Slide 7 of 12
Overlay cracking can easily be influenced by welding machine settings such as Amps and Volts. On the left drawing if we assume a perfectly good overlay which is free of cracking and having an FN=8 and for some reason either the volts or amps are increased, the FN will be driven down. This occurs because of two main reasons, (1) overheating, (2) nitrogen introduction into the weld pool. In the former case, the cooling rate slows and so does the formation of ferrite. In the latter case nitrogen from the atmosphere may be introduced from the atmosphere and thus retard the formation of ferrite. In either case the ferrite is lost and cracking will take place.