<p>The synergistic mechanism of multiple process parameters on the solidification structure of niobium containing austenitic stainless steel during continuous casting is complex, which seriously affects the quality of continuous casting billets and seamless pipes. In order to optimize the quality of continuous casting billet, a finite element model of solidification and heat transfer in continuous casting process was established for the secondary cooling process of continuous casting billet. The control variable method was used to explore the influence of casting speed and superheat on the solidification process. At the same time, an orthogonal scheme was designed to study the coupling effect of multiple process parameters on the heat transfer and solidification state of continuous casting billets, and optimized process parameters were selected. The optimization results of process parameters were verified through production experiments, and it is found that the enrichment of coarse niobium compounds directly causes the initiation and propagation of inner wall cracks during the large deformation hot piercing of S30432 seamless tubes. Process parameter optimization, especially the synergistic effect of the decrease of superheat and increase of specific water flow promotes the grain refinement and expension of equiaxed crystal zone, thereby mitigating the segregation of Nb elements and improving the distribution of niobium compounds.</p>