Continuous Strip Casting Research Articles

Effects of SiC/ZrO2 ratio on the key service performance of BN-ZrO2-SiC composites

BN-ZrO2-SiC composites have excellent comprehensive performance, which can be used in iron and steel metallurgy, such as side dams for thin strip continuous casting. In this paper, the influence of SiC/ZrO2 ratio on the structure and properties for BN-ZrO2-SiC composites was investigated, and the atmosphere used for corrosion tests was more closely to the real usage situation. The results show that with the increase of SiC/ZrO2 ratio, the thermal shock resistance of BN-ZrO2-SiC composites increases, as well as the corrosion resistance by molten steel decrease. When the SiC/ZrO2 ratio is 35:15, the BN-ZrO2-SiC composites present the best comprehensive performance, and its hardness and modulus of elasticity are higher than those of other samples, which are 165.8 MPa and 101.9 GPa, respectively.

Investigation on tribological properties of high-velocity air fuel spraying WC–Cr3C2–Ni coating on the surface of continuous casting crystallization rollers

To overcome the wear problem of the substrate of thin-strip continuous casting crystallization rollers and improve economic efficiency, high-velocity air fuel (HVAF) technology was used to deposit WC–Cr3C2–Ni wear-resistant coatings on the surface of the crystallization rollers. The existing performance and wear condition of curved WC–Cr3C2–Ni coatings during continuous casting were investigated by the ring-block wear system. The experimental results showed that the WC–Cr3C2–Ni coating with a thickness of 300 μm effectively reduced the coefficient of friction (by 16.4 %) and the wear rate (by 82.5 %) on the surface of the crystallization roller and significantly reduced the roughness of the wear interface (by 71.2 %), which provided reliable protection for the substrate. The results of high-temperature (200 °C) wear tests showed that the WC–Cr3C2–Ni coating deposited via HVAF protected the substrate in actual long-cycle production and exhibited an excellent resistance to the emergence and expansion of failure cracks. This study provided a theoretical basis for the selection and preparation of surface coatings for thin strip continuous casting crystallization rollers.

MgAl2O4–C refractories with balanced properties for a delivery device used in the double-roll thin strip continuous casting

To realize the double-roll thin strip continuous casting process for the production of high-quality steels, it is necessary to seek a new type of refractory material tailored for delivery device employed in this process. Therefore, the present study aimed to design and prepare MgAl2O4–C refractories for this purpose as well as to study their physical and mechanical properties, thermal shock resistance, oxidation kinetics, and to perform molten steel experiments after pre-oxidation treatment. The results of the present study demonstrated that the specimens could maintain high mechanical and thermal shock properties even after pre-oxidation treatment. After pre-oxidation at 1100 °C/1 h, the cold compressive strength of the specimen reached 17.63 MPa, with a residual strength ratio (thermal shock resistance) of 77.99%. Analysis of oxidation kinetics based on the shrinking core model indicated an increase in the effective diffusion coefficient and complete oxidation time with higher pre-oxidation temperature. Pre-oxidation of MgAl2O4–C refractories has been shown to be effective in reducing carbon penetration into the molten steel from carbon-containing refractories, thus maintaining the stability of the molten steel composition. This effect was attributed to enhanced contact and wettability between the steel and refractories, an augmented thickness of the pre-oxidized decarburized layer, the formation of a dense magnesium oxide layer, and the emergence of the MgAl1·9Fe1O4 phase. Consequently, an MgAl2O4–C refractories designed for the delivery device was proposed along with anticipated applicability in the double-roll continuous casting process.

Study on wear properties of high hardness and high thermal conductivity copper alloy for crystallization roller

The crystallization roller in thin strip continuous casting combines the cooling function of the plate crystallizer with the rolling function of the roll, thereby significantly enhancing process efficiency. This also imposes higher demands on the thermal conductivity and hardness of the crystallization roller. During the utilization of the crystallization roller, as it comes into contact with the billet, the base material must exhibit exceptional wear resistance. The thermal conductivity and mechanical properties of high-strength beryllium copper alloy C17200 and traditional crystallization material CrZrCu alloy C18150 were assessed at various temperatures using a laser thermal conductivity meter (LFA-427) and microhardness meter (ZD-HVZHT-10), respectively. Detailed analysis confirms the potential suitability of C17200 as an alternative material for crystallization rollers. The hardness of C17200 was twice that of C18150 while maintaining the original thermal conductivity. The wear characteristics of C17200 were investigated at room temperature (25 °C) and simulated operating conditions (300 °C) using a reciprocating wear tester (MZF-1). Additionally, the wear mechanism of C17200 at different temperatures was studied using scanning electron microscopy (SEM). The findings demonstrated that C17200 exhibited favorable wear resistance even at a temperature of 300 °C, thereby satisfying the performance criteria for the crystallization roller during operational usage.

Densification mechanism and corrosion resistance of h-BN/ZrO2 ceramics prepared by spark plasma sintering

The dense h-BN/ZrO2(30 wt%) composites without additives were rapidly fabricated by spark plasma sintering. The relative density, apparent porosity, fracture toughness, flexural strength, phase composition and microstructure of h-BN/ZrO2 composites were systematically investigated. Besides, the corrosion resistance of h-BN/ZrO2 composites in molten steel was also studied in detail. Especially, the h-BN/ZrO2 composites were sintered at 1800 °C exhibiting a relative density of 96.6% and the flexural strength of ≈ 157 MPa. The corrosion of h-BN/ZrO2 composites was mainly due to the oxidative decomposition of BN, and the corrosion process was clarified by a parabolic law. The excellent corrosion resistance of the h-BN/ZrO2 composites was attributed to ZrO2 residual layer formed at the interface. The corrosion thickness of h-BN/ZrO2 composites was only ∼116 µm even using the longest corrosion time (80 min). The composites could be a promising candidate material applied to fabricated thin strip continuous casting side sealing plates.

Effect of ZrO2 on sintering behavior and properties of h-BN/ZrO2 composites by spark plasma sintering

The h-BN/ZrO2 composites with different 3Y–ZrO2 content were prepared by spark plasma sintering at 1800 °C. The sintering behavior, bulk density, apparent porosity, thermal conductivity, thermal expansion coefficient, bending strength, thermal shock resistance, microstructure and phase were analyzed. The optimum specimens were used to test the resistance to corrosion of molten steel for 10, 20, 40, 80 min respectively. The results indicated that ZrO2 could facilitate the sintering process of h-BN matrix under the action of spark plasma. Especially, for the composites with 30 wt% 3Y–ZrO2, the porosity could decrease to 1.1% and the flexural strength could exceed 150 MPa. The microstructure showed the h-BN grains and 3Y–ZrO2 grains are closely combined. The XRD patterns indicated that the t-ZrO2 diffraction peak gradually enhanced with the increase of density. With the increase of erosion time, the erosion rate increased significantly. After the surface of the specimen is eroded, the erosion resistance of the matrix would decrease significantly. This h-BN/ZrO2 could be as side-dam used in the thin strip continuous casting process.

Numerical simulation of the nozzle configuration in strip casting process

This work examines the design of nozzles in continuous strip casting process. Three-dimensional (3D) simulations of steady turbulent (k-ε) flow are done at the upper part of the mould using a finite-volume (CFX) model. This is performed for different inlet systems, including the inlet nozzle jets with a free stream, the submerged nozzle jets, the slot inlet system, and the slot-submerged inlet system. The resulting heat flux to the solidifying shell has also been studied. Numerous operating parameters are examined, including the shape, size, position, and thickness of the ports and the bottom geometry. It is found that different inlet nozzle configurations change the molten flow and heat patterns, mainly in the upper region of the mould. By applying the slot nozzle inlet system, turbulence and values of the averaged velocity field in that area decrease significantly.

Corrosion mechanism of BN-ZrO2 based side-dam by molten steel

BN-ZrO2-based side-dam is a hot spot for research and application of the thin strip continuous casting process. The corrosion mechanism of BN-ZrO2 based side-dam by molten steel has been demonstrated using contemporary detection technologies and microscopic analysis (I) Amorphous generation: BN oxidizes and volatilizes quickly at first. Residual products and steel inclusions combine to create the amorphous, which serves as a mass transfer medium. (II) Dissolution-precipitation: the components of side-dam such as m-ZrO2, Al2O3, etc., which undergo dissolution-precipitation mass transfer through the amorphous in the working layer to achieve dependent growth as enrichment between crystals such as m-ZrO2, corundum, and spinel. (III) Solid-phase skeleton formation: m-ZrO2, corundum, spinel, and other coarse-grained particles unite and form a skeleton, with amorphous filling the structure, generating a slag mass, and sintering primarily in the solid phase, which is increasing macroscopically.

An experimental and numerical study on the modelling of fluid flow, heat transfer and solidification in a copper continuous strip casting process

An experimental and “numerical study (first part of this study study) was carried out to investigate the solidification process in a copper continuous strip casting process. The model has been tuned by experimental results (i.e. cooling water flow measurements, temperature measurements and metallographic analysis). Further, the results have been used to study the possibility of improved productivity. In this report (second of the study) the flow pattern of the molten copper during a strip casting process as a manufacturing method has been studied using a full-scale water model. The dynamic similarity between model and real system has been studied. Six different types of inlet system to the mould have been studied: inlet nozzle jets with free stream, submerged nozzle jets, slot-submerged inlet system, semi slot-submerged inlet system, submerged-slot inlet nozzle jets and finally submerged-slot inlet nozzle jets with jet killer. Moreover, the effects of nozzle angle, nozzle diameter, casting speed, tundish adjustment and misalignment of the inlet nozzle jets on the flow pattern have been investigated. The vortex formation and bubble entrainment, depending upon the nozzle configuration, immersion depth and the fluid level in the mould have also been studied. It was found that the slot-submerged inlet nozzle jets with jet killer arrangement showed an obvious improvement of the fluid flow characteristics, yielding better tracer distribution in the flow pattern, lower values of back mixing flow, lower turbulence and lower vortex and recirculation flow.

Chemical composition influence on element segregation and properties of steel strip manufactured by strip casting route

The article presents the results of the chemical composition influence on element segregation and properties of steel strip manufactured by strip casting route. It is shown that in the transition from the slab production with a thickness of 220 mm to slabs with a thickness of 1.2 mm, the thickness of the segregated diffusion layer in the case of the continuous strip casting process is 4.1 - 12.4 times less than in the case of traditional continuous casting. The carbon, nitrogen, copper, tin, phosphorus and sulfur segregation percentage in the continuous strip casting process is 1.7 - 5.1 times less than in traditional continuous casting. A method is proposed for calculating the element segregation based on the equality of the segregation level in traditional and strip continuous casting. It has been established that the content of elements in steels during two-roll continuous casting can be increased for impurities such as S, O, N, P, H from a minimum of 3 for P to a maximum of 497% for S. For residual elements such as Pb, Bi, Sn, Cu, Sb, Zn, As minimum increase from 1.1 for Zn to maximum 401% for Pb. The content of such alloying elements as B, Se, Al, Te, Ca, Mg, Ce, C, La, Nb, Ti, Mn, Ni, Si can be increased from a minimum of 1.1 for Si and Mn to a maximum of 675% for B. The time and rate of cooling of a 20-ton coil of steel strip are calculated, which are, respectively, 13.7 hours and 0.0051 oC/s. Such cooling conditions create the prerequisites for the precipitation of chromium carbides and an increase in the tendency of steel to intergranular corrosion. It was found that for eliminate this problem, it is necessary to increase the cooling time with water after rolling to a strip temperature from 300 to 400 oC.

Research on cast-rolling force in twin-roll continuous strip casting based on uncertainty analysis

The uncertainties of various parameters, including casting temperature, rolling velocity and roll gap are investigated in twin-roll continuous strip casting process for S304 stainless steel. A sample-based stochastic model based on Latin hypercube sampling is established to evaluate the influence of various uncertain parameters on the height of Kiss Point and the cast-rolling force. A polynomial mathematical model combined with numerical simulation is built with full factorial design approach. The convergence of variance is used to represent the variability of the input parameters, and Inter Quartile Range (IQR) is adopted to qualify the uncertainty of output parameters. The IQR analysis shows that casting temperature is the most dominant factor among all output parameters including roll gap and rolling velocity.

Microstructure and Mechanical Properties of Al-5Mg-0.8Mn Alloys with Various Contents of Fe and Si Cast under Near-Rapid Cooling

Al-5Mg-0.8Mn alloys (AA5083) with various iron and silicon contents were cast under near-rapid cooling and rolled into sheets. The aim was to study the feasibility of minimizing the deteriorating level of the harmful Fe-rich phases on the mechanical properties through refining the intermetallics by significantly increasing the casting rate. The results showed that the size and density of the intermetallic particles that remained in the hot bands and the cold rolled sheets increased as the contents of iron and silicon in the alloys were increased. However, the increment of the particle sizes was limited due to the significant refinement of the intermetallics formed during casting under near-rapid cooling. The mechanical properties of the alloys reduced as the contents of iron and silicon in the alloys increased. However, the decrement of tensile strengths and ductility was quite small. Therefore, higher contents of iron and silicon could be used in the Al-5Mg-0.8Mn alloy (AA5083 alloy) when the material is cast under near-rapid cooling, such as in the continuous strip casting process.

In situ-formed, low-cost, Al-Si nanocomposite materials

Aluminum-Silicon (Al-Si) alloys are the “bread-and-butter” of the aluminum foundry industry being cast at an annual rate of over 2 million tonnes/year in North America for use mainly in transportation. Coarse microstructure of these alloys limits their specific mechanical properties and consequently their potential for vehicle lightweighting. Purpose: We report on a new family of cast Al-Si alloys producing in-situ formed nanocomposites of up to 25 vol.% ultrafine equiaxed silicon particles in Al alloy matrix which can be ductile, or reinforced by nano-scale spinodal constituents. Design/methodology/approach: The hypereutectic Al-Si-X alloy (A390) was melted, solidified and cooled on the novel High Pressure Die Casting Universal Metallurgical Simulator and Analyser Technology Platform (HPDC UMSA) at specific process parameters. The HPDC cast samples consecutively were solution treated and artificially aged to spheroidize the Si and to dissolve the intermetallics in Al(SS) and to re-precipitate them in the solid state as nano-sized spinodal structures. The heat treatment was performed using the High Temperature UMSA Technology Platform. Findings: The nano scale structure of these new materials gives them significantly improved strength, hardness, and wear resistance while retaining adequate toughness and ductility for applications in the transportation applications. Research limitations/implications: Desired composite nanostructures have been produced and characterized in-situ in small laboratory test samples. Practical implications: These new materials can be produced by conventional casting technologies such as continuous strip casting, or high-pressure die-casting from conventional low-cost Al-Si melts. Originality/value: These materials can be produced with a significantly higher volume fraction of ultrafine Si dispersoids than has been done to date in in-situ formed materials, while retaining and improving the density-specific mechanical properties.

Computational and Experimental Study of the Transient Transport Phenomena in a Full-Scale Twin-Roll Continuous Casting Machine

To gain a fundamental understanding of the transient fluid flow in twin-roll continuous casting, the current paper applies both large eddy simulation (LES) and full-scale water modeling experiments to investigate the characteristics of the top free surface, stirring effect of the roll rotation, boundary layer fluctuations, and backflow stability. The results show that, the characteristics of the top free surface and the flow field in the wedge-shaped pool region are quite different with/without the consideration of the roll rotation. The roll rotation decreases the instantaneous fluctuation range of the top free surface, but increases its horizontal velocity. The stirring effect of the roll rotating makes the flow field more homogenous and there exists clear shear flow on the rotating roll surface. The vortex shedding induced by the Karman Vortex Street from the submerged entry nozzle (SEN) causes the “velocity magnitude wave” and strongly influences the boundary layer stability and the backflow stability. The boundary layer fluctuations or the “velocity magnitude wave” induced by the vortex shedding could give rise to the internal porosity. In strip continuous casting process, the vortex shedding phenomenon indicates that the laminar flow can give rise to instability and that it should be made important in the design of the feeding system and the setting of the operating parameters.

The influence of Mn on the microstructure and mechanical properties of the Al–5Mg–Mn alloy solidified under near-rapid cooling

Abstract

Effect of Fe, Si and Cooling Rate on the Formation of Fe- and Mn-rich Intermetallics in Al–5Mg–0.8Mn Alloy

The Fe- and Mn-rich intermetallics are of great effect on the mechanical properties of the AA5083 type alloy (Al–5Mg–0.8Mn). The effect of Fe, Si and cooling rate on the formation of the intermetallics were investigated by analyzing the microstructures of the alloys with different Fe and Si contents. The results indicated that increasing the Fe content resulted in the increase of the Al6(Fe,Mn) phase in both amount and size. In the alloys with high Fe content, the platelet-like Al6(Fe,Mn) compounds lined up and formed a band. Increasing the content of Si resulted in the increase of the Mg2Si phase which formed a network structure. Increasing the cooling rate significantly refined the intermetallics. However, increasing the cooling rate did not change the characteristic of the intermetallic compounds in the alloys with low or medium Si contents. For the alloys with high contents of Fe and Si under the condition of near-rapid cooling, the Fe- and Mn-rich intermetallic compound changed to the quaternary Al15(Fe,Mn)3Si phase and displayed a fine fish bone or Chinese script structure. The refinement of the intermetallics would allow higher tolerance of Fe and Si contents in the AA5083 alloy produced, for instance, via the continuous strip casting process.

Structure evolution of Fe–15 wt-%Mn sub-rapidly solidified strips under different cooling rates

Owing to the effect of the transformation-induced plasticity (TRIP) or the twinning-induced plasticity (TWIP), Fe–Mn-based alloys have excellent mechanical properties and attract more attention as a promising structural material. Thin strip continuous casting was considered as an effective method to produce high-Mn steels, which were hard to produce by traditional methods. In this paper, the effect of different cooling rates by changing the trip thickness on the microstructure of Fe–15 wt-%Mn alloy prepared under sub-rapid solidification was investigated. The experimental results showed that α′-martensite and ϵ-martensite directly formed in the sub-rapidly solidified strips. The formation of ϵ-martensite in the 1·5 mm and 1 mm thickness strips suppressed with increasing cooling rate, while some nanocrystallines were obtained in these strips. The size of martensite phases was very fine in all strips, and the ϵ-martensite still existed after the heat treatment at 1000°C for 2 h.

Thermodynamics of Amorphous Silicon Oxides in Sub-Rapid Solidified Low Carbon Steel

Strip casting technology leads a new revolutionary change for steel industry, which solidification rate could be 100-1000 K/s. The study on the size and structure of deoxidation products from the sub-rapid solidification will be of great significant in promoting the mechanical properties of the strip continuous casting steels. In the paper, the silicon oxide inclusions precipitated in sub-rapid solidified low carbon steel were investigated by transmission electron microscopy. The experimental results indicated that a large number of spherical silicon oxides were dispersed as amorphous state, and the size range was in hundreds nanometers. According to the thermodynamic calculation and inference, the silicon oxides would precipitate during the sub-rapid solidification of low carbon steel. SiO2, which structure is as approximate “liquid” and the melting temperature has been reduced under nanoeffect, has been frozen in amorphous state under high solidification rate. Amorphous SiO2 precipitated in steel may be due to the structural relaxation caused by high viscosity. The larger average size of amorphous SiO2 was detected at higher solidification rate, which is attributed to the cause to the higher hardening rate.

Numerical Simulation of the Fluid Flow, Heat Transfer, and Solidification in a Twin-Roll Strip Continuous Casting Machine

In this paper, a three-dimensional enthalpy–porosity mixture solidification model is employed to describe the basic rules of heat transfer and solidification in a twin-roll strip continuous casting machine equipped with a multi-port trough-shaped feeding system, and reasons for the formation of these rules are analyzed. The two-layer zonal turbulence model is used to incorporate the turbulence in fluid flow, and the fluid flow in the wedge-shaped pool region in various conditions is studied. The results show that the fluid flow field in the pool region is quite different with/without the consideration of rotating rolls when the solidification is ignored, which indicates the importance of the consideration of rotating rolls in the water modeling equipment design. There are three aspects including molten steel jet impingement, roll rotating, and backward flow of the mushy zone, which strongly influence the temperature distribution in the pool region. The solidification process in the pool region could be divided into three stages: at the first stage, there exists a fast solidification region which obeys the square root law, and an approximately linear growth region could be found at the second stage, while a parabolic growth region could be found at the last stage. The formation of the first stage and the last stage could be mainly due to the geometry of the feeding system and the backward flow of the mushy zone, respectively. The first stage of solidification could be modified by a better designed feeding system, but the backward flow of mushy zone determined by the properties of metals and casting parameters could be one of the biggest obstacles for commercial production of steel sheets by a twin-roll caster.

405 縦型双ロール法による銅合金の薄板連続鋳造(OS4-(2),OS4 オーガナイズドセッション≪材料・組織と加工≫)

405 縦型双ロール法による銅合金の薄板連続鋳造(OS4-(2),OS4 オーガナイズドセッション≪材料・組織と加工≫)