Wrought material as well as physically simulated welding heat affected zone (HAZ) samples of an UNS S32304 duplex stainless steel were subjected to electrochemical corrosion tests and electron microscopy characterization. An impaired corrosion resistance of the HAZ microstructures compared to the wrought material microstructure was observed. Calphad-based numerical simulation of phase transformations and solute redistribution taking place during welding provided an explanation of the observed corrosion behavior. The poor corrosion resistance of the HAZ microstructures studied was mainly attributed to a decrease in corrosion resistance of ferritic grains after welding, which exhibited lower chromium content than ferritic grains in the wrought material.