Adjusting mechanisms for ultrafine-grained microstructures during hot deformation of Ni−38Cr−3.8Al alloy via pre-ageing precipitation

• • At 560 °C, incomplete discontinuous precipitation (DP) restrains DRX, yielding necklace-like microstructures; above 640 °C, complete DP with fully lamellar structures promotes DRX, producing ultrafine-grained (UFG) microstructures. This threshold dictates whether hot deformation yields desirable UFG or heterogeneous necklace structures, directly impacting mechanical property uniformity. • • Increasing pre-ageing temperature reduces critical strain and peak strain for DRX initiation and increases DRX volume fraction. This acceleration of DRX lowers the deformation resistance and energy consumption during hot forming, enhancing industrial process efficiency. • • Pre-precipitated α-Cr lamellae undergo dissolution fragmentation and spheroidization into finer particles, stimulating DRX via continuous DRX (CDRX); coarse α-Cr particles enhance DRX through particle-stimulated nucleation (PSN) and discontinuous DRX (DDRX). The interplay of these mechanisms governs final grain size and texture, affecting component performance in aerospace and nuclear applications. • • For UFG microstructures, pre-ageing should precipitate fully lamellar structures. This processing recommendation enables targeted microstructure engineering, potentially improving high-temperature strength and corrosion resistance of Ni−38Cr−3.8Al alloy components.