Quality In Continuous Casting Research Articles

Secondary cooling parameter optimisation for vertical continuous casting of AISI H13 large round bloom

ABSTRACT The generation of bulging and macro-segregation owing to surface temperature rebound and stress fluctuation are detrimental for the final quality of continuous casting (CC). In this study, physical and mathematical modelling of a large-bloom vertical CC is established. The Sasaki equation is optimised, and the accuracy of calculation model is verified by nail-shooting experiment and the temperature measurement. By regulating specific water flow in secondary cooling zone, the influence on surface temperature, stress fluctuation, macro-segregation and macro-structure are investigated. Results show that the decreasing specific water flow decreases surface temperature rebound and stress fluctuation. Besides, when specific water flow decreases from 0.25 to 0.09 L kg−1, the positive and centre negative segregation of bloom is improved, the content of C at bloom centre increases from 0.25 to 0.32. The equiaxed crystal ratio increase from 38.51% to 43.57%. In conclusion, a lower specific water flow can reduce the defects.

Electromagnetic Forces in Continuous Casting of Steel Slabs

This paper reviews the current state of the art in the application of electromagnetic forces to control fluid flow to improve quality in continuous casting of steel slabs. Many product defects are controlled by flow-related phenomena in the mold region, such as slag entrapment due to excessive surface velocity and level fluctuations, meniscus hook defects due to insufficient transport of flow and superheat to the meniscus region, and particle entrapment into the solidification front, which depends on transverse flow across the dendritic interface. Fluid flow also affects heat transfer, solidification, and solute transport, which greatly affect grain structure and internal quality of final steel products. Various electromagnetic systems can affect flow, including static magnetic fields and traveling fields which actively accelerate, slow down, or stir the flow in the mold or strand regions. Optimal electromagnetic effects to control flow depends greatly on the caster geometry and other operating conditions. Previous works on how to operate electromagnetic systems to reduce defects are discussed based on results from plant experiments, validated computational models, and lab scale model experiments.

Determining the quality of continuous casting from billet caster

There are various methods and practical examples to determine and to evaluate the production quality level. They include measuring, sensory, calculation, data-recording, sociological and expert methods. Among the variety of general-purpose statistical methods, only seven of them are chosen, which are applied by different specialists. They allow timely detecting and showing the problems, revealing the main points to start with, and helping to distribute the efforts to effectively fulfill main tasks.

A particle swarm approach for optimization of secondary cooling process in slab continuous casting

Secondary cooling control is the key factor for stabilizing and enhancing slab quality in continuous casting. In view of practical importance of critical boundary conditions in offline or online simulation and control during continuous casting process, accurate estimation for heat transfer coefficient of secondary cooling zone is of utmost significance. To optimize the cooling process and temperature behavior of continuous casting slab, a novel method was presented to predict the heat transfer behavior in secondary cooling process. This approach applies the particle swarm optimization (PSO) algorithm in conjunction with the mathematical heat transfer model and the experimental temperature to determine the heat transfer coefficient. Through verifying the validity and efficiency of the integrated method proposed, the temperature variation of slab surface is more coincident with measured temperatures along the casting direction. The calculation results confirm that the heat transfer coefficient could be estimated precisely with measurement temperatures using PSO algorithm. The combined approach offers an applicable technology for optimization of cooling strategy and solidifying process in continuous casting.

Comparative Analysis of Bulge Deformation between 2D and 3D Finite Element Models

Bulge deformation of the slab is one of the main factors that affect slab quality in continuous casting. This paper describes an investigation into bulge deformation using ABAQUS to model the solidification process. A three-dimensional finite element analysis model of the slab solidification process has been first established because the bulge deformation is closely related to slab temperature distributions. Based on slab temperature distributions, a three-dimensional thermomechanical coupling model including the slab, the rollers, and the dynamic contact between them has also been constructed and applied to a case study. The thermomechanical coupling model produces outputs such as the rules of bulge deformation. Moreover, the three-dimensional model has been compared with a two-dimensional model to discuss the differences between the two models in calculating the bulge deformation. The results show that the platform zone exists in the wide side of the slab and the bulge deformation is affected strongly by the ratio of width-to-thickness. The indications are also that the difference of the bulge deformation for the two modeling ways is little when the ratio of width-to-thickness is larger than six.

Sensitivity Analysis for Controlling Molten Steel Temperature in Tundish

Controlling temperature of molten steel is crucial for product quality in continuous casting. In this paper, sensitivity analysis is carried out on a statistical model for predicting temperature in tundish, and influential operations for controlling temperature are identified.

Finite Element Thermal-Mechanical Coupled Analysis of Strand Bulging Deformation in Continuous Casting

In order to reduce the internal cracks and control the quality of the steel strand in continuous casting, a thermal-mechanical model considering the movement of the strand, real roll arrangement and caster structure, has been established with the elasto-viscoplastic constitution to predict the three dimensional temperature distribution and bulging deformation of the strand. Using the sequentially coupled finite element method the model is solved numerically, and is validated by the comparisons of the simulation results and measured data. The model is suitable for future research on the whole strand bulging deformation to help improve the strand quality in continuous casting.

Thermal behaviour of moulds with different water channels and their influence on quality in continuous casting of beam blanks

Two-dimensional finite element heat transfer models have been developed to predict temperature distribution in beam blank moulds with large and small hole water cooling channels. The effects of water channel design and grinding thickness on transverse temperature profile in meniscus region were analysed in detail. The effects of both moulds during plant trials are also compared. The results show that the peak temperature is found in the fillet area of the large hole mould and is 20°C higher than that of the small hole mould. With increasing grinding thickness, peak temperature in both moulds decreases linearly, and when the grinding thickness reaches 9 mm, the peak temperature of the small hole mould exceeds that of the large hole mould. The transverse temperature uniformity of the hole mould is superior to that of the large hole mould. It is also found that longer mould life, better strand surface quality and more homogeneous surface microstructure are obtained when using the small hole mould.

Development of high value added tin plate steels at CST

CST has supplied 1.5 million tons of tin plate slabs to the world market since 1997 for several final applications, including D&I, Draw Cans, Double Reduction, Easy Open End. After CSTs hot strip mill was commissioned in September 2002, the Company has supplied hot coils for the foreign market tin plate production since March 2003. In partnership with its customers, CST defined criteria for slab application based on continuous casting quality events and continuous casting parameters, and their relationship with the quality results on the final product.

Investigations of Flow Conditions and Solidification in Continuous Casting Moulds by Advanced Simulation Techniques

Concerning further improvement of product quality in continuous casting, advanced simulation techniques are successfully used to investigate and optimise the complex flow and temperature conditions and the physical phenomena related to them. The work presented here focuses on the mould and discusses the corresponding application of selected mathematical and physical simulation techniques. Transient numerical simulations considering multiphase flow conditions and solidification with mould oscillation provide detailed information on the so-called solidified hook formation directly below the meniscus. Concerning mould powder performance, the numerical simulation approach is carried out considering the flux flow in the meniscus region in order to obtain information e.g. on the mould powder consumption. With physical model investigations performing simultaneous and time dependent measurements of flow field and mould level behaviour, an optimised SEN design for the thin slab casting could be developed, which allows significantly higher casting velocities and yield, respectively. Operational plant trials confirm these results.

Swirling Flow Effect in Immersion Nozzle on Flow in Slab Continuous Casting Mold.

With increasing requirement of steel productivity and quality in continuous casting in the conventional casting system using an immersion nozzle with side pouring holes, it is very difficult to establish a reasonable molten flow pattern. In order to overcome this difficulty, we propose a new method imparting a swirling motion to the flow in the immersion nozzle and to control the flow pattern in the mold. Obtained results are as follows: 1) High amplitudes of oscillation with a period of 10 to 15 sec are observed in the outlet flow of the immersion nozzle and meniscus flow in the conventional casting system, while these phenomena are remarkably suppressed using swirling motion in the immersion nozzle, which leads to very calm and uniform flow pattern at the outlets of the immersion nozzle, in the mold and on the meniscus in the mold. 2) The steady outlet flow softly impinges on the side wide face, and then turns around as a reverse flow along the other wide face describing a S-shaped curve in the cross section and clock-wise rotational flow in the vertical section. This outlet flow exerts a shearing-effect on the inner wall of the mold, leads to the considerable energy consumption and exerts a braking effect in the flow which results in suppression of self-excitation-vibration in the bulk mold flow and biased flow on the meniscus. In other words, imparting a swirling motion to the flow in the immersion nozzle, remarkably reasonable bulk mold flow can be obtained.

Prevention of Air Suction from the Contact-part between Sliding Gate and Immersion Nozzle.

With increasing requirement of steel quality in continuous casting, it is extremely important to regulate reasonably flow rate of molten steel without either biased flow or reoxidation by the suction of air from around the contact-part between sliding gate (SG) and immersion nozzle (SEN). In this study, a novel/method to prevent the suction of air from all around the contact-part between the SG and SEN during controlling the flow rate of molten steel, has been developed by giving a step to the SEN. The effects of the step in the SEN on the prevention of air suction from all around the contact-part can be summarized as follows: (1) The flow squeezed passing through the SG is turned abruptly just before the step in the SEN and, as a reverse flow, passes towards the contact-part between the SG and SEN, where its kinetic energy is converted into the pressure energy as a kind of impinging-flow-action, resulting in a positive pressure on the contact-part. (2) With increasing amount of sliding-gate-opening, the distance downstream from the gate to the step, that is necessary for the contact-pressure to be positive on the contact-part, becomes wider. Over some opening amount, the contact pressure is always positive under the condition that a dimensionless step width (ratio of step-width to inner-diameter of nozzle) is over 0.15. From the above-mentioned issues, it is found possible to prevent the air suction from all around the contact-part between the SG and SEN using the SEN with the step beneath the sliding gate.

96/04219 Electromagnetic braking improves steel quality in continuous casting

96/04219 Electromagnetic braking improves steel quality in continuous casting

Simulation of Shell Strength Properties by the SSCT Test.

Initial shell formation and surface quality in continuous casting are affected by thermal and mechanical stresses which may lead to crack formation during solidification. Thus, detailed knowledge of high temperature strength properties as function of steel composition is required under given conditions. To simulate shell straining by tensile force perpendicular to the main dendrite growth axis, the Submerged Split Chill Tensile (SSCT) test was (and still is) further developed. The present report details updated results for ferritic and austenitic iron, and compares different chill materials. The determined effect of P-content on shell strength is quantified. Primary dendrite arm spacing without and with load appears to indicate that tensile elongation is not uniformly distributed over the test length.

Influence of alloying elements on central billet quality of continuous casting

Influence of alloying elements on central billet quality of continuous casting