The microstructure and fracture mode of physically simulated heat-affected zones of a weld metal used with 500 MPa offshore steel – part 1: impact toughness test results

Offshore steels are developed to have excellent toughness to withstand harsh conditions needed in applications such as offshore oil-drilling platforms, wind power turbines and ships. The heat-affected zones (HAZ) are widely studied but there is less information about the changes in weld metal during multipass welding. In this study the microstructures and impact energy values in the physically simulated HAZ subzones of the weld metal were analysed: coarse-grained (CGHAZ-W) and intercritical (ICHAZ-W) zones. Subzones with 3 different cooling times (t_8/5 = 5, 15 and 30 s) were simulated using Gleeble 3500 simulator. The increase of cooling time slightly reduced the hardness in the subzones. The impact energy values of subzones were below the unaffected weld metal but safely above the required value of the base material standard. Ductile and ductile/brittle behavior were observed. Longer cooling time resulted lower impact energy in ICHAZ-W, however this tendency was not observed in CGHAZ-W.