Method for the quantitative assessment of transverse weld metal hydrogen cracking
Diffusible hydrogen introduced during the welding process can drastically reduce the toughness and ductility of welds in steel structures. In welds experiencing high levels of longitudinal residual stress (such as upper passes in multipass thick sections), transverse weld metal cracking can occur. While there are methods available for assessing susceptibility of heat affected zones in the parent material to hydrogen cracking, there are few that are applicable to the deposited weld metal, and none that are quantitative in relation to transverse cracking. Therefore, the current work was undertaken to develop a test that isolates and quantitatively assesses the effects of diffusible hydrogen on transverse cracking in the weld metal. The test method was based on four point bending of as-deposited weld metal with controlled levels of diffusible hydrogen. It is proposed that such a test configuration allows quantitative assessment of the relationship between applied stress/strain, hydrogen content, microstructural characteristics and the fracture behaviour. There were two variations on the test method; the first involved rectangular specimens machined from bead on plate welds providing a geometrically regular specimen with low variability in test results, and the second involved an as-welded bead on plate specimen (un-machined) which inherently has a higher level of variability due to greater irregularity in the specimen geometry, but which has the potential for industrial application due to the much simplified sample preparation and handling required. The method shows a high level of reproducibility and shows great potential for future application for both assessment of susceptibility of weld metals to hydrogen embrittlement, as well as more fundamental studies of the physico-chemical mechanis ms underlying hydro gen embrittlement phenomena.