What Factors Will Affect The Welding Of Titanium Plates?

Titanium and titanium alloy welding has very strict protection requirements during welding. When the carbon content of the weld is 0.55%, the plasticity of the weld almost disappears and becomes a very brittle material. Post-weld heat treatment cannot eliminate this brittleness. The national standard technical conditions stipulate that the carbon content of the titanium alloy base material shall not exceed 0.1%, and the carbon content of the weld shall not exceed the carbon content of the base metal. There are many elements in titanium alloys, which have an impact on the physical properties of titanium. Carbon is a common impurity in titanium and titanium alloys. When the carbon content is less than 0.13%, the carbon is deep in α titanium, and the weld strength is limited. There is some improvement and some decrease in plasticity, but not as strong as the effect of oxygen and nitrogen. However, when the carbon content of the weld is further increased, network TiC appears in the weld, and the number increases with the increase in carbon content, causing the plasticity of the weld to drop sharply, and cracks are prone to occur under the action of welding stress.

1. The impact of carbon. During the welding process of titanium and titanium alloys, at room temperature, the liquid droplets and molten pool metal have a strong ability to absorb hydrogen, oxygen, and nitrogen, and in the solid state, these gases have interacted with them. As the temperature increases, the ability of titanium and titanium alloys to absorb hydrogen, oxygen, and nitrogen also increases significantly. Titanium begins to absorb hydrogen at about 250°C, oxygen at 400°C, and nitrogen at 600°C. After the gas is absorbed, it will directly cause the welding joint to embrittle, which is an extremely important factor affecting the welding quality.

2. The influence of hydrogen. Hydrogen is a factor among gas impurities that has a serious impact on the mechanical properties of titanium. Changes in the hydrogen content of the weld have a significant impact on the impact properties of the weld. The flake or needle-like TiH2 precipitated in the weld increases. The strength of TiH2 is very low, so the effect of flaky or needle-shaped HiH2 is that the impact properties are significantly reduced; the change in the hydrogen content of the weld has little effect on the improvement of strength and the reduction of plasticity.

3. Effect of oxygen. The hardness and tensile strength of the weld increase significantly, and the oxygen content of the weld basically rises linearly with the increase in the oxygen content of the argon gas. The plasticity is significantly reduced. In order to ensure the performance of welded joints, oxidation of the weld seam and welding heat-affected zone should be strictly prevented during the welding process.

4. Effect of nitrogen. Nitrogen and titanium plates will react violently, forming brittle and hard titanium nitride (TiN) at high temperatures above 700°C. Moreover, the degree of lattice distortion caused by the formation of interstitial solid solution between nitrogen and titanium is greater than that caused by the same amount of oxygen. The consequences are more serious. Therefore, nitrogen is more significant than oxygen in improving the tensile strength and hardness of industrial pure titanium welds and reducing the plastic properties of welds. When the nitrogen content of the weld is above 0.13%, the weld will be due to excessive Be brittle and cause cracks.