There are many elements in titanium and titanium alloys, which have an effect on the physical properties of titanium. Among them, carbon is a common impurity in titanium and titanium alloys. When the carbon content is less than 0.13%, carbon is used in α-titanium. The limit is somewhat improved, the plasticity is somewhat reduced, but the effect of oxygen and nitrogen is not strong. However, when the carbon content of the weld is further increased, the number of meshed TiC in the weld increases with the increase of the carbon content, which causes the plasticity of the weld to drop sharply, and the crack is easy to occur under the welding stress. When the weld carbon content is 0.55%, the weld plasticity almost completely disappears and becomes a very brittle material. Post-weld heat treatment also does not eliminate this brittleness. According to the national technical conditions, the carbon content of the titanium alloy base material is not more than 0.1%. The carbon content of the weld does not exceed the carbon content of the base metal.

1. Hydrogen is affected

The change in hydrogen content of the weld has the most significant effect on the weld impact performance. The amount of sheet-like or needle-like TiH2 precipitated in the weld increases. The effect of the change in hydrogen content of the weld on the strength and the decrease in plasticity is not obvious.

2. The effect of oxygen

The hardness and tensile strength of the weld are significantly increased. The oxygen content of the weld is basically as the oxygen content of the weld increases as the oxygen content in the argon increases.

3. The effect of nitrogen

The action of nitrogen and titanium, at temperatures above 700 °C. The formation of brittle hard titanium nitride TiN and the formation of interstitial solid solution between nitrogen and titanium form a degree of lattice turbulence, which is more serious than the effect caused by the same amount of oxygen. Therefore, nitrogen improves the tensile strength of industrial pure titanium welds. Strength, hardness, and plasticity of the weld are more pronounced than oxygen.

4. The impact of carbon

Titanium and titanium alloys are relatively stable but are exposed to normal temperatures during the welding process. Liquid droplets and molten pool metals have a strong absorption of hydrogen, oxygen, and nitrogen, and in the solid state, these gases have interacted with them. With the increase of temperature, the ability of titanium and titanium alloy to absorb hydrogen, oxygen and nitrogen also increases obviously. At about 250 °C, titanium begins to absorb hydrogen, absorbs oxygen from 400 °C, and absorbs nitrogen from 600 °C. After the gas is absorbed, it will directly cause embrittlement of the welded joint, which is an extremely important factor affecting the quality of the weld.

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