Table of Content

05 October 2015, Volume 31 Issue 5

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Slag splashing process optimization and results in BOFs with high oxidizability slag

2015, 31(5):  1-6. 

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Experiment Study

Thermodynamics and kinetics research of nitrogen dissolution in steel

2015, 31(5):  7-11. 

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In order to explore the low cost of nitrogen microalloyed steel smelting technology by direct alloying with nitrogen, the dissolution behavior of N2 in three kinds of steel which are the mainly productions of one domestic steelmaking factory is studied, and thermodynamics and dynamics of steel liquid nitrogen absorption model is verified by using the experimental data. Model calculation results and the measured values are in good agreement, and the experimental results show that the nitrogen partial pressure, the greater the solubility of nitrogen in the steel, the greater the [Mo] and [Ni] element has a significant effect on the nitrogen content in steel; Steel liquid nitrogen absorption and denitrification reaction is first order reaction and nitrogen balance absorption time of 25 min, nitrogen balance time for 40 min.

The research on the oxidizing dephosphorization of stainless steel using BaO-CaO slag system

2015, 31(5):  12-15. 

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Due to the chromium loss of stainless steel caused by oxidating dephosphorization，the experiment of dephosphorization was carried out in the medium frequency induction furnace，with 20%CaO-45%BaO-15%Fe2O3-10%Cr2O3-10%CaF2 slag system. On the basis of thermodynamic calculations，through deploying BaO mass fraction，the initial carbon mass fraction and steel processing temperature，dephosphorization rate was super than 50%，and chromium loss rate was less than 8%. The results showed that the new slag system was better than CaO based slag system and was equal to BaO based slag system. With the increasing of carbon mass fraction in the molten steel, the dephosphorization rate was increased and the chromium loss rate was decreased. As the temperature increased, the dephosphorization rate and chromium loss rate were decreased. When the temperature was 1750K, the dephosphorization rate and chromium loss rate were at the optimization level.

Dynamic estimation model of LF refining slag

2015, 31(5):  16-20. 

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In order to estimate the effect of LF feeding materials on chemical compositions of refining slag, slag mass and slag materials cost, based on the element conservation law, the feeding materials’ components and the sample analysis results of steel and slag of the 75t LF in a certain steel plant were calculated, and the volatilization rate and dissolution rate of each element were obtained. To simplify calculations, some assumptions were made, then the relationships of the slag compositions, slag mass and slag materials cost with feeding materials mass were deduced and programmed using the VisualBasic software, and dynamic estimations on chemical compositions of refining slag, slag mass and slagging materials cost were achieved with the programmed model. The industrial verification results showed that the absolute errors between estimation values and real values of CaO, SiO2, Al2O3, MgO, slag mass and slag materials cost were -3.17%~3.61%, -0.97%~1.44%, -2.69%~0.46%, -1.59%~2.49%, -10~70kg and -0.7~0.7yuan/t respectively. The 45 steel’s refining slag was optimized with the LF estimation model, and the slag materials cost was decreased by 7.4yuan/t.

Experimental study on calcium treatment optimization of low carbon Al-killed steel in CSP process

WANG Chun-fengChun-Feng vicent

2015, 31(5):  21-26. 

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In order to improve the cleanliness and castability of low carbon Al-killed steel for CSP production line of WISCO, the changes of composition and inclusions of molten steel with different calcium treatment were studied by industry trial. And the effects of calcium treatment were analyzed by thermodynamics. The results show that most inclusions are CaS-Al2O3-CaO with high mass fraction of CaS after calcium treatment. Then the inclusions become liquid Al2O3-CaO and CaS-Al2O3-CaO with low mass fraction of CaS in subsequent process. Thermodynamic study reveals that inclusions modification can be realized by low mass fraction of Ca, and the mass fraction of Al and S are the major factors influencing calcium treatment effects. So the mass fraction of Ca, Al and S should be considered together to realize inclusions modification during calcium treatment. And the inclusions in tundish should be liquid after calcium treatment.

Study on crystal morphology of refining slag for GCr15 bearing steel

2015, 31(5):  27-31. 

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In order to solve the problem that lots of solidified crust of the refining slag during the production process of the GCr15 bearing steel，which resulted the sharply increase of gas and inclusion content in steel，the microstructure and crystal morphology of the refining slag was investigated by SEM and XRD, and the effect of the different composition on crystal morphology was studied. The results showed that the refining slag contained several crystalline phases，and numerous high-melting phases separated out with the decrease of temperature and wrapped up calcium aluminates or strengthened calcium aluminates，which made the refining slag crusted. The composition was optimized in low-melting phase zone，which prevented the solidified crusts effectively. And the qualified rate of w（N）and w（O） were increased by 7.07% and 6.26% in rolled bar，the qualified rate of non-metallic inclusions was increased by 14.70%，the cleanliness of GCr15 steel was improved.

Application of swirling flow nozzle technology for bloom continuous castings

2015, 31(5):  32-37. 

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To control and solve the problem that the equiaxed grain rate can not meet the product quality requirement in Shaoguan Iron & Steel Co.，Ltd.，Baosteel，the influence of swirling flow nozzle (SFN) casting technique on the CC mould performance has been investigated by employing the coupled mathematical mold of fluid flow and heat transfer. Results show that the effective horizontal swirling flow，which is beneficial to melt superheat dissipation，has been observed in the whole bloom continuous casting mould by using SFN. Moreover，the successful practice for bloom continuous casting in SGISC indicates that the erosion length and strength is mitigated，the center crack removed and the equiaxed grain ratio increased. The equiaxed grain ratio increased from 12.6% to 36.8% and from 39.7% to 41.2% when use SFN alternate the normal straight nozzle and don’t plus and plus M-EMS. Furthermore，the metallurgical performance of M-EMS can be improved by the adoption of SFN，which provides a possible mean to not only reduce the strand production cost，but also improve the strand internal quality.

The research and application of soft reduction on pressure control for heavy slab continuous caster

2015, 31(5):  38-41. 

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In order to improve the inner quality of heavy slab, one type soft reduction technology which dependented on pressure control was developed, and dynamic casting machine soft reduction without solidification model control condition was achieved. The controlling means was established by writing PLC control program that the system could calculate the cylinder feedback pressure of segment in real time，and compared with the statistical pressure standard values in production in realtime, and the pressure standard values range was reached by controlling the roll gap of the caster segment. The results showed that the ratio of centerline segregation above level C2.5 of the slab improved from 75% to 90%, and the ratio of center crack below 0.5 increased from 50% to 80%.

Effect of secondary cooling patterns on corner subsurface microstructure of microalloyed steel slab during continuous casting

2015, 31(5):  42-46. 

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In order to decrease and prevent the occurrence of slab transverse corner crack, effect of secondary cooling pattern on slab corner subsurface microstructure and related surface corner transverse crack was investigated via casing of P510L steel using a slab arc continuous caster. It is shown that, under the mild cooling pattern, the formation of continuous matrix was separated by the film-like ferrite along the prior austenite grain boundary, which decreased the hot ductility of slab subsurface; under the control cooling pattern, the microstructure was even and film-like ferrite was inhibited in the range of 2-3mm to the slab surface, resulting in promoting the reduction of transversal cracking susceptibility. And compared to the mild cooling pattern, under the optimized cooling pattern, the crack index fell from 3.2 down to 0.4.

Production Practice

Research and application of converter steelmaking with limestone partial replacement lime

2015, 31(5):  47-50. 

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The process and application of 260 t converter steelmaking with limestone partial replacement lime were researched in Handan Iron and Steel Company，Hebei Iron and Steel Group Co.，Ltd. The temperature of molten iron which meet the limestone calcinations requirements, lime melting mechanism of slag formation, limestone decomposition mechanism of melting slag, limestone cooling effect and reasonable addition were analyzed. The research showed that limestone could partly replace lime, steelmaking production tests with limestone instead of part lime slag forming were carried out.The results showed that when limestone average addition 3.5~3.8t per furnace, the dephosphorization rate of plain carbon steel and low carbon steel increased respectively from 84.8% and 89.1% to 87%, 90.1%, consumption of lime respectively reduced from 10.3, 10.2t per furnace to 8.4, 8.5t per furnace, gas recovery reached 150m3/t, the cost decreased more than 2 yuan/t.

Nitrogen control technology of molten steel at the endpoint of semi-steel steelmaking converter

2015, 31(5):  51-55. 

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To solve the problem of high nitrogen content at the endpoint of semi-steel steelmaking converter in Pangang Group Xichang Iron & Steel Co., Ltd., the variation and influence factor of nitrogen during blowing have been carried out. And then, control measures of nitrogen mass fraction were raised, such as controlling the scrap consumption, reducing reblowing, using custom-made bottom blowing system and charging foaming agent. Application effect indicated that by using these technologies, the average nitrogen mass fraction at the end-point of 200 t converter was reduced from over 18×10-6 to less than 13×10-6, and nitrogen mass fraction less than 15×10-6 was carried out. The technology has been widely use during the production of low nitrogen steel, which provide technical support for the production of low nitrogen steel.

Technical of making stainless steel with hot metal from laterite nickel ore

2015, 31(5):  56-60. 

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Rational utilization of low-grade nickel oxide ore（known as laterite nickel ore） is an important way to make up for shortage of nickel in the stainless steel industry of our country. The new technology on the primary smelting of 300 series stainless steel was presented，which used the hot metal containing Ni as raw material and after pretreatment by converter，instead of traditional process of “ferro nickel ingot + EAF”，and then provided stainless steel liquid to AOD，completing the refining process of stainless steel. The technology has been applied in a domestic stainless steel factory and the production data indicated that：the semi steel of pretreatment converter endpoint average carbon is 2.5%；average silicon is 0.27%，desiliconization rate is about 84.3%；average phosphorus is 0.028%，dephosphorization rate is about 61.5%. The chemical composition of SUS304 product produced by the new process，completely meet the requirements of GB/T20878—2007，and the cost of production is reduced greatly.

Practice of submerged arc process improvement in LF refining for hard wire steel

2015, 31(5):  61-65. 

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The submerged arc performance was not good in the 65 t LF refining process for hard wire steel in certain plant, which resulted in power consumption and w(N) absorption increasing and heating ratio of liquid steel decreasing by 20%. Through analyzing LF refining for hard wire steel, power supply model and slag-forming process were optimized. The fourth voltage grade was used in heating phase. Short arc length was applied to heating in the slag-making stage to ensure slag melting and heating up stable, while middle or long arc length was used in the middle and final stages. The quantity of lime, wollastonite and fluorite was controlled strictly to be 800—900 kg per heat. Reductant (0.6—0.9 kg/t) was put into ladle by little quantity and more frequency in the slag-forming process. If necessary, the blister material was added by 2—3 bags per heat to ensure the refining slag foaming. The results show that the unburied arc heat percentage for hard wire steel refining decreases from 2.5% to 0.3%. The power consumption in hard wire steel refining is 60.32kWh/t, which decreases by 16.92kWh/t. The mass fraction of N absorption in LF process decreases by 8.6×10-6, and the heating rate of liquid steel is 4.1 ℃/min.

Analysis and prevention of sticker breakout for high carbon steel billets

ma jianchao

2015, 31(5):  66-69. 

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In order to solve the problem that sticker breakout ratio of high carbon steel billets were high in certain plant, sticker breakout mechanism was studied by analyzing the microstructure evolution and the movement law of the shell in the mold. The main reason of sticker breakout was found out by investigating the continuous casting production parameters and the mould powder characteristics. The results showed that sticking originated at the secondary meniscus and then the sticking shell was torn, after that, with several re-solidification and tear with the mold’s oscillating up and down, the breakout happened till the sticker shell came out of the mold. The causes to sticker breakout of high carbon steel billets had been analyzed, including mold powder, mold level fluctuation, superheat and casting speed. After adopting feasible control measures, the sticker breakout ratio of the high carbon billet decreased from 8.4% to 1.5%.

Design and Transform

The development and application of mechanical delivery technology in ladle drainage sand

2015, 31(5):  70-73. 

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Artificial delivery drainage sand to the ladle was used in the steel-making plant of Laiwu Iron and Steel Group Corporation. In order to solve problems, such as wasting drainage sand, increasing inclusions, reducing the free-opening rate of water slot and restricting production of steel-smelting. Mechanical delivery of drainage sand was achieved through developing a delivery technology of drainage sand by a composite shunt and optimizing the brick cup of water slot. The new technology increased the free-opening rate of water slot from 95.5% to 99.2%, and the consumption of drainage sand reduced to 0.37kg/t.

Design features of hydraulic system of converter slide gate in Shougang Qian’an

2015, 31(5):  73-77. 

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Application characteristic of the accumulator, directional valve and filter in the hydraulic system of slag stopper by slide gate is analyzed. Application shows that using accumulators correctly in hydraulic system not only conserve energy, but also reduce the operating costs; selecting filters correctly according the function can maximum limit to reduce the oil pollution, ensure the normal operation of hydraulic system, improve hydraulic system contamination resistibility and reduce operating costs; using electromagnetic directional valve reasonably can improve the response speed of the actuator. Obvious effects can be get in Shougang Qian’an Iron and Steel Co., and the success rate of blocking slag come up to 100% after using quick changing type converter slag stopper.