Mechanical Soft Reduction Research Articles

Industrial Application of Mechanical Reduction on Continuous Casting of Bearing Steel Bloom

Industrial experiments of mechanical soft reduction in continuous casting were conducted in the present study aiming to improve the internal quality of the bearing steel blooms. Two methods were developed to verify the solidification model for a reliable crater end in the caster, which is provided by SMS CONCAST. The verified solidification model was applied to determine the solidification status of the bloom and provides theoretical reduction region. Several trials were conducted to study the optimization of the reduction rate regarding the V-shaped and centerline segregation of the bloom. The results show an obvious improvement of internal quality in the bearing steel bloom by applying appropriate reduction during casting.

Shape of slab solidification end under non-uniform cooling and its influence on the central segregation with mechanical soft reduction

Shape of slab solidification end under non-uniform cooling and its influence on the central segregation with mechanical soft reduction

Influence of differential reduction rate in adjacent roll reduction zone on internal cracks of high carbon bloom induced by mechanical soft reduction

To comprehensively investigate and alleviate internal cracks in high carbon bloom induced by mechanical soft reduction (MSR), a 3D thermal-mechanical coupled model, containing two adjacent pairs of reduction rolls, was developed to investigate the influence of differential reduction rate on evolution of stress concentration and displacement in as-cast bloom. In order to effectively provide theoretical basis for actual production, the reduction rate was calculated according to the appropriate reduction amount of each pair of reduction rolls, which can be adopted in the MSR to determinate the appropriate roll reduction amount in adjacent roll reduction zone. With the differential reduction rate of MSR increasing from −2.67 mm/m to 5.33 mm/m, the maximum equivalent stress of cracking area in as-cast bloom significantly decreased under first roll reduction position, the maximal displacement along the bloom width direction is significantly decreased with increasing of the differential reduction rate of MSR under end roll reduction position. According to the results of industrial experiment, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments.

A new method for determination of the theoretical reduction amount for wide-thick slab during the mechanical reduction process

Mechanical soft reduction (MSR) is an effective method for elimination of the centerline segregation and porosity of the continuous casting steel slab, and the reduction amount is a key parameter that determines whether the MSR could be applied successfully. In the present work, a 2D heat transfer model was developed for predicting the non-uniform solidification of the wide-thick slab. The measured shell thickness by nail shooting experiment and the measured slab surface temperature by infrared camera were applied to validate the 2D heat transfer model. A new calculation method of theoretical reduction amount that could consider the influence of non-uniform solidification of the wide-thick slab was then derived. Based on the predicted temperature field by the 2D heat transfer model and the newly-proposed calculation method, the required theoretical reduction amount and reduction gradient/rate for the wide-thick slab were calculated and discussed. The difference between the newly-proposed method and the previous method, the influence of the casting speed and slab thickness on the required theoretical reduction amount and reduction gradient/rate were also investigated.

Improvement of carbon segregation in cast bloom and heredity in hot-rolled bar

In this study, the effect of mechanical soft reduction on carbon segregation in the continuous casting of 300 × 400 mm 42CrMo alloy structural steel blooms was comparatively investigated by adjusting the casting speed, which was systematically optimized through numerical simulation. When the casting speed is 0.60 m · min−1, during the soft reduction process, the central solidification structure of the bloom becomes dense, and carbon segregation is improved. Moreover, the distribution of carbon in the samples before and after rolling was analyzed. Combined with the soft reduction process, the uniformity of carbon across the cross section of the bloom /bar distinctly improved for casting speeds of 0.50 m · min−1, 0.55 m · min−1 and 0.60 m · min−1, this was predominantly reflected in the core areas. The effective segregation length proportion of the bloom and rolled bar is approximately 40%. This phenomenon fully verifies the heredity characteristics of the elements in the rolling process.

Controlling centre segregation and shrinkage cavities without internal crack in as-cast bloom of steel GCr15 induced by soft reduction technologies

ABSTRACT To investigate the alleviation technology of internal cracks, center shrinkage cavities and center segregation of as-cast bloom simultaneously, a three-dimensional finite element model was developed to calculate and analyze the strain fields and deformation behavior of as-cast bloom induced by soft reduction process. In the present work, a multi-stage mechanical soft reduction (MSR) has been developed to simultaneously alleviate center segregation and shrinkage cavities without internal cracks, which aims to provide theoretical basis for improving the internal quality of high carbon as-cast blooms induced by soft reduction technologies. According to the experimental results, the internal cracks were effectively alleviated and center shrinkage cavities were nearly eliminated by optimum designed experiments, the homogeneity and compactness of as-cast bloom can been remarkably improved in comparison with that induced by the conventional soft reduction process. The carbide size and bandwidth of the carbides in the hot-rolled wire were both decreased.

On the formation of centreline shrinkage porosity in the continuous casting of steel

A recent asymptotic model for solidification shrinkage-induced macrosegregation in the continuous casting of binary alloys is extended for the purposes of understanding the link between solute segregation and centreline shrinkage porosity, a defect that commonly occurs in the continuous casting of steel. In particular, the analysis elucidates the relationship between microsegregation, mushy-zone permeability, heat transfer and centreline pressure, yielding an inequality that constitutes a criterion for whether or not centreline porosity will form. The possibilities for developing this approach to take account of gas porosity and the implementation of mechanical soft reduction to reduce macrosegregation and shrinkage porosity are also discussed.

Additional shearing impact on the effectiveness of MSR technology in conditions of billet CCM

Aside from electromagnetic stirring, casting with low superheat and intensive cooling of the strand in the upper range of secondary cooling zone, Mechanical Soft Reduction (MSR) has proved, above all, to be very effective in reducing segregation and axial porosity in continuously cast billet. Implementation of MSR technology in the production of continuously cast billets has a number of features that are due to their square shape. In this case, particularly promising is the use of blocks of segment design, so called pinch-roll segment. The presence in CCM line of MSR block of such design allows to implement a two-stage deformation scheme. The paper proposes a new two-stage scheme of MSR technology realizing the combined deformation on the basis of cobbing in vertical plane and shearing relative displacement of the faces at the first stage, and at the second stage – deformation on the basis of cobbing in vertical plane. This approach additionally helps to correct deformations of the profile cross section, namely the rhomboidity defect. We present the results of a comparative study using physical modeling methods to assess the contribution of additional shear relative displacement of faces in the horizontal plane to the overall efficiency of MSR technology of continuous casting. The use of a flat model in conjunction with the proposed form of deforming rolls and a combination of modeling materials allowed to achieve a good similarity in geometric criterion, as well as in the criterion of stress ratio equivalence arising at the interface of crystallization front. The obtained experimental data helps to develop ideas about the mechanisms of additional positive effect from the application of shear action. In particular, the deformation of metal surface and adjacent layers of the billet in the rolls with a special above-described profiling will improve their quality due to the occurrence of shear deformations intensifying the process of collapse of subcortical bubbles, “healing” of microcracks, etc. In turn, the artificial creation of torque effect in cross section of the billet will contribute to the occurrence of shear deformations in the crystallized “bridges” of axial liquid-solid region of the ingot, thereby intensifying the process of their destruction and improving the quality of the billet’s macrostructure.

Application of Numerical Model of Continuous Cast Bloom Crystallization to Improve the Efficiency of Mechanical Soft Reduction Technology

The paper presents the results of the analysis of thermal state of continuous cast bloom on the stage of incomplete crystallization in the area of possible places of application of technology of Mechanical Soft Reduction (MSR), received during simulation on mathematical model, which was implemented in the software package using the finite element method. For the conditions of continuous cast bloom with a cross section of 360-400 mm, we studied the characteristics of temperature change over the cross section of the bloom, the growth dynamics of the solid shell, the number of the solidified component, and the end point position of solidification depending on the technological parameters for continuous casting of A516, 5140 1070 and AISI steel brands. The obtained data on the thickness of the crystallized shell of continuous cast bloom and the amount of solid phase depending on the casting speed and steel grade allowed us to conclude about the possible place of installation of the MSR unit. The results of mathematical simulation can be transferred in a digital form to the strength model of deformation of continuous cast bloom at the stage of incomplete crystallization.

High-efficiency continuous casting of GCr15 bearing steel bloom based on cooperative control technique of complex electromagnetic stirring and soft reduction

GCr15 bearing steel exhibits comparatively serious center macro-segregation in the continuous casting of bloom with the increase of casting speed. In the present work, the influence of complex electromagnetic stirring (M + F-EMS) and mechanical soft reduction (MSR) on the center macro-segregation in the continuous casting of 220 × 260 mm blooms of GCr15 bearing steel have been comparatively investigated to increase casting speed in order to ensure a good internal quality. Based on numerical simulation and experiments, M + F-EMS and MSR have been comprehensively evaluated and compared by combination of industrial trials. The results show that center carbon segregation first decreases and then increases with the increase of casting speed in both processes without optimization. For M + F-EMS process, when casting speed increases from 0.75 to 0.85 m · min−1, the average degree of center carbon segregation decreases from 1.2 ∼ 1.26 to 1.18 ∼ 1.25 by asymmetrical optimization; with regard to combination of M + F-EMS and MSR process, when casting speed increases from 0.75 to 0.9 m · min−1, the average degree of center carbon segregation decreases from 1.2 ∼ 1.26 to 1.08 ∼ 1.1 and the solute element distribution becomes homogeneous by optimization. In comparison, significant reduction of the center macro-segregation with the increase of casting speed can be achieved for combination of M + F-EMS and MSR process, however, it is infeasible for M + F-EMS process in the present technology situation.

Applied Mathematical Modelling of Continuous Casting Processes: A Review

With readily available and ever-increasing computational resources, the modelling of continuous casting processes—mainly for steel, but also for copper and aluminium alloys—has predominantly focused on large-scale numerical simulation. Whilst there is certainly a need for this type of modelling, this paper highlights an alternative approach more grounded in applied mathematics, which lies between overly simplified analytical models and multi-dimensional simulations. In this approach, the governing equations are nondimensionalized and systematically simplified to obtain a formulation which is numerically much cheaper to compute, yet does not sacrifice any of the physics that was present in the original problem; in addition, the results should agree also quantitatively with those of the original model. This approach is well-suited to the modelling of continuous casting processes, which often involve the interaction of complex multiphysics. Recent examples involving mould taper, oscillation-mark formation, solidification shrinkage-induced macrosegregation and electromagnetic stirring are considered, as are the possibilities for the modelling of exudation, columnar-to-equiaxed transition, V-segregation, centreline porosity and mechanical soft reduction.

Influence of Soft Reduction on the Fluid Flow, Porosity and Center Segregation in CC High Carbon- and Stainless Steel Blooms

Mechanical soft reduction, MSR, is today an established technique for reducing center segregation and center porosity in the continuous casting of blooms. The bloom cross section is reduced by pinc ...

Reducing macro segregation of high carbon steel in continuous casting bloom by final electromagnetic stirring and mechanical soft reduction integrated process

The influence of final electromagnetic stirring (F-EMS) combined with mechanical soft reduction (MSR) on reducing macro segregation has been investigated in order to improve inner quality of high carbon steel bloom with 1 wt.% carbon. A 2D heat transfer model was developed to predict the solidification process of bloom by taking into account thermo-physical properties which were obtained by experiments. The predicted surface temperature and shell thickness were verified by infrared temperature and nail shooting measurement results, respectively. In addition, roll-gap calculation model was established by a segmented slope method to calculate the proper soft reduction zone and determine the distribution of total reduction amount. The optimum F-EMS implement position and soft reduction zone with the goal of minimum macro segregation of high carbon steel bloom were theoretically determined by the heat transfer model associating with high temperature tensile test. The industrial research results showed that macro segregation has been significantly improved by the optimum combination with F-EMS and MSR processes, and the risk of center negative segregation and internal cracks could be avoided by modifying F-EMS implemented position and the distribution of total reduction amount. Besides, compared with the combination of mold electromagnetic stirring (M-EMS) and F-EMS processes, the reasonable center solid fraction of bloom at the F-EMS implemented position in F-EMS and MSR integrated process was much lower.

Improving Inner Quality in Continuous Casting Rectangular Billets: Comparison Between Mechanical Soft Reduction and Final Electromagnetic Stirring

The comparison between the mechanical soft reduction (MSR) and final electromagnetic stirring (FEMS) on center carbon macrosegregation and v-segregation has been investigated in order to improve the inner quality of high carbon 82A steel with a section of size 180 mm × 240 mm. A heat transfer calculation model by using C++ programming language is developed and applied to calculate the appropriate casting speed of continuous casting during the FEMS and MSR processes. The calculated action zone of FEMS and MSR is at the location with a solid fraction of 0.28–0.41 and 0.30–0.90, respectively. The industrial results show that the effects of MSR in improving the center carbon segregation, reducing the shrinkage cavity and suppressing the V-segregation are more effective than FEMS. The mean center carbon segregation degree reduces from 1.19 to 1.15 with FEMS and decreases from 1.19 to 1.07 with MSR. Besides, compared with FEMS, MSR can eliminate shrinkage cavity and V-segregation but may generate center negative segregation and transverse cracks subjected to reduction pressure.

Numerical Study about the Influence of Small Casting Speed Variations on the Metallurgical Length in Continuous Casting of Steel Slabs

Numerical simulations are prepared to investigate the influence of small casting speed variations between 715 and 735 mm min−1 on the metallurgical length in continuous casting of 285 mm thick steel slabs. The effect of considering/ignoring the melt flow in the numerical continuous casting model for predicting the metallurgical length is also investigated. The simulations are based on an Eulerian two‐phase solidification model including melt (liquid phase) and columnar dendrites (solid phase). Solidification of a binary Fe–C‐alloy is calculated. Two 25 m long straight strand geometries of industrial scale are modeled. Both of these geometries have waved surfaces to consider periodical strand surface bulging. In order to consider a defined mechanical softreduction (MSR) configuration as well, the cross‐section of one of these geometries decreases at a rate of 1 mm m−1 within a defined length. For a given casting configuration and for defined cooling conditions, the influence of small casting speed variations on the metallurgical length, on the average solid fraction and on the enthalpy flux are determined. The simulation results can be used to optimize the settings for operating continuous casting plants, e.g., to adapt the MSR position.

Macrosegregation Quality Criteria and Mechanical Soft Reduction for Central Quality Problems in Continuous Casting of Steel

In order to study the central quality of continuously cast tool steel slabs, the simple model has been developed to simulate the macrosegregation quality criteria. The model calculates different quality criteria such as average macro-segregation level criterion “ASL”, its fluctuation level “FSL” and its segregation quality number “SQN”. These criteria are calculated based on the previous measurements of carbon and sulfur concentrations distributions in final region of spray zones and centerline area of lower and upper slab sides. The effect of mechanical soft reduction Technique “MSR” on the slab centerline quality is examined and analyzed. The model results show that MSR affects the quality of centerline areas significantly by different ways based on the casting speed. The experimental and theoretical results clarify that the qualities of different slab sides are different for all collected samples. The model results show also that the accuracy of the macro-segregation quality criteria increases quantitatively with increasing the number of analyzed segregated elements. Therefore, the macrosegregation quality criteria and their distributions can be considered as the most simple and vital tool to evaluate the various slab qualities. Finally, the mechanism of centerline segregation formation with mechanical soft reduction is discussed in this study.

Modeling the Effects of Strand Surface Bulging and Mechanical Softreduction on the Macrosegregation Formation in Steel Continuous Casting

Positive centerline macrosegregation is an undesired casting defect that frequently occurs in the continuous casting process of steel strands. Mechanical softreduction (MSR) is a generally applied technology to avoid this casting defect in steel production. In the current paper, the mechanism of MSR is numerically examined. Therefore, two 25-m long horizontal continuous casting strand geometries of industrial scale are modeled. Both of these strand geometries have periodically bulged surfaces, but only one of them considers the cross-section reduction due to a certain MSR configuration. The macrosegregation formation inside of these strands with and without MSR is studied for a binary Fe-C-alloy based on an Eulerian multiphase model. Comparing the macrosegregation patterns obtained for different casting speed definitions allows investigating the fundamental influence of feeding, bulging and MSR mechanisms on the formation of centerline macrosegregation.

Features of Deformation of Partly Crystallization Blooms at their Two-Stage Soft Reduction

Steady increase of requirements to quality an axial zone continuously cast blooms stimulated in last time development of principles of its deformation at the end of solidifications with the purpose of suppression of axial porosity and segregation: soft reduction or mechanical soft reduction. The technology of soft reduction is one of the most effective ways of improvement quality of internal layers continuously cast blooms. In this case the central part of section of continuously cast blooms is in liquid or liquid-solid condition (mushy zone). At the same time, in practice now there are, at least, some original technical decisions for realization of this method.

Using a Two-Phase Columnar Solidification Model to Study the Principle of Mechanical Soft Reduction in Slab Casting

A two-phase columnar solidification model is used to study the principle of mechanical soft reduction (MSR) for the reduction of centerline segregation in slab casting. The two phases treated in the model are the bulk/interdendritic melt and the columnar dendrite trunk. The morphology of the columnar dendrite trunk is simplified as stepwise growing cylinders, with growth kinetics governed by the solute diffusion in the interdendritic melt around the growing cylindrical columnar trunk. The solidifying strand shell moves with a predefined velocity and the shell deforms as a result of bulging and MSR. The motion and deformation of the columnar trunks in response to bulging and MSR is modeled following the work of Miyazawa and Schwerdtfeger from the 1980s. Melt flow, driven by feeding of solidification shrinkage and by deformation of the strand shell and columnar trunks, as well as the induced macrosegregation are solved in the Eulerian frame of reference. A benchmark slab casting (9-m long, 0.215-m thick) of plain carbon steel is simulated. The MSR parameters influencing the centerline segregation are studied to gain a better understanding of the MSR process. Two mechanisms in MSR modify the centerline segregation in a slab casting: one establishes a favorable interdendritic flow field, whereas the other creates a non-divergence-free deformation of the solid dendritic skeleton in the mushy region. The MSR efficiency depends not only on the reduction amount in the slab thickness direction but also strongly on the deformation behavior in the longitudinal (casting) direction. With enhanced computation power the current model can be applied for a parameter study on the MSR efficiency of realistic continuous casting processes.

Use of Simulation Techniques for the Design and Process Control of Continuous Casting Machines

This article presents the latest solutions implemented by Concast AG in the field of process simulation and illustrates the use of finite element method (FEM) models for the engineering of continuous casters and for process control in continuous casting. The first application presented is the use of FEM models for the design of the new Integrated Mould concept, which combines the benefits of both tube- and plate moulds for bloom casters. Second, the Concast real-time solidification model is presented. The article describes this model and its use for controlling the secondary cooling as well as to control mechanical soft reduction (MSR) as function of the actual casting parameters like temperature, casting speed, cooling intensity, both during steady and transient times. Field results show that this model permits us to improve the internal quality of continuous-cast blooms compared to static soft reduction. Finally, the development of a modular program for the design of continuous casters is presented. This integrated program is based on FEM and CAD and permits a fast optimisation of the caster design variables by linking together geometry, solidification, and mechanical calculation of strand solidification, bulging, and support. This approach contributes to a faster and more effective definition of any continuous caster in the early phase of the project, which results in cost and time savings.