Steel Slabs Research Articles

Formation and control of longitudinal cracks in hypoperitectic steel slabs

ABSTRACT Hot delivery and charging techniques can significantly reduce energy consumption, carbon emissions, and the production cycle of products. The defect-free slab is the precondition of this techniques. Herein, the morphological characteristics of the longitudinal cracks were described in detail. The actual phase transition process and solidification shrinkage behavior were analyzed considering the effect of alloy elements. Due to the unreasonable submerged entry nozzle (SEN) structure, the vertical heat transfer is not optimal around the meniscus. When the gap cannot be filled with sufficient liquid slag, an air gap is easily formed between the solidified shell and the mould plates. The effect of uneven solidification and stress concentration on the crack formation will be enlarged by the air gap. A novel SEN with a reasonable structure can significantly improve the thickness of the liquid slag layer and solidification uniformity, and decrease the crack sensitivity of the steel.

Research Mechanism of Formation on Transverse Corner Cracks in the Continuous Casting Slab of Peritectic Steel

To figure out the formation mechanism of transverse corner cracks at the inner and outer arc of peritectic steel slab, the metallurgical microscope, scanning electron microscope with energy‐dispersive X‐ray spectroscopy, and electron probe‐X‐ray microanalysis, are used to study cracks. High‐temperature mechanical properties and the stress distribution of the outer arc of the bending section under different roll gap schemes are studied and simulated. The outer arc cracks expand along the grain boundary, while the inner arc cracks not only extend along the grain boundary but also traverse along the grains. The outer arc cracks are mainly generated at the bending section and are formed and expanded along the ferrite film. The inner arc cracks' cracking temperature is higher than the temperature of austenite transformation to ferrite. The third brittle temperature ranges are 650–850 °C, and the transverse corner crack sensitivity zone is 680–837 °C. The inner arc cracks are generated because of the element segregation and low temperature of the corner and then extended at the straightening section, and new cracks exist. The weakened cooling intensity and bending earlier at the bending section help to reduce the equivalent stress on the slab. The optimized experiments are conducted, and the transverse corner cracks are reduced significantly.

Surface Quality of Fe, Ni and Cr added Hyper-eutectic Al-Si Automotive Alloys under Up-milling and Down-milling Operation

Effect of the elements Fe, Ni, and Cr on the surface quality under machining of hyper-eutectic aluminium-based Al-Si automotive alloys has been carried out as the elements improve the properties of this alloy. Machining is done on a horizontal type milling machine using a high-speed steel slab milling cutter in dry condition. Only the cutting speed varies throughout the experiment, while the machining feed and depth of cut remain fixed. The experimental results show that the addition of these alloying elements increases the roughness and hardness specially due to formation of Fe-rich intermetallic . However, the needle-like has been refined with the addition of Cr, as seen by the microstructure. The SEM fractography shows a huge cleavage of the brittle phase, which initiates the crack propagation for Fe added alloys. The downward force causes compressive stress exerted in down-milling operation, so the results depict higher hardness and better surface finish. Besides, shorter chips are formed in down-milling than up-milling process, which rather causes the brittleness of the alloys. When the cutting speed is raised, the surface quality deteriorates due to high temperature, while the hardness improves initially due to formation of precipitates then decreases due to coarsening of precipitates.

Investigation of the punching shear behaviors of reinforced concrete slab–steel reinforced concrete L-shaped column connections

To study the punching behaviors of reinforced concrete (RC) slab–steel reinforced concrete (SRC) L-shaped column connections, four slab–column connection tests were designed and completed, and a new punching shear resistance measure proposed. The test variables were column section shape, slab thickness and column cap. The test results show that the failure mode of L-shaped column was mainly two-way shear. Meanwhile, increasing slab thickness and installing column cap can effectively improve the ultimate bearing capacity of the slab–column connection. The punching angles formed by the punching cone and horizontal direction at the final failure of the connection were between 23.5° and 49.5°. In addition, a numerical simulation analysis was carried out using ABAQUS software, and the effects of various parameters on the performance of slab–column connections were studied. It was found that the change of column section shape will lead to more complex shear stress distribution and stress concentration phenomenon. However, the punching capacity of the special-shaped column was higher than that of the equivalent square column with the same section area. As a new punching shear resistance measure, inverted T-shaped steel can effectively improve the ultimate bearing capacity of the connections. In addition, when the ratio of slab thickness to web width of inverted T-shaped steel was less than 0.75, the failure mode of the connection changed from brittle punching failure to flexural failure.

Stress Development During Cooling of Continuously Cast Boron-Containing Steel Slabs

Stress Development During Cooling of Continuously Cast Boron-Containing Steel Slabs

Effect of nozzle clogging on flow and inclusion transport in GCr15 steel casting process

Nozzle clogging affects molten steel flow, inclusion transport and slab quality. In this paper, a numerical simulation model for the nozzle clogging and the effect of the relevant parameters on the nozzle clogging simulation is studied. The nozzle clogging impact on the flow, inclusion transport and the nozzle clogging formation process are studied. The numerical simulation of the flow in the mold and nozzle is verified by particle image velocimetry measurement of the mold. The obtained simulation results of the clogged nozzle are verified by industrial experiments. The nozzle clog growth rate increases when the higher inclusion magnification factor is used. However, the nozzle clogging simulation results show that a hole exists in the nozzle clog. The deviation between the nozzle clog thickness obtained by the simulation results and those obtained from the experiments increase when the inclusion magnification factor increases from 1 to 20. The increase of the random walk model parameter increases the randomness of the inclusion transport. It is beneficial to increase the homogeneous simulation results of the nozzle clog thickness. The nozzle clogs that are initially formed in the upper section of the nozzle and extend then to the nozzle port. The nozzle clogs change the inner shape of the nozzle and result in the jet stream disperse, and the impact depth of the jet stream decreases when the solution time increases. The solid shell captures more inclusions, and the solid shell cleanliness decreases when the solution time increases.

Bubble Characterization in a Continuous Casting Mold: Comparison and Identification of Image Processing Techniques

Gas injection is a common practice in numerous metallurgical vessels, and continuous casting mold is one of the examples of such vessels. Argon gas injection into the submerged entry nozzle contributes to increasing the sequence length. However, in some unfavorable conditions, these bubbles become responsible for the occurrence of steel defects such as blister, sliver, and mold slag exposure, etc. Bubbles size distribution in the mold is one of the indicators of cast steel slab quality. Previous studies on estimating the bubble size distribution in mold lack in providing the challenges of automatic image processing (IP) techniques employed to measure the size of the bubbles. On the other hand, bubble size measurement studies performed on other reactors such as bubble columns, etc., are programming intensive and need in-depth knowledge of coding. Some automatic IP techniques also exist which facilitate a user-friendly environment and quick estimation of bubble characteristics. Even though these IP techniques are easy to use, an assessment of their applicability with respect to experiments performed in a particular study is required. Therefore, in this study, details of imaging and automatic IP techniques are discussed through a comprehensive comparative analysis. Three different IP techniques were examined for measuring the bubble sizes, and the performances of these techniques were compared with respect to a newly developed manual benchmark technique. One of the identified techniques, Ellipse Split, was applied to estimate the bubble size distribution at different gas fractions for validation.

From Patient to Agent

From Patient to Agent

Analysis of transverse corner cracks from continuous casting process and comparison to laboratory experiments

Low alloyed steel slabs produced by continuous casting can present transverse corner cracks, which are critical due to the oxide layer formed within the crack. Understanding this type of failure and reproducibility of the phenomenon through laboratory tests is of great value for dealing with this problem. The present work analyzed samples from slab corners, where cracks were identified. The fracture surfaces were examined using a scanning electron microscope (SEM) and cut to have their microstructure analyzed with a light optical microscope (LOM). Using etching to reveal the microstructure of the samples from the slabs, it was seen that the cracks were initiated and propagated at the prior austenite grain boundaries. Furthermore, the SEM images from the corner samples were compared to those from the physical simulation of the continuous casting process from previous work, and the structure found was like the ones tested at critical temperatures. The same was noted for the microstructure analysis, where cracks were also seen to follow the grain boundaries. Therefore, it was concluded that the behavior resulted from the laboratory tests performed with in-situ melted samples with the BETA 250-5 machine were in good accordance with the reality of the continuous casting process.

Are edger rolls useful to control the plate motion and camber in a reversing rolling mill?

In heavy-plate hot rolling, reversing rolling mills are typically used to reduce the thickness of steel slabs. Some reversing rolling mills are equipped with edger rolls to control the width of the rolled plate. At best, the straight plate centerline coincides with the lateral centerline of the rolling mill and the desired rectangular shape is exactly realized. In reality, lateral asymmetries like temperature gradients and thickness inhomogeneities cause a lateral movement, a camber, and a wedge-shaped cross section of the plate. These effects can reduce the product quality and entail collisions with the mill stand or other equipment along the roller table. To prevent this, active control of the lateral position and contour shape is desirable. In this work, a roughing mill where the roll gap adjustment is self-retaining, meaning that it can only be adjusted between rolling passes, is considered. As a control input during the rolling passes, the lateral position of the edger rolls is exploited. A mathematical model for both the lateral motion and the resulting shape of the plate is derived. The model is validated by measurement data recorded in an industrial plant. Based on the validated model, the question if edger rolls are useful to control the plate motion and shape is discussed. A two-degrees-of-freedom control concept composed of an optimization-based feedforward controller and a proportional feedback controller with Smith predictor is derived for the lateral motion and shape. The performance of the proposed control concept is demonstrated in simulation studies based on the validated model.

Experimental and numerical research on reinforced concrete slabs strengthened with POZD coated corrugated steel under contact explosive load

In recent years, with the rising of terrorism around the world, new materials and new protection technologies have developed rapidly. In this article, the anti-blast performance of reinforced concrete (RC) slabs strengthened with polyisocyanate oxazolidine (POZD) coated corrugated steel has been studied through contact blast tests and numerical simulations. Two specimens were fabricated, including RC slabs strengthened with corrugated steel and RC slabs strengthened with POZD coated corrugated steel. The failure characteristics of the structure were analyzed. The damage mechanism was revealed by the transmission of stress waves. Additionally, the finite element model of the specimens was established by the Arbitrary-Lagrangian-Eulerian method. The damage modes of the structure under different TNT charges were studied. Then the empirical expressions between failure characteristics (maximum mid-span displacement, bulge long diameter, bulge short diameter) and TNT charges were fitted by dimensionless analysis. The influence of POZD on the anti-blast performance of the structure was studied from three perspectives (maximum mid-span displacement, stress wave attenuation rate, and internal energy absorption). The results demonstrated that with the increase of TNT, the failure characteristics of the structure showed an approximate linear growth trend. When the ratio of the thickness of corrugated steel to the thickness of POZD was 3:2, the explosion resistance was the best.

Influence of Mineralogical Structure of Mold Flux Film on Heat Transfer in Mold during Continuous Casting of Peritectic Steel.

The mineralogical structure of flux films is a critical factor in controlling heat transfer in the mold and avoiding the longitudinal cracking of slabs during the continuous casting of peritectic steel. In this study, the layered structure, crystallization ratio, mineralogical species, and morphology features of flux films were characterized by optical microscopy, X-ray diffraction, and electron-probe microanalysis. Microstructural observation revealed that the normal flux films for peritectic steels present a multilayered structure and high crystallization ratio (60~90 vol%), mainly composed of well-developed crystalline akermanite and cuspidine. In contrast, the films with outstanding flux characteristics with abundant longitudinal cracks on the slab surface have a low crystallization ratio (<50 vol%) or vast crystallite content (>80 vol%). Furthermore, heat transfer analysis showed that the low crystallization ratio and the vast crystallite content of flux films worsen the heat transfer rate or uniformity in the mold, whereas the appropriate thickness and cuspidine content of flux films can improve the heat transfer performance. From the above results, it is concluded that using strong crystalline flux to obtain the ideal mineral phase structure of flux film is one of the important measures for reducing longitudinal cracks during continuous casting of peritectic steel slabs.

Application of Graphite Electrode Plasma Heating Technology in Continuous Casting.

In this study, the industrial, experimental effect of a plasma heating system in the form of graphite electrode in the tundish of double-strand slab caster was evaluated for the first time. The system uses three graphite electrodes, two of which are cathodes and one of which is an anode, to form a conductive loop through molten steel in the tundish. The system is built on an old two-strand slab caster and is installed on the premise that the original ladle tundish equipment remains unchanged. The normal working power of the system is up to 1500 kW, and the heating rate of molten steel in the tundish can reach 1.0 °C/min under conditions of 5 t/min total steel throughput and a tundish capacity of 50 t. After the system was put into operation, the purity of molten steel undergoing heating was investigated. The sample analysis of low carbon steel and ultra-low carbon steel before and after heating showed that the contents of N and O in the steel did not increase, while the size of the oxide inclusions near the heating point increased but showed little change in terms of the overall quantity. This process benefited from the addition of inert gas during the heating process to control the atmosphere in the heating area, which prevents reoxidation. The sample analysis also showed that there is no obvious carbon absorption phenomenon after heating, and the fluctuation in C content is within 0.0001%, which is consistent with the general production results. By using this system, the temperature of molten steel in the steelmaking process can be reduced by 10~15 °C, allowing continuous low superheat casting to be supported, which is helpful for reducing production costs and improving the solidified structure inside the slab. The results of the study show that the plasma heating technology can be applied to the continuous casting of low carbon–nitrogen steel slabs, which shows the benefits of reducing emissions and improving production efficiency.

Experimental and numerical study on joint-free bridges with steel or gfrp-reinforced ecc link slab subjected to static loading

Engineered Cementitious Composite (ECC) and Glass Fiber-Reinforced Polymers (GFRP) have shown substantial durability benefits compared with conventional steel-reinforced concrete. This makes ECC and GFRP ideal materials for construction of durable bridge deck link slabs routinely subjected to extreme weather/environmental conditions. This paper presents experimental results of a two-span joint-free bridge with GFRP-reinforced ECC link slab compared with its companion steel reinforced counterpart. Furthermore, finite element (FE) models of the joint-free bridges were developed and their performance validated based on experimental results using ABAQUS software. FE models were then used to conduct parametric study to investigate influence of various material properties on link slab stiffness, girder rotational capacity and failure modes. Experimental results showed that the use of low-modulus GFRP bars helped to improve bending flexibility and strain distribution in the link slab. Crack development and width control were also enhanced by the use of GFRP bar reinforced ECC link slab. As per the parametric study, greater link slab stiffness and tensile capacity resulted in lower girder end rotation at any given load. Analytical models were found to be good in predicting load capacities of steel/GFRP reinforced bridges with ECC link slabs.

Experimental analysis of shear-lag effect in reinforced concrete T-beams

The non-uniform distribution of normal stresses within wide flanges of beam sections is typically referred to as shear-lag effect. Shear lag is a result of the interaction of normal and tangential stresses or correspondingly by the influence of shear strains on longitudinal strains. In structural engineering, the shear-lag effect has been a concern in the flanges of thin-walled metallic structures or the slab of composite steel–concrete elements, among others. Though existing codes of practice provide a simplified way to address shear lag by means of the effective width concept, such provisions can be insufficient for concrete structures, for which a deeper knowledge on the real influence of shear lag is necessary due to the current trend to design wide concrete bridge girders, with geometric configurations of the cross-sections which can be sensitive to shear lag (i.e. box- or T-sections). Moreover, the influence of the behaviour of structural concrete (cracking, rheology, yielding of reinforcement) has not been dealt with in detail so far. In the present paper, an experimental campaign on two reinforced concrete T-beams is presented. The beams have been subjected to two types of tests: firstly, to time-dependent effects governed by concrete shrinkage and creep; secondly, to the application of increasing direct loads to cover the whole concrete behaviour (uncracked, cracked and ultimate stage). The strain distribution at the top slab of the T-sections has been studied with extensive strain measurements at different cross-sections. The experiments have shown a distinct intensity of shear-lag effect depending on the load type. Moreover, the shear-lag impact varies longitudinally for each cross-section. In case of direct load tests, it has been also found that the strain distribution on the top slab changes as a function of the load level, which indicates that the different behavioural stages of concrete affect the shear lag, especially cracking. The experimental results have been analyzed with the help of analytical and numerical models, which have allowed understanding the progressive modification of the strain distribution within the top slab and the shear-lag intensity.

Mechanism of crack initiation and propagation in high-alloy steel slabs during the cooling and scarfing processes after the continuous casting process

The continuous casting process, which is the initial process of manufacturing alloys, has drawn significant attention from researchers. In the continuous casting process, the molten alloy is solidified to form a slab, and most researchers have focused on the formation of cracks and microstructural changes during this process. Currently, various alloying elements, such as titanium, chromium, niobium, boron, and manganese, are added to high-carbon steel to obtain a light-weight and high-strength alloy. In some of these steel alloys, cracks are generated and fracture occurs during the cooling process preceding the next process after the continuous casting process. To investigate the phase transformation in the cooling process and the subsequent scarfing process following the continuous casting process, thermal analysis and thermal stress analysis were performed through finite element analysis. The probability of fracture according to the steel components was comparatively evaluated based on the 2000 MPa hot press forming steel, which fractured during the cooling process after the continuous casting process. In addition, the fracture toughness and impact toughness were measured for six types of steel alloys. The analysis confirmed that cracks are mainly formed at the corner of the slab during spontaneous cooling. Thus, the probability of fracture occurrence could be predicted. It was confirmed that fracture occurred due to the transverse cracks formed on the surface of the steel slabs during the scarfing process. In natural cooling conditions, it was found that the probability of cracking was highest after the scarfing process when the steel has carbon content of 0.3 wt% and without additive such as titanium, chromium, niobium, boron, or manganese. We also found that the cracking mechanisms were different during the cooling process and scarfing process. Based on this study, we proposed a method to suppress cracks formed by these mechanisms in steel.

Productivity Enhancement by Prediction of Liquid Steel Breakout during Continuous Casting Process in Manufacturing of Steel Slabs in Steel Plant Using Artificial Neural Network with Backpropagation Algorithms.

Breakout is one of the major accidents that often arise in the continuous casting shops of steel slabs in Bokaro Steel Plant, Jharkhand, India. Breakouts cause huge capital loss, reduced productivity, and create safety hazards. The existing system is not capable of predicting breakout accurately, as it considers only one process parameter, i.e., thermocouple temperature. The system also generates false alarms. Several other process parameters must also be considered to predict breakout accurately. This work has considered multiple process parameters (casting speed, mold level, thermocouple temperature, and taper/mold) and developed a breakout prediction system (BOPS) for continuous casting of steel slabs. The BOPS is modeled using an artificial neural network with a backpropagation algorithm, which further has been validated by using the Keras format and TensorFlow-based machine learning platforms. This work used the Adam optimizer and binary cross-entropy loss function to predict the liquid breakout in the caster and avoid operator intervention. The experimental results show that the developed model has 100% accuracy for generating an alarm during the actual breakout and thus, completely reduces the false alarm. Apart from the simulation-based validation findings, the investigators have also carried out the field application-based validation test results. This validation further unveiled that this breakout prediction method has a detection ratio of 100%, the frequency of false alarms is 0.113%, and a prediction accuracy ratio of 100%, which was found to be more effective than the existing system used in continuous casting of steel slab. Hence, this methodology enhanced the productivity and quality of the steel slabs and reduced substantial capital loss during the continuous casting of steel slabs. As a result, the presented hybrid algorithm of artificial neural network with backpropagation in breakout prediction does seem to be a more viable, efficient, and cost-effective method, which could also be utilized in the more advanced automated steel-manufacturing plants.

LCA & LCC analysis of hybrid glued laminated Timber–Concrete composite floor slab system

The increasing request for energy-saving and saving materials and growing concern related to the impacts of materials used on environmental and economical has driven the construction industry toward redesigning critical structural systems and elements. This research proposes solutions for mitigating ecological effects and sustainable built environments. For example, the floor slab is considered the top environmental impact emission after walls compared to other non-load-bearing elements among different building components. Therefore, this research expands the new slab comprising Glued laminated timber (GLT) with concrete as a novel lightweight flooring system. The related methodology includes life cycle assessment (LCA) and life cycle cost (LCC) analysis. Thus, the environmental and economic impacts of three common slab systems were compared to the proposed slab. The evaluation results revealed that GLT-concrete has lower emissions in all environmental categories, namely: Global warming potential (GWP), Eutrophication Potential (EP), human toxicity potential (HTP), fossil depletion potential (FDP), terrestrial Ecotoxicity (TE), and Acidification Potential (AP). Likewise, Embodied energy value showed that GLT-concrete has a lower value by 26%, 9%, and 24% than Lightweight steel slab, Precast reinforced slab, and Cofradal slab. Finally, the result of LCC shows a new GLT-concrete slab despite having a higher construction cost, but by considering the end of life scenario as reuse, it will have a lower total cost. Thus, current research can expand the assessment of environmentally friendly floor structures and step toward sustainable construction.

Steady-State Heat Flux Prediction to Slabs in a Walking Beam Furnace

After casting steel slabs are reheated in a reheat furnace to temperatures in the range 1200-1250 °C in order to be suitable for rolling. The high energy requirements and the importance of reheating for quality control are the motivation behind numerically modeling the furnace. Computational fluid dynamics allows us to understand the fundamental physics with great detail. It is however unclear how assumptions of such models influence the results of the simulations. In this work a steady-state model was analyzed, and it was found that the chosen slab temperature profile can underestimate the average heat flux on the slab surface by 30%. A slab model was employed to simulate the transient slab temperatures which results in an underestimation of the average slab temperatures by about 500 °C for the case with reduced fluxes. The uniform slab temperature assumption also results in the overestimation of heat fluxes on its front and side face.

Determination of structural reliability of a reinforced concrete slab under fire Load

Four reinforced concrete rooms are used in this study, with varying floor areas, openings, and fuel loads. These rooms are office, Classroom, computer, and chemical laboratories of institutional buildings. The time versus Eurocode (EC) parametric fire relationship is determined and compared with ISO 834 and ASTM 119. The performance of the slab is evaluated based on the EC target reliability index of 3.8 for 50 years design period using the First Order Reliability Method (FORM). The probability of failure and structural reliability of each fire compartment at different fire duration is determined. Variables used were concrete compressive strength, a reduction factor of concrete compressive strength, steel yield strength, concrete cover, slab depth, unit width, and area of steel reinforcement provided. The reliability is determined at each 30 minutes fire duration for all fire compartments. The starting point is ambient temperature, then after every thirty minutes until the time when the maximum gas temperature is reached. The fire compartments were able to show fire resistance for two hours and then started to drop over time. Yield strength reduction factor, concrete cover, and area of reinforcement respectively were the most significant variables to determine the reliability index. The structure was able to withhold fire until two hours with a reliability of more than 3.8after that, the slab reliability was less than the target reliability and will need a repair.