Inclusions In Tundish Research Articles

Evolution of Non-Metallic Inclusions in 27SiMn Steel

To study the evolution of non-metallic inclusions in 27SiMn steel, the 27SiMn steel produced using the LD-LF-CCM process was sampled in various stages in a steel factory. The evolutionary behavior of inclusion in various processes was systematically analyzed by scanning electron microscopy (SEM-EDS), and the total oxygen content and nitrogen content in 27SiMn steel were measured at various production steps. On the basis of the calcium treatment for 27SiMn steel, the equilibrium reactions for Ca-Al were calculated according to the thermodynamic equilibrium model. The results showed that the types of inclusions at the start of LF stations are mainly Al2O3-FeO and MnS-Al2O3. Before calcium treatment, the inclusions are mostly calcium aluminate and CaO-MgO-Al2O3. Compared with the process after soft blowing, the number density of inclusions in tundish increased by 77.88%, possibly due to secondary oxidation. From the soft blowing process to the continuous casting round billet, the inclusions translate into spherical CaO-MgO-Al2O3-SiO2, and a large number of CaS were observed. One part of the CaS precipitated separately, the other part was semi-wrapped with the composite inclusions. At the same time, calcium treatment increases the number density, mean diameter, and the area fraction of inclusions. The mass fraction of T.O. (total oxygen content) increased significantly after soft blowing, and the N content increased greatly from station to tundish. The change trend of N content in steel was basically consistent with that of T.O. content. It was necessary to prevent the secondary oxidation of molten steel during calcium treatment and the casting process. When the liquidus temperature of liquid steel is 1873 K, w[Al] = 0.022%, and w[Ca] in steel is controlled between 1.085 × 10−6 and 4.986 × 10−6, the Al2O3 inclusion degeneration effect is good.

Increasing efficiency of rail steel refining in CCM tundish based on rational organization of hydrodynamic processes

Quality and operational properties of rails determine duration of their operational service. The main parameters that determine quality of steel are chemical heterogeneity and presence of non-metallic inclusions in metal. Efficiency of homogenization of metal melt and its refining from non-metallic inclusions in tundish is largely determined by organization of hydrodynamic processes, internal geometry of ladle, and presence of additional refractory elements. Using physical and mathematical modeling, study of the influence of additional refractory elements of various configurations of intermediate ladle on processes of melt flow was carried out. Physical modeling of hydrodynamic processes in the tundish taking into account requirements of similarity theory was made on specially created laboratory-experimental complex. Numerical experiments were carried out using computational fluid dynamics methods (finite volumes) on three-dimensional turbulent mathematical model with a singlephase representation of metal melt flow in tundish. To evaluate efficiency of melt homogenization according to results of physical and mathematical modeling, new technique has been developed based on analysis of distribution of time of liquid placement in continuous flow reactor. According to the results of experiments, configuration of the internal volume of tundish of four-strand CCM is proposed. A construction is considered that provides effective homogenization of molten rail steel and its refining from non-metallic inclusions. The design of full-profile compartments was developed and tested under industrial conditions, which ensure rational organization of melt flows, its homogenization and efficient refining of rail steel from non-metallic inclusions in the tundish. Industrial research was carried out under the conditions of four-strand CCM No. 1 of EAF shop at JSC “EVRAZ ZSMK”.

Effect of different removal conditions on the growth and removal of inclusions in the molten steel in a two-strand tundish

In the current study, mathematical models were developed to predict the concentration, size distribution of inclusions in a two-strand tundish. The effect of the floating velocity, the velocity of the molten steel, and the turbulent fluctuation velocity on the removal of inclusions at the interface between the molten steel and slag was also studied. Meanwhile, the composition, amount, and size of inclusions in the steel were detected and the content of the total oxygen was obtained from the industrial trial. The calculated results were well validated by the measured ones. The strong stirring energy was greatly beneficial to the collision and growth of inclusions in the molten steel. When only considering the floating velocity, the removal fraction of inclusions was 23.4%. Furthermore, the contribution of the velocity of the molten steel and the turbulent fluctuation velocity to the removal fraction of inclusions at the top surface in the tundish was 23.2% and 14.5%, respectively. Finally, the mathematical model only considering the floating velocity can accurately predict the growth and removal of inclusions in the tundish.

Formation Mechanism of SiO2-Type Inclusions in Si-Mn-Killed Steel Wires Containing Limited Aluminum Content

The origin, formation mechanism, and evolution of SiO2-type inclusions in Si-Mn-killed steel wires were studied by pilot trials with systematical samplings at the refining ladle, casting tundish, as-cast bloom, reheated bloom, and hot-rolled rods. It was found that the inclusions in tundish were well controlled in the low melting point region. By contrast, MnO-SiO2-Al2O3 inclusions in the as-cast bloom were with compositions located in the primary region of SiO2, and most CaO-SiO2-Al2O3-MnO inclusions lied in primary phase region of anorthite. Therefore, precipitation of SiO2 particles in MnO-SiO2-Al2O3 inclusions can be easier than in CaO-SiO2-Al2O3-MnO inclusions to form dual-phase inclusions in the as-cast bloom. Thermodynamic calculation by the software FactSage 6.4 (CRCT-ThermFact Inc., Montreal, Canada) showed that mass transfer between liquid steel and inclusions resulted in the rise of SiO2 content in inclusions from tundish to as-cast bloom and accelerated the precipitation of pure SiO2 phase in the formed MnO-SiO2-Al2O3 inclusions. As a result, the inclusions characterized by dual-phase structure of pure SiO2 in MnO-SiO2-Al2O3 matrix were observed in both as-cast and reheated blooms. Moreover, the ratio of such dual-phase SiO2-type inclusions witnessed an obvious increase from 0 to 25.4 pct before and after casting, whereas it changed little during the reheating and rolling. Therefore, it can be reasonably concluded that they were mainly formed during casting. Comparing the evolution of the inclusions composition and morphology in as-cast bloom and rolled products, a formation mechanism of the SiO2-type inclusions in wire rods was proposed, which included (1) precipitation of SiO2 in the formed MnO-SiO2-Al2O3 inclusion during casting and (2) solid-phase separation of the undeformed SiO2 precipitation from its softer MnO-SiO2-Al2O3 matrix during multipass rolling.

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.

Numerical Simulation of Fractal Agglomerating-Growth of Al2O3 Inclusions in Tundish

Based on the Al2O3 inclusion analysis of low-carbon aluminum killed steel in tundish of a domestic steel company and fractal theory analysis, a mathematical model of fractal agglomerating-growth of Al2O3 inclusions in tundish was established. The results indicated that: large swirl flows exist in both sides of inlet, space between weir and dam, and large zone above outlet, in which monomer and agglomerated inclusion particles accumulate easily; the agglomerated inclusions with hydrodynamic diameter of 6 — 9.8 μm were quickly generated less than 16 s, but those inclusions with hydrodynamic diameter more than 11 μm were difficult to form; the number density of agglomerated inclusion rapidly increased first, then slowly reduced, so the form and quantity distribution of agglomerated inclusions can be controlled by controlling the residence time of inclusion particles in tundish.

Formation and Control of Inclusions during Steelmaking Process

The variation of non-metallic inclusions and total oxygen contents in different steel grades were investigated by taking samples in steelmaking process, including gear steel, anchor chain steel, hard wire steel, bearing steel and spring steel. The inclusions mainly were Al2O3, MnS, and their composite inclusions in aluminum killed steel at the beginning of LF refining due to addition of FeAl alloy during the tapping from EAF and feeding of Al wire in LF process, and then Al2O3 inclusion changed to the Al2O3 - CaO composite inclusions after feeding of SiCa wire. The inclusions at the beginning of LF refining mainly were MnS, SiC and their composite inclusions in non-aluminum killed steel due to addition of the composite deoxidation and slagging agents (mainly including CaC2 and SiC) when EAF taping, while the inclusions in tundish mainly were MnS, CaO - SiO2 - Al2O3 composite oxide - sulfide inclusions. It is showed that the inclusions in bearing steel and spring steel samples were mainly globular oxide inclusions and silicate inclusions with higher rated results. Therefore, the refining process should be improved to remove globular oxide inclusions. The inclusions in molten steel were controlled by enhancing the diffusion deoxidation process, adjusting and controlling the basicity and composition of refining slags, respectively, and satisfactory results were obtained. The industrial test shows that the total oxygen content of the aluminum killed steel in the test heat after feeding wire reached the minimum value, which indicates that the optimized slag has a strong ability of absorbing Al2O3 inclusions. For non-aluminum killed steel, the total oxygen content was 0.0027 % to 0.0029 % in rolled products. The inclusions in the end of refining and rolled product were small and dispersed composite inclusions, and the separate Al2O3 inclusions can not be found in the non-aluminum killed steel after optimization of the refining process.

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.

Forced flotation of inclusions in tundish

With increased usage of steel for critical applications, the demand for cleaner steel has increased. Existing technologies have been improved and new technologies are being introduced all along the process route to minimise the size and quantity of inclusions. In continuous casting, the function of tundish has changed from its early role as a liquid steel buffer to a multifunctional vessel, dominating quality adjustments, specifically inclusion flotation. To meet stringent cleanliness requirements, a methodology of forced flotation of inclusions by controlled bubbling of inert gas in tundish was developed and investigated. Location of the bubbling arrangement was optimised using the flow profile generated by water modelling experiments. Optimum gas flowrates were calculated mathematically and further adjusted with a series of experiments. Extensive plant scale trials were used to optimise the process parameters and bring the technology to practice. There was a 33–70% reduction in inclusions of size greater than 50 μm and a 13–36% reduction in inclusions 25–50 μm. Inclusion removal reduced at higher casting speeds. Under steady state conditions, efficiency of inclusion flotation was found to be a function of casting speed. Additionally, a significant reduction in oxide build-up and nozzle clogging was observed thus lengthening refractory life.

Simulation of coagulation of non-metallic inclusions in tundish and their trapping into solidified shell in continuous casting mould

A mathematical model simulating the coagulation and flotation of non-metallic inclusions in the tundish and continuous casting mould was developed based on turbulence coagulation and Stokes coagulation. From the simulation in the tundish, it was found that Stokes coagulation is dominant in the tundish. In the mould, the simulation result was that argon bubbles become the desirable sites where alumina inclusions are gathered and form large alumina clusters. The influence of the liquid steel flow in the mould applied by an in-mould electromagnetic stirring technique on the trapping rate of non-metallic inclusions into the solidified shell was examined. The horizontal flow in front of the shell was found to be effective for disturbing the trapping and decreasing the population of large non-metallic inclusions in the shallow surface layer of cast slabs. This effect was interpreted by the lift force applied to non-metallic inclusions in the velocity boundary layer formulated.