Center Of Billet Research Articles

Effect of Sulfur Content on Precipitation Behavior of Dendrite Sulfide Inclusion in Continuous Casted 20CrMnTi Gear Steel

The effect of sulfur content on sulfide inclusion and dendrite MnS in continuous casted 20CrMnTi gear steel is investigated. There are two main types of sulfides in 20CrMnTi steel: pure MnS and TiN–MnS composite inclusions. The number of TiN–MnS is higher than MnS, especially in the edge of the billet. TiN–MnS is smaller both in area and size than pure MnS. The statistical results of dendrite MnS show that the increase of S content decreases the average size of sulfides, whereas raises the number and the maximum size of sulfides. With the S content increasing, the proportion of large‐sized dendrite MnS in steel decreases, but the amount of large‐sized dendrite MnS increases, which results in the increase of number of large‐sized dendrite MnS. The average area of dendrite MnS inclusions first increased and then decreased from the edge to the center of billet, and the maximum area appeared at about 1/2 radius of the billet. Comparison with the microstructure of the two billets, the proportion of ferrite increased with the increase of S content.

Remelting of Aluminum Scrap Into Billets Using Direct Chill Casting

An as-cast aluminum billet with a diameter of 100 mm has been successfully prepared from aluminum scrap by using direct chill (DC) casting method. This study aims to investigate the microstructure and mechanical properties of such as-cast billets. Four locations along a cross-section of the as-cast billet radius were evaluated. The results show that the structures of the as-cast billet are a thin layer of coarse columnar grains at the solidified shell, feathery grains at the half radius of the billet, and coarse equiaxed grains at the billet center. The grain size tends to decrease from the center to the surface of the as-cast billet. The ultimate tensile strength (UTS) and the hardness values obtained from this research slightly increase from the center to the surface of the as-cast billet. The distribution of Mg, Fe, and Si elements over the cross-section of the as-cast billet is inhomogeneous. The segregation analysis shows that Si has negative segregation towards the surface, positive segregation at the middle, and negative segregation at the center of the as-cast billet. On the other hand, the Mg element is distributed uniformly in small quantities in the cross-section of the as-cast billet.

Primary columnar crystal growth characteristics affected by double stirrings in continuous casting square billet

The primary columnar crystal deviates due to forced flow induced by a mold electromagnetic stirrer (M-EMS). On this basis, the flow field can be qualitatively analyzed. As the growth characteristics of primary columnar crystal by double stirrings are still unknown, an electromagnetic swirling flow in the nozzle (EMSFN) approach was applied with M-EMS during a plant trial of continuous casting square billet. We first investigated the deflected angle of the primary columnar when using M-EMS or EMSFN solely. The deflected angle reduces gradually from the billet surface to the center when using only M-EMS. With increasing the EMSFN current, the deflected angles increase first, then reduce. When double stirrings with opposite directions are applied, the deflected angles fluctuate between positive and negative values near the billet surface. When the current is 600 A, the ratio of negative angles reaches 45%. This fluctuation of growth direction forms an interlaced dendrite structure, which restrains the solute migrating to the billet center.

Precipitation behavior of TiN in solidification of 20CrMnTi under continuous casting conditions

This paper focused on the relationship between the precipitation of TiN and the continuous casting process of 20CrMnTi billet. A reliable cross scale simulation combining the heat transfer, solute micro-segregation, and TiN precipitation was carried out. Results show that for a specific site, the cooling rate in the mushy state increases with the solidification proceeding, especially in the later stage of solidification. The closer to the center of billet, the lower the initial cooling rate is. However, the cooling rate in the later stage of solidification near the center of billet is higher than that of the intermediate site. The solidification path of 20CrMnTi at 20, 40, and 60 mm below the inner arc surface is L → L + δ → L + δ + γ → L + γ → γ, and the peritectic reaction occurs at the solid fraction of 0.81. The solute segregates more severe as the site moves to the inner billet, especially among the coarse equiaxed dendrites at 60 mm. The precipitation of TiN just slows down the enriching rate of Ti in the liquid phase, but causes the concentration of N declining. The predicted maximum sizes of TiN are 6.128, 7.836, and 7.593 μm at 20, 40, and 60 mm, and its tendency is consistent with the measurements in the billet. With the decrease of N's initial content, the formation of TiN is postponed to higher solid fraction, and TiN becomes smaller. Moreover, the decisive factor for TiN's size at 40 and 60 mm changes from the concentration difference to the growth time. In addition, increasing the secondary cooling intensity can also refine TiN.

Effects of Pulsed Magnetic Field Melt Treatment on Grain Refinement of Al-Si-Mg-Cu-Ni Alloy Direct-Chill Casting Billet

Al-Si-Mg-Cu-Ni alloy is widely used in the manufacture of high-performance car engine parts. Coarse, dendritic α-Al and large primary Si are common in Al-Si-Mg-Cu-Ni alloy DC casting billet, which is harmful to the performance of the final product. In this paper, a pulsed magnetic field melt treatment technique was applied to the melt in the launder of a DC casting platform to modify the α-Al and primary Si in the billet. A transient numerical model was established to analyze the electromagnetic field, flow field and temperature field in the melt during the pulsed magnetic field treatment. The effect of the magnetic energy on the clusters in the melt was analyzed. We found that during the pulsed magnetic field melt treatment, the number of clusters close to the critical size was increased due to the cluster formation work being reduced by the magnetic energy, which facilitated nucleation and refined the solidification structure. Furthermore, the flow velocity increased, and temperature homogenized in the melt during the pulsed magnetic field melt treatment, which benefitted the clusters close to the critical size distributed and maintained in the melt uniformly. The experimental results show that the α-Al and primary Si were small and homogeneous following the pulsed magnetic field melt treatment. The size of α-Al and primary Si was reduced by 25.6–44.4% and 32.2–54.1%, respectively, in the billet center compared to the conventional process.

The influence of radial shear rolling on the structure and properties of 58Ni-Cr-Mo-B-Al-Cu superalloy

The work is devoted to a study of the microstructure and microhardness of the heat-resistant nickel-based superalloy 58Ni-Cr-Mo-B-Al-Cu after radial-shear rolling. The radial-shear rolling was carried out at a temperature of 925°С in three stages. It was found that the grain size of γ-phase after all rolling stages decreased in the radial direction from the center to the periphery from 62 ± 2 to 2.5 ± 0.2 µm. At the third rolling stage, the grains size was reduced twice in the billet center in a comparison to the initial state. At the same time, individual grains with a size of 100 μm in the billet surface are observed, and grains with a size of 1±0.1 μm are present at the periphery. The microhardness changes in inverse proportion to the grain size, the values increase in the radius direction. The maximum microhardness value is achieved in the peripheral part of the sample and is equal to 5.4 ± 0.6 GPa. According to the EBSD analysis, there is no texture at the billet periphery, but at the middle of the radius there is a two-component axial texture of the <001> + <111> type along the billet axis. The billet center is characterized by the presence of a more pronounced two-component axial texture of the <001> + <111> type along the billet axis. The obtained results indicate the possibility of the gradient structure formation by radial-shear rolling in the heat-resistant nickel-based superalloy 58Ni-Cr-Mo-B-Al-Cu with the initial coarse-grained structure.

Evaluation of chilled casting and extrusion-shear forming technology based on numerical simulation and experiments

Abstract Magnesium alloys on the surface of billets might be refined by chilled casting process, but the grains of the center of billets are coarse, and there are a lot of void defects in the center of billets. These defects can be eliminated by hot extrusion, while fibrous microstructures and strong basal textures might be formed. This paper presents a new short process technology which includes chilled casting and extrusion-shear (CCES). It is crucial to understand the effects of die structures on the deformation behaviors, strain distribution and load requirements. Three selections of processes and die structures were done by simulations and experiments which include CCES process with 4 times consecutive shearings plastic deformation, CCES process by lateral extrusion with 90° shearing angle, and combined CCES process mode. The research results show the third selection is recommended. Three-dimensional (3D) geometric models with different channel angles (30°, 45°) for the third selection CCES dies were designed. The heterogeneities of plastic deformation by CCES dies with different channel angles were analyzed from the simulation results. The simulation results show strains decrease with rising of channel angles. The lower channel angles improve the deformation heterogeneity of magnesium alloy billets. Smaller channel angles obtain higher strains and produce tinier sub-grains. The forces of the CCES process decrease with rising of channel angles. The analysis results showed that finer and uniform microstructures can be obtained if channel angles in the CCES dies are appropriate.

ЭКСТРЕМАЛЬНО-ОПТИМИЗИРУЮЩЕЕ АВТОМАТИЗИРОВАННОЕ УПРАВЛЕНИЕ НАГРЕВОМ НЕПРЕРЫВНОЛИТЫХ ЗАГОТОВОК В ПЕЧАХ ПРОХОДНОГО ТИПА

This article deals with a strategy of advanced extreme-optimal high-output energy-saving uniform exploratory control for the heating of concast slabs under the broad hot-rolling mill working modes with unsteady outputs to achieve guaranteed metal heating. The implemented advanced extreme-optimal exploratory control development strategy for production processes is analyzed using the specific example of efficient guaranteed optimum control of the heating parameters in through-feed furnaces. We review the best variational and exploratory extreme control methods for three interrelated heating processes: the distribution of fuel along the length of the furnace body and over time; the optimal control of fuel-burning to obtain the best calorific effect possible; the optimum heat-saving control for combustion product ejection through the reduced heat losses due to suction and knocking out. The operability and feasibility of the suggested extreme-optimal control are achieved using the simplified dynamic heat exchange model along the “fuel consumption” - “billet center temperature” channel with the surface temperature of the heated billets used as the main monitoring and control parameter. We analyzed the efficient method of automated autonomous positive control for the real thermal condition of each of the billets before they are ejected from the furnace to prevent the possibility of feeding underheated billets to the rolling mill, as well as emergencies in the mill. This system provides a forecast for the expected breakdown temperature for each of the billets before they are ejected from the furnace under the energy-saving operational mode. We present the results of the practical implementation of the extreme-optimal control for metal heating at four Russian high-output rolling mills that have a significant economic effect with minimum costs of software (digital) implementation of the suggested control concept.

Floating Grain Characterization and Its Effects on Centerline Segregation of Direct-Chill Cast Al–Mg–Si Alloy Billets

Microstructure and microsegregation analysis were performed on a direct-chill (DC) cast Al–Mg–Si alloy billet, aiming to quantitatively investigate the microscopic features of floating grain and its contribution to the negative centerline segregation. Microstructure results show some irregular grains, whose grain size and secondary dendrite arm spacing (DAS) are two times larger than that of the regular fine grains, appear only in the billet central region. The duplex grain structure, a mixture of internal coarse and peripheral finer dendrites within one grain, was clearly shown by the EPMA results, exhibiting special microsegregation features. The coarse dendrites are more solute-depleted than the nearby finer-DAS structure, in which the average concentration of solute Mg nearly equals to the nominal content. Based on the microscale features and solidification information of the alloy, the irregular grains exhibiting duplex dendrite feature are confirmed to be floating grain, which internal coarse dendrites are believed to mainly contribute to the negative centerline segregation. And the resulting segregation degree is quantitatively evaluated to be ∼0.041 for solute Mg considering the floating grains in the billet center as against with the assumed 100% fine-DAS microstructure.

Numerical simulation of macrosegregation in continuously cast gear steel 20CrMnTi with final electromagnetic stirring

A 3D/2D hybrid multi-physical-field mathematical model, which takes into consideration the thermosolutal buoyance, was developed to predict the macrosegregation of gear steel 20CrMnTi continuously cast by a curved billet caster with size of 160 mm × 160 mm, and investigated the effect of final electromagnetic stirring (F-EMS) on the fluid flow, heat transfer and solute distribution in the liquid core of continuously cast steel. The results show that the application of F-EMS eliminates the effect of thermosolutal buoyancy on the asymmetric distribution of carbon concentration in the cross section of billet and accelerates the final solidification of resident molten steel in the liquid core of strand, but promotes the negative carbon segregation near the billet center. When the gear steel 20CrMnTi is cast at the temperature of 1803 K and speed of 1.7 m/min, the solidification end advances forward from 9.84 to 9.72 m, and center carbon segregation ratio of billet decreases from 1.24 to 1.17 with the increase in current density of F-EMS from 0 to 350 A.

Dynamic recrystallization analysis of reduction pretreatment process by multi-phase field method

The reduction pretreatment (RP) process is an effective method to improve billet quality, and the deformation recrystallization plays an important role in the process. Exploring the RP process parameters, a dynamic recrystallization model of GCr15 steel was established by the phase-field method and physical simulation. The recrystallization kinetics and flow stress curves during hot compression were simulated by using this mode. The effects of deformation parameters and initial grain size on the dynamic recrystallization were investigated. Moreover, by using the results obtained by Finite element method (FEM), dynamic recrystallization during the RP process was investigated though this model. It was found that increasing the deformation temperature, deformation rate and decreasing the initial grain size can promote the dynamic recrystallization kinetics. Large Zener-Hollomon parameters can enhance recrystallized grain refinement, while the recrystallized grain size was not affected by the initial grain size. During the RP process, when the reduction is insufficient (10%), partial recrystallization occurs in the billet. With the increase of reduction from 10% to 16%, the area of complete recrystallization increases gradually. When the reduction is the same, the recrystallization in the billet center increases with the decrease of casting speed. When the reduction is 10%, partial recrystallization occurs in the billet center at a casting speed of 0.7 m min−1, and fully recrystallization occurs in the billet center with a casting speed of 0.5 m min−1. Thus, when the reduction is difficult to increase further, the recrystallization in the billet center can be improved by decreasing the casting speed.

Structure Refinement Upon Ultrasonic Melt Treatment in a DC Casting Launder

This work focuses on ultrasonic melt treatment (UST) in a launder upon pilot-scale direct chill (DC) casting of 152-mm-diameter billets from an AA6XXX alloy with Zr addition. Two casting temperatures (650°C and 665°C) were used to assess their effect on the resulting microstructure (grain size, particle size, and number density).Structure refinement results show the feasibility of UST in the DC casting launder. This is quantified through the corresponding reduction of grain size by around 50% in the billet center, or more towards the billet surface, reduction of the average Al3Zr particle size, and increase in the particle number density. A higher Al3Zr particle density was obtained when the alloy was cast at 665°C. Numerical simulation results and suggestions on how to improve the treatment quality of UST in DC casting launder are also provided.

Effect of reduction pretreatment process on evolution of micro-porosity in 42CrMo billet

Reduction pretreatment (RP) process, which is implemented after the billet is completely solidified, is an alternative process to further improve billet quality. Finite element method and experiment were used to investigate the effect of the RP process on the internal quality of 42CrMo billet. An ultrasonic testing technology was used to study the influence of the RP process on the micro-porosities. Through a three-dimensional finite element model, the mechanism of the RP process on the porosity closure was studied. The experimental results show that the RP process eliminates the macro-porosities of the billet center. The number of micro-porosities in the billets is effectively reduced, and the increase in deformation contributes to the reduction in micro-porosities. Compared with isothermal rolling, the RP process leads to a larger equivalent strain and hydrostatic integration in the billet center because of the temperature gradient, and the effect of the temperature gradient is greater with the increase in deformation. The closure effect of micro-porosity is related not only to the stress state, but also to the distribution of micro-porosity. The increase in three-dimensional compressive stress is beneficial to the porosity closure. If the micro-porosities distributed densely, excessive stress could induce micro-porosity coalescence, which has the risk of inducing cracks.

Electrical drives of continuous casting machine withdrawal rolls: a model and practical implementation of limitations on longitudinal forces in billets

The research is aimed at increasing the quality of a concast billet macrostructure by limiting static and dynamic longitudinal forces created in billets by electrical drives of withdrawal rolls during wear and bending of the withdrawal roll body and random and periodic slips of drives. The paper analyzes process requirements for electrical drives of withdrawal rolls: contains a procedure for calculating dynamic longitudinal forces created in billets by drives of withdrawal rolls, determines whether influence of operating modes of the said drives on changes in billet withdrawal force is relevant, contains developed techniques and algorithms of withdrawal roll drive automated control limiting static and dynamic longitudinal forces in billets, and includes the experimental analysis of efficiency of methods and technical solutions on operating drives. Research was carried out at the Russian large iron and steel works. When performing the research, the authors applied analytical and numerical methods of solving algebraic and differential equations and systems, methods for structural modeling. As a result of the research, the authors developed and experimentally confirmed methods for “soft” restoring of the contact between the withdrawal roll and the billet and adjusting phases of fluctuating changes in load currents of motor groups. The obtained results are transferred as technical specifications and taken for introduction, when revamping electrical equipment of existing continuous casting machines. Results of mathematical simulation and experimental research are used to design automated electrical drives of withdrawal rolls in the secondary cooling zone of the bow-type continuous casting machine. Impact dynamic loads were decreased by 3 times, resulting in an average increase of 8% in the quality of the billet center with regard to all types of defects.

Comparison of the Microstructure of M2 Steel Fabricated by Continuous Casting and with a Sand Mould

AISI M2 steel was smelted in a 150 kg medium-frequency induction furnace and cast to form round billets with a cross-section diameter of 100 mm via a vertical continuous caster and sand mold. The secondary dendrite arm spacing (λ2), cooling rates, permeability and size and distribution of grains and network carbides of the two billets were studied. The results show that the continuous casting process can effectively decrease the λ2 value, permeability and size of the grains and carbides and improve the distribution of the grains and carbides during solidification. The λ2 values of the billets cast with a sand mold and continuous caster are 37.34 μm and 21.14 μm, respectively, and the cooling rate is 3.6 K·s−1 and 12.0 K·s−1, respectively. The area fractions of carbides at the center of the billets cast with the sand mold and continuous caster are 0.24 and 0.16, respectively, and increase by 27.7% and 25.4%, respectively, compared with their average values. The average grain size of billets cast with the sand mold and continuous caster is 69.4 μm and 50.5 μm, respectively. Compared with the sand mold billet, the grain size at the center of the continuous casting billet is reduced by 25.5%. The relationship between the grain size and cooling rate is presented in this paper.

Comparison of Transverse Uniform and Non-Uniform Secondary Cooling Strategies on Heat Transfer and Solidification Structure of Continuous-Casting Billet

Water flux distribution largely influences the heat transfer and solidification of continuously-cast steel billets. In this paper, a secondary cooling strategy of transverse non-uniform water flux (i.e., higher flux density on billet center), was established and compared with the uniform cooling strategy using mathematical modeling. Specifically, a heat transfer model and a cellular automaton finite element coupling model were established to simulate the continuous casting of C80D steel billet. The water flux was measured using different nozzle configurations to assist the modeling. The mathematical results were validated by comparing the surface temperature and the solidification structure. It is shown that the non-uniform cooling strategy enables the increase of corner temperature and reduction in surface temperature difference, while a higher reheating rate is found on the surface center of the billet. Moreover, the non-uniform cooling strategy can enhance the cooling effect and refine the solidification structure. Accordingly, the liquid pool length is shortened, and the equiaxed crystal density is increased along with the decreased equiaxed crystal ratio. The uniform cooling strategy contributes to reducing internal cracks of billet, and the non-uniform one is beneficial for surface quality and central segregation. For C80D steel, the non-uniform cooling strategy outperforms the uniform one.

Numerical simulation for macrosegregation in direct-chill casting of 2024 aluminum alloy with an extended continuum mixture model

Abstract An extended continuum mixture model for macrosegregation is applied to predicting Cu and Mg segregation in large-size ingot of 2024 aluminum alloy during direct chill casting (DC). A microsegregation model using the approximate phase diagram data was coupled with macroscopic transport equations for macrosegregation profiles. Then, the impacts of transport mechanisms on the formation of macrosegregation were discussed. It is found that copper and magnesium have a similar segregation configuration from the billet center to surface. Negative segregation is observed in the centerline and subsurface, whereas positive segregation is obtained in the surface and somewhat underestimated positive segregation in the middle radius. Further, the discrepancy between the predicted and experimental results was discussed in detail. The results show that the magnesium to some extent alleviates the copper segregation in ternary alloy, compared with that in binary alloy. The predicted results show good agreement with measured experimental data obtained from literatures.

Effect of Dendritic Morphology and Central Segregation of Billet Castings on the Microstructure and Mechanical Property of Hot-Rolled Wire Rods

Microscopic dendritic morphology and central macrosegregation in continuously cast high carbon steel billets with a cross section 150 × 150 mm2 are investigated to elucidate their effect on the microstructure and mechanical property of the following hot-rolled wire rods, whose diameters are 10 and 6.5 mm, respectively. Experimental observations and numerical simulations for the steel billets under different casting conditions are carried out. It is found that the secondary dendrite arm spacing (SDAS) in the billets increases with the increase of superheat temperature, while decreases with the increasing specific water flow. Smaller SDAS in the billet center leads to lower segregation index of carbon (rC) and manganese (rMn) due to the low permeability in the final solidification stage. The measured rMn and rC in billets are in an approximately linear relationship. In addition, for the same rolling and cooling process, the severer carbon segregation in the center of the billets is, the lower the sorbite rate of the rods and the worse stability in the mechanical property of the rods. The tensile strength of wire rods can be improved by adjusting the casting parameters to decrease the SDAS and reduce the central carbon segregation of the billets.

Modeling of Solidification in Continuous Casting Round Billet with Mold Electromagnetic Stirring (M-EMS)

A fully couple flow of molten steel, heat transfer, and solidification in the mold region of a continuous casting round billet under mold electromagnetic stirring (M-EMS) are investigate with computational tools of fluid flow and electromagnetic simulations. A finite element model is employed to simulate the electromagnetic stirrer in the mold and calculate the Lorenz force distribution. The Lorenz forces are applied as a source term in the Navier–Stokes equations of the fluid flow model, which was solved through a finite volume model. The flow pattern produced by the stirrer is mainly rotational, with velocities of 0.37 m s−1 close to the solidifying shell for the higher current. The results indicate that a higher M-EMS current produces a reduction of the temperature in the strand center; a decrease of 42 °C is observed for a current of 350 A/4.25 Hz. The M-EMS also produces a thinner shell close to the stirrer center and a larger region of solid fraction in the billet center.

Solidification Structure and Macrosegregation of Billet Continuous Casting Process with Dual Electromagnetic Stirrings in Mold and Final Stage of Solidification: A Numerical Study

Coupling macroscale heat transfer and fluid flow with microscale grain nucleation and crystal growth, a mixed columnar–equiaxed solidification model was established to study the SWRT82B steel solidification structure and macrosegregation in 160 mm × 160 mm billet continuous casting with dual electromagnetic stirrings in mold and final stage of solidification (M-EMS and F-EMS). In the model, the phases of liquid, columnar, and equiaxed were treated separately and the initial growing equiaxed phase, which could move freely with liquid, was regarded as slurry. To obtain the equiaxed grains nucleation and columnar front evolution, the unit tracking method and the columnar front tracking model were built. The model was validated by magnetic induction intensity of stirrer, billet surface temperature, and carbon segregation. The equiaxed phase evolution and the solute transport with effect of fluid flow and grains transport were described in this article. The results show that the equiaxed phase ratio will not increase obviously with higher current intensity of M-EMS, while the negative segregation near the strand surface becomes more serious. The negative segregation zone near the billet center and the center positive segregation come into being with the effect of equiaxed grains sedimentation and liquid thermosolutal flow. It is also found that the liquid solute transport in the F-EMS zone becomes the main factor with higher current intensity rather than the solidification rate, and therefore, the final billet center segregation decreases first and then turns to rise with the current intensity. The optimal current intensities of M-EMS and F-EMS proposed for SWRT82B billet continuous casting are 200 and 400 A, respectively.