Steelmaking

The research & development and application of channel type tundish induction heating and refining technology for continuous casting

HJB

2015, 31(1): 1-6.

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The channel type tundish induction heating and refining technology for continuous casting was summarized in this paper, meanwhile its general development situation in foreign countries was introduced. The differences between this technology and plasma heating were compared briefly，a simple and clear survey about working mechanism of heating and inclusion removing was given, a domestic independently developed, possessing autonomous intellectual property, “V” shaped channel type tundish induction heating and refining technology as well as its characteristics were presented especially, the reliability, operability, controllability and security of this technology and its good metallurgical effect due to fine heating and inclusion removing were tested and verified by examples applicated in two steel plants, the possible influence to continuous casting technology by this technique was briefly looked ahead.

The design of special production line（slab）continuous caster

2015, 31(1): 7-11.

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With better understanding about continuous caster, the design concept of continuous caster changes gradually from traditional omnipotent caster to special production line and permanent casting speed caster. Based on the opportunity to build several casters in the same time in Zhanjiang Iron & Steel Company, the thesis elaborates the specific content of special production line and permanent casting speed of the continuous caster, and further analyses of the traditional and special production line and permanent casting speed caster design concept, the casting speed range differences, advantages and disadvantages.

Improving cleanness of liquid of sulfur and aluminum bearing gear steel

2015, 31(1): 12-16.

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According to the fact that it is difficult to achieve multiple ladles continuous casting for the steel bearing sulfur and aluminum in Shijiazhuang Steel Co.，Ltd.，the smelting technology for improving the cleanliness and castablity with LD→LF→VD→CC is systematically studied for this steel. The following technologies arc developed: high carbon control in the end of converter, Al-Si-Al deoxidation type during steel tapping，special refining slag for this steel，variation of argon blowing with the refining time，protective casting with repressing oxidize when continuous casting. The results show that，it can casting more than 8 heats. After rolling bars，the total oxygen content is lower than 12×10-6，the inclusion ratio decreases to 0.06 % from 2.3%，the UT qualified rate increases from 65% to 93.5%.

Study on dephosphorization technology of low phosphorous steel smelting in 120 t BOF

2015, 31(1): 17-21.

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In order to make the requirement of phosphorus mass fraction is less than 0.010 % for low phosphorous steel, and according to the effect of temperature, slag basicity，w(FeO) of slag and mixing parameters on dephosphorization, the offgas analysis dynamic control steelmaking model was applied on 120 t BOF of Ma’anshan Iron & Steel Company Limited. “Slag-Remaining+Double-Slag” technology, suitable loading system, slagging system and oxygen supply system, optimizing dephosphorization parameter were used in steelmaking. Through the analysis and comparison of 500 experiments, dephosphorization rate 95.2 % can be achieved by taking measures such as the temperature and the carbon mass fraction of the first turning down 1 540~1 580 ℃ and 0.10 %~0.25 %, final slag basicity 3.0~3.5, w(FeO) =15 %~23 %, and suitable stirring intensity. And the phosphorus mass fraction of converter tapping is less than 0.070 % and the hit rates of carbon content and temperature both meet the requirement of 96.4 %.

Study on low-cost & high-efficient technology for carbon steel production

ran menglun

2015, 31(1): 22-26.

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In order to control the sulfur content in steel in the process of carbon steel production, countermeasures were carried out. On the basis of theoretical analysis and calculation, the desulfurization process of hot metal and LF refining was optimized according to the sulfur content in hot metal. Otherwise, temperature and composition control, quantity and method of slag addition, as well as desulfurization time and argon blowing were optimized and designed systematically. Industrial tests showed that, nice application effects were obtained, which the hot metal loss was reduced, the temperature of hot metal before converter melting was increased by 28℃, and temperature loss was reduced by 13℃. Moreover, the effective rate of manganese alloy was increased by 6.22%, and sulfur content in steel product was controlled in 0.005%~0.021%, and 0.0156% on average, which could meet the needs of the requirement of customer.

Refining process and practice of welding wire steel in 65 t LF

2015, 31(1): 27-30.

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The safe reform of equipment and workshop building for the steelmaking in Long Product Department of Tangshan Iron and Steel Company of Hebei Iron and Steel Group was put into effect in 2013. According to the project scheduling and considering the production plan of branch steel, the 50 t ladle furnace was removed and a 65 t ladle furnace was constructed. The device parameter, process stipulation, the arc heat, slag-making, argon blow and wire injection of 65 t LF were briefly introduced in the paper. The welding wire steel productive practice showed that the refining periodic time was 50—60 min, the power consumption was 60 kWh/t, the heat speed was 5 ℃/min, sulphur percent was 0.010 %~0.020 %, nitrogen percent was less than or equal to 30×10-6, and the liquid steel quality and purity reached users demand.

The research of the key smelting technology of high-strength steel of CSP

2015, 31(1): 31-34.

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The BOF→LF→RH→CC process, by which the data shows the higher alloy yield rate and component-targeting rate, and the less nitrogen content in the steel, has been adopted in the production of high-strength steel WYS700 after the contrast test. In order to ensure a smooth casting, the molten steel has been light calcium treated, in which the dosage of calcium silicon was 0.88 kg/t. After that, the continuous casting has been raised from 4 heats to 7 heats. Through the scanning electron microscope, the nonmetallic inclusion in tundish was observed as sphere and scattered basically, small than 5 μm in principle, which can denature to improve the continuous cast-ability. Through the optimization of component, temperature, water yield, casting powder, and flow field, the leakage rate of high-strength steel was reduced from 1.90 % to 0.35 %, and the crack defective percentage of casting blank was reduced from 5.5 % to 0.45 %.

Analysis of generated cause and counter measure of flocculating flow

2015, 31(1): 35-39.

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Based on analyzing the reasons of flocculation during casting, combined with industrial test results, some key measures to deal with flocculation during casting were established, such as optimizing operation system of converter, tapping with skimming, skimming in ladle, modifing the top slag in ladle, stiring by blowing Ar from the bottom of ladle, nozzle design, deoxidization process, modifing inclusion in molten steel by feeding cored wire etc. The results showed that, controlling the tapping carbon mass fraction at the range of 0.04 %—0.06 % for ultra-low carbon steel, slag quantity at the range of 3—5 kg/t, adding 3—5 kg/t active lime for modifying the top slag in ladle, acid aluminium content at lower limit, optimizing design of submerged nozzle structure, increasing the nozzle diameter and side flow hole diameter, the temperature of firing tundish above 1200 ℃ etc, the flocculation could be alleviated. Comparison with aluminum deoxidization, Si+Al deoxidization process had failed to ease flocculation, but the shape of inclusion was changed, the requirement of thin sheet steel for inclusion also could be satisfied.

Research of direct alloying with manganese ore during converter tapping process

2015, 31(1): 40-43.

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In order to solve the problem of low manganese yield rate by adding manganese ore in the converter, the technology of converter tapping process with manganese ore direct alloying was studied. The results showed that the technology of converter tapping process with manganese ore direct alloying was feasible by the analysis of thermodynamics and dynamics. The plant practice of 100 t converter tapping process with manganese ore direct alloying showed that the manganese yield was more than 80 % and the maximum was 95 %, the comprehensive cost was reduced by more than 3.43 yuan/t. Meanwhile, the molten steel was rarely polluted and the content of sulphur，phosphorus was rarely increased.

Study on decarburization and conservation of niobium in Nb-bearing hot melt by bottom-blown oxygen

2015, 31(1): 44-47.

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The oxidation of carbon, silicon and niobium in Nb-bearing hot metal were studied in a medium-frequency induction furnace by bottom-blown oxygen with SiO2-CaO-CaF2 slag-forming element or no slag at 1 350 ℃，1475 ℃ and 1515 ℃. The results showed that oxidation rate of silicon in Nb-bearing hot metal with SiO2-CaO-CaF2 slag or no any slag was 97 %, and oxidation rate of carbon was 20 % at 1350 ℃; however, oxidation rate of silicon was 15 % at 1475℃ and oxidation rate of carbon was 84 % at 1515℃ with basic SiO2-CaO-CaF2 slag. Niobium mass fraction of the hot metal was not change until silicon content decreased to 0.1 %. The carbon content decreased to 0.66 % with acid SiO2-CaO-CaF2 slag-forming element at 1515℃, by which decarburization and conservation of niobium was carried out during bottom-blown oxygen.

The influence of top slag composition on plasticization of CaO-Al2O3-SiO2-MgO inclusions

2015, 31(1): 48-51.

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The generation plasticization control of CaO-Al2O3-SiO2-MgO inclusions was discussed by thermodynamic calculation, and the effect of the top slag composition on inclusions was studied in the lab and industry. As a result, in the CaO-Al2O3-SiO2-MgO(10 %) diagram, when w（CaO）=8 %~48 %, w（SiO2）=35 %~75 %, w（Al2O3）=0~32 %, inclusions were in plastic zone. With the increase of the content of Al2O3 in the slag, the content of Al2O3 in inclusions of tire cord steel increased. And the distribution of inclusions became scattered with the mass fraction of Al2O3 increasing in the slag. Combined with laboratory results and industrial trials, when the basicity of top slag between 0.7 and 0.9, w (Al2O3) s=2 %~5 %, the non-metallic inclusions in steel could be plastified and wire breaking reduced by 30 % through the composition of refining slag controlling, so as to the quality of wire rod improved.

Controlling of nitrogen content in molten steel during LF refining

2015, 31(1): 52-55.

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In order to solve the problem of excessive nitrogen content in liquid steel in LF refining process, each process of smelting was analyzed. The results showed that the initial slagging stage of LF refining was the mainly process for nitrogen content increasing. Through the sampling analysis and thermodynamic analysis, it was confirmed that the increasing of nitrogen content in molten steel was mainly caused by the AlN in the aluminum dross. The synthetic slag with high Al2O3 and low nitrogen content was used instead of aluminum dross, and the usage of aluminum dross was reduced from 2.6 kg/t to 0.6 kg/t, the nitrogen mass fraction could be decreased in 42 % at the endpoint of LF refining in a cast of seven furnaces. It is drawn that the synthetic slag reduces the nitrogen content in liquid steel caused by raw materials without affecting the refining effect.

Practice for decreasing nozzle clogging problem in continuous casting

2015, 31(1): 56-60.

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Nozzle clogging is one of the most famous problems during casting aluminum killed steel. Nozzle clogging can be divided into four kinds according to the position, ladle nozzle clogging, stopper head beard, upper nozzle clogging and SEN clogging, which summarized combining with production practices. The middle-size inclusions plays big role in clogging, which usually results from secondary oxidization. In the meantime, low casting speed would increase the probability of clogging, and inappropriate calcium treatment would make it happens much more seriously. In order to prevent nozzle clogging, the cleanliness of molten steel should be higer, and the measures for preventing secondary oxidization should be taken during casting, and w（Ca）/ w（Alin）≥1.2 should be ensured during calcium treatment. The rate of clogging decreased from 20.6 % to 4.52 %, and the heat number of sequence increased from 8.2 to 10.3 after taking the above actions.

Optimization of F-EMS parameters of bloom continuous casting

2015, 31(1): 61-64.

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In combination with the actual situation of the bloom caster in the plant, a heat-transfer mathematical model was established with the help of ProCAST software. The model was modified on the basis of nail-shooting results to improve its accuracy. According to the simulation results, the principles of the installation position of F-EMS such as the position where the solidification rate was 0.6—0.7 or at pool thickness of 35—55 mm didn’t apply in this case. When studying the characteristics of solidification, the central solid fraction of the boom nearby 0.1 maybe a good position for F-EMS, which also corresponds to another rule: to install at three quarters of the length of liquid core. Under these rules, current casting speed 0.78 m/min is a little faster when superheat is 28 ℃ and water ratio is 0.6 L/kg, and the optimum casting speed is 0.70 m/min. In the process of actual casting, the superheat of hot steel is always changing, so the study also calculated the relationship between casting speed and superheat. Base on the findings, industrial plant trial was conducted and the results showed that the problem of inner composition segregation improved significantly.

Development of mold powder for high-strength weathering steel containing vanadium

2015, 31(1): 65-68.

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Because of high content of vanadium and nitrogen in high-strength weathering steel, as well as carbon content in peritectic reaction zone, subcutaneous net cracks on slab were easy to generate in continuous casting process. The reasons of cracks defects were analyzed, and on this basis, mold powder, which could meet the needs of continuous casting process for this kind of steel grade, were studied and developed. Industrial tests showed that, when the casting speed was increased from 0.70~0.75 m/min to 0.90~0.95 m/min, the thickness and consumption of liquid powder in mold could be controlled in 9~11mm and 0.45～0.65 kg/t respectively. The acceptable ratio of slab surface quality for Q450NQR1 steel is as high as 90.14 %, and furthermore, the peeling defect ratio on hot rolled coil was reduced from 41.29 % to 4.24 %.

Development and application of converter dry dedusting ash based composite slagging agent

2015, 31(1): 69-72.

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A new composite slagging agent for BOF steelmaking was developed by using dust. The new composite slagging agent could meet the requirements for the stable operation of dry dedusting and metallurgical properties. Through using this new type of composite slagging agent, the oxygen consumption of converter steelmaking was decreased by 2.65m3/t, the dephosphorization rate was increased by 3.31%, the ferrous charge consumption was reduced by 0.69kg/t, the volume of gas recovery was increased by an average of 5m3, and the cost of steel materials was reduced by 2.68 yuan per ton.

Total Waste Heat Recovery Device for Off-gas from Electric Arc Furnace

2015, 31(1): 73-77.

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A great amount of high temperature off-gas with dust is generated during the smelting process of electric arc furnace (EAF). There are many problems such as part of the waste heat is not recovered, high de-dusting load, low steam pressure and difficult utilization in the off-gas cooling ways, which are widely used now. According to this situation, Total Waste Heat Recovery Device for off-gas from Electric Arc Furnace is developed. This device can recover 2100℃～250℃ total waste heat of off-gas from the EAF fourth hole and has the advantages of proper excess air factor, high sedimentation efficiency, high pressure steam, long life span boiler and so on. A demonstration project was built on a 110t EAF and tests were carried out, the test results show that the temperature of the off-gas at the outlet of the tube waste heat boiler is 250℃ below， sedimentation efficiency of the sedimentation chamber is more than 94%. These results reach the expected index of the device. Meanwhile the problems of the Total Waste Heat Recovery Device are analyzed.

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