Crack is a common defect in titanium plate welding. The weld crack of titanium belongs to cold crack, which is mainly caused by hydrogen in the weld. The main sources of hydrogen are water and oil in plate and welding wire. The main reason of hydrogen increase in weld is environmental humidity.
During welding, a large amount of hydrogen is dissolved in the molten pool under the action of high temperature. During the cooling and solidification process of weld, hydrogen is easy to escape due to the rapid decrease of solubility. If the cooling rate of the weld is too fast, the hydrogen will not escape and remain in the weld, which will make the hydrogen in the weld in the supersaturated state. Therefore, hydrogen should be vigorously diffused and further embrittlement will be promoted in this area.
If there is notch effect in this region and the hydrogen concentration is high enough, cracks may occur. Especially in the winter construction, the environment temperature is low, and the water vapor is attached to the titanium plate, which creates conditions for the weld hydrogen. Because the titanium plate is too thin (1.2mm), the steel plate is "hot", the temperature rises slowly, and the cooling speed of the corresponding titanium clad weld is too fast. During the cooling process, the residual hydrogen in the weld has no time to escape, and exists in the form of supersaturation in the weld, which eventually leads to the appearance of cracks.
Therefore, in the welding process of titanium steel clad plate, the surface of base metal and welding wire should be carefully cleaned, and the ambient temperature should not be lower than 5 ℃. In winter construction, flame preheating is used to preheat the steel surface of the base course, one is to remove the water around the weld, the other is to increase the temperature of the weldment and reduce the cooling rate of the weld.
