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Grain boundary (GB) precipitation-induced cracking is a significant issue for S31254 super austenitic stainless steel during hot working. Investigating the deformation behavior based on precipitate morphology and distribution is essential. In this study, continuous smaller and intermittent larger precipitates were obtained through heat treatments at 950 °C and 1050 °C. The microstructure evolution and mechanical properties influenced by precipitates were experimentally investigated using an in situ tensile stage inside a scanning electron microscope (SEM) combined with electron backscatter diffraction (EBSD). The results showed that continuous precipitates at 950 °C had a stronger pinning effect on the GB, making grain rotation difficult and promoting slip deformation in the plastic interval. Continuous precipitates caused severe stress concentration near GB and reduced coordinated deformation ability. Additionally, the crack propagation path changed from transcrystalline to intercrystalline. Furthermore, internal precipitates were a crucial factor affecting the initial crack nucleation position. Interconnected precipitates led to an intergranular fracture tendency and severe deterioration of the material's plasticity, as observed in fracture morphology. [ABSTRACT FROM AUTHOR]

The effect of boron (B) addition coupled with 500 ℃ pre-aging on the corrosion resistance of S31254 was systematically investigated. The results suggested that the diffusion of Mo to grain boundaries (GBs) played a crucial role in enhancing intergranular corrosion resistance. Additionally, the addition of B further promoted the uniform distribution of Mo during the pre-aging process by suppressing Mo segregation at GB. Ultimate, the B microalloying coupled with the pre-aging strategy optimized the composition of passive film through promoting the formation of Mo-rich passivation film, which significantly enhanced the corrosion resistance of Mo-containing stainless steel. • B inhibits Mo segregation to the grain boundaries at 550–600 ℃. • B alloying coupled with pre-aging promotes the formation of Mo-rich passive film. • Mo-rich passive film markedly improves the corrosion resistance of S31254. [ABSTRACT FROM AUTHOR]