Steelmaking

KR hot metal pretreatment production practice of 300 t BOF steelmaking system

2014, 30(2): 1-5. doi:

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Aimed at hot metal pretreatment process selection problem of 300 t BOF steelmaking system in Masteel, from the thermodynamic conditions，kinetic conditions，the desulfurization effect and cost,etc, combined with the existing raw material condition, opted for KR mixing method after comprehensive consideration. The devices of KR hot metal pretreatment came into use successfully and achieved good desulfurization effect. In production，successfully solves the mixing head life, iron losses, “blocking material”,etc influence production problems. And according to the hot metal conditions and the different requirements of different varieties to sulfur, formulated the different hot metal pretreatment desulphurization process. Full releases the capacity of KR hot metal pretreatment, greatly reduces the cost of production, building laid a solid foundation for low cost high efficiency of clean steel platform.

Development and application of the process with the low cost slag-recycle steel-making of converter

2014, 30(2): 6-8,13. doi:

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Hansteel practices the process of recycle of the final slag of converter, which are sufficient using the final slag with the high basicity during the process, dumping the dephosphorization slag at the appropriate opportunity of the blowing and reforming the slag, thereby reducing the slag, the iron and steel material and the cost of the production. The lime consumption reduced by 29.3 %, the amount of the slagreduced by 32.8 %, the iron and steel material reduced by 5 kg/t after used the process, which has obtained excellent economic.

Production practice of HRB400 steel by slag steel and slag iron with electric furnace

2014, 30(2): 9-13. doi:

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HRB400 steel production by metallurgical secondary resources such as slag steel and slag iron with “ETB electric furnace →LF → billet continuous casting” process was introduced. According to controlling the process parameters of ETB electric furnace and LF refining and billet continuous casting reasonably, it was achieved that the batch production of HRB400 steel meeting GB 1499.2—2007 and the effective utilization of the secondary resource.

Study and practice on smelting process of high toughness wind power flange steel

2014, 30(2): 14-17. doi:

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The present paper introduces experiments on production of high toughness wind power flange steel by EAF→LF→RH→CC process route at the special steel plant of Masteel，the experimental study determines main process condiction of high toughness wind power flange steel and control measures of the harmful elements by discussing in detail 4 key processing points of EAF smelting，LF refining，RH vacuum refining and continuous casting.The chemical compositions of the steel meet requirements，inclusions grade is low，all the mechanical performances meet the specification. The results provide scientific basis for future batch production.

Control of surface sliver defect in hot-rolled SPHC strip

2014, 30(2): 18-21,2. doi:

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Morphology, distribution and chemical composition of surface sliver defect in hotrolled SPHC strip were investigated. The result shows that mold powder entrapment during continuous casting process is the key reason for the surface sliver defect. After the adjustment of steelmaking process, alumina inclusion was decreased, and the pourability of the molten steel was improved. In addition, with the modification of stopper argon flow rate and the viscosity of mould flux, mould level fluctuation was controlled in the range of ±3 mm, and the degrade ratio of the strip due to silver defects reduced from 15 % to 7 %.

Study on the causes and controlling of defects for cold-rolled sheet

2014, 30(2): 22-25. doi:

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The character and cause of surface defect on coldrolled sheet produced after continuous casting with high speed were studied by means of Aspex scanning electron microscope. The results shows that the surface defect is caused by Al2O3clusters, Ar+Al2O3 typed inclusions and the entrapped mold powder and the entrapped mold powder is the main part. After using FC mold in continuous casting with high speed and optimization the SEN, a followup occurrence rate of surface defect is from 3 % down to 1.5 %.

Analysis and control of surface defects on IF steel for galvanized steel sheet

2014, 30(2): 26-29. doi:

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The surface defects and continuous casting process of IF steel for galvanized steel sheet of SGJT were analyzed. The results showed that the main reasons of the surface defects were the higher possibility of inclusions contents in the second slabs, nozzlechanged slabs and middle slabs. The surface defects were decreased remarkably through several measures such as steel remaining, refractory quality improving, cold steel removing in RH and tundish structure opitimizing. The product fraction defective caused by surface inclusions defects decreased to 2.59 %from 7.87 %.

Industrial experimental on dephosphorization pretreatmentin combined-blowing converter

2014, 30(2): 30-34. doi:

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Through field test on dephosphorization in 300 t combined-blowing converter of Shougang Jingtang Iron ＆ Steel United Co. Ltd., the effects of semi-steel temperature, slag oxidation, dephosphorization slag basicity as well as semisteel w(C)/w(P) on dephosphorization rate and phosphorus partition werestudied. The results showed that the finished mass fraction of phosphorus in semi-steel could be controlled less than 0.030 % under the condition of semisteel temperature and slag basicity controlled within 1 290-1 310 ℃ and 1.9-2.5 respectively, which could make the average mass fraction of phosphorus reach to 0.026 % in semisteel, and the rate of w(P)<0.030 % reach 81.01 %. The average phosphorus content and dephosphorization rate were improved obviously.

Experiment of molten steel cleaning technology by finebubble method in killed carbon steel

2014, 30(2): 35-37,4. doi:

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This article introduce a removing inclusions process method by fine bubble coming from fine solid in molten steel, and the tests were proceeded in killed carbon steel in steel making plant. The results indicate that it may reduced markedly inclusions in the molten steel. Compared with conventional inclusion removal technology, the number of the oxide inclusion can be decreased to a lower level and the inclusion size becomes finer. Using this technology, the mass fraction of total oxygen in the ascast slab can approach to 0.000 7 %，and the purity of molten steel was improved.

Inclusions control study of DC06 steel in 300 t ladle

2014, 30(2): 38-43. doi:

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According to various samples taken from steel and slag in ladle, the variations of inclusions in static steel and the efficiently absorptive conditions of inclusions in ladle slag were analyzed by using electrolytic method in nonaqueous solution and Factsage software. The results indicate that small inclusions collide into big inclusions and T.O levels decreases at the first 17 min of holding time, after 24 min inclusions aggregate into cluster inclusions and number of it reduces and the holding time should be remain at 28-33 min; the amount of Al2O3 dissolved when saturated is now 1.85 times of its original content if the slag basicity is stayed around 6.5-7.5，w(CaO)/w(Al2O3) of the slag is kept in 1.5-1.7, the mass fraction of SiO2 is stayed around 6 %-8 %, the mass fraction of MgO is kept less than 5 %. It could provide theoretical basis for reducing the content of macro inclusions.

Effect of nozzle bottom design on jet characteristics in continuous casting slab mold for high speed casting

2014, 30(2): 44-48,5. doi:

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A full scale water model was built to investigate the effect of bottom-design (mountain-, wave-, well-, flat-and round bottom) of submerged entry nozzles (SENs) on jet characteristics, backflow zone area and jet symmetry in continuous casting slab mold with propeller velocimeter and camera recording. The results show that the jet characteristic is stable for mountain- and wave-bottom SEN, however, shows a swirl flow for well-, flat- and round-bottom SEN with an alternative anticlockwise and clockwise rotating. The order of backflow zone area (BFZ) is: mountain-bottom>wave-bottom >well-bottom>flat-bottom>round-bottom, plant trial results show that the large backflow zone is one cause for nozzle clogging. Furthermore, the order of jet velocity asymmetry degree is similar to that order in high speed casting (steel throughput: 4.48 t/min). The spectrum powder analysis of jet velocity fluctuations show that the jet with mountain- and wave- bottom SEN have less turbulence but more kinetic energy than any other SENs, which result in larger backflow zone. While round bottom SEN has much turbulent yet less kinetic energy jet, which result in smaller backflow zone.

Research on the ultra-low-carbon steel with billet continuous casting process

2014, 30(2): 49-52. doi:

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The practice of ultra-low-carbon steel for billet continuous casting at Xingtai Iron & Steel CO., Ltd. is introduced. By comparing different refining process routes, an optimized process of “BOF→LF→RH→CC” is put forward. Studies have found that without ladle slag modifier, the mass fraction of (FeO)，(MnO) is high and volatile (9 %-14 %, 1 %-3 % respectively), result in flocculating flow. With three step slag modification process(topslag modification in BOF, LF and RH), the mass fraction of (FeO+MnO) can be controlled at about 3 %, which is favorable for calcium treatment to avoid flocculating flow, and continuous casting with more heats realized, the average mass fraction of carbon of finished product can be controlled at 0.008 % (BOF→RH→LF→CC process is 0.0102 %).

Cooling process of the third generation of automobile steelon the internal crack of continuous casting slabs

2014, 30(2): 53-56. doi:

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The continuous cooling transformation curve (CCT curve) was obtained by a Gleeble1500 hot simulator to investigate the cooling transformation of the third generation of automobile steel (TG steel). Steel ingots were produced by a vacuum induction furnace, and the internal quality and the microstructure of ingots produced under different cooling conditions were analyzed. The effect of cooling process on the microstructure and the internal crack of continuous casting slabs were researched to provide theoretical guidance for the improvement of internal crack in TG steel industry.

Study on cleanliness of X80 pipeline steel

2014, 30(2): 57-61,6. doi:

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By the methods of metallographic observation, sampleelectrolyzing and scanning electron microscopy (SEM) analysis, the nonmetallic inclusions in X80 pipeline steel were investigated. The results showed that inclusions had a significant downward trend from LF inlet to microscopic in casting process with a fall of 77.77 %, the number of inclusions reduced most obviously in LF and RH refining process. The main types of inclusions in slab are CaO-CaS-Al2O3 composite inclusions, xCaO/xAl2O3 is less than 1.71of 12CaO·7Al2O3, inclusion modification effect is poorer. From converter end to casting process, the average total oxygen content had a downward trend. From LF inlet to the calcium treatment process finished, the average mass fraction of T.O decreased less than 3×10-6, the average mass fraction of T.O reduced 2.27×10-6 in RH refining process. It needs to improve the level of LF refining operation and RH refining operation stability. RH outbound to the slab was a process of increasing nitrogen, the mass fraction of nitrogen increased 2.27×10-6, protective casting level was higher. The large inclusions quantity was 1.46 mg/10 kg, inclusions are mainly spherical calcium aluminate inclusions, silicon aluminate inclusions and composite inclusions with magnesiaalumina spinel.

Study on the grindability of steelmaking slag modified by silica

2014, 30(2): 62-65. doi:

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The modifier of silica was added to synthetic slag system of CaO-SiO2-MgO-Fe2O3 to study the change of grindability of slag. Experimental results indicate that, with addition amount of silica increasing, the content of dicalcium silicate in slag increases, calcium ferrite decreases, and the grindability of slag is enhanced. The results provide guidance for the utilization of converter slag in cement industry.

Influence of fluorite on viscosity and crystalline phase of concasting mold powder

2014, 30(2): 66-69. doi:

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The viscosity of the mold powder and the crystallization rates, mineral compositions of solidified slag samples were analyzed on the basis of the study in industrial mold powder and slag film. The result shows that: The mineral composition of in industrial mold powder are wollastonite, quartz, fluorite and sodium carbonate. The crystalline phase of flux film of nothing wrong on casting slab quality is melilite, and the crystallization rate is 90 %. With the content of fluorite being increased, the viscosity of the mold powder is reduced, and with the test temperature declined, the viscosity is elevated. The mineral composition of solidified slag are melilite, cuspidine and glassiness. With the content of fluorite being increased, the crystallization rates and the contents of cuspidine is increased, the content of melilite is reduced.

Improvement of processing the data of level fluctuation at continuous casting mold

2014, 30(2): 70-74. doi:

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The original data of mold level measurement during continuous casting are not level fluctuation but level position varied with time. In the current study, the real level fluctuation were obtained by subtracting the smoothed value from the measured level position data. The effect of operation parameters of continuous casting on level fluctuation at the mold were discussed. Unsteady continuous casting resulted in greater fluctuation than steady state. With increased casting speed and larger mold width, the level fluctuation became more serious with larger amplitude. With 1.8 m/min casting speed, with FC-Mold electromagnetic brake the level fluctuation slightly decreased than that without FC-Mold. The fluctuation vertical velocity of mold level was obtained by perform derivative of the level fluctuation, which affected the entrapment of casting powder during continuous casting.

Design and optimization of 120 t RH refining feeding system

2014, 30(2): 75-78. doi:

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In this article the 120 t RH feeding system in Masteel Electric Furnace Plant was studied. The technological layout and the composition of feeding system， the problem of the RH feeding system which have put into production were summaried. And the design of the feeding system from four aspects as feeding time，weighing accuracy，unplanned feeding and vacuum rotary slide pipe were optimized. The good effect was achieved. The feeding system was put into production, the goal of energy saving and consumption reducing was achieved，and the design idea of RH feeding system was broadened.

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