Table of Content

05 October 2014, Volume 30 Issue 5

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Control Performance of Nonmetallic Inclusion in Molten Steel using Mg-treatment

2014, 30(5):  1. 

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On the basis of thermodynamic calculations, Mg-treatment experiments were carried out in 120 t ladle. The results showed that the slow-release cored wires containing magnesium can be injected smoothly into molten steel. Total magnesium mass fraction in molten steel was measured in the range of 0.001 0 %-0.001 6 %. During the process, nitrogen pick-up was not found. However total oxygen mass fraction was decreased 50 %, also cleanliness of steel was improved. After Mg-treatment, inclusions in SPHC changed from Al2O3 to spinel or pure MgO, and the size decreased from 3-5 μm to 1-2 μm. The magnesium mass fraction in inclusions presented a good correspondence with addition of magnesium alloy.

Analysis and application of hot metal containing vanadium and titanium desulfurization process

2014, 30(5):  5. 

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The physical properties of hot metal containing V-Ti and the choice of desulfurization process in china’s V-Ti steel making factory have been discussed in this paper. The process principle of Magnesium Lime Co-Injection desulfurization and the advantages of its application to hot metal containing V-Ti desulfurization are summarized. By comparing two process flow of extracting vanadium and desulfurization, the advantage of first extracting vanadium then desulfurization was analyzed. Through the analysis of production data in a certain steel plant, a conclusion was reached that the desulfurization agent consumption and blowing time were equivalent between semi-steel desulfurization after extracting vanadium and hot metal desulfurization by using Magnesium Lime Co-Injection method. And the consumption of magnesium powder increases as the semi-steel temperature increases. Relatively, effects of desulfurization agent injection quantity and injection time on semi-steel temperature drop are not obvious.

Analysis and control of end-point manganese content of liquid steel in 150 t converter

2014, 30(5):  9. 

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Improving end-point manganese content of liquid steel could reduce manganese alloy consumption and smelting cost. The variation of manganese during BOF smelting was described and the factors of end-point manganese content of liquid steel were analyzed. The results showed that in production process the manganese content of hot metal and the end-point temperature of liquid steel in converter had no significant effect on end-point manganese content, but oxidization of liquid steel and slag quantity was the key factors. By application of a series of measures such as increment oxygen supply, controlling lance position, controlling top-bottom combined blown, controlling end-point content, applying converter model and adjusting charging system, the end-point manganese content of liquid steel was increased to 0.081 % and manganese alloy consumption was saved 0.32 kg/t.

Change Behavior of Inclusions in High Strength Cold Heading Steel during LF Refining

2014, 30(5):  14. 

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In this paper , the change of inclusions in 40Cr cold heading steel during LF refining was systematically studied by a variety of analysis methods , it was found that the area of inclusions and total O in steel changed consistently during LF refining , inclusion’s area ratio in steel was reduced from 1.41% to 0.45% after LF refining ; And LF refining could effectively remove the large inclusions whose equivalent diameter ECD>10μm , most of the equivalent diameter of inclusions are fall in the range of 2 ~ 5μm . Moreover, when high basicity and highly reductive slag was used in LF refining, combining with calcium treatment technology, it could effectively transfer Al₂O₃ inclusions to MgO-Al₂O₃ system、CaO-Al₂O₃ system and CaO-MgO-Al₂O₃ system inclusions, therefore, the casting performance and cold-flow properties of steel were improved; But calcium treatment process is necessary to be controlled more reasonably in order to reduce the liquid steel slag and secondary oxidation and improve cleanliness of molten steel.

Study on recarburization of low carbon steel produced by LD→LF process

2014, 30(5):  18. 

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In order to effectively control recarburization of low carbon steel, based on the production data of LD→LF process for low carbon steel in a steel plant, this paper analyzed the reasons of recarburization taking for example SWRCH6A, SWRY11 and SAE1006. The results showed that the behavior of recarburization mainly occur in LF refining process，and the increased carbon mostly come from carbide, electrode and ladle lining; Oxygen content in steel have important influence on recarburization of carbide; By adjusting use time and amount of carbide, reducing oxygen content in steel before LF process, the mass fraction of carbon pick-up of SWRY11 and SWRCH6A respectively decrease from 0.022 %, 0.029 % to 0.015 %, 0.017 %.

Controlling of nitrogen content and oxygen content on ER70S-6 steel

2014, 30(5):  22. 

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Measures had been taken which decreased the content of nitrogen and oxygen, increased the production ration of welding wire and improved the welding metallurgy performance during the producing process of ER70S-6 steel in domestic steel-making plant. The results showed that nitrogen content falled 3×10^-6, 4×10^-6 and 2×10^-6 during converter, refining and continuous casting respectively. Nitrogen content decreased 11×10^-6 in whole process and total oxygen content decreased 27×10^-6 in roll product. Macro metallographic picture showed that the quantities of inclusions got lower, the diameters of particles becomed smaller, and distribution morphology changed from chain to disperse. Meanwhile the micro metallographic photo showed that the granularity augmented slightly and the inclusions precipitated along the boundary were improved.

Optimization of SPHC steel process produced by BOF→RH→CC

2014, 30(5):  26. 

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To resolve the issues that phosphorus content in steel was over the upper limits, and the castability of liquid steel was poor, the influence of tapping temperature and tapping carbon content on phosphorus content in steel was investigated, the effect of ladle slag and RH operation on steel cleanliness was also investigated through thermodynamic calculation and production data analysis. After the optimized measures were taken, which included tapping temperature and carbon content decreased, slag modification agent added, tapping hole enlarged, RH deoxidation schema improved, BOF tapping time shortened by 0.9 min, the temperature drop during BOF tapping decreased by 15 ℃, the target ratio of phosphorus at BOF end increased from 87.1 % to 94.3 %, the ratio of oxygen-blowing at RH station decreased from 30.2 % to 14.3 %, and the continuously casting heat increased from 4 heats to above 8 heats in a single tundish.

The numerical simulation and application of oxygen lance in 120 t BOF of Pansteel

2014, 30(5):  30. 

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This research is based upon the 120 t steelmaking converter of Pangang Group Panzhihua Steel & Vanadium Co., Ltd. The flow state about oxygen in the lance and converter were numerically simulated by means of computer, the flow of melting steel below the action of high-speed oxygen current was also simulated. In this paper, the velocity decay with distance for different lance nozzle were simulated, the flow behavior about oxygen and melting steel under different oxygen jet were presented, the mixing time of bath under different angles of oxygen lance nozzle were  numericated. Through numerical simulation, the optimum angle parameter of the oxygen lance nozzle is 16°. According the numerical simulation, the optimized oxygen lance 536-16 has a good performance in the industrial practice.

Study of bottom-blowing process of Cheng-Steel 120 t ladle funace

2014, 30(5):  34. 

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Base on water simulation results, three-dimensional mathematical model for a 120 t ladle furnace of Chengde Iron and Steel Company, Hebei Iron and Steel Co., Ltd., had been built in present work. The simulation results showed that velocity and turbulent kinetic energy of bath increased by 11.8 % and 18.3 %, with the dead region decreased by 33.7 %，which was good at heat transfer, mass transfer and inclusion removal. To test the simulation results, the position of the bottom blown nozzles applied to 120 t ladle furnace of Chengde Iron and Steel Company. The results showed that the total oxygen removal rate was improved by 5.9 %, and the nitrogen content was reduced by 6.4 %. The rate of inclusions removal was improved by 5.5 %, and the rate of large-sized inclusion removal improved by 4.9 %, which achieved the purpose of flow field optimization of 120 t ladle furnace.

Study on circulation characteristics in 150 t RH refining unit by water modeling

2014, 30(5):  38. 

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1︰4 water model has been established for 150 t RH refining unit in Wuhan Iron and Steel (Group) Co. based on analogy theory. The flow regime of molten steel and the effect of the diameter and the number of argon blowing holes were investigated by water model. The circulation parameters of different process conditions were also studied by orthogonal tests. The results show that there is little effect of the diameter of argon blowing holes on circulation parameters, while the mixing time reduces obviously as the number of argon blowing holes increase from 12 to 16. The optimal processes for mixing are the pressure less than 67 Pa, the argon flow rate 130 m³/h and the immersion depth of snorkel 650 mm.

Composite solidification coefficient determination of continuous casting billet and process optimization

2014, 30(5):  43. 

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Nail-shooting technique was applied in measurement of billet produced by Jiyuan Iron & Steel Company，then the thickness of solidified slab shell in secondary cooling region was measured. The liquid core length and the solidification coefficient of continuous cast billet were calculated by use of the solidification law. Reasonable casting speed and the radio of water for cooling effect of the caster were provide, and effects of casting speed, the radio of water, superheat of liquid steel on the solidification of the continuous casting billet were taken further research. According to the current end position of the electromagnetic stirring condition on Jiyuan No.2 caster, the reasonable installation position and optimization results of the specific process parameters were put forward. The result showed that the steel carbon segregation index was below 1.11 after improvement, which met the enterprise control requirements of the product quality.

Study of cleanliness of high nitrogen steel in ESR

2014, 30(5):  48. 

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Inclusions before and after ESR process were compared and the influence of two slag systems and oxygen content in consumable ingots were analyzed. The results show that different slag systems will affect the result of inclusions removal, higher w（CaO）/ w（Al₂O₃） will reduce the level of inclusion and total oxygen content. In ESR process, the sort and chemical composition of inclusion have no difference with different oxygen content in consumable ingots（in inclusions w(MnO)/w(MnO+Al₂O₃)≈0.23~0.32）, which means oxygen content in consumable ingots have no direct relationship with cleanness of ESR ingots. Using consumable ingots, whose oxygen contents diverse from 40×10^-6 to 100×10^-6, both total oxygen contents after ESR are（20~30）×10^-6.

Simulation and controlling on drift in billet continuous casting mold

2014, 30(5):  52. 

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Taking the billet with a section of 160 mm×160 mm as the object of study, the fluid flow bias in the billet was analyzed by using numerical simulation and physical simulation. The results show that, the billet flow bias is due to the existence of the crystallizer radian and the center line alignment. The billet flow bias will make the shell of the inner arc side thin, the liquid flow asymmetric, and the high speed point easy to arrive. Furthermore, slag entrapment is easily occurred. In order to solve this problem, the mould nozzle is offset 6~8 mm outward arc side. After offset, the number of pore defects declined more than 30 %; the arc difference inside and outside was basically eliminated. The statistics show that the billet surface depression and mould slag entrapment rate decreased by 21 %, 56 % respectively.

Numerical Simulation of Solidification Rule in Continuous Casting Process of Φ600mm Round Billet Solidification Q345E Steel

2014, 30(5):  57. 

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A mathematical model of solidification and heat transfer process was established for the Φ600mm round billet of Q345E steel. The result generated by ProCAST was in agreement with the nail test. The simulation results showed: casting temperature had little impact on the surface, central temperature of the round billet and the distribution of solid-liquid phase; as the casting speed increased by 0.02m/min, the surface temperature almost remained unchanged and the mushy zone moved ahead, the distance from the mould to the solidification end increased by around 1.75m; as the specific water flow of secondary cooling zone raised by 0.01L/kg, the surface temperature of secondary cooling zone decreased by about 30℃ and mushy zone moved back slightly, the distance from the mould to the solidification end raised by around 0.3m. Therefore, the proper condition was at T=1539℃, v=0.22m/min and R=0.08L/kg. The practical product of Φ600mm round billet of Q345E steel can reach the national standard, with central shrinkage of 0.5, central porosity of 1.0 and central carbon segregation of ≤1.09.

The influence of dust and mud pellets on torpedo lining corrosion

2014, 30(5):  62. 

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Dust and mud conglomeration were confected with carbon reducer in dust and mud containing iron, which could self-deoxidize. Ferric and zinc oxide were self-deoxidized in existing equipments, which would not affect steel-making. During the process, the torpedo lining corrosion were found. The research based on the problem of corrosion on torpedo lining caused by dust and mud pellets were carried out. The main reason for influencing the torpedo service life was the interaction of slag flow and hot water flow. Now the original process was changed by adding a turning slag process. After that the slags in torpedo will be decreased, the contact time and area between slags and torpedo lining will also be reduced. And the capacity of the torpedoes will be increased at the meantime.

Application of the passivation lime in the hot metal desulfurization process by compound injection

2014, 30(5):  66. 

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In this paper, the desulfurization mechanism and the role of the passivation lime in the hot metal desulphurization by compound injection were analyzed. According to the production practice of the 80 t hot metal desulphurization by compound injection in TISCO, the passivation lime could be helpful for improving the utilization rate and the desulfurization rate, strengthening the deep desulfurization ability, decreasing the temperature loss, the resulfurization content and the iron loss, and reducing the cost of desulfurization in the hot metal desulphurization process by compound injection. When initial sulphur contends in the hot metal was 0.02 %~0.03 % and the final sulphur contends was less than 0.003 %, compared with the single injection of magnesium grains, the desulfurizer cost of the compound injection was lower by 2.96 yuan/t. The iron loss was lower by 1.08 yuan/t. The slag skimming cost decreased by 0.23 yuan/t. The desulfurization cost was lower by 4.02 yuan/t totally.

Heat transfer effect on compound heat reflecting and insulation board of 210 t steel ladles

2014, 30(5):  70. 

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The finite element model of heat transfer in steel containing period of ladle has been established by using of commercial software ANSYS in order to test the slab heat preservation effect of the insulation board on 210 t ladles. Through the calculation of the model, the molten steel temperature-drop rate has been obtained during static period in two kinds of ladle adding insulation board or not. The use effect of insulation board has been investigated through comparison with the same location temperature of two kinds of same-age ladle. The results of experiment and finite element models show that: the ladle wall temperature has been significantly reduced because of the application of insulation board (the average temperature drop77～83 ℃), and the molten steel temperature-drop rate has been decreased 0.105 ℃/min.

Design and practice of improved top relining method for large converter

2014, 30(5):  75. 

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The converter relining is an important part of BOF. In order to satisfy the needs of large converter relining, an economical and efficient large converter top relining method was improved, based on integrating several popular forms of converter top relining methods, which was adapted for the current development of domestic steelmaking plant. Practice shows that it was a rational, reliable, economical method with high automation. It could greatly reduce the labor intensity, shorten the time of relining, and improve the working environment of workers.