Agglomeration Of Inclusions Research Articles

Evaluation of inclusion agglomeration behavior in molten steel based on the modified model of cavity bridge force

Inclusion agglomeration behavior in molten steel is a key factor that affecting steelmaking process and steel quality. In this work, the modification on the Laplace pressure of cavitation interaction between inclusions has been made according to the calculation model of cavity bridge force. The effects of the distance between inclusions, the diameter of inclusions, the surface tension of molten steel, and the contact angle between inclusions and molten steel on the cavity bridge force were quantitatively investigated by using this modified model. The results show that the contact angle between inclusions and molten steel has a significant influence on inclusions agglomeration. The inclusions cannot agglomerate by cavity bridge force when the contact angle is less than 90°. Subsequently, the agglomeration tendency of different inclusions was calculated and compared. The order of cavity bridge force and critical agglomeration distance of inclusions in molten steel is MgO·Al2O3 < CaO < MgO < Ti2O3 < AlN < Al2O3. Then the high temperature experiments were carried out to investigate the evolution of inclusions sizes in molten steel. It is found that the average size of Al2O3 is larger than that of AlN, which indicates that the agglomeration tendency of AlN inclusions is much weaker than that of Al2O3 inclusions. This calculation model can accurately evaluate the agglomeration behavior of inclusions and provide theoretical guidance for inclusions control.

Research on directional solidification combined with electron beam melting and refining for recycling of FGH4096 alloy scraps

The constraints of traditional manufacturing techniques have led to the generation of a considerable amount of waste superalloy, causing substantial resource wastage. The primary concern with waste superalloys lies in the excessive presence of inclusions and impurity elements, rendering them unsuitable for further utilization. This study proposes the use of directional solidification combined with electron beam melting and refining (EBMR) to prepare FGH4096 superalloy ingots (Φ120 mm), which offers a promising approach to produce large-sized powder superalloy master alloy ingots with high-purity and high homogeneity. It is found that the secondary dendrite arm spacing and the size of the γ’ phase in the alloy are significantly reduced after EBMR treatment. The concentration of O and N can be decreased to 5.7 and 0.6 ppmw, respectively. The size of inclusion can be reduced below 8.69 μm and the inclusion numbers reduce by over 50 % compared with both conventional ingots. A droplet transfer mode and melt convection mode mechanism have been proposed, which accurately predicts the melting temperature and melt flow. A quantitative study is conducted on the influence of inclusion density, the contact angle between inclusions and melt, and the surface tension of the melt on capillary forces. The results indicate that the capillary forces between inclusions in the melt range from 1.8 × 10−19 N and 1.9 × 10−17 N. Furthermore, the collision-aggregation behavior of inclusions in the melt is discussed, and an estimate of the tendency of inclusion collision-aggregation is provided. The enrichment of inclusions in the EBMR ingot is primarily the result of turbulent collision. The Marangoni effect and the extremely high surface temperature of the melt promote the collision and agglomeration of inclusions, causing them to accumulate rapidly at the melt surface. Moreover, the thorough removal of inclusions through the decomposition and dissolution process of the electron beam offers theoretical backing for the preparation of superalloys through electron beam melting and high-purity refining.

Effect of P and Ti on the agglomeration behavior of Al2O3 inclusions in Fe–P–Ti alloys

Abstract Nozzle clogging occurs in the interstitial free (IF) steel with high phosphorus (P) more frequently than in IF steel with lower P. To explore the effect of P and Ti on the inclusion behavior in liquid steel, the in situ experiment and theoretical calculations were conducted. High-temperature confocal laser scanning microscopy was used in situ to observe the inclusion behavior at the liquid Fe–P–Ti alloy surfaces, and the attractive and capillary forces were also calculated to quantitatively estimate the effect of P and Ti on the inclusion behavior. The results show that the agglomeration of Al2O3 inclusions involves four steps: dispersed Al2O3 particles in liquid alloy; formation of Al2O3 chain structure; bending of the Al2O3 chain, and sintering and densification of the chain structure. The addition of Ti and P in the steel can increase the agglomeration time of inclusions, indicating the impeding effect of P and Ti on the inclusion aggregation. Furthermore, the orientation factor is proposed to estimate the direction of movement of the small inclusion crossing between large inclusions, and the experimental results confirm its validity.

Abnormal improvement of high-temperature stress rupture life in a new low cost Ni-based single crystal superalloy by adding minor nitrogen

Generally, elevated nitrogen (N) content promotes the precipitation of nitrides, which increase the size and quantity of porosity and thus degrade the mechanical performance of superalloys. However, in this study, N content was found to have a beneficial impact on the stress rupture property of single-crystal (SX) superalloys. The results indicated that as the N content increased from 5 ppm to 35 ppm, the porosity first decreased and then increased. The porosity of the sample with 14 ppm N was the lowest, 0.072% ± 0.011%, which was mainly attributed to the TiN phases in interdendritic pools that compensated for volume shrinkage by lattice expansion. The addition of N reduced the volume fraction and antiphase boundary energy of the γ′ phase because TiN nitride formation consumed Ti in large quantities. Additionally, the rupture life at 1100 °C/130 MPa was abnormally improved to 251.67 h ± 19 h as the N content was increased to 14 ppm, while it was markedly decreased as the N content was continuously increased to 35 ppm. The improved stress fracture life of the alloy was primarily attributed to the formation of TiN with a small size, which retarded microporosity formation and effectively impeded dislocation movement in γ channels. Moreover, during the stress rupture test, the size of the tertiary γ′ phase first reduced to a minimum in the alloy containing 14 ppm N, which increased the resistance to dislocation movement. However, excessive addition of N drastically reduced the stress fracture life as the precipitation and solid solution strengthening in the γ′ phase weakened. In addition, the agglomeration of nitride inclusions formed defects that aggravated crack nucleation and propagation. The overall N impact was studied, and the optimal N content was ascertained to provide further instructions for the commercial development of Re-free second-generation SX alloys.

In-Situ Observation of Steel/Slag/Inclusion Interaction by Means of High-Temperature Confocal Scanning Laser Microscopy

Non-metallic inclusions (NMIs) in steels have been the focus of various experimental studies due to their detrimental character. While isolated processes, such as agglomeration or dissolution, have been well investigated, holistic in-situ views with high-temperature confocal scanning laser microscopy (HT-CSLM) have been rare. In this work a novel and suitable method is presented to simultaneously observe agglomeration, movement, detachment, and dissolution of non-metallic inclusions by combined the melting of steel and slag with a dual-crucible approach. Therefore, different steel/slag combinations were tested. It is shown that, with transparent that does not become tarnished by the ions stemming from the steel, the steel’s surface and non-metallic inclusions are observable. Furthermore, technological limitations are discussed, including restrictions regarding the melting point of steels and certain steel/slag combinations.

Effects of Rare Earth La–Ce Alloying Treatment on Modification of Inclusions and Magnetic Properties of W350 Non-Oriented Silicon Steel

In order to study the effects of rare earth La–Ce alloying treatment on the characteristics of inclusions in non-oriented silicon steels, industrial experiments were conducted studying the composition, morphology, size and quantity of inclusions in W350 non-oriented silicon steel during the RH (Ruhrstahl-Hereaeus) refining process and tundish process, after rare earth treatment. The products were analyzed by means of ICP-MS (inductively coupled plasma mass spectrometry), SEM/EDS (scanning electron microscope-energy dispersive spectrometry), and ASPEX (automated SEM/EDS inclusion analysis). The research results showed that the types of inclusions in experimental steel changed significantly after rare earth treatment. The types of inclusions after RE (rare earth) treatment are typically rare earth composite inclusions that are mainly composed of (La, Ce)Al2O3, and conventional inclusions. The addition of rare earth promotes the agglomeration of inclusions; the morphologies of the inclusions are mostly blocky, and some are distributed in long strips. After rare earth treatment during the RH refining process, the number of inclusions with sizes of 1.0~3.5 μm in the experimental steel is increased, and the average size of the inclusions is 2.66 μm. In addition, the number of inclusions larger than 4 μm in the specimens increases due to the collision and growth of inclusions caused by the RH circulation. After rare earth treatment during the tundish process, the number of micro inclusions with sizes of 1.0~2.5 μm in the specimen steels decreases, while the number of inclusions larger than 5 μm increases. The size distribution of micro inclusions in hot-rolled sheets after rare earth treatment was studied using TEM (transmission electron microscopy). In the specimens without rare earth, the content of micro inclusions (≤1 μm) is 51,458.2/mm2 and the average size is 0.388 μm. In the specimens with rare earth added, the content of micro inclusions (≤1 μm) is 24,230.2/mm2 and the average size is 0.427 μm. Compared to sheet produced by the original process, the iron loss of the 0.35 mm finished experimental sheet is reduced by 0.068 W/kg, and the magnetic induction is increased by 0.007 T. The iron loss of the 0.50 mm finished experimental sheet is reduced by 0.008 W/kg, and the magnetic induction is increased by 0.004 T. After rare earth treatment, the average size of micro inclusions increases and the magnetic properties are obviously improved.

Local behavior of inclusions in reactors metallurgical: Aggregation and deposition on the walls

Populations of inclusions conditioned very early in the alloy production process metals, during the refining and liquid metal treatment stages, are likely to drastically impact mechanical performance, especially fatigue resistance. Control performance of these materials therefore requires control of the inclusion populations, requiring in particular a very good knowledge of the mechanisms which govern their evolution in number and size in refining reactors. Inclusive behaviors in supply chains steel and aluminum have already been the subject of numerical studies at the process scale (Bellot et al., 2014 ; Waz et al., 2016) in which the transport and agglomeration of inclusions are modelled. In order to improve the modelling of key phenomena such as the aggregation and capture of wall inclusions, local simulations, at the scale of an inclusion pair and a layer limit to the wall of a reactor, are carried out here using a lattice Boltzmann method (Sungkorn and Derksen, 2012).

Inclusion Agglomeration on Ultra-Low C Liquid Steel Surface: Roles of Ti in the Steel and the Oxygen Potential

Inclusion Agglomeration on Ultra-Low C Liquid Steel Surface: Roles of Ti in the Steel and the Oxygen Potential

Interaction of molten Armco iron with various ceramic substrates at 1600 °C

Ceramic substrates (Al2O3·MgO, CA6, CaZrO3, AZT (Al2O3 based substrates containing ZrO2 and TiO2)) were interacted with liquid Armco iron under a low oxygen partial pressure in the heating microscope. No noticeable dissolution of the ceramic substrates and reaction was observed for most of the substrates. Furthermore, deposition of SiO2 and Fe was found on the cross section between iron and these substrates. However, for the substrate AZT, a reaction layer of complex composition was found on the interface between the iron sample and the AZT substrate. After all experiments, the total number of inclusions in the iron samples greatly decreased. The deposition, agglomeration of inclusions, and the evaporation of some elements were the factors for the inclusions decreasing. Furthermore, the stability of oxides consisted of substrates under low oxygen partial pressure was confirmed by the thermodynamic calculation.

Liquid Inclusion Collision and Agglomeration in Calcium-Treated Aluminum-Killed Steel

This work addresses conflicting results in the literature regarding liquid inclusion agglomeration. To assess whether liquid calcium aluminates do agglomerate in liquid steel, laboratory experiments were performed: melting electrolytic iron, deoxidizing the melt with aluminum and subsequently calcium treating the deoxidation products (alumina and magnesia-alumina spinel inclusions). Under laboratory conditions, solid spinels and alumina inclusions were successfully modified, producing a new population of much smaller calcium aluminate inclusions. The new population of inclusions forms because the presence of calcium in the liquid steel destabilizes alumina and MgO-alumina inclusions, which then dissolve into the melt. The liquid inclusions exhibited a weak but statistically significant tendency to agglomerate. Laboratory results were assessed in the light of different collision mechanisms. Agglomeration mainly occurs by Stokes and laminar fluid flow collision when no external stirring is imposed. Monte Carlo simulations of collisions agree reasonably well with experimental results. For industrial conditions, where the liquid steel is agitated by argon bubbling and/or electromagnetic stirring, turbulent collisions dominate.

Effect of Impeller and Gas Stirring on Agglomeration Behavior of Polydisperse Fine Particles in Liquid

Agglomeration, coalescence and flotation of non-metallic inclusions in steel melt are effective for obtaining “clean steel.” In this study, the agglomeration and breakup behaviors of particles with a primary particle size distribution (hereinafter, polydisperse particles) in a liquid under impeller and gas stirring were compared by numerical calculations and model experiments. The particle-size-grouping (PSG) method in the numerical agglomeration model of particles was combined with a breakup term of agglomeration due to bubble bursting at the free surface. Polydisperse and monodisperse polymethylmethacrylate (PMMA) particles were used in the agglomeration experiments. The agglomeration rate of the polydisperse particles under impeller stirring was increased by an increasing energy input rate, whereas the agglomeration rate under gas stirring decreased under this condition due to the larger contribution of the breakup of agglomerated particles during bubble bursting in gas stirring. At the same energy input rate, agglomeration of polydisperse particles was larger under impeller stirring than under gas stirring. The agglomeration rate of polydisperse particles was larger than that of monodisperse particles under both impeller and gas stirring at the same energy input rate. The computational temporal changes in the total number of particles were in good agreement with the experimental results. This means that the difference in the agglomeration behaviors observed in impeller and gas stirring can be explained by the turbulent coagulation and subsequent agglomerated particle breakup in gas stirring. The computational temporal change in the number of each group approximately agreed with the experimental change in both impeller and gas stirring.

Agglomeration Characteristics of Various Oxide Inclusions in Molten Steel Containing Rare Earth Element under Different Deoxidation Conditions

Comprehensive investigation of agglomeration behavior of oxide inclusions in steel-containing rare earth (RE) under different deoxidation conditions is essential for improving the nozzle-clogging problem during continuous casting. The present study first optimized the thermodynamic model by supplementing thermodynamic data of the RE-compound to study the formation of various inclusions in the Ce–Si–Al–O system. On this basis, laboratory-scale experiments with different deoxidation conditions were designed to obtain samples containing one single type of inclusions, viz., SiO2, SiO2–Ce2O3 or SiO2–Al2O3–Ce2O3, respectively. Subsequently, the agglomeration behavior of inclusions was observed in situ by confocal laser scanning microscopy (CLSM), and the corresponding attractive forces were calculated to compare the agglomeration tendency of various inclusions. The results indicate that, in the Si deoxidized samples, SiO2–Ce2O3 inclusions agglomerate to form clusters with the attractive force of 4.3 × 10−17N to 4.2 × 10−15N, which is weaker than that of Al2O3 and Al2O3–Ce2O3 inclusions after Al deoxidation. Although SiO2 inclusions can agglomerate, their attractive force is only 6.3 × 10−19N to 1.2 × 10−16N, which is the weakest of the above inclusions. In the case of Si/Al complex deoxidization, spherical SiO2–Al2O3–Ce2O3 liquid inclusions are formed after Ce treatment, and no agglomeration of such inclusions was observed in situ. The study could provide theoretical guidance for improving the nozzle-clogging problem of RE-containing steel from inclusion-controlling perspective under different deoxidation conditions.

Kinetics on Formation, Growth and Removal of Alumina Inclusions in Molten Steel

A series of Al deoxidation mechanisms from the nucleation and growth of Al2O3 nuclei immediately after the addition of Al to the growth, agglomeration, and removal of Al2O3 inclusions after the deoxidation equilibrium has been analyzed in light of the kinetics taking into consideration the influences of the interfacial properties on the basis of Al deoxidation experiments of molten steel. The nucleation number density of Al2O3 is (0.72 to 1.62) × 1014 m−3 and increases as the degree of supersaturation increases and the interfacial tension between the nuclei and molten steel decreases. These tendencies can be explained by the homogeneous nucleation theory, and the average interfacial tension, frequency factor, nucleation time, and average nucleation rate are respectively estimated to be 1.43 N·m−1, 4.27 × 1035 m−3·s−1, 0.01 s, and 1.96 × 1016 m−3·s−1 for the nucleation of Al2O3. Al2O3 nuclei rapidly grow to Al2O3 single inclusions having diameters of 2.0 to 2.6 µm through diffusion growth of supersaturated O in molten steel within 2.2 to 3.7 s after the addition of Al, and the molten steel reaches the deoxidation equilibrium. In the subsequent deoxidation equilibrium, the growth rate of Al2O3 single inclusions increases as the O concentration in molten steel increases, and their growth mechanism can be explained by Ostwald ripening. Meanwhile, Al2O3 cluster inclusions grow with the increase in the agglomeration force while agglomerating not only with single inclusions dispersed in molten steel but also with other cluster inclusions existing in the floating paths.

Model for Inclusion Precipitation Kinetics During Solidification of Steel Applications in MnS and TiN Inclusions

A simulation model for inclusion precipitation kinetics during solidification of steel was proposed in this work. With the aim to calculate the inclusion size distribution during solidification of steel, the microsegregation calculation combined with the Kampmann–Wagner numerical (KWN) model for nucleation and growth of inclusion was incorporated into the present simulation model for calculating the evolution of inclusion size distribution during solidification of steel. The inclusion agglomeration due to Brownian collisions was also taken into account. The present simulation model was first applied in simulating precipitation of MnS during steel solidification and validated by the experimental data available in the literature. The effects of cooling rates and sulfur concentrations on the precipitation of MnS were investigated by the model calculations. Then, the present simulation model was applied in simulating the precipitation of TiN inclusions during steel solidification. The calculated mean size was found to be in good agreement with data available in the literature. Finally, the model was employed for studying the effects of interfacial tension between TiN and steel due to sulfur concentration change and cooling rates on the inclusion precipitation kinetics. It was found that interfacial tension between TiN and steel has a crucial influence on the precipitation of TiN. With an increase of the cooling rate, the size distribution of TiN transforms from the lognormal distribution to the bimodal distribution.

Agglomeration Characteristics of Various Inclusions in Al-killed Molten Steel Containing Rare Earth Element

The nozzle-clogging problem is closely related to the agglomeration behavior of inclusions in steel-containing rare earth (RE). The present study first optimized the thermodynamic model by supplementing thermodynamic data of the RE compound to study the formation of various inclusions in the Ce-Al-O-S system. Based on that, laboratory-scale experiments with different Ce and Al contents were designed to obtain samples containing a single type of inclusions, viz., Al2O3, Ce-Al-O, Ce2O3, and Ce-O-S, respectively. Additionally, the agglomeration behavior of inclusions was observed in situ by confocal laser scanning microscopy (CLSM), and the calculated attractive forces were used to compare the agglomeration tendency of the four inclusions. The results show that the agglomeration of Al2O3 inclusions is attributed to the strongest attractive force (1.0 × 10−15N to 3.0 × 10−14N) among the four kinds of inclusions. Although Ce-Al-O and Ce2O3 inclusions have the weaker attractive forces (1.3 × 10−16N to 2.0 × 10−14N), they can also agglomerate together and form large-sized clusters. The attractive forces between Ce-O-S inclusions are the weakest (2.1 × 10−18N to 6.0 × 10−16N), that is, this kind of inclusion is more difficult to agglomerate than other inclusions. The study can provide theoretical support for improving the nozzle-clogging problem of RE-containing steel from the inclusion-controlling perspective.

Synthesis of metal-metal oxide (Me-MenOm) nanocomposites by partial reduction and cold sintering

Metal matrix nanocomposites (MMNCs) require the development of new manufacturing techniques that enable enhanced control over their microstructure and mechanical performance. The approach for MMNC fabrication proposed in this work combines the partial reduction of the oxide nanopowder with the subsequent cold sintering. We show that it is possible to avoid unwanted structural changes such as grain coarsening and inclusion agglomeration. We reveal that a core-shell structure of partially reduced Fe2O3 particles facilitates reliable sintering and enables the fabrication of near-dense MMNCs reinforced by iron oxide nanoparticles. The fabricated composites exhibit a homogeneous distribution of reinforcing oxide inclusions and demonstrate high mechanical strength.

Investigation of Inclusion Agglomeration and Flotation During Levitation Melting of Ni-Based Superalloy in a Cold Crucible

Inclusion agglomeration and flotation during levitation melting in a cold crucible were investigated. The morphology, number and chemical composition of inclusions were characterized by scanning electron microscopy and transmission electron microscopy with energy-dispersive x-ray spectroscopy analysis. In the billet, inclusions were mainly single mixed inclusions (oxide as the core, nitride as the shell), and their size was in the range of 1–7 μm. After levitation melting, approximately 81% of inclusions existed in the form of clusters. The number of clusters was higher at the top, and the size was larger at the top (150–250 μm). The mechanism of levitation melting removing inclusions was discussed by collision theory. First, nitrides dissolved, and the core oxides were exposed. Then, oxides collided, agglomerated, and floated. Turbulent collision played the leading role in inclusion agglomeration, while Stokes collision was predominant for inclusion flotation. Finally, nitrides precipitated again during solidification.

Modelling of non-metallic inclusions in steel

ABSTRACTIn the current paper, extensive studies of the current authors on the modelling of non-metallic inclusions were summarised. Kinetic studies included the nucleation, collision and agglomeration of inclusions, the interaction between inclusion and bubble in the molten steel, the motion, collision, and removal of inclusions in the molten steel during refining and continuous casting and the entrapment of inclusions in a continuous casting slab strand. Thermodynamic studies included the deoxidation of steel and precise calcium treatment of Al-killed steels. The variation in the composition of inclusions during heating treatment of stainless steels was summarised. The studies ranged from nanoscale of molecules to sub-mili meter scale of inclusions within a meter scale metallurgical vessels, over 10 order in size, and clarified mechanisms for the generation, growth, motion and removal of inclusions in steel.

Effect of Interfacial Properties on Agglomeration of Inclusions in Molten Steels

Effect of Interfacial Properties on Agglomeration of Inclusions in Molten Steels

Application of Inhomogeneous Discrete Method to the Simulation of Transport, Agglomeration, and Removal of Oxide Inclusions in a Gas-Stirred Ladle

The behavior of oxide inclusions in a gas-stirred ladle is characterized by a wide inclusion size distribution that evolves continuously owing to their transport, aggregation, and removal. Due to the high temperature and opacity of the ladle, a computational fluid dynamics-based method coupled with a suitable population balance algorithm is required to analyze this evolution process. In this work, the inhomogeneous discrete method is applied to solve the population balance equations associated with the behavior of Al2O3 inclusions in a gas-stirred ladle, and the effect of the number of subphases is evaluated. The calculated flow and mixing characteristics of molten steel and the size distribution of inclusions in the ladle agree well with measured values reported in literature. The results indicate that the inclusion size distribution for one, two, and three subphases differs from that obtained for four and five subphases, while the refinement from four to five subphases produces a similar distribution, hence use of the inhomogeneous discrete method with four subphases is suggested to study the behavior of inclusions in a gas-stirred ladle.