Abstract
A water-shower cooling method was developed. In the new method, the surface of one side of a plate is heated by welding torch, and then it is immediately cooled by a water-shower. Temperature around the surface of the plate decreases rapidly when the water-shower begins. But the temperature inside of the plate remains high. During cooling, tensile stress occurs only on the surface of the plate. And tensile plastic strain remains near the surface of the plate. After moderate cooling, the tensile plastic strain generates compressive residual stress. To estimate the efficiency of this method, temperature histories during the welding process and residual stresses in type 316L stainless-steel plates were analyzed by finite element analysis. The analytical results were verified by comparing them with experimental measurements. The results can be summarized as follows. In the case that a plate was welded at heat-input rate of 30 kJ/cm with preheating at 215℃, and then cooled rapidly by water-shower, longitudinal and transverse residual stresses at the surface of the plate were decreased and became compressive; the highest value of this compressive stress was more than 200 MP3. In the case that a plate was welded in a rate of 30 kJ/cm without preheating and was cooled rapidly by water-shower, longitudinal and transverse residual stresses at the surface of the plate were reduced. On the other hand, in the case that a plate was welded and cooled in ambient-air, tensile residual stress occurred at the welded surface. The highest value of the tensile stress was more than 150 MP3. It can be concluded from these results that the new water-shower cooling method can effectively reduce tensile stress in welded joints.
