Crack is a common defect in titanium plate welding. Titanium weld cracks belong to cold cracks, mainly caused by H2 in the weld. The main source of H2 is the water and oil in the plate and welding wire, and the environmental humidity is the main reason for the increase of H2 in the weld.

During welding, a large amount of H2 is dissolved in the molten pool under the action of high temperature. During the cooling and solidification process of the weld, H2 is easy to escape due to the rapid reduction of solubility. If the cooling speed of the weld is too fast, the H2 has no time to escape and remain in the weld, which will make the H2 in the weld in a supersaturated state, so the H2 should be vigorously diffused and promote further embrittlement in this area.

If there is a notch effect at this site, and the H2 concentration is high enough, a crack may occur. Especially in the winter construction, the ambient temperature is low, and the water vapor is attached to the titanium plate, creating conditions for the welding seam H2 enhancement. Because the titanium plate is too thin (1.2mm), the temperature rises slowly, and the weld cooling speed of the corresponding titanium composite layer is too fast. During the cooling process, the residual H2 in the weld has no time to escape and exists in the form of susaturation in the weld, which eventually leads to the crack.

Therefore, in the welding process of titanium steel composite plate, the surface of the base metal and welding wire should be carefully cleaned, and the ambient temperature should not be lower than 5℃. Winter construction, the application of flame preheat base steel surface, one is to remove the moisture around the weld; The second is to increase the weldment temperature and reduce the weld cooling speed.