Agglomeration Of Inclusions Research Articles

Agglomeration of Solid Inclusions in Molten Steel

Agglomeration of alumina inclusions in the molten steel is investigated through the free energy analysis of the cavitation between inclusions. The mechanism of agglomeration, the activation state, the stable state, the equilibrium state, and the critical separation for the cavitation are discussed. The equilibrium energy is proportional to the square of the inclusion radius, EEq = 0.710R P 2 , while the critical separation is directly proportional to the inclusion radius, dC = 0.146RP. Agglomerates of micron inclusions are hardly broken up by the turbulence in steelmaking practice.

In Situ Observations of Agglomeration of Non-metallic Inclusions at Steel/Ar and Steel/Slag Interfaces by High-Temperature Confocal Laser Scanning Microscope: A Review

The agglomeration behavior of non-metallic inclusions in the steelmaking process is important for controlling the cleanliness of the steel. In this work, the observation of agglomeration behaviors of inclusions at steel/Ar and steel/slag interfaces using a high-temperature confocal laser scanning microscope (HT-CLSM) is summarized. This HT-CLSM technique has been applied to observe phase transformation during solidification and heat treatment and the engulfment and pushing behavior of inclusions in front of the solidified interface. In the current work, the inclusion agglomeration behavior at steel/Ar and steel/slag interfaces is summarized and discussed. Subsequently, the development of the theoretical work investigating inclusion agglomeration at steel/Ar and steel/slag interfaces including the initial capillary force model and Kralchevsky–Paunov model is described. Finally, the Kralchevsky–Paunov model is applied to investigating nitride inclusion agglomeration at high-manganese steel/Ar interfaces. This work aims to give a critical review of the application of HT-CLSM in secondary refining as well as a better control of inclusion elimination for clean steel production.

Copper/Iron Brake Friction for Military Aircraft Application

The present study assesses the infl uence of non-metallic constituents and manufacturing parameters, such as compaction pressure and sintering temperature, to produce a metal matrix composite (MMC) of copper/iron, based on the brake disc of aircraft AT-29 SuperTucano. The samples were produced with six different compositions, by varying the amount of abrasive particles (quartz and zirconia silicate) and the solid lubricant (graphite), with one of the compositions manufactured without the addition of graphite. The compaction pressures were 210 and 420 MPa, with sintering temperatures of 950°C and 1050°C in a furnace with controlled atmosphere of argon + 10% H2. After sintering, the effectiveness of the sintering process was evaluated through the apparent density (Archimedes’s method), Brinell and Vickers hardness, and the microstructure by Scanning Electron Microscopy (SEM). The sintering process was severely affected by the solid lubricant (graphite): its reduction resulted in a density increase near 18%, and the hardness of the compound up to 62%. The hardness values demonstrated significant variation with compaction pressure, with a pronounced effect on compounds with less non-metallic elements. SEM analysis demonstrated that not only graphite, but also the ceramic particles affected the sintering process through the agglomeration of inclusions into the metal-metal interface. The samples without graphite exhibited almost the same value of pores after sintering, regardless of the compaction pressure, indicating that the graphite content affects directly the sintering process, regardless of the compaction pressure.

Inclusion agglomeration in electrified molten metal: thermodynamic consideration

ABSTRACTThe effect of electric current on inclusion agglomeration in molten metal has been investigated. It is found that the agglomeration is dependent on the electric current density, distance between inclusions and orientation of electric field. Electric current retards the agglomeration unless two inclusions are aligned along or closely to the current flow streamlines and the distance between inclusions is less than a critical value. The mechanism is also validated in the computation of cluster agglomeration. The numerical results provide a comprehensive indication for the current-induced inclusion removal and current-induced inclusion elongation. When the inclusions are in long-thin shape, the calculation predicts the current-induced microstructure alignment and current-induced microstructure refinement phenomena.This paper is part of a themed issue on Materials in External Fields.

Agglomeration of Non-metallic Inclusions at Steel/Ar Interface: In-Situ Observation Experiments and Model Validation

Better understanding of agglomeration behavior of nonmetallic inclusions in the steelmaking process is important to control the cleanliness of the steel. In this work, a revision on the Paunov simplified model has been made according to the original Kralchevsky–Paunov model. Thus, this model has been applied to quantitatively calculate the attractive capillary force on inclusions agglomerating at the liquid steel/gas interface. Moreover, the agglomeration behavior of Al2O3 inclusions at a low carbon steel/Ar interface has been observed in situ by high-temperature confocal laser scanning microscopy (CLSM). The velocity and acceleration of inclusions and attractive forces between Al2O3 inclusions of various sizes were calculated based on the CLSM video. The results calculated using the revised model offered a reasonable fit with the present experimental data for different inclusion sizes. Moreover, a quantitative comparison was made between calculations using the equivalent radius of a circle and those using the effective radius. It was found that the calculated capillary force using equivalent radius offered a better fit with the present experimental data because of the inclusion characteristics. Comparing these results with other studies in the literature allowed the authors to conclude that when applied in capillary force calculations, the equivalent radius is more suitable for inclusions with large size and irregular shape, and the effective radius is more appropriate for inclusions with small size or a large shape factor. Using this model, the effect of inclusion size on attractive capillary force has been investigated, demonstrating that larger inclusions are more strongly attracted.

Agglomeration of Non-metallic Inclusions at the Steel/Ar Interface: Model Application

Inclusion agglomeration is an important element in several industrial problems during steelmaking, such as nozzle clogging. In parallel work by the authors, a revised Kralchevsky-Paunov model has been established and the performance of this model has been validated against the experimental data from in-situ observations using confocal laser scanning microscopy. In this work, the revised model has been applied to quantitatively evaluate the attractive capillary force for the agglomeration of various inclusions at the interface between Ar and liquid iron/steel. A parametric study of the effects on the capillary force of the inclusion density, contact angle between the inclusion and liquid steel, and the surface tension of the liquid metal are quantitatively investigated. The results show that inclusion density and contact angle have a more marked effect on the capillary force than surface tension of liquid metal. Moreover, the inclusion agglomeration behavior in the liquid iron/steel matrix is discussed. The coagulation coefficient of various inclusions is calculated. Both the calculation results of the attractive capillary force of inclusions at the interface between Ar and liquid iron/steel and coagulation coefficient of inclusions in the liquid iron/steel matrix can offer a close agreement; moreover, the order of magnitude of inclusion agglomeration tendency is suggested. By using the coagulation coefficient, the inclusion collision volume and collision rate are calculated and the effects of inclusion composition, size, and number density are investigated. The evaluation results show that the tendency for affecting inclusion collision is inclusion number density > inclusion size > inclusion composition.

Characteristic and evolution of inclusions in Al-Killed titanium alloyed steel during air contact process

Re-oxidation inclusions in steel are extremely detrimental to the quality of final products due to their complex compositions and large sizes. The detailed knowledge of the re-oxidation process and the evolution of re-oxidation inclusions are preconditions for the removing of inclusions and controlling of steel cleanness. This paper simulates the re-oxidation behavior and tracks the evolution of re-oxidation inclusions in Al-killed titanium alloyed steel by controlling the contact between molten steel and air atmosphere. The experimental results show that the elements aluminum (Al), titanium (Ti), and manganese (Mn) are almost oxidized simultaneously after the exposure of molten steel to air. Large spherical Al-Ti-Mn-Fe-O oxides lump Al2 O3 , and spherical Mn-Fe-O inclusions appear successively after re-oxidation happens in Al-killed titanium alloyed molten steel. Inclusions in re-oxidation are greatly different from the ones in start material, which include clustered Al2 O3 , granular Al2 O3 or TiN-type inclusions. The mechanisms of agglomeration and growth of inclusions are inferred from the grooves and voids on the surfaces of inclusions. Rod-like inclusions are formed when inclusions collide with each other end-to-end. The characteristics of re-oxidation inclusions in plant samples differ from those in laboratory samples because a series of reactions between inclusions and the elements Al and Ti in molten steel happen continuously.

PSG Method for Simulating Agglomeration of Al2O3Inclusions in Liquid Steel

A quantitative description of the non-metallic inclusions removal from liquid steel is the most important element of secondary metallurgy. Authors made an attempt at calculating balance of Al2O3 particles during turbulent flow, which represents the steel refining conditions. For this purpose a special program was worked out. The agglomeration of non-metallic inclusions in liquid steel was modeled with the particle grouping method. Calculations were performed for steel with 300 and 500 ppm oxygen content. Then the quantity of generated aluminum oxide was calculated. Various mixing rates of the melt, corresponding to the actual conditions in the ladle, were applied. Simulations were performed for 6 groups of particles for the initial size of inclusions 1, 3, and 5 μm. The size interval for each group was predefined very strictly. The diameter increase and particle number reduction of the successive groups were graphically presented in plots. In the initial phase the rate of particle removal was very high, especially when high mixing energies were involved. This calculation procedure realistically describes the agglomeration and elimination of non-metallic inclusions in the secondary metallurgical processes and can be implemented for modeling this type of processes.

Investigation of metallurgical phenomena related to process and product development by means of High Temperature Confocal Scanning Laser Microscopy

An increased interest for high temperature metallurgical processes appeared during the last decades, in order to achieve the high quality requirements in steel products. A defined steel cleanness and microstructure essentially influence the final product quality. The high temperatures involved in metallurgical processes and the lack of in situ observations do not only complicate the verification of simulation model predictions but also make significant conclusions regarding the industrial processes difficult. For that reason, new tools and techniques are necessary to develop. By combining the advances of a laser, confocal optics and an infrared image furnace, the High Temperature Confocal Scanning Laser Microscopy (HTCSLM) is a strong tool which enables high temperature in situ observations of different metallurgical phenomena. Next to solidification processes and phase transformations also the behavior of inclusions at different interfaces in the system steel-slag-refractory can be observed. The present study focuses on the aspects of inclusion agglomeration in the liquid steel and the inclusion behavior at the steel/refractory interface in two different steel grades. Out of the obtained experimental data, attraction forces are calculated and compared. This information provides an important basis for a better understanding of inclusion behavior in industrial processes and the therewith related process optimization, like for example the clogging phenomenon during continuous casting.

Surface stress and agglomeration effects on nonlocal biaxial buckling polymeric nanocomposite plate reinforced by CNT using various approaches

In this article, the surface stress effect on the biaxial critical buckling load of nonlocal polymeric nanocomposite rectangular plate reinforced by carbon nanotubes (CNTs) is presented. Various approaches such as Eshelby–Mori–Tanaka, the extended mixture rule, Halpin–Tsai, and micromechanical are used to determine the effective material properties of polymeric nanocomposite plate. The governing equations of equilibrium are obtained by using Hamilton’s principle. The Navier’s method is considered to obtain the biaxial critical buckling load of polymeric nanocomposite rectangular plate for simply supported boundary conditions. A detailed parametric study is conducted to explain the effects of aspect ratio, elastic foundation, surface stress and agglomeration on the biaxial buckling of nanocomposite plate. The results show that surface stress effect plays an important role at nanoscale. Also, the biaxial critical buckling load decreases with increasing the CNTs volume fraction in the inclusion (agglomeration effect). The results of this research can be used for micro-electro-mechanical and nano-electro-mechanical devices.

Effect of TurboSwirl on Inclusions during Ingot Casting of Steels

The use of TurboSwirl to obtain an improved steel cleanliness during filling of an ingot was numerically studied by VOF and DPM models. It was found that a radius-reduced TurboSwirl or a proper tapered mold entrance nozzle with an adequate developed region for steel flow can reduce the risk of mold flux entrapment in a mold. The ingot casting process can create highly turbulent conditions inside the mold during the initial stages of casting. Since the TurboSwirl generates much calmer filling conditions it can promote separation of large nonmetallic inclusions. The TurboSwirl also collects large inclusions (200 μm) towards the axis of rotation, which should promote agglomeration. In addition, the residence time for inclusions of small sizes can be prolonged, increasing chance of agglomeration, which indirectly promotes their separation from steel. Moreover, the average turbulent dissipation rate in an ingot casting swirl setup is about 40 % higher than that in a no swirl setup. This further facilitates the agglomeration of inclusions before they enter the mold. The removal of nonmetallic inclusions is thus enhanced because of an increasing inclusion collision rate due to both Stokes collisions and turbulent collisions, while maintaining a calm flow inside the mold.

In Situ Observation on Behaviors of CaO-MgO-Al2O3-SiO2 Complex Inclusions at Solid–Liquid Interface of Low-Oxygen Special Steel

The movements of CaO-MgO-Al2O3-SiO2 inclusions at solid–liquid (S–L) interface during the solidification of low-oxygen special steel were observed in real time by the confocal laser scanning microscope, in an attempt to explore the possible formation mechanism of the D-type and DS-type inclusions. It was found that S–L interfaces showed strong interaction with the inclusions, especially when the inclusions were captured. Collision and agglomeration between inclusion in liquid steel and inclusion captured by the S–L interface were reproducibly observed, followed by an obvious size growth. During this process, inclusions in liquid steel acted as the guest particles, while the S–L interface capture inclusions acted as the host particles. There were also inclusions first moved toward and then later away from the S–L interfaces. To explain the behaviors of inclusion pairs, the forces acted on inclusions were estimated and discussed. Based on the obtained result, it can be cautiously pointed out that collision and agglomeration of inclusions at S–L interface during the casting of steel are probably important reasons for the frequent existence of D-type and DS-type inclusions during the production of low-oxygen special steel despite the high cleanliness. Therefore, minimization of inclusion size is significant except for the reduction of the inclusion numbers.

Modeling the Dynamics of Precipitation and Agglomeration of Oxide Inclusions in Liquid Steel

Deoxidation and refining of liquid steel is the site of many complex phenomena, such as liquid–gas–solid multiphase flow, turbulence, precipitation, agglomeration, and extraction of multicomponent inclusions. The steel industry is very interested in developing a framework to integrate these different mechanisms. This is based on three pillars: chemical thermodynamics, population balance, and transport phenomena. Accordingly, a homebrewed thermo-kinetics code is interfaced with a commercial Computer Fluid Dynamic code through a population balance module. The population balance module resorts to the classic Quadrature Method of Moments extended to multicomponent inclusions. This paper is focused on a comparison between three-dimensional numerical results obtained with or without taking into account precipitation kinetics. This distinction is important since under an assumption of local equilibrium, harmful inclusions are completely dissolved before the continuous casting occurs, whereas when using precipitation kinetics, harmful inclusions can be present in the final product. This is consistent with industrial samples.

Direct Measurement of Agglomeration Force Exerted between Alumina Particles in Molten Steel

As a fundamental study to clarify the agglomeration and coalescence of alumina inclusions in molten steel from the viewpoint of interfacial chemical interactions, it has been experimentally verified for the first time that significant agglomeration force is exerted between alumina particles in aluminum deoxidized molten steel by using a newly established experimental method. In this method, the agglomeration force exerted between alumina particles in molten steel is directly measured separately from the effect of molten steel flow. In addition, it has been quantitatively demonstrated that the contact angles measured between aluminum deoxidized molten steel and an alumina plate are larger than those between the molten iron-oxygen alloy and the alumina plate, which have already been measured by other researchers. Moreover, it has also been indicated by analyzing the actual measurement values of agglomeration force with an interaction model taking contact angles and interfacial properties into consideration that the agglomeration force between the alumina particles in aluminum deoxidized molten steel derives not from the van der Waals force but from the cavity bridge force occurring due to molten steel, which is unlikely to wet the alumina particles. Meanwhile, it has been assumed that the agglomeration force on spherical alumina inclusions in aluminum deoxidized molten steel calculated on the basis of the interaction model according to the cavity bridge force is greater than the buoyant force and drag force, and the alumina inclusions once coming into contact are therefore not prone to be simply dissociated even under molten steel flow. Thus, they maintain the agglomeration state and are subsequently sintered and form comparatively solidly bonded alumina clusters.

Effect of Inclusion Agglomeration and Percolation on the Dynamic Stiffness of Composite Materials with Coated Spherical Inclusions

Effect of Inclusion Agglomeration and Percolation on the Dynamic Stiffness of Composite Materials with Coated Spherical Inclusions

Multi‐Functional Filters for Metal Melt Filtration

Safety for road and railway vehicles as well as aircrafts requires highly stressable metallic components. The efficiency of these components is highly determined by the materials quality and purity. During the production process, contaminations within the metal melt can occur resulting in defects in the form of inclusions. It is difficult or even sometimes impossible to reduce or remove those inclusions. Within the Collaborative Research Center 920 “Multi-functional filters for metal melt filtration – a contribution toward zero defect materials” funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) in 2011 at the Technische Universität Bergakademie Freiberg focuses on researching a new generation of metal qualities via melt filtration with superior mechanical properties for use in light weight structures and high demand construction materials. The aim of the collaborative research center is an enormous reduction of non-metallic inclusions in the metal matrix by the use of intelligent filter materials as well as filter systems due to functionalized filter surfaces. So called “active” coatings based on the same chemistry as the inclusions can attract more effective the non-metallic particles and lead to a higher deposition on the filter surface. In addition, new “reactive” coatings are investigated in terms of a chemical reaction between the functionalized filter surface and the gases in the metal melts. The surface design, the tailored thermal shock performance with regard to sufficient corrosion and creep resistance are most challenging tasks requiring an understanding of the control of the structural properties of the filter materials in the nano-, micro-, and macro-ranges, interaction at interfaces as well as temperature related phase transformations. The flow dynamic conditions in the filter during casting are of great importance for the proper design of the filter macro-structure. A material as well as a flow computer aided micro- and macrostructure filter design based on investigated filtration mechanisms can lead to high filtration efficiencies with superior properties – strength, fracture toughness, fatigue- of the casted steel, iron, aluminum, silicon, and magnesium components. In addition, other applications such as recycling of metals, the electronic industry via filtration of copper, or the thin steel and aluminum foil production can adapt part of the generated results. The present special issue focuses in a comprehensive way on selected results covering the entire chain of filtration, from the research of the filter materials, the agglomeration and deposition of inclusions on the functionalized filter surfaces, up to properties of the end metallic product. A total of 16 scientific projects with more than 20 funded researchers are working together by bridging different disciplines. A very important subject is also the qualification of the research assistants with the aim of getting a doctorate degree completed by different soft skills. On behalf of the whole team, we would like to thank all the journal editors as well as review members and invite you to share with us our results and awake your curiosity getting in touch with our CRC for fruitful discussions in this interdisciplinary scientific field. Christos G. Aneziris Institute of Ceramic, Glass and Construction Materials

A three‐phase model for polymer curing including diffusive motion and agglomeration of inclusions.

AbstractIn this work, a phenomenological three‐phase model is formulated to simulate agglomeration and breakup of particles contained in a polymer. It shall serve as a starting point for modelling the same phenomena in curing polymers. While isothermal processes are assumed, the model is stated in the framework of continuum mechanics of mixtures. The phenomenological model consists of a polymer phase, and two particle phases. Agglomeration and breakup is modeled as a concentration exchange between the two particle phases. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of Al Particle Size and Lead Zirconate Titanate (PZT) Volume Fraction on the Dielectric Properties of PZT-Epoxy-Aluminum Composites

Two-phase PZT-epoxy piezoelectric composites and three phase PZT-epoxy-Al composites were fabricated using a poling voltage of 0.2 kV/mm. The influence of aluminum inclusion size (nano and micron) and (lead zirconate titanate) PZT volume fraction on the dielectric properties of the three phase PZT-epoxy-aluminum composites were experimentally investigated. In general, dielectric and piezoelectric properties of the PZT-epoxy matrix were improved with the addition of aluminum particles. Composites that were comprised of micron scale aluminum inclusions demonstrated higher piezoelectric d33-strain-coefficients, and higher dielectric loss compared to composites that were comprised of nanosize aluminum inclusions. Specifically, composites comprised of micron sized aluminum particles and PZT volume fractions of 20%, 30%, and 40% had dielectric constants equal to 405.7, 661.4, and 727.8 (pC/N), respectively, while composites comprised of nanosize aluminum particles with the same PZT volume fractions, had dielectric constants equal to 233.28, 568.81, and 657.41 (pC/N), respectively. The electromechanical properties of the composites are influenced by several factors: inclusion agglomeration, contact resistance between particles, and air voids. These composites may be useful for several applications: structural health monitoring, energy harvesting, and acoustic liners.

Observation on Physical Growth of Nonmetallic Inclusion in Liquid Steel During Ladle Treatment

The behaviors of several types of inclusions at a high temperature were examined using a confocal scanning laser microscope (CSLM, 1LM21H/SVF17SP). Although alumina inclusions tended to impact on each other, agglomerate, and grow quickly, no other inclusion type, such as spinel as well as solid and liquid calcium aluminate, was observed to attract each other. The results of confocal microscope study were compared with the industrial investigation. For this purpose, many steel samples were taken at different stages of ladle treatment. The samples were analyzed by scanning and light optical microscopes. Approximately 50,000 inclusions of several types were examined. Only alumina inclusions were attracted to each other and agglomerate. No agglomeration by attractive behavior was observed in the other types of inclusions, including liquid inclusions. Both the industrial data and the in situ observation by CSLM indicate that, although the attraction force and the agglomeration play a significant role in the growth of alumina inclusions, the agglomeration of spinel and calcium aluminate inclusions does not need special consideration in ladle treatment. The agglomeration of liquid calcium aluminate inclusions took place only when they occasionally met as a result of external force, which led to low collision probability. However, the agglomeration of the liquid calcium aluminate inclusions along with alumina particles could be detrimental in the casting process.

Pilot plant study of nozzle clogging mechanisms during casting of REM treated stainless steels

A pilot scale bottom teemed high frequency furnace with a nominal capacity of 600 kg and an adjustable nozzle temperature was used to study clogging of rare earth metal (REM) treated stainless steels. The influence of the following variables on the clogging was studied: amount of REM, fraction of oxide clusters, total oxygen content in the steel, reoxidation, aluminium additions before REM additions and silicon additions during casting. Overall, the results show that, during the present experimental conditions, mainly two typical clogging rates could be identified, fast and slow clogging. Two main differences could be detected between the fast and slow clogging rates. Steel containing mainly small single inclusions clogged faster than steel containing mainly large inclusion clusters. The reason was believed to be that the small inclusions could stick to the nozzle wall at narrow passages where the steel flow velocity was high while the larger ones could not. The source of the small inclusions was believed to be reoxidation. It was also found that the main part of the nozzle accretion was caused by agglomeration of inclusions and inclusion clusters, while only a thin oxide film along the nozzle wall was caused by oxide precipitation at the nozzle wall.