Table of Content

05 April 2020, Volume 36 Issue 2

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Water modeling study and industrial application of bottom blowing technology in 260t converter

2020, 36(2):  1-5. 

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A 1:10 water model for a 260 t converter has been established and the effect of bottom-blowing gas flow rate, the quantity and position of bottom nozzles on bath mixing time has been investigated. The typical feature of flow field in the bath has been observed under differentbottom blowing condition. The results show that mixing time of converter bath reduces with the increase of bottom blowing gas flow rate. When total flow rate is 12 L/min, mixing time is longest with twelve bottomblowing nozzles at 0.6R position. When eight nozzlesis used, the life of nozzles reaches 5000 heats,[%C]•[%O] is smaller than 0.0024, and the mean value is 0.0020 in the converter campaign.Flow field in bath shows a circulation from the center to the wallof converter. Vibration of bath appears when bottom blowing gas flow rate exceeds the critical value.

Pressure swing adsorption for oxygen generation and its application in EAF steelmaking

2020, 36(2):  6-9. 

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In the this paper, the development, equipment characteristics, and the process feature of pressure swing adsorption for oxygen generation technology as well as its application in metallurgical field were introduced. After equipped with the VPSA of ZO-1X6000/93 system in ultra-high power electric arc furnace of 100 t Consteel in Guiyang Minda Iron and Steel Co., Ltd., it is found the oxygen utilization increased by 22.31%, smeltingelectricity consumption decreased by 10.69 %, oxygen cost decreased by 82.88 %, and the smelting time reduced by 4 min, which contributes to the improvement of economic returns largely.

Study on decarburization model for RH refining furnace

2020, 36(2):  10-16. 

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In order to improve production efficiency and reduce production cost, the decarbonization process of RH refining furnace in JISCO was studied based on the full-mixing model.The carbon component prediction model was developed and programmed with C# language.The online operation of the model was realized and the carbon content in the actual production process was predicted.The comparison with the actual production data shows: for the end carbon mass fractionprediction, the hit rate is 100% for the error within ±5×10-6, and the hit rate is 80% for the error within ±3×10-6;for the process carbon mass fractionprediction, more than 90% of the predictioniswithin theerrors of±10×10-6.The influences of initial carbon, oxygen and aluminium contents, as well as vacuum time, on decarbonization are discussed.The following conclusions are obtained:in order to obtain molten steel with a lower terminal carbon content, the initial carbon content must be controlled at a low level and the amount of oxygen blowing is preferably controlled to be greater than the theoretical amount of (200～300)×10-6,at the same time, the treatment time should be controlled within the corresponding interval.

Research and practice of increasing circulation flow rate during RH refining

2020, 36(2):  17-21. 

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Aiming at the problem of poor circulation of RH refining process in a steelmaking plant of WISCO, the scheme of enlarging the inner diameter of the snorkel and increase the driving gas flow rate was put forward to improve the circulation flow and refining effect of RH. The optimization effect was verified by adding a copper tracer to the steel in RH refining process. Industrial test results showed that after the RH refining cycle flow rate increased, the average carbon mass fraction of the decarburization end point reduced by 1.210-6, and the total oxygen removal rate increased to 74% from 62.33%. At the same time, the service life of refractory increased, and the refractory consumption reduced by 0.04 kg/t. The comprehensive economic benefits are significant.

Thermodynamics and industrial practice on the formation of non-metallic inclusions in GCr15 bearing steels during deoxidation process

2020, 36(2):  22-28. 

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The thermodynamic software FactSage 7.0 and industrial practice were applied to study the formation of non-metallic inclusions in GCr15 bearing steels during deoxidation process at 1 873 K. Calculated results show that inclusions in molten steel shift Al2O3 to MgO•Al2O3 when the [Mg] mass fraction is larger than 1×10-6. Solid MgO inclusions form when the [Mg] mass fraction is over 10×10-6. Solid CaO•6Al2O3 and CaO•2Al2O3 inclusions generate when the [Al] mass fraction is over 100×10-6 and the [Ca] mass fraction is over 0.1×10-6. Liquid calcium aluminate and solid CaO inclusions appear when the [Ca] mass fraction exceeds 2×10-6 and 13 ×10-6, respectively. Thermodynamic calculated results are in good agreement with measured ones. Besides, evident deviations of deoxidation thermodynamics between pure iron and bearing steel are found, indicating that thermodynamics of pure iron can’t be used to guide the production of bearing steels.

Evolution of non-metallic inclusion composition during cooling and solidification process of Q345 steel

2020, 36(2):  29-33. 

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Inclusions in Q345 steel were modified by calcium treatment. Inclusions in tundish molten steel were MgO•Al2O3 spinel with CaO-Al2O3 wrapped outside. The average composition of inclusions in molten steel was 45.71%Al2O3-40.22%CaO-6.50%MgO-6.60%CaS-0.97%SiO2. Transformation of inclusions occurred during solidification of slab. Near the surface of the slab, phase transformation of inclusions did not have enough time. Therefore, the composition of inclusions was almost the same as in molten steel. At the 1/4 of slab width from the loose side, the inclusions were MgO•Al2O3 spinel with CaS-MnS wrapped outside. The average composition of inclusions was 56.00%Al2O3-9.28%CaO-9.07%MgO-25.06%CaS-0.58%SiO2 while MnS was neglected. From surface to center of slab, the Al2O3 and CaS content of inclusions increased, CaO content decreased, while area fraction of sulfides increased from 0.000 01 %to 0.002 9 %, indicating the precipitation of sulfides. Transformation of inclusions in Q345 steel during cooling and solidification process was calculated using Factsage 7.0. The results were of good consistence to the detected ones, especially for inclusions with smaller size.

Calculation of high temperature solidification characteristics and high temperature physical properties of high strength steel containing niobium

2020, 36(2):  34-41. 

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Based on Ueshima’s hexagonal solidification model, a two-phase solute micro-segregation model was established by FDM. The effect of solute elements on the solidification segregation of high strength steel was analyzed. The high temperature physical properties of high strength steel under CC were analyzed by theoretical calculation. The analysis shows that when the C content is lower than the peritectic point, the degree of segregation of P, S, Nb and Ti decreases with the increase of C content. When the C content is higher than the peritectic point, the segregation tendency of elements is opposite. The value of high temperature physical property parameters of niobium containing steel under fixed composition is quantitatively calculated. Since the high physical parameters of different phases of iron are inconsistent, it can be seen that an accurate phase composition is very important for determining the parameters of high temperature physical properties.

Application of reducer in splayed channel type induction heating tundish

2020, 36(2):  42-47. 

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Taking the six-strand splayed channel type induction heating tundish used by a domestic factory as the research object,in order to improve the flow field characteristics of prototype tundish,reduce the temperature drop, and uniform the temperature of each outlet,a scheme of add a reducerwas proposed andthe flow field and temperature field of the eight-character induction heating tundish were studied by means of water simulation and numerical simulation.The results show that the flow field distribution in the prototype tundish is unreasonable and the temperature difference is obvious.The flow to the middle of the tundish is less, and there is a large low temperature zone in the middle of the tundish.The temperature of each outlet is 1768 K, 1765.54 K,1753.23 K;After the addition of the reducer, the distribution of the flow field can be effectively improved, the flow to the middle of the tundish can be increased, and the temperature uniformity can be improved. The temperature difference of each outlet is controlled within 3 K, the temperature of each outlet is 1761.77 K, 1760.46 K, 1763.08 K.

Numerical simulation of longitudinal cracks in billet surface

2020, 36(2):  48-52. 

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According to the actual production conditions of 165mm×165mm ER80-G steel, the two-dimensional billet thermal coupling model based on the genetic characteristics of continuous casting billet was established by using finite element software ANSYS. The inner cavity size of the mold was optimized for the longitudinal cracking of the billet. The results show that the small taper of the original mold causes the slow growth of the shell in the "hot spot" region, and the high break temperature of the mold flux aggravates the influence of the air gap. The maximum air gap in the corner area of the original mold was 1.46 mm, the maximum difference of the surface temperature of the shell was 130℃,and the the thickness of the shell in the "hot spot" region of the temperature was about 1.5 mm thinner than that in the central region of the surface. The "hot spot" was eliminated by taper optimization, and the thickness of the shell at the exit of the mold 15 mm from corner increased from 12.3 mm to 19 mm.Meanwhile, the break temperature of the mold flux was adjusted from 1 200℃ to 1 050 – 1100 ℃, which promoted the lubrication between the shell and the mold, and the incidence of cracks decreased from 2% to 0.46%.

Causes analysis and control measures of longitudinal cracks on the surface of continuous casting round billet

2020, 36(2):  53-59. 

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The formation mechanism of longitudinal crack of round billet was expounded. The main causes of longitudinal crack of round billet were found out by field investigation and data analysis through anatomical analysis of longitudinal crack shell of round billet at Masteel. The main causes were as follows: harmful element sulfur content in molten steel, poor performance of mold fluxes, off-center and improper inserting depth of submerged entry nozzle, inappropriate temperature and speed of casting, inappropriate radian o and cooling intensity of the mould . According to the actual production situation on the spot,some measures were taken to reduce the longitudinal crack rate of round billet from 0.63 % to 0, the longitudinal crack of round billet was controlled, and the zero longitudinal crack breakout rate was realized.

Research and application of key technology of high speed billet casting machine

2020, 36(2):  59-62. 

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The high casting speed of billet casting machine is the development direction, which can improve the casting machine productivity and better realize the problem of matching with large converter.This paper analyzes several key technologies which have great influence on high casting speed, including high efficiency mould, high precision oscillation device, mold powder and high pressure secondary cold water.The production practice shows that the casting speed of billet casting machine can reach 5.0m/min and the billet quality is good.

Analysis and control of peeling defects of 65Mn steel in cold rolling

2020, 36(2):  63-69. 

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Scanning electron microscope and metallographic examination were carried out to determine the cause of peeling defect of 65Mn steel during rolling. The results showed that the crack in casting billet was the main reason of strip discontinuous cold rolling. The bubble and pinhole defects were the main causes of peeling defects in cold rolling. After optimizing the continuous casting process, the occurrence of cracks, bubbles and pinholes in the billet was reduced. Finally, the strip discontinuous peeling defect reduced from 1.7% to 0.04%, the spot peeling defects were completely controlled, and product quality was recognized by users.

Improvement practice of line scale defect of 304 stainless steel cold rolled plate

2020, 36(2):  70-75. 

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In view of the line scale defect on the surface of 304 stainless steel cold rolled sheet in a factory, the morphology and composition of the defect surface and cross section were analyzed by scanning electron microscopy, and the factors affecting the line scale defect were discussed. The results show that the linear scale defects of 304 stainless steel are mainly caused by CaO-SiO2-Al2O3-MgO slag inclusions.The melting point of inclusions in 304 stainless steel slab is reduced by using low aluminium ferrosilicon or reducing the basicity of AOD tapping slag in AOD reduction stage, which is beneficial to improving the plastic deformation ability of inclusions.In addition, the tundish changing rhythm is accelerated, the minimum tundish tonnage proportion is increased to more than 85%，and the tundish flow field is stabilized.At the same time, the amount of remaining molten steel in large ladle should be increased to 5－6 t, so as to avoid large ladle slag entering tundish, limit inclusions from the source and improve the purity of molten steel.After the implementation of the above improvement measures, the degradation rate of line scale defect of 304 stainless steel cold rolled sheet can be stably controlled within 0.2%.

Evolution rules of inclusions in high quality bearing steel produced by BOF-LF-RH-CC and EAF-LF-VD-CC process

2020, 36(2):  76-80. 

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Bearing steel inclusions produced by BOF-LF-RH-CC and EAF-LF-VD-CC were compared and analyzed by taking two different bearing steel production processes of a company as an example. The furnace tapping at the beginning of the carbon content of the early stage of the LF refining effect on the number of inclusions as well as the composition, the carbon mass fraction of steel for 0.07 % in the BOF,LF refining the early inclusion and quantity for 5.04 per mm2 was mainly for Al2O3 inclusions, the carbon mass fraction of steel for 0.58 % in the EAF, LF refining the early inclusion and quantity for 2.49 per mm2 was mainly for MgO·Al2O3 style inclusions, but at the end of the LF refining steel carbon content have less effect on the number of inclusions. CaO activity in LF refining slag has an impact on CaO content in inclusions. LF refining slag of BOF-LF-RH-CC process has an CaO activity of 0.632, and the CaO mass fraction in inclusion is 5 % at the end of refining. The CaO activity of LF refining slag in EAF-LF-VD-CC process is 0.965, and the CaO mass fraction of inclusion at the end of refining is 18 %. By comparing and analyzing the composition and quantity changes of bearing steel inclusions after RH and VD, it is found that the number of MgO·Al2O3 high-melting point inclusions decreases from 1.02 per mm2 to 0.01 per mm2 after RH. MgO･Al2O3 style high melting point inclusion quantity by 0.18 per mm2 was reduced to 0.01 per mm2 after VD and inclusions are mainly low melting point of CaO-Al2O3, but from CaO-Al2O3-MgO style class inclusion quantity analysis found on RH treatment after a sharp decline in the number of inclusions and inclusions after VD amount is not large drop, think of VD process of MgO･Al2O3 style inclusions decrease of slag due to sharp steel slag mix at VD process of MgO·Al2O3 style disguised “calcium treatment” results.