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Laboratory experiments are performed to study the effect of T.Ca content in the molten steel on the composition, size, and quantity of inclusions. Different amounts of SiCa alloys are added into the molten steel to obtain samples with varied T.Ca contents. Samples are taken at 1, 5, 10, 15, and 20 min after the calcium addition to study the transformation of inclusions with time. After the addition of calcium into the molten steel, the size of pure liquid inclusions is small which are more difficult to be removed from the molten steel than solid ones, while partially liquid inclusions are easily removed from the molten steel so that the total oxygen content of the molten steel is lower. The size of solid inclusions is large due to their large coagulation coefficient value. The number density and area fraction of liquid inclusions are larger than solid inclusions due to the higher adhesion work required for the removal of liquid inclusions. The corrosion of MgO crucible easily occurs by the dissolved calcium in the molten steel. Then, the reaction between the reduced magnesium and inclusions in the molten can occur, leading to the generation of MgO–Al2O3 and CaO–MgO–Al2O3 inclusions. [ABSTRACT FROM AUTHOR]

The localized corrosion induced by different kinds of inclusions in low‐nickel stainless steel is studied through immersion tests and first‐principles calculations. The galvanic corrosion between the steel matrix and different kinds of inclusions occurs in the corrosive environment due to the difference in the electron work function of the steel matrix and inclusions. The electron work function of MnS, CeS, and Ce‐O‐S is smaller than that of the steel matrix, thus, these inclusions first dissolve as the anode. However, the electron work function of cerium‐containing oxides is bigger than that of the steel matrix, and the steel matrix dissolves prior to cerium‐containing oxides. The order of the volume expansion rate of pits induced by inclusions is CeS > Si‐Mn(‐Al)‐O > MnS > Ce‐C‐O‐S > Ce‐Si‐Mn(‐Al)‐O > Ce‐O‐S. For cerium‐containing inclusions, the electron work function of inclusions increases with the increase of the O/Ce ratio and the S/Ce ratio of inclusions. The order of the electron work function of cerium‐containing inclusions is cerium oxides > cerium sulfides > cerium oxysulfide. [ABSTRACT FROM AUTHOR]

Two types of inclusions in the stainless steels are detected: MnO·Cr2O3–MnS dual‐phase ones and pure MnS ones. The increase of sulfur content can inhibit the formation of MnO–Cr2O3–MnS inclusions and reduce the harm of MnO·Cr2O3–MnS inclusions on the pitting corrosion of stainless steels. When the sulfur content increases from 26 to 70 ppm, the average pitting potential increases from 0.34 to 0.4 VSCE due to the decrease in the number density of MnO–Cr2O3–MnS inclusions. A Cr‐depletion zone exists in the steel matrix around MnO–Cr2O3–MnS inclusions. The size of pits induced by MnO·Cr2O3–MnS inclusions is larger, which poses a more serious threat to the pitting resistance of stainless steels. [ABSTRACT FROM AUTHOR]

Herein, plant trials are conducted to investigate the effect of slag modification on inclusions in Si–Mn‐killed 304 stainless steels. The slag basicity has a significant influence on inclusion compositions in 304 stainless steels. The Al2O3 content in inclusions shows a slight increase tendency with the slag basicity of 1.9. The addition of CaO increases the slag basicity from 1.9 to 2.2, which is beneficial to the removal of inclusions while increasing the Al2O3 content in inclusions from roughly 20% to 40%. The low slag basicity lowers the Al2O3 content in inclusions to around 20% while resulting in a higher total oxygen (TO) at the ladle furnace (LF) end. A kinetic model of slag–steel–inclusion reactions is developed to simulate the effect of slag modification on inclusion composition using FactSage Macro Processing. Evolutions of slag, steel, and inclusions during the slag modification process are well predicted. [ABSTRACT FROM AUTHOR]

The transformation of inclusions in a heavy rail steel during heating is investigated in laboratory experiments. When the steel is heated at 1000–1300 °C, inclusions of CaO–SiO2–Al2O3–MgO are transformed into CaS–MgO·Al2O3 ones and the contents of CaS and Al2O3 in inclusions increase, whereas those of CaO and SiO2 decrease. When the steel is heated at 1400 °C, the MgO·Al2O3 phase in inclusions precipitates, whereas CaS, CaO, and SiO2 still exist, which is caused by the lower thermodynamic driving force at high temperature. With the holding time increasing from 0 to 7 h, the composition of inclusions tends to the equilibrium value which is predicted using Factsage. The transformation phenomenon is validated using thermodynamic analysis and a kinetic model is established to predict the composition of inclusions during heating. The MgO·Al2O3 phase formed in inclusions in the steel during heating results in an exposure of MgO·Al2O3 spinel inclusions after rolling, which are rigid and harmful to the performance of steel rails. [ABSTRACT FROM AUTHOR]

Industrial trials and theoretical analysis are performed to study the effect of addition sequences of calcium and sulfur on inclusions in a calcium‐treated and resulfurized Al‐killed steel. The evolution path of inclusions at each production step is Al2O3 → Al2O3–CaO–MgO → Al2O3–MgO and Al2O3–CaS–CaO → Al2O3–MgO–CaS with the calcium treatment before sulfur addition. Calcium treatment after the sulfur addition promotes the formation of (Mn, Ca)S complex sulfide inclusions and is beneficial to modify the shape of sulfide inclusions to spherical ones in the rolled steel, where the size of sulfide inclusions is smaller than that of the heat of calcium treatment before sulfur addition. The relative plasticity of (Mn, Ca)S complex inclusions has a linear relationship with the content of CaS. Thermodynamic calculation results show that the critical solute sulfur content corresponding to the formation of CaS in the molten steel decreases sharply with the increase of the calcium content. With the same amount of calcium in the steel, the calcium treatment after sulfur addition promotes the formation of small (Mn, Ca)S complex sulfide inclusions with lower deformability during the hot rolling process, which is helpful for the mechanical property of the calcium‐treated and resulfurized Al‐killed steel. [ABSTRACT FROM AUTHOR]

• A full 3D numerical model for transient flow field, temperature, solidification, and segregation during slab continuous casting. • An improved capture criterion for inclusion entrapment that including the primary dendrite arm spacing, solute concentration, force analysis, and critical capture speed is proposed. • Prediction on the number, size, and spatial distribution of inclusions on the entire cross section of the CC slab. • Four accumulation zones of inclusions along the thickness of the CC slab are predicted. In the current study, the LES turbulent model, heat transfer, solidification, species transport model, and discrete phase model (DPM) were coupled to investigate the three-dimensional transient flow, temperature, solidification, segregation, and inclusion transport during the slab continuous casting (CC) process. The number, size, and spatial distribution of inclusions on the entire cross section of the CC slab were successfully predicted using the coupled full solidification model, DPM, and capture criteria at the solidification front. The improved capture criteria that considering the primary dendrite arm spacing (PDAS), different forces acting on inclusions, and the critical capture speed, successfully eliminated the banded distribution characteristics of inclusions under the simple capture criterion. The prediction results were in good agreement with the detection results. Four accumulation zones of inclusions along the thickness of the CC slab were predicted, including the 1/4 thickness and 3/4 thickness from the loose side, and the layer beneath the surface of the CC slab. Two accumulation zones near the layer beneath the surface of the CC slab were issued from the double roll flow pattern in the CC strand. The probability of inclusions contacting the solidification front in the upper recirculation zone increased, increasing the entrapment rate. The accumulation zones near the 1/4 thickness and 3/4 thickness from the loose side were corresponded to the peak value of the Marangoni force on inclusions at the 1/4 thickness and 3/4 thickness from the loose side. The Marangoni force increased the probability of inclusions being pushed to the solidification front. In addition, the accumulation near the 1/4 thickness from the loose side became more severe as the diameter of the inclusions increased due to the buoyancy. [Display omitted] [ABSTRACT FROM AUTHOR]

In the current study, laboratory experiments of the slag‐steel reaction are performed to investigate the effect of CaF2 contents in the refining slag on the inclusion absorption of the bearing steel. The increase of the CaO/Al2O3 ratio effectively enhances the absorption of inclusions by slag. The increase of the CaO/Al2O3 ratio enhances the driving force of the inclusion dissolution and lowers the slag viscosity. It is noted that the excessive CaO/Al2O3 ratio led to the formation of solid phases in the slag, lowering the absorption effect of slag. The appropriate addition of CaF2 in the slag is helpful to remove inclusions while aggravating the corrosion of MgO crucibles. The addition of CaF2 mainly reduces the viscosity and melting temperature of slag. The inclusion removal factor is proposed to effectively evaluate the inclusion removal rate in steel during slag steel reaction. As a result, the most recommended composition of slags is 7% CaF2; the CaO/Al2O3 ratio is 2.0. [ABSTRACT FROM AUTHOR]

Abstract: Filters coated with AlF3 can be used to filter molten aluminum to simultaneously remove nonmetallic inclusions and dissolved alkali and alkaline earth metal impurities. Coating experiments were carried out in which anhydrous HF gas was generated from reactions involving NaF or CaF2 and concentrated H2SO4, and used in a reaction with Al2O3 ceramic foam filter to produce a layer of AlF3 coating on the surface of the Al2O3 filter. Samples from these experiments were studied by X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Preliminary results of the coating experiments showed that it is possible to coat Al2O3 filters with AlF3 by this method. Increasing the pressure of HF gas increased the yield of AlF3 in the filter. Theoretical evaluation of the removal efficiency of dissolve impurity elements showed that dissolved calcium can be removed up to 99.8% within 30s of contact time between the filter material and the molten aluminum. [Copyright &y& Elsevier]

Abstract: This study investigated the removal of SiC and Si3N4 inclusions from top-cut solar cell silicon scraps by filtration with foam filters. Laboratory experiments tested various models for the removal mechanism of inclusions and the efficiency of ceramic foam filters. Inclusions in solar cell silicon top-cut scraps were mainly needle-like Si3N4 particles and lumpy SiC inclusions. SiC and Si3N4 inclusions sometimes agglomerated as clusters. Si3N4 inclusions were usually more than 500μm long with diameters of ∼20μm, and SiC inclusions were usually smaller than 500μm. After filtration, no Si3N4 inclusions were found. The remaining inclusions were mainly SiC inclusions smaller than 10μm. Filters with smaller pores improved the removal of inclusions. It was discovered that contamination of the silicon may occur from components of the filters themselves, especially from binders. The crucible was also a source of contamination. A filtration process that does not produce contamination of its own should be developed before being used in real industrial processes. Mechanisms for the removal of inclusions from silicon through filtration are as follows: (1) cake filtration, for the removal of large Si3N4 rods and large SiC inclusions; (2) deep-bed filtration of smaller Si3N4 inclusions and most SiC particles; (3) formation of large SiC clusters and bridges across pores, and (4) silicon dissolution into carbon filters, and a subsequent reaction to form layers of SiC. [Copyright &y& Elsevier]

The effect of calcium addition on inclusions (oxides and sulfides) in heavy steel ingot is investigated via lab experiments and thermodynamic calculation. The characteristics (chemistry, size, morphology, and number) of inclusions in the steel samples are investigated by scanning electron microscope with an energy‐dispersive spectrometer. The three‐dimensional morphology of inclusions is investigated by the nonaqueous solution electrolysis method. Inclusions in the fast‐quenched steel are changed from Al2O3 to Al2O3–CaO, Al2O3–CaO–CaS, and CaS after Ca addition. After slow cooling, inclusions in the solid steels are changed from Al2O3, single MnS, and Al2O3–MnS complex inclusions to Al2O3–CaO–CaS–MnS and CaS–MnS. The evolution trajectory of inclusions is Al2O3→Al2O3–CaO→Al2O3–CaO–CaS→Al2O3–CaO–CaS–MnS. With increasing Ca content in the steel, the number density and proportion of single MnS inclusions decrease. The formation mechanism of inclusions after Ca addition is explained by thermodynamic calculation. [ABSTRACT FROM AUTHOR]

Herein, the effect of total sulfur (T.S) on the transformation of inclusions in Al‐killed steels is investigated through lab experiments and kinetic calculations. During the heating process, CaS content in inclusions obviously rises up, while the CaO content reduces. The CaO content in inclusions with 11 ppm S in steel is higher than 15%, while it is less 5% for the steel with 25 ppm S. The initial CaO–Al2O3 inclusions before heating change to CaS–MgO–Al2O3 at 1200 °C. The higher T.S promotes the transformation of inclusions in low sulfur Al‐killed steels, leading to the higher CaS content in inclusions after the heat treatment. A kinetic model is developed to predict the transformation of inclusions in low sulfur Al‐killed steels during the heat treatment. The transformation fraction of inclusions decreases with the larger size of inclusions and increases with the higher T.S content in steel at the heating temperature. [ABSTRACT FROM AUTHOR]

The existence of the dissolved aluminum and other impurity elements in alloys would inevitably lead to the formation of the Al2O3 component of inclusions in Si–Mn killed steels. Herein, the effect of dissolved oxygen at the endpoint of basic oxygen furnace (BOF) on the control of inclusions in a Si–Mn killed steel is investigated. With the increase in the dissolved oxygen at the BOF endpoint, the (FeO + MnO) content in the refining slag increases and the dissolved aluminum in the steel decreases as a whole. Meanwhile, the proper increase in the dissolved oxygen hardly deteriorated the cleanliness of the steel. As the equilibrium dissolved oxygen at the BOF endpoint increased from 148 to 402 ppm, the Al2O3 content of inclusions could be lowered to <4 wt%. Both industrial trials and the thermodynamic consideration indicate that increasing the dissolved oxygen at the endpoint of BOF can be an efficient approach to achieve the ultralow Al2O3 content of inclusions in the Si–Mn killed steel due to the oxidation of the dissolved aluminum by the oxygen both in the molten steel and in the refining slag. [ABSTRACT FROM AUTHOR]

Herein, laboratory experiments are conducted to evaluate the effect of sulfur and lanthanum content in the steel on the modification of inclusions. The amount, composition, morphology, and size of nonmetallic inclusions in the steel are observed using an automatic scanning electron microscope. Results show that as the lanthanum content in the steel increased from 0 to 72 ppm, the inclusions in the steel with 12 ppm sulfur are modified in the following order: Al2O3–CaO–MgO → LaAlO3 → LaAlO3–La2O2S → La2O2S. Similarly, when the sulfur content is 27 ppm, inclusions transformed in the order of Al2O3–CaO–MgO → LaAlO3 → LaAlO3–La2O2S → La2O2S → La2O2S–LaxS → LaxS as the lanthanum content increases from 0 to 150 ppm. Thermodynamic analysis using FactSage based on a private database is employed to reveal the mechanism for the modification of inclusions. Additionally, a kinetic model is established to study the transformation rate of inclusions in the steel after the addition of lanthanum and sulfur. Liquid Al2O3–CaO–MgO inclusions disappear after 800 s when the steel contains 12 ppm sulfur and 12 ppm lanthanum. The composition of inclusions is 53%LaAlO3–47%La2O2S at 1800 s, while it is 100%La2O2S and 80%La2O2S–18%LaxS–2%CaS when the lanthanum content is 33 and 72 ppm, respectively. [ABSTRACT FROM AUTHOR]

Herein, the cerium treatment is used to modify large MnS inclusions in a 303‐ton carbon manganese steel ingot. When the cerium content in steel in the tundish is 90 ppm, the inclusions are CeAlO3 with a small amount of Ce2O2S. The precipitation sequence of inclusions during the solidification and cooling process in the ingot is MgO·Al2O3 + CeAlO3→Ce2S3→MnS→MgS. Due to the inevitable macrosegregation, a small amount of elongated MnS inclusions is precipitated at the radial center. The maximum diameter is 257.80 μm, and the average aspect ratio is 3.28. For heterogeneously nucleated sulfide, the average diameter is less than 13.39 μm, and the average aspect ratio is less than 1.88. The morphology of MnS inclusion is well controlled when the mass ratio of Ce/S in steel is in the range of 0.7–2.8. The average aspect ratio of homogeneously nucleated MnS is less than 1.9. In addition, the formation of CeAlO3 clusters is avoided. According to the atomic mismatch obtained by the edge‐to‐edge matching model, the possibility of heterogeneous nucleation of MnS on the oxide core is CeAlO3 > Ce2O2S > MgO·Al2O3. The Ce2S3 inclusions are mainly precipitated with the core of MgO·Al2O3. [ABSTRACT FROM AUTHOR]

The effect of cerium on inclusions and solidification structure of a low‐nickel Si–Mn‐killed stainless steel is studied using laboratory experiments. When the cerium content in steel increased from 0 to 250 ppm, modification sequence of inclusions is Si–Mn(–Al)–O and MnS → Ce–Si–Mn–O–S → Ce(–Si)–O–S → CeS and CeC2. The number density and area fraction of inclusion first decrease with the increase in the cerium content and then increase due to the formation of CeC2 inclusions when the cerium content is bigger than 150 ppm, which is precipitated in solid steel during solidification. When the cerium content increases from 0 to 250 ppm, the fraction of equiaxed grain zones of steel ingot first increases and reaches a maximum value when the cerium content is 54 ppm; then the fraction of equiaxed grain zones decreases with the increase of the cerium content. 2D lattice misfit calculations are performed and it is found that there are no heterogeneous nucleation cores in the steel without cerium during solidification. For the steel with cerium, Ce4.67Si3O13, Ce2O2S, and CeS inclusions act as heterogeneous nucleation cores, increasing the fraction of the equiaxed grain zone. Bigger effective heterogeneous nucleation cores number density leads to a larger fraction of the equiaxed grain zone. [ABSTRACT FROM AUTHOR]

Based on the principle of minimum Gibbs free energy, a thermodynamic model is established to predict the composition of inclusions in the Al‐killed steel during the calcium treatment process. The Wagner model combined with coexistence theory is applied to calculate the Gibbs free energy of the steel‐inclusion system. The composition evolution of inclusions is accurately predicted through the current thermodynamic model which is widely applied to predict the modification of inclusions by the calcium treatment process with different contents of total oxygen (T.O), total sulfur (T.S), and total calcium (T.Ca) in the molten steel. Alumina inclusions can be modified to liquid calcium aluminate inclusions with appropriate T.Ca contents. Solid CaS or CaO inclusions can be formed as a result of the excessive calcium addition to molten steel, while the insufficient calcium addition can hardly modify alumina inclusions to liquid ones. The effect of the T.O and T.S contents on the liquid window is also discussed. The relationship between the value of T.S/T.O in the molten steel and the composition of inclusions is also studied. Based on the established thermodynamic model, a software for the precise control of inclusions is also developed to guide the calcium treatment operation timely in the accrual refining process. [ABSTRACT FROM AUTHOR]

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 LaSx shell is preferentially generated at the outside of Al2O3 and forms multiphase inclusions. With time increasing, the La2O2S or LaSx shell gradually reacts with the Al2O3 core and generates stable lanthanum‐containing inclusions. At the initial stage of lanthanum treatment, many transient inclusions including LaSx, 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 → LaSx, which is consistent with thermodynamic analysis. [ABSTRACT FROM AUTHOR]

Laboratory experiments are performed to study the transient evolution of inclusions in Si–Mn‐killed stainless steels with additions of 40, 100, and 400 ppm cerium. With the increase of the cerium content in the molten steel, the evolution path of inclusions is Al2O3–SiO2–MnO–CaO → Ce2O3–Al2O3–SiO2–MnO–CaO → Ce2O3 → Ce2O3–CeS. The addition of 40 ppm cerium gradually increases the Ce2O3 content in liquid oxide inclusions. After the addition of 100 ppm cerium, inclusions first evolve to Ce2O3–Al2O3–SiO2–CaO–CeS, then to Ce2O3. The CeS is generated as a transient product then disappears. After the addition of 400 ppm cerium, liquid Al2O3–SiO2–MnO–CaO inclusions are modified to solid Ce2O3–CeS ones. The addition of 40 ppm cerium into the steel lowers the size from 1.74 to 1.53 μm. After the addition of 100 and 400 ppm cerium into the steel, the size of inclusions immediately decreases due to the formation of small Ce2O3–CeS inclusions and then increases owing to the collision of solid inclusions. A higher cerium content in the steel promotes the collision of Ce‐rich inclusions. [ABSTRACT FROM AUTHOR]

In the current study, the entrapment of inclusions by hooks under electromagnetic brake (EMBr) is investigated through hook reveal and inclusion detection at the subsurface of slabs. Simulation is performed to present the fluid flow and the temperature at the meniscus of the mold. With the application of EMBr in the simulation, the steel jet from the submerged entry nozzle (SEN) deflected upward, the speed of upper backflow increased, and the temperature of steel at the meniscus also increased. The measured average depth of hooks and the number density of >10 μm inclusions without EMBr are larger than those with EMBr. With the application of EMBr, the high temperature of the liquid steel at the meniscus prevented the growth of hooks, and small hooks could only capture few inclusions. Hence, the surface quality of slabs could be improved with EMBr. The entrapment of inclusions by hooks under electromagnetic brake (EMBr) is investigated through mathematical simulation, hook reveal, and inclusion detection at the subsurface of slabs. With the application of EMBr, the high temperature of the steel at the meniscus prevents the growth of hooks, small hooks could only capture few inclusions, and then the surface quality of slabs is improved. [ABSTRACT FROM AUTHOR]

• Both micro-sized inclusions and fine precipitates were statistically analyzed. • Proper La addition reduced inclusions, and enhanced grain size and texture factors. • The steel with 0.0006 wt% La possessed the best magnetic properties. • Excess rare earth sulfides deteriorated grain size and textures of steels. The effect of rare earth elements (REMs) on the magnetic properties of non-oriented electrical steels was studied using industrial trials. The variation of the magnetic properties was discussed in terms of the effect of inclusions, precipitates, grain size, and textures in the steel with and without REMs. Inclusions of MgO·Al 2 O 3 -CaS and (Mg, Mn, Ca)S in REMs-free steel were modified into composite ones of MgO·Al 2 O 3 -LaAlO 3 , La 2 O 2 S-MgO and (La, Ca)S in the steel with 0.0006% lanthanum, and to (La, Ce) 2 O 2 S-CaS-MgO, (Ce, La)S in the steel with 0.0007% lanthanum and 0.0015% cerium. The number density of fine MnS was remarkably decreased by the addition of REMs, leading to an increase in the average grain size. The steel containing 0.0006 wt% lanthanum possessed the best combination of core loss and magnetic induction due to the decrease of micro-sized inclusions and fine MnS, the increase of grain size, and the optimization of recrystallization textures. For the steel with excess REMs addition, the large number density of rare earth sulfides with the size of approximately 1 μm tended to deteriorate the grain size and textures. [ABSTRACT FROM AUTHOR]

Inclusions in 304 stainless steels are transformed from manganese silicate to manganese chromite (spinel) upon heating in the range of 1000–1350 °C, while this transformation is not observed when heating temperature is 1400 °C. Thermodynamic analysis with software FactSage™ is applied in interpreting the transformation. Manganese chromite spinel, with light color under SEM, is deemed to be formed on the surface of MnO–SiO2 inclusions by the reaction between Cr in steel matrix and MnO–SiO2 in inclusions. Heating experiments with different time at 1235 °C (rolling insulation temperature) are carried out to confirm the kinetics of the transformation reaction. Mass transfer coefficients of inclusions' composition, SiO2, MnO, and Cr2O3 are ranging from 5 × 10−7 to 9 × 10−7 m s−1, depending on diameters and components of inclusions. [ABSTRACT FROM AUTHOR]