Abstract
In this study, the effects of applied stress, diffusible hydrogen content, hardnesses of HAZ and weld metal on the crack initiation site were studied utilizing the small-sized TRC test for HT60, HT80, HY130 and 2 1/4Cr-1Mo steels in order to reveal the criterion under which cold cracking in root pass welding occurred alternatively in HAZ or weld metal. The vickers hardness ranges in HAZ and weld metal were 290-390 and 360-410, respectively. The diffusible hydrogen contents range was 2-7 ml/100 g.
Consequently, in the diffusible hydrogen content range 2 to 4 ml/ 100 g, the cold cracking in weld metal occurred under the higher hardness of weld metal, the higher applied stress and the higher diffusible hydrogen content in the weld metal hardness range about 315 to 370 and occurred only in the weld metal in more than 370. Then, "critical stress vs. time diagram" which represented the change in the critical stress in weld metal and HAZ vs. time laspe was proposed as the criterion considering the distribution of diffusible hydrogen in weld zone. The tendencies of crack initiation in root pass welding as mentioned above could be well explained by combining the progress of applied stress and "critical stress vs. time diagram".
