Thermal aging response of microstructure and mechanical properties in direct energy deposition built GX4CrNi13-4 stainless steel

GX4CrNi13-4 stainless steel (SS), due to its exceptional mechanical property and corrosion resistance, has been a crucial material for preparing main turbine impellers at pressurized water reactors (PWR), yet the resistance to performance degradation caused by thermal aging is still a gap. It is crucial for plant reliability and needs to be studied. After the thermal aging test lasted for 4500 h, equivalent service time of 18.85 years, thermal aging induced microstructural evolution and property variation for GX4CrNi13-4 SS prepared via traditional forging and direct energy deposition (DED) were investigated and compared. This study presents a case that a better resistance to ductility degradation occurred in aged DED built GX4CrNi13-4 SS (from 8.5 % to 4.5 %) than forging one (from 18.5 % to 7.5 %) via the delaying effect of exclusive ferrite on carbide precipitation, which can weaken ductility severely. This result emphasizes the crucial role of ferrite in alleviating ductility decline and ensuring a better thermal aging resistance. These findings underscore that the superiority of DED in enhancing thermal aging resistance and no topological obstacles during preparation makes it suitable for production or even on-line repair of main turbine impellers at PWR.