Solidification Of Molten Steel Research Articles

Simulation and Experimental Study of Fluid Flow and Solidification Behavior in Thin Slabs Continuous Casting Process under Secondary Electromagnetic Stirring

During the thin slab continuous casting process of silicon steel, electromagnetic stirring (EMS) can control the flow, heat transfer, and solidification of molten steel through electromagnetic force. Herein, a 3D mathematical model coupling the fluid flow, heat transfer, solidification, and the electromagnetic field is built. The effects of varied current intensities on the flow, heat transfer, and solidification of molten steel in the thin slab under secondary EMS are explored based on applying the electromagnetic brake in the mold region. In the findings, it is demonstrated that increasing the current intensity increases the flow rate and vorticity of the molten steel in the second cooling zone, eliminating the superheating phenomenon and improving the uniformity of the molten steel's temperature distribution. Meanwhile, based on the nucleation and growth parameters determined from thermal simulation experiments, the cellular automation finite‐element model is used to simulate the microstructure evolution during the solidification of thin slab. In the results, it is shown that the stirring energy increases when the current intensity increases, potentially promoting equiaxed crystal growth and grain refinement. Compared to the production sample, a reasonable qualitative agreement is achieved for the grain morphology, equiaxed crystal ratio, and columnar to equiaxed transition.

Simulation of Inclusion Particle Motion Behavior under Interfacial Tension in Continuous Casting Mold

Inclusions entrapped by the solidifying front during continuous casting adversely affect the properties of the final steel products. In this study, we investigated the effect of the interfacial tension due to surfactant concentration, particularly sulfur, on alumina inclusion motion behavior during molten steel solidification in a continuous casting mold. A two-dimensional numerical model was developed in Ansys Fluent software to simulate the inclusion motion in a continuous casting mold. Further, the impacts of different values of the alumina inclusion diameter, sulfur concentration, and melt temperature were studied to understand the inclusion motion behavior. The inclusion diameter affected the inclusion distribution throughout the domain. The alumina inclusion entrapment percentage varied in the case of sulfur mixing (using an empirical relationship for modeling). It was found that the removal percentage varied according to the sulfur concentration. The addition of sulfur at concentrations from 10 ppm to 70 ppm resulted in a 4% increase in the removal of alumina inclusions (trapped in the solidifying shell), except for the 100-ppm case. Smaller-sized inclusion particles had a 25% higher chance of entrapment at the top level of the mold. Under the effect of a higher surface tension gradient between inclusions and the melt, the predicted findings show that inclusions were vulnerable to engulfment by the solidification front.

Influence of Mg addition on inclusions and mechanical properties of Cr12Mo1V1 steel under high pressure

Conventional methods that involve an increase in pressure are used to improve the solubility and yield of Mg in the steelmaking. Under high pressure, the effect of Mg addition on the number, morphological characteristics, composition, size, and density of inclusions in Cr12Mo1V1 steel (C: 1.40–1.60 wt%, Si: ≤0.60 wt%, Mn: ≤0.60 wt%, S: ≤0.03 wt%, P: ≤0.03 wt%, Cr: 11.00–13.00 wt%, V: ≤1.00 wt%, and Mo: 0.70–1.20 wt%) is studied. The experiments are made under three contents of Mg: 0, 0.0012 wt% and 0.0041 wt%. Results show that Al2O3 and MnS inclusions transform into approximately spherical MgO·Al2O3 spinel and spherical MgO·MgS inclusions, respectively. At ~0.07 wt% dissolved aluminum content, the micro content of Mg in molten steel leads to the formation of MgO·Al2O3 spinel inclusions. The MgO·Al2O3 inclusions disappear completely when the mass fraction of Mg is larger than 39.734 × 10−6. Further, as the Mg content increases, the number of inclusions <1 μm increases, whereas the number of inclusions >2 μm decreases. Meanwhile, during molten steel solidification, MnS and MnS–MgS precipitate around MgO·Al2O3 and MgO inclusions, respectively. The densities of MgO·Al2O3 spinel inclusions are lower than those of alumina inclusions. As the Mg content in Mg-containing inclusions increases, the density of inclusions decreases, leading to an improvement in inclusion removal efficiency. The role of Mg in the mechanical properties, tensile fracture morphology, and inclusions of quenched and tempered Cr12Mo1V1 steel is also investigated. As the Mg content increases from 0 wt% to 0.0041 wt%, at the tensile fracture, the area of shear lip goes through a process from small to large, the dimples go through a process from generation to deepening, and the strength and plasticity correspondingly increase.

Thermal Analysis of Solidifying Steel Shell in Continuous Casting Process

A finite element simulation of the steel shell formation in continuous casting has been developed. The current research is focused on the solidification of molten steel during the initial stages of the mould cooling. The model allows predicting the temperature field throughout the process: temperature gradient, solidification front, cooling rates. In stationary state, the prediction of shell thickness reasonably agrees with analytical models and experimental observations. The simulation tool is used to study the alteration of the mould thermal field in case of sticking defects encountered in industrial practice. A numerical analysis increases the understanding of the phenomena.

Study on dispersion of nano ZrO2 particles in pure iron based on high temperature laser confocal

Nano ZrO2 particles were modified and their morphology were analyzed and characterized. The distribution and dispersion of untreated nano ZrO2 particles and pre-dispersed nano ZrO2 particles were compared. Instead of traditional induction heating furnace, physical melting model was constructed by high temperature laser confocal microscope. Pre-dispersed modified nano ZrO2 particles and untreated nano ZrO2 particles were added to the iron powder respectively. The movement and morphology of nanoparticles during solidification of molten steel were observed. Scanning electron microscopy was used to observe the distribution of nanoparticles. Morisita’s index was used to calculate the dispersion uniformity quantitatively. The results show that the untreated nano ZrO2 particles agglomerate at the edge, and it is difficult to exist stably in the metal. The pre-dispersed nano ZrO2 particles are evenly dispersed in molten steel without obvious agglomeration and have better dispersion.

Effect of Ti(C, N) Particle on the Impact Toughness of B-Microalloyed Steel

Simultaneously improving the toughness and strength of B-microalloyed steel by adding microalloying elements (Nb, V, Ti) has been an extensively usedmethod for researchers. However, coarse Ti(C, N) particle will precipitate during solidification with inappropriate Ti content addition, resulting in poor impact toughness. The effect of the size, number density, and location of Ti(C, N) particle on the impact toughness of B-microalloyed steel with various Ti/N ratios was investigated. Coarse Ti(C, N) particles were investigated to act as the cleavage fracture initiation sites, by using scanning electron microscopy (SEM) analysis. When more coarse Ti(C, N) inclusions were located in ferrite instead of pearlite, the impact toughness of steel with ferrite–pearlite microstructure was lower. Meanwhile, when the size or the number density of Ti(C, N) inclusions was larger, the impact toughness was adversely affected. Normalizing treatment helps to improve the impact property of B-microalloyed steel, owing to the location of Ti(C, N) particles being partly changed from ferrite to pearlite. The formation mechanism of coarse Ti(C, N) particles was calculated by the thermodynamic software Factsage 7.1 and Thermo-Calc. The Ti(C, N) particles formed during the solidification of molten steel, and the N-rich Ti(C, N) phase precipitated first and, then, followed by the C-rich Ti(C, N) phase. Decreasing the Ti and N content is an effective way to inhibit the formation of coarse Ti(C, N) inclusions.

Numerical study on the characteristics of solute distribution and the formation of centerline segregation in continuous casting (CC) slab

To reveal the characteristics of solute distribution and the formation of centerline segregation in continuous casting (CC) slab, a 3D simulation model for the prediction of centerline segregation during a slab CC process was developed. Experiments including the morphology of strand transverse section obtained by acid etch and the segregation degree of C tested by chemical analyzer were carried out to verify the accuracy of the numerical model. The maximum deviation between the calculated and experimented results reaches as low as 3.22%. In the turbulent flow region, the solute distribution in the liquid pool is relatively uniform and its distribution pattern is similar to that of flow pattern. In the final stage of solidification during a slab CC process, the solidification of molten steel in the centerline region is not simultaneous and the pattern of solute distribution is highly depended on the shape of liquid pool. The final solidification and serious segregation occur at a position roughly 595 mm from the slab center. Moreover, the quantitative relations between the position of solidification front and the solute concentration on the centerline were studied. The results show that solute redistribution and the solidification front moving continuously toward centerline lead to the formation of centerline segregation in CC slab. The central segregation degree of solutes in steel Q345 arranged in weakening order is S, C, P, Si, and Mn.

Numerical Simulation of Inclusion Capture in the Slab Continuous Casting Considering the Influence of the Primary Dendrite Arm Spacing

AbstractIn the present work, a coupled three-dimensional numerical model of fluid flow, heat transfer, and inclusion motion during the solidification of molten steel in slab continuous casting mold has been developed. Based on the model, this paper has studied the inclusion capture during the process. The influence of the primary dendrite arm spacing on inclusion capture has been considered. The inclusion distributions, total masses, and average diameters at different depth from the slab surface have been given out in the present paper. The simulation results revealed the inclusion concentration existed in the solidification process, and the inclusion capturing area varies with the depth from the slab surface.

Effect of Slag-Steel Reaction on the Initial Solidification of Molten Steel during Continuous Casting

With the mold simulator technique, the effect of slag-steel reaction on the initial shell solidification as well as the heat transfer and lubrication behavior of the infiltrated mold/shell slag film was studied in this article. The results showed that the Al2O3 content, the CaO/SiO2 ratio, and the viscosity of mold flux were increased with the progress of the slag-steel reaction during casting. The slag-steel reaction has two major effects on the initial shell solidification: one is increasing the mold heat flux and shell thickness by the decrease of slag film thickness. The other is the reduction of mold heat flux by the increase of crystal fraction in slag film. Mold flux with a lower basicity, viscosity, and crystallization temperature would result in a larger liquid slag consumption and the uneven infiltration of slag into the mold and shell gap that eventually leads to the irregular solidification of initial shell with a poor surface quality, such as slag entrapment and depressions as well as glaciation marks. Conversely, mold flux with a higher viscosity, basicity, and crystallization temperature would result in a smaller liquid slag consumption, which would cause the poor mold lubrication, the longitudinal shell surface defects, and drag marks.

Initial Solidification and Its Related Heat Transfer Phenomena in the Continuous Casting Mold

The initial solidification of molten steel in the mold is very important, as it is the origin of the final slab, which associates with the surface defects and determines the final quality of casting slab. In this article, six main topics, including the initial solidification study method, molten steel solidification, mold flux structure, fluid flow, oscillation marks formation, and breakout are reviewed with the purpose to explore the intrinsic mechanism of the complex initial solidification process and its related multi-phase heat transfer phenomena. The results summarized here can provide a foundational understanding of the initial solidification and heat transfer phenomena occurring in the continuous casting mold.

Energy Saving Through the Control of Initial Solidification During Continuous Casting

With the development of advanced continuous-casting technology, saving energy and reducing greenhouse gas emissions are crucial for its future development. Controlling the initial solidification of molten steel in the mold to improve the quality of casting products would tend to minimize extra postcast treatment like scarfing, etc., which leads to a large amount of energy savings in the continuous-casting process through the minimization of the extra labor and energy consumption. In this article, factors such as mold flux, mold oscillation, cooling potential conditions, and fluid flow in the vicinity of meniscus that correlate with the molten steel initial solidification are discussed with the aim to provide strategy and guidelines for the optimization of molten steel solidification and energy savings in continuous casting.

Analysis of Titanium Microalloying in As-Received and Oxidized Crofer® 22 APU

The addition of titanium to ferritic stainless steel alloys has been shown to benefit the high temperature characteristics of these alloys for use in solid oxide fuel cell (SOFC) interconnects. TiN precipitates can reduce the fractional softening of interconnects at high temperatures by preventing recrystallization and recovery of the cold-worked alloy [1]. TiN has a lower solubility in austenite than ferrite [2]. During solidification of molten steel, TiN precipitates in the austenitic region and is then annealed in the ferritic region [2]. During long term SOFC operation, titanium oxide forms and provides a keying effect at the interface of the alloy and chromia scale [3]. Titanium oxide also forms at the surface of the chromia scale to reduce chromium volatilization [4]. Analysis of an interconnect alloy, Crofer ® 22 APU, before and after oxidation was performed to show the initial development of titanium precipitate morphology, structure, and diffusion.

Numerical Simulation of the Piercing Process of Large-Sized Seamless Steel Tube

In the piercing process of the large-sized seamless steel tube, the rollers and plug affected on the billet with extrusion and friction. It made that the stress and strain state of metal is very complicated. In the complex state, the casting shrinkage and void produced by molten steel solidification became the crack defect in the middle of tube wall. The simulation of the piercing process of large sized seamless steel tube was performed by FEM in this paper. The material is stainless steel TP321. The distribution of stress was analyzed. It was obtained that the circumferential shear stress is the necessary condition of produced the layered defects in the tube wall. The paper studied the state of strain in the tube. The distribution of all kinds of strain was gotten. That could provide the theory guide for the elimination of the crack defect in the large-sized seamless steel tube.

Mathematical modelling of billet casting with secondary cooling zone electromagnetic stirrer

A three-dimensional unsteady coupled mathematical model has been applied to analyse the turbulent flow, temperature fields and macroscopic solidification of molten steel in billet continuous casting with electromagnetic stirring (EMS). Induction currents caused by fluid flow and the stirrer end effect have been investigated. The Lorentz force and Joule heat caused by induction currents have also been taken into account. The application of EMS in the secondary cooling zone results in significant changes in molten steel flow and temperature distribution, and the flow patterns on the horizontal cross-section agree well with the results in other references. Joule heat and Lorentz force are mainly located at the surface layer of the billet and decrease rapidly with penetration depth. The degree of superheat is reduced or eliminated rapidly when molten steel is stirred by EMS, hence is beneficial to generate more equiaxed grains. Stirring intensity is highest in the regions near the two ends of the stirrer. The Joule heat produced by induction has limited influence and can be ignored. The industrial trials showed that the EMS can effectively suppress the central shrinkage cavity and the centre C segregation to improve product quality.

Numerical Simulation of Mold Filling and Solidification Process for Beam Blank Continuous Casting

Mold filling and solidification of molten steel for 750mm×450mm×300mm continuous casting mold of single SEN and double SEN are simulated by using CFD commercial code Flow-3d. The distributing diagrams of velocity field and temperature field and the location and shape diagrams of free-surface during mold filling process are obtained. Influences of single SEN model and double SEN model on velocity field and solidification are analyzed. It is found that double SEN model can lighten circumfluence intensity at the upper of mold, quicken solidification speed of steel liquid in the mold, which is favorable to improving the quality of billet and enhancing pull speed.

Numerical simulation of fluid flow and solidification in continuous slab casting mould based on inverse heat transfer calculation

A mathematical model based on an inverse heat transfer calculation was built to determine the heat flux between the mould and slab based on the measured mould temperatures. With K–ϵ turbulence model, a mathematical model of three-dimensional heat transfer and solidification of molten steel in continuous slab casting mould is developed. Solidification has been taken into consideration, and flow in the mushy zone is modelled according to Darcy’s law as is the case of flow in the porous media. The heat flux prescribed on the boundaries is obtained in the inverse heat conduction calculation; thus, the effect of heat transfer in the mould has been taken into consideration. Results show that the calculated values of mould temperature coincide with the measured ones. Results also reveal that the temperature distribution and shell thickness are affected by the fluid flow and heat transfer of slab which is governed by the heat flux on the mould/slab interface.

Effects of U-Shape Inner Cooler on Flow and Solidification of Molten Steel in Slab Continuous Casting Mold

An inner-outer coupled cooling technology of molten steel for 1240×200mm slab continuous casting, that is to set an inner cooler—U shape pipes in the mold, is put forward in order to enhance the efficiency of transmitting heat and improve inner structure of billet. The flow status and solidification status of molten steel under coupling flow field and temperature field in inner-outer coupled cooling mold are simulated by using fluid dynamics software, and compare with those in traditional mold. It is found that setting inner cooler in the mold can make molten steel flow status even, which is favorable to floating up of the inclusion, quickening the solidification of steel liquid and improving the quality of billet.

Ti-Deoxidized Products and Formation Mechanism of Intragranular Ferrite in High Grade Pipeline Steels

High grade pipeline steels were prepared using vacuum carbon deoxidization process combined with a final Ti-deoxidation process. The microstructure of the as-cast steels was investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM observation shows that the formation of intragranular ferrite (IGF) structure is induced by fine inclusions. TEM selected area diffraction (SAD) patterns and elemental distribution analysis indicate that these inclusions are mainly Ti 2O 3 and MnS. It is also found that Ti 2O 3 may act as nucleus in the formation of MnS during solidification process. Raman spectroscopic analysis demonstrates the presence of another phase, MnTiO 3, which could be formed through entrapment of Mn by Ti 2O 3. It is believed that the formation of Mn-depleted region in the inclusions and thus the formation of MnTiO 3 phase will increase the Mn pickup from matrix and promote the formation of IGF during solidification of molten steel.

RETRACTED: Use of a computer program in the solidification of molten steel using a front-tracking method

RETRACTED: Use of a computer program in the solidification of molten steel using a front-tracking method

Research on the Crack Forming and Control of Centrifugal Cast High Speed Steel Rolls

The effects of roll materials, mould parameter, pouring parameter and cooling parameter on the crack of high speed steel (HSS) roll fabricated by a centrifugal casting have been analyzed. The modification of HSS roll was researched. The structures and properties of HSS roll modified by potassium and rare earth were improved. The hot tearing force of modified HSS roll increased by 32.77% and reached 158N. Modification was able to decrease the line constriction. The adoption of variable speed centrifugal casting technique, variable flux pouring technique and variable speed solidification cooling technique was able to adjust the temperature field and stress field of the roll, which benefited the filling and solidification of molten steel and eliminated the crack of HSS roll.