Behavior Of Non-metallic Inclusions Research Articles

Detachment of a Soluble Particle at the Slag-Argon Interface: CFD Study and Experimental Observations

The behavior of non-metallic inclusions at interfaces of high-temperature melt and molten slag affects the removal of inclusions and the consequent melt cleanness. This study presents real-time in situ observations on the behavior of an oxide particle in the vicinity of the slag-argon interface by means of high-temperature confocal scanning laser microscopy (HT-CSLM). On top of that, CFD simulations are conducted to investigate the underlying mechanisms of particle-interface interactions. In addition to revealing the particle motion process from the argon phase toward the slag, a significant particle morphology alteration associated with its dissolution in the slag is experimentally observed. Particularly, upon detachment from the slag-argon interface, the particle exhibits more dissolution at the near-interface area. By combining with numerical simulations, this study indicates that particle separation at the interface can be characterized as two stages. First, a short-term capillary force-driven motion stage happens until the particle initially settles at the interface. The settling position estimated by simulation shows good consistency with experimental measurement. Second, the particle takes a relatively long time to eventually detach from the interface, and this period is accompanied by particle dissolution. Investigations suggest that the concentration variation near the interface arising from particle dissolution triggers a Marangoni flow. This flow, in turn, enhances the local dissolution rate, consequently causing a significant particle morphology change that influences the detachment. This study provides new insight into the mechanism of inclusion removal through slag absorption in metallurgical processes. Both particle dynamics and dissolution kinetics, especially the effect of solutal Marangoni convection, are highlighted in detaching a small-scale particle from the fluid-fluid interface.

NONMETALLIC INCLUSIONS IN AUSTENITIC STAINLESS STEEL AISI 303 MICROALLOYED WITH ZIRCONIUM AND TELLURIUM

The control of formation of nonmetallic inclusion and the characterization present the basis of improvement of steel product properties and lead to sustainable development in design of new steel grades. In order to produce steels with better machinability, such as AISI 303 grades, a modification of inclusions with carefully designed chemical composition is presented. Sulphur by creating sulphide inclusions reduces friction and cutting resistance, and increases the brittleness of the chip.Considering its harmful effect in steel, as well as the fact that non-metallic inclusions have been insufficiently tested for this type of high-alloyed steel, the aim of this research is to determine effects of microalloying on the possibility of modification of non-metallic inclusions. Modification with zirconium favorably affects the ductile properties of steel, and a step forward in this study is a modification of inclusions with tellurium.It is of particular importance to determine the behavior of non-metallic inclusions in the process of production of the structural part and in subsequent exploitation. Therefore, plastic processing of austenitic stainless steel was also carried out, forging and rolling with two different level of processing.

THE BEHAVIOUR OF HETEROPHASE INCLUSIONS “PHASES ARE BESIDE” UNDER STEEL PRESSURE FORMING

Purpose. The technological ductility of steels is largely determined by the behavior of non-metallic inclusions at different deformation temperatures. The aim of the work was to study the shape change of heterophase inclusions of the “phases are beside” under different conditions of steel processing by pressure. Methods. Identification of inclusions of the “phases are beside” before and after deformation according to different modes was carried out by several methods: metallographic, petrographic, X-ray spectral analysis. Results. It has been established that the phase-mineralogical composition of the heterophase inclusions of the “phases are beside” determines the processes of their change under hot and cold deformation. The level of plasticity of the phases of inclusions determines the nature of their interaction between themselves and the steel matrix during their joint deformation. A different combination of phases in the inclusions of the “phases are beside” implies a different shape change of the inclusion as a whole during hot or cold rolling of steels. Scientific novelty. The shape-changing features of heterophase inclusions of the “phases are beside” during hot and cold deformation were established. The important role of interfacial friction processes was shown, which develops on sections of the inclusion-matrix boundaries (with different inclusion phases) and on the internal boundaries in inclusions whose phases have different plasticity. It was shown that the character of the shape change of the“phases are beside” inclusions is determined by the mutual influence of inclusions phases on their joint deformation. The possibility of transforming the inclusion of “phases are beside” in the process of hot and cold deformation when machining steel with a vice is shown. Practical significance. The obtained results of the study dedicated to features formation of heterophasic inclusions of the “phases are beside” can be used in the development of technologies for producing steels with the regulated content of heterophase non-metallic inclusions, including the type of “phases are beside”. These results contribute to solving important problems associated with improving the technological ductility of steels for various purposes, as well as preventing the formation of defects during the processing of steels by pressure.

Evolution behaviour of nonmetallic inclusions in Ti-bearing 11Cr stainless steel with calcium treatment

ABSTRACTNonmetallic inclusions formed during the Ti-stabilized stainless steelmaking process can induce the clogging in the submerged entry nozzle during continuous casting. To investigate the formation mechanism of nonmetallic inclusions in Ti-stabilized stainless steel, steel specimens were taken at different stages in industrial trials. The characteristics of inclusions and the chemical compositions of steel were analysed. After 10 min of Al deoxidation, the main type of inclusions in samples was irregular MgO·Al2O3. With titanium addition after calcium treatment, the irregular dual phase CaO–TiOx–Al2O3–MgO inclusions were formed. The steel compositions of most samples were located in or close to the Al2O3–TiOx liquid oxide phase field. According to experiment and thermodynamic results, the solid CaTiO3 and/or CaO·2Al2O3 inclusions were formed during titanium addition when the molten steel contained more than 20 ppm calcium. The effect of the initial calcium content on the formation of Ca–Al–Ti–O inclusions during titanium addition was discussed.

Behavior of Non-metallic Inclusions in a Continuous Casting Tundish with Channel Type Induction Heating

A generalized three dimensional mathematical model, which adopted the Euler-Lagrange approach, has been developed for the motion of inclusions in a continuous casting tundish with channel type induction heating. The inclusion trajectories were obtained by numerical solution of the motion equation including gravity, buoyancy, drag, lift, added mass, Brownian, electromagnetic pressure and thermophoretic forces. Besides, the collision and coalescence of inclusions and adhesion to the lining solid surfaces were also taken into account. The Brownian, Stokes and turbulent collision were clarified, separately. Then the effect of induction heating power on the inclusion behavior was demonstrated. A reasonable agreement between the experimental observation and numerical results was obtained. The results indicate that the electromagnetic pressure force significantly promotes the removal of inclusions, especially for the bigger inclusion. Although the thermophoretic force goes against the removal of inclusions, its influence is negligibly small. The removal ratio of inclusions in the tundish with induction heating increases from 67.45% to 96.43%, while the power varies from 800 kW to 1200 kW. The collision and coalescence should be included when model the inclusion motion, because it can promote the removal of inclusion. The turbulent and Brownian collision becomes more active with the increasing power, while the Stokes collision is just opposite.

Mathematical Modeling of Behaviour a Liquid Steel Flow and a Non-Metallic Inclusions in the One Strand Wedge Type Tundish with a Subflux Turbulence Controller and a Low Dam

The numerical modelling technique is successfully used for simulation of liquid metal movement and behaviour of non-metallic inclusions in the continuous casting devices. The CFD (Computational Fluid Dynamic) method allows information on physical, chemical and hydrodynamic phenomenon in the metallurgical processes to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring especially of non-metallic inclusions is very essential because a quantity of non-metallic inclusions in the liquid steel limit the quality of final steel product. The paper presents the results of computing simulation of behaviour a liquid steel flow and non-metallic inclusions in the one-strand tundish with stopper rod system. The subject of simulation was a one-strand tundish of a nominal capacity of 30 tons. The tundish is used in the polish steel mill to process of continuous casting slabs. In the paper authors analysed two tundish i.e. tundish with a low dam and tundish with a subflux turbulence controller and a low dam. The Ansys-Fluent® program was used for solved mathematical model of casting process. The computer simulations were performed for unsteady and nonisothermal conditions. The population balance model was used to description of non-metallic inclusions growth process. As a result of computations, fields of liquid steel flow, fields of secondary phase volume fraction, fields of volume fraction for particular bins and non-metallic inclusions growth curve were obtained.

Investigation on Non-Metallic Inclusions in LCAK Steel Produced by BOF-LF-FTSC Production Route

The behavior of non-metallic inclusions in LCAK (low carbon aluminum killed) steel produced by BOF (basic oxygen furnace)-LF (ladle furnace) refining-FTSC (flexible thin slab continuous caster) production route was investigated. The results showed that, LF refining for LCAK steel could decrease the ωT[o] significantly, and the inclusions were modified by Ca treatment, which prevented nozzle clogging efficiently. However, owing to the unstable casting condition in the earlier stage of casting, a severe reoxidation occurred, accompanied with mold slag entrapment. The transformation of non-metallic inclusions during the steelmaking process was Al2O3 → MgO-Al2O3 type inclusion→MgO-Al2O3-CaO type inclusion with a CaS ring, and the mechanism of the transformation was proposed and discussed via thermodynamic and kinetic analysis. Besides, to avoid CaS precipitation, the product of ω2[Al] × ω[s] in steel should be less than 2.0 × 10−10 at 1873 K, which remands higher desulfurization ratio during LF refining.

Behavior of Non-metallic Inclusions in Steel during Hot Deformation and the Effects of Deformed Inclusions on Local Ductility

In order to clarify both the behavior of non-metallic inclusions during hot deformation and the effects of non-metallic inclusions on the local ductility of steel with aluminum deoxidized and containing lower sulfur content at about 0.002–0.01% were investigated. Both the commercial-quality 440 MPa-class plain carbon steel and super ultra-low carbon steel were studied. To investigate the distribution, morphology, and chemical composition, along with the change in such characteristics, during the hot deformation of non-metallic inclusions, thermo-mechanical treatment with a compression test was carried out. Moreover, the reduction of area with the tensile test species, which refers to the local ductility of steel, was examined, and the effect of the distribution, morphology, and chemical compositions of both the Al2O3 inclusions and the elongated MnS inclusions were studied.Consequently, metal sulfur content of higher than 60 ppm and elongated MnS inclusions of over 10 regarding the aspect ratio were observed. In addition, the elongated MnS inclusions had a stronger influence on local ductility than the smaller Al2O3 inclusions, and drastic effects on the nucleation of voids. Thus, a fracture is most likely to be initiated by void formation at the interface of the elongated MnS inclusions and metal matrix notched by MnS, and thus would experience coalescence in accordance with a brittle fracture in the soft MnS inclusions. The local ductility in steel including elongated MnS inclusions is small because the fracturing and deformation of metal are most likely to be related to the elongated MnS inclusions.

Numerical simulation of liquid steel flow and behaviour of non-metallic inclusions in one-strand slab tundish with subflux turbulence controller and gas permeable barrier

The paper presents computation results from the simulation of liquid steel flow in a one-strand slab tundish used in a Polish steel plant. This is a wedge type tundish with a depression in the bottom of the discharge zone. Fluent software was used for solving the mathematical model of the casting process, and Euler–Lagrange description was chosen for the description of interactions between the continuous phase (liquid steel) and the discrete phase (inert gas). To verify the mathematical model and the numerical simulation results, test results obtained from industrial experiments were applied. The internal geometry of the facility under consideration was changed by two types of flow control devices, a subflux turbulence controller and a gas permeable barrier mounted on the tundish bottom. A number of variants were tested including flowrate and position of the argon. For all variants of modification, the quantity of non-metallic inclusions removed from liquid steel has been obtained.

Numerical Simulation of Steel Flow and Behaviour of Non-Metallic Inclusions in the Six-Strand Tundish with Stopper Rod System

The numerical modelling technique is successfully used for simulation of steel flow and behaviour of non-metallic inclusions in the tundish. The CFD (Computational Fluid Dynamic) method allows information on steel motion, flow, flow turbulence and steel temperature distribution in the tundish to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring of steel flow is very essential because steel flow has influence on the behaviour of non-metallic inclusions. The paper presents the results of computing simulation steel flow and flotation of non-metallic inclusions in the six-strand tundish with stopper rod system. The subject of simulation was a six-strand tundish unprovided with flow control devices. The tundish is used in the polish steel mill to process of continuous casting billets. The Fluent program was used for solved mathematical model of casting process. The numerical simulation of steel flow was performed for whole test facility without the “symmetry” boundary condition. As a results of numerical simulation maps of directions flow and temperature of steel, Residence Time Distributions curve type of (F) and (E) and distributions of non-metallic inclusions between slag phase and particular tundish outlets has been obtained.

Behavior of nonmetallic inclusions in front of the solid-liquid interface in low-carbon steels

Behavior of nonmetallic inclusions in front of the solid-liquid interface in low-carbon steels

Behavior of nonmetallic inclusions in front of the solid-liquid interface in low-carbon steels

The present study is concerned with the interaction phenomena of nonmetallic inclusions in front of a moving solid-liquid interface. The in situ observation was done in a high-temperature experiment by using a laser microscope. Alumina inclusions in an aluminum-killed steel with low oxygen content exhibited the well-known clustering behavior. The velocity of the advancing interface first increased while approaching the particle, but became stagnant during engulfment and increased again after that. Alumina-magnesia complex inclusions in a magnesium-added steel with high oxygen content were very finely dispersed in the molten pool. These inclusions escaped from the advancing interface during solidification, but gathered again at the retreating interface during remelting. The tiny inclusions were thought to behave just as tracer particles of a local flow. The velocity of particles was measured on a video image, and the significant acceleration or deceleration was found near the interface. It was concluded that the flow was induced by the Marangoni effect due to the local difference in temperature and oxygen content in front of the interface, particularly in the case of a higher oxygen content. However, the flow was weak in the case of a low oxygen content.

Hydrogen trapping on non metallic inclusions in cr-mo low alloy steels

The behavior of non metallic inclusions was investigated on undeformed and plastically deformed ferritic steels. Damaging of non metallic particles increases with strain level. Extensive cracking of the inclusions is generated by cathodic charging at a high current density. High resolution tritium autoradiography shows that manganese sulphides containing iron, silicon-rich particles and titanium nitrides are preferential trapping sites for hydrogen. The decrease in the hydrogen diffusivity, the larger amount of diffusible hydrogen observed when the sulphur content increases and the full outgassing of hydrogen at 523 K are representative of a moderate binding energy of hydrogen with sulphide compounds.

凝固シェル近傍での介在物挙動に与える溶鋼流動の影響

In in-mold electromagnetic stirring (EMS), horizontal flow is generated by Lorenz force so that non-metallic inclusion entrapment is avoided. Though the effect of EMS is popular by many reports, there are few studies about the behavior of non-metallic inclusions near solidfied shell under horizontal flow. In this study, a model experiment using water and particles made of ion-exchange resin is performed to analyze relations between behavior of non-metallic inclusions near solidified shell and horizontal fluid. As a result of the model experiment, it is cleared that the main factor avoiding nonmetallic inclusion entrapment is the force given by the horizontal flow and that influence of Saffman force can be negligible.

Thermo-fluid-dynamics Modelling of the Solidification Process and Behaviour of Non-metallic Inclusions in the Continuous Casting Slabs.

A numerial model has been fitted and used to describe the main features of the steel casting and solidification process. Information on the interaction between the thermal aspects (temperature trends at the slab surface and development of the shell growth) and the fluid-dynamics ones (flow pattern inside the mould and at the meniscus) has been achieved. In the latter case, such a tool allows checks on the operating conditions, in particular size and shape of the Submerged Entry Nozzle (SEN). In the former, it gives data on the superheat dissipation and the shell growth rate, also allowing an evaluation on the microstructure. Starting from the so obtained thermo-fluid dynamics field, the path of typical non-metallic inclusions has finally been described, and comparison with experimental and literature data has been made as far as their impact point on the growing shell is concerned.

溶鉄の凝固界面前面における介在物と気泡の挙動

溶鉄の凝固界面前面における介在物と気泡の挙動

Numerical calculation of fluid flow in a continuous casting tundish

The deposition of deoxidation and reoxidation products in continuous casting tundish nozzles results in poor surface quality of the cast product and in extreme cases, disruption of the operating schedule. Since the flow of steel in the tundish is central to the behavior of nonmetallic inclusions in the tundish, the details of the flow field are determined numerically by appropriate solutions of the equations of change. The effects of the changes of the internal configuration of the tundish and various casting parameters on the computed velocity fields, particle trajectories, and particle residence times are investigated. The conclusions drawn from the computed results are compared with the results of various independent water model studies.

Fumeless In-Line Degassing and Cleaning of Liquid Aluminum

Arising from a basic study of the generation and behavior of non-metallic inclusions in liquid aluminum, a process has been developed for fumeless degassing and cleaning of aluminum on an in-line basis. No prior fluxing or degassing is needed in melting and holding furnaces, the metal being treated continuously in a unit placed between holding furnace and casting point. The metal first enters a degassing chamber where it is treated with nitrogen under a liquid flux cover; it then passes through a bed of flux-coated coarse refractory granules to complete the cleaning operation, and finally through a bed of uncoated coarse granules to remove entrapped flux. Over 15 million lb. of various alloys have been processed in this way. Gas contents have been lower than with conventional chlorine degassing and metal cleanliness similar to that achieved with the flake alumina filter described by Brondyke and Hess (Transactions of AIME, 1964, Vol. 230, pp 1553–56.) The process is suitable for treating primary metal and can be used to control sodium content at low levels. In addition to eliminating the need for fume treatment plant in casting shops, the process offers savings in operating cost, processing time, and metal loss through dross formation.

高炭素クロム鋼中の非金属介在物の挙動に関する研究

高炭素クロム鋼中の非金属介在物の挙動に関する研究

Study on the Behaviour of Nonmetallic Inclusions in High Carbon Chromium Steel

Study on the Behaviour of Nonmetallic Inclusions in High Carbon Chromium Steel