Key Takeaways & Executive Findings
- •• A finite element model of solidification and heat transfer was established for the secondary cooling process of S30432 continuous casting billet, enabling systematic study of process parameters. • Orthogonal experiments revealed the coupling effects of casting speed, superheat, and specific water flow on solidification structure, leading to optimized process parameters. • Production verification showed that coarse niobium compound enrichment causes inner wall cracks during hot piercing, and optimized parameters mitigate Nb segregation and improve grain refinement. • The synergistic decrease of superheat and increase of specific water flow promotes equiaxed crystal zone expansion, improving billet quality and hot workability.
Abstract
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.
1. Introduction
Austenitic heat-resistant stainless steel has become an important choice for seamless steel tubes of supercritical and ultra-supercritical power station boilers due to its excellent high temperature stability [1-3]. However, due to the solidification conditions of the continuous casting process and the low solute balance distribution coefficient of Nb element, serious grain boundary segregation occurs in the solidified structure of S30432 with a high Nb content, forming a large amount of unevenly distributed niobium compounds, which greatly reduces the quality and hot working performance of the billet, and leads to the formation of pores and initiation of cracks [4]. Moreover, the bulk NbC primary phase is difficult to be removed by subsequent heat treatment. Therefore, it is urgent to find a method to control the quality of continuous casting billets and seamless tubes.
The current research has gradually realized the regulation of solute element distribution in the solidification process of continuous casting through thermodynamic design, refinement of process parameters, and auxiliary technological innovation [5-9]. Researchers often improve billet quality by optimizing the relevant modules of the continuous casting process, such as immersion nozzle structure and immersion depth [10-12], distribution of mould fluxes [13, 14], mold structure and vibration frequency [15], electromagnetic stirring parameters [16-23], secondary cooling water [24-29], casting speed [30-32], superheat [33, 34] and continuous casting supporting equipment [35]. In addition, the optimization of alloy composition design combined with thermodynamic calculation is also an important aspect [36-40]. For example, the precipitation kinetics of Nb(C, N) can be controlled by changing the content of C, N, and Nb elements, which can weaken the tendency of element segregation to a certain extent. However, the accuracy of alloy composition design optimization is attributed to the accuracy of the phase diagram calculation database and how to consider the interaction between a large number of alloy elements [41, 42]. In addition, it is also necessary to maintain the service performance and production cost of the alloy in its operating environment [43-45]. Therefore, in the actual production process, it is difficult to optimize the quality of the billet by directly changing the composition.
In the actual continuous casting production process, the molten steel needs to pass through the mold, the foot roll...
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Zhi-qiang Li, Ying-xuan Shan, Li Wu, Hua Hou, Yu-hong Zhao (2026). Optimization of multi-process parameters in secondary cooling solidification process of S30432 continuous casting billet. China Foundry. https://doi.org/10.1007/s41230-026-5185-3
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Frequently Asked Questions
What is the main objective of this study?
The main objective is to optimize the multi-process parameters in the secondary cooling solidification process of S30432 continuous casting billet to improve billet quality and reduce cracks caused by niobium segregation.
How was the optimization of process parameters carried out?
A finite element model of solidification and heat transfer was established, and the control variable method was used to study the influence of casting speed and superheat. An orthogonal scheme was designed to investigate the coupling effects of multiple parameters, and optimized parameters were selected and verified through production experiments.
What are the key findings regarding niobium compounds?
The enrichment of coarse niobium compounds directly causes inner wall cracks during hot piercing. Optimized parameters, especially lower superheat and higher specific water flow, promote grain refinement and expansion of the equiaxed crystal zone, mitigating Nb segregation and improving niobium compound distribution.
What is the significance of this research for industrial applications?
The findings provide a practical method to control the quality of continuous casting billets and seamless tubes, reducing defects and improving hot working performance, which is crucial for supercritical and ultra-supercritical power station boilers.
What methods were used to validate the optimization results?
The optimization results were validated through production experiments, which confirmed the improvement in solidification structure and reduction in cracks, demonstrating the effectiveness of the optimized process parameters.
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