Table of Content

05 October 2011, Volume 27 Issue 5

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生产实践

Optimization of 300 t top bottom combined blown converter process

2011, 27(5):  1-5.  doi:

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In light of the problems existing in the original process of 300 t topbottom combined blown converters in Ma’anshan Iron and Steel Co., Ltd., the nozzles of the oxygen lance, position of the blowing lance, materials charging and bottom blowing process are optimized by way of measurement on the pressure loss of the tube in the oxygen lance system, analysis on the parameters of the nozzles of the oxygen lance and water modeling of the blowing system in the laboratory as well as learning from the experiences concerned. Production practice shows that positive results have been achieved to some extent in the aspects of stabilization of the converter operation, improvement in the final slag, reduction of the endpoint oxygen content in the hot metal and improvement in the control level of inprocess and endpoint control of steelmaking.

Production practice of spring steel 60Si2CrVAT

2011, 27(5):  6-9.  doi:

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The Φ17～28 mm rod of spring steel 60Si2CrVAT is produced by the production route of 90 t BOF→100 t LF→100 t RH→CC. By taking such a few operation measures as controlling the end point compositions and temperature of steel and quantity of slag in converter tapping, confining the LF refining slag basicity R≥4 and w(T.Fe+MnO) ≤0.05 %, ensuring no less than 20 minutes for vacuum treatment and adopting the technology of complete protective casting the high cleaning spring steel has been developed at Huai Steel. Test results show that in the spring steel the oxide content is less than 10×10^-6 and the hydrogen content less than 1.1×10^-6, A thin and C thin series rating of inclusions, less than 0.5, B thin and D thin series rating of inclusions, less than 1.0. The fatigue life of the products is over five million times.

Application of slag blocking technology in 120 t converters in Baotou Iron & Steel Corp.

2011, 27(5):  10-12.  doi:

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The principle of technology about blocking BOF slag by gas and actual results of application of the slag blocking equipments in the 120 t converter in Baotou Iron &Steel (Group) Co., Ltd. are described. In the initial stage problem of slag adhesion occurs and it has to be eliminated manually. The problem is finally solved by painting proper paint material. By adoption of this technology the average thickness of exhausted slag is reduced to 46.9 mm from the original 97.3 mm. As the results not only the phosphor pickup is decreased but also the yield of alloy elements increased. Thus prominent economical efficiency has been achieved.

Practice of vacuum treatment process development for No.3 RH in Panzhihua Steel

2011, 27(5):  16-19.  doi:

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On the basis of analysis of the quality requirements for the steel grade the vacuum treatment patterns and process schedule have been established for such a few steel grades as the alloyed structure steel, seamless tube, rail steel, high pressure vessel steel and steel for forged piece and etc in light of the concrete conditions of the No.3 RH equipments and operating processes in the Vanadium Extraction and Steelmaking Plant of Panzhihua Steel. Production practice shows that by implementation of vacuum treatment at the No.3 RH the qualified rate of chemical compositions of the output liquid steel reaches as high as 100 %, accuracy of compositions is controlled in the range of w(C)±0.02 %, w(Si) ±0.03 % and w(Mn) ±0.05 % is 88.6 %, and qualified rate of liquid steel temperature comes to 98.7 %. The effect of dehydrogenation is perfect and the cleanliness of the liquid steel is prominently improved and the requirements for the high quality steel grade are satisfied.

Optimization of slagging process for LF refining of 82B hard wire steel

2011, 27(5):  20-22.  doi:

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Aiming at the long time slagging, serious crust for top slag and poor effect of submerged arc during refining process of 82B steel, the reasons for these problems were investigated in this article. The process of slagging for LF refining was improved by slag infiltration of CaOAl₂O₃ based slag instead of lime. And the final slag of refining was controlled in the range of w(CaO)/w(SiO₂)＝2.5～3.5，w(Al₂O₃)<15 %.The test results show that good submerged arc can be obtained and no crust phenomenon can be found in the surface of slag. Slag melting is suitable and desulfurization rate
is high, and the inclusions in molten steel are greatly reduced.

Selection and production practice of SWRS82B refining slag

2011, 27(5):  23-36.  doi:

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Proceeding from the requirement of steel grade SWRS 82B for sulphur content the present paper analyzes the effects of compositions of the LF refining flux on the allowable sulphur content, fluidity and interfacial tension of and determines the basic compositions of the refining flux as CaO-SiO₂-MgO-Al₂O₃ series as well as the optimal content. By means of strengthening slag stopping, optimizing deoxidation and argon blow and controlling the temperature the desulphurization rate reaches 68.60 % in the process of refining CaO-SiO₂-MgO-Al₂O₃ and the sulphur content of the product comes up to 0.006 5 % and thus the requirements for the products can be better satisfied.

Application of high intensity of secondary cooling water on billet caster of Shougang

2011, 27(5):  27-29.  doi:

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The present paper studied the effect of water ratio in secondary cooling zone on center carbon segregation and internal quality of high carbon steel billet (130 mm×130 mm) casting under the condition of final electromagnetic stirring. The result shows that the average center carbon segregation index decreased to 1.04 from 1.10 with increase of water ratio in secondary cooling zone to 1.5L/kg from 0.8 L/kg as well as acceleration of the cast speed to 2.8 m/min from 2.4 m/min. The high secondary cooling intensity and high speed are fit for producting high carbon steel with the billet in Shougang.

Analysis on the cause for disqualification of Z-direction property and control measures

2011, 27(5):  30-34.  doi:

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The reason for the disqualification of Z-direction property during the production of Nanyang Hanye Special Iron and Steel Co., Ltd. is analyzed by SEM, metallographic examination and EDS. The results show that the disqualification of Z-direction property is mainly caused by the nonmetallic inclusions of manganese sulfide, the aggregation of high melting point Nb(Ti)C and center segregation. Besides existence of hard phase structures such as the bainite in the segregation area accelerates expansion of the fracture leading to disqualification of Z-direction property. By way of optimization of chemical composition design, enhancement of the process control of refining, improvement in the casting process, drawup of proper rolling schedule and heat treatment process desirable results have been achieved.

试验研究

Mechanism of surface and splash droplet decarburization ofRH treatment for ultralow carbon steel

2011, 27(5):  35-38,4.  doi:

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The mechanism of hot metal surface decarburization and splash droplet surface decarburization has been studied by a decarburization math model for RH vacuum treatment. Model calculation results show that vacuum degree is the primary factor affecting the surface decarburization reaction of the hot metal and splash droplets; splash droplets decarburization dominates 9 minutes after vacuum treatment and at the end of decarburization the quantity of decarburization reaches as high as 72 %; the quantity of hot metal surface decarburization and the aggregated quantity of the splash droplets decarburization is 18.7 % and 24.4 % and the total of them comes up to 43.1 %. They play an important role in the overall process of decarburization.

Experimental research on smelting high nickelchromium containingweatherresistance steel

2011, 27(5):  39-43.  doi:

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In view of the characteristics of higher nickel and chromium content in the weather resistant steel 06CuPNi1Cr2 experimental research and development of the steel grade have been carried out by converter thermal state simulation and vacuum refining. In the converter thermal simulation experiments the top blown oxygen intensity is designed to be 3.0～3.3m³/(min·t), the bottom blown nitrogen intensity is 0.02～0.05 m³/(min·t), the endpoint carbon mass fraction is less than 0.05 % and bath temperature is higher than 1 610 ℃. The vacuum degree is held at the level of 0.06 MPa and the tapping temperature maintains at 1 620～1 650 ℃. As the results the chemical compositions of the liquid steel conforms with the design requirements of steel grade 06CuPNi1Cr2.

Research on the possibility of dephosphorization and desulfurization simultaneously at same location in the secondary refining process

2011, 27(5):  44-48.  doi:

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According to the reaction time and location of hot metal dephosphorization and desulfurization the hot metal pretreatment technologies using one single flux for dephosphorization and
desulfurization simultaneously in the process of hot metal pretreatment or in the secondary refining can be basically divided into 3 categories, namely: dephosphorization and desulfurization at the same location and at the same time period; dephosphorization and desulfurization at the same time period but not at the same location; dephosphorization and desulfurization at
the same location but not at the same time period. For the purpose of studies on the possibility of dephosphorization and desulfurization of hot metal at the same location but not at the same time period firstly proper theoretical studies and discussion are carried out and then further exploration and experiments conducted in LF. Results of the studies show that dephosphorization and desulfurization of the hot metal at the same location but not at the same time period can be possibly realized by using BaO flux series in the process of the secondary refining.

Research on optimization of 45 t single strand tundish flow distribution

2011, 27(5):  49-52,7.  doi:

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The flow behavior of the CSP 45 t single strand tundish is investigated by means of hydraulic model. Proportion of model of the tundish is 1∶3. Experiment conditions satisfies Froude number similarity. Minimum residence time distribution (RTD) curves are determined by pulse response. The proportion of the plug flow, mixed flow and dead volume are calculated. By means of optimization of the new turbulence inhibitor design and optimization of the combination plan of dams and weirs in connection with flow control the dead volume (V_d) in the tundish is reduced to 11.36 %, about 67.8 % decrease in comparison with that by the original plan. Production contrast tests show that by means of the optimized flow control solution, removal of oxide inclusions in slab increases by 35.3 %.

Prediction model for end point temperature of molten steel in RH-TOP refining

2011, 27(5):  53-56.  doi:

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The prediction models for the end point temperature of molten steel in RHTOP refining under the conditions of oxygen blowing and nonoxygen blowing are established respectively by mean of multiple regression analysis method. Results of statistical analysis on temperature prediction show that under the condition of nonoxygen blowing the hitting probability of prediction deviation of ±5 ℃ and ±10 ℃ is 83 % and 99 % respectively; under the condition of oxygen blowing the hitting probability of prediction deviation of ±5 ℃ and ±10 ℃ is 79 % and 96 % respectively.

Research on heat equilibrium based heat transfer mathematic model for bloom continuous casting

2011, 27(5):  57-59.  doi:

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On the basis of principle of heat equilibrium the heat transfer mathematic model has been established for bloom continuous casting. By dissection of the secondary cooling zone and solution of the simultaneous equations such a few parameters at the specified location of the secondary cooling zone as the thickness of the strand shell, surface temperatures, latent heat of solidification and heat dissipation can be quickly achieved. Numerical simulation and onsite temperature measurements on the basis of the bloom continuous caster at a specific steelmaking plant show that under the casting conditions of the section area of the bloom 260 mm×340 mm, casting speed 0.5 m/min and 0.6 m/min the results of simulation calculation are completely in agreement with the law of solidification and deviation between the calculated temperature and the onsite measured one is less than 2 %. The results of calculation can be used as the basis for optimization of the operating process of soft reduction of the bloom.

Study on the mould flux composition and properties during Q235B liquid steel continuous casting

2011, 27(5):  60-62,6.  doi:

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n light of the phenomenon of sticking breakout in the production of Q235B by slab continuous casting the use of mould flux in continuous casting was investigated. Then the chemical compositions were analyzed and the physical properties were measured for the original mould flux, slag rim and sticking breakout slag samples taken from LY Steel. The results show that the greatest change of quality fraction of Al₂O₃ in the flux just before and after casting is 2.7 %; The melting temperature, melting rate and viscosity are 15 ℃、6 s and 0.04 Pa·s respectively after casting. There is no great change in the physical properties of the flux before and after casting.

Macro-segregation in cast bloom of gear steel and its formation mechanism

2011, 27(5):  63-67.  doi:

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The present paper mainly researched on the carbon macrosegregation and etched macrostructures of cast bloom of gear steel 20CrMnTiH2 produced by Xiangtan Steel with cross section of 300 mm×430 mm in order to find out the relations between the carbon macrosegregation and etched macrostructure and the formation mechanism of carbon macrosegregation. The results show that the segregation degree was positive in columnar zone and columnar to equiaxed transition (CET) boundaries, negative in equiaxed zone and positive again in the center of cast bloom. The carbon segregation distribution morphology turned out to be W style. The carbon content shows a clear relation with the etched macrostructure and it indicates that carbon macrosegregation is related closely with solidification.

Study on factors affecting titanium yield in LF refining and continuous casting

2011, 27(5):  68-71.  doi:

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Factors affecting titanium yield for high strength steel in LF refining and continuous casting are analyzed by experimental data and thermodynamic calculation．Results show that when the hot metal temperature rises above the liquid phase line temperature and the quality fraction of acidsoluble aluminum comes to 0.025 % the 0.02 % titanium in the liquid steel can not react with the soluble oxygen, and in the process of refining and continuous casting titanium can neither react with nitrogen in the hot metal nor with that in the atmosphere, and when silicon quality fraction arrives at 0.25 % at 1 600 ℃ the titanium of 0.02 % quality fraction in the hot metal can react with SiO₂ in the slag and thus titanium oxides generate and they will exist in the slag. On the basis of the experiments measures for controlling the stability of titanium content are put forward and thus the purpose of controlling the deviation of titanium quality fraction within the limit of (0～2)×10^-6is realized in the actual production.

综 述

Study on the selection of recovery processes of stainless steel dust in China

2011, 27(5):  72-77.  doi:

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The features of the main recovery processes for the stainless steel dust in the foreign countries are described. The common feature of the
recovery processes is summarized. In combination with the practical conditions of the production and research of our country in this field the
method of reclaiming the stainless steel dust powder is advanced, namely collecting the stainless steel dust with the tunnel kiln technology which is used for production of the sponge iron and the feasibility of this method is analyzed as well. The conclusion of the article provides a
reference for selection of the stainless steel dust recycling processes of our country.