Powder Casting Research Articles

Visualization of inclusions in a water model for continuous casting of steel

With the water model, we experimentally confirmed the possibility of using a suspension to imitate the molten casting powder (slag) at the upper edge of the melt during the continuous casting of steel. The project requires that the slag particles do not leave the suspension layer during operation or that they return to it from the molten steel. It turns out that this is possible if the selected suspension particles mimic sufficiently large inclusions in the real system. The imitation of slag particles in a real system with suspension particles in water model is ensured by the equal terminal flotation velocities of both. Among the discussed polyethylene and cork particles, only cork particles, with a size of 0.2 mm to 0.5 mm, and a density of around 400 kg/m3, meet this condition. It was shown that the presented methodology could be used to estimate the proper position of the submerged entry nozzle.

Investigating the Origin of Non-Metallic Inclusions in Ti-Stabilized ULC Steels Using Different Tracing Techniques

Since steel cleanness comes to the fore of steel producers worldwide, it is necessary to understand the formation mechanism and modification of non-metallic inclusions (NMIs) in more detail. One central point is the identification of the source of especially interfering NMIs to prevent their evolution in the future. The present study applies two approaches to determine the source of NMIs in Ti-stabilized ultra-low carbon (ULC) steels—the active and the passive tracing. Both approaches are applied to an industrial experiment. The active tracing technique is focused on investigating the clogging layer formation in submerged entry nozzles and, hence, the origin of alumina particles. This method adds rare earth elements (REEs) directly to the melt to mark pre-existing deoxidation products at a certain point of the steelmaking process. The main concern of the passive method, the so-called REE fingerprint, is the determination of the source of mesoscopic NMIs. For the REE fingerprint, the pre-existing concentration of REEs in different potential sources and the investigated NMIs are measured by using an inductively coupled plasma mass spectrometer (ICP-MS). The resulting patterns are compared after normalizing the contents to chondrites, and the NMIs’ origins are identified. Concerning the EDS analysis and the resulting patterns from the REE fingerprint, the mold slag and, respectively, the casting powder were the sources of the investigated NMIs.

Rheology of a Liquid Powder for Continuous Casting: The Critical Aspect in Its Technological Application

It is herein considered a new product composed of solid–liquid dispersion of a conveniently formulated continuous casting powder in synthetic oil‐based esters, where hypothetical limit to consider this liquid slurry as a liquid powder is a mix with at least 50% in weight powder load preserving suitable fluidity for effective and stable pumping. After a relatively long and intense industrial application period, one of most critical points when using liquid powder for steel continuous casting proves to be mold feeding. This is mainly because of weird properties of such material which behaves as a non‐Newtonian fluid. A thorough rheological study on samples of liquid powder for continuous casting is carried out. Based on meticulous characterization of a set of laboratory samples, the dispersion flow curve is determined. Most commonly used rheological models are then tested for fitting with the experimental data. Sisko model is identified as the best fitting one. This model is then implemented to derive the system curve describing its behavior under its industrial application conditions. The mathematical process to apply Sisko model and its numerical solutions is explained. The results found are consistent with the field experience of the industrial application of the material under study.

Effect of Magnesium Powder Application on the Microstructure and Properties of Rods Extruded by the Forward-Backward Rotating Die Extrusion Method.

The effects of severe plastic deformation (SPD) with a forward-backward rotating die (KOBO extrusion) on pure magnesium, in the form of cold-compacted powder, sintered powder, or cast ingots as reference, were examined. This method is known to reinforce metals, but the role of the initial form of magnesium applied in the fabrication of metal-based rods, as well as related phenomena, has not been characterized until now. The problem is important in the potential processing of commercial metal powders, the recycling of metal shavings, and the fabrication of metal matrix composites with discontinuous reinforcing phases. In the presented experiments, rods of 8 mm in diameter and 400 mm in length were obtained, and the structural effects induced by KOBO that occurred on a macro- and microscale on the surface and cross sections were characterized. Changes in the size and orientation of α-Mg crystallites were determined by XRD. The porosity, hardness, tensile strength, and compressive strength were measured, and the mechanisms of decohesion dependent on starting metal form were analyzed. After KOBO extrusion, significant differences were observed in the microstructure and properties between the materials derived from cold-compacted powder, sintered powder, and reference cast magnesium. Due to the application of KOBO, apart from α-Mg grain refinement, the MgO derived from the initial powder’s surface was refined to fine regular particles surrounded by magnesium. Their bands curved in the perpendicular plane and were oriented with the extrusion direction of the formed network, which augmented some mechanical properties and changed the decohesion mechanism. The conducted experiments revealed that before extrusion by KOBO, the magnesium powder required sintering under pressure.

Microstructure, surface topography and mechanical properties of slip cast and powder injection moulded microspecimens made of zirconia

Abstract Investigations on ceramic microspecimens made of Y2O3- stabilized ZrO2 produced by slip casting or micro powder injection moulding are introduced. During the production of the microspecimens, feedstocks and sintering conditions were varied. Differently moulded specimens were examined with respect to their microstructure and surface topography using light microscopy, scanning electron microscopy (SEM) and confocal white light microscopy. Additionally, the mechanical characteristics were investigated by three-point bending tests using a micro universal testing device. The statistical analysis was realised by means of the Weibull theory and interpreted by the aid of SEM images of fracture surfaces. This research allowed to understand correlations between different feedstocks used, process parameters like the sintering conditions applied and the resulting characteristics as well as material properties of the microspecimens. These results could be used to improve the production process.

Designing Non‐Newtonian Mold Powders and Optimization of Process for Continuous Casting of Billet

The current article describes the approach followed to design new shear‐thinning casting powders that minimize slag entrainment without sacrificing mold lubrication during continuous casting of steel. Enhanced shear‐thinning is achieved by controlling the degree of polymerization through Si3N4, characterized with an improved viscometry methodology where viscosity is a function of temperature as well as shear rate in contrast to the standard practice. Chemical analysis reveals a considerable loss in N accompanied by a gain in SiO2 during premelting which can represent a hindrance for industrial application. In parallel, a 3D numerical model is developed to characterize the shear‐thinning behavior through a mapping of the viscosity for temperature and shear rate. This model is used to optimize casting conditions for an industrial billet caster with electromagnetic stirring (EMS) through a response surface analysis. Finally, plant trials with the new powder show potential to reduce entrainment after postmortem analysis of the rolled materials. No critical issues are found during the industrial application despite a slight increase in mold friction and decrease in powder consumption. Ultimately, the combination of improved characterization and numerical modeling can be used as design tools for effective optimization of the shear‐thinning effects under specific casting conditions.

Prediction of longitudinal facial crack in steel thin slabs funnel mold using different machine learning algorithms

PurposeLongitudinal facial cracks (LFC) are one of the major defects occurring in the continuous-casting stage of thin slab caster using funnel molds. Longitudinal cracks occur mainly owing to non-uniform cooling, varying thermal conductivity along mold length and use of high superheat during casting, improper casting powder characteristics. These defects are difficult to capture and are visible only in the final stages of a process or even at the customer end. Besides, there is a seasonality associated with this defect where defect intensity increases during the winter season. To address the issue, a model-based on data analytics is developed.Design/methodology/approachAround six-month data of steel manufacturing process is taken and around 60 data collection point is analyzed. The model uses different classification machine learning algorithms such as logistic regression, decision tree, ensemble methods of a decision tree, support vector machine and Naïve Bays (for different cut off level) to investigate data.FindingsProposed research framework shows that most of models give good results between cut off level 0.6–0.8 and random forest, gradient boosting for decision trees and support vector machine model performs better compared to other model.Practical implicationsBased on predictions of model steel manufacturing companies can identify the optimal operating range where this defect can be reduced.Originality/valueAn analytical approach to identify LFC defects provides objective models for reduction of LFC defects. By reducing LFC defects, quality of steel can be improved.

Scale Formation on HSLA Steel during Continuous Casting Part II: The Effect of Surface Conditions

The present research addresses the effect of surface condition on oxide scale formation at high temperatures such as those experienced during secondary cooling in Continuous Casting. Tests were carried out in clean, as-cast and surfaces covered with casting powder to replicate the oxidation/re-oxidation after the mould. Specimens oxidized at 1000, 1100 and 1200 °C under dry air and water-vapour conditions revealed that the oxide scale formation is strongly influenced by temperature, environmental and surface conditions. The oxide scale thickness increases with temperature alterations in the surface (e.g., as-cast and covered with powder) where oxides and carbonates from the casting powder accelerate oxidation kinetics leading to thick and unstable scales. A high amount of carbon is present on surfaces covered with casting powder where it diffuses through the oxide scale forming CO and CO2 which lead to stress accumulation that makes scales prone to defects such as pores, voids and micro-cracks. Ultimately, if wüstite remains attached to the steel surface or inside oscillation marks, it may disturb heat transfer during secondary cooling which has deep industrial implications for crack formation and overall casting yield. Therefore, accurate insights on scale type and growth mechanisms could lead to accurate control of its formation during casting.

Powder Casting: Producing Bulk Metal Components from Powder Without Compaction

Powder casting was developed to produce metal components with near-theoretical density from low-cost, loose powder using hydrogen sintering and phase transformation. This has significant implications for non-beam metal additive manufacturing processes (e.g., metal extrusion AM, binder jetting, and ordered powder lithography), which produce green parts with relatively low densities. Additionally, powder casting can enable the production of geometries typically not suitable for powder processing, such as plate and bar stock. In the current study, Ti-6Al-4V, Zr, and Hf were densified to 99.2%, 95.7%, and 94.0% of their respective theoretical densities, when sintered from loose powder at 1200°C for 4 h. The relative density and pore size distributions of Ti-6Al-4V produced by powder casting were very similar to those produced by press-and-sinter HSPT. The powder-cast Ti-6Al-4V samples also displayed ductility consistent with press-and-sinter HSPT. However, they exhibited lower strength due to unintentional overheating during the dehydrogenation step.

New technique for producing items from TiC-(Ni-alloy) cermet for severe application conditions

A new technique for producing complex-shaped items from wear-resistant TiC-(Ni-alloy) cermets is described. Cermets are produced by infiltration of TiC-preforms with Ni-alloy, which combines the advantages of powder metallurgy and casting. A special vacuum induction furnace is designed to effectively implement the new technique, which enhances the production capacity and quality of a cermet item against other known technologies. The structure of new cermets is characterized by a uniform distribution of TiC grains in the Ni matrix. During infiltration, a considerable part of tungsten and some part of molybdenum migrate in TiC grains forming solid solution shells on them. The shell ensures the connection between TiC and Ni-alloy and high physical and mechanical properties of the cermet. The physical and mechanical properties of the TiC-(Ni-alloy) cermet at temperatures up to 1100 °С and the results of practical use of items from cermets in production are presented. The shop tests showed the increase of the durability of a cermet ball valve by more than 6 times as compared with conventional wedge valves.

Metallurgical Analyses of Surface Defects in Cold-Rolled Steel Sheets

Six cold-rolled steel sheet samples having surface defects like slivers and dents have been metallurgically analyzed to identify the reasons for generation of such defects. In all the cases, large inclusions/entrapments were located at the defect site. Energy-dispersive spectroscopy (EDS) of the entrapments in samples 1 and 2 having dents revealed incidences of O, Mg and Ca, confirming that these entrapments are essentially complex oxides of probable slag genesis. The dents in samples 1 and 2 must have occurred due to heavy cold rolling load on the preexisting cracks in the coil. Apart from dents, sliver defects were also observed in some of the samples. Slivers are, however, of various types and appearances, and there could be many reasons for occurrences of these slivers in the cold-rolled sheets. In the present study, the SEM–EDS analyses of the subsurface entrapment/deposit observed in sample 3 revealed complex oxides of CaO-MgO of possible slag genesis and could be the reason for incidences of slivers in this sample. On the other hand, the wavelength-dispersive spectroscopy of samples 4 and 5 having sliver defects carried out in an electron probe microanalyzer (EPMA) revealed subsurface chains of dark and angular brittle inclusions of either alumina or silicate of possible deoxidation product genesis. EPMA analysis of sample 6 having pencil line sliver defects, however, revealed entrapments of possible casting powder origin.

Mathematic simulation of atomic structure of multicomponent oxide-fluoride melt for continuous casting machines

Determination of relation between oxides melts properties, based on silicates and calcium alum-silicates and magnesium and their chemical composition and structure is an important condition to provide a rational slag mode in a continuous casting machines mold. A mathematical simulation of slag melts and casting powders accomplished. The oxide-fluoride system was chosen for the simulation, for which the structure after solidification was determined by experiment. Results of molecular-dynamic simulation of CaO–SiO2–Al2O3–MgO–Na2O–K2O–CaF2–FeO system, correspondent to industrial casting powders composition, used during steel casting for slag formation in a CCM mold (35.35 % SiO2; 30.79 % CaO; 8.58 % Al2O3; 1.26 % MgO; 13.73 % CaF2; 7.57 % Na2O; 0.88 % K2O; 1.82 % FeO). Taking into account the concentration, a re-calculation was accomplished to mole shares and correspondent number of ions in the model for each component calculated. Simulation of the 8-component oxide-fluoride melt with 2003 ions size in the main cube (a side length of 31.01 Å) was accomplished at the experimentally determined temperature of solidification onset (1257 K) under periodic boundary conditions and fixed volume. The Coulomb interaction was taken into account by the Ewald–Hansen method. The time step was 0.05t0, where t0 = 7,608×10–14 sec is the internal unit of time. The melt density was taken as 3.04 g/cm3 based on the experimental data. The inter-particle interaction potentials were chosen in the Born–Mayer form. According to the simulation results, the structure of sub-crystalline groups of atoms present in the melt at the temperature of the onset of solidification was determined. A discussion of the simulation results and their comparison with the literature data presented.

The analysis of gas evolved from casting powder during heating in the mold

In this paper, the thermal stability of two commercial casting powders was assessed with respect to registered mass changes and evolved gas analysis using a combination of TG/DTA/EGA simultaneous thermal analysis methods. The experiments were conducted in a temperature range of 50 ÷ 1300 °C, in an oxidation atmosphere, with a heating rate of 10 K min−1. The results presented in the article perfectly fit into the research trend related to the emission of gases from powders, using for this purpose coupled TG/EGA techniques of thermal analysis. Thermogravimetric measurements together with simultaneous EGA analysis of gases released from the samples enable the identification of the main reactions responsible for mass disturbance. The main registered mass losses were associated with carbon oxidation and thermal decomposition of carbonates presented in investigated powders. Based on the DTA results, melting temperature, as well as other endo/exothermal effects of reactions taking place in the system, was elaborated. The possibility of FactSage usage, to elucidate the influence of selected components on the viscosity of investigated casting powders, is also presented. On the basis of the conducted research, it was found that recorded mass disturbance was not associated with the evaporation of components affecting the viscosity of casting powder.

Development and Implementation of Combined Structuroscopes for Dispersion Metallic Materials

Only some from series of non-destructive testing methods of material defects are employed for measurement of structural parameters of materials. The principle of acoustic and magnetic structuroscopy of cast irons and steel is explained. The examples of exploitation and equipment are described. At least two methods must be used simultaneously for strength and heat resistance measurement of composites, powder metallurgy products and cast irons. Development of this combined structuroscopy of cast irons. The equipment TELIT 3 was developed for evaluation of cast iron quality at critical sites of complicated castings (cylinder blocks of transport engines). The direction of furher research was indicated – exploitation of magnetic excited acoustic wave and combined structuroscopy of thin composite layers.

Enhancing ductility and strength of nanostructured Mg alloy by in-situ powder casting during spark plasma sintering

Due to internal processing defects, bulk nanostructured Mg alloys have high strength but extremely poor ductility. A novel and facile process was designed and in-situ powder casting was initiated during spark plasma sintering. This process significantly reduced processing induced defects, enhanced inter-particle bonding and introduced significant precipitation without extra ageing treatment, leading to improvement of the compressive strength and ductility. The compressive strain of bulk sample consisting of pure cryomilled powder was 3.6% with an ultimate strength of 500 MPa, while cryomilled powder mixed with eutectic Mg-Zn alloy powder obtained a compressive strain of 6.6% and ultimate strength of 506 MPa. The ductility of the sample with mixed powder was increased by 83% without any sacrifice of strength compared to the sample consisting of only pure cryomilled powder.

Green gelcasting of aluminum nitride using environmental sustainable ovalbumin natural binder

Ceramic powder casting technique using ovalbumin, i.e., egg protein, as natural amino-based binder. The study has shown successful gelcasting of high-performance 3D thermal conductivity aluminum nitride (AlN) for application in the 3D integrated circuits (3D-IC). The green body has a good flexural strength of 3 MPa, which is sufficiently be trimmed with computerized numerical controlled (CNC) machining prior to the pyrolysis manufacturing processes, i.e., sintering technologies. Different particle sizes of AlN powder was being investigated and the results indicated bimodal particle size ratio of 1.5 to 2 attributed the most favorable combination in this study. Doped of rare earth element, yttrium oxide (Y2O3) nano particle size, has shown an improvement in overall thermal conductivity of 3D sintered objects. SEM images also well demonstrated higher thermal conductivity value are linked with a compact structure of higher density of 3D ceramic objects.

Laser additive manufacturing foam aluminium-12 wt-% silicon with different addition TiH2 foaming agent

ABSTRACTThe aim of this work is to study the effects of laser additive manufacturing on microstructure and mechanical properties of foam Al–12 wt-%Si aluminium alloy with/without TiH2 foaming agent. The results showed that low porosity closed foam Al–12Si was successfully obtained. The effect of processing parameters on the porosity is discussed. The porosity was changed from initial 20.9% without foaming agent to 32.3 and 45.9% with 5 and 10% addition of foaming agent, respectively. Average micro-hardness values of the obtain foam Al–Si alloy is varied from 100 to 130 HV and the shape of compressive stress–strain curve is as the same as foam aluminium made by powder metallurgy and casting methods.

Master decomposition curve of carbonaceous materials used in casting powders

Casting powders are used in the continuous casting process of steels. These powders contain several oxides, fluoride compounds and carbonaceous materials. The decomposition kinetics of these carbonaceous materials regulates the melting rate of casting powders. In a previous work, a decomposition kinetics of two carbonaceous materials (coke and graphite) added to a casting powder was studied. Based on those data, in the present work, master decomposition curves (MDC) of these powders were constructed. For this, the values of both the activation energy (E) and the degree of decomposition (α), obtained in the thermogravimetric tests, were used for each heating rate (β). Then, the work of decomposition (θ D) was calculated and the MDC was obtained. From the MDC, it was possible to predict the time (t) needed to produce a given degree of decomposition (α) at different temperatures (T). Taking this into account, it was possible to validate the master decomposition curves through different thermal treatments, where the degree of decomposition was calculated by interpolating the MDCs. These values were compared with those determined experimentally by measuring the mass loss in each heat treatment. In all cases, the results showed a good correlation between the predicted and measured values. It is concluded that the use of the MDC represents a useful tool to evaluate and compare the behavior of carbonaceous materials added to casting powder.

In-situ monitoring and characterization of airborne solid particles in the hostile environment of a steel industry using stand-off LIBS

The analytical possibilities of laser induced breakdown spectroscopy (LIBS) to carry out in-situ and real-time detection and compositional characterization of aerosols in the atmosphere of a steelmaking factory, have been evaluated. To this aim, a compact and versatile dual-pulse LIBS analyzer, able to sample at distances up to eight meters, has been designed to work in these hostile industrial environments. Due to the discrete nature of the particulate matter, the particle sampling rate was less than 2.5% and 6% for single- and double-pulse regimes, respectively. An efficient statistical procedure, based on the calculation of standard deviations, is used to qualitatively characterize the elemental composition of the aerosol. Then, a conditional analysis based on the limit of detection, is employed to assess the elemental sampling rate. This experimental methodology has been used to evaluate the influence on the aerosol formed of the oxycutting process in a continuous casting machine producing steel slabs, revealing a strong presence of elements derived from the casting powder used in the production. Moreover, chromium, present in the steel cast, is detected in aerosol suspension in the steel shop. An increase in the concentration of particulate matter was expected when oxycutting was on. Single-pulse and dual-pulse excitation modes are also evaluated.

In situ-growth of silica nanowires in ceramic carbon composites

An understanding of the processing and microstructure of ceramic–carbon composites is critical to development of these composites for applications needing electrically conducting, thermal shock resistant ceramic materials. In the present study green compacts of carbon ceramic composites were prepared either by slurry processing or dry powder blending of one or more of the three — clay, glass, alumina and carbon black or graphite. The dried green compacts were sintered at 1400 °C in flowing argon. The ceramic carbon composites except the ones without clay addition showed formation of silica nanowires. The silica nanowire formation was observed in both samples prepared by slip casting and dry powder compaction containing either carbon black or graphite. TEM micrographs showed presence of carbon at the core of the silica nanowires indicating that carbon served the role of a catalyst. Selected area electron diffraction (SAED) suggested that the silica nanowires are amorphous. Prior studies have reported formation of silica nanowires from silicon, silica, silicon carbide but this is the first report ever on formation of silica nanowires from clay.