During welding, a large amount of hydrogen is dissolved in the weld pool under the action of high temperature. During the cooling and solidification process of the weld, hydrogen is easy to escape due to the rapid decrease of solubility. If the cooling rate of the weld is too fast for hydrogen to escape and remain in the weld, hydrogen in the weld will be in the supersaturated state, so hydrogen should be diffused vigorously and further embrittlement in this area should be promoted.
If there is a notch in this area and the hydrogen concentration is high enough, a crack may occur. Especially in winter construction, the ambient temperature is low, water vapor attached to the titanium plate which create conditions for the weld to increase hydrogen. Because the titanium plate is too thin (1.2mm), the steel plate absorbs the temperature and the temperature rises slowly, and the corresponding titanium composite layer weld cools too fast. In the cooling process, the residual hydrogen in the weld has no time to escape and exists in the form of supersaturation in the weld, eventually leading to the emergence of cracks. Therefore, in the welding process of titanium steel composite board, it is necessary to carefully clean the surface of the base material and welding wire, and keep the ambient temperature not less than 5℃. In winter construction, the flame is used to preheat the steel surface of the base to remove the moisture around the weld. The other reason is to increase the temperature of welding parts and reduce the cooling rate of welding seams.
