The thermal cycles of the Coarse Grain Heat Affected Zone (CGHAZ) and Intercritical Reheated Heat Affected Zone (ICRHAZ) of Gas Metal Arc Welds (GMAW) have been reproduced using a Gleeble thermo-mechanical simulator. An upper bainite microstructure was observed in the CGHAZ while a granular bainite forms in the ICRHAZ. Instrumented Charpy tests were performed in the CGHAZ and ICRHAZ. A deterioration in toughness can been observed in the ICRHAZ in comparison to CGHAZ. This was attributed to a higher MA fraction and coarser MA structure, and was associated with higher crack initiation and crack propagation energy in the CGHAZ during impact tests. Coarser MA can initiate cracks and undergo debonding more readily in the ICRHAZ, which leads to a drop in crack initiation and crack propagation in the ICRHAZ.