Alumina Inclusions Research Articles

Simultaneous Analysis of Soluble and Insoluble Oxygen Contents in Al-Killed Steels of Various C Contents and Supersaturation Phenomena in the Steel

Soluble and insoluble O contents ([S. O] and [I. O], respectively) in Al-killed steels of various C contents (0 to ~2 mass pct.) were simultaneously measured using “two-stage” inert gas fusion infrared absorptiometry, where majority of the inclusions was alumina. Several steel specimens were used for the O content analysis where the specimens were either taken from a steel plant or prepared in this laboratory. In addition to this, several pretreatment methods of the specimens were tested in order to provide reliable analysis results. It was found that mechanical grinding of the specimen’s surface should be carefully carried out in order not to induce unwanted surface oxidation. This resulted in overestimation of the O content of the specimen. [S. O] and [I. O] in the steel specimens were successfully analyzed using the “two-stage” gas fusion method in the context of inert gas fusion infrared absorptiometry. Considerable portion of total O content ([T. O] = [S. O] + [I. O]) was the [S. O], which was higher than the equilibrium O content of the known Al deoxidation equilibria. Therefore, the supersaturation in the Al deoxidation was confirmed. The analyzed [I. O] was independently validated by measuring area of the exposed alumina inclusions on the polished section of the specimen using SEM. It was also found that increasing C content in the steel lowered the [S. O] while [I. O] hardly changed. It is concluded that C in the steel, mechanical stirring, and remelting, could relieve the supersaturation.

Magnetoquantum oscillations in the specific heat of a topological Kondo insulator

Surprisingly, magnetoquantum oscillations (MQOs) characteristic of a metal with a Fermi surface have been observed in measurements of the topological Kondo insulator SmB6. As these MQO have only been observed in measurements of magnetic torque (dHvA) and not in measurements of magnetoresistance (SdH), a debate has arisen as to whether the MQO are an extrinsic effect arising from rare-earth impurities, defects, and/or aluminum inclusions or an intrinsic effect revealing the existence of charge-neutral excitations. We report here the first observation of MQO in the low-temperature specific heat of SmB6. The observed frequencies and their angular dependence for these flux-grown samples are consistent with previous results based on magnetic torque for SmB6 but the inferred effective masses are significantly larger than previously reported. Such oscillations can only be observed if the MQO are of bulk thermodynamic origin; the measured magnetic-field dependent oscillation amplitude and effective mass allow us to rule out suggestions of an extrinsic, aluminum inclusion-based origin for the MQO.

Modification Mechanism of Lanthanum on Alumina Inclusions in a Nonoriented Electrical Steel

The modification mechanism of lanthanum on alumina inclusions in a nonoriented electrical steel at 1600 °C is investigated using laboratory experiments. Inclusions are analyzed using an automatic scanning electron microscope equipped with energy‐dispersive spectrum at 1, 5, 10, and 30 min after lanthanum treatment. The contents of total oxygen (TO), total sulfur (TS), and total lanthanum (TLa) in steel are analyzed. Results show that Al2O3 inclusions are modified by lanthanum in two ways. One is that the dissolved lanthanum directly reduces the aluminum in Al2O3 inclusions and forms LaAl11O18 or LaAlO3 ones. The other is that a new La2O2S or LaS x shell is preferentially generated at the outside of Al2O3 and forms multiphase inclusions. With time increasing, the La2O2S or LaS x shell gradually reacts with the Al2O3 core and generates stable lanthanum‐containing inclusions. At the initial stage of lanthanum treatment, many transient inclusions including LaS x , La2O2S, and La–P(–As) are formed due to the high concentration of lanthanum, while gradually redissolving with time increasing. With the increase in TLa content in steel, the formation sequence of stable inclusions is Al2O3 → LaAl11O18 → LaAlO3 → La2O2S → LaS x , which is consistent with thermodynamic analysis.

Microstructure and mechanical properties of a welded joint obtained by friction stir welding of thin copper and aluminum plates

Friction stir welding was used to produce a welded joint of 1 mm thick plates of copper M1 and aluminum alloy AMg2M. The microstructure of the shoulder-side of the joint had areas of mixing of aluminum and copper. In the area of aluminum, copper inclusions were observed, and in the area of copper, aluminum inclusions were observed in the form of particles and thin lamellas. The bottom side of the joint consists mainly of copper. X-ray diffraction showed the presence of intermetallic phases Al2Cu, Al4Cu9 from the side of the shoulder. The formation of intermetallic phases occurred in the solid-state, without melting the initial materials. The presence of copper particles in the region of aluminum and aluminum particles and lamellas of various lengths in the regions of copper, intermetallic phases led to the formation of a composite-like structure. The formation of a composite-like structure during friction stir welding of copper and aluminum plates affects the mechanical properties of the joint. Thus, the microhardness of the joint increased in comparison with the microhardness of the initial plates. The distribution of microhardness over the thickness of the joint is almost uniform. The formation of composite-like structure using friction stir welding are discussed.

Effect of Physicochemical Properties of Slag on the Removal Rate of Alumina Inclusions in the Ruhrstahl–Heraeus (RH) Refining Conditions

Effect of Physicochemical Properties of Slag on the Removal Rate of Alumina Inclusions in the Ruhrstahl–Heraeus (RH) Refining Conditions

Imaging Measurement for the Inclusion Analysis of Steel Materials in Emission Spectrometry

This paper reviews three emission spectrometric methods that can be applicable to the inclusion analysis in steel materials, which provides information on the number, the size and distribution, as well as the chemical composition of inclusion particles. Cathodoluminescence (CL), X-ray-excited optical luminescence (XEOL), and beam-scanning laser-induced breakdown spectrometry (LIBS) are employed for the imaging measurement of the inclusions. As a typical specimen, alumina inclusions are evaluated to compare their analytical performance. The easy handling and rapid response of them are significant features for an application to the on-site/in-line analysis in the production site of steel.

Size and Shape Effects on Fatigue Behavior of G20Mn5QT Steel from Axle Box Bodies in High-Speed Trains

In this paper, the axial loading fatigue tests are at first conducted on specimens ofG20Mn5QT steel from axle box bodies in high-speed trains. Then, the size and shape effects on fatigue behavior are investigated. It is shown that the specimen size and shape have an influence on the fatigue performance of G20Mn5QT steel. The fatigue strength of the hourglass specimen is higher than that of the dogbone specimen due to its relatively smaller highly stressed region. Scanning electron microscope observation of the fracture surface and energy dispersive X-ray spectroscopy indicate that the specimen size and shape have no influence on the fatigue crack initiation mechanism. Fatigue cracks initiate from the surface or subsurface of the specimen, and some fracture surfaces present the characteristic of multi-site crack initiation. Most of the fatigue cracks initiate from the pore defects and alumina inclusions in the casting process, in which the pore defects are the main crack origins. The results also indicate that the probabilistic control volume method could be used for correlating the effects of specimen size and shape o the fatigue performance of G20Mn5QT steel for axle box bodies in high-speed trains.

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

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

Localized Corrosion Occurrence in Low-Carbon Steel Pipe Caused by Microstructural Inhomogeneity.

In this study, the cause of failure of a low-carbon steel pipe meeting standard KS D 3562 (ASTM A135), in a district heating system was investigated. After 6 years of operation, the pipe failed prematurely due to pitting corrosion, which occurred both inside and outside of the pipe. Pitting corrosion occurred more prominently outside the pipe than inside, where water quality is controlled. The analysis indicated that the pipe failure occurred due to aluminum inclusions and the presence of a pearlite inhomogeneous phase fraction. Crevice corrosion occurred in the vicinity around the aluminum inclusions, causing localized corrosion. In the large pearlite fraction region, cementite in the pearlite acted as a cathode to promote dissolution of surrounding ferrite. Therefore, in the groundwater environment outside of the pipe, localized corrosion occurred due to crevice corrosion by aluminum inclusions, and localized corrosion was accelerated by the large fraction of pearlite around the aluminum inclusions, leading to pipe failure.

Study of microstructure & mechanical properties of TIG welded aluminized 9Cr-1Mo steel

Aluminide coating on 9Cr steel is candidate coating for blanket module applications of fusion reactors. The welding fabrication processes associated with coated steels are still an issue as the presence of Al in weld metal has several detrimental outcomes. To address this, the authors have attempted a study on conventional TIG welding with V-groove to mitigate the effect of coating on weld metallurgy. This work emphasizes the comparison of mechanical properties and microstructures of aluminide coated and uncoated/bare 9Cr-1Mo steel. Microstructural observations indicated presence of un-dissolved alumina inclusions at the weld fusion line. Despite such inclusions, the observed tensile strength of the weld joint for coated steel is 648 MPa±16 MPa which is in line with the weld joint of un-coated steel (667±14 MPa) and substrate (643 MPa±18 MPa). Impact toughness tests carried out at 0 °C,-25 °C and room temperature also indicate that there is no drastic effect of coating on weld joint and the observed toughness values are acceptable as per the reported data (45 J).

Diffusional behavior of nanoscale lead inclusions in crystalline aluminum

Abstract In-situ transmission electron microscopy (TEM) observations reveal a permanent chaotic motion of nanosized liquid Pb inclusions embedded in thin aluminum foils. Individual trajectories of the inclusions were analysed to determine the character of their motion. The inclusions moving freely inside a crystal display motion with three-dimensional random walk characteristics while inclusions attached to dislocations display spatially confined random motion localized to the close vicinity of the dislocation lines. The diffusion coefficients of inclusions moving freely in the matrix were determined using Einstein’s classical equation for diffusion of Brownian particles. The diffusion coefficients of inclusions trapped on dislocations were found using an equation based on Smoluchowski’s analysis of Brownian motion of a particle under the action of a linear elastic restoring force. The dependence of the diffusivity on the size of the inclusions suggests that their mobility is controlled by kinetic processes on the inclusion/matrix interfaces. The Arrhenius analysis exhibits two regions with different temperature dependencies. We suppose that this is related to the existence of {111} facets on the inclusion/matrix interfaces.

Effect of lining refractory and high-basicity slag on non-metallic inclusions in a high carbon Al-killed steel

Laboratory experiments on the effect of lining refractory and high-basicity slag on non-metallic inclusions in a high carbon Al-killed steel were carried out. Alumina inclusions in the steel could hardly be affected by the Al2O3 refractory, however, would be transformed into MgO · Al2O3 when the MgO refractory was used. After the steel-slag-MgO lining-inclusion reaction, the high-basicity slag was saturated with MgO due to the dissolution of MgO from the refractory into the slag, meanwhile, original Al2O3 inclusions were transformed into MgO via MgO · Al2O3, regardless of the slag basicity. After the steel-slag-Al2O3 lining-inclusion reaction, the CaO/Al2O3 ratio of slag decreased significantly due to the dissolution of Al2O3 refractory into the slag, resulting in the slight increase of the magnesium content in steel and the transformation of Al2O3 inclusions into MgO · Al2O3. The reduction of the MgO in the lining refractory and top slag by the dissolved aluminum ([Al]) in molten steel occurred independently, and a higher CaO/Al2O3 ratio of slag would result in a higher activity of MgO, which was beneficial for the reduction of MgO. The CaO in the slag was hardly reduced by the [Al] in the molten steel, thus, it was proposed that CaO-Al2O3 type inclusions could hardly be generated from the steel-slag reaction during the production of high carbon Al-killed steels.

Electrochemical behaviour of lead-free Sn-In-Al solders alloys in 3.5 wt.% NaCl solution

The corrosion properties of lead-free solder alloy can not be ignored in the field of the electronic industry. However, there is no literature on the effect of aluminium on Sn-In binary solder alloys. This study looked at the corrosion of a lead-free solder alloy in a 3.5 wt.% NaCl simulated seawater environment. Three isopleths were created with varying aluminium content in the Sn-In-Al system while maintaining Sn and In radio constant (1:1). The vacuum sealing process was used to create the samples. The corrosion resistance of this lead-free solder ware was investigated at room temperature in a 3.5 wt.% NaCl solution. Corrosion resistance improves with Al content, according to the potentiodynamic polarization test. By lowering the current density (Icorr), the inclusion of aluminium refines the microstructure. It enhances the corrosion resistance of Sn-In-Al solder alloys, resulting in high resistance of the passive layer produced by lowering the current density (Icorr). Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDS) was used to analyze of surface morphology of the non-corroded and corroded Sn-In-Al solder alloys. Intermetallic compound (IMC) of non-corroded and corrosion products on the surface corroded solder alloys were studied using X-ray diffraction (XRD). According to XRD analysis, the composition of corrosion products altered as the aluminium content changed, forming phases such as Sn3O(OH)2Cl2, oxides, and chlorides of Sn.

Formation of Complex Inclusions in Gear Steels for Modification of Manganese Sulphide

Suitable MnS inclusions in gear steel can significantly improve the steel machinability and reduce the manufacturing costs. Two gear steel samples with different sulphur contents were prepared via aluminium deoxidation followed by calcium treatment. The shape, size, composition and percentage distribution of the inclusions present in the steel samples were analyzed using an electron probe micro-analysis (EPMA) technique. The average diameter of MnS precipitated on an oxide inclusion is less than 5 µm. It was found that the steel with high sulphur content contains a greater number of elongated MnS precipitates than low sulphur steel. Moreover, there are more oxide inclusions such as calcium-aluminates and spinels with a small amount of solid solution of (Ca,Mn)S in low content sulphur steel after calcium treatment, which indicates the modification of solid alumina inclusions into liquid aluminates. The typical inclusions generated in high sulphur steel are sulphide encapsulating oxide inclusions and some core oxides were observed as spinel. The formation mechanisms of complex inclusions with different sulphur and calcium contents are discussed. The results are in good agreement with thermodynamic calculations.

Numerical modeling of energy storage unit during freezing of paraffin utilizing Al2O3 nanoparticles and Y-shape fin

Freezing process inside an annulus zone was reported numerically in this article. The domain is filled with paraffin (Tm=82 °C) and for improving thermal features, nanoparticles were added. Fins with various sizes and positions were applied and two levels for fraction of nanomaterial were utilized. Exergy drop is main outputs of current research and contours in three time stages were reported. Unsteady phenomena were reported with considering structure grid. Average values of significant parameters were extracted as function of time. Non-zero values of velocity show the impact of buoyancy force. For verification, experimental outputs of published paper have been utilized. Exergy drop (Xd) declines with rise of time because of reduction of temperature. The value of Xd decrease about 91.14% when time increases from 1 to 15 min for case 8. The geatest case win lowest needed time is case with thinner fins over the outer wall and it needs 17.86 min to reach complete solidification. Inclusion of alumina in to paraffin makes freezing time to decrease about 11.7%. Changing the position of fins from inner to outer causes the freezing rate to increase about 14.45%.

Analysis of predictors for modification of alumina inclusions in medium carbon steel

Currently in steelmaking, “inclusions engineering” has occupied a relevant space in terms of improvements in processes and products. This is because these compounds, depending on the chemical nature, morphology, physical state, size and distribution, can harm both the processes and the mechanical properties of the final product. Thus, the present work aimed to evaluate the modification of alumina inclusions by Ca addition in a medium carbon steel, by modeling the relationship between possible predictor variables in order to establish the fraction of liquid inclusions at the end of the secondary steel refining process. To achieve this goal, it was performed a statistical significance analysis by multiple linear regression. Feature engineering and feature selection methods were used, such as Pearson correlation filtering, “best subsets” method and statistical metrics like p-value, standard error, residuals plot, Durbin–Watson test and adjusted R2. Then, a statistically significant model was finally reached. Through the statistical and metallurgical discussion, the model indicated that the oxidation of steel, the titanium and sulfur content in steel are the main obstacles to the modification of non-metallic inclusions. In addition, computational thermodynamics proved to be an important ally in making decisions about the process.

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 yttrium treatment on alumina inclusions in high carbon steel

Effect of yttrium treatment on alumina inclusions in high carbon steel

Experimental detection and shape reconstruction of inclusions in elastic bodies via a monotonicity method

We deal with the detection and shape reconstruction of inclusions in elastic bodies based on a monotonicity method and aim to reconstruct them with experimental measurements. Thus, we base our studies on the rigorously proven theory of the linearized monotonicity tests for noisy measurement data, where the so-called Neumann-to-Dirichlet operator, its Fréchet derivative and the corresponding monotonicity properties play an essential role. Further on, we give an insight into the lab experiment itself. More specifically, we take a look at Makrolon plates with one or two circular aluminium inclusions. Concerning the realization of the measurements, we have to deal with missing data which cannot be measured due to the set-up of the experiment. Hence, we take a look at a modified spline interpolation in order to determine this data. In doing so, we state the required steps for the implementation of the linearized monotonicity tests. Finally, we present our reconstructions based on experimental data and compare them with the simulations obtained from artificial data, where we want to highlight that all inclusions can be detected from the noisy experimental data, thus, we obtain accurate results. This paper combines the rigorously proven theory of the monotonicity methods developed for linear elasticity with the explicit application of the methods, i.e. the implementation and simulation of the reconstruction of inclusions in elastic bodies for both artificial and experimental data.

Computational Fluid Dynamics (CFD) Simulation of Inclusion Motion under Interfacial Tension in a Flash Welding Process

Non-metallic inclusions particles are detrimental to the mechanical properties of a material. It is very important to understand the motion behavior of inclusion particles in molten metal. The motion behavior of non-metallic inclusion particles during weld pool solidification and their distribution in joint areas is dependent on various factors. In the alternative current (AC) flash welding process, inclusions motions are dependent on welding plate movement, interfacial tensions, etc. Apart from this, the temperature of the molten metal in the welding zone and the size of inclusion particles also play an important role. Secondly, the Marangoni forces are developed due to interfacial tension which affects the movement of inclusion particles at the solid-liquid interface in a solidifying welding pool. The interfacial tension varies with the change in surfactant concentration and other factors. In this work, the effect of upsetting rate and interfacial tension on alumina inclusions has been studied. The interfacial tension controls the pushing and engulfment of non-metallic inclusions at the solid-liquid interface. A two-dimensional multiphase mathematical model has been developed to study the inclusion motion behavior at the solid–liquid interface in a solidifying weld pool. The numerical model has been developed by adding the volume of fluid method (VOF), a dynamic mesh model and discrete phase model for a realistic approach. The predicted results show that the upsetting setting parameters have a substantial effect on the overall non-metallic inclusion motion. The inclusions were seen moving away from the welded joint due to the high up-setting rate. The results also reveal that the inclusions were engulfed by the solidification front under the effect of the strong interfacial tension between the non-metallic inclusions and the molten steel.