Influence of Segmented Rolls on Homogeneity of Cooling in Continuous Casting

This paper deals with secondary cooling in a continuous caster. In particular, it deals with cooling inhomogeneity caused by spray arrangement and segmented rolls used for leading the strand. The cooling section is placed under the mold. Segmented rolls are supported by bearings in several places across the strand. Sprayed water can flow in the gaps between rolls where the bearing pocket is located. The main question that was experimentally studied is how this geometry with segmented rolls can influence homogeneity of cooling. Two experimental approaches developed for this study were applied, and both used full-scale geometrical configuration. The first one was a cold test where water flow and water distribution were observed using a transparent board with the studied surface structures (rollers and bearing pockets) and four spraying nozzles. The second one was a cooling test using a heated steel plate with rolls and bearing pockets. Cooling homogeneity was studied based on the temperature distribution on the rear side of the sample, which was recorded using an infrared camera. Homogeneity of cooling distribution was experimentally studied for three levels of cooling intensity that are used in typical cooling sections in plants. The hot tests showed that the bearing pockets do not provide significant cooling inhomogeneity despite the fact that a large amount of water flows through the gap between the rollers (which has been observed in cold tests).

Optimal Design of the Submerged Entry Nozzle for Thin Slab Continuous Casting Molds

For the purpose of increasing the capacity of an Angang Strip Production (ASP) continuous caster and the surface quality of a medium-thin slab with mold sections of 150 × (1020–1540) mm2, the present work investigated the influences of the submerged entry nozzle (SEN) structure and main operating parameters on the flow characteristic and temperature distribution in the mold by physical and numerical simulations. The results showed that the typical “double-roll” flow and a central jet were formed through the three-port SEN. With the original SEN, the mean wave height exceeded the critical value of 5.0 mm after the casting speed was increased due to the strong upper recirculation flow. By the slight increment of the bottom port area and the side port angle of SEN, the mean wave height was obviously decreased below 4.4 mm due to the depressing of the upper recirculation flow after the casting speed increased. Meanwhile, the temperature distribution was slightly changed by using the optimized SEN. The practical application showed that the breakout rate decreased from 0.349% to 0.107% and the surface defect rate decreased from 0.54% to 0.19% by using the optimized SEN, while throughput reached the new level of 3.96 t/min.

Optimization of the Continuous Casting Process of Hypoeutectoid Steel Grades Using Multiple Linear Regression and Genetic Programming—An Industrial Study

Štore Steel Ltd. is one of the major flat spring steel producers in Europe. Until 2016 the company used a three-strand continuous casting machine with 6 m radius, when it was replaced by a completely new two-strand continuous caster with 9 m radius. For the comparison of the tensile strength of 41 hypoeutectoid steel grades, we conducted 1847 tensile strength tests during the first period of testing using the old continuous caster, and 713 tensile strength tests during the second period of testing using the new continuous caster. It was found that for 11 steel grades the tensile strength of the rolled material was statistically significantly lower (t-test method) in the period of using the new continuous caster, whereas all other steel grades remained the same. To improve the new continuous casting process, we decided to study the process in more detail using the Multiple Linear Regression method and the Genetic Programming approach based on 713 items of empirical data obtained on the new continuous casting machine. Based on the obtained models of the new continuous casting process, we determined the most influential parameters on the tensile strength of a product. According to the model’s analysis, the secondary cooling at the new continuous caster was improved with the installation of a self-cleaning filter in 2019. After implementing this modification, we performed an additional 794 tensile tests during the third period of testing. It was found out that, after installation of the self-cleaning filter, in 6 steel grades out of 19, the tensile strength in rolled condition improved statistically significantly, whereas all the other steel grades remained the same.

Combined Effects of EMBr and SEMS on Melt Flow and Solidification in a Thin Slab Continuous Caster

Electromagnetic fields have emerged as powerful tools for addressing current problems in thin slab continuous casting processes in the iron and steel industry. Substantial studies have been undertaken on the fundamental effects of electromagnetic brakes (EMBr) and strand electromagnetic stirring (SEMS). However, little attention has been focused on melt flow and solidification in a thin slab continuous caster with the simultaneous application of an EMBr and SEMS. The present study aimed to predict transient fields in the caster using a large eddy simulation and an enthalpy-porosity method. The electric potential method was applied in the braking process, and the conductivity change with solidification was considered. The suppressive effect on the intensity of the nozzle jet, the balance effect on the mold flow, and a dispersion effect could be observed. The dispersion effect was a novel finding and was beneficial to a flatter nozzle jet. In contrast, SEMS caused a highly turbulent flow in the strand. A large vortex could be observed in the casting direction. The solidified shell became more uniform, and the solidification rate became obviously slower. These findings supported the view that a high-quality thin slab can be produced by the application of an EMBr and SEMS.

Deep Learning Sequence Methods in Multiphysics Modeling of Steel Solidification

The solidifying steel follows highly nonlinear thermo-mechanical behavior depending on the loading history, temperature, and metallurgical phase fraction calculations (liquid, ferrite, and austenite). Numerical modeling with a computationally challenging multiphysics approach is used on high-performance computing to generate sufficient training and testing data for subsequent deep learning. We have demonstrated how the innovative sequence deep learning methods can learn from multiphysics modeling data of a solidifying slice traveling in a continuous caster and correctly and instantly capture the complex history and temperature-dependent phenomenon in test data samples never seen by the deep learning networks.

The Spontaneous Emulsification of Entrained Inclusions During Casting of High Aluminum Steels

Mold slag entrainment during the continuous casting process presents a late stage source of non-metallic inclusions (NMI) with a high likelihood of ending up in the final product. The reaction between the entrained slag phase and surrounding liquid steel in the continuous casting mold affects the inclusion morphology and properties. However, there is a lack of information on the kinetics of the NMI-steel reaction. A novel approach, utilizing controlled synthetic inclusion/metal samples, has been developed to study the reactions between free inclusion-slag droplets and steel. The technique combines High-Temperature Confocal Scanning Laser Microscopy (HT-CSLM), X-ray Computed Tomography (XCT) and advanced electron microscopy techniques offering rapid controlled heating performance and extensive characterization of the samples. This method offers the ability to observe the size, shape and composition of an unconstrained reacting inclusion and to investigate the interface between the materials with respect to reaction time. This study interrogates a low aluminum steel (0.04 wt pct) and a high aluminum steel (1 wt pct) in contact with an inclusion-slag phase with a starting composition aligned to a typical mold slag. It was found that the reaction between silica and aluminum across the interface of the two phases provided a driving force for spontaneous emulsification to occur. Products of such emulsification will have a significant effect on the inclusion size distribution and potentially the prevalence of inclusion retention in molten steels solidifying in the continuous caster (for example if emulsified buoyancy forces are reduced to near zero) and hence in the subsequent solid product.