To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction re...To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction reaction process of the Fe-Si bath and the migration behavior of valuable elements in the solidification and crystallization process of silicothermic reduction tailings were investigated,and a treatment method for efficiently separating and enriching REE,Nb and Ti was explored.Thermodynamic analysis indicated that at 1600℃,with a 6 wt.%addition of Si as the reducing agent,the niobium oxide in the REE-Nb-Ti-containing slag could be selectively reduced to metallic Nb.In the Fe-Si bath reduction process,the Nb mass fraction in the metal phase increased with prolonged reaction time,peaking at 2.77%,while the Ti mass fraction consistently stayed below 0.12%.Lowering the w(CaO)/w(SiO_(2))enhanced the migration of Nb from slag to metal phase and reduced the Ti impurities.During solidification and crystallization,a significant quantity of perovskite precipitated from reduction tailings,with the REE dissolving into this perovskite.By adjusting the w(CaO)/w(SiO_(2))in tailings to 1.2-1.9 and maintaining a temperature of 1100℃for 4 h,the perovskite area fraction in the final slag could exceed 37%.Finally,a method was proposed to separate and enrich valuable elements in REE-Nb-Ti-containing slags via Fe-Si bath smelting reduction and crystallization control.展开更多
The reaction behavior between CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags and La-bearing FeCrAl melt was quantitatively characterized,which was further compared with the reaction behavior of CaO–SiO_(2)-based slags.Bas...The reaction behavior between CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags and La-bearing FeCrAl melt was quantitatively characterized,which was further compared with the reaction behavior of CaO–SiO_(2)-based slags.Based on this,the new type of mold flux for La-bearing FeCrAl alloy continuous casting was designed and its basic properties were evaluated.The results showed that the order of reaction degree of fluxing agents in CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags is(Na_(2)O)>(B_(2)O_(3))>(Li_(2)O),and the percentages of mass change of fluxing agents were 85.8,54.29 and 42.35 wt.%,respectively.Moreover,the addition of(Li_(2)O)and(Na_(2)O)promoted the reaction between(CaO)and[Al],and the reaction degree of the former was weaker than that of the latter,which was due to the greater effect of(Na_(2)O)on the activity of(CaO)and(Al_(2)O_(3))than(Li_(2)O).Compared with the reactivity of CaO–SiO_(2)-based slags,the percentages of mass change of Al and La caused by slag–steel reaction decreased by 10.63–14.36 and 39.78–50.49 wt.%,respectively.The percentages of mass change of(Al_(2)O_(3)),(La_(2)O_(3))and(CaO)in slags highest increased by 17.71,17.98,and 7.81 wt.%,respectively.The reactivity of CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags was significantly weakened.Ultimately,the new type of mold flux was designed and the composition range was determined.The fundamental properties of new mold flux basically meet the theoretical requirements for La-bearing FeCrAl alloy continuous casting.展开更多
The formation of large-sized inclusions cluster severely impacts the continuous casting process and product quality of titanium-containing steel.Thermodynamic calculations were initially conducted to predict the forma...The formation of large-sized inclusions cluster severely impacts the continuous casting process and product quality of titanium-containing steel.Thermodynamic calculations were initially conducted to predict the formation of various complex oxide inclusions,namely Al_(2)O_(3),TiO_(x)and Al-Ti-O.Based on that,laboratory-scale experiments were designed to prepare samples with a single type of inclusions.Then,the scanning electron microscope-energy dispersive spectrometer was used for quantitative characterization.Subsequently,the agglomeration behavior of inclusions in Fe-Al-Ti-O melt was observed in situ by high-temperature confocal laser scanning microscopy.Furthermore,a quantitative analysis of the agglomeration characteristics of the various inclusions was conducted based on the attractive forces in accordance with Newton's second law and the capillary forces as described by the Kralchevsky-Paunov model.The results indicate that the size of Al_(2)O_(3)inclusions is larger than that of TiO_(x)and Al-Ti-O,but the number density of TiO_(x)is the highest.Based on the in situ observation and the theoretical calculation,Al_(2)O_(3),TiO_(x)and Al-Ti-O inclusions can all agglomerate into large-sized clusters without segregation,but the agglomeration tendency of Al_(2)O_(3)and TiO_(x)is stronger than that of Al-Ti-O.The attractive force between Al_(2)O_(3)inclusions’pair is the largest,ranging from 2.26×10^(-15)to 6.12×10^(-14)N,followed by TiO_(x)(7.13×10^(-16)to 3.56×10^(-14)N)and Al-Ti-O(1.16×10^(-17)to 3.77×10^(-16)N).展开更多
For the control of surface defects in interstitial-free(IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. Th...For the control of surface defects in interstitial-free(IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. The results show that, at casting speeds of 0.8 and 1.0 m/min, a thin liquid mold flux layer forms and non-uniform floating of argon bubbles occurs, inducing the entrainment and subsequent entrapment of the liquid flux; fine inclusion particles of Al_2O_3 can also aggregate at the solidification front. At higher casting speeds of 1.4 and 1.6 m/min, the liquid mold flux can be entrained and carried deeper into the liquid steel pool because of strong level fluctuations of the liquid steel and the flux. The optimal casting speed is approximately 1.2 m/min, with the most favorable surface flow status and, correspondingly, the lowest number of inclusions near the slab surface.展开更多
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 f...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（ w（CaO）/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（CrxAl（1- 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.展开更多
A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microseg- regation of solute elements during solidification of heat-resistant steel containing cerium was established. Then ...A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microseg- regation of solute elements during solidification of heat-resistant steel containing cerium was established. Then the model was validated by the SEM analysis of the industrial products. The type and amount of inclusions in solidifica- tion structure of 253MA heat-resistant steel were predicted by the model, and the valuable results for the inclusions controlling in 253MA steel were obtained. When the cerium addition increases, the types of inclusions transform from SiO2 and MnS to Ce2 O3 and Ce2O2 S in 253MA steel and the precipitation temperature of SiO2 and MnS decrea- ses. The inclusions CeS and CeN convert to Ce2 O3 and Ce2 O2 S as the oxygen content increases and Ce2 O3 and CeN convert to Ce2 O2 S, Ce3 S4, and MnS as the sulfur content increases. The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increa ses. There is only a small quantity of inclusions containing cerium in 253MA steel with high cleanliness, i. e. , low oxygen and sulfur contents. By contrast, a mass of SiO2 , MnS and Ce2 O2 S are formed in steel when the oxygen and sulfur contents are high enough. The condition that MnS precipitates in 253MA steel is 1.2wEo[O] ＋W[s]〉0. 01% and SiO2 precipitates when 2w[O] ＋wrs[S]〉0. 017% （W[S]0. 005%） and w[O]〉0. 006% （w[S]〉0. 005%）.展开更多
To reveal the formation and evolution behavior of inclusions during magnesium treatment and resulfurization in Al-killed free-cutting steel, both laboratory experiments and thermodynamic calculations were carried out....To reveal the formation and evolution behavior of inclusions during magnesium treatment and resulfurization in Al-killed free-cutting steel, both laboratory experiments and thermodynamic calculations were carried out. The extracted samples were polished and analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results indicated that MgO formed immediately and then transferred to MgO·Al2O3 with the homogenization of [Mg] in steel in the case of low magnesium addition (w[Mg] < 0.0020%). However, MgO would keep stable in the case of high magnesium addition (w[Mg] ≥ 0.0020%). In the process of resulfurization, the addition of sulfur forced the transformation of MgO to MgO·Al2O3 accompanied with the formation of MgS if the mass fraction of [S] in steel was in the range 0.15%-0.70%. MgS precipi-tated as a solid solution containing a quantity of MnS, and the composition of the sulfide solution was calculated to be (Mg0.85Mn0.15)S when the mass fraction of [Mn] was 1.2%. The formation mechanisms of inclusions after magnesium and sulfur additions were discussed comprehensively, and proper models for the evolution of inclusions were set up.展开更多
As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the...As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope（OM）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, and energy disperse spectrometer（EDS）. Results show that Al2O3 and a few（Nb,Ti）N particles form when titanium addition is 0.01 %.Furthermore, inclusions are mainly Ti N and Al2O3–Ti Ox–Ti N duplex inclusions when titanium addition is more than0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process.Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.展开更多
Spinel is an appropriate phase for sequestrating chromium in stainless steel slag to prevent chromium from polluting,and the crystal size of spinel has a significant effect on the stability of chromium and the extract...Spinel is an appropriate phase for sequestrating chromium in stainless steel slag to prevent chromium from polluting,and the crystal size of spinel has a significant effect on the stability of chromium and the extraction efficiency of spinel.The enrichment behavior of chromium in spinel during cooling process was investigated,and the growth process of spinel was studied based on the crystal size distribution theory.The results showed that the enrichment degree of chromium in spinel increased from 88.5% to nearly 100% during the cooling process from 1773 to 1573 K at a rate of 5 K/min.The mean diameter of spinel in stainless steel slag had an obvious growth in the cooling process,and a rapid growth of spinel occurred during the cooling process from 1623 to 1523 K.Leaching results indicated that the leaching amount of chro- mium could reduce to less than 0.01 mg/L by controlling the cooling condition.The growth mechanism of spinel was investigated and proposed to consist of two stages:in the first stage,the spinel was in the surface-controlled growth with a decaying nucleation rate from 1773 to 1573 K,and in the second stage,the growth mechanism was transformed to supply- controlled Ostwald ripening-below 1573 K.展开更多
The extraction of chromate from chromite via the sulfuric acid leaching process has strong potential for practical use because it is a simple and environmentally friendly process. This paper aims to study the sulfuric...The extraction of chromate from chromite via the sulfuric acid leaching process has strong potential for practical use because it is a simple and environmentally friendly process. This paper aims to study the sulfuric acid leaching process using chromite as a raw material via either microwave irradiation or in the presence of an oxidizing agent. The results show that the main phases in Pakistan chromite are ferrichromspinel, chrompicotite, hortonolite, and silicate embedded around the spinel phases. Compared with the process with an oxidizing agent, the process involving microwaves has a higher leaching efficiency. When the mass fraction of sulfuric acid was 80% and the leaching time was 20 min, the efficiency could exceed 85%. In addition, the mechanisms of these two technologies fundamentally differ. When the leaching was processed in the presence of an oxidizing agent, the silicate was leached first and then expanded. By contrast, in the case of leaching under microwave irradiation, the chromite was dissolved layer by layer and numerous cracks appeared at the particle surface because of thermal shock. In addition, the silicate phase shrunk instead of expanding.展开更多
The sulfuric acid leaching process is regarded as a promising, cleaner method to prepare trivalent chromium products from chromite; however, the decomposition mechanism of the ore is poorly understood. In this work, b...The sulfuric acid leaching process is regarded as a promising, cleaner method to prepare trivalent chromium products from chromite; however, the decomposition mechanism of the ore is poorly understood. In this work, binary spinels of Mg–Al, Mg–Fe, and Mg–Cr in the powdered and lump states were synthesized and used as raw materials to investigate the decomposition mechanism of chromite in sulfuric acid–dichromic acid solution. The leaching yields of metallic elements and the changes in morphology of the spinel were studied. The experimental results showed that the three spinels were stable in sulfuric acid solution and that dichromic acid had little influence on the decomposition behavior of the Mg–Al spinel and Mg–Fe spinel because Mg^(2+), Al^(3+), and Fe^(3+) in spinels cannot be oxidized by Cr^(6+). However, in the case of the Mg–Cr spinel, dichromic acid substantially promoted the decomposition efficiency and functioned as a catalyst. The decomposition mechanism of chromite in sulfuric acid–dichromic acid solution was illustrated on the basis of the findings of this study.展开更多
The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing ...The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching con- ditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional re- lationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leach- ing process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ.mol-1.展开更多
Descaling of hot-rolled stainless steel is generally implemented through pickling process in HNO_3-HF mixed acids,which induces severe environmental concerns of nitrogen oxide（NOx）gases and nitrites.According to the...Descaling of hot-rolled stainless steel is generally implemented through pickling process in HNO_3-HF mixed acids,which induces severe environmental concerns of nitrogen oxide（NOx）gases and nitrites.According to the electrochemical measurement,the mass loss test and the appearance analysis,a new pickling process which employed HCl-based solution was proposed and evaluated to provide theoretical basis for the development of environment-friendly and highly effective pickling process.Under the experimental condition,the HCl-based solution can compete with ordinary HNO_3-HF mixed acids in terms of pickling efficiency,surface integrity and the removal of Crdepleted layer.The descaling process of 430hot-rolled stainless steel in the HCl-based solution consisted of three steps.The descaling solution penetrated the oxide scales into the underlying metal,dissolving the Cr-depleted layer and part of substrates.The oxide scales peeled off from the stainless steel and a polished and smooth surface was exposed.The descaled stainless steel was dissolved uniformly in the HCl-based solution;therefore,the pickling duration was vital for desired surface integrity.Under the static condition,the appropriate descaling time of 430 hotrolled stainless steel in HCl-based solution was 400 s.展开更多
To verify the formation behaviors and mechanisms of intra-granular acicular ferrite（ IAF） grains nucleated by Mg-Al-O in low carbon steel,the steels containing different Mg contents were refined in a vacuum inductio...To verify the formation behaviors and mechanisms of intra-granular acicular ferrite（ IAF） grains nucleated by Mg-Al-O in low carbon steel,the steels containing different Mg contents were refined in a vacuum induction furnace. The effect of Mg addition on the formation of IAF structure in Al-killed low carbon steel was investigated by optical microscope（ OM） and scanning electron microscope with energy dispersive X-ray spectroscope（ SEM-EDX）. It reveals that the IAFs are only detected in Mg-added steels,and the volume fraction of IAF increases with the Mg concentration from 8 × 10^（-6） to 26 × 10^（-6）. It shows that not only the MgO-Al_2O_3-MnS and MgO-Al_2O_3-P_2O_5 particles are the effective nucleation sites for IAF,but also the pure MgO·Al_2O_3 phase can promote the ferrite nucleation. A Mn-depletion zone（ MDZ） is characterized adjacent to the MgO-Al_2O_3-MnS,which is believed to be one of the possible mechanisms to explain the IAF nucleation. The MDZ around the MgO-Al_2O_3-MnS inclusion would be induced by the Mn S precipitation on the inclusion. It seems that the ability of Mg-containing inclusions to induce the nucleation of ferrite might be attributed to a new mechanism,i. e.,the Prich zone formed on a few Mg-Al-O inclusions might be another factor for promoting the IAF formation.展开更多
The effects of different hot deformation amounts on the evolution of inclusion and microstructure in Ti-Zr deoxidized steel were studied by utilizing the Thermecmaster-Z hot simulation test machine,automatic scanning ...The effects of different hot deformation amounts on the evolution of inclusion and microstructure in Ti-Zr deoxidized steel were studied by utilizing the Thermecmaster-Z hot simulation test machine,automatic scanning electron microscope equipped with energy-dispersive spectrometer,and electron backscattered diffraction.The results indicated that hot deformation amount has no significant effect on the number density of oxide,but the MnS that precipitated on the Ti-Zr oxide surface undergoes extension and breakage,resulting in the changes in oxide aspect ratio.Moreover,the fracture of nitride mainly occurs in the sample with the second pass deformation amount of 42.9%and 71.4%,and the degree of fragmentation of nitride is more serious with the deformation amount increasing.During the hot compression,sulfide undergoes breakage and extension,and with the second pass deformation amount increasing,the breakage and extension of sulfide present a periodic change.Finally,with the increase in hot compression amount,the ferrite types in microstructure change from acicular ferrite and bainitic ferrite to polygonal ferrite,and the ferrite grain size is refined.When the total deformation amount increases from 30%to 80%,the ferrite grain sizes of grain boundary with the misorientation of 4°and 15°decrease from 4.14 and 5.67μm to 3.47 and 4.40μm,respectively.However,when the total deformation amount increases to 80%,the harmful ferrite/pearlite banded structure appears in the micro structure.Refining ferrite grain size and avoiding harmful microstructure are the key for the optimization of hot compression process.展开更多
Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was s...Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450 EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g·m-2·h-1. The rust of S450 EW weathering steel was mainly constituted of Fe OOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-Fe OOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450 EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.展开更多
To shorten the time required for the pickling process and to enhance the quality of ferritic stainless steel plates,the effects of oxidants including hydrogen peroxide（H2O2）,potassium permanganate（KMnO4）,and potas...To shorten the time required for the pickling process and to enhance the quality of ferritic stainless steel plates,the effects of oxidants including hydrogen peroxide（H2O2）,potassium permanganate（KMnO4）,and potassium chlorate（KClO3）on the pickling behavior in HCl-based electrolyte as well as the surface quality of hot-rolled and blasted 430 stainless steel（430-SS）were studied.Experiments were conducted using mass-loss tests,microstructure analyses,potentiodynamic polarization curves,and electrochemical impedance spectroscopy measurements.The results showed that the addition of oxidants substantially accelerated the pickling process of 430-SS by enhancing the cathodic reaction rate and reducing the charge transfer resistance.In electrolytes comprising 5-8mass% HCl at a temperature of 40-60 ℃ and at the same concentration within the range from 0to 2mass%,H2O2 was demonstrated to be superior to KMnO4 and KClO3in accelerating the pickling process.The surface quality of 430-SS pickled in the presence of H2O2 was better than those of specimens pickled in the presence of KMnO4 and KClO3 when the removal of the oxide layer,intergranular corrosion,and surface roughness were collectively considered.When 1mass% H2O2 was added,the mass loss rate of 430-SS was increased by 629%and no residual oxide layer or intergranular corrosion was observed on the surface of the steel;in addition,the roughness was only 1.7μm.H2O2 was determined to be a better oxidant than KMnO4 and KClO3 when the pickling process,surface quality,solution recycling,and environment protection were considered as a whole.展开更多
To improve the efficiency of melting modification for stainless steel(SS) slag, a shear force was introduced in this work and its effects on the spinel and silicate melt were experimentally investigated. The results i...To improve the efficiency of melting modification for stainless steel(SS) slag, a shear force was introduced in this work and its effects on the spinel and silicate melt were experimentally investigated. The results indicated that the use of shear force changed the nucleation and growth behaviors of spinel and that the effects of shear force varied with its intensity. The aggregation behavior of spinel under different shear-force conditions was studied, revealing that large spinel clusters could be formed when the stirring speed was controlled. However, no notable change in the melt structure of the silicate was detected in this study. The optimal stirring speed for the melting modification treatment was 50 r·min^(-1), which substantially promoted spinel growth and aggregation, resulting in modified SS slag with excellent chromium sequestration capability.展开更多
基金supported by the National Key R&D Program of China(No.2021YFC2901200)National Natural Science Foundation of China(Nos.52174383 and 52374412)Liaoning Provincial Natural Science Foundation of China(No.2022-YQ-09).
文摘To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction reaction process of the Fe-Si bath and the migration behavior of valuable elements in the solidification and crystallization process of silicothermic reduction tailings were investigated,and a treatment method for efficiently separating and enriching REE,Nb and Ti was explored.Thermodynamic analysis indicated that at 1600℃,with a 6 wt.%addition of Si as the reducing agent,the niobium oxide in the REE-Nb-Ti-containing slag could be selectively reduced to metallic Nb.In the Fe-Si bath reduction process,the Nb mass fraction in the metal phase increased with prolonged reaction time,peaking at 2.77%,while the Ti mass fraction consistently stayed below 0.12%.Lowering the w(CaO)/w(SiO_(2))enhanced the migration of Nb from slag to metal phase and reduced the Ti impurities.During solidification and crystallization,a significant quantity of perovskite precipitated from reduction tailings,with the REE dissolving into this perovskite.By adjusting the w(CaO)/w(SiO_(2))in tailings to 1.2-1.9 and maintaining a temperature of 1100℃for 4 h,the perovskite area fraction in the final slag could exceed 37%.Finally,a method was proposed to separate and enrich valuable elements in REE-Nb-Ti-containing slags via Fe-Si bath smelting reduction and crystallization control.
基金supported by the National Natural Science Foundation of China(Grant Nos.52174321,52274339 and 52074186).
文摘The reaction behavior between CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags and La-bearing FeCrAl melt was quantitatively characterized,which was further compared with the reaction behavior of CaO–SiO_(2)-based slags.Based on this,the new type of mold flux for La-bearing FeCrAl alloy continuous casting was designed and its basic properties were evaluated.The results showed that the order of reaction degree of fluxing agents in CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags is(Na_(2)O)>(B_(2)O_(3))>(Li_(2)O),and the percentages of mass change of fluxing agents were 85.8,54.29 and 42.35 wt.%,respectively.Moreover,the addition of(Li_(2)O)and(Na_(2)O)promoted the reaction between(CaO)and[Al],and the reaction degree of the former was weaker than that of the latter,which was due to the greater effect of(Na_(2)O)on the activity of(CaO)and(Al_(2)O_(3))than(Li_(2)O).Compared with the reactivity of CaO–SiO_(2)-based slags,the percentages of mass change of Al and La caused by slag–steel reaction decreased by 10.63–14.36 and 39.78–50.49 wt.%,respectively.The percentages of mass change of(Al_(2)O_(3)),(La_(2)O_(3))and(CaO)in slags highest increased by 17.71,17.98,and 7.81 wt.%,respectively.The reactivity of CaO–Al_(2)O_(3)–La_(2)O_(3)-based slags was significantly weakened.Ultimately,the new type of mold flux was designed and the composition range was determined.The fundamental properties of new mold flux basically meet the theoretical requirements for La-bearing FeCrAl alloy continuous casting.
基金support of Postdoctoral Fellowship Program of CPSF(GZC20230393)Natural Science Foundation of Liaoning Province in China(2023-BSBA-112)Fundamental Research Funds for the Central Universities(N2425032).
文摘The formation of large-sized inclusions cluster severely impacts the continuous casting process and product quality of titanium-containing steel.Thermodynamic calculations were initially conducted to predict the formation of various complex oxide inclusions,namely Al_(2)O_(3),TiO_(x)and Al-Ti-O.Based on that,laboratory-scale experiments were designed to prepare samples with a single type of inclusions.Then,the scanning electron microscope-energy dispersive spectrometer was used for quantitative characterization.Subsequently,the agglomeration behavior of inclusions in Fe-Al-Ti-O melt was observed in situ by high-temperature confocal laser scanning microscopy.Furthermore,a quantitative analysis of the agglomeration characteristics of the various inclusions was conducted based on the attractive forces in accordance with Newton's second law and the capillary forces as described by the Kralchevsky-Paunov model.The results indicate that the size of Al_(2)O_(3)inclusions is larger than that of TiO_(x)and Al-Ti-O,but the number density of TiO_(x)is the highest.Based on the in situ observation and the theoretical calculation,Al_(2)O_(3),TiO_(x)and Al-Ti-O inclusions can all agglomerate into large-sized clusters without segregation,but the agglomeration tendency of Al_(2)O_(3)and TiO_(x)is stronger than that of Al-Ti-O.The attractive force between Al_(2)O_(3)inclusions’pair is the largest,ranging from 2.26×10^(-15)to 6.12×10^(-14)N,followed by TiO_(x)(7.13×10^(-16)to 3.56×10^(-14)N)and Al-Ti-O(1.16×10^(-17)to 3.77×10^(-16)N).
基金financially supported by the National Natural Science Foundation of China (No. 51674069)the National Key R & D Program of China (No. 2017YFC0805100)
文摘For the control of surface defects in interstitial-free(IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. The results show that, at casting speeds of 0.8 and 1.0 m/min, a thin liquid mold flux layer forms and non-uniform floating of argon bubbles occurs, inducing the entrainment and subsequent entrapment of the liquid flux; fine inclusion particles of Al_2O_3 can also aggregate at the solidification front. At higher casting speeds of 1.4 and 1.6 m/min, the liquid mold flux can be entrained and carried deeper into the liquid steel pool because of strong level fluctuations of the liquid steel and the flux. The optimal casting speed is approximately 1.2 m/min, with the most favorable surface flow status and, correspondingly, the lowest number of inclusions near the slab surface.
基金financial support by the National Natural Science Foundation of China(Project No.51374059 and 51304042)
文摘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（ w（CaO）/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（CrxAl（1- 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.
基金Sponsored by National Key Basic Research Program of China(2012CB626812)National Natural Science Foundation of China(51104039)Program for New Century Excellent Talents in University of Ministry of Education of China(NCET-11-0077)
文摘A coupled thermodynamic model of inclusions precipitation both in liquid and solid phase and microseg- regation of solute elements during solidification of heat-resistant steel containing cerium was established. Then the model was validated by the SEM analysis of the industrial products. The type and amount of inclusions in solidifica- tion structure of 253MA heat-resistant steel were predicted by the model, and the valuable results for the inclusions controlling in 253MA steel were obtained. When the cerium addition increases, the types of inclusions transform from SiO2 and MnS to Ce2 O3 and Ce2O2 S in 253MA steel and the precipitation temperature of SiO2 and MnS decrea- ses. The inclusions CeS and CeN convert to Ce2 O3 and Ce2 O2 S as the oxygen content increases and Ce2 O3 and CeN convert to Ce2 O2 S, Ce3 S4, and MnS as the sulfur content increases. The formation temperature of SiO2 increases when the oxygen content increases and the MnS precipitation temperature increases when the sulfur content increa ses. There is only a small quantity of inclusions containing cerium in 253MA steel with high cleanliness, i. e. , low oxygen and sulfur contents. By contrast, a mass of SiO2 , MnS and Ce2 O2 S are formed in steel when the oxygen and sulfur contents are high enough. The condition that MnS precipitates in 253MA steel is 1.2wEo[O] ＋W[s]〉0. 01% and SiO2 precipitates when 2w[O] ＋wrs[S]〉0. 017% （W[S]0. 005%） and w[O]〉0. 006% （w[S]〉0. 005%）.
基金The authors gratefully acknowledge the support from the National Natural Science Foundation of China(Grant No.NSFC 51674069)the National Key Research and Development Program of China(Grant No.2017YFC0805100).
文摘To reveal the formation and evolution behavior of inclusions during magnesium treatment and resulfurization in Al-killed free-cutting steel, both laboratory experiments and thermodynamic calculations were carried out. The extracted samples were polished and analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results indicated that MgO formed immediately and then transferred to MgO·Al2O3 with the homogenization of [Mg] in steel in the case of low magnesium addition (w[Mg] < 0.0020%). However, MgO would keep stable in the case of high magnesium addition (w[Mg] ≥ 0.0020%). In the process of resulfurization, the addition of sulfur forced the transformation of MgO to MgO·Al2O3 accompanied with the formation of MgS if the mass fraction of [S] in steel was in the range 0.15%-0.70%. MgS precipi-tated as a solid solution containing a quantity of MnS, and the composition of the sulfide solution was calculated to be (Mg0.85Mn0.15)S when the mass fraction of [Mn] was 1.2%. The formation mechanisms of inclusions after magnesium and sulfur additions were discussed comprehensively, and proper models for the evolution of inclusions were set up.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. N100602011)the National Natural Science Foundation of China (No. 51104039)+4 种基金the National Key Basic Research Program of China (No. 2012CB626812)the Program for New Century Excellent Talents in University (No. NCET-11-0077)Liaoning Provincial Natural Science Foundation of China (No. 201102062)Liaoning Provincial Science and Technology Plan (No. 2012221013)the National Innovation Experiment Program for University Students
文摘As the raw materials in the post process of rolling and heat treatment, ingots have great effects on the properties of the final products. Inclusions and solidification structures are the most important aspects of the quality of ingots. Niobium and titanium are usually used to react with carbon and nitrogen to improve the properties of ferritic stainless steels. In this research, combined with thermodynamic calculation, effects of niobium and titanium on the inclusions and solidification structures in three kinds of high pure ferritic stainless steels with different titanium additions were investigated by optical microscope（OM）, scanning electron microscope（SEM）, transmission electron microscope（TEM）, and energy disperse spectrometer（EDS）. Results show that Al2O3 and a few（Nb,Ti）N particles form when titanium addition is 0.01 %.Furthermore, inclusions are mainly Ti N and Al2O3–Ti Ox–Ti N duplex inclusions when titanium addition is more than0.10 %. Those two types of inclusions are in well distribution, and can afford nuclei to the solidification process.Therefore, the ratio of equiaxed zone increases with the increase of titanium addition. The ratio increases from42.1 % to 64.0 % with the titanium addition increasing from 0.01 % to 0.10 %, and it increases to 85.7 % when the titanium addition reaches 0.34 %.
基金National Key R&D Program of China (No. 2017YFC0805100)National Natural Science Foundation of China (Project No.51704068 and 51374059)+2 种基金China Postdoctoral Science Foundation (No.2017M610184)Fundamental Research Funds for the Central Universities (No.N172504020)Postdoctoral Foundation of Northeastern University (No.20170305).
文摘Spinel is an appropriate phase for sequestrating chromium in stainless steel slag to prevent chromium from polluting,and the crystal size of spinel has a significant effect on the stability of chromium and the extraction efficiency of spinel.The enrichment behavior of chromium in spinel during cooling process was investigated,and the growth process of spinel was studied based on the crystal size distribution theory.The results showed that the enrichment degree of chromium in spinel increased from 88.5% to nearly 100% during the cooling process from 1773 to 1573 K at a rate of 5 K/min.The mean diameter of spinel in stainless steel slag had an obvious growth in the cooling process,and a rapid growth of spinel occurred during the cooling process from 1623 to 1523 K.Leaching results indicated that the leaching amount of chro- mium could reduce to less than 0.01 mg/L by controlling the cooling condition.The growth mechanism of spinel was investigated and proposed to consist of two stages:in the first stage,the spinel was in the surface-controlled growth with a decaying nucleation rate from 1773 to 1573 K,and in the second stage,the growth mechanism was transformed to supply- controlled Ostwald ripening-below 1573 K.
基金financially supported by the National Natural Science Foundation of China (No. 51374059)
文摘The extraction of chromate from chromite via the sulfuric acid leaching process has strong potential for practical use because it is a simple and environmentally friendly process. This paper aims to study the sulfuric acid leaching process using chromite as a raw material via either microwave irradiation or in the presence of an oxidizing agent. The results show that the main phases in Pakistan chromite are ferrichromspinel, chrompicotite, hortonolite, and silicate embedded around the spinel phases. Compared with the process with an oxidizing agent, the process involving microwaves has a higher leaching efficiency. When the mass fraction of sulfuric acid was 80% and the leaching time was 20 min, the efficiency could exceed 85%. In addition, the mechanisms of these two technologies fundamentally differ. When the leaching was processed in the presence of an oxidizing agent, the silicate was leached first and then expanded. By contrast, in the case of leaching under microwave irradiation, the chromite was dissolved layer by layer and numerous cracks appeared at the particle surface because of thermal shock. In addition, the silicate phase shrunk instead of expanding.
基金financially supported by the National Key R&D Program of China (No.2017YFC0805100)the National Natural Science Foundation of China (Nos.51704068 and 51374059)+1 种基金the China Postdoctoral Science Foundation (No.2017M610184)the Postdoctoral Foundation of Northeastern University (No.20170305)
文摘The sulfuric acid leaching process is regarded as a promising, cleaner method to prepare trivalent chromium products from chromite; however, the decomposition mechanism of the ore is poorly understood. In this work, binary spinels of Mg–Al, Mg–Fe, and Mg–Cr in the powdered and lump states were synthesized and used as raw materials to investigate the decomposition mechanism of chromite in sulfuric acid–dichromic acid solution. The leaching yields of metallic elements and the changes in morphology of the spinel were studied. The experimental results showed that the three spinels were stable in sulfuric acid solution and that dichromic acid had little influence on the decomposition behavior of the Mg–Al spinel and Mg–Fe spinel because Mg^(2+), Al^(3+), and Fe^(3+) in spinels cannot be oxidized by Cr^(6+). However, in the case of the Mg–Cr spinel, dichromic acid substantially promoted the decomposition efficiency and functioned as a catalyst. The decomposition mechanism of chromite in sulfuric acid–dichromic acid solution was illustrated on the basis of the findings of this study.
基金support from the China Scholarship Council (CSC) for the visit of Qing Zhao to bo Akademi University, FinlandThe National Key Basic Research Program of China (No. 2012CB626812)+2 种基金the Program for New Century Excellent Talents in Universities of the Ministry of Education of China (No. NCET-11-0077)the Natural Science Foundation of Liaoning Province of China (No. 201102062)the "123 Project" of Liaoning Environmental Research of Geping Green Acts
文摘The sulfuric acid leaching kinetics of South African chromite was investigated. The negative influence of a solid product layer constituted of a silicon-rich phase and chromium-rich sulfate was eliminated by crushing the chromite and by selecting proper leaching con- ditions. The dimensionless change in specific surface area and the conversion rate of the chromite were observed to exhibit a proportional re- lationship. A modified shrinking particle model was developed to account for the change in reactive surface area, and the model was fitted to experimental data. The resulting model was observed to describe experimental findings very well. Kinetics analysis revealed that the leach- ing process is controlled by a chemical reaction under the employed experimental conditions and the activation energy of the reaction is 48 kJ.mol-1.
基金Item Sponsored by National Natural Science Foundation of China(51304042,51374059)New Century Excellent Talents in University of China(NCET-11-0077)
文摘Descaling of hot-rolled stainless steel is generally implemented through pickling process in HNO_3-HF mixed acids,which induces severe environmental concerns of nitrogen oxide（NOx）gases and nitrites.According to the electrochemical measurement,the mass loss test and the appearance analysis,a new pickling process which employed HCl-based solution was proposed and evaluated to provide theoretical basis for the development of environment-friendly and highly effective pickling process.Under the experimental condition,the HCl-based solution can compete with ordinary HNO_3-HF mixed acids in terms of pickling efficiency,surface integrity and the removal of Crdepleted layer.The descaling process of 430hot-rolled stainless steel in the HCl-based solution consisted of three steps.The descaling solution penetrated the oxide scales into the underlying metal,dissolving the Cr-depleted layer and part of substrates.The oxide scales peeled off from the stainless steel and a polished and smooth surface was exposed.The descaled stainless steel was dissolved uniformly in the HCl-based solution;therefore,the pickling duration was vital for desired surface integrity.Under the static condition,the appropriate descaling time of 430 hotrolled stainless steel in HCl-based solution was 400 s.
基金Item Sponsored by National Natural Science Foundation of China(51374059,51374060)Scientific Research Fund of Liaoning Provincial Education Department of China(2012221013)
文摘To verify the formation behaviors and mechanisms of intra-granular acicular ferrite（ IAF） grains nucleated by Mg-Al-O in low carbon steel,the steels containing different Mg contents were refined in a vacuum induction furnace. The effect of Mg addition on the formation of IAF structure in Al-killed low carbon steel was investigated by optical microscope（ OM） and scanning electron microscope with energy dispersive X-ray spectroscope（ SEM-EDX）. It reveals that the IAFs are only detected in Mg-added steels,and the volume fraction of IAF increases with the Mg concentration from 8 × 10^（-6） to 26 × 10^（-6）. It shows that not only the MgO-Al_2O_3-MnS and MgO-Al_2O_3-P_2O_5 particles are the effective nucleation sites for IAF,but also the pure MgO·Al_2O_3 phase can promote the ferrite nucleation. A Mn-depletion zone（ MDZ） is characterized adjacent to the MgO-Al_2O_3-MnS,which is believed to be one of the possible mechanisms to explain the IAF nucleation. The MDZ around the MgO-Al_2O_3-MnS inclusion would be induced by the Mn S precipitation on the inclusion. It seems that the ability of Mg-containing inclusions to induce the nucleation of ferrite might be attributed to a new mechanism,i. e.,the Prich zone formed on a few Mg-Al-O inclusions might be another factor for promoting the IAF formation.
基金The present work was financially supported by the National Natural Science Foundation of China(Nos.52074207 and 51874081)Key Laboratory of Ecological Metallurgy of Multimetallic Mineral(Northeastern University)of Ministry of Education.
文摘The effects of different hot deformation amounts on the evolution of inclusion and microstructure in Ti-Zr deoxidized steel were studied by utilizing the Thermecmaster-Z hot simulation test machine,automatic scanning electron microscope equipped with energy-dispersive spectrometer,and electron backscattered diffraction.The results indicated that hot deformation amount has no significant effect on the number density of oxide,but the MnS that precipitated on the Ti-Zr oxide surface undergoes extension and breakage,resulting in the changes in oxide aspect ratio.Moreover,the fracture of nitride mainly occurs in the sample with the second pass deformation amount of 42.9%and 71.4%,and the degree of fragmentation of nitride is more serious with the deformation amount increasing.During the hot compression,sulfide undergoes breakage and extension,and with the second pass deformation amount increasing,the breakage and extension of sulfide present a periodic change.Finally,with the increase in hot compression amount,the ferrite types in microstructure change from acicular ferrite and bainitic ferrite to polygonal ferrite,and the ferrite grain size is refined.When the total deformation amount increases from 30%to 80%,the ferrite grain sizes of grain boundary with the misorientation of 4°and 15°decrease from 4.14 and 5.67μm to 3.47 and 4.40μm,respectively.However,when the total deformation amount increases to 80%,the harmful ferrite/pearlite banded structure appears in the micro structure.Refining ferrite grain size and avoiding harmful microstructure are the key for the optimization of hot compression process.
基金Item Sponsored by National Natural Science Foundation of China(51104039)Fundamental Research Funds for the National Key Basic Research Program of China(2012CB626812)
文摘Weathering steel is widely used in various fields due to its excellent mechanical properties and high corrosion resistance. The effect of chromium content on the S450 EW weathering steel in cyclic immersion test was studied. The results indicated that the corrosion resistance of S450 EW weathering steel is closely related to chromium content. The addition of chromium significantly inhibited the weathering steel corrosion. The corrosion rate of experimental steel after 96 h immersion was 1.101 g·m-2·h-1. The rust of S450 EW weathering steel was mainly constituted of Fe OOH and Fe3O4 phase, and the elevation of chromium content promoted the formation of α-Fe OOH. The fine precipitates of the two phases contributed to the formation of dense dust layer of test steel. Furthermore, the increase of chromium is beneficial for the cure of original defects and cracks of the rust layer via the enrichment of chromium. The corrosion potential and the resistance of corrosion process were thus increased, protecting the experimental steel from further corrosion. A S450 EW steel with corrosion resistance more than 1.5 times of Q450NQR1 steel was prepared.
基金Item Sponsored by Liaoning Province Programs for Science and Technology Development of China(2012221013)
文摘To shorten the time required for the pickling process and to enhance the quality of ferritic stainless steel plates,the effects of oxidants including hydrogen peroxide（H2O2）,potassium permanganate（KMnO4）,and potassium chlorate（KClO3）on the pickling behavior in HCl-based electrolyte as well as the surface quality of hot-rolled and blasted 430 stainless steel（430-SS）were studied.Experiments were conducted using mass-loss tests,microstructure analyses,potentiodynamic polarization curves,and electrochemical impedance spectroscopy measurements.The results showed that the addition of oxidants substantially accelerated the pickling process of 430-SS by enhancing the cathodic reaction rate and reducing the charge transfer resistance.In electrolytes comprising 5-8mass% HCl at a temperature of 40-60 ℃ and at the same concentration within the range from 0to 2mass%,H2O2 was demonstrated to be superior to KMnO4 and KClO3in accelerating the pickling process.The surface quality of 430-SS pickled in the presence of H2O2 was better than those of specimens pickled in the presence of KMnO4 and KClO3 when the removal of the oxide layer,intergranular corrosion,and surface roughness were collectively considered.When 1mass% H2O2 was added,the mass loss rate of 430-SS was increased by 629%and no residual oxide layer or intergranular corrosion was observed on the surface of the steel;in addition,the roughness was only 1.7μm.H2O2 was determined to be a better oxidant than KMnO4 and KClO3 when the pickling process,surface quality,solution recycling,and environment protection were considered as a whole.
基金financially supported by the National Natural Science Foundation of China(No.51704068)the National Key Technologies R&D Program of China(No.2017YFC0805100)the Fundamental Research Funds for the Central Universities(No.N172504020)
文摘To improve the efficiency of melting modification for stainless steel(SS) slag, a shear force was introduced in this work and its effects on the spinel and silicate melt were experimentally investigated. The results indicated that the use of shear force changed the nucleation and growth behaviors of spinel and that the effects of shear force varied with its intensity. The aggregation behavior of spinel under different shear-force conditions was studied, revealing that large spinel clusters could be formed when the stirring speed was controlled. However, no notable change in the melt structure of the silicate was detected in this study. The optimal stirring speed for the melting modification treatment was 50 r·min^(-1), which substantially promoted spinel growth and aggregation, resulting in modified SS slag with excellent chromium sequestration capability.
