In this study, the grain boundary character distribution (GBCD) of a B10 alloy was optimized, employing thermomechanical processing consisting of friction stirring processing (FSP) and annealing treatment. Using electron backscatter diffraction, the effects of rotational speed of FSP and annealing time on the evolution of GBCD were systematically investigated. The GBCD evolution was analyzed concerning various parameters, such as the fraction of low-Σ coincidence site lattice (CSL) boundaries, the average number of grains per twin-related domain (TRD), the length of longest chain (LLC), and the triple junction distribution. The experimental results revealed that the processing of a 1400 rpm rotational speed of FSP followed by annealing at 750 °C for 60 min resulted in the optimum grain boundary engineering (GBE) microstructure with the highest fraction of low-Σ CSL boundaries being 82.50% and a significantly fragmented random boundary network, as corroborated by the highest average number of grains per TRD (14.73) with the maximum LLC (2.14) as well as the highest J2/(1 − J3) value (12.76%). As the rotational speed of FSP increased from 600 rpm to 1400 rpm, the fraction of low-Σ CSL boundaries monotonously increased. The fraction of low-Σ CSL boundaries first increased and then decreased with an increase in annealing time. The key to achieving GBE lies in inhibiting the recrystallization phenomenon while stimulating abundant multiple twinning events through strain-induced boundary migration.

This study presented an application of thermomechanical processing consisting of cold rolling and subsequent annealing in SP2215 heat-resistant steel to investigate the effects of thermomechanical processing parameters on the evolution of grain boundary character distribution (GBCD) and to elucidate the relationship between GBCD and creep properties. The experimental results show that the optimal process, characterized by 10% cold rolling reduction followed by annealing at 1100 °C for 10 min, was determined to significantly increase the fraction of low-Σ coincidence site lattice (CSL) boundaries up to 74.27%, and effectively disrupt the connectivity of the random boundary network, as corroborated by the highest average twin-related domain (TRD) size of 42.58 μm and average number of grains per TRD of 7.28. Such a modified GBCD leads to a notable enhancement in creep performance, resulting from the induction of a high fraction of low-Σ CSL boundaries and the disruption of the random boundary network, which effectively inhibits intergranular crack initiation and propagation during creep deformation.