Selection of a better strip for feeding into high-alloy stainless steel 654SMO: A promising technology to improve solidification structure

Abstract

Strip composition is a crucial parameter in feeding strip technology because it affects the improvement of the solidification structure; however, there is limited research on this topic. In this study, different strips were fed into 654SMO molten steel, and their influence on the solidification structure was investigated. The results indicated that the effectiveness of the feeding strip depended on its composition and melting point. The 316 L strip with a higher melting point did not melt completely. Feeding 654SMO strip slightly improved the dendritic structure, while feeding 904 L strip significantly expanded the equiaxed zone, refined the dendrites, reduced central Mo segregation, and inhibited σ-phase precipitation. The following mechanisms were revealed. The melting strip produced floating dendrites that acted as nucleation particles. The 654SMO strip and floating dendrites melted quickly, offering a limited refining effect on the dendritic structure. By contrast, the higher melting-point 904 L strip exhibited a longer melting time, and the 904 L floating dendrites survived and proliferated better, thereby markedly improving the dendritic structure. Moreover, feeding the 904 L strip resulted in stronger abilities to inhibit the columnar grain growth and Mo-rich interface movement, discretize and refine Mo segregation regions, and shorten the solidification time. Moreover, the 904 L strip with lower Mo content (4.38 wt%) diluted the central Mo content. All these roles significantly reduced central Mo segregation. Additionally, feeding the 904 L strip could better increase the critical nucleation radius of the σ phase by reducing the driving force and initial formation temperature, and it suppressed the σ-phase growth by slowing Mo diffusion and narrowing the growth space, thereby considerably inhibiting the precipitation of σ phase.