Aggregation Kinetics of Inclusions in Swirling Flow Tundish for Continuous Casting

 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.     

Application of Hot Strength and Ductility Test to Optimization of Secondary Cooling System in Billet Continuous Casting Process

By means of Gleeble-1500 dynamic thermomechanical simulator, the continuous casting process for HRB335C steel was simulated using solidifying method and hot ductility and strength of the steel were determined. The test results indicate that there are three temperature regions of brittleness for HRB335C billet in the temperature range from 700 ℃ to solidification point; the first temperature region of brittleness is 1 300 ℃ to solidification point of the billet, the second temperature region of brittleness is 1 200-- 1 000 ℃, and the third temperature region of brittleness is 700-850 ℃ ; the steel is plastic at 850--1 000 ℃. The cracking sensitivity was studied in the different temperature zones of the brittleness for steel HRB335C and the target surface temperature curve for the secondary cooling is determined. With optimized process, the mathematical model of the steady temperature field with two-dimensional heat transfer for 150 mm×150 mm HRB335C steel billet was established to optimize the secondary cooling process. The conic relation of water distribution between secondary cooling water flux and casting speed is regressed. Keeping the surface temperature of billet before the straightening point above 1 000 ℃, the results of billet test indicate that there is free central shrinkage cavity. The billet defect is decreased greatly, and the quality of billet is obviously improved.     

Modelling Effect of Circulation Flow Rate on Inclusion Removal in RH Degasser

Based on the similarity principles,a 1∶ 7 scale physical model was established to study the behavior of molten steel flow and inclusion removal in a 145 t Rheinsahl-Heraeus( RH) degasser.On the basis of the quantitative measurements of the circulation flow rate and inclusion removal under various lifting gas flow rates,the effect of circulation flow rate on inclusion removal was investigated in the RH degasser.The inclusion removal rate shows the trend of first increase and then decrease twice with increasing the circulation flow rate when the circulation flow rates are smaller than 104.7 L/min.Whereas,the inclusion removal rate increases again with the further increase in circulation flow rate when the circulation flow rate is larger than 104.7 L/min.At lower circulation flow rates,inclusions are mainly removed by Stokes flotation to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow.At higher circulation flow rates,the collision and aggregation of inclusions improves the inclusion removal efficiency.With the further increase in the circulation flow rate,inclusions are mainly removed by following the turbulent fluctuation( turbulent diffusion)to the slag/steel interface after inclusions are transferred near the slag/steel interface by the circulation flow.     

Applications of EMS and Its Development in Baosteel

EPM-related technologies are widely used in Baosteel,where a full-time working team is making their effort in various topics for better qualities of steel products.In this paper,applications and new developments of EMS technology in Baosteel are mainly introduced.Although EMS has already become conventional means for improving steel billet/bloom and slab qualities,there still exist problems due to low efficiency or unsatisfactory application results.To solve these problems,not only the internal mechanical structure of the EMS equipments,but also the relationship between EMS and solidification process,physical properties as well as fluid mechanics should be carefully investigated.By using of computer simulation,laboratory and on-line experiments,our understandings of EMS technology have been upgraded based on the obtained results.For improvement of equiaxed crystal ratio,the magnitude of EMS force plays a much more important role than superheat.And the nonlinear relations between power source frequence and EMS force are quite different for different types of EMS equipments,which means adjustment of frequence to a proper value is very important.     

Estimation of maximum inclusion by statistics of extreme values method in bearing steel

A statistic method,statistics of extreme values(SEV),was described in detail,which can estimate the size of maximum inclusion in steel.The characteristic size of the maximum inclusion in a high clean bearing steel(GCr15)was evaluated by this method,and the morphology and composition of large inclusions found were analyzed by scanning electron microscopy(SEM).When standard inspection area(S0)is 280 mm~2,the characteristic size of the biggest inclusion found in 30 standard inspection area is 23.93μm,and it has a 99.9% probability of the characteristic size of maximum inclusion predicted being no larger than 36.85μm in the experimental steel.SEM result shows that large inclusions found are mainly composed of CaS,calcium-aluminate and MgO.Compositing widely exists in large inclusions in high clean bearing steel.Compared with traditional evaluation method,SEV method mainly focuses on inclusion size,and the estimation result is not affected by inclusion types.SEV method is suitable for the inclusion evaluation of high clean bearing steel.     

Effect of Rare Earth Composite Modification on Microstructure and Properties of a New Cast Hot-Work Die Steel

The effects of RE modification on structure and the properties of a new cast hot-work die (CHD) steel were investigated. The grains of the CHD steel are refined by RE modification. With the increase of RE addition, both grain size and inclusion amount are reduced. Appropriate amount of RE results in decrease in inclusion amount and formation of spheroidal inclusions uniformly - distributed in steel, so that the morphology and distribution of inclusions are improved. RE composite modification favors the formation of bainite, austenite and fine lath martensite with dense dislocation. When the residual RE content reaches 0.02 %, no obvious changes in strength and hardness are found, while fracture toughness and threshold of fatigue crack growth are increased. The impact toughness, elongation and reduction of cross sectional area are increased by a factor of two, and thermal fatigue resistance is also improved.     

Numerical Simulation of Inclusion Removal in Tundish With Babbling Curtain and Electromagnetic Field

According to the structure and the operating parameters of tundish at some plant,the inclusion removal in tundish with babbling curtain and electromagnetic field was simulated by numerical calculation method,and based on the optimization,the actual-service test were put into effect.The results show that:compared with the bubble-gap soft filter of multiple gas curtains,the composite filter with traveling wave magnetic field and bubbling curtains in the tundish can further improve the inclusion removal rate.A large number of small particle inclusions are removed primarily by bubble flotation through the assisting of electromagnetic field.While the removal rate of inclusions which diameters are less than50μm is increased by 48%,especially the removal rate of inclusions which diameters are less than 20μm is increased by76%.The efficacy of the composite filter of traveling wave magnetic field and bubbling curtain is obviously.     

Technology of nitrogen-argon mixed gas blowing on the tundish stopper

Bubble defect is one of the main defects of an automobile sheet.To solve this defect,the technology for nitrogen-argon mixed gas blowing on the tundish stopper is developed,the theoretical research on nitrogen absorption in the molten steel is performed,the nitrogen-argon mixed gas blowing equipment is developed and experimented in the plant.The expected effect is achieved in the industrial test,and the slab inclusion density and quality degradation ratio of the automobile sheet are significantly reduced.     

Effect of Structure Parameters on Power and Magnetic Field in Electromagnetic Soft-Contact Continuous Casting System

To design a power source system and mold for electromagnetic soft-contact continuous casting process and to theoretically estimate the heat losses from the charges and the system power, the effect of structure parameters on system power and magnetic flux density distribution was calculated using finite element method. The results show that as for electromagnetic soft-contact continuous casting system with partial-segment type mold, the power consumption is much more than that with a full-segment type mold; about 62% of electric power is dissipated in the mold, and the effective acting range of magnetic field is relatively narrow. Optimizing mold structure is a crucial measure of remarkably reducing mold power consumption and saving electric energy. Increasing slit number, width, and length can remarkably increase the magnetic flux density in the mold and can reduce the electric energy consumption. Among structure parameters, slit number and slit width are relatively more effective to reduce energy consumption. For a round billet electromagnetic continuous casting system with diameter of 178 ram, the reasonable slit number, width, and length are about 24--32, 0. 5--1.0 mm, and 160 mm, respectively.     

Microstructure,Tensile and Impact Toughness Properties of Friction Stir Welded Mild Steel

 Microstructure, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel are revealed in this paper. The 5 mm thick AISI 1018 mild steel plates were friction stir welded with tool rotational speed of 1000 rpm and welding speed of 50 mm/min with tungsten base alloy tool. Tensile strength of stir zone is higher (8%) when compared to the base metal. This may be due to the formation of finer grains in the weld nugget region under the stirring action of the rotating tool. The ductility and impact toughness of the joints are decreased compared to the base metal and this is due to the inclusion of tungsten particles in the weld region.     

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积极参与国际标准制定是我国跨越贸易技术壁垒的重要对策犤刊.中犦郁//上海金属2003年1-8～11在我国加入WTO后,随着WTO所倡导的关税壁垒的大幅度降低,更为隐蔽、更具有杀伤力的贸易技术壁垒出现在我们面前。将技术标准做为贸易保护壁垒,是WTO规则允许采用的手段。许多发达国家和地区,都在积极从技术进步这一生产力发展源头上下功夫,形成一国自己的技术标准,并且为国际所承认。一流企业定标准,二流企业做品牌,三流企业卖产品。宝钢上海钢铁工艺技术研究所开发的梅花齿形冷压连接接头,在国内有较强的技术优势,在国际上有一定知名度。1999…     

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