Exploration and Practice of Nitrogen Addition Process for LF Refining Ladle Bottom Blowing Nitrogen Steel Liquid

This article discusses and analyzes the law of nitrogen increase in liquid steel and the main factors affect-ing the nitrogen increasing of molten steel,through the way of adding nitrogen to molten steel by bottom blowing nitrogen gas in LF refining process.It is considered that the main factors affecting the nitrogen increasing instability of molten steel are the initial temperature of LF refining,nitrogen relative element,surface active elements[O]and[S]of steel liquid,and bottom blowing rate of ladle.The large-scale production practice shows that T[O]not more than 50×10-6 and[S]is not more than 0.020 in LF refining at the initial temperature of not less than 1570.The liquid steel nitrogen enrichment test is carried out by ladle bottom blowing nitrogen gas after 20 min of refining,the flow rate is set as(6.0~7.0)NL/min per ton,and it is turned to 2 NL/min at 6 min before the end of refining,the nitrogen increasing rate of liquid steel is basically stable at(5~6)×10-6 per minute.

Study on Flow and Mixing Characteristics of Molten Steel in RH and RH-KTB Refining Processes

The flow and mixing characteristics of molten steel during the vacuum circulation refining, including RH(Ruhrstahl Heraeus) and RH KTB(Ruhrstahl Heraeus Kawasaki top blowing) processes, were investigated on a 1/5 linear scale water model of a 90 t multifunction RH degasser. The circulation rate was directly and more accurately determined, using a new method by which the more reliable results can be obtained. The fluid flow pattern and flow field in the ladle were demonstrated, observed and analyzed. The mixing time of liquid in the ladle was measured using electrical conductivity method. The residence time distribution in the RH model was obtained by tracer response technique. The influence of the main technological and geometric factors, including the gas top blowing (KTB) operation, was examined. The results indicated that the circulation rate of molten steel in the RH degasser can be fairly precisely calculated by the formula: Q lp =0.0333 Q 0.26 g D 0.69 u D 0.80 d(t/min), where Q g-the lifting gas flow rate (NL/min); D u and D d-the inner diameters of the up and down snorkels (cm), respectively. The maximum value of circulation rate of molten steel in the case of the 30 cm diameters either of the up and down snorkels for the RH degasser (the “saturated” rate) is approximately 31 t/min. The corresponding gas flow rate is 900 NL/min. Blowing gas into the vacuum chamber through the top lance like KTB operation does not markedly influence the circulatory flow and mixing characteristics of the RH process under the conditions of the present work. There exist a major loop and a large number of small vortices and eddies in the ladle during the RH refining process. A liquid liquid two phase flow is formed between the descending stream from the down snorkel and the liquid around the stream. All of these flow situation and pattern will strongly influence and determine the mixing and mass transfer in the ladle during the refining. The correlation between the mixing time and the stirring energy density is τ m∝ε -0.50 for the RH degasser. The mixing time rapidly shortens with an increase in the lifting gas flowrate. At a same gas flow rate, the mixing times with the up and down snorkel diameters either of 6 and 7 cm are essentially same. The 30 cm diameters either of the up and down snorkels for the RH degasser would be reasonable. The concentration time curve showed that three circulation cycles are at least needed for complete mixing of the liquid steel in the RH degasser.

Hybrid Neural Network Model for RH Vacuum Refining Process Control

A hybrid neural network model,in which RH process(theoretical)model is combined organically with neural network(NN)and case-base reasoning(CBR),was established.The CBR method was used to select the operation mode and the RH operational guide parameters for different steel grades according to the initial conditions of molten steel,and a three-layer BP neural network was adopted to deal with nonlinear factors for improving and compensating the limitations of technological model for RH process control and end-point prediction.It was verified that the hybrid neural network is effective for improving the precision and calculation efficiency of the model.

Toward the development of Mg alloys with simultaneously improved strength and ductility by refining grain size via the deformation process

Magnesium(Mg) alloys, as the lightest metal engineering materials, have broad application prospects.However, the strength and ductility of traditional Mg alloys are still relativity low and difficult to improve simultaneously.Refining grain size via the deformation process based on the grain boundary strengthening and the transition of deformation mechanisms is one of the feasible strategies to prepare Mg alloys with high strength and high ductility.In this review, the effects of grain size on the strength and ductility of Mg alloys are summarized, and fine-grained Mg alloys with high strength and high ductility developed by various severe plastic deformation technologies and improved traditional deformation technologies are introduced.Although some achievements have been made, the effects of grain size on various Mg alloys are rarely discussed systematically and some key mechanisms are unclear or lack direct microscopic evidence.This review can be used as a reference for further development of high-performance fine-grained Mg alloys.

Physical Modeling of the Vacuum Circulation Refining Process of Molten Steel

The available studies in the literature on physical modeling of the vacuum circulation (RH, i.e. Ruhrstahl Heraeus) refining process of molten steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was employed to investigate the flow and mixing characteristics of molten steel under the RH and RH KTB (Kawasaki top blowing) conditions and the mass transfer features between molten steel and powder particles in the RH PTB (powder top blowing) refining. The geometric similarity ratio between the model and its prototype (a multifunction RH degasser of 90 t capacity) was 1:5. The effects of the related technological and structural factors were considered. These latest studies have revealed the flow and mixing characteristics of molten steel and the mass transfer features between molten steel and powder particles in these processes, and have provided a better understanding of the refining processes of molten steel.

An energy saving and fluorine-free electrorefining process for ultrahigh purity lead refining

The present paper reports a new fluoride-free and energy-saving lead electrolytic refining process in order to solve the serious problems of the existing Betts lead electrorefining process, such as low production efficiency,high energy consumption and fluorine pollution. In the process, a mixed solution of perchloric acid and lead perchlorate(HClO4-Pb(ClO4)2) with the additives of gelatin and sodium lignin sulfonate is employed as the new electrolyte. The cathodic polarization curves show that HClO4 is very stable, and there is no any reduction reaction of HClO4 during the electrolytic process. The redox reactions of lead ions in HClO4 solution are very reversible with an ultrahigh capacity efficiency, so the HClO4 acts as a stable support electrolyte with higher ionic conductivity than the traditional H2SiF6 electrolyte. The results of the scale-up experiments show that under the optimal conditions of 2.8 mol·L-1 HClO4, 0.4 mol·L-1 Pb(ClO4)2 and electrolysis temperature of 45 ℃, the energy consumption is as low as 24.5 kW·h·(t Pb)-1 , only about 20% of that by Betts method at the same current density of 20 mA·cm-2, and the purity of the refined lead is up to 99.9992%, much higher than that specified by Chinese national standard(99.994%, GB/T 469-2013) and European standard(99.99%, EN 12659–1999).

Mathematical Modeling of the Vacuum Circulation Refining Process of Molten Steel

The available studies in the literature on mathematical modeling of the vacuum circulation (RH) refining process of molten steel have briefly been reviewed. The latest advances obtained by the author with his research group have been summarized. On the basis of the mass and momentum balances in the system, a new mathematical model for decarburization and degassing during the RH and RH KTB refining processes of molten steel was proposed and developed. The refining roles of the three reaction sites, i.e. the up snorkel zone, the droplet group and steel bath in the vacuum vessel, were considered in the model. It was assumed that the mass transfer of reactive components in the molten steel is the rate control step of the refining reactions. And the friction losses and drags of flows in the snorkels and vacuum vessel were all counted. The model was applied to the refining of molten steel in a multifunction RH degasser of 90 t capacity. The decarburization and degassing processes in the degasser under the RH and RH KTB operating conditions were modeled and analyzed using this model. Besides, proceeded from the two resistance mass transfer theory and the mass balance of sulphur in the system, a kinetic model for the desulphurization by powder injection and blowing in the RH refining of molten steel was developed. Modeling and predictions of the process of injecting and blowing the lime based powder flux under assumed operating modes with the different initial contents of sulphur and amounts of powder injected and blown in a RH degasser of 300 t capacity were carried out using the model. It was demonstrated that for the RH and RH KTB refining processes, and the desulphurization by powder injection and blowing in the RH refining, the results predicted by the models were all in good agreement respectively with data from industrial experiments and practice. These models may be expected to offer some useful information and a reliable basis for determining and optimizing the technologies of the RH and RH KTB refining and desulphurization by powder injection and blowing in the RH refining and for controlling the processes.

Application of novel constrained friction processing method to produce fine grained biomedical Mg-Zn-Ca alloy

In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.

Thermal Analysis Simulation of Germanium Zone Refining Process Assuming a Constant Radio-Frequency Heating Source

Three-dimensional thermal a nalysis simulation of a horizontal zone refining system is conducted for germanimn semiconductor materials. The considered geometry includes a g＇ral）hite boat filled with germanium placed in a cylindrical quartz tube. A flow of Ar and H2 gas mixture is purged througll the tube. A narrow section of the, boat is assmned to be exposed to a constant heat rate produced b v an rf coil located outside the quartz tube. The results of this analysis provide essential information about various parameters such as the shape of tile molten zone, required power and temperature gradient in the system.

Refining the Production Process

WHILE much of Africa＇s oil production is exported in its crude form, Uganda is primed to build its own oil refinery. This ambition is set to be realized after the China National Offshore Oil Corp. （CNOOC） struck a $2-billion licensing deal to develop a vast petroleum field in Uganda. Signed in late September, it was the first oil production license to be issued in Uganda,

Refinement of packet size in low carbon bainitic steel by special thermo-mechanical control process

The packet size of bainitic steel can be refined by a specialrelaxation-precipitation-control phase transformation (RFC) technology. When processed by RPCprocess, the low carbon bainitic steel composes of two kinds of main intermediate transformationphases. One is ultra-fine lath-like bainitic ferrite and the lath is less than 1μm in width andabout 6 μm in length; the alignment of laths forms a refined packet, and the size of packets isabout 5-7 μm in length and about 3-4μm in width. The other is acicular structure. The morphologyand distribution of these acicular structures are influenced by relaxation process, the thin andshort acicular structures cut the prior austenite grain and refine the bainitic packet size. For theoptimum relaxation time, the packet size can be refined to the finest. The mechanical propertiesare influenced by relaxation time and the 800 MPa grade low carbon bainitic steel with excellenttoughness can be obtained by RPC process.

Effect of Process Parameters on Morphology and Grain Refinement Efficiency of TiAl_3 and TiB_2 in Alumimum Casting

This paper presents the effects of different process parameters in producing Al-STi-1B grain refiner,i.e.various sequences and reaction time,on grain refinement efficiency of aluminum castings.It was found that different process parameters resulted in different morphology and size distribution of TiAl-3 and TiB-2 in grain refiner. The experiment was carried out by adding KBF-4 and K-2TiF-6 to molten aluminum.The melting temperature was controlled at 800℃in an electric resistance furnace.Three different sequences of KBF-4 and K-2TiF-6 additions were applied,i.e.,adding KBF-4 before K-2TiF-6,adding K-2TiF-4 before KBF-4 and mixing both KBF-4 and K-2TiF-6 before adding to molten aluminum.Three different holding time at 1 min,30 min and 60 min were applied.The results showed that no significant difference of morphology and size distribution was found by varying three different sequences.Whereas,the different holding time provided major differences in both morphology and size distribution,which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAI3 and TiB2.If the reaction time was longer than 30 rain,morphology of both TiAl-3 and TiB-2 became too large.If the reaction time was too short,less reaction between TiAl-3 and TiB2 to form would be obtained.For grain refinement efficiency, it was found that mixing KBF-4 and K-2TiF-6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.

Refinement of primary Si grains in Al–20%Si alloy slurry through serpentine channel pouring process

In this study, a serpentine channel pouring process was used to prepare the semi-solid A1-20%Si alloy slurry and refine primary Si grains in the alloy. The effects of the pouring temperature, number of curves in the serpentine channel, and material of the serpentine channel on the size of primary Si grains in the semi-solid A1-20%Si alloy slurry were investigated. The results showed that the pouting temperature, number of the curves, and material of the channel strongly affected the size and distribution of the primary Si grains. The pouring tempera- ture exerted the strongest effect, followed by the number of the curves and then the material of the channel. Under experimental conditions of a four-curve copper channel and a pouring temperature of 701℃, primary Si grains in the semi-solid A1-20%Si alloy slurry were refined to the greatest extent, and the lath-like grains were changed into granular grains. Moreover, the equivalent grain diameter and the average shape coefficient of primary Si grains in the satisfactory semi-solid A1-20%Si alloy slurry were 24.4 μm and 0.89, respectively. Finally, the re- finement mechanism and distribution rule of primary Si grains in the slurry prepared through the serpentine channel pouring process were analyzed and discussed.

Improvement in grain refinement efficiency of Mg-Zr master alloy for magnesium alloy by friction stir processing

Previous studies have proved that the zirconium(Zr)alloying and grain refining performance of a Mg-Zr master alloy on Mg alloy is closely related to the distribution of Zr particle size,and a Mg-Zr master alloy with more Zr particles in size range of 1-5μm exhibits a better refining efficiency.In this paper,friction stir processing(FSP)was used to modify the Zr particles size distribution of a commercially available Mg-30 wt.%Zr master alloy,and the subsequent grain refinement ability was studied by trials on a typical Mg-3Nd-0.2Zn-0.6Zr(wt.%,NZ30K)alloy.It is found that plenty of large Zr particles in the as-received Mg-30%Zr master alloy are broken by FSP.Grain refinement tests reveal that the refining efficiency of Mg-30%Zr alloy is significantly improved by FSP,which is attributed to the better distribution of Zr particles.The refinement effect by adding 0.6%FSP-ed Mg-30%Zr is approximately equivalent to that by adding 1.0%as-received Mg-30%Zr.Due to the easy and convenient operation of FSP,this study provides a new method to develop a more efficient Mg-Zr refiner.

Grain refinement of low carbon steel produced by CSP process

In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM, TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to -125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm, respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process. The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.

Optimization of processing parameters for preparation of Al-3Ti-1B grain refiner

Al-3Ti-1B master alloys were prepared at different processing parameters by the reaction of halide salts,and the grain refining response of Al-7Si alloy was investigated with Al-3Ti-B master alloy.The microstructure of master alloy and its grain refining effect on Al-7Si alloy were investigated by means of OM,XRD and SEM.Experimental results show that,the size of Al3Ti particles presented in Al-3Ti-1B master alloys increases with the increase of reaction temperature and decreases with the increase of cooling rate.The grain refining efficiency of Al-3Ti-1B master alloy on Al-7Si alloy is mainly attributed to heterogeneous nucleation of Al3Ti particles,and the morphology ofα(Al)changes from coarse dendritic to fine equiaxed.As a result,Al-3Ti-1B master alloy is prepared by permanent mold,and holding at 800 ℃for 30min,which has better grain refining performance on Al-7Si alloy.

Overview on Routes for Development of China's Petroleum Refining Technology

China has formed a complete and packaged system of domestic petroleum refining industry. Till 2020 the demand for petroleum products in China will record a sharp growth. However, China is currently confronted with a shortage of oil resources, unsatisfactory quality of petroleum products, a widening gap between demand and supply of steam cracking feedstocks, and a stern situation in environmental protection.In this context the petroleum refiners of China, while taking into account the actual conditions, should seek for the way of deep processing to produce transportation fuels and chemical feedstocks that can hardly be replaced by other energy forms, continue to bring into full play FCC process as core process for making finished oil products, speed up the development of hydrocracking to achieve integration between refining and chemical production, adopt measures that can combine feedstock pre-treatment, novel FCC technologies and after-treatment of products to improve the quality of finished products, as well as realize the recycling of wastewater and control over air pollution caused by SOx to accelerate the development of petroleum processing industry in China.

Mechanism of Grain Refinement Induced by Laser Shock Processing in AZ31 Magnesium Alloy

In order to study the mechanism of grain refinement induced by laser shock processing （LSP） in AZ31 magnesium alloy, the specimens were processed with Nd：glass pulse laser shocking and the microstructures of LSP specimens near the surface were examined by optical microscopy and transmission electron microscopy. Optical microstructure pictures show that the size of grains formed in the top surface layer is about 4-6 μm, which is obviously different from the original grains （with an average size of 20-30 μm） in the substrate in AZ31 magnesium alloy. Transmission electron microscopic observations show that the grain refinement process of AZ31 alloy by laser shock processing includes three stages. At the early stage of LSP, the lower strain and strain rate activates the three dislocation slip systems which include basal plane system, prismatic plane system and pyramidal plane system, with the deformation governed mainly by dislocation. At the intermediary stage, dislocation slip is hindered at grain boundaries and becomes more difficult to continue during LSP. Then, parallel twins appear, which divide the original coarse grains into finer twin platelets. Finally, high-density dislocation walls are formed and subdivide twins into sub-grains. Dynamic recrystallization occurs in the process of further deformation and forms recrystallized grains when strain energy reaches the value needed by recrystallization, which leads to refinement of the grains in the top surface layer.

造纸高浓度磨浆机浓度控制系统设计

造纸工业中的高浓度磨浆机是一个关键的工艺设备,其性能和控制直接影响到纸张的最终质量和生产效率。基于此,从高浓度磨浆机的结构和工作原理入手分析,关注浓度控制系统的设计和关键组成部分,研究数据采集、处理和分析的方法,此外探讨多目标优化控制模型以及力学能耗模型,以确保磨浆机在不同工况下能够实现最佳性能,进而实现可持续和高效的造纸生产过程。