How to avoid crack when deopsite weld for valve sealing surface?
Many factory Welding Worker face potential crack risk when deposite weld valve seat and disc, especially for those experience less fresh welding worker.This phenomen is more widely exsist for complicated workpieces when using easy-crack electrode.
Surfacing in the most commonly encountered problem is cracking, to prevent cracking of the main methods are:
1, preheat, interpass temperature control, slow cooling after welding.
2, stress relief heat treatment after welding.
3, to avoid cracking when welding layers, using low hydrogen welding electrodes.
4, when necessary, weld layer transition between the base material and surfacing layer(use low carbon equivalent, high toughness electrodes).
Cracking is mainly relate to the workpiece deposited weld metal carbon content, alloying elements , so preheat temperature is generally based electrodes used to by estimating the carbon equivalent.
Carbon equivalent formula is as follows:
Ceq = C +1 / 6Mn +1 / 24Si +1 / 5Cr +1 / 4Mo +1 / 15Ni
This estimation formula is suitable for low, medium and high carbon steel and low alloy steel materials.
Carbon equivalent (%) preheating temperature carbon equivalent (%) preheating temperature
≤ 0.40 100 ℃ ≤ 0.70 250 ℃ or more than
≤ 0.50 150 ℃ ≤ 0.80 300 ℃ or more above
≤ 0.60 200 ℃ ≤ 0.90 350 ℃ or more above
High manganese steel and austenitic stainless steel are not required to preheat before welding. High-alloy steel preheat temperature should be higher than 400 ℃.