In this contribution, a series of isothermal compression tests for the 825 nickel-based alloy were performed using a Gleeble-3800 computer-controlled thermomechanical simulator at the compression temperature range of 850 °C to 1150 °C and the strain rate range of 0.14 s⁻¹ to 2.72 s⁻¹. The hot deformation equation of the alloy is derived from the piecewise model based on the theory of work hardening-dynamic recovery and dynamic recrystallization (DRX), respectively. Comparisons between the predicted and experimental data indicate that the proposed constitutive model had a highly accurate prediction. The deformation rate and temperature effect were associated with microstructural change, and the evolution of the microstructure was analyzed through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The dislocation densities of the alloy at the deformation of 850 °C and 2.72 s⁻¹ is higher than at the other deformation, the higher dislocation density is the higher stored energy and the higher degree of DRX. As well, two types of DRX nucleation mechanisms have been identified: discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). Changes in grain boundary have significant effect on the DRX nucleation of the alloy, twin boundaries act as potential barriers limiting dislocation slip and motion and eventually leading to the accumulation of dislocation during plastic deformation. This study identified that the major contribution which results in the growth of new twins in DRX grains is the new boundary of Σ3 twins.

High-carbon–chromium martensitic stainless steel (MSS) is widely used in many fields due to its excellent mechanical properties, while the coarse eutectic carbide in MSS deteriorates corrosion resistance. In this work, nitrogen was added to the MSS to improve corrosion resistance. The effects of nitrogen on the microstructure and corrosion resistance of MSS were systematically studied. The results showed that the addition of nitrogen promoted the development of Cr₂N and reversed austenite, effectively inhibiting the formation of δ-ferrite. Therefore, the durability of the passivation film was improved, the passivation zone was expanded, and the susceptibility to metastable pitting was decreased. As a consequence, nearly two orders of magnitude have been achieved in the pitting potential (E_pit) of MSS containing nitrogen, and the polarization resistance value (R_p) has gone up from 4.05 kΩ·cm² to 1.24 × 10² kΩ·cm². This means that in a corrosive environment, nitrogen-treated MSS stainless steel is less likely to form pitting pits, which further extends the service life of the material.