Cause: A large stress is generated after the heat affected zone of the weld shrinks. The base metal contains more hardened structure and is prone to cracks after cooling. There is a fairly high hydrogen concentration in the weld. And other harmful element impurities, etc., prone to cold and hot cracks.

Control measures: mainly from the elimination of stress and the correct use of welding materials and a sound operating process to solve. Pay attention to the groove form of the welded joint to eliminate uneven heating of the weld and to cool the crack caused by thermal stress. For the butt welding of steel plates of different thicknesses, the thick steel plates are to be thinned. The materials selected must meet the requirements of the design drawings, strictly control the source of hydrogen, the electrodes should be dried before use, and carefully clean the oil, moisture and other impurities in the groove. 

In the welding, select reasonable welding parameters, so that the input heat is controlled between 800~3000 °C cooling temperature to improve the microstructure of the weld and heat affected zone. In the welding environment, the temperature is lower and the material is thinner. In addition to increasing the operating environment temperature, it should be preheated before welding. At the end of the welding, it is necessary to maintain the slow cooling and post-weld heat treatment to eliminate the delayed crack generated by the residual stress of the weld during the cooling process.