Continuous Casting Rolling Research Articles

Rheological characteristics of steel in continuous roll casting-rolling

Problems. In the process of obtaining a strip in a casting and rolling device, the question arises of combining the process of hot rolling of the solidified material and the process of crystallization of the liquid melt. This makes it possible to implement an efficient technology for producing thin-sheet products.
 Purpose of the study. Determination of rational parameters for performing mathematical modeling of material behavior during roll casting requires clearly defined recommendations. The material for the rolling process is steel. The starting material was used in solid, solid-liquid and liquid states.
 Implementation technique. The analysis of the properties of steel was carried out on the basis of the results of experiments obtained at the Physico-Technological Institute of Metals and Alloys of the National Academy of Sciences of Ukraine. To analyze the rheological properties of steel, the dependences of the yield stress for alloyed and carbon steels were used in a certain temperature range. The selected temperature range includes solidus and solid-liquid state of steel, located above 0.8 melting point.
 Research results. Based on the research results, the analysis of the rheological properties of steel in solid, solid-liquid and liquid states during continuous casting-rolling on rolls was carried out. The use of the obtained dependencies makes it possible to perform mathematical modeling of the deformation and hydrodynamics of the material during continuous casting-rolling of steel strips using roll casting-rolling devices.
 Conclusions. The constructed dependences, together with studies of the viscosity of steel in the liquid state and the resistance of steel to deformation in the solid state, most fully describe the rheological properties of steels during casting-deformation processes. The obtained dependences will make it possible to implement an ultra-efficient technology for producing thin-sheet rolled products.

Height of Water Pool in the Roll Nip of Secondary Cooling Zone in Continuous Slab Caster: Application of Open Channel Hydraulics

In continuous casting of steel, the strand is cooled in the upper part of the secondary cooling zone with water sprayed by nozzles towards the strand surface. The water accumulates in the nip of the lower roll of a roll pair, forming a water pool which then drains off towards the ends of the roll. In the present work, open channel hydraulics was applied for computation of the water pool height in the nip between roll and strand in continuous slab casting. The differential equation describing the change of pool height for the spatially varied flow with increasing discharge was solved with the Runge–Kutta technique using as boundary condition the pool height at the end of the nip. The effects of the Manning friction factor n and the energy coefficient α were determined in sets of computation. It was shown that the hydraulic theory could predict water profiles in the nip of continuous casting rolls to a good approximation.

Simulation of the Refining Process of Ultra-Low Carbon (ULC) Steel

The standard production route for mild steels for automotive purposes is still based on conventional continuous casting (CC) and hot strip rolling (HSR). The current trend towards the “zero-carbon car” will demand the abating of material emissions in the future. Thin slab casting and direct rolling (e.g., Arvedi endless strip production (ESP)) is an approach to reduce CO2 emissions by 50% compared to CC and HSR. One of the main limitations in applying ESP for the production of ultra-low carbon/interstitial free (ULC/IF) steels is clogging. Clogging is the blockage of the submerged entry nozzle due to the build-up of oxide layers or an oxide network. The high clogging sensitivity of IF steels results most probably from the FeTi addition, and hence, a general change of the deoxidation practice might be an option to overcome these problems. In the present work, the thorough refining process of ULC steel was simulated by addressing the different deoxidation routes and the influence of titanium (Ti) alloying on steel cleanness. The developed ladle furnace (LF) and the Ruhrstahl Heraeus (RH) refining models were applied to perform the simulation. Before the simulations, the models are briefly described and validated by the published industrial data.

Technological Aspects of Minimization of the Sizes of a Continuous Casting-Rolling Unit in the Production of Wire Rods from Fire-Refined Copper

In the production of wire rods made of fire-refined copper by minor and medium regional producers, the problem of minimization of the sizes of technological lines of continuous casting-rolling machines (CCRM) is most often solved by decreasing the number of structural components in the applied technological system, including the decrease in the number of rolling stands in the roll mill train. We estimate the influence of minimization of the number of rolling stands under the conditions of continuous casting-rolling in a 9-stand rolling mill of the Southwire Company on the ease of realization of the process of production and the quality of the products. It is shown that the realization of stable rolling process and the required quality of wire rods becomes possible as a result of decreasing the cross-sectional area of the original continuously cast ingots in the form of a trapezoid by 6.71% and an increase in the area of workpieces in all stands of the mill with an aim to prevent the overflow of the passes with the metal (the so-called “fin” defects), which enables one to get finished product with transformed “lap” defects. It is shown that the section of transition from the rough group of stands to the finishing group, i.e., the 3v stand (round pass), should be regarded as the most problematic from the viewpoint of formation of fin-type defects. We also perform the correction of the shape of plane oval specified for this stand. The practical implementation of the entire proposed complex of technological adjustments makes it possible to stabilize the process of rolling and to obtain copper wire rods 8 mm in diameter with regular geometric shapes and the required quality of macrostructure of the metal in the absence of lap-type defects.

Establishing the cause of failure in continuous casting rolls

This paper investigates failure of repair welded continuous casting rolls. Observed failures are in the form of localized corrosion, initiated at boundaries between two welding passes. Defects were categorized into three typical damages: zebra lines, partially interconnected zebra lines, and fully connected zebra lines. In some cases, star like features were also distributed on the surface of the roll. Optical microscope, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to characterize microstructure of failed rolls. Damage is appeared to be initiated from elongated greyish phases, which are rich in Cr. These phases are at intermediate states between delta ferrites and sigma phase. Cr enrichment of delta ferrite during service is associated with Cr depletion of the matrix and this in turn makes these phases susceptible to the initiation of corrosion.

An Experimental Investigation on the Effect of Cooling Rate During Combined Continuous Casting and Rolling Process on Mechanical Properties of 7075 Aluminum Alloy

When a combined continuous casting–rolling (CCCR) process is employed for making Al plates and sheets, considerable savings in both the cost and the production time are attained. In the present research, the variation and control of temperature of the material flowing through the cooling jacket during CCCR of 7075 aluminum alloy were investigated. Employing three temperature profiles for this passage, it was shown that the best mechanical properties and grain size of the finally rolled product could be attributed to the exponential profile. It was also found through a heat transfer analysis that the difference in the free convection heat transfer from the top and bottom surfaces of the slab exiting the cooling jacket can result in a temperature gradient through the thickness of the plate, and this can consequently lead to certain variations in the hardness through the thickness of the finally rolled 7075 Al plate.

Finite element analysis and experiment on induction heating process of slab continuous casting-direct rolling

To reduce the energy consumption of reheating billets between the continuous casting and hot rolling processes, the continuous casting-direct rolling (CC-DR) process is developed, of which one of the key technologies in CC-DR is compensative heating between the processes. Considering the compensative heating technology requirements in the actual production of slab CC-DR, the finite element models of longitudinal flux induction heating (LFIH) and transverse flux induction heating (TFIH) are established to analyse the slab heating process. The results show that LFIH is good for heating surfaces of the slab, but cannot solve the problem of low temperature on the edges, which can effectively be heated with TFIH. The temperature distribution of the slab can be made more uniform by choosing the appropriate current and moving speed. Besides, induction-heating prototypes are developed to inspect the effect of induction heating. The measured results are consistent with the simulated ones. The results of the analysis have direct significance on the induction heating process in the actual production of slab CC-DRs.

The Integration of Process and Product Metallurgy in Niobium Bearing Steels

A review of the technological integration of both the process and physical metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) steels have evolved into the development of higher quality steels for more demanding end user requirements. The connection of process and physical metallurgy is evolving through the integration of research that is aimed at improving product quality. However, often the connection of the process metallurgical parameters is not reported, especially with industrial data. The importance of this innovative metallurgical connection is validated by the market demand for reduced fuel consumption, improved quality, and CO2 emissions in both the automotive and construction sectors. This situation has further increased the demand for new higher quality Nb-bearing steel grades. This integrative process/physical metallurgical (IP/PM) approach applies to both low and high strength steel grades in numerous applications. Often, the transition from laboratory melted and TMCP to the production scale is challenging. The methodology, process control, and key production steps that are required during the melting, ladle metallurgy, continuous casting, thermal, and hot rolling production conditions often vary significantly from the laboratory conditions. Understanding the reasons and corrective action for these variations is a critical product development success factor. These process metallurgy parameters for the industrial melting, casting, reheating, and hot rolling of Nb grades are connected and correlated to the resultant microstructures, physical metallurgy, and mechanical properties. These advanced high strength steels are microalloyed with Nb, V, Ti and/or other elements, which affect the austenite-ferrite transformation. Niobium enables the achievement of substantial grain refinement when the plate or sheet is rolled with the proper reheat, hot reduction, and thermal schedule. A recently developed key metallurgical transition is in progress applying this integrative approach with the use of MicroNiobium. A reduction of Mn and C levels with the complementary refinement of the microstructural grain size through MicroNiobium additions improves the robustness of the steel to better accommodate some process metallurgy variations. Applications are evolving in lower strength steels with Nb to achieve complementary grain refinement.

Application and Research Twin Roll Casting-Extruding Process for Production Longish Deformed Semi-Finished Products from Aluminum Alloys

At present, Russia is actively developing methods of combined treatment of aluminum alloys, one of which is the method of twin roll casting-extruding. It is very suitable for processing aluminum alloys having a relatively low melting point. The method consists in pouring a melt into the rotating rolls, crystallizing it on the roll surfaces, rolling with a predetermined reduction amount, pressing out in front of the die and squeezing out the product of the predetermined configuration and dimensions through it with drawing ratio in the range of values 10-40. Analysis of technical and economic indicators showed that this method has a number of advantages in comparison with traditional technologies of semicontinuous extruding and continuous casting-rolling. So the output of a good metal at high production volumes can reach 95-97% at a productivity of up to 3-4 tons per hour. In addition, it is possible to quickly move from one profile size to another by changing the matrix. The authors proposed and patented various designs and methods for producing solid and hollow press products from non-ferrous alloys. On their basis, laboratory and pilot-industrial units for combined processing have been created, on which experimental studies have been carried out to obtain long-dimensioned deformed semi-finished products from aluminum alloys series 5xxx, 6xxx, 8xxx and others. The energy-power parameters of the process are determined and found that they are significantly smaller in comparison with traditional technologies (in 10-50 times). Investigations of the mechanical characteristics of press products have been carried out, which showed that when implementing such a treatment scheme, even when producing extruded products from low-plastic alloys, they have a high level of plastic and strength properties. Developed technologies based on the method twin roll casting-extruding now are tested in a laboratory of combined treatment methods in School of Non-ferrous Metals and Material Science in Siberian federal university and industrial conditions of a number of metallurgical plants.

Ferrochromium slag as a protective coating material against oxidation for caster rolls

In this study, ferrochromium (FeCr) slag, which is available as an industrial waste, is proposed as a protective surface coating material particularly for protection of continuous casting rolls against oxidation. FeCr slag was successfully deposited with atmospheric plasma spray (APS) method. Before the coating process, FeCr slag powder prepared in the particle size range of 5-38 μm, was investigated using conventional characterization methods (XRD, SEM, TGA etc.). Thermal Barrier Coating (TBC) system was used as a basis for deposition processes. Accordingly, NiCoCrAlY (Amdry, −45 + 5 μm) was firstly deposited as metallic bond coat layer onto the surface of AISI 420 substrate, and then FeCr slag layer was deposited as the top coating layer. After the deposition of FeCr slag powder, the resulting coating layer was found to have low porosity with a homogeneous microstructure. The deposited FeCr slag coatings were subjected to isothermal oxidation tests at different temperatures and test durations for determination of their oxidation behavior and upper operating temperature limits. The results obtained from this study indicate that FeCr slag can be considered as an alternative protective coating material for caster rolls which are subjected to high temperatures up to 800°C.

Effect of continuous induction annealing on the microstructure and mechanical properties of copper-clad aluminum flat bars

Copper-clad aluminum (CCA) flat bars produced by the continuous casting–rolling process were subjected to continuous induction heating annealing (CIHA), and the effects of induction heating temperature and holding time on the microstructure, interface, and mechanical properties of the flat bars were investigated. The results showed that complete recrystallization of the copper sheath occurred under CIHA at 460°C for 5 s, 480°C for 3 s, or 500°C for 1 s and that the average grain size in the copper sheath was approximately 10.0 μm. In the case of specimens subjected to CIHA at 460–500°C for longer than 1 s, complete recrystallization occurred in the aluminum core. In the case of CIHA at 460–500°C for 1–5 s, a continuous interfacial layer with a thickness of 2.5–5.5 μm formed and the thickness mainly increased with increasing annealing temperature. After CIHA, the interfacial layer consisted primarily of a Cu9Al4 layer and a CuAl2 layer; the average interface shear strength of the CCA flat bars treated by CIHA at 460–500°C for 1–5 s was 45–52 MPa. After full softening annealing, the hardness values of the copper sheath and the aluminum core were HV 65 and HV 24, respectively, and the hardness along the cross section of the CCA flat bar was uniform.

High Quality TMCP Production and Metallurgy of Niobium Bearing Steels

The technological and metallurgical advancements of value-added niobium (Nb) microalloyed thermo-mechanical controlled process (TMCP) plate steels continue to be developed for more demanding end user requirements. The market demand for reduced fuel consumption and CO2 emissions in the automotive and construction sectors have further increased the demand for these new and advanced higher quality Nb-bearing steel grades. Often, the transition from laboratory melted and TMCP hot rolled heats to the production scale requires some continuous casting, thermal and mechanical metallurgy adjustments from the laboratory results in order to accomplish proper industrial continuous casting and hot rolling processes. These advanced high strength steels are microalloyed with Nb, Mo and/or other elements which affect the austenite-ferrite transformation. Niobium enables achievement of substantial grain refinement when the plate is rolled with the proper reduction and thermal schedule. The effects of these microalloying elements on the continuous cooling transformation behavior must be carefully controlled during the reheating and rolling process to successfully achieve the desired mechanical properties. TMCP applications have been successfully developed in numerous product sectors with thickness exceeding 120 mm. Since the very fine grained microstructure improves toughness and increases the yield strength, this TMCP process enables the required tensile properties with the growing trend to leaner chemical composition designs (less than 0.10%C) and excellent toughness properties. The consequence of leaner chemical compositions, especially lower carbon content and lower carbon equivalent enhances mechanical properties, fabrication and weldability.

Influence of microalloying on the coiled strip (strength class K56) produced in a casting and rolling complex

The influence of Nb and Ti microadditions on the microstructure and mechanical properties of coiled strip (strength class K56) produced by continuous casting and immediate rolling in a casting and rolling complex at AO OMK Stal’ (Vyksa) is investigated. High niobium content (0.08%) improves the cold strength of the steel in impact-flexure tests and drop tests at temperatures down to–80°C. Adding titanium to steel with 0.04% Nb reduces its strength but improves its plasticity, ductility, and cold strength down to–60°C.

Study on the evolution mechanism of oxidation and copper diffusion and precipitation phenomena and their effect on the surface quality of steel plates

Purpose – Identification of the critical process conditions that enhance Cu diffusion in ferrite grain boundaries and promote precipitation of Cu-rich particles in the proximity of steel semi-finished products surface is crucial for every steel maker as it leads to the creation of hot shortness cracks in final products deteriorating surface condition. The purpose of this paper is to reveal the possible effect of Cu segregation in the metal/oxide interface, its role in surface crack initiation and, finally, to propose actions to prevent from hot shortness issues throughout the production chain of steel products. Design/methodology/approach – The here presented study was based on S355 steel plate production starting from re-melting of scrap in an EAF, followed by metallurgical treatment in a Ladle Furnace, continuous casting, re-heating (RH) and thermo-mechanical rolling in a reversing mill. For the purposes of this study, more than ten heats, 100 t of steel each, were analyzed. Here presented are depicted steels in the high and low end of the permitted Cu-wt-% spectrum, 0.4 wt-% Cu (0.15 wt-% C, 1.1 wt-% Mn, VTi micro-alloyed steel) and 0.25 wt-% Cu (0.09 wt-% C, 1.2 wt-% Mn, NbTi micro alloyed steel), respectively. Findings – Although Cu levels of 0.25-0.40 wt-% are well below the Cu solubility in austenite and ferrite (8 percent wt-% and 3 wt-% Cu, respectively) and within specifications, precipitation of Cu-rich particles is observed in industrial semi-finished and/or final products. Cu-rich precipitates and Cu segregation along grain boundaries near the steel surface lead to hot shortness cracks in industrial products. Research limitations/implications – Hot shortness surface defects related to Cu presence in steel having significantly lower Cu amounts than its maximum solubility in austenite and ferrite does not make sense in first place. Correctly, Cu is expected to remain in solid solution. Identification of Cu-rich particles is explained on the basis of the development of double diffusion actions: interstitial diffusion of carbon (decarburization) and substitution diffusion of copper. Root cause analysis and reliable countermeasures will save financial and material resources during steel production. Originality/value – Automobile scrap re-melting results in noticeable Cu amounts in EAF produced steel. Presence of Cu-rich particles in grain boundaries near the surface of intermediate or final products deteriorates surface quality through relevant surface defects. Identification of Cu-rich particles is explained on the basis of the development of double diffusion actions: interstitial diffusion of carbon and substitution diffusion of copper. Pre condition for metallic Cu precipitation in ferrite is the Cu amount to be above 3 wt-%, which is ten times higher than the usual permitted Cu amount in such steel grades. This pre-condition is met through austenite oxidation during RH.

Causes of the hot ductility drops of steels

The effect of conditions of continuous casting and hot rolling of steel on the high-temperature ductility of a microalloyed pipe steel of strength class Kh42 and 17G1S-U steel is studied. A Gleeble-3800 thermomechanical facility is used to perform physical modeling of the hot ductility of steel. The temperature dependence of the hot ductility of steel is determined under various slab cooling conditions in a continuous caster and during hot rolling. The ductility drops of iron and steels is found to be mainly caused by an increase in the elastic modulus near the temperatures of the polymorphic transformation caused by first- and secondorder phase transformations (polymorphic and magnetic transformations, respectively). Structural factors, such as the grain size, excess-phase inclusions located along initial grain boundaries, and interstitial impurities, lead to an additional decrease in the ductility.

Hot Ductility Behaviors of HRB600 Vanadium-Containing Steel Rebar

Hot ductility behaviors of HRB600 vanadium-containing steel rebar was study with thermal simulation test and the fracture was observed and analyzed by scanning electron microscope (SEM). The result shows that, the contraction ratio of cross sectional area (Z) in 1050°C - 1300°C was more than 60%, tensile sample showed good ductility; Z in 750°C-1000°C was less than 60%, tensile sample showed brittle, namely third brittle zone. Then third brittle zone should be avoided or minimize stays in the development process of continuous casting and hot rolling. The fracture mode and the morphology of fracture surfaces were different at different temperatures.

Research and Application of Integrated Scheduling Management System of Steelmaking-Casting-Rolling Based on Heat Process Model

by studying steelmaking-casting-rolling production process, a mathematical model of integrated batch planning is established innovatively to minimize processing costs of whole line and computed by an intelligent optimization ant algorithm. On the premise of utilizing and coordinating capacity of steelmaking and rolling, the mathematical model of integrated batch planning can create integrated batch planning to combine steelmaking-casting-rolling closely according to each process constraint conditions and optimization objective. Furthermore, another mathematical model of job scheduling based on heat process model is proposed to not only guarantee the logistics balance between continuous casting and hot rolling, but also acquire the highest ratio of DHCR and lowest energy consumption.

Evaluation of the quality of cladding deposited on continuous steel casting rolls

Abstract This paper presents the quality analysis of cladding layers deposited on continuous steel casting rolls made of 41CrMo4 (EN 10083-1-91). The effect of filler used on the tribological properties of claddings was analyzed. There was minimal mixing between the base material and interlayer observed in the process of hard surfacing. The microstructure of the interlayer and the coatings is martensite–ferrite. Dispersed carbides MC, M 7C3, and Cr23C6 were observed in the interlayer. Small amounts of carbides were also observed in the cover layer along with Cr2N and CrN, which was confirmed by energy dispersive X-ray analysis. The highest average hardness, 410 HV30, was measured in the cover layer at a distance of 1 mm from the surface. The lowest hardness was found in the base material, 239 to 243 HV30. The hardness of the interlayer metal is affected by mixing of cladding and cover layer metal. The cladding metal showed a martensite–ferrite structure and fine precipitates in the interlayer, and diffraction spectra of the carbides had the characteristics of MC, M 7C3, and Cr23C6 carbides. Lower abrasive wear has been reported in the reference material (a roll with a surface-hardened layer), which is in line with the contact surface hardness of test samples.

Recycling of steel plant mill scale via iron ore sintering plant

During the processing of steel in steel mills, iron oxides will form on the surface of the metal. These oxides, known as mill scale, occur during continuous casting, reheating and hot rolling operations. Mill scale is a valuable metallurgical raw material since it contains 65–70% iron. JSW Steel Ltd is a 7 Mtpa integrated steel plant and generates 270 t of mill scale per day. Most of the materials of steel plant wastes are recycled through sinter making in most of the countries. Because of its physical, chemical and mineralogical properties, it can be used as a raw material in a process like sintering. The mill scale contains high amounts of Fe and low amounts of silica and alumina. Thus, recycling it through the sintering process helps in the saving of raw materials like iron ore and limestone. This paper presents preliminary findings of a study that investigates the potential for recycling steel mill scale in the sintering process. Experiments were conducted using the mill scale in sinter making from 0 to 70 kg/t of sinter. The total Fe and FeO contents of the sinter increased with the increase in mill scale addition. The sinter productivity decreased with the increase in mill scale addition due to a decrease in sinter bed permeability. The sinter strength and sinter mean size initially increased and reaches a maximum at mill scale addition of 40–50 kg/t of sinter and afterwards declines with the increase in mill scale addition. Sinter reduction degradation index and reducibility decreased with the increase in mill scale addition due to the increase in FeO content. Except sinter productivity, other desired sinter properties can be obtained with the use of 40–50 kg mill scale per tonne of sinter.

A New Type of Submerged-Arc Flux-Cored Wire Used for Hardfacing Continuous Casting Rolls

It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitrogen replacing part of carbon and addition of the nitrogen-fixing elements of niobium and titanium. And microstructure, degree of hardness and high-temperature wear resistance of its deposited metal samples were also investigated. It is found that the microstructure is martensite, residual austenite and carbonitride precipitates. As a result, the hardfacing metal with homogeneous distribution of very fine carbonitride particles had high hardness and excellent wear-resisting property during high-temperature wear, which could significantly extend the service life of continuous casting rolls.