controlled within a suitable range.
Control the welding environment: The welding site needs to be kept dry and clean to avoid the influence of moisture and dust on the welding process. It is necessary to avoid welding in an environment with high wind speed to prevent the shielding gas from being blown away.
Post-weld treatment
Post-weld heat treatment: Post-weld heat treatment can eliminate residual stress and harmful gases such as hydrogen in the welded joint, and improve the plasticity and toughness of the welded joint. The heat treatment temperature is generally controlled between 500-700℃, and the holding time depends on the characteristics of the titanium material and the thickness of the weldment.
Nondestructive testing: After welding, nondestructive testing (such as X-ray testing, ultrasonic testing, etc.) is required for the welded joint to ensure that there are no defects such as cracks and pores inside the welded joint.
Taking the medical-grade, aerospace-grade, industrial-grade pure titanium, titanium alloy, and nickel-titanium alloy rods and wires produced by Changzhou Bokang Special Material Technology Co., Ltd. as an example, these products are well-known in the industry for their excellent performance and stability. During the production process, the welding process of titanium round bars is strictly controlled and optimized.
Welding method selection: Tungsten inert gas arc welding (TIG) is used for welding titanium round bars to ensure stable arc and good protection effect.
Welding process parameter optimization: Through a large number of tests and studies, the process parameters such as welding current, arc length and welding speed suitable for titanium round bars of different specifications have been determined to ensure that the temperature and shape of the molten pool are effectively controlled.
Preparation before welding: Before welding, the surface of the titanium round bar is thoroughly cleaned and the weldment is preheated to a suitable temperature to reduce welding stress and deformation.
Protection during welding: Use high-purity argon gas to protect the molten pool, and ensure that the flow and pressure of the protective gas are controlled within the appropriate range. The company has strengthened the control of the welding environment to avoid the influence of moisture and dust on the welding process.
Post-weld treatment: After welding, the welded joint is heat treated and non-destructively tested to ensure that there are no defects such as cracks and pores inside the welded joint.
Through the implementation of the above measures, Changzhou Bokang Special Material Technology Co., Ltd. has successfully controlled the generation of defects such as cracks and pores in the welding process of titanium round bars, and improved the quality and reliability of welded joints. The titanium alloy materials produced by the company not only have extraordinary brightness, but also excellent roundness and smoothness, and the straightness reaches the industry-leading level. These advantages ensure that the material can perform to the extreme in a wide range of applications.