Flow efficiency in a two-strand continuous casting tundish is studied by analyzing the residential time distribution (RTD) curves in a small-scale tundish water model using a conductive NaCl solution tracer. The velocity fields in the tundish water model are measured by particle image velocimetry, which is used to validate the results of the mathematical model in the article. It is found that the tracer concentration has a significant impact on the predicted dead volume fraction in the RTD analysis. Validated mathematical modeling of the computational fluid dynamics (CFD) technology is performed to explore the root cause of the defective results in the RTD analysis. It is found that the flow inside the tundish is sensitive to density variations caused by the injected tracer. A denser tracer will stay lower in the tundish by gravity and flow out of the tundish more quickly. A proper tracer concentration in the water model experiments is discussed to visualize the dead volume and improve tundish furniture design efficiently for future work, a new method using CFD modeling is proposed in this article, which can directly demonstrate the dead volume's location.
Lamellar heterostructure design is widely recognized as a potential method to improve strength and ductility simultaneously of high-performance steel. However, the high mechanical contrast among soft/hard phase and inharmonic plastic deformation lead to complex fracture mechanisms and limit the improvement of plasticity. Herein, the plasticity and tensile fracture mechanisms of two types of δ-ferrite and lath martensite heterolamellar steels with and without α-ferrite are investigated. The sample without α-ferrite shows a combination of cleavage in δ-ferrite and dimple zones in the martensite. The microcracks initiate in the martensite early and the then the cleavage fracture occurs in the δ-ferrite due to the stress concentration. In contrast, the sample with α-ferrite has lower plasticity. Failure of the samples with α-ferrite is govern by the microcracks initiating in the interface of martensite/α-ferrite. Eliminating the impact of the effect of α-ferrite, the total elongation increases from 8.9% to 11.6%, and the ultimate tensile strength (UTS) increases from 1567 to 1652 MPa. This study investigates the critical factor in plasticity control of dual-phase heterostructure and promotes the development and application of lamellar structure.