Conventional Continuous Casting Research Articles

Microstructure of conventional/PBF-LB/M 316L stainless steel hybrid joints brazed with nickel-based brazing alloys

AbstractDue to the additive manufacturing principle, laser-melted materials (PBF-LB/M) such as the austenitic chromium-nickel steel 316L have a different microstructure compared to materials produced by conventional continuous casting. The PBF-LB/M-produced 316L has a thermally metastable, anisotropic microstructure with epitaxially grown grains in which a cellular substructure is located. When brazing hybrid joints from the conventional and additive manufacturing routes with nickel-based brazing alloys, different diffusion mechanisms occur simultaneously in both joining partners. This occurs due to the different microstructural characteristics of the parent materials. The altered diffusion mechanisms lead to a new distinct microstructure in the joining zone, which influences the achievable quality of the brazed joint in a previously unknown way.

Solidification Principle in Large Vertical Steel Casting Under the EMS Effect

The surging demand for large high-quality rotor shafts or similar steel components in heavy industries (energy sector) poses new challenges to steelmakers. Based on the experience of conventional ingot and continuous casting, several new process concepts have been proposed, e.g., vertical continuous casting (VCC), semi-continuous casting (SCC), and segment casting (SC), but none of them are optimally put in operation. The main problems include the control of the as-cast structure and macrosegregation. Electromagnetic stirring (EMS) is necessary to obtain the center equiaxed zone, but EMS-induced multiphase flow can cause severe macrosegregation and uneven distribution of the as-cast structure between equiaxed and columnar. In this study, an advanced mixed columnar-equiaxed solidification model was used to investigate the formation of the as-cast structure and macrosegregation in an example of SCC with a large format (diameter 1 m). The main role of EMS is to create crystal fragments by fragmentation, which is regarded in this work as the only origin of equiaxed grains. The created equiaxed grains are brought by the EMS-induced (primary and secondary) flow and gravity-induced sedimentation to the central/lower part of the casting. The main goal of this study was to understand the solidification principle of SCC. In addition, a numerical parameter study by varying the EMS parameters was also performed to demonstrate the model capability towards the process optimization of SCC.

Microstructure evolution and corrosion mechanism of AZ91 magnesium alloy in chloride environments for commercial purposes prepared by Ohno continuous casting

Billets of commercially used AZ91 magnesium alloy were prepared by Ohno continuous casting (OCC) process. Microstructure of AZ91 magnesium alloy was observed by performing optical microscope images. In addition to microstructure analysis, effect of OCC process comparing to the conventional continuous casting on corrosion performance of AZ91 in solutions consisting of 0.01, 0.1, 1M NaCl was evaluated by using potentiodynamic polarization. In addition, immersion test in 0.1M NaCl was used to reveal the corrosion mechanism. Results revealed that chloride ion concentration affected corrosion kinetics and thermodynamics. SEM images of corroded surfaces after potentiodynamic polarization supported the influence. Differences in microstructure play an important role on the corrosion kinetics especially at higher salt concentrations (1M NaCl) what is proven in this study.

Continuous Casting Practices for Steel: Past, Present and Future

This historical review of casting methods used to produce sheets of steel for automobiles, household products, rocket bodies, etc., all point toward the development of one-step commercial processes, which are capable of casting liquid steel directly into a final sheet product. Progress towards this goal is confirmed by successful advances being made, but there remain major difficulties in reaching it. We concur that the conventional continuous casting method remains the current process of choice for highest-quality steel sheet products, but the ESP TSC (Endless Strip Production—Thin Slab Caster) approach is now highly competitive. Similarly, the original goal of Sir Henry Bessemer to produce a direct strip-making twin-drum caster, in 1856, finally came to lasting commercial fruition at CASTRIP/NUCOR. Nonetheless, a newer approach, promoted by Salzgitter, termed DSP (Direct Strip Production), or promoted by MMPC/MetSim as HSBC (Horizontal Single Belt Casting), has several advantages over CASTRIP in terms of microstructures and productivity. As such, the pros and cons of current methods are reviewed within this brief history of casting.

Impingement Density Analysis on Heat Transfer and the Appearance of Edge Cracks in Conventional Slab Using Hydraulic Nozzles

In this work, the fluid dynamics and heat transfer of two hydraulic nozzles used in the secondary cooling of the conventional slab continuous casting machine were analyzed. Impingement density maps, the jet opening angle and heat flux associated with different operating conditions (impingement distance, pressure) were experimentally determined. The opening angle and impingement density footprint were found to vary considerably in shape and magnitude with varying operating pressure and distances. Finally, it was found that when short operating distances are used, a greater heat extraction gradient occurs in the major axis of the impingement footprint, which promotes edge-cracks in the slab in plant.

Simulation of the Refining Process of Ultra-Low Carbon (ULC) Steel

The standard production route for mild steels for automotive purposes is still based on conventional continuous casting (CC) and hot strip rolling (HSR). The current trend towards the “zero-carbon car” will demand the abating of material emissions in the future. Thin slab casting and direct rolling (e.g., Arvedi endless strip production (ESP)) is an approach to reduce CO2 emissions by 50% compared to CC and HSR. One of the main limitations in applying ESP for the production of ultra-low carbon/interstitial free (ULC/IF) steels is clogging. Clogging is the blockage of the submerged entry nozzle due to the build-up of oxide layers or an oxide network. The high clogging sensitivity of IF steels results most probably from the FeTi addition, and hence, a general change of the deoxidation practice might be an option to overcome these problems. In the present work, the thorough refining process of ULC steel was simulated by addressing the different deoxidation routes and the influence of titanium (Ti) alloying on steel cleanness. The developed ladle furnace (LF) and the Ruhrstahl Heraeus (RH) refining models were applied to perform the simulation. Before the simulations, the models are briefly described and validated by the published industrial data.

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 < 0.03%, S < 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.

Near Net Shape Casting: Is It Possible to Cast Too Thin?

With increased efforts across the steel industry to produce steel in more economical ways, interest in near net shape casting has increased. Although much has been reported on the production of exotic alloys via these methods, to make the investment in new casting equipment, capability to produce current high value steels by these methods would derisk the capital expenditure. This study assesses the production of a dual phase steel (DP800) by belt casting and compared to that of conventional continuous casting. Although a drop in yield and tensile strength was seen in the belt cast-produced material, the increased elongation allowed for a comparable/improved UTS × elongation factor. A combination of in situ dendrite measurements, thermal modeling, and lab-scale belt casting has allowed insight into the relationship between cast thickness and final band spacing. The inherent lack of deformation of near net shape casting results in coarser band spacing and is not accounted for by the refinement of the secondary arm spacing caused by the faster solidification rates. This limits the strength achievable for a given martensite volume fraction. This has been predicted across the full range of casting thicknesses (1 to 230 mm) and good agreement has been shown with experimental results.

Thermal characteristics of induction heating with stepped diameter mold during two-phase zone continuous casting high-strength aluminum alloys

High-strength aluminum alloys prepared by conventional continuous casting have highly susceptible to hot tearing and poor cold workability due to nonuniform cooling. In this paper, a 3D two-phase zone continuous casting (TZCC) model was established and verified to calculate the temperature field during continuous casting. Influences of the structure and controlled temperature of the mold on the temperature field in the mushy zone were numerically calculated and analyzed, the 2D12 aluminum alloy was continuously casted based on the optimization of mold structure and temperature. The calculated results are in good agreement with the measured values. The results show that the groove in the stepped diameter mold weakens the electromagnetic coupling, which promotes the uniformity of magnetic field in the mold. Moreover, stronger electromagnetic coupling in the convex plate of the stepped diameter mold results in higher vertical temperature gradient in the mushy zone, and lower radial temperature difference appears near the solidus temperature within the controlled mold temperature of 783 to 823 K. Based on the calculated results above, the 2D12 aluminum alloy bar with good surface quality and paralleled columnar crystals was successfully prepared by the TZCC technique with optimized stepped diameter mold and controlled temperature, which has excellent elongation of 16.2%.

Thermal characteristics and uniformity of microstructures during temperature controlled mold continuous casting profiled copper alloy strip

Nonuniform temperature field at cross section of profiled billets during conventional continuous casting always results in serious defects and inhomogeneous microstructures. In this paper, a 3D temperature controlled mold continuous casting (TCMCC) model for preparing profiled copper strip was established and verified to calculate the magnetic and temperature field during continuous casting process. Under different controlled temperatures of TCM and casting speeds, the temperature fields in the TCM and melt were numerically calculated, and the variation of temperature fields in the mushy zone was analyzed. The calculated temperatures are in good agreement with the measured values. The results indicate the uniformity of temperature gradient (uG) at the profiled section improves significantly when the controlled temperature of TCM is higher than the liquidus temperature of alloy, further, the uG gradually reaches the minimum and then increases with increasing casting speed. Based on the calculated results, the profiled KFC copper alloy strips with good surface quality were successfully prepared by the TCMCC under controlled TCM temperature of 1423 K and casting speeds of 15–60 mm/min. The value of the uniformity of primary dendrite spacing at the cross section of the profiled strips reaches the minimum with the casting speed of 45 mm/min.

A Numerical Simulation of Transport Phenomena During the Horizontal Single Belt Casting Process Using an Inclined Feeding System

Horizontal single belt casting (HSBC) has great potential to replace current conventional continuous casting (CCC) processes for sheet metal production, by directly casting 3 to 1 mm sheet for the automobile industry. In the present paper, two-dimensional mathematical models were developed to study transport phenomena, for the case of an inclined wall feeding system for a liquid aluminum wrought alloy (AA6111). Based on the commercial software ANSYS FLUENT 14.5 and user-defined functions, a two-layer turbulence model was used to examine the fluid flow emanating from a slot nozzle set above a water-cooled, high-speed, steel belt. The Volume of Fluid (VOF) method was used to predict the shape of the melt-air interface. A transformed coordinate system (x′, y′) was established in order to analyze the fluid flow on the inclined wall of the feeding system. The total pressure gauge gradient (∂ptotal/∂x) was used to describe the behavior of the melt film inside the slot nozzle of the head box. The modeling results show that during the melt film falling process, the total gauge pressure varies within the slot nozzle, which can decrease the stability of the falling film. The first impingement between the falling film and the inclined refractory wall of the feeding system gives rise to a local oscillation, and this influences the stability of the melt film moving downwards. At the rear meniscus position between the inclined wall and the moving belt, there is a clear vibration of the air-melt interface, together with a recirculation zone. The weak vibration of the air-melt interface could be induced by the periodic variation of the melt-air interface. Moreover, the formation of tiny air pockets is predicted. Finally, on the inclined wall of the feeding system, a suitable length of the transition area is needed to avoid over-acceleration of the melt film due to the force of gravity.

Simple iterative procedure for the thermal–mechanical analysis of continuous casting processes, using the element-free Galerkin method

ABSTRACTThe present work has been conducted to develop a straightforward procedure for solving the thermal–mechanical problem in a conventional continuous casting (CC) process using the element free Galerkin method. The linear momentum balance equation has been developed on the basis of this global weak formulation. The model has been solved under a nodes-fixed mixed Eulerian–Lagrangian description to estimate the mechanical behavior of a round billet during the CC process in the mold region. The proposed approach is developed in a predictor–corrector scheme, which provides a solution involving simultaneously all the materials configuration downwards the mold without the requirement of a viscoplastic tangent operator. The results have revealed that this technique could be used successfully in the modeling of continuous casting thermal–mechanical problems.

Conventional and near net shape casting options for steel sheet

The conventional continuous casting (CCC) of steel, starting in the 1950s, has now become the dominant casting process, worldwide. It presently accounts for about 1.5 billion tonnes of steel cast per year. Nonetheless, given the inexorable forces favouring near net shape casting (NNSC) of semi-finished products, for reasons of economy of scale, process rationalisation and the protection of the environment, the question of how long CCC can continue to dominate in the casting of steel, must remain a question. Two NNSC candidates for steel are the twin roll casting (TRC) and horizontal single belt casting (HSBC) processes. While the TRC of steel sheet by ‘CASTRIP’ has now been operating commercially for some 12 years within NUCOR, producing low carbon steel sheets, HSBC has only just been commercialised, at Salzgitter’s Peine Plant, in Germany, under the name ‘Belt Cast Technology’. It had to await the strong demand for high strength high ductility steels for the auto industry. The McGill Metals Processing Centre has been involved in both casting processes since 1987, its research being aimed at addressing the various technical aspects and fundamental problems associated with these two NNSC processes for forming steel sheet material. This paper addresses the pros and cons of NNSC processes versus CCC, and the differences between TRC and HSBC, for future steel sheet production.

Stress Analysis of a Continuous Casting Process, on the Basis of the Element‐Free Galerkin Formulation

The present work has been conducted in order to develop an alternative solution to the thermal‐mechanical problem in a conventional continuous casting (CC) process using the element‐free Galerkin (EFG) method. The linear momentum balance equation has been developed on the basis of this global weak formulation. The resulting equation system has been adapted to an axisymmetric stress–strain distribution over a round billet into the mold region. The constitutive laws, nonlinear aspects, path‐dependent variables, and boundary conditions have been specified. Finally, the model has been solved under a mixed Eulerian–Lagrangian description in order to estimate the mechanical behavior of the billet during the CC process. A brief discussion on the importance of including the field forces into the analysis is also presented. The results have revealed that this technique could be used successfully in the modeling of continuous casting thermal‐mechanical problems. The solution by means of this formulation has exhibited a remarkable sensitivity with the casting parameters and the approach implemented to compute inelastic strains during the δ ferrite–austenite transformation.

Effect of segregations on mechanical properties and crack propagation in spring steel

Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.

Development of a new cost effective Fe–Cr ferritic stainless steel for SOFC interconnect

A new cost effective ferritic stainless steel for interconnect in solid oxide fuel cell (SOFC), named 460FC, has been developed and fabricated by the conventional continuous casting and rolling process. The oxidation characteristics and high temperature properties of 460FC were investigated at 800 °C and compared with those of Crofer22 which is a well-known representative alloy for the same application. Although the 460FC does not contain rare earth metals and does not limit the content of Si to extremely low level, it shows good electrical conductivity and low Cr evaporation rate. The performance of 460FC in the real cell was also evaluated with 25 cm2 active area single cell test up to 500 h and the degradation rate was almost similar or superior to Crofer22.

The Computational Fluid Dynamic (CFD) Modeling of the Horizontal Single Belt Casting (HSBC) Processing of Al-Mg-Sc-Zr Alloy Strips

Al-Mg-Sc-Zr alloys have shown exceptional potential as structural materials for transportation applications. These alloys have proved to be good candidates to be processed as thin strips via the horizontal single belt casting (HSBC) process. The HSBC process is a near-net-shape casting technology, which involves casting molten metal directly into thin strips, close to the final product thickness, at higher cooling rates than conventional continuous casting and thin-slab casting processes. It offers an efficient, economical, and environmentally friendly approach to the production of metal strips. Fluid mechanics and associated heat transfer are important aspects of any casting process, and the novel HSBC process is no exception. Three-dimensional computational fluid dynamics simulations using ANSYS FLUENT 14.5 were performed, in order to assess the importance and effects of the various operational conditions of the HSBC process. This enabled process parameter optimization. Numerical predictions were validated against experimental casting results.

Influence of production methods on creep deformation of cold rolled 329LA lean duplex stainless steel in continuous annealing condition

The effects of processing methods, line tension, cold reduction and temperature on creep deformation of 329LA lean duplex stainless steel under continuous annealing condition are investigated. Two different processes, conventional continuous casting followed by hot rolling process and strip casting process, were used to make steel plates. Creep tests were carried out at 1010°C up to 1100°C using cold rolled specimens with various cold reductions for both kinds of specimen. It was found that continuous cast specimens show higher strain rate than strip cast specimens when tested with the same cold reduction and stress condition at all temperatures. Creep strain rate increases with the increase of line tension, temperature and the amount of cold reduction. The measured strain rate sensitivity values (m), around 0.5, show the superplastic behavior of both continuous and strip cast specimens at all test conditions, while the stress exponents (n), around 2, are consistent with the model of grain/phase boundary sliding as the rate controlling mechanism. The strip cast specimen has a very inhomogeneous microstructure which leads to larger average grain size, while the continuous cast specimen shows a uniform distribution of ferrite (δ) and austenite (γ). Electron back scattered diffraction (EBSD) results show that cold rolled texture is destroyed during heating to deformation temperature and δ/γ interface becomes high angle boundary which slides easily. Lastly, phase boundary sliding during creep deformation was confirmed by scanning transmission electron microscopy (STEM) in both specimens.

Element-Free Galerkin Formulation by Moving Least Squares for Internal Energy Balance in a Continuous Casting Process

The present work has been conducted in order to develop an alternative solution to the heat transfer problem in a conventional continuous casting (CC) process using an Element-Free Galerkin (EFG) technique with shape functions formulated by a moving least squares approximation. The Internal Energy Balance Equation (Eulerian Description) has been developed with this weak formulation in order to solve the heat transfer problem. The EFG features and the shape functions construction have also been described. The resulting equation system has been adapted to a 2-D steady-state temperature distribution over the longitudinal thickness of a solidifying wide slab into the mold region. The transport laws, the nonlinear aspects, and the boundary conditions have been specified. Finally, the model has been solved in order to estimate the thermal distribution and the solidified shell evolution. The results have revealed that this technique could be used successfully in the modeling of CC heat transfer problems.

Physical Simulation of the Flow Field in a Vertical Twin Roll Strip Caster – A Water Model Study

Twin‐roll strip casting is a near‐net shape method for the production of metal strips in the range of several millimeters. The benefit in comparison to other methods is the short length of the facility and the lowered energy consumption in comparison to conventional continuous slab casting. This results in a reduction of costs and large energy savings by up to 85%. In this work the flow inside the pool of a twin roll strip caster is investigated. A modular submerged entry nozzle (SEN) was designed, which allows an adjustment of the flow for the single submerged faces of the SEN in the pool. This makes it possible to control the flow in several ways, to create different flow patterns. The measurements were made for a steady state. For the measurements in the pool the particle image velocimetry method (PIV) was used to determine two‐dimensional velocity fields. The surface motion at the rolls was investigated by video analysis. It was shown that this experimental setup is suitable to create several characteristic flow patterns inside the pool by combining the three main flows (front, long, and bottom). Also, it was obtained that high volume flows through the front chambers create a very uneven meniscus with large differences in height. The best result correlated to the meniscus was achieved for a medium volume flow at the long chambers and a high volume flow through the bottom.