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1.
The mechanism of inclusion aggregation in liquid steel in swirling flow tundish is analyzed by applying the theory of flocculation which was developed in the field of colloid engineering. The gas bridge forces due to the micro bubbles on hydrophobic inclusion surfaces were considered responsible for the inclusion collision and agglomeration, which can avoid the aggregation to breakup. The quantity of micro bubbles on hydrophobic inclusion particle is more than that on hydrophilic one. The trend of forming gas bridges between micro bubbles on particles is strong in the course of collision. The liquid film on hydrophobic particles is easy to break during collision process. Hydrophobic particles are liable to aggregate in collision. According to the analysis of forces on a non-metallic inclusion particle in swirling chamber, the chance of inclusion collision and aggregation can be improved by the centripetal force. Hydrophobic particles in water are liable to aggregate in collision. Hydrophilic particles in water are dispersed although collision happens. The wettabiliy can be changed by changing solid-liquid interface tension. The non-metallic inclusion removal in swirling flow tundish is studied. It shows that, under certain turbulent conditions, the particle concentration and the wettability between particles and liquid steel are the main factors to induce collision and aggregation. 相似文献
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在连铸生产中采用大流量长水口吹氩,并采用“冷钢片沾钢法”沾取中间包钢液试样,成功沾取了中间包钢液中微小氩气泡。冷钢片沾样表面气泡为中间包上部钢/渣界面和炉渣中氩气泡,尺寸主要位于1.0~3.0 mm,但该尺寸不能反映中间包钢液内部长水口吹氩生成气泡,冷钢片沾样内部气泡为钢液内部长水口吹氩生成的气泡。结合扫描电镜和共聚焦显微镜对沾取试样内部气泡形貌、尺寸和数量进行了分析,结果表明大部分气泡为独立圆形气泡,偶见少量粘连和聚合气泡;钢液内部氩气泡尺寸主要位于100~1000 μm,平均尺寸为500 μm左右;气泡在长水口出口及其下方较为弥散,气泡数量可达15.2 cm?2。采用扫描电镜结合能谱分析,发现部分气泡内粘附有夹杂物,有些气泡粘附多个夹杂物;气泡粘附Al2O3夹杂物的几率高于粘附CaO(?MgO)?Al2O3?SiO2复合夹杂物的几率。 相似文献
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Solomon Boakye-Yiadom Abdul Khaliq Khan Nabil Bassim 《Metallurgical and Materials Transactions A》2014,45(12):5379-5396
Impacting hardenable steel such as 4340, results in the formation of adiabatic shear bands (ASBs). Previous studies have shown that the presence of carbides/second-phase particles in the pre-deformation microstructures of 4340 steel increases their susceptibility to the formation of ASBs. The current study examines the role of carbides on the microstructure and properties within evolved ASBs in 4340 steel after impact. Geometric phase analysis was used to map local deformation fields within the evolved ASBs. It was observed that carbide fragmentation due to plastic deformation of carbides produces both residual carbides and residual carbide particles in regions away from the shear bands. Extensive carbide fragmentation produces fine residual carbide particles which are redistributed within the ASBs. This is attributed to strain localization within the ASBs which result in higher local strain and strain rates within the shear bands than in regions outside the bands. In addition, it is observed that the residual carbide particles trap and pin dislocations within the shear bands and contribute to an increase in local hardening. A more homogenous distribution of narrower and shorter rotational and shear-strain fields were revealed by the local deformation maps within the evolved ASBs. Lattice deformation mapping revealed that the ferrite matrix, prior to impact, had broader and longer rotational and shear-strain fields perpendicular to the direction of impact. This is attributed to lattice-invariant deformation and shape deformation processes that occur on specific crystallographic planes during martensitic transformation. It is concluded that strain localization during high strain rate deformations does not occur on specific crystallographic planes. This results in a more regular distribution of internal lattice rotational and strain fields within the evolved ASBs. 相似文献
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The molten steel flow in the continuous casting mold and entrapment of inclusions and bubbles on the inner surface of the solidified shell are examined to clarify the mechanism of internal defects in steel products. Defects on steel sheets are caused by bubbles and inclusions entrapped on the solidified shell during casting. It was found that bubbles penetrate deeply due to an unbalanced time‐dependent flow. This phenomenon can be explained by the Large Eddy Simulation model, which can predict the time‐dependent flow. The number of inclusions increases as the bubble diameter and the distance of the position of entrapment from the top free surface increase. This indicates that bubbles collect inclusions while traveling in the molten steel in the continuous caster. A simple mathematical model is presented to explain the mechanism by which inclusions become attached to bubbles. 相似文献
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Incomplete separation of bubbles at liquid‐liquid interfaces during steel casting can lead to subsurface problems in castings that can ultimately result in product defects. An oil‐water model was used to study the separation of bubbles at an oil‐water interface. It was found that rest times of droplets and bubbles at the interface are quite variable with average rest times a function of chemistry and temperature (due to viscosity and interfacial tension changes) and bubble size. The results of these studies were compared to a study of bubbles separating at a steel‐slag interface conducted by X‐Ray Fluoroscopy. All of the phenomena noted in the separation of bubbles at an oil‐water interface were also documented in high temperature experiments. The low temperature results were repeatable and allowed a better understanding of the factors controlling separation. It is postulated that the mechanism of film rupture after drainage is responsible for the variation in measured rest times and accounts for the fact that observed rest times are significantly greater than observed or calculated drainage times. 相似文献
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With the aid of surface and interfacial tension data it has been possible to clarify the effect of the elements nickel, titanium and sulphur in steel and titanium oxide and sulphur in slag on the emulsifying or separating tendencies of liquid steel/molten slag phases. This has been related to the tendency of (scattered) liquid steel films to adhere to gas bubbles crossing the interface, which in turn leads to the formation of metal droplets in the slag phase. Nickel containing steels tend to form emulsions, whereas titanium, both dissolved in the steel and as titanium oxide in the slag, tends to suppress adherence of the steel to the bubbles and promotes steel/slag separation. Sulphur containing steels show also an emulsifying tendency in contact with both sulphur containing and sulphur free slags. With sulphur present in the slag, however, the opposite effect is observed, so that, as sulphur transfer proceeds between the steel and the slag during desulphurization, the emulsifying tendency is markedly reduced, leading to steel/slag separation. 相似文献
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A. C. Stauffer D. A. Koss J. B. McKirgan 《Metallurgical and Materials Transactions A》2004,35(4):1317-1324
The presence of microstructural bands in AL-6XN stainless steel plate has been examined. The bands, which consist of a high
density of second-phase particles, are located near the midthickness of the plate, range in thickness up to 300 μm, and are continuous over lengths up to 50 mm. Chemical analyses of the microstructural bands indicate elevated levels of
chromium and molybdenum, while orientation imaging microscopy identified primarily sigma-phase particles within the bands;
a small volume fraction of chi phase was also found. Tensile specimens oriented in the short transverse direction of the plate
show low ductility and exhibit a large variation in failure strains, depending on the continuity of the bands as well as the
presence of large precipitate particles within the bands. When oriented in either the longitudinal or the long transverse
direction of the plate, circumferentially notched tensile specimens exhibit comparatively high ductility, although at high
stress triaxialities, the material was susceptible to specimen splitting parallel to the tensile axis due to cracking along microstructural bands. 相似文献
11.
通过理论计算研究和分析了钢液气泡直径、吹气量和吹气时间对精炼时去氢和夹杂的影响。氩气经透气砖进入钢液后会形成大量的气泡,小气泡在钢液中能有效地增大脱气面积,有利于减小钢液中的氢含量。夹杂物与气泡的粘附上浮是钢液中去除夹杂物的一种有效方式,气泡越小、夹杂物越大,夹杂物就越容易去除。在钢包精炼过程中,应使用小气泡来达到较好的去氢和去夹杂效果,气泡的最优直径为1~3 mm。 相似文献
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During centrifugal casting of copper alloys containing graphite particles, both particles and bubbles move under the influence
of centrifugal forces and influence the final microstructure, including porosity and the distribution of graphite. The movement
of graphite particles and bubbles in the melts of copper alloys, originally containing 7 and 13 vol pct graphite particles
and centrifugally cast at 800 and 1900 rpm in horizontal rotating molds, has been examined. Microstructural observations of
sections of these centrifugal castings show that the graphite particles are segregated near the inner periphery and the amount
of porosity in the graphite-rich zone is higher than the porosity in the graphite-free and transition zones. The intimate
association of porosity with graphite particles in the graphite-rich zone was explained on the basis of attachment of graphite
particles to bubbles in the melt and the viscosity of the melt, which increases with increasing concentration of graphite
particles near the inner periphery of the castings. It was found that the amount of the porosity in the graphite-rich zone
increases with volume fraction of graphite particles used in this study; the size of the porosity in the graphite-rich zone
also increases with increasing rotational speed of the mold. This suggests that the graphite particles and bubbles were attached
to each other in the melt and they did not get separated during centrifugal casting conditions of the present study. The present
experiments qualitatively confirm theoretical computations. 相似文献
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Optimum Position of Electromagnetic Brake on Slab Caster 总被引:1,自引:0,他引:1
SymbolList B———Magneticfluxdensity ,T ; CD———Dragcoefficient; d———Diameter ,m ; g———Gravitationalacceleration ,m·s-2 ; h———Timestep ,s ; J———Currentdensity ,A·m-2 ; la,lb———Sizeofslabcross section ,m ; ln———Immersiondepthofnozzle ,m ; p———Pressure ,Pa ; t———Time ,s ; u→ ———Velocity ,m·s-1; vc———Castingspeed ,m·min-1; X→ ———Displacement ,m ; ———Electricpotential,V ; ρ———Density ,kg·m-3;… 相似文献
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《Acta Metallurgica Materialia》1990,38(11):2067-2072
This paper reports a microstructural investigation of the changes induced by Ne-implantation in stainless steel of the austenitic type. At a critical dose of 2.3·1017/cm2 a martensitic phase transformation was observed. In particular, attention has been paid to the effect of the stress field of neon bubbles on the nucleation of martensite. It is found that the critical size of the nucleus as well as the activation energy is drastically lowered. No definite orientation relationship between martensite and austenite has been detected. This is probably caused by the small size of martensite particles and the deformation in the vicinity of the bubbles. 相似文献
16.
�ߡ���������£����ء��죬���ϻ������������ 《钢铁研究学报》2015,27(8):24-28
The phenomenon of inclusion removal by fine and uniform heterophases in the molten steel in the ladle was simulated in the water model. The movement behavior of small bubbles and inclusions was analyzed by using of high-speed video camera and image processing technology. Furthermore, the experiment in inclusion simulant removal by purifying agent in three ball-making modes was also carried out in the water model. The effects and causes of inclusion removal under different bubble generation method were analyzed to improve the cleanliness of molten steel. The results show that the purifying agent promotes the removal of inclusions. There is the phenomenon of the bubble capturing multiple inclusion simulants. The rate of inclusion removal by the heterophases at different time is higher than the rate of inclusion removal without small bubbles and the average number raises 13.66%. The composite sphere produced outer layer of purifying agent and the kernel of simulants is most likely to produce fine bubbles and to remove inclusions 100% in three ball-making modes. Because the bubbles are generated, the bubbles impact on the core material to promote cracking of the purifying agent, so more bubbles are generated. 相似文献
17.
Removal of non-metallic inclusions in molten steel is important from the viewpoint of improvement of quality, property and yield of the products. As a removal method of inclusions from molten metal, gas bubble flotation adhering inclusions is well known. Gas bubbling is particularly effective for the removal of fine inclusions. Water model experiment is reported the quantitative analysis of the removal ratio of dispersed particles removed from water by gas bubbles. 相似文献
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An innovative steelmaking process is suggested using an electromagnetic driven swirling flow in the up‐leg of an RH vacuum degassing vessel. The effectiveness of this new process depends on the two‐phase flow behaviour of molten steel and argon gas. A physical and a mathematical model are developed to understand the effect of electromagnetic driven swirling flows on the behaviour of gas bubbles in the up‐leg of an RH vessel. Both water model experiments and numerical simulation show the distribution and trajectories of the gas bubbles. The gas bubbles’ trajectories are spiral and move towards the centre of the up‐leg in the swirling flow field. The accumulation of gas bubbles depends on the swirling number. At the same time, the swirling flow can prolong the residence time and trajectories of non‐metal inclusions in the vessel. The viscous drag force becomes important for small bubbles in the RH degassing vessel, and small bubbles have the trend to rotate with the swirling flow. 相似文献
20.
Pavlína Basařová Jan Zawala Mária Zedníková 《Mineral Processing and Extractive Metallurgy Review》2019,40(6):410-426
ABSTRACTThe interaction between bubbles and solid particles is an important mechanism in many industrial processes and flotation is a significant component of the most utilized applications. While flotation of mineral ores deals with fine particles and larger bubbles, the aim of this review is to focus on the opposite case; the interaction between smaller bubbles and larger particles encountered mostly in plastic flotation. Plastic flotation seems to be one of the appropriate methods for separating plastics, which is necessitated by increasing plastic consumption and the growing need to recycle. The first part of the article focuses on the problem of the collision of a bubble with a particle, both spherical and planar. The collision efficiency is discussed. The second part is devoted to the problem of liquid film rupture and the creation of the three-phase contact line. The third and final part focuses on the problem of the three-phase line expansion and the effect of surfactants on the resulting bubble stability. 相似文献