The causes and solutions of cracks in titanium plates and titanium-steel composite plates

Cracks are defects that often occur in the welding of titanium plates. Titanium weld seam cracks belong to cold cracks, mainly caused by hydrogen in the weld seam. The main sources of hydrogen are moisture and oil stains in the sheet metal and welding wire. Environmental humidity is the main reason for hydrogen increase in the weld seam.

During welding, under the effect of high temperature, a large amount of hydrogen dissolves in the molten pool. During the cooling and solidification process of the weld seam, due to the rapid decrease in solubility, hydrogen is very likely to escape. If the cooling rate of the weld seam is too fast, hydrogen cannot escape in time and remains in the weld seam, which will cause the hydrogen in the weld seam to be in a supersaturated state. Therefore, hydrogen has to diffuse vigorously and promote further embrittlement in this area.

If there is a notch effect at this part and the concentration of hydrogen is high enough, cracks may occur. Especially during winter construction, when the ambient temperature is low, water vapor adheres to the titanium plates, creating conditions for hydrogenation of the weld seams. Due to the titanium plate being too thin (1.2mm), the steel plate is relatively "heat-sensitive", and the temperature rises slowly. Correspondingly, the cooling rate of the titanium composite layer weld is too fast. During the cooling process, the residual hydrogen in the weld cannot escape in time and exists in the form of supersaturation in the weld, eventually leading to the appearance of cracks.

Therefore, during the welding process of titanium-steel composite plates, the surfaces of the base material and welding wire should be carefully cleaned, and the ambient temperature should not be lower than 5℃. During winter construction, the base steel surface should be preheated with a flame. One reason is to remove the moisture around the weld seam. The second is to increase the temperature of the welded piece and reduce the cooling rate of the weld seam.