Cracks are defects that often occur in the welding of titanium plates. Titanium weld cracks are cold cracks, mainly caused by hydrogen in the weld. The main sources of hydrogen are the moisture and oil stains in the plate and the welding wire. The environmental 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 is dissolved in the molten pool. During the cooling and solidification of the weld, due to the rapid decrease in solubility, hydrogen easily escapes. If the cooling rate of the weld is too fast, the hydrogen will not escape and remain in the weld, which will cause the hydrogen in the weld to be supersaturated, so the hydrogen will be diffused as much as possible and this area will be further embrittled.
If there is a notch effect at this location and the hydrogen concentration is high enough, cracks may occur. Especially in the winter construction, the ambient temperature is low, and the water vapor is attached to the titanium plate, which creates conditions for the hydrogen increase of the weld. Because the titanium plate is too thin (1.2mm), the steel plate is relatively “eat warm” and the temperature rises slowly. The corresponding titanium composite layer weld seam cools too fast. During the cooling process, the residual hydrogen in the weld seam is too late to escape It 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 plates, the surface of the base metal 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 flame. One is to remove the moisture around the weld. The second is to increase the temperature of the weldment and reduce the cooling speed of the weld.