Microstructural evolution in GH3536 alloy during staged-temperature forging and short-time solution treatment

To elucidate the synergistic effects of the temperature path during multi-pass forging and subsequent short-time solution treatment on the microstructure and mechanical properties of GH3536 alloy, an industrial electroslag-remelted ingot with a diameter of 285 mm was investigated. After partial homogenization at 1190 °C for 24 h, the billets were subjected to either a constant-start-temperature forging route (IF) or a staged-temperature forging route (NIF), followed by solution treatment at 1180 °C for 5–60 min. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction were employed to characterize the carbides, grain structure, and grain-boundary character distribution. Room-temperature tensile testing and fractographic analysis were also performed. The results showed that NIF transformed coarse, agglomerated, and quasi-continuous grain-boundary carbides into finer and more dispersed particles. Meanwhile, the average grain size in the as-forged condition decreased from 53.7 μm for IF to 25.9 μm for NIF. The geometrically necessary dislocation density estimated from EBSD increased from 1.8 × 10¹³ m⁻² for IF to 5.6 × 10¹³ m⁻² for NIF, indicating that the intermediate low-temperature passes suppressed dynamic recovery and increased the stored deformation energy. The fractions of Σ3 and Σ9+Σ27 boundaries in the NIF specimen reached 62% and 5.4%, respectively, both exceeding those in the IF specimen, which were 54% and 3.37%. After 5 min of solution treatment, the low-angle grain-boundary fractions in both groups decreased rapidly to approximately 1%, indicating pronounced recovery accompanied by static recrystallization. Grain growth subsequently became the dominant microstructural process. The specimens derived from NIF retained smaller average grain sizes throughout solution treatment. After 15 min, the Σ9+Σ27 boundary fraction reached a maximum of 8.7%, accompanied by the most developed local clusters of twin-related boundaries. The ultimate tensile strength, 0.2% yield strength, and elongation of the as-forged NIF specimen were 774 MPa, 411 MPa, and 41%, respectively. After solution treatment at 1180 °C for 15 min, these values changed to 724 MPa, 318 MPa, and 54.0%, respectively. Extending the holding time to 30 min resulted in corresponding values of 716 MPa, 310 MPa, and 57.0%, indicating a further change in the strength–ductility balance. Fracture remained predominantly ductile and was governed by microvoid nucleation, growth, and coalescence. These results demonstrate that staged-temperature forging refines the as-forged microstructure through an “intermediate low-temperature strain-storage–final high-temperature recrystallization” mechanism. The NIF-derived specimens retained higher ultimate tensile and yield strength than their IF-derived counterparts after both 15 and 30 min of solution treatment, highlighting the influence of the preceding forging route on the subsequent mechanical response.