Influence Mechanism of Boron Addition on the Precipitation Behavior of Super Austenitic Stainless Steel S32654

The influence mechanism of Boron (B) addition on the precipitation behavior of S32654 was systematically investigated in this work. The results indicated that B significantly inhibited the nucleation and growth of σ phase through its non-equilibrium grain boundary segregation (NGS) at 1000 °C. The segregation of B at grain boundary (GB) decreased GB energy and suppressed Cr and Mo segregation, thus reducing the nucleation sites of intergranular σ phase. B also segregated at vacancies and dislocations during its reverse diffusion process, reducing the nucleation sites of intragranular σ. Meanwhile, B markedly decreased the nucleation rate of σ phases. In addition, B inhibited the growth of σ phase through segregation at σ/γ interface. Under the combined inhibitory effects of B, the precipitation of σ phase was markedly suppressed. By comparation, the addition of B has little effect on the precipitation of Cr₂N. B decreased the nucleation position but accelerated the nucleation rate. Under the joint action of these two opposing factors, the nucleation ability of Cr₂N has not significantly changed. Additionally, the segregation tendency of B at Cr₂N/γ interfaces was weak, leading to a little inhibition effect on the Cr₂N growth. Therefore, the precipitation tendency of Cr₂N in B-bearing and B-free steels was basically the same.