Abstract: Prokhorov considered that the hot ductility decreased with the increase of deformation speed, the decrease of cooling speed could reduce the deformation speed and susceptibility to hot cracking in weldment, preheating and slow cooling were therefore proposed to prevent hot aacking in weldment. Our investigations show that local forced cooling to the weld can reduce the deformation in hot brittle temperature range and the increase of the deformation speed could enhance the hot ductility of the metal in the lower part of the brittle temperature range. It therefore increases the allowable deformation rate and decreases the hot cracking in weldment. On the basis of the theory the experiments were carried out with the material 30CrMnSiA. The hot pipe was used to follow the welding torch to cool the welding beam. It is shown that the local foroed cooling to the welding beam greatly decreases the hot cradcing in welding.