Development of a Flow-Stress Constitutive Model and Hot-Processing Window for a High-Nb, Ultra-High-Strength (205 ksi) Nickel-Based Corrosion-Resistant Alloy

The development of unconventional deep oil and gas resources requires 205 ksi high-Nb Ni-based corrosion-resistant alloys; however, the lack of hot-forming databases and processing maps for this grade has frequently resulted in hot cracking during ingot forging. To address this gap, this study investigated the hot-deformation behavior of this alloy and optimized its forming parameters. Isothermal-compression tests were performed using a Gleeble 3800-GTC simulator (Dynamic Systems Inc., Poestenkill, NY, USA) at 1173–1323 K and strain rates of 0.01–10 s−1, followed by quantitative electron backscatter diffraction (EBSD) characterization of grain size, kernel average misorientation (KAM), and grain-boundary misorientation. A strain-compensated Arrhenius constitutive model was developed, giving a deformation activation energy of 540.33 kJ/mol and an average absolute relative error of only 4.77%. Dynamic materials model (DMM)-based power-dissipation and instability maps were constructed for this alloy for the first time, and an optimal hot-working window of 1260–1300 K and 0.01–0.1 s−1 was identified. Under the representative condition of 1273 K and 0.1 s−1, a uniform fine-grained microstructure with well-developed dynamic recrystallization was obtained without cracking, with an average grain size of 10.91 μm, a dynamic recrystallization (DRX) fraction of 48.4%, and an average KAM value of 0.476°. This work establishes the first complete hot-processing map system for the 205 ksi high-Nb Ni-based alloy, clarifies the coupled effects of dislocation evolution and dynamic recrystallization, and provides theoretical guidance for industrial hot cogging and microstructural control.