COLD CRACKING BEHAVIOR OF HEAT AFFECTED ZONES OF STEEL AFFECTED BY MULTIPASS WELDING THERMAL CYCLES.

It is well known that the under-bead crackings are occurred at multipass welds in high-strength steels. In this study, relative susceptibility to hydrogen-assisted cracking in the HT-80 steel welds is evaluated by using 2 pass implant method, the simulation technique of weld HAZ (heat affected zone) and the method of hydrogen chargong into the synthetic HAZ. Results indicate that, the shortest incubation time to fracture is observed at the first pass bond region subjected to heat cycle of 500-600 degree C at second pass, due to the stress and hydrogen concentration at the part. The morphology of crack growth is predominantly integranular. Those tendency are observed for both the implant and the simulation tests.