| Summary: | The optimization of grain boundary character distribution (GBCD) is of great significance to improve the GB-related properties for heavy-gauge austenitic stainless steels worked in harsh environments such as reactors of nuclear power, which can usually be realized by regulating the thermomechanical process. In this paper, special solution annealing processes for a hot-rolled nuclear grade 316H plate were designed to introduce different character distribution of Σ3<sup>n</sup> boundaries (1 ≤ n ≤ 3) and random high-angle GBs (RHAGBs), and the regulation principle among them were clarified. It was worked out that the optimized GBCD by characterization of large twin related domains, abundant interconnected Σ3<sup>n</sup> boundaries and interrupted topology network of RHAGBs could be effectively facilitated through solution annealing with a long time period at lower temperature or short time period at higher temperature, in which the recrystallization, grain growth and GB migration during heat treatment process played key roles. Moreover, the length fraction of Σ3<sup>n</sup> boundaries were found to be hardly changed when they reached about 77%, but their character distribution could be continuously optimized.
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