In welding of high strength steel, toe crack and/or weld metal crack often occurred though the restraint was relatively small.
To reproduce such cracks, the strain-concentrated type multi-pass welding crack test was devised. Since they were classified into cold cracks due to diffusible hydrogen, the most effective countermeasurement for preventing weld cracking was to control the preheat and interpass temperature in the second side welding, but the critical preheat and interpass temperature increased in the welded joint whose welding strain was large. It was also clarified that the welding strain produced by the second side welding concentrated at the gorge of weld metal and toe of the first side welded zone as hot strain in the temperature range of blue embrittlement.
To investigate the effect of hot strain on the cold crack sensitivity of toe, tensile tests for synthetic heat affected zone (HAZ) were examined. Though the notch tensile strength without diffusible hydrogen at room temperature inrceased due to work hardening by hot strain, the notch tensile strength with diffusible hydrogen decreased due to the combination of hot strain embrittlement and hydrogen embrittlement.
As a result the cold crack sensitivity of toe where hot strain concentrated in the temperature range of blue embrittlement was higher than that estimated by Ceq and PCM through JIS oblique y groove welding crack test.
