What is weld decay and knifeline attack?
Weld Decay – During welding the temperature of the parent metal is highest at the weld junction but it gradually decreases on both sides of the weld as we move away from the junction. At some point the weld thermal cycle brings part of the heat-affected zone into the sensitization range. Carbides precipitate and a zone becomes susceptible to Intergranular corrosion. This type of attack is called Weld Decay, low temperature heat affected zone corrosion. Knife Line Attack – When steel is heated to a very high temperature (above 1230C) columbium and its carbides dissolve in the metal and remain in solution when the metal is subsequently heated in the chromium carbide precipitation range (550-850C) and columbium carbides do not form, and the steel sensitizes or behaves as though it were an unstabilized grade. This type of attack is called Knife line Attack.
