Table of Content

05 December 2019, Volume 35 Issue 6

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Numerical analysis of stirring flow field of hot metal desulfurization by KR method

2019, 35(6):  1-5. 

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Referring to the KR desulfurization and agitation process of a steel mill in China,using Fluent software,the VOF model was used to numerically analyze the agitated flow field in the tank,and the flow field characteristics under different blade shapes and eccentric stirring were studied to provide reference for the improvement of KR desulfurization equipment and process in order to improve the columnar revolving zone and “dead zone” phenomenon in the KR desulfurization process.The results show that compared with the conventional threeblade stirring,the “dead zone” is not improved in the spiral threeblade mixing flow field,and the area of the columnar rotating zone is increased,the flow velocity and the turbulent energy are reduced.Eccentric stirring basically eliminates the columnar revolving zone and the “dead zone” phenomenon,and the improvement effect is best when the eccentric distance is 30 mm.

Application and practice of new swirl oxygen lance nozzle in 120 t converter

2019, 35(6):  6-11. 

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Aiming at the design and application of swirling oxygen lance nozzle in Yinshan steelmaking plant of Laiwu Iron and Steel Group,a series of problems restricting the promotion of swirling oxygen lance nozzle have been solved through the combination of laboratory test and industrial test for three years,and a complete set of technical problems for the popularization and application of swirling oxygen lance nozzle has been formed.Key integration technologies include design process of swirl oxygen lance nozzle parameters,selection criteria of swirl angle,data analysis method of gas simulation test,optimization approach of swirl oxygen lance nozzle parameters,automatic steelmaking control model of swirl oxygen lance nozzle,slag splashing optimization model,etc.By formulating a set of scientific,complete and rigorous operational specifications,the swirling oxygen lance nozzles have been popularized and applied in 120 t and 150 t converters.The slag blowing time is 30-40 s earlier than that of the normal lance nozzles,the overall blowing time can be shortened by 40-60 s,the average lance life is over 300 heats,and the bottom blowing effect is still good when 5 300 heats are in operation.The good slagging effect and slag splashing effect of the swirling oxygen lance nozzle are verified,and it has a good popularization prospect.

Nitrogen behavior in high nitrogen steel during near equilibrium condition

2019, 35(6):  12-15. 

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Nitrogen loss was primal problem during solidification process of HNS (High Nitrogen Steel). Based on thermodynamic analysis and near equilibrium experiment, the effects of wire steel composition and cooling rate on nitrogen content in melt pool were researched. Under the present conditions, it came to the following conclusions. When the nitrogen mass fraction in wire steel increase from 0.15 % to 0.90 %, the nitrogen content in pool was increased by more than two times. It will be useful to increase ratio of nitrogen in shielding gas. More and more nitrogen were kept in pool as solid-solution state rather than nitrogen bubble with increasing of cooling rate. The nitrogen content increased by more than 30 % under forced cooling design developed in the present study. The results of this paper will provide theoretical guide for controlling the escape of nitrogen element in HNS.

Effects of operation parameters on dephosphorization results of BOF atlow temperature and low basicity

2019, 35(6):  16-23. 

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In this paper, the 180 t BOF industrial tests of double slag and remaining slag technology were carried outto study the effects of the temperature, TFe of dephosphorization slag and especially the basicities varied over a wide range on the phosphorus distribution ratio of LP, dephosphorization ratioand deslagging time under the condition of high phosphorus containing hot metal, and the phase compositions of dephosphorization slag were alsoanalyzed.The results show that when the basicity of slag varies from 0.9 to 2.6, the phosphorus distribution ratio of LP and dephosphorization ratio are increased with increasing basicity, and the calculated values of LPwith Ogawa empirical formula are slightly higher than the actual values with reasonable extents, when the temperature is relatively low in the range of 1345–1420℃. When the temperature of the dephosphorization end point is increased, the phosphorus distribution ratio LP and dephosphorization ratioare decreased. When the TFe in the dephosphorization slag is changed in the range of 11.30 %–19.42%, the effect of TFe change on the dephosphorization reaction is not obvious.The dephosphorization slag phase consists mainly of a dark gray phaseofCa3Mg(SiO4)2, a light gray phaseof CaFeSiO4, and awhitephaseof Ca2Fe2O5. Among them, P content is the highest in the dark gray phase, which is the mainphosphorus-rich phase.

Mathematical simulation and plant trial on soft blowing process of ladle furnace

2019, 35(6):  24-30. 

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In the current study, the Eulerian-Lagrangian method was adopted to simulate the soft argon blowing process of a 100 t ladle. The effect of different blowing argon flow on flow field, bubble movement, surface morphology, and inclusion removal was investigated by mathematical calculation. It was found that, a argon blowing flow rate of 100～200 L/min is beneficial to improve the surface morphology and inclusion removal. In addition, the mathematical modeling of the ladle soft blowing process was applied by an industrial experiment. With an argon blowing flow rate of 150 L/min, the early stage of the soft blowing, the large size inclusions were obviously removed. Ten minutes of soft blowing can effectively enhance the level of molten steel cleanliness.

Effect of holding time after VD on large-sized inclusions of gear steel

2019, 35(6):  31-34. 

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The inclusions at different holding time after VD were detected by Zeiss electron microscope + INCA software for gear steel produced at Baosteel. It is found that the amount of inclusions larger than 5 〖WTBZ〗μ〖WTB4〗m is positively correlated with the amount of inclusions larger than 10 μm, and decreases first and then increases with the increase of holding time. The largest inclusions are mainly spherical CaO-Al2O3+MgO-Al2O3 composite inclusions at different holding time after VD. The size of inclusions increases with the increase of CaO-Al2O3 area proportion of the inclusion. It is suggested that the holding time should be controlled for about 15 minutes.

Study of temperature distribution of continuous casting chamfer mold based on heat flux distribution model

2019, 35(6):  35-40. 

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A mathematical model for the coupling of cooling water flow and heat transfer of copper narrow face in arc chamfer mold for slab continuous casting was established based on the heat flux distribution model. The expression for describing the heat flux distribution along the height of the mold were obtained by means of multiple regression fitting in the study.The heat flux distribution of copper hot surface along the casting direction are non-linear. The heat flux near meniscus increases first and then decrease dramatically, which reaches maximum value at 0.1 m from the meniscus.The results of the calculation show that the surface temperature of the copper plate in the 150～200 mm range from the mold top reaches the highest 608～678 K, and is lower than that of the 723 K chrome-zirconium copper recrystallization softening temperature.Although the maximum temperature of the copper plate water slot surface is nearly 420 K, it does not affect the overall heat transfer.The calculated copper plate temperatures agree with the measured values of thermocouples.

Optimization of current parameters of electromagnetic stirrer for Φ380 mm 40 Cr steel continuous casting round billet crystallizer

2019, 35(6):  41-45. 

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In order to study the influence of the electromagnetic stirring technology of the mold in the production process of the Φ380 mm 40Cr steel continuous casting round billet on the quality of the billet, the magnetic induction intensity of the mold electromagnetic stirrer (M-EMS) was tested, and the magnetic field distribution law of the electromagnetic stirrer and the different current parameters on the quality of continuous casting large round billet were studied.The test results show that the central carbon segregation index of Φ380 mm 40Cr steel continuous casting round billet can be stably controlled below 1.05 when the electromagnetic stirring current and frequency of the crystallizer are 300 A and 2.5 Hz respectively.

Development of internal mixed atomizing nozzles in secondary cooling zone of continuous casting

2019, 35(6):  46-51. 

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In the highspeed continuous casting, the cooling intensity of the secondary cooling zone is large, and the heat transfer uniformity is higher. It is closely related to the highspeed droplet formation and migration behavior of the internal mixing atomizing nozzle. Increasing the cooling uniformity and cooling strength of the nozzle can improve the quality of the cast slab for high speed continuous casting. Based on previous studies, this paper summarizes the heat transfer mechanism between the atomized droplets and the surface of the high temperature slab and the influencing factors of the atomization effect of the internal atomizing nozzle, and proposes the research direction for the subsequent studies.

Metallurgical process development for IF steel in Shougang Jingtang

2019, 35(6):  52-59. 

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The paper involved in intrduction of metallurgical process development for IF Steel in Shougang Jingtang. The key processes of IF steel include carbon, nitrogen content control and coil surface quality control (dealing with the inclusions and nozzle clogging). The key points for carbon control are decarburization in RH process, resistance to recarburization from the end of RH process to tundish, with which the actions are controlling the w(C)≤0.04 % before decarburization, decreasing the scrap addition in RH process, bottom argon blowing along with the decarburization, clean alloy charging, using carbon-free refractory, and so on. The key points for nitrogen control are denitrification in converter process, resistance to renitrification from the RH process to tundish. One of the main defects on surface of IF coil is “inclusion” kind defects. Some anti-inclusion actions usually include low oxygen content at end of converter process, deoxidation for ladle slag, w(Als)/w(Alt)＞0.94 in steel at end of refining process and tundish. After the metallurgical process development, the tundish component of carbon and nitrogen decrease with amount of 3.7×10-6 and 5.9×10-6, the degraded coil percent decreases from 2.3 % to 1.0 %-1.5 %。

Evolution of Inclusions in Pipeline Steel Producted by the Route of BOF-LF-RH-Ca Treatment-CC

2019, 35(6):  60-66. 

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The evolution of inclusions in the pipeline steel producted by the route of “BOF→LF→RH→Ca treatment→CC” was investigated. It was found that the polyhedral Al2O3 changed to spherical MgO-Al2O3-CaO-CaS complex inclusions after LF refining. There was no obvious change on the composition of inclusions, on the contrary, both the number density and the size of inclusions decreased during the RH refining process. After Ca treatment, the contents of CaO and CaS in inclusions increased, induced the increase of CaO/Al2O3, and the moving out from the low melting point zone of inclusions. During the continuous casting, the contents of Als and T.Ca in steel decreased due to the reoxidation, leading to the decrease of CaO and CaS in inclusions and the increase of the number density and maximum size of inclusions. Thus, protective casting should be strengthened to ensure the effect of calcium treatment. Due to the equilibrium movement between steel and inclusions during the cooling process, inclusions changed from liquid CaO-Al2O3 in tundish to high-melting-point inclusions in slab, which were mainly of Al2O3-CaS and MgO-Al2O3 types.

Research on process technology of 40Cr10Si2Mo gas valve steel cleanliness

2019, 35(6):  67-71. 

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In order to solve the problem of low qualification rate of inclusions in 40Cr10Si2Mo gas valve steel rolled by special steel factory. The following measures were taken: the evolution rule of the inclusions in the steel from refining to continuous casting was analyzed, and the existing process system was analyzed. On the basis of laboratory research, the continuous casting argon blowing process and the tundish covering fluxes were optimized. After the application of this technology, the qualified rate increased from 71 % to 97 % of the 40Cr10Si2Mo valve steel inclusions.

Study on surface quality improvement of low nickel austenitic stainless steel

2019, 35(6):  72-76. 

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Thermo-Calc thermodynamic simulation was utilized to analyze the solidification behavior and the phase transition temperature of low nickel stainless steel. Gleeble-3800 thermal simulator was applied to study the high temperature plasticity, EPMA was adopted to study the microstructure and chemical composition of the coil surface crack defects. The results show that there exists the peritectic reaction for low nickel austenitic stainless steels, which is similar to the low carbon steels. The peritectic reaction would lead to the reduction of high temperature plasticity and therefore the high risk of surface longitudinal crack of slab. Based on these studies, the chemical composition of low nickel austenitic stainless steel was optimized. After optimizing the composition, longitudinal crack of slab decreased from 8.92 % to 2.64 %，and the surface crack of coil decreased from 12.45 % to 3.77 %.

Comparative study on the oxide metallurgical effect of Ti-Zr-Mg treatment and Ti-Zr treatment

2019, 35(6):  77-81. 

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Oxide metallurgy has been widely used in the fields of non-quenched and tempered steel and large wire energy welding steel.The oxide metallurgy effects of Ti-Zr-Mg treatment and Ti-Zr treatment were systematically compared through pilot production and simulated welding, charpy impact, scanning electron microscopy and other analytical means, including nonmetallic inclusions, steel plate microstructure and mechanical properties.Compared with Ti-Zr deoxidized , the strength, toughness and impact properties of Ti-Zr-Mg treatment steel platewere not significantly improved, but the welding properties are improved; The microstructure of the rolled plate was basically the same, and the volume of acicular ferrite in the heat affected zone (HAZ) increased. The amount of nonmetallic inclusions in the steel with Mg treated increased slightly, and the inclusions were smaller in size.