Effect of Flow Field Optimization of an Asymmetric Multi-Strand Tundish on the Quality Consistency of Cracking Con-Rod Steel

Abstract

Cracking con-rod is an advanced high-precision connecting structure based on brittle expansion, breaking and reconnection of steel, to solve the problem of assembly circle missing. High carbon micro-alloyed steel C70S6, as a dominant material for the production of cracking con-rod, has extremely strict requirements on non-metallic inclusions in steel and microstructure stability. Continuous casting tundish plays an important role in removing large-sized inclusions and stabilizing casting quality. Aiming at the inconsistent casting quality of C70S6 steel produced by a three-strand asymmetric tundish and the frequent occurrence of slag entrapment problems in Xining Special Steel, the tundish structure was optimized by means of physical modelling combined with numerical simulation, and the quality of the bloom castings and subsequent hot-rolled products before and after optimization were compared based on volume production. The results show that a new flow control design to the tundish can effectively improve the consistency of its metallurgical effect for each of the three strands and the following overall product quality, in which the flow field and temperature field in the tundish are more uniform. This is due to the adoption of a vortex inhibitor and an optimized wall structure according to the measured RTD curve, ink trajectory and numerical simulation on the 3-D streamline contours and temperature distribution in the tundish. The peak concentration of outlet 1 is decreased from 6.5 before optimization to less than 2.0 after optimization, which means the elimination or alleviation of the local short-circuit flow. The maximum temperature difference of C70S6 molten steel measured at the outlets of the tundish three strands is decreased from 2–5 °C to 1–3 °C, which is in good agreement with the numerical simulation results. The difference in columnar crystal ratio of the corresponding bloom castings is decreased from 2.27–3.17% to 1.26–1.85%, and the consistency of central carbon segregation index is also significantly improved. In addition, the difference in oxygen content among the three strand blooms is decreased from 1.7–3.5 ppm to 0.8–1.9 ppm. As a result, the overall mechanical properties and microstructure stability of the hot-rolled products are improved statistically, in which the hardness fluctuation is decreased from 84 HBW to 60 HBW, the inclusion grade of types B + C + D + Ds is reduced to 1.105, and the occurrence rate of Ds dropped to 0.118%. Accordingly, the failure rate of the cracking con-rod is controlled stably within 4‰, and the fracture is generally smoother than that before tundish optimization. In summary, the flow field optimization to a multi-strand asymmetric tundish has a clear effect on improving the overall quality of its bloom castings and rolled products, which should be paid more attention industrially. Meanwhile, the present study provides a reliable theoretical and experimental reference for the improvement of metallurgical effects of an asymmetric-typed tundish commonly used in special steel production.

Structural optimisation of three-strand asymmetric tundish for super large round bloom continuous casting

“…Moreover, production trials have identified that the structures of multi-strand asymmetric tundishes and the instability of steel cleanliness during non-steady-state casting are major constraints in the production of high-quality steel. 22,23 Therefore, this study aims to optimise the structure of a super-large round bloom casting three-strand asymmetric tundish at a certain steel plant. By employing a combination of physical experiment and numerical simulation methods, the research enhances the flow field and temperature field distribution within the tundish.…”

Comparison of Fluid Flow and Tracer Dispersion in Four-Strand Tundish under Fewer Strand Casting and Sudden Blockage of Strand Conditions

“…To meet the demands of producing clean steel, researchers have employed both physical [1][2][3][4][5] and mathematical [6][7][8][9][10][11] simulation methods, focusing on the flow of molten steel. This entails optimizing flow control devices [12,13], adjusting process parameters [14,15], implementing gas blowing in the tundish [16,17], and utilizing induction heating technology [18,19]. These endeavors aim to continuously improve the tundish flow field [20,21], temperature distribution [22,23], and enhance inclusion removal efficiency [6,24,25], ultimately elevating the quality of steel products.…”

Evaluation of Molten Steel Flow Behaviors in a Multistrand Tundish via Numerical Simulation and Grey Relational Analysis with a New Dimensionless Operator

“…The worse the consistency, the greater the difference in casting quality between the strands. To reduce the inconsistent casting quality of C70S6 steel, Tie et al [ 21 ] optimized the tundish structure based on numerical simulations and industrial trials. After optimization, the difference in the columnar crystal ratio of the corresponding bloom casting decreased from 2.27%–3.17% to 1.26%–1.85%, and the consistency of the central carbon segregation index improved significantly.…”