Direct Observation of SR Crack Initiation in Welds by Laser Scanning Confocal Microscopy

Many evaluation methods for SR cracking susceptibility have been developed. However, there is a little information from the viewpoint of “time for the cracking”. We believe that the time for SR cracking can be defined as the critical time of crack-initiation.

In the present study, we develop the assessment method of effect of grain boundary segregation on the intergranular fracture based on the in-situ observation technique using high temperature Laser Scanning Confocal Microscopy. The tensile-test specimens with one-sided notch were inserted into the infared furnace and the constant stress were loaded. Then the specimens were heated to an elevated temperature. Direct observation of crack initiation under the high temperature conditions gives critical time of crack-initiation as a measure of the intergranular embrittlement. In the present study, with the Cr-Mo steel welds, the effect of vanadium was investigated by using the developed assessment methods.