Generalized stability criterion for columnar to equiaxed grain transition during solidification upon vertical twin roll casting
(1. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China;
2. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China;
3. State Key Laboratory of Super Hard Materials, Jilin University, Changchun 130012, China;
4. Analytical & Testing Center, Northwestern Polytechnical University, Xi’an 710072, China)
2. State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China;
3. State Key Laboratory of Super Hard Materials, Jilin University, Changchun 130012, China;
4. Analytical & Testing Center, Northwestern Polytechnical University, Xi’an 710072, China)
Abstract: To promote the columnar to equiaxed grain transition (CET) to obtain uniform equiaxed grain, most of the available theoretical works mainly focus on the growth but ignore the nucleation. Regarding it, a systematical framework integrating nucleation catalyzed by refiners with dendritic growth, was constructed, where, a new conception of generalized stability (GS), considering evolving thermodynamic driving force (？G) and kinetic energy barrier (Q) upon solidification of VTC, was adopted to study the CET position, the grain radius and the mechanical properties. By adding the refiners, especially the Al-5Ti-1B refiner, the larger thickness of 5-6 mm for equiaxed grain and finer grain radius of 19 μm are exhibited by increasing the ？G for nucleation and the GS for growth, possessing simultaneously improved strength and plasticity. Following a criterion of high ？G-high GS, the refiner diameter is optimized to be 0.3 μm.
Key words: generalized stability; refiner; columnar to equiaxed grain transition; twin roll casting