Slab Casting Research Articles

Transformation Delay and Texture Memory Effect of Columnar Grained Cast Slab in Low Grades Non-oriented Electrical Steels

The cast slab of low grades non-oriented electrical steels experiences twice diffusional solid phase transformation and demonstrates the features of strong morphological memory referring to columnar structure and texture memory referring to the preferred <100> texture at room temperature. In this paper, electron backscatter diffraction (EBSD), quasi-insitu observation of heating samples, and dilatometry are used to study and analyze the two kinds of memory phenomena. The results show that the cast slab consists of about 70% coarse columnar grains and 30% small equiaxed grains. Many small equiaxed grains show Σ3 misorientations with columnar grains indicating K-S orientation relationship obeyed during phase transformation. Coarse columnar grains show a typical <100>||growing axis orientation which is the same as solidified columnar grains. The quasi-insitu observation shows that transformation of columnar grained ferrite to austenite is very sluggish and columnar grained ferrite can still be seen even at a superheating degree of 176°C for 1 hour. Dilatometry measurement indicates that the starting transformation temperatures for a columnar-grain-dominant sample and a small-equiaxed-grain-dominant sample are similar, whereas their transformation extents are quite different with columnar grained sample showing a low dilatational amount due to insufficient transformation. It is most likely that the coarse columnar grains in cast slab are retained and untransformed high temperature δ-ferrite are not subjected to twice complete transformations. These retaining columnar grains in low grades of electrical steels can be used to improve magnetic properties through optimizing processing parameters.

Feeding Steel Strip Technology in Continuous Casting Process: A Review

Feeding strip into continuous casting mold is a technique that can reduce the central segregation and increase the equiaxed zone ratio of continuous casting slab. Over the past decades, some steel mills have gradually applied this technique, but it still lacks a comprehensive understanding of the control theory of process parameters. Many parameters joint the influence of the steel strip melting process and strip feeding ratio, deciding the inner quality of the slab eventually. Herein, the mechanism and heat transfer of feeding strip technology are analyzed. Parameter sensitivity studies and feeding strip experiments are summarized and some new conclusions are proposed. Finally, some suggestions for industrial production will give an outlook for future work.

The Role of Elements Partition and Austenite Grain Size in the Ferrite-Bainite Banding Formation during Hot Rolling.

The partitioning and diffusion of solute elements in hot rolling and the effect of the partitioning and diffusion on the ferrite-bainite banding formation after hot rolling in the 20CrMnTi steel were experimentally examined by EPMA (electron probe microanalysis) technology and simulated by DICTRTA and MATLAB software. The austenite grain size related to the hot rolling process and the effect of austenite grain size on the ferrite-bainite banding formation were studied. The results show that experimental steel without banding has the most uniform hardness distribution, which is taken from the edge of the cast slab and 1/4 diameter position of the cast slab, heating at 1100 °C for 2 h and above 1200 °C for 2–4 h during the hot rolling, respectively. Cr, Mn, and Si diffuse and inhomogeneously concentrate in austenite during hot rolling, while C homogeneously concentrates in austenite. After the same hot rolling process, ΔAe3 increases and ferrite-bainite banding intensifies with increasing initial segregation width and segregation coefficient K of solute elements. Under the same initial segregation of solute elements, ΔAe3 drops and ferrite-bainite banding reduces with increasing heating temperature and extension heating time. When ΔAe3 drops below 14 °C, ferrite-bainite banding even disappears. What is more, the austenite grain size increases with increasing heating temperature and extension heating time. When the austenite grain size is above 21 μm, the experimental steel will not appear to have a banded structure after hot rolling.

Modeling of Inclusion Capture in a Steel Slab Caster with Vertical Section and Bending

Particles in molten steel, including argon-gas bubbles, slag droplets, and non-metallic inclusions, are removed into the surface-slag layer or captured by the solidifying steel-shell during continuous steel casting. Captured particles often become serious defects in the final steel product, so understanding particle-capture mechanisms is important for steel quality. Slab casters often have a straight mold and upper-strand prior to a curved lower-strand. The present work investigates particle capture in such a caster using computational modeling with a standard k-ε model for molten-steel flow, a discrete phase model for inclusion transport, and an advanced capture criterion for inclusion entrapment and engulfment into the steel shell. A new postprocessing methodology is presented and applied to predict inclusion-capture rates in commercial cast product. The locations and size distributions of particles captured into the shell, and actual capture rates are quantified. The model predictions are validated with ultrasonic-test plant measurements of the locations of large particles captured in a steel slab. The results reveal how large-inclusion capture accumulates in the beginning of the curved strand, leading to a capture band in the slab inside radius. Finally, the capture fractions and locations due to all capture mechanisms are compared for different inclusion sizes, and the implications are discussed.

Influence of External Action on the Internal Structure of Continuously Cast Slab Produced from Tube Steel

The paper compares the internal structure of two continuously cast slabs with a section of 300 × 2600 mm from a tube steel of the strength class K60, one of which is molded with a soft reduction, and the other is without external influence. A comparative analysis of the structure of two templates showed that the location of areas with an increased metal pickle ness in the axial part of the templates varies. On the template from a slab cast without reduction, this section is below the geometric center of the work-piece in thickness, at a distance of 49.2% from the underside, that is, the "lower" asymmetry of the slab structure is observed. On the template from the slab cast off with soft reduction, the area with an increased pickle-ness is located above the middle of the work-piece: at a distance of 51.7% of the side of the large radius, an "upper" asymmetry of the slab structure is formed. Consequently, as a result of the external action on the cast work-piece, the location of the axial sponginess, relative to the geometric centre of the slab, is changed by moving from the lower to the upper half of the work-piece. The metal of the axial part of the reduced slab has a denser structure, the degree of development of axial looseness in the metallographic evaluation is reduced by an average of 0.5 points. The work shows the change in the content of chemical elements along the thickness of slabs. In the reduced metal, the maximum value of the degree of zonal inhomogeneity of the most impurities is higher than in the metal without external influence. This is explained by the fact that, as a result of reduction, the zone of location of the axial chemical heterogeneity in the slab becomes smaller in width.

Settlements of spread footing foundations on quick clay stabilized with lime and cement

Since the early 70’s ground improvement by use of stabilizing agents such as lime and cement has been widely used for solving geotechnical problems; either as a way to improve slope stability, reduce settlements or vibrations, or to reinforce the inside of braced excavations. On a recently constructed motorway project in south of Trondheim, two bridges were founded with spread footings on a medium stiff, quick Norwegian clay stabilized with lime and cement. The post-tensioned concrete bridges are 78 m and 110 m long, with respectively 4 and 5 spans. In this article, evaluation of various foundation solutions is performed based on cost estimates. This showed that the cost of founding the bridges on stabilized ground to be the most viable alternative. Further, the article discusses the calculation methods used to evaluate settlement properties of the foundations. Settlement measurement is performed for about two years after completion of the structures. A comparison of the calculated deformations and measured settlements is conducted in this work. Settlements are measured to be 3-10 mm after one and a half year, except for one abutment that measured 21 mm of vertical displacements. Then the deformations nearly stop for many of the foundations. The measurements show a higher deformation rate in the first six months after casting of the bridge slab, than expected from the calculations. After some time, the measurements coincide well within the upper and lower bounds in the calculations done in the geotechnical design. Possible reasons for these observations are discussed.

DTA study and thermodynamic prediction of the solidification interval of boron 500HB abrasion-resistant steel

Special wear-resistant steels are essential in applications with extreme abrasion conditions. Main applications of low-alloyed, weldable abrasion-resistant steels are found in mining, agriculture, and elsewhere. They are normally produced via continuous casting process and then hot rolled into heavy plates of desired thickness and width. This paper focuses on the strand casting part where the solidification interval of boron 500HB steel is studied through DTA heating curves and compared with thermodynamic predictions using Thermo-Calc (TCFE7 and TCFE9 database) and JMatPro with internal database General steel. Liquidus temperatures measured from the second heating curve are in good agreement with the thermodynamic approach using both commercial software. Additionally, the invariant peritectic temperature was experimentally determined and a reasonable agreement is achieved with predictions. All databases revealed a similar solidus temperature if the calculation was performed without boron included. By including 23 ppm of boron into the calculation, only one commercial software predicted the solidus temperature in good agreement with the measured value determined by DTA, the other result differed significantly. This study shows that important variation of the predicted metallurgical length in the strand slab caster exists if the solidus position is estimated using thermodynamic prediction. As the studied samples were taken directly from an industrial plate, a qualitative evaluation of micro-segregation through the cross-section of the thickness was also done and taken into account with thermal analysis.

Experimental study on evolution of oxidation behavior on high-temperature continuous casting slab surface

The oxidation kinetics, oxide layers composition and thicknesses of X70 steel, Y55 steel and 304 stainless steel are investigated. The results show that the oxidation rate of X70 steel increases rapidly at 1000 °C, while that of Y55 steel and 304 stainless steel increases rapidly at 1100 °C. The oxidation kinetic coefficients of X70 steel, Y55 steel and 304 stainless steel are exp (10.7), exp (11.58) and exp (30.15), respectively, and the apparent activation energy of oxide layer are 196879.7 J/mol, 207608.1 J/mol and 469284.3 J/mol, respectively. The cross-sectional morphology and element distribution of oxide layer are obtained. With the oxidation time increases from 30min to 80 min at 1100 °C, the oxide layer thickness of X70 steel and Y55 steel increases by 1242.33 μm and 965.59 μm respectively when the weight of steels increases by 1 mg/mm2, and the oxide layer of Y55 steel is denser than that of X70 steel. A variable temperature oxidation mathematical model of the slab surface is established to predict the oxide layer thickness of slab surface.

Characteristics and main controlling factors of Ordovician deep subsalt reservoir in central and eastern Ordos Basin, China

In recent years, the subsalt dolomite reservoirs in the Ordovician strata of the Ordos Basin have indicated good exploration results and are expected to have a high hydrocarbon potential. This study targets the Ma 3 and Ma 4 reservoirs below the salt rock of the Ordovician in the central and eastern Ordos Basin. It investigates the reservoir characteristics and main controlling factors of high-potential reservoirs by combining core observations, cast slabs, scanning electron microscopy, physical property analysis, and mercury injection data. The results show that the Ma 3 reservoir is dominated by gypsum-bearing dolomite deposited in evaporation environments, whereas the Ma 4 reservoir is dominated by calcite dolomite under a transgressive environment. The types of Ma 4 reservoir space mainly include dissolved pores (dissolved holes), intra-crystalline pores, intra-crystalline dissolved pores, and microcracks. The types of Ma 3 reservoir space mainly include microcracks, gypsum mould pore, dissolved pores (dissolved holes), and intergranular pores. The pore structures of reservoirs are complex. The capillary pressure curves can be divided into four types: dissolved pore type, intra-crystalline (dissolved) pore type, microcrack type, and micro-porous type. Based on available information, the average porosity values of the Ma 3 and Ma 4 reservoirs are 2.1% and 2.3%, respectively, and the average permeability values are 0.19 × 10−3μm2 and 0.22 × 10−3μm2, respectively. The Central paleo-uplift, the Wushenqi secondary paleo-uplift, and the Shenmu low uplift controlled the sedimentary facies and favorable lithofacies distributions. Sedimentary microfacies control rock fabric, and the rock fabric affects the physical properties of the reservoirs. The limestone and dolomite reservoirs with gypsum and sand cutting texture have relatively good physical properties. Diagenesis is also a key factor in the development of sub-salt reservoirs. Intra-crystalline pores are mainly formed under various dolomization mechanisms. The surficial and buried diagenetic environments facilitate the formation of a large number of secondary pores, such as dissolved pores (dissolved holes), intra-crystalline dissolved pores, and gypsum mould pores. In addition, the Yanshan tectonic activity played a vital role in the development of reservoir microcracks. The microcracks can significantly improve reservoir physical properties. It is favored that the tectonic setting, rock fabric, diagenetic, and microcrack alterations collectively determine the sub-salt reservoirs' storage capacity and are the main controlling factors for forming high-quality reservoirs.

Formation and Control of Transverse Corner Cracks in the Continuous Casting Slab of a Microalloyed Steel

To investigate transverse corner cracks for a microalloyed steel continuous casting slab, the metallography, microtopography, and three‐dimensional (3D) morphology of cracks are studied, respectively. High‐temperature mechanical properties are investigated and compared from two positions where samples are extracted from both the slab corner and surface of the slab center. The thermal history of the slab is simulated and optimized experiments are conducted. Transverse corner cracks are generated on the valley of oscillation marks. Mold powder and wear elements of the mold are not detected. Microstructures are refined near the cracks. Cracks are generated in secondary cooling zones and the cracking temperature is higher than Ar3 temperature. The extension path of cracks is not linear and cracks extend along the grain boundary. The third brittle temperature ranges (TBTR) are 764–832 °C and 793–808 °C in the two positions, respectively. The temperature at the slab corner in the bending and straightening zone falls into the brittle zone during the original water cooling condition, leading to the formation of cracks. The secondary cooling scheme is optimized to prevent the temperature at the slab corner in the bending and straightening zone from entering the TBTR, significantly reducing the occurrence of transverse corner cracks.

Primary Recrystallization Behaviors of Hi-B Steel with Lower Initial Nitrogen Produced by the Thin Slab Casting and Rolling Process

Based on low-temperature high-permeability grain-oriented silicon steel designed with an initial nitrogen content of 0.0055% and produced by the thin slab casting and rolling process, the effect of total nitrogen content and nitriding temperature on primary recrystallization microstructure and texture were studied by optical microscope, scanning electron microscope, transmission electron microscope, and electron backscatter diffraction. The nitriding temperature affects the primary recrystallization behaviors significantly, while the total nitrogen content has a small effect. As the nitriding temperature is 750–850 °C, the average primary grain size and its inhomogeneity factor are about 26.58–26.67 μm and 0.568–0.572, respectively. Moreover, the texture factor is mostly between 0.15 and 0.40. Because of the relatively sufficient inhibition ability of inherent inhibitors in a decarburized sheet, the nitriding temperature (750–850 °C) affects the primary recrystallization microstructure and texture slightly. However, as the nitriding temperature rises to 900–950 °C, the average primary grain size and its inhomogeneity factor increase to 27.75–28.26 μm and 0.575–0.578, respectively. Furthermore, because of the great increase on the area fraction of {112} &lt;110&gt; grains, part of texture factor is increased sharply. Therefore, in order to obtain better primary grain size and homogeneity, better texture composition, and stability of the decarburized sheet, the optimal nitriding temperature is 750–850 °C.

Processing of Low-Carbon Deep-Drawing Steel with High Plastic Anisotropy Using Two-Stage Batch Annealing Cycle

Anisotropy in texture determines capacity of the steel to achieve maximum plastic flow in the plane of the sheet and maximum resistance to flow in a direction perpendicular to the sheet. Present work has been carried out to explore the potential of maximizing plastic anisotropy (rm) value in extra deep-drawing steel. Industrial heat was made with low carbon (0.03 wt.%), low manganese (0.15 wt.%), and low sulfur (0.007 wt.%) levels. Continuously cast slabs were hot-rolled and then cold-rolled to 1 mm thickness. The cold-rolled sheets were subsequently subjected to annealing in an annealing simulator furnace adopting specially designed two-stage batch annealing cycle. In batch-annealed steel samples, grains were found to be recrystallized and had undergone grain growth preferentially along the longitudinal direction with strong gamma fiber, comparable to that of Interstitial Free steel. Excellent combination of strength and forming properties, in terms of yield strength 190 MPa, ultimate tensile strength 290 MPa, and total elongation 45%, YS/UTS: − 0.66 with very high plastic anisotropy (rm): 2.45, could be achieved. Properties achieved have been correlated with the alloy chemistry, processing path history, percentage reduction, two-stage batch annealing cycle and the resultant grain size, microstructure and texture.

Fatigue Behavior of Age-Hardening Cu-6Ni-1.5Si Alloys with Different Grain Sizes

On the thermomechanical treatments of Cu-Ni-Si alloy, cold-rolling (CR) before solution heat treatment (SHT) is commonly conducted to eliminate defects in a casting slab. In addition, a rolling is applied to reduce/adjust the thickness of casting slab before SHT. In a heavily deformed microstructure by CR, on the other hand, grain growth during a heating in SHT is likely to occur as the result of recrystallization. In general, tensile strength and fatigue strength tend to decrease with an increase in the grain size. However, the effect of difference in grain sizes produced by with and without CR before SHT on the fatigue strength is unclear. In the present study, fatigue tests of Cu-6Ni-Si alloy smooth specimens with a grain fabricated through different thermomechanical processes were conducted. The fatigue behavior of Cu-Ni-Si alloy was discussed.

Modification for prediction model of austenite grain size at surface of microalloyed steel slabs based on in situ observation

The initial solidification process of microalloyed steels was simulated using a confocal scanning laser microscope, and the growth behavior of austenite grain was observed in situ. The method for measuring the initial austenite grain size was studied, and the M 0 * (the parameter to describe the grain boundary migration) values at different cooling rates were then calculated using the initial austenite grain size and the final grain size. Next, a newly modified model for predicting the austenite grain size was established by introducing the relationship between M 0 * and the cooling rate, and the value calculated from the modified model closely corresponds to the measured value, with average relative error being less than 5%. Further, the relationship between Tγ (the starting temperature for austenite grain growth) and equivalent carbon content CP (CP > 0.18%) was obtained by in situ observation, and it was introduced into the modified model, which expanded the application scope of the model. Taking the continuous casting slab produced by a steel plant as the experimental object, the modified austenite grain size prediction model was used to predict the austenite grain size at different depths of oscillation mark on the surface of slab, and the predicted value was in good agreement with the actual measured value.

Bonding agents to mitigate interfacial strength loss during multi-layer concrete casting

Self-consolidating concrete (SCC) is very sensitive to interruptions or delays during the placement process. Current literature converges that interfacial bond strength between successive casting lifts could drop by up to 60%, compared with monolithic casting. In this study, two series of SCC mixtures were tested to assess the suitability of bonding agents to mitigate the drop in interfacial bond strength resulting from successive casting lifts. The slabs were cast in two layers separated by 60 or 120 min rest intervals; different bonding agents, including styrene–butadiene rubber (SBR), waste latex paint and cement/water and cement/SBR slurries were compared. The results showed that the application of polymeric bonding agents on top of the first cast is efficient to improve tensile strength and restore the integrity of the hardened member. This is attributed to the polymer particles that coalesce and fuse to form continuous close-packed films between the first and second SCC layers. The cement/water slurry did not lead to considerable improvement in pull-off strength between cast layers. Series of charts enabling the prediction of the drop in bond for a given SCC composition and rest interval as a function of the polymer dosage to the area of the cast slab are presented.

Thickness influence on element segregation in continuously cast steel slabs

The article presents the results of a study of the effect of slab thickness on the element segregation of during continuous casting of billets. The process of accumulation of elements on the surface of dendrites during crystallization of steel slabs for various thicknesses is considered. The theoretical dependence of the process of accumulation of elements on the dendrite surface during the crystallization of steel slabs for various thicknesses has been established. It is shown that the efficiency of accumulation of elements on the dendrite surface depends significantly from the crystallization and cooling rate of the slab. The established dependence makes it possible to determine the permissible increased element content in strips, which is equivalent to their content in thick slabs during continuous casting of billets. The element segregation searching shows that at pouring of thin steel strips, an increasing of the element content is possible compared to continuous casting of thick slabs with an identical level of segregation. The elements are arranged as possible to maximize the impurities content in AISI 1006 carbon steel in the following decreasing sequence: S, O, N, P, H. Another sequence is observed for stainless steel AISI 304: O, S, P, H, N. The following sequences are observed in the case of residual elements: for steel AISI 1006 - Pb, Bi, Sn, As, Zn, Sb, Cu; for steel AISI 304 - Cu, Sb, Sn, Bi, Pb, As, Zn. The sequences are as follows for the alloying elements: for steel AISI 1006 - B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si, Cr; for steel AISI 304 - Ca, Te, Al, Ti, Mg, C, La, Ce, Nb, Se, V, B, Si, Cr, Mn.

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.

Исследование трансформации поверхностных трещин непрерывнолитых слябов из низколегированных трубных сталей при горячей прокатке

A finite-element mathematical model of surface crack transformation of continuously cast slabs made of low-alloy pipe steels to sheet defects during hot rolling has been constructed. The transformation of axial, edge, corner and side cracks of the slab was investigated. It has been established that, depending on deformation conditions, surface cracks during rolling of the slab to a thick sheet can close in the first passes under the action of compressive stresses, move to the surface, form folds, twist towards the edge, or roll out completely.

Estimation of minimal slab reduction to eliminate of axial porosity

In the production of the continuous cast slabs using continuous-casting machine, the formation of axial porosity is observed. Method for determination of the minimal reduction of the workpiece during hot rolling in order to eliminate the axial defect is presented. The theoretical dependences for transformation of the axial porosity on drawing and the reduction rate of continuously cast slab during hot rolling are obtained based on assumptions.

Nonmetallic inclusions and secondary structure of continuous casting steels

The article presents the results of a study of the non-metallic inclusions and secondary structure of continuous casting steels It is estimate that main quantity of non-metallic inclusions (»72%) it inputted in steel during the deoxidization and the secondary oxidation, therefore the casting processes need to be managed very well to decrease the quantity of non-metallic inclusions in liquid steel. Reducing the secondary dendrite arms spacing for the strip casting process, in comparison with the conventional continuous casting process of thick slab, will reduce the size of non-metallic inclusion and as result could improve the mechanical properties of steel. Content of the endogenous non-metallic inclusions in stainless steel with Ti, in carbon steel and in electrical steel grades decreases in ladle and tundish in 2.7–3.2 times in comparison with quantity of non-metallic inclusions before pouring from furnace. The increasing of the tundish width decreases in 20 times the quantity of nonmetallic inclusions by sizes from 70 to 80 mm, and in 5–6 times by sizes 220–230 mm. Increasing of the tundish height reduces of the oxygen content in continuous casting of slab It was development the dependence of the secondary dendrite arm spacing with cooling rate. Analysis shown, that the secondary dendrite arms spacing for the strip casting process decreases from 5.91 to 8.31 times in comparison with the conventional continuous casting process of thick slab of thickness 220 mm. Simultaneously non-metallic inclusions sizes to decrease, too. Rapid solidification reduces the number of large non-metallic inclusions: the inclusion number larger than 1 mm is decreased by a ratio of 5 in comparison with the conventional slabs process. It was estimated influence of main parameters on the average grain sizes and the steel microstructure for the strip and conventional casting processes. The dependence of the grain size of carbon and low alloying steels grades (C = 0.08–0.6%, Si = 0.4–0.6%, Mn = 0.4–1.4%, P &lt; 0.03%, S &lt; 0.03%), (C = 0.04–0.6%, Si = 0.11–0.3%, Mn = 0.3–1.12%, P = 0.01–0.035%, S = 0.005–0.035%, Nb = 0.013%, V = 0.001%) and high chromium and stainless steels of type AISI 430 and 304 (C = 0.03–0.12%, Si = 0.83–1.0%, Mn = 0.8–1.0%, Cr = =16.0–18.4%, Ni = 8.47%, N = 0.03%) from casting speed range, final thickness of slab or sheet, reduction, temperature range is estimated by a multi regression analysis. The grain size of steel obtained by the strip casting process, in range 1300 to 1400 oC, is 2.3 time smaller than for the slab casting processes with slab thickness from 50 to 220 mm.