Table of Content

05 December 2014, Volume 30 Issue 6

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Research and application on fluorine free slagging process in 300 t combined blowing BOF

2014, 30(6):  1-4. 

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Through industrial test of Shougang Jingtang 300 t combinedblowing BOF semisteel process with fluorine and fluoridefree，the conditions of melting fluorinefree slag was illustrated theoretically. Compared to two kinds of slagging process by industrial test, the results show that combination with using residue, high lance position operation, slag agent addition and reduce the heating speed of bath which can obtain good effect of slagging. Fluorinefree process has been realized that reduce costs an average of 0.904 million yuan one month, expecting cut the cost to increase the profit of 10.85 million yuan one year.

Research on recycling technology of steelmaking sludge

2014, 30(6):  5-9. 

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n the study, steelmaking sludge, quartz sand and manganese ore were mixed at a specific ratio to make slag former for semisteel steelmaking, and this method was experimental vivificated to feasible, steelmaking sludge was cyclic utilized. Industrial test show that the new slag former had a better metallurgical effect than the old one. Slag forming time was shortened by 0.5 min, the dephosphorization rate and manganese mass fraction of the molten steel was improved by 1.2 % and 0.01 % respectively, the mass fraction of T.Fe was reduced by 0.55 % in slag and phase composition of the slag completely meet the requirement of splashing, by which a better splashing effect was obtained.

150 t ladle porous plug bottom argon blowing optimization and industrial tests

2014, 30(6):  10-13. 

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The influence of twoholebottom argon blowing position and flow on steel mixing time in 150 t ladle was studied by the method of water simulation. Vacuum pump oil was simulated as top slag to compare the area of steel exposed under different blowing position and flow. The results show argon blowing at the position 11 and 15 (at the angle of 180, 0.6R far to the center of ladle) is the firstrate choice. At this position, the area of steel exposed and the scour to the ladle refractories is the minimal. Industrial tests show that through the optimization of argon blowing position and soft bubbling flow and time after Catreatment, the increase of w(T.O) in liquid steel Catreatment decreases by 28×10-6 and the decline rate was 78 %. The content of w(T.O) decreases by 34×10-6 after LF refining process and the decline rate reaches 45 %.The control of T.O content has improved significantly.

Application and research of the 60 t tundish level controlling by hydraulic model

2014, 30(6):  14-17. 

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Flow field character of tundish was analyzed by means of hydraulic model at the change ladle period for WISCO 60 t twostrand tundish. Minimum steellevel of tundish was confirmed at the change ladle period which avoided terminal steel of previous ladle flowing into the mould. Productive test and technology optimization were made by practical situation. The results show that the mass fraction of T.O in tundish was 20×10-6 at the change ladle period, which is lower 10×10-6 than the former value and more stable. Cleaning degree of steel increased obviously in tundish. Downgrading of low carbon Alkilled steel due to inclusionrelated quality problem was reduced from 0.8 % to 0.4 %.

Produce on the hot recycling of casting residue from ladles

2014, 30(6):  18-21. 

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The hot recycling of casting residue from ladles in steelmaking plant in Pangang was introduced. Hot recycling of casting residue achieved by protection reform of the turntable and the ratio of recovery increased to 24.1 %. Process data such as the process time of the refining, quality of the steel, the flux consume and recovery rate of continuous casting were analyzed, results indicated that by hot recycling of casting residue, consume of flux decreased by 1.1 kg/t. The produce also contributed to quickly melting of the slag during refining, to reduce the time of refining and insure the quality of the steel. With the hot recycling of casting residue, the cost was reduced by 43.02 million Yuan, and achieved good economic and social benefit.

High speed casting of 2.5 m/min on SGJT No.3 slab caster

2014, 30(6):  22-27. 

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Based on the application of 2.5 m/min high speed continuous casting on low carbon conventional slab in SGJT No.3 caster, the mathematical model of fluid, heat transfer and friction force validated by actual data was established to analyze the related technology. The results show that the mold level could be well controlled by the use of FC mold and SEN with the angle of －20°. The crater end point validated by pin shooting method even at 2.5 m/min was in the range of caster length by improving the secondary cooling water flow rate while the highest temperature in the hot side of mold copper plate was beyond 350 ℃. Furthermore, a kind of mold powder with lower viscosity and better lubrication was employed, and the consumption rate was less that 0.3 kg/m2 at 2.0 m/min or over while there was no breakout occurring. In the near future, development of nonsinusoidal oscillation curve may be a feasible choice. Finally, subsurface inclusions of slab decreased and surface quality of cold coils was improved with casting speed increase.

Analysis and control of hotrolled coil surface inclusions of low carbon low silicon aluminium killed steel

2014, 30(6):  28-31. 

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Hotrolled coil surface inclusions of low carbon low silicon aluminium killed steel was investigated, and the cause of hotrolled coil surface inclusions was analysised by LF and slab continuous casting production. Through the optimization of steelmaking and LF refining, T.O content was reduced in the steel. Through improving the quality of continuous casting refractory, the secondary oxidation was reduced , and the calcium treatment effect was stabilized. Through improving submerged nozzle structure and mould powder performance, the problem of mould powder entrapment and hotrolled coil surface inclusions were solved.

Effect of alumina on hot metal desulphurization with the CaO based desulphurization flux

2014, 30(6):  32-36. 

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Effect of alumina on hot metal desulphurization has been investigated by hot metal desulphurization experiment using CaO based desulphurization flux with various Al2O3 contents. The results indicated that the desulphurization ratio and apparent desulphurization rate constant increased with increasing the Al2O3 contents, following by a decrease with further increasing the Al2O3 contents. The utilization of lime increased with the increase of the Al2O3 contents. The melting point of the lime and desulphurization production, which was covered the surface of the lime particle, was lower with the increase in the Al2O3 contents. An excess of alumina should reduce the ratio of the CaO content, which was the main desulphurization component, and weaken the beneficial effect of CaF2 in the desulphurization flux. It is suggested that the Al2O3 mass fraction in desulphurization flux should be 10 % to get better desulphurization effect and higher utilization ratio of the flux.

Influence of dust and mud pellets on the hot metal temperature

2014, 30(6):  37-41. 

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Confecting dust and mud conglomeration with carbon reducer in dust and mud containing iron, which can self deoxidize by add the pellets into fish torpedo before accepting hot metal. The pellets were warmed up to a high temperature by the residual energy in the empty fish torpedo. So the energy loss will be reduced to some extent. After accepting the hot metal at the trough, the pellets will be deoxidized via the effect of dynamic impact and hot energy of the hot metal. The ferric and zinc oxide carry out self deoxidize in existing equipments to reclaim metal, which will not affect steelmaking. Focus on the influence of hot metal temperature drop caused by the pellets in this article. The test approve that the temperature of hot metal will not drop by adding the pellets, through both theory analysis and production practice. This method has been widely used in Ansteel. The economic and social benefits are notable and 200 million yuan has been created from 2009.

Effect of deoxidation schema on SEN clogging for H08C welding wire steel

2014, 30(6):  42-45. 

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H08C welding wire steel was produced using two deoxidation schemas, one schema is using siliconmanganese to predeoxidize the steel, afterward using ferrotitanium deeply deoxidize the steel; the other one is adding aluminum to deeply deoxidize the steel, then proceeding titanium alloying. The morphology and chemical composition of inclusions in liquid steel and clogs on the submerged entry nozzle were characterized by SEM/EDS，inclusions in liquid steel samples were extracted by sampleelectrolysis method and were quantitatively characterized. The results indicates the inclusion type at LF end is the same for the two deoxidation schemas, which is MnO-Al2O3-SiO2-TiOx, MgO-Al2O3-TiOx, the mass fraction of TiOx inclusion for the first schema is 0.003 3 % in molten steel, and 0.000 8 % for the second schema. The compositions of nonmetallic phase in clogs are the same as the inclusion compositions in liquid steel respectively for both of the two schemas, but there is much iron bulk in the clogs for the first schema, and almost no iron bulk for the second schema. The second deoxidation schema is beneficial to the castability of liquid steel.

Behavior of nonmetallic inclusions in SPA-H steel during LF refining

2014, 30(6):  46-49. 

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The behavior of non-metallic inclusions in SPA-H steel produced by BOF→LF→CSP production route of WISCO during LF refining was investigated. Molten steel samples, slag samples were taken from two industrial heats systematically, and the compositions, size distribution and number of inclusions were analyzed using Aspex explorer. The results showed that, the distributions of inclusion compositions in CaO-Al2O3-MgO ternary phase diagram were like straight lines when the interface reactions equilibrium of slag/metal and refractories/metal were attained. Comparing the inclusions transformation of the two industrial heats, by controlling the composition of slag and refining time, a part of the Al2O3 inclusions could be transformed into lowmelting CaO-Al2O3-MgO inclusions，which were eliminated readily during argon gas light bubbling.

Study on the phase and cooling process of LF refining slag

2014, 30(6):  50-53. 

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X-ray fluorescence、X-ray diffraction、SEM and EDS were used to study the phase composition and microstructure of the 260 t ladle furnace refining slag of a steel mill, and the thermodynamic software FactSage was used to study the precipitation process of each precipitated phase in the cooling process of the LF refining slag.The results indicate that the main phases of the LF refining slag are calcium aluminum phase and calcium silicon phase, and also a small amount of Ca(OH)2 and MgO. Calcium aluminum phase appears as different shapes based on whether it contents sulphur or not; calcium silicon phase mainly appears as round or irregular oval shape, and in accumulation state; free MgO phase has irregular shape, mainly distributed around the calcium silicon phase. In the slow cooling process of the LF refining slag, the final precipitated phases are calcium aluminate contenting MgO(Ca3MgAl4O10),CaO,a small amount of Ca2(Al,Fe)2O5 and γ-C2S, and the precipitating temperatures of each phase are respectively 1 280 ℃,1 100 ℃,1 100 ℃ and 850 ℃.

The quantitative analysis of inclusions in ULC steel slab

2014, 30(6):  54-56. 

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In order to quantitative analyse weather the inclusions in ULC steel slab can meet the requirements of coldrolled sheet，the ULC slab inclusions distribution, composition, size and area ratio was quantitative analysed using Aspex SEM. The inclusions were evenly distributed on the slab section, very few size range were 50～100 μm. Some cluster inclusions larger than 100 μm were existed in slab butts and tail. It was shown that werather oxygen blowing or not in RH,but the same activity oxygen after RH decarbonrization in different heats, the total inclusion number and area ratio were also same. The exicted production was stable, but the slab butts and tail can't use thin plate cold rolling.

Research on direct charging of low alloy steel wide-thick slab

2014, 30(6):  57-61. 

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For the development of direct charging on low alloy steel, Q345B steel was chosen for direct charging study, three regions were divided according to the temperature on the slab surface , found that surface crack less when direct charging in low and high temperature zone, more found in moderate zone, the thin ferrite layers around austenite grain boundary is the prime reason; analysis of cold bending crack on the direct charging plate in the low temperature zone, the results show that band structure and MnS inclusion are the main reason; analysis the effect of microstructure, inclusions, precipitates to the quality of direct charging plate, concludes that direct charging process must avoid the twophase region (austenite and ferrite), avoid the formation of thin ferrite layers, reduce the sulfur content or adding a certain amount of RE for modifying the shape of MnS inclusions, adjust the content of microalloying elements in order to guarantee the strengthening effect.

Study on plasticization control of oxide inclusions in tire cord steel

2014, 30(6):  62-66. 

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In order to transform oxide inclusions in tire cord steel to plastic inclusions with low melting point, the compositions of inclusions, molten steel and top slag were studied in laboratory. On this basis, technical program of industrial test was proposed, and the industrial tests were carried out. With these studies, the components of inclusions can be controlled in low melting point area, and the oxide inclusions are transformed to plastic inclusions with low melting point. The results show that, the wires are not broken for 2 000 m when the diameter transforms from 1.25 mm to 0.2 mm, and the ratio of broken wire is only 0.47 times for per ton wire in industrial production. Otherwise, there are only 3 inclusions in wires per square millimeter.

Effect of pulsed electric field on reaction between Fe-C-i(Si, Mn) and CaO-Al2O3-MgO

2014, 30(6):  67-70. 

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This paper studies the effect of pulsed electric field on slagmetal reactions between Fe-C-i(Si, Mn) alloy and CaO-Al2O3-MgO slag. After applying 2 V pulsed electric field to slag-metal system for 30 s and 60 s respectively, the content of Si and Mn in slag grows with time increasing. The Si mass fraction in slag increases from 0.31 % to 0.63 % and that of Mn mass fraction from 0.02 % to 0.049 % respectively. The difference of the content of Si and Mn in metallic matrix between the upper surface and lower surface decreases gradually, that is w(Si) in metal decreases from 0.06 % to 0.01 % and w(Mn) from 0.32 % to 0.022 % respectively. The sizes of inclusions containing SiO2 or MnO in metallic matrix decease, and the most obvious is SiO2 inclusions, namely the size decreases from 45 μm to 5 μm in average diameters.

Investigate the properties of calcium carbonate rocks which can be used to make slag in converter

2014, 30(6):  71-74. 

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This paper studies the macro and micro states and thermal properties of calcium carbonate rocks such as limestone, calcite and iceland spar by X-ray fluorescence spectroscopy, differential thermal analysis to analyze the crystallinity and the degree of powder of these ore and the grain size and lattice distortion of the calcined lime. The conclusions are as follows: with the increase of mineral grains, the possibility of fragmentation increases； the decomposition temperature of calcite and iceland spar are similar to limestone, they can be used as slag former in converter, but their heat consumptions differ in decomposition process； four original stone are calcined in a muffle furnace at a rate of 10 ℃/min until temperature reach 820 ℃.The grain size of CaO is 61－85 nm, while the grain sizes of calcite and iceland spar with bigger original grains are smaller and have higher degrees of activity which is better for salg forming in converter.

Effects of continuous casting vibration feeding strip on the slab structure

2014, 30(6):  75-78. 

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Taking low carbon steel Q235B, 250 mm×1 600 mm billet as research object, effects of the vibration feeding steel strip on the slab structure and performance was studied in one steel mill. Results show that, porosity in the center of cast billet and macro segregation of dispersion decreased through the continuous casting mould vibration feeding steel strip technology, which can improve the quality of macro structure and reduce the chemical heterogeneity shaft direction to the regional and then improve the plasticity in thick rolling plate.