Slab Continuous Casting Research Articles

Thickness influence on element segregation in continuously cast steel slabs

The article presents the results of a study of the effect of slab thickness on the element segregation of during continuous casting of billets. The process of accumulation of elements on the surface of dendrites during crystallization of steel slabs for various thicknesses is considered. The theoretical dependence of the process of accumulation of elements on the dendrite surface during the crystallization of steel slabs for various thicknesses has been established. It is shown that the efficiency of accumulation of elements on the dendrite surface depends significantly from the crystallization and cooling rate of the slab. The established dependence makes it possible to determine the permissible increased element content in strips, which is equivalent to their content in thick slabs during continuous casting of billets. The element segregation searching shows that at pouring of thin steel strips, an increasing of the element content is possible compared to continuous casting of thick slabs with an identical level of segregation. The elements are arranged as possible to maximize the impurities content in AISI 1006 carbon steel in the following decreasing sequence: S, O, N, P, H. Another sequence is observed for stainless steel AISI 304: O, S, P, H, N. The following sequences are observed in the case of residual elements: for steel AISI 1006 - Pb, Bi, Sn, As, Zn, Sb, Cu; for steel AISI 304 - Cu, Sb, Sn, Bi, Pb, As, Zn. The sequences are as follows for the alloying elements: for steel AISI 1006 - B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si, Cr; for steel AISI 304 - Ca, Te, Al, Ti, Mg, C, La, Ce, Nb, Se, V, B, Si, Cr, Mn.

Estimation of minimal slab reduction to eliminate of axial porosity

In the production of the continuous cast slabs using continuous-casting machine, the formation of axial porosity is observed. Method for determination of the minimal reduction of the workpiece during hot rolling in order to eliminate the axial defect is presented. The theoretical dependences for transformation of the axial porosity on drawing and the reduction rate of continuously cast slab during hot rolling are obtained based on assumptions.

Multiscale Convolutional and Recurrent Neural Network for Quality Prediction of Continuous Casting Slabs

Quality prediction in the continuous casting process is of great significance to the quality improvement of casting slabs. Due to the uncertainty and nonlinear relationship between the quality of continuous casting slabs (CCSs) and various factors, reliable prediction of CCS quality poses a challenge to the steel industry. However, traditional prediction models based on domain knowledge and expertise are difficult to adapt to the changes in multiple operating conditions and raw materials from various enterprises. To meet the challenge, we propose a framework with a multiscale convolutional and recurrent neural network (MCRNN) for reliable CCS quality prediction. The proposed framework outperforms conventional time series classification methods with better feature representation since the input is transformed at different scales and frequencies, which captures both long-term trends and short-term changes in time series. Moreover, we generate different category distributions based on the random undersampling (RUS) method to mitigate the impact of the skewed data distribution due to the natural imbalance of continuous casting data. The experimental results and comprehensive comparison with the state-of-the-art methods show the superiority of the proposed MCRNN framework, which has not only satisfactory prediction performance but also good potential to improve continuous casting process understanding and CCS quality.

Clogging‐Induced Asymmetrical and Transient Flow Pattern in a Steel Continuous Casting Slab Strand Measured Using Nail Boards

Herein, the fluid flow pattern in a continuous casting slab strand with varied degree of clogging of the submerged entry nozzle is measured using nail boards in industrial trials. The influence of clogging on meniscus velocity, top surface position, surface level fluctuation, and slag entrainment of the strand is investigated. The number density and area fraction of nonmetallic inclusions including Na2O and K2O‐bearing entrained slag ones within the subsurface of steel slabs are inspected using an automatic scanning electron microscope (SEM). The flow pattern in the strand periodically transforms from a double roll flow to a complex flow and/or a single roll flow. The fluid field in the continuous casting mold is unstable and asymmetric under the condition of varied degree of clogging with time. The variation of the meniscus velocity and the surface level fluctuation with time is stochastic. The percentage of >3 mm level fluctuation increases from 4.7% to 10.6% with a serious clogging of the submerged entry nozzle. The amount of entrained slag inclusions with serious clogging is approximately 1.6 times than that with slight clogging. In addition, slag entrainment mechanisms of the shear‐layer instability and the vortex formation are discussed.

Influence of Austenitizing Parameters on the Microstructures and Mechanical Properties of 22MnB5 Hot Stamping Steel Produced by TSCR Process

Thin gauge hot strip steel can be produced by thin slab continuous casting and rolling (TSCR) process without the aid of cold rolling. However, few attempts have been made to produce hot stamping steel by using TSCR technology. As given steel, the hot stamping steel produced by the TSCR process was used to study the influence of austenitizing parameters on the final microstructures and mechanical properties. A Gleeble3500 thermal simulator was employed to heat the samples to obtain different austenite microstructures. After quenching, the Vickers hardness examination along the thickness of the sample and tensile testing were conducted. The microstructure was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that on the condition of relatively lower temperature and shorter holding time, the sample exhibited better mechanical properties at the cost of microstructure uniformity along the thickness, although higher austenitizing temperature enhanced the carbide dissolution which would increase the effective carbon content in the martensite matrix. Lower heating temperature led to small prior austenite grain size and small blocks which contributed greatly to the mechanical properties.

End-to-End Quality Evaluation of Continuous Cast Slabs and Hot-Rolled Sheet Products from Ship-Delivered Batches

The results of an end-to-end quality evaluation of continuous cast SS400 steel slabs, followed by its hot-rolled thick-sheet products in ship-delivered batches, are presented. The evaluation of the frequency distribution of defects for each of the continuous casting machines (CCMs) revealed the following: even during control fire cleaning, the surface quality of slabs from CCM No. 1 was slightly lower (1.1–2.0%) than from CCM No. 2; the finished sheets from slabs casted at CCM No. 1 have a better quality than from slabs casted at CCM No. 2. At the same time, on both machines, the quality of slabs from strand No. 2 is better than from strand No. 1. The unstable internal quality of the sheet with a thickness of 30–45 mm was due to restrictions imposed on the maximum thickness of the sheet which was 25.0 mm. During microstructural analysis of the causes of cracks and segregation nature, it was found that the presence of non-metallic inclusions in the sheet structure serves, in fact, as a source of crack development. Analysis using energy-dispersive x-ray spectroscopy (EDX) showed that nonmetallic inclusions in the dominant mass are manganese sulfides.

Improvement of Technology for Producing Rolled Sheet from Continuously Cast Steel Slabs. Part 1. Experimental Study of Casting Using a Pressure Submersible Nozzle

It is proposed to use a new submersible nozzle with eccentric apertures in order to improve continuously-cast slab quality. Calculations show that up to 38% of the heat of steel overheating is removed in the upper part of the crystallizer. The number of equiaxed crystals increases by several factors with an increase in crystallization rate. Pilot plant approval of advanced continuous casting of low-carbon and low-alloy steels makes it possible to improve hot rolled metal strength and toughness. Forecasting low-carbon steel sheet ultimate strength and relative elongation is conducted using known experimental equations. Rolled steel quality is evaluated from slabs selected from eight melts. The slab sulfur content obtained using a nozzle with eccentric apertures is somewhat higher than in slabs cast through existing nozzles.

Effect of Magnesium Treatment on the Hot Ductility of Ti-Bearing Peritectic Steel

Surface cracking is a major defect in the production of continuous casting slabs of peritectic steel. The difference in crystal structure between δ phase (before peritectic transformation of steel) and γ phase (after peritectic transformation) results in volume contraction, which leads to uneven cooling of mold and thus forming slab shells with different thicknesses. Then, coupled with the concentration of local stress, surface cracking occurs on slabs. In this paper, the effect of magnesium treatment on the hot ductility of Ti-bearing peritectic steel was studied, and the characteristics of solidification structure and TiN particles were analyzed. Magnesium treatment for Ti-bearing peritectic steel could significantly improve the hot ductility of continuous casting slabs by refining the original austenite structure. After the magnesium treatment, the average grain size of the original austenite of peritectic steel decreased by about 18.7%, and the size of Mg-rich TiN particles decreased by about 41%. In addition, the minimum reduction of area at the third brittle zone after the magnesium treatment was higher than 60%, and the fracture appearance changed from intergranular fracture to ductile fracture after the treatment. The contents of Mg, Ti, O, and N in peritectic steel and the cooling conditions were adjusted reasonably to promote the formation of highly dispersed Mg-rich TiN particles with a sufficient number density and a proper size in the initial solidification stage of peritectic steel, so as to induce the high-temperature δ-ferrite nucleation. Based on the fine δ structure formed by peritectic transformation, through the use of structure heredity and the pinning effect of secondary-precipitated nano TiN particles on the austenite grain boundary, a fine and dense original austenite structure could be obtained to improve the hot ductility of peritectic steel. Industrial tests showed that through the magnesium treatment, the surface cracks of Ti-bearing peritectic steel were effectively restrained, and the corner cracks of slabs were basically eliminated.

The Three-Dimensional Morphology and Distribution of CaS Inclusions in Continuous Casting Slab of Ni20Mn6 Steel.

Calcium sulfide (CaS) inclusion with large and irregular shape is detrimental to the properties of steel. Understanding the shape and distribution of CaS inclusions in a continuous casting (CC) slab is of significance for improving the rolling properties. In this study, CaS inclusions were extracted from CC slab of Ni20Mn6 steel using the electrolytic extraction and investigated by scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX). The CaS inclusions morphologies vary with their locations in the CC slab and, thus, are classified into five categories. The thermodynamics calculated results showed that CaS inclusions precipitated at the end of solidification due to the microsegregation of sulfur and calcium in the interdendrite liquid and finally precipitated along the austenite grain boundary. The macrosegregation degree of solutes in different regions is one of the reasons that affect the size of CaS inclusion. The morphologies of CaS inclusion are affected by the solidification structure of slab and austenite grain boundary.

Modeling of breakout prediction approach integrating feature dimension reduction with K-means clustering for slab continuous casting

Breakout is a catastrophic accident in continuous casting. The existing breakout prediction methods based on logical judgment and neural networks need to constantly adjust the prediction parameters or prepare high-quality samples as the input, resulting in poor robustness and unstable precision stability. Therefore, it is particularly important to develop a breakout prediction method that not only can predict breakout accurately but also avoid human intervention significantly. This work proposes a novel approach for breakout prediction combining K-means clustering and feature dimension reduction. The method uses feature dimension reduction to obtain the typical feature vector (TFV) that can characterize the original temperature change trend, and then a K-means clustering model is established to realize online detection of breakout prediction. The results show that the model has a 100% alarm rate for the true breakout, and meanwhile, reduces the number of false alarms from 555 to 217 compared with the on-line breakout prediction system (BPS). The proposed method does not need to adjust the prediction parameters frequently or prepare the input samples carefully, which not only avoids the human intervention but also meets the requirements of online monitoring for the practicality and applicability of the breakout prediction method.

A 3D model coupled inverse algorithm for the non-uniform thermal behavior of a continuous casting mold

A 3D finite element model of a copper plate in a continuous casting mold, including arc-shaped water slots and a nickel layer with increasing thickness, was built to reflect the flexible and non-uniform thermal behavior of the mold during wide-thick slab continuous casting. The inverse algorithm was applied to calculate the heat flux from temperatures measured by thermocouples, which were buried in various locations inside the mold. The model can reflect the real thermal behavior of the mold wall and further evaluate the effects of the nickel layer and water slots on heat transfer of mold. Along the casting direction, the temperature peaks appear approximately 100 mm below the meniscus. The temperature gradient in the nickel layer in the thickness direction is larger than that in the copper plate. The average temperature at the root of deepwater slots is higher than that of shallow ones by 10 °C. The model can further improve casting parameters and operations.

Effect of the microstructure on the crack initiation during thermal cycling of Nb–Ti-bearing continuous casting slabs

ABSTRACT To discussed the influence of reheating and cooling on the crack initiation mechanism under the hot cycle mode of a continuous casting slab, during thermal cycling and analysed the relationship between the lower grain size and the crack initiation toughness under different temperature fluctuations. A thermal expansion tester and a Gleeble-3500 thermodynamical simulator were used to perform thermal processing experiments on the samples, where in the temperature fluctuations during solidification were 25 K, 50 K, and 75 K. Scanning electron microscopy (SEM), optical microscopy (OM) and other characterization methods were used to analyse the morphology, microstructure, thermoplasticity and residual stress of the cracked tensile test samples, which were taken from the Nb-Ti-bearing slabs. The result shows that with the intensification of the temperature-returning process, the grain size at the fracture and the size of the slab fracture toughness are increases, which leading to a decrease in crack initiation toughness.

Effect of vertical-combine EMBr on steel/slag interface in the funnel shape mold of thin slab continuous casting

Effect of vertical-combine EMBr on steel/slag interface in the funnel shape mold of thin slab continuous casting

Prediction of spatial distribution of the composition of inclusions on the entire cross section of a linepipe steel continuous casting slab

In the current study, the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a linepine continuous casting slab was predicted. During cooling and solidification of the continuous casting strand, Al2O3-CaO inclusions reacted with the bulk steel and transformed to CaS-Al2O3-MgO-(CaO) ones in the continuous casting slab. The composition of inclusions on the cross section of the slab varied with locations due to the varied cooling rate. A model was established to predict the distribution of the composition of inclusions on the cross section of the continuous casting slab, coupling solidification and heat transfer of the continuous casting slab, the kinetic mass transfer of the dissolved elements in the solid steel, and thermodynamic calculation of inclusion transformation at different temperatures. The composition transformation of inclusions mainly occurred at the temperature between the liquidus and solidus of the linepipe steel. Inclusions were mainly CaS-Al2O3-MgO-(CaO) in slab center and were MgO-Al2O3-CaO-CaS within the subsurface of the slab. In the slab, the transformation fraction of inclusions was less than 10 % at corners while it reached 70 % at 50 mm below the surface of the slab.

Physical Simulations of Macromixing Conditions in One‐Strand Tundish during Unsteady Period of Continuous Slab Casting Sequence

The tundish as a flow reactor has a special feature, that is, the liquid metal stays in its working capacity for a certain period of time before it enters the mold. This time is effectively used to correct the chemical composition of cast steel. The object of investigation is the wedge‐type tundish, being a component of the continuous casting slab machine. According to the criterion of similarity, the glass model of the tundish is built to a 0.4 linear scale. A tracer is fed into water using the pulse‐step method. During the casting sequences, the time for starting the alloying process, the depth of immersion of the ladle shroud, and the location of feeding the alloy addition change. On the basis of the recorded tracer concentration curves, the mixing time is calculated between the start of feeding the marker to the water and obtaining the required level of chemical homogenization in the water flowing out of the tundish model. Based on the conducted experiments, it is stated that mixing time depends on feeding positions, time of feeding initialization, and hydrodynamic conditions in the tundish during particular stages of the casting sequence.

An Optimization Control Method for Heat Transfer Model during Slab Continuous Casting

Solidification of continuous casting slab is a complex process including a series of phenomena such as heat transfer, mass transfer and flow. The secondary cooling process plays an important role in the production quality of continuous casting slab. In this paper, an improved particle swarm optimization algorithm has been proposed. The simulation results show that the optimized slab temperatures have more reasonable and uniform distribution. The purpose of slab quality improving is achieved and the feasibility of secondary cooling water distribution scheme is verified.

Prediction Approach of Bulging Position and Deformation Based on Hilbert–Huang Transform in Slab Continuous Casting

Bulging is the typical shape defect of continuous cast slab, which could often lead to center segregation, shrinkage porosity and slab cracks, even causing casting interruption in severe cases. Online prediction for the bulging is of great significance for stabilizing and improving slab quality. Up to now, there are few mature or reliable approaches to predict the accurate information of bulging’s position and deformation. Taking into account that the bulging is closely related to the periodic fluctuation of mold level, this work applied Hilbert–Huang Transform method (HHT) to extract and investigate the periodic fluctuation characteristics, bulging frequency and fluctuation component of mold level caused by bulging. The position and deformation of bulging are predicted with the frequency and amplitude of the component mentioned above. The results informed that the proposed method could accurately detect and locate the position of bulging, and the predicted results of bulging deformation were consistent with that of empirical equations. Meanwhile, the abnormal periodic transverse depressions on the slab surface could also be detected. The proposed approach for slab bulging prediction based on HHT does not need to install additional sensing and measuring elements, which provides a feasible way for predicting position and deformation of bulging.

Numerical simulations of solidification and hot tearing for continuous casting of duplex stainless steel

Hot tearing is one of the major defects in continuous casting of steels, which severely limits the productivity of steelmaking processes. To further understand the defect, the problem of hot tearing in duplex stainless steel produced by a vertical continuous caster was investigated. A three-dimensional heat transfer and elastic–plastic model was developed based on the realistic roller layout in continuous slab casting, using ProCAST software. According to the hot tearing indicator criterion, the influence of operating parameters on the hot tearing susceptibility was evaluated. The results show that the surface temperature distribution is not sensitive to the superheat. The center of wide surface shell at the mold exit is the thinnest, and the thickness is about 10.52 mm at the superheat temperature of 40 °C. The hot tearing mainly concentrates on the slab solidification front and near the narrow face. However, corner cracks are prone to appear near the corner. With the increase in casting speed and the decrease in the cooling intensity in the secondary cooling zone, the solidification end point is rushed, which leads to the position of hot tearing lowering accordingly.

Study on the horizontal continuous casting of Cu-based bulk metallic glass slab

To improve the fabrication efficiency of bulk metallic glasses (BMGs) with high mechanical properties and low costs, Cu47Zr45Al8 and (Cu47Zr45Al8)98.5Y1.5slabs with the cross-section of 50 ×6 mm were produced by horizontal continuous casting method (HCC). It is proved that by adding Y to Cu47Zr45Al8, the crystallization behavior could be significantly decreased, and an amorphous structure was obtained when it was casted at DT=80 K. The obtained amorphous structure was proved by XRD, TEM, DSC analysis. The glass transition behavior and crystallization were identified with Tgof 671 K, Txof 771 K, ΔTxof 80 K, andΔH0of 46.2 J/g, respectively. In terms of mechanical properties, the compressive strength and Vickers hardness reached 1803 MPa and 493 HV, respectively. Fracture morphology revealed that the fracture is characterized by limited rheological deformation and high localization of shear band expansion, which results in a mixed fracture mode of ductile and brittle.

Transient influence of cerium on inclusions in an Al-killed non-oriented electrical steel

ABSTRACT Industrial trials and thermodynamic analysis were performed to investigate the transient influence of cerium on inclusions in an Al-killed non-oriented electrical steel. Inclusions were statistically analyzed using an automatic scanning electron microscope. Without cerium addition, inclusions in the molten steel were predominately MgO·Al2O3 ones as well as a small number of Al2O3–MgO–CaO ones, and precipitates of AlN and MgS formed in the continuous casting slab. In the steel with approximately 10 ppm total oxygen and 10 ppm total sulphur, inclusions of MgO·Al2O3 were modified into homogeneous Ce2O2S ones and Ce–Al–Mg–Ca–S–O dual-phase ones by 35 ppm cerium. With increasing time, the content of cerium decreased to 23 ppm in the tundish and dual-phase inclusions of Ce–Al–Mg–Ca–S–O transformed into CeAlO3 ones. During cooling, inclusions of CeAlO3 transformed into dual-phase MgO–Ce x S ones in the steel with approximately 14 ppm total magnesium. Thermodynamic analysis was in good agreement with observed results.