Microstructural Evolution and Mechanical Behavior of a Fe–Ni-Based Alloy During Heat Treatment

This study investigates the effect of solution treatment temperature on the grain size, precipitate phase, and room temperature mechanical properties of a Fe–Ni-based alloy through solution treatment and aging. The results show that within the temperature range of 850 °C to 1100 °C, as the solution treatment temperature increases, the grain size grows from 13.84 to 55.19 μm. At a solution temperature of 1000 °C, the grain size sharply increases from 14.96 to 40.19 μm, exhibiting a three-stage characteristic of “slow increase–rapid increase–fast increase.” The activation energy for grain growth of the Fe–Ni-based alloy, calculated using the Sellars model, is Q = 142 kJ/mol. The width of the precipitate-free zone (PFZ) at the alloy grain boundaries gradually increases, with the interlamellar spacing of the lamellar structure first increasing and then decreasing, reaching a peak at 900 °C. After the solution treatment temperature reaches 1000 °C, no γ′ phase precipitates are observed within the alloy. The tensile strength of the alloy decreases from 1323 to 1199 MPa, yield strength drops from 911.5 to 737.5 MPa, the reduction of area increases from 31 to 40 pct, elongation at fracture increases from 19.25 to 26 pct, the room temperature hardness decreases from 45.1 HRC to approximately 38.5 HRC, and the impact energy increases from 23 to 47 J. Overall, as the solution treatment temperature increases, the alloy’s strength and hardness decrease, while its ductility and toughness improve. Additionally, this study analyzes and calculates the contribution of various strengthening factors within the alloy to the yield strength, concluding that as the width of the precipitate-free zone (PFZ) increases, the yield strength of the alloy decreases.