Advanced microalloying strategies for improving the thermoplasticity of S31254: The roles of boron and niobium synergistic effects

The effect of niobium (Nb) microalloying on the thermal deformation behavior of boron-containing super austenitic stainless steel S31254 was investigated at 1000 °C and 1100 °C. Grain boundary precipitation of σ-phase, a detrimental factor leading to stress concentration and uneven deformation, was significantly suppressed by Nb addition. At 1000 °C, Nb promoted dynamic recrystallization, refined recrystallized grains, and reduced localized stress by forming Nb–Mo nanoclusters within the grains, which effectively pinned dislocations and minimized grain boundary precipitation. At 1100 °C, the Nb addition further enhanced deformation uniformity by promoting the formation of fine equiaxed recrystallized grains while restraining their growth. This dual mechanism—suppressing harmful grain boundary precipitation and stabilizing the intercrystalline structure—improved the thermoplasticity and hot-working performance of the alloy. These findings provide insights into alloying strategies to optimize the microstructure and high-temperature deformation behavior of boron-containing super austenitic stainless steels.