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1.
Thermodynamic properties of chromium oxides in molten slags are very important for optimization of stainless steel refining processes as well as reduction processes of chromium ores. The solubility of chromite into molten slags has been found to vary drastically with oxygen partial pressure and slag composition in the former studies by the authors. In the present study, activity data and redox equilibria of chromium oxides measured under moderately reducing conditions, PO2= 6.95×10?11 atm, at 1873 K are summarized. For the CaO‐SiO2‐CrOx system, the activity coefficient of chromium oxide increased with increasing basicity and the optimized slag composition for stainless steel refining is assessed as that saturated with CaCr2O4 and Cr2O3 using the phase relations determined. On the other hand, the presence of MgO and Al2O3 brings about different behaviour of chromium oxide activity and redox equilibria and the 44 mass per cent CaO ‐ 39 mass per cent SiO2 ‐11 mass per cent Al2O3 ‐ 6 mass per cent MgO slag is recommended to reduce the chromium oxidation loss in the practical stainless steel refining process at 1873 K. 相似文献
2.
Juliana Gutirrez‐Paredes Antonio Romero‐Serrano Gabriel Plascencia‐Barrera Marissa Vargas‐Ramírez Beatriz Zeifert Víctor Arredondo‐Torres 《国际钢铁研究》2005,76(11):764-768
Experimental and theoretical studies were performed in order to estimate the effect of the basicity of the slag as well as the amount of reducing agents on the reduction of chromium oxide from a slag in contact with molten steel at 1600 °C. The aim of this work was to compare the efficiency of magnesium and silicon as reducing agents of Cr2O3. The slag system contained CaO, MgO, SiO2, CaF2 and Cr2O3 together with Fe‐alloys (Fe‐Si or Fe‐Si‐Mg). The maximum Cr yield was about 81% with Fe‐44%Si‐9%Mg and 88% with Fe‐75%Si. That means that the reducing effect of Mg was much better than that of Si. Some experiments were conducted to study the effect of initial Cr in steel on the chromium oxide reduction reaction. Three initial Cr contents were tested (0.15, 2 and 4 mass%). It was found that chrome was partially bound into stable spinel phase MgO·Cr2O3 in the final slag. Thermodynamic estimations were made to determine the effect of process temperature, slag basicity and the amount of reducing agents in the slag on the Cr recovery. The efficiency of Cr reducing agents increased in the order: Si, Al, Ca and Mg. The Cr yield increased with slag basicity and amount of reducing agents. 相似文献
3.
The slag system of CaO‐SiO2‐Al2O3‐MgO‐Cr2O3‐MnO‐FetO relevant to refining chromium‐containing steels such as bearing steel is thermodynamically assessed at 1873 K. The activity coefficient of FetO shows an initially rapid increment followed by a gradual reduction according to Cr2O3 content at a constant basicity, and decreases with increasing slag basicity. γMnO is decreased abruptly by increasing Cr2O3 content and thereafter, maintains a nearly constant level. From the standpoint of inclusion control, the Cr2O3 presence in ladle refining slags is thermodynamically harmful in that it minimizes the inclusion level by inducing the increment of γFetO even though Cr2O3 exists in extremely small amounts. However, it is beneficial in that it diminishes AI reoxidation by decreasing γMnO. The presence of carbon in slag decreases γFetO and γMnO, which turns out to be favourable for the reduction of Al reoxidation. The thermodynamic equilibria of chromium and manganese are quantified in terms of FetO and Cr2O3 content as well as slag basicity by using multiple regression analysis. LCr and LMn are increased by the presence of Cr2O3, indicating a low recovery efficiency of Cr and Mn in the treatment of ferroalloy addition. In determining LS values, Cr2O3 is not so important as the basicity of slags. 相似文献
4.
Cooling regime of stainless-steel slag has a great influence on the migration rule of chromium. Effect of cooling rate on chromium distribution in CaO–SiO2–MgO–Al2O3–FexO–Cr2O3 system has been studied by FactSage, XRD and SEM-EDS in this paper. Results showed that the main phases in stainless-steel slag are spinel, bredigite, wustite, lime and periclase. Chromium was enriched in the stable phases. With the decrease in cooling rate, the size of chromium-rich phase increased relatively while chromium content in spinel phase reduced. Rapid cooling was favourable to the chromium enrichment in spinel phase in high basicity (high than 2.0) stainless-steel slag. 相似文献
5.
《钢铁冶炼》2013,40(6):425-436
AbstractA study of the typical characteristics of electrical arc furnace (EAF) slags in the production of the stainless steel (AISI 304L) was carried out. Twenty-eight slag samples were taken from 14 heats. Simultaneously with each slag sampling, the temperature of the steel was measured, and one steel sample was taken. The selected slag samples were studied both using SEM–EDS and light optical microscopy. Computational thermodynamics was used as a tool to predict the equilibrium phases in the top slag as well as the amount of these phases at the process temperatures. It was observed that, at process temperature, the stainless EAF slag generally consists of liquid oxides, spinel particles and metallic droplets. Under normal operation, the amount of spinel particles is 2–6 wt-%. In addition, the influence of the slag temperature, basicity, MgO content and Cr2O3 content on the amount of spinel precipitates and thereby on the foaming index of the top slag is also illustrated and discussed. More specifically, it was found that, within the compositional range of the slag samples, the critical parameter affecting the amount of solid spinel particles in the slag is the chromium oxide content. 相似文献
6.
《钢铁冶炼》2013,40(1):22-28
AbstractKinetic experiments were performed in an induction furnace to investigate the reduction of chromite ore by carbon dissolved in a high carbon ferrochromium alloy melt under conditions of varying Cr2O3 concentration, slag basicity, and temperature. The results obtained show that chromite reduction by dissolved carbon in slag systems of the type MgO-CaO-SiO2-FeO-Cr2O3- Al2O3 occurs principally by a stagewise process encompassing an intermediate reaction in which the divalent chromium oxide species is involved. During the fast period, Cr2O3 reduction is controlled by the diffusion of oxygen species in the slag for which a mass transfer coefficient of 0·003 cm s-1 was calculated. An activation energy value of 117 kJ mol -1 obtained for the reduction of Cr2O3 implies the rate controlling step is mass transfer of Cr2O3 from the slag to the slag/metal interface, since activation energies for metal phase control are typically <70 kJ mol -1. The second period represents a pseudo-equilibrium condition with respect to Cr2O3 reduction that is probably under thermodynamic control by a step or mechanism involving the reduction of divalent chromium oxide to chromium. 相似文献
7.
The reduction of chromium oxide from a basic steelmaking slag (45 wt pct CaO, 35 wt pct SiO2, 10 wt pct MgO, 10 wt pct A12O3) by silicon dissolved in liquid iron at steelmaking temperatures was studied to determine the rate-limiting steps. The reduction
is described by the reactions: (Cr2O3) + Si = (SiO2) + (CrO) + Cr [1] and 2 (CrO) +Si = (SiO2) + 2 Cr [2] The experiments were carried out under an argon atmosphere in a vertical resistance-heated tube furnace. The
slag and metal phases were held in zirconia crucibles. The course of the reactions was followed by periodically sampling the
slag phase and analyzing for total chromium, divalent chromium, and iron. Results obtained by varying stirring rate, temperature,
and composition defined the rate-limiting mechanism for each reaction. The rate of reduction of trivalent chromium (reaction
[1] above) increases with moderate increases in stirring of the slag, and increases markedly with increases in temperature.
The effects of changes in composition identified the rate-limiting step for Cr+3 reduction as diffusion of Cr+3 from the bulk slag to the slag-metal interface. The rate of reduction of divalent chromium does not vary with changes in
stirring of the slag, but increases in temperature markedly increase the reaction rate. Thus, this reaction is limited by
the rate of an interfacial chemical reaction. The reduction of divalent chromium is linearly dependent on concentration of
divalent chromium, but is independent of silicon content of the metal phase. 相似文献
8.
The influence of basicity and Al2O3 content of LF refining slag on T.[O] (total oxygen) as well as type, number and size of non-metallic inclusions in Al killed 60Si2MnA spring steel was investigated. The results showed that with the increase of slag basicity R(CaO/SiO2) or the decrease of Al2O3 content in slag, the T.[O], number and size of non-metallic inclusions decreased significantly. On the one hand, as the slag basicity increased, inclusions in steel were transformed from Al2O3–SiO2–CaO–MgO quaternary system to Al2O3–SiO2–CaO–MgO–CaS quinary system, which made the formation of voids between inclusions and steel matrix to decrease. Furthermore, thermodynamic calculations showed that CaS could only form in steel (R?≥?3.4). Al2O3–SiO2–CaO–MgO came close to the compositions of the low melting point area, while Al2O3–SiO2–CaO–MgO–CaS deviated from this. On the other hand, as the Al2O3 content in slag increased, Al2O3–SiO2–CaO–MgO–CaS came close to the compositions of the low melting point area. In conclusion, the cleanness and fatigue life of 60Si2MnA spring steel had been improved by the increase of slag basicity or the decrease of Al2O3 content in slag. 相似文献
9.
The results of thermodynamic simulation of the desulfurization of a medium-carbon steel by slags of the CaO–SiO2–MgO–Al2O3–B2O3 system are presented. The HSC Chemistry 6.12 software package is used for the simulation. The thermodynamic simulation is performed for 20 various chemical compositions of slags with various B2O3 contents (1–4%)1 and basicities ((CaO)/(SiO2) = 2–5). The computations are performed using the Equilibrium Compositions module in the temperature range from 1500 to 1700°C with an increment of 50°C at a gas phase pressure of 0.1 MPa. The main results of the calculations are presented as the dependences of the change in the sulfur content in steel [S] on the temperature, the content of B2O3, and the slag basicity. An increase in the temperature of metal desulfurization from 1500 to 1700°C exerts a favorable effect on the sulfur content for the studied range of slag basicities. In particular, the sulfur content in steel decreases from 0.012 to 0.009% when steel is processed with the slag having 3% B2O3 and a basicity (CaO)/(SiO2) = 2. A positive effect of an increase in the slag basicity from 2 to 5 on metal desulfurization is observed: the degree of desulfurization increases from 61.1 to 97.2% at 1600°C and 3% B2O3 content in the slag. As the B2O3 content in a slag increases from 1 to 4%, its refining properties decrease significantly in the range of basicity not higher than 2. In the range of high slag basicities (3–4), the negative effect of acidic oxide B2O3 on the refining properties of the slag decreases, providing low sulfur contents (which do not exceed [S] = 0.003–0.004% at 4% B2O3). At a slag basicity of 5, the sulfur content in steel decreases to 0.001%, all other things being equal. The simulation results can be used for the calculation of steel desulfurization processed by slags containing B2O3. 相似文献
10.
The present study was aimed at highlighting the effect of silica on chromium distribution and enrichment in certain stainless-steel slag when basicity ranged from 0.96 to 1.96. Industrial slag samples of the CaO–Al2O3–MgO–SiO2–CrOX–FeXO system were investigated with different silica addition contents and soaked at the targeted regime. X-ray diffraction, electron probe micro-analyzer with wavelength-dispersive X-ray spectrometer, as well as Fourier-transform infrared spectroscopy and NIH ImageJ software were used for sample characterisation. FactSage version 6.4 was employed to calculate phase equilibria at 1200°C for the slag system to understand the crystallisation procedure. Results indicated that chromium was enriched in CaCr2O4 at high basicity, but in spinel at lower basicity. The spinel phase increased in size and chromium distribution with Fe(II) participated in growth with the decrease in depolymerisation of the slag structure. 相似文献
11.
Electroslag remelting (ESR) is increasingly used to produce some varieties of special steels and alloys, mainly because of its ability to provide extreme cleanliness and an excellent solidification structure simultaneously. In the present study, the combined effects of varying SiO2 contents in slag and reoxidation of liquid steel on the chemistry evolution of inclusions and the alloying element content in steel during ESR were investigated. The inclusions in the steel before ESR refining were found to be oxysulfides of patch-type (Ca,Mn)S adhering to a CaO-Al2O3-SiO2-MgO inclusion. The oxide inclusions in both the liquid metal pool and remelted ingots are CaO-Al2O3-MgO and MgAl2O4 together with CaO-Al2O3-SiO2-MgO inclusions (slightly less than 30 pct of the total inclusions), which were confirmed to originate from the reduction of SiO2 from the original oxide inclusions by dissolved Al in liquid steel during ESR. CaO-Al2O3-MgO and MgAl2O4 are newly formed inclusions resulting from the reactions taking place inside liquid steel in the liquid metal pool caused by reoxidation of liquid steel during ESR. Increasing the SiO2 content in slag not only considerably reduced aluminum pickup in parallel with silicon loss during ESR, but also suppressed the decrease in SiO2 content in oxide inclusions. (Ca,Mn)S inclusions were fully removed before liquid metal droplets collected in the liquid metal pool. 相似文献
12.
In thermodynamic modeling of the desulfurization of steel by CaO–SiO2–MgO–Al2O3–B2O3 slag on the basis of HSC 6.12 Chemistry software (Outokumpu), the influence of the temperature (1500–1700°C), the slag basicity (2–5), and the B2O3 content (1–4%)1 on the desulfurization is analyzed. It is found that the sulfur content is reduced with increase in the temperature from 1500 to 1700°C, within the given range of slag basicity. At 1600°C, the sulfur content in the metal is 0.0052% for slag of basicity 2; at 1650°C, by contrast, its content is 0.0048%. Increase in slag basicity from 2 to 5 improves the desulfurization, which increases from 80.7 to 98.7% at 1600°C. If the B2O3 content in the slag rises, desulfurization is impaired. At 1600°C, the sulfur content in the metal may be reduced to 0.0052 and 0.0098% when using slag of basicity 2 with 1 and 4% B2O3, respectively; in the same conditions but with slag of basicity 5, the corresponding values are 0.00036 and 0.00088%, respectively. Note that desulfurization is better for slag without B2O3. According to thermodynamic modeling, metal with 0.0039 and 0.00019% S is obtained at 1600°C when using slag of basicity 2 and 5, respectively, that contains no B2O3. The results obtained by thermodynamic modeling for the desulfurization of metal by CaO–SiO2–MgO–Al2O3–B2O3 slag of basicity 2–5 in the range 1500–1700°C are consistent with experimental data and may be used in improving the desulfurization of steel by slag that contains boron. 相似文献
13.
HSC 6.1 Chemistry software (Outokumpu) and a simplex–lattice experiment design are employed in thermodynamic modeling of the equilibrium boron distribution between steel containing 0.2% C, 0.35% Si, and 0.028% Al (wt % are used throughout) and CaO–SiO2–Al2)3–8% MgO–4% B2O3 slag over a broad range of chemical composition at 1550 and 1600°C. For each temperature, mathematical models (in the form of a reduced third-order polynomial) are obtained for the equilibrium boron distribution between the slag and the molten metal as a function of the slag composition. The results of simulation are presented as graphs of the composition and equilibrium distribution of boron. The slag basicity has considerable influence on the distribution coefficient of boron. For example, increase in slag basicity from 5 to 8 at 1550°C decreases the boron distribution coefficient from 160 to 120 and hence increases the boron content in the metal from 0.021% when L B = 159 to 0.026% when L B = 121. In other words, increase in slag basicity favorably affects the reduction of boron. Within the given range of chemical composition, the positive influence of the slag basicity on the reduction of boron may be explained in terms of the phase composition of the slag and the thermodynamics of boron reduction. Increase in metal temperature impairs the reduction of boron. With increase in temperature to 1600°C, the equilibrium distribution coefficient of boron increases by 10, on average. On the diagrams, we see regions of slag composition with 53–58% CaO, 8.5–10.5% SiO2, and 20–27% Al2O3 corresponding to boron distribution coefficients of 140–170 at 1550 and 1600°C. Within those regions, when the initial slag contains 4% B2O3, we may expect boron concentrations in the metal of 0.020% when L B = 168 and 0.023% when L B = 139. 相似文献
14.
《钢铁冶炼》2013,40(4):271-275
AbstractChromite reduction by carbon dissolved in a high carbon ferrochromium alloy melt has been investigated in the temperature range 1580-1640°C using a slag system based on CaO2-FeO-Cr2O3-SiO2-Al2O3. Although the reduction is essentially first order with respect to Cr2O3 concentration, it exhibits both zero order and first order reaction kinetics. The zero order period is occupied by the preferential reduction of iron oxide, during which time there is no significant change in the concentration of Cr2O3. The predominance of the divalent chromium oxide in the slag phase is seen to provide further evidence that the reduction of chromite occurs by a stagewise process, involving the thermodynamically stable CrO species. While high basicity slags may be recommended to minimise the generation of CrO, and hence improve reaction kinetics and the extent of Cr2O3 reduction, there is a limitation imposed by chemical erosion of the alumina crucible as the slag basicity is increased above unity, with the dissolving Al2O3 further retarding the reduction kinetics. There is also evidence to suggest the participation of a reductant other than carbon (possibly silicon) in the reduction of chromite. 相似文献
15.
Spinel phase is considered to be the optimal phase for stabilization of chromium in stainless steel slag.In order to restrain chromium leaching from slag for the effective environmental protection,Al2O3 was utilized for the modification treatment,and the effects on the enrichment and stabilization of chromium were investigated.The mineral phases and the existence state of chromium in slag with various Al2O3 contents at different basicities (wCaO/w SiO2) were analyzed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD).The results showed that chromium mainly existed in the glass and spinel phases at basicity of 1.0 and 1.5.As the slag basicity increased to 2.0,chromium was also found in periclase phase.Al2O3 in the stainless steel slag reacted with MgO and Cr2O3,which could generate the Al-rich Mg(CrxAl1-x)2O4 solid solution.Moreover,the addition of Al2O3 was favorable to reduce the solubility of chromium oxide in liquid phase and suppress the precipitation of periclase phase.The experimental results demonstrated that Al2O3 modification has a positive influence on the enrichment and the stabilization of chromium in the stainless steel slag. 相似文献
16.
Contrasting experiments of Al killed 60Si2MnA spring steel were carried out between using and excluding calcium treatment under LF refining slags with low and high basicity ratios (R: CaO/SiO2?=?3.4, 5.0), respectively. Results showed the high basicity refining slag had a certain effect on controlling inclusions and improving the cleanness of spring steel similarly to calcium treatment. The T.[O] (total oxygen) content of steel without calcium treatment got to below 15?ppm and the fatigue life was long, up to 7.8?×?106?cycles. But in order to reduce the T.[O] below 10?ppm, as well as inclusion number and size in spring steel further, meanwhile, the appropriate calcium treatment should still be used. Besides, as the [Ca] content in the steel with calcium treatment increased, inclusions transformed from Al2O3–SiO2–CaO–MgO to Al2O3–SiO2–CaO–MgO–CaS completely, which reduced the formations of voids between inclusions and steel matrix, and voids decreased with the increase of CaO/Al2O3 value and CaS content of inclusions. Finally, the fatigue life of spring steel with high basicity slag and calcium treatment increased to 9.1?×?106 cycles. 相似文献
17.
The selective separation phosphorous rich phase from steel slag could be an effective way to utilise the steel slag. The mineralogical phase after cooling of steel slag is essential to selective separation of steel slag. In the present work, the mineralogical phases of CaO–FeOx–SiO2–P2O5 slag after controlled cooling were investigated by X-ray diffraction and scanning electronic microscopy and energy dispersed spectroscopy technique. It was found that the heat treatment at 1573?K would lead to the precipitation of Ca2SiO4–Ca3P2O8 (C2S-C3P) solid solution for all samples. The heat treatment at 1273?K would lead to the precipitation of C2S-C3P, CaSiO3 and Fe2O3. The increase of basicity would promote the crystallisation of CaO–FeOx–SiO2–P2O5 slag. The Effects of additions of MgO and MnO on phase formations of CaO–FeOx–SiO2–P2O5 slag were also studied. Fe2O3 gradually transformed into MgFe2O4 and MnFe2O4 in slag after crystallisation with addition of MgO and MnO, respectively. The sizes of MgFe2O4 and MnFe2O4 crystals increased with increases of MgO and MnO content. The increase of MgO and MnO content would promote the precipitation of MgFe2O4 phase and MnFe2O4, respectively. The precipitation of crystals from slag during cooling was interpreted by the kinetic and thermodynamic factors. It was proposed that addition of MgO and MnO in slag would be beneficial to magnetic separation of steel slag. 相似文献
18.
The influence of silicon (0.1–0.8%), aluminum (0.005%), and carbon (0.1%) in steel on the reduction of boron from slag (basicity 5) at 1400–1700°C is studied by thermodynamic analysis on the basis of HSC 6.1 Chemistry software (Outokumpu). Experiments on the boron distribution between CaO–SiO2–MgO–Al2O3–B2O3 slag and steel are conducted in a high-temperature Tamman resistance furnace. Low-carbon steel with different silicon content is employed. According to the thermodynamic modeling and the experiments, direct microalloying of steel with boron is possible on the basis of its reduction by the silicon present in the steel. The reduction of boron from slag by silicon is theoretically analyzed and experimentally confirmed. The results of thermodynamic modeling indicate that boron may be reduced from CaO–SiO2–MgO–Al2O3–B2O3 slag by silicon despite its low content in the steel (0.1–0.8%). With increase in the initial Si content in the steel, the boron concentration in the steel also increases. The influence of the Si content and the steel temperature on the final boron content is studied. When steel is held under slag containing 4.3% B2O3, the boron is reduced, mainly by silicon, whose content in the steel is 15–22% lower after the experiment. More boron is present in the steel sample with an elevated Si content. The degree of assimilation of boron is 5.8–6.9%; this is consistent with the thermodynamic modeling. The boron content in the metal may be regulated by adjusting the temperature and the silicon content of the steel. On the basis of the results, a technology for the direct microalloying of steel with boron may be developed. 相似文献
19.
Marissa Vargas‐Ramirez Antonio Romero‐Serrano Federico Chavez‐Alcala Beatriz Zeifert Manuel Hallen‐Lopez 《国际钢铁研究》2002,73(9):378-384
This work estimated the reduction of MnO in slags of the CaO‐SiO2‐FeO‐CaF2‐MnO system and liquid steel with the initial composition (mass contents) 0.75 %Mn, 0.16 % Si and 0.5 to 2.0 % C, as an alternative to introducing Mn to the steel melt. The slag basicities (CaO/SiO2) In the experiments were 2 and 3. MnO was obtained from manganese ore. The experiments were carried out in an open 10 kg induction furnace using Al2O3‐based refractory at 1873 K. The oxygen potential was measured throughout the experiments with a galvanic cell (ZrO2‐solid electrolyte with a Cr/Cr2O3 reference electrode). The MnO reaction mechanism was analysed in terms of the slag basicity, the silicon and the initial carbon contents in the melt. The rate and the degree of MnO reduction were found to increase with the increasing of initial carbon content; however, the effect of slag basicity was less important. A kinetic analysis of the process was performed using a coupled reaction model. 相似文献
20.
The dispersion of metal droplets in slag was investigated through analysis of slag samples taken during ladle refining at Scana Steel in Björneborg, Sweden. The chemical composition of steel droplets found in the ladle slag was determined for five industrial‐scale heats. Possible reactions occurring between the steel droplets and slag were identified, as were differences in steel‐droplet and steel‐bulk composition. Three different slag models were used to calculate the activities of oxide components (Al2O3 and SiO2) in the slag. These results were then used in the dilute‐solution model, whereby oxygen activities in the steel droplets were calculated and compared with measured oxygen activities in the steel bulk. Significant differences were found in the comparison of both the calculated and measured oxygen activities and the steel bulk and droplet compositions. 相似文献