Cracks are defects that often occur in titanium plate welding. Titanium weld cracks are cold cracks, which are mainly caused by hydrogen in the weld. The main source of hydrogen is the moisture and oil in the plate and welding wire, and the ambient humidity is the main reason for the increase of hydrogen in the weld.
Under the action of high temperature during welding, a large amount of hydrogen dissolves in the molten pool. During the cooling and solidification process of the weld, due to the rapid decrease in solubility, hydrogen is easy to escape. If the weld seam cooling speed is too fast, the hydrogen will not have time to escape and remain in the weld seam, which will make the hydrogen in the weld seam in a supersaturated state, so the hydrogen will try to diffuse and promote the further embrittlement of this area.
If there is a gap effect in this part, and the concentration of hydrogen is high enough, cracks may occur. Especially in winter construction, the ambient temperature is low, and water vapor adheres to the titanium plate, creating conditions for the hydrogenation of the weld. Because the titanium plate is too thin (1.2mm), the steel plate is relatively "warm", and the temperature rises slowly. The corresponding titanium composite layer weld is cooled too fast. During the cooling process, the residual hydrogen in the weld has no time to escape. It exists in the form of supersaturation in the weld, which eventually leads to the appearance of cracks.
Therefore, during the welding process of titanium-steel clad plates, the surface of the base metal and welding wire should be carefully cleaned, and the ambient temperature should not be lower than 5°C. During construction in winter, flame preheating is used to preheat the steel surface of the base, one is to remove moisture around the weld; the other is to increase the temperature of the weldment and reduce the cooling rate of the weld.
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