We have some cone vessels to welding overlay. The top diameter of the cone is 1000mm,while the other is 300mm,and the thickness of the cone is 12mm duplex steel,that is SA516 Gr.70 base and 316l caldding steel.Fisrtly, we had a 3mm thickness of 309Mol overlay with FCAW. Then we have to get 5mm thickness of CoCr-A alloy overlay. We took the method of SMAW with the stick electrode of Stellite 6. Since the thickness is 5mm, we have to do 2 layers.When we finished the first Stellite 6 layer, there is no cracking found.However, When we finished the second layer and let it cool gradually wrapping the cone with insulate material, we could see some crackings on the second.Most crackings are perpendicular to the welding seam.Before welding,we preheat the work to 200-300deg.C. and keep the interpass temperature.That's why? How i can avoid it?
THANK YOU!