Nitride precipitation in weld HAZs of a duplex stainless steel

In order to obtain more information on the precipitation of nitrides, especially cubic type nitride CrN in weld heat affected zones of duplex stainless steels, the microstructures of thermally simulated weld heat affected zones (HAZs) of a commercial duplex stainless steel were characterized. The precipitates in the simulated weld HAZs were carefully examined with a transmission electron microscope. Not only Cr2N but also CrN was found in the weld HAZs. The CrN appeared as film-like or tiny platelet-like, and precipitated at the regions adjacent to rod-like Cr2N precipitates of high density. The orientation relation between CrN and delta ferrite matrix was [110]CrN//[111]delta and (001)CrN//(110)delta. Besides Cr, Fe, V and Mo were also detected in both the two types of nitrides. The CrN precipitation might be understood using previous thermodynamic analysis results of Fe-Cr-Ni-Mo-N system and considering the difference in the diffusibilities of chromium and nitrogen atoms in delta ferrite during cooling.