Formation mechanism and control of MgO·Al_2O_3 inclusions in non-oriented silicon steel

On the basis of the practical production of non-oriented silicon steel, the formation of Mg O·Al2O3 inclusions was analyzed in the process of ＂basic oxygen furnace（BOF） → RH → compact strip production（CSP）＂. The thermodynamic and kinetic conditions of the formation of Mg O·Al2O3 inclusions were discussed, and the behavior of slag entrapment in molten steel during RH refining was simulated by computational fluid dynamics（CFD） software. The results showed that the Mg O/Al2O3 mass ratio was in the range from 0.005 to 0.017 and that Mg O·Al2O3 inclusions were not observed before the RH refining process. In contrast, the Mg O/Al2O3 mass ratio was in the range from 0.30 to 0.50, and the percentage of Mg O·Al2O3 spinel inclusions reached 58.4% of the total inclusions after the RH refining process. The compositions of the slag were similar to those of the inclusions; furthermore, the critical velocity of slag entrapment was calculated to be 0.45 m·s^-1 at an argon flow rate of 698 L·min^-1, as simulated using CFD software. When the test steel was in equilibrium with the slag, [Mg] was 0.00024wt%–0.00028wt% and [Al]s was 0.31wt%–0.37wt%; these concentrations were theoretically calculated to fall within the Mg O·Al2O3formation zone, thereby leading to the formation of Mg O·Al2O3 inclusions in the steel. Thus, the formation of Mg O·Al2O3 inclusions would be inhibited by reducing the quantity of slag entrapment, controlling the roughing slag during casting, and controlling the composition of the slag and the Mg O content in the ladle refractory.

A review of use of metallurgical slag for its carbonation products:processes,crystallization behavior,and application status

In response to the pressing global issue of reducing carbon emissions and the crucial technical challenges of fully utilizing steel slag,researchers have been studying an accelerated carbonation process that entails the carbonation of basic oxides in steel slag to store CO_(2).However,despite its promising potential,the process has yet to see widespread industrial application.The latest research progress in the area of mineral carbonation processes,both direct and indirect,that are used to capture,utilize,and store carbon in steel slag are summarized.Given the limited scale of steel slag carbonation and the underutilized products that can be derived from it,a new research focus is proposed for examining the regulation of calcium carbonate crystal forms during carbonation using the Ca source in steel slag.Precise control of synthesis variables will help to ensure accurate control of calcium carbonate precipitation in the carbonation process.A summary of the effects of synthesis variables on CaCO_(3)crystal form and the latest research findings on controlling aragonite morphology are provided.The review is concluded with a discussion of the potential applications and future development prospects of CaCO_(3)whiskers.

Hot Ductility of Ti-V Bearing Microalloyed Steel in Continuous Casting

Hot ductility of Ti-V bearing steel was studied by theoretical calculation and thermal simulation experi ment. Meanwhile, microsegregation and precipitates were analyzed. The results showed that elements S, Ti and O were enriched at the grain boundaries, while the hot ductility was deteriorated by inclusions of （Fe, Mn, Si, Al）（S, O） in the interdendritic region. At tbe temperature of 1 100℃, large TiN particles had little effect on hot ductility. In the temperature range from 975 to 925 ℃, reduction of area （R. A） declined rapidly from 81. 88% to 63.16% with the size of particles decreasing from 40 to 20 nm and quantity increasing from 1.4 to 11.9 μm 2, respectively. In the temperature range from 875 to 825℃, R. A reduced unobviously from 35.14% to 28.6% with ferric films thickening gradually. The critical stress, 88.79 MPa, was equal to tensile strength at 825℃. Intergranular fracture was easy to occur with higher critical stress below 825℃.

Leaching behavior and mineralogical evolution of vanadium released from sodium roasted-acid leaching tailing of vanadium slag

The sodium roasted-acid leaching tailing(SRALT)of vanadium slag with a certain amount of vanadium exhibits potential environmental risk.To investigate the leaching behavior of vanadium from the SRALT,neutral batch leaching tests were performed.The evolution of vanadium concentration,pH,redox potential(Eh),dissolved oxygen,and conductivity as a function of time was measured.Pourbaix diagrams of V–H2O system with different vanadium concentrations were obtained to identify the ionic speciation of vanadium in leachate.X-ray diffraction,X-ray photoelectron spectroscopy,field emission-scanning electron microscopy,and thermogravimetry–differential scanning calorimetry analysis were conducted to investigate the mineralogical evolution of the SRALT during the leaching process.It was found that the major minerals of the original SRALT are titanomagnetite,spinel,olivine,and augite.The valence states of V existing in the original SRALT are V^(3+)and V^(5+).The pH and Eh values of the obtained leachates are 10.00–10.58 and(−43)–(+67)mV,respectively.In this pH and Eh region,the released vanadium is mainly present as HVO_(4)^(2−).The FeOOH and CaCO_(3)would form during the leaching process.The HVO_(4)^(2−)would be mainly adsorbed by the FeOOH and slightly incorporated into the CaCO_(3),resulting in the decline in the vanadium concentration.The vanadium concentration above 27 mg L^(−1)and the dissolved oxygen value below 5.0 mg L^(−1)can be obtained after a short leaching period.As a V(V)-releasing and oxygen-depleting substance,the leaching toxicity of the SRALT should not be ignored.

Properties of ten-year-aged argon oxygen decarburization stainless steel slag

The characteristics of argon oxygen decarburization slag(AODS)for smelting stainless steel that has been aged for 10 years were analyzed.Three types of AODSs distributed at three positions in a slag heap were sampled for comparison experiments.Chemical analysis,mineral phase identification,thermogravimetric analysis,and micromorphology analysis were used to study the element migration trends and carbonation behavior of AODS after long-term aging.Sequential leaching tests were performed to study the chromium leachability of the aged AODS.The results show that during the long-term aging process,the AODS heap had undergone oxidation and carbonation,accompanied by element migration and mineralogical evolution.The surface slag had the highest degree of carbonation but the weakest chromium leachability.The chemical composition of the middle slag was the closest to that of the original slag.In the bottom steel slag,in addition to magnesium,certain depositions of other elements were present.The matrix phases in the aged slag were dicalcium silicate and merwinite,and the chromium was mainly wrapped in these matrix phases in the form of oxides,spinels,or alloys.Under the combined effects of carbonation and oxidation,the leaching characteristics of the chromium in the aged slag varied greatly depending on the location.The bottom slag had the strongest chromium leachability,and the hexavalent chromium had long-term continuous leachability.

Kinetic model of chromium release from argon oxygen decarburisation(AOD)slag in a neutral leachate

Valorisation of argon oxygen decarburisation(AOD)slag,a suitable recycling resource,is limited by the release of a notable amount of heavy metals,such as chromium.The mineralogical component of AOD slag was characterised by X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray spectrometry.To explore the release kinetics of chromium from AOD slag,neutral leaching tests were performed at various temperatures.The results indicated the existence of two leaching stages:quick and slow leaching stages.In 2 h,the chromium release fraction increased sharply as the leaching time increased.As the leaching time in creased,the chromium release rate gradually decreased.Based on the shrinking core model,chromium release kinetic models for the quick and slow leaching stages from the AOD slag were independently determined.The chromium release was controlled by solid product diffusion during the quick leaching stage and a complicated process in the slow leaching stage.The activation energy of chromium leaching was calculated based on the Arrhenius equation.Solid product diffusion was the velocity-determining step during the 2 h leaching process.In the slow leaching stage,chromium release was controlled by complicated hybrid control dominated by solid product diffusion.