Evolution of inclusions from laddle furnace (LF) to continuous casting in Ti–Mg oxide metallurgy treatment were studied. The resuluts suggested that the composition of inclusions changed from ...MnS-MnO·SiO2 to (Ti–Ca–Mg–Al–O)–MnS. Furthermore, EDS results indicated that the content of Mg decreased because of reduction reaction, float and gasification. The average size of inclusions was decreased from 0.73 µm to 0.47 µm and the number density decreased from 977/mm2 to 595/mm2 after continuous casting. The microstructures changed from polygonal ferrite (PF) and ferrite side plate (FSP) to acicular ferrite (AF), PF and bainite (B) gradually after inclusion treatment (Ti–Mg oxide metallurgy) in LF furnace and Ca treatment in RH furnace. Heterogeneous nucleation of AF was observed on the surface of Ti–Mg oxides.
A large amount of spent MgO–C refractory is generated in steel plant every year. Because of the similarities in chemical and mineralogical composition of slag formers and MgO–C refractory, it is ...possible to reuse the spent MgO–C refractory as a steelmaking flux. To achieve this goal, it should promote the dissolution of MgO–C refractory during slag forming. In this study, the effect of slag composition on the dissolution behavior of spent MgO–C refractory in the CaO–SiO2–FeO slag system and the dissolution kinetics were investigated. It showed that the dissolution rate of MgO–C refractory was controlled by surface chemical reaction. The dissolution of MgO–C refractory led to an increase in the MgO content in slag while the FeO content decreased because the graphite in refractory was oxidized by FeO. Increasing temperature significantly promoted the dissolution of MgO–C refractory. The MgO–C refractory was readily dissolved in the low-basicity slag. A higher FeO content in slag was beneficial for the oxidation of graphite in refractory, resulting in better dissolution. The dissolution thickness of MgO–C refractory could exceed 4.0 mm under these conditions and its dissolution supplied some MgO to slag.
In this study, the effect of the silicate structure of calcium-silicate based mineral phases on their Ca elution behaviors into water was investigated. The Ca elution behaviors of Ca-silicate based ...mineral phases with different skeleton silicate structures in ion-exchanged water were analyzed using the powder leaching test. The elution amount of Ca was in the order alite (Ca3SiO5) > belite (γ-Ca2SiO4) > rankinite (Ca3Si2O7) > pseudowollastonite (α-CaSiO3) > wollastonite (β-CaSiO3) ≈ cuspidine (Ca4Si2O7F2) > diopside (CaMgSi2O6) > hedenbergite (CaFeSi2O6) > tremolite (Ca2Mg5Si8O22(OH)2) > anorthite (CaAl2Si2O8). This suggests that the elution amount of Ca decreased with the skeleton silicate structure became more complicated.
CO2 emissions from steel production account for about 8% of the global anthropogenic CO2 emissions and the majority (over 70%) of these emissions occur during the reduction of iron ore to iron. ...Hence, the steel industry is striving to reduce its dependence on carbon-based energy sources and reducing agents, like the coke used in a traditional blast furnace. Approaches such as hydrogen-based direct reduction are being considered since they can drastically reduce the overall CO2 emissions of the steel-making process. Here, we report an electrified process for reducing iron ore particles using atmospheric pressure hydrogen plasma powered by microwave energy. The process has the potential to be entirely carbon-free and overcome common challenges of other hydrogen reduction approaches, including other plasma-based approaches. Relative reduction rates achieved are as high as 15.5% /s, on par or faster than the highest rates reported in the literature operating at lower temperatures and hydrogen concentrations. When compared to thermal reduction under otherwise close to identical conditions, the microwave plasma reduction is three to four times faster, suggesting the importance of plasma generated reactive species like atomic hydrogen. A promising mass scaling is observed, with increasing the mass load 50 times requiring only 7 times longer reaction, which points to a good potential for further scale-up of the technology.
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•Carbon-free steel making can reduce current global CO2 emissions by up to 8%.•Microwave hydrogen plasma is new zero-carbon method to reduce iron ore to iron.•Rapid reduction of iron oxide to iron is possible within seconds.•Plasma method is faster than thermal reduction due to energetic plasma species.
The knowledge of FexO activities in molten slags at lower temperatures is necessary for effective dephosphorization in hot metal pretreatments. However, there have been still differences among the ...reference data in the FexO–CaO–SiO2 pseudo-ternary system at 1573 K. In the present study, the FexO activities were measured with an electrochemical technique in order to reevaluate the iso-activity curves of FexO. Subsequently, the CaO and SiO2 activities along liquidus lines were calculated by the Gibbs-Duhem equation, and the equilibrium phosphorus contents in molten iron coexisted with dephosphorization slags were estimated by using the present results.
Gas‐based direct reduction in a shaft furnace is the dominant process in the world for production of direct reduced iron. As fresh reducing gas passes through the iron ore burden, it is diluted by ...the gas emitted from the reacted iron ores which decreases the reduction potential of the reducing gas. Previous reduction experiments mostly used single pellet which could not examine this phenomenon. In this study, hematite pellets arranged in multiple layers inside a molybdenum basket are reduced isothermally at 1173–1273 K using 50% CO + 50% CO2% and 100% CO gases under flow rates of 0.2–5.0 NL min−1 to simulate the dilution of CO by CO2 in the shaft. It is discovered that the reduction of pellets in the basket is highly uneven even in pure CO atmosphere. Pellets in the middle layer are reduced ≈2 times less than the pellets in the top and bottom layers. The top side of a pellet is also less reduced than the bottom side facing the gas inlet. During melting of incompletely reduced pellets at 1873 K, intensive interaction between the unreduced iron oxides and the alumina crucible was observed. Thus, smelting of incompletely reduced iron could potentially shorten the refractory lifetime.
This article investigated the reduction of multi‐layered hematite pellets in CO‐CO2 atmosphere. The reduction degree of hematite was observed to vary across different pellet layers and within different regions inside a pellet. Pellets at the center of the samples were found to be two times less reduced than the pellets at the top and the bottom layers.
Non-metallic inclusions in steels – origin and control Costa e Silva, André Luiz Vasconcellos da
Journal of materials research and technology,
July-September 2018, 2018-07-00, 2018-07-01, Letnik:
7, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Non-metallic inclusions (NMIs) play a key role in many important properties of steel, influencing both processing and application of steel products. In this work, the current understanding of the ...origin and classification of NMIs is reviewed, highlighting the dramatic development of the last decades. This includes the discussion of the thermodynamics of inclusion formation and the current knowledge on the effects of melt shop processing variable on NMIs composition, amount and size distribution. The development of inclusion engineering – tailoring the process to obtain the desired NMIs is highlighted and the development in selected areas – tire cord, springs and bearing steels as well as prevention of nozzle clogging – is used to illustrate this development. The promising field of “oxide metallurgy” is also discussed in the context of inclusion engineering. Finally, the difficulties in meaningfully characterizing and quantifying NMIs are briefly commented. In summary it is concluded that inclusion control in steels has evolved significantly in the last decades. This is due to the progress in understanding the interplay between thermodynamics, steel and slag chemical composition as well as melt shop processing. This made possible the tailoring of non-metallic inclusions via processing, to optimize steel properties. Nonetheless, some important problems remain and must still be solved to improve inclusion control and optimization.
Phosphorus recovery from wastes has become a worldwide concern. The P-bearing steelmaking slag generated from steel plant is considered a potential phosphorus source. In this study, a novel process ...of selective leaching–precipitation–alkaline wash was proposed to recover high-quality phosphate from steelmaking slag. During leaching, most of the P was dissolved from slag and Fe was almost insoluble. Increasing temperature and solid-liquid ratio significantly suppressed the dissolution of Si due to the formation of silica sols. An excellent selective leaching of P was achieved at pH 3 and 333 K. The dissolution ratio of P reached 83.5% while only 22.6% of Si was dissolved. The residue containing 49.5% Fe2O3 and 0.9% P2O5 can be reused as a steelmaking feedstock, achieving the recycling in plant. In the dilute leachate, the precipitation of Si and Ca was significantly suppressed as the pH increased and a precipitate with higher P2O5 content and lower SiO2 content was extracted. A large amount of SiO2 was removed from the precipitate by alkaline wash. A precipitate containing 30.1% P2O5 and 45.5% CaO was recovered in this process. This study provided a cost-effective approach to recovering high-quality phosphate.
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•Increasing temperature and solid-liquid ratio reduced the dissolution of Si.•A precipitate with higher P2O5 content was extracted from the dilute leachate.•Some SiO2 was removed from the precipitate by alkaline wash.•A precipitate containing 30.1% P2O5 was recovered from slag.•Selective leaching–precipitation–alkaline wash was proposed to recover P.
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