Table of Content

05 June 2009, Volume 25 Issue 03

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生产实践

Desulfurization technology by using Mg+CaO powder injection in hot metal ladle

2009, 25(03):  1-4.  doi:

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The hot metal desulfurization processes including TDS (Torpedo Car desulphurization), PTC (Hot Metal Pretreatment Center) and single lance and double lances desulfurization in a hot metal ladle at Baosteel are analyzed. It’s shown that the desulphurization process of Mg＋CaO powder injection into a hot metal ladle is prominently superior over the powder-injection desulhurization process in a torpedo car in the fields of injection duration, desulphurization effects, powder consumption, production organization and economic efficiencies. The injection duration for desulphurization can be reduced by over 50%, the end point sulphur content up to 0.001%~0.003%, the total powder consumption only 50% as much as the total consumption of CaC2 powder and 20% of CaO powder and the composite cost of this desulphurization process 18%~30% lower than that by TDS and PTC in a torpedo car. The desulphurization mode of Mg＋CaO powder injection into the hot metal ladle with a double lance is the best one.

Optimization of bottom blowing position on the 300 ton converter of MaSteel and its effect

2009, 25(03):  5-7.  doi:

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This article introduces the characteristics of the bottom blowing system of 300 ton converter of NO.4 Steel-making & Rolling General Plant of Ma’anshan Iron & Steel Co., Ltd.. In order to advance metallurgical effect of bottom blowing system the position of bottom blowing elements has to be optimized. The optimal position of the bottom blow elements is finally determined through water model simulation tests along with a comprehensive consideration of the positions of the top lance and su-blance positions as well as the construction of the converter. Production practice demonstrates that the bottom blow of those elements is very effective.

Research on refining process of ultra-low-carbon steel for thin slab casting

2009, 25(03):  8-10.  doi:

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The smelting and refining practice of ULC Steel for thin slab casting at BenXi Iron & Steel (Group) Co., Ltd is introduced. .By comparing different refining process ways , an optimized refining way of LF+RH is put forward, thereby, some elements difficult to control such as C、N、Si etc. can be controlled stably, re-oxidation phenomena in liquid steel decreased greatly, the cleanliness and castability of liquid steel improved , and continous casting with more heats realized.

Study on nitrogen behavior in RH-MFB refining process

2009, 25(03):  11-15.  doi:

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According to analysis and discussion of the restrictive step of nitrogen removal in steel during vacuum smelting, and combining with the actual production of RH-MFB at Lianyuan Steel, the limit step and model equation of denitrogenation in RH-MFB of Liansteel are determined. At the same time, the influence factors of nitrogen removal from liquid steel are also analyzed. The results show that the diffusion of nitrogen in liquid-phase boundary layer is the restrictive link of nitrogen removal in RH-MFB of Liansteel and yet the reaction follows first order kinetics. Keeping the necessary circulation time under the working pressure(67Pa) is helpful to denitrogenation of steel. After deep deoxidation, the oxygen content in molten steel has little influence on the removal of nitrogen. While the sulphur content in liquid steel is always relatively low, it has little effect on denitrogenation. The sharp decrease of carbon content in steel drives the process of denitrogenation reaction so as to exhibit a faster denitrogenation rate. The interfacial reaction and argon blowing play a major role in the nitrogen desorption when the carbon content in liquid steel is stable.

Control on microstructure and mechanical properties of ML20MnTiB high strength cold-heading steel

2009, 25(03):  16-18,7.  doi:

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The process control in producing the ML20MnTiB high strength cold- heading wire rod by the process route of BOF→LF→billet continuous caster→high speed wire rod mill is introduced and the modification process and mechanism of the boron bearing cold heading steel probed into and the relationship between the various microstructures already achieved and its correspondent mechanical properties found out.By properly controlling the tempered structure the requirements for production of 10.9 grade and 12.9 grade high strenghth standard elements can be realized.

Optimization of production process for 18-8 grade clean stainless steel and its effect

2009, 25(03):  19-21,5.  doi:

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The stainless steel production line newly introduced in the No.2 Steel-making Plant of Taiyun Iron & Steel Group is a line which uses the pretreated hot metal and alloy elements as its primary raw materials. This new line has brought the superiority of extremenely low content of 5 harmful elements Cu, P, S and etc…in the main raw material, the hot metal and VOD vacuum metallurgy into full play in developing the 18-8 grade stainless steel. By optimization of LF refining stainless steel process as well as optimization of the flow field of the tundish the inpurity of O and Al2O3 in the 18-8 grade stainless steel slab is reduced to less than 30×10-6 and 5×10-6 respectively. And by metallographical observation it’s found that the total amount of inclusions in 50 mm2 area of a slab is reduced by around 40% and the inclusions larger than 20 μm in size are controlled in 5% or less.

Quality control of round billet for high pressure gas bottle tube

2009, 25(03):  22-24.  doi:

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The paper describes the principal equipments of the 90 t EAF+LF+VD+CC production line Valin Hengyang Steel Tube Co.,LTD has introduced from Danieli and analyses in detail process quality control of gas bottle tube from scrap through EAF, LF and VD to CC. Process quality control of gas bottle tube is very strictly implemented and the physical quality of the products can meet the requirement of the standards at home and abroad.

Practice in controlling center segregation of slab

2009, 25(03):  25-28.  doi:

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Center segregation is the common inner defect of slab. By insisting on day to day macrographic analysis on the structures of the slab, adopting the soft reduction technology and the EMS process, properly controlling the roller gap, improving the secondary cooling schedule and maintaining well the secondary cooling equipments in the recent years the grade A segregation has been eliminated and the rate of grade B segregation controlled within the limit of 5% below in the No.2 Steel-making Plant of WISCO.

Research of the relationship between the desulfurization rate and the flaw detection eligibility rate

2009, 25(03):  29-30,6.  doi:

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Through comprehensive analysis on the desulfurization rate of molten steel and the flaw detection eligibility rate of the low alloy steel 16MnR(AR) plate produced in the Steel-making Plant of Chongqing Iron and Steel Corp. from 2006 to 2007 it’s shown that the H content in steel and the extent of segregation in the slab are two important factors affecting the flaw detection eligibility rate and moreover the H content in steel is strongly dependent upon the S content in steel. Thus it’s concluded that the flaw detection eligibility rate tends to rise with the increase of S content in steel.

试验研究

Application of fuzzy Self-adapt Control in positioning convertor lance position

2009, 25(03):  31-33,7.  doi:

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In light of the characteristics of the lance position control the PID parameters are adjusted by means of the fuzzy PID self-adaptive scheme so as to realize the control of the oxygen lance positioning. The controlled object is simulated on the basis of draw-up of a detailed design plan of the fuzzy controller. Results show that in comparison with the conventional PID control method the fuzzy self-adaptive PID control is featured of better static and dynamic performance.

Distribution of free-calcium oxide in converter slags and its stabilization

2009, 25(03):  34-36,4.  doi:

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The distribution of free calcium oxide (f.CaO) in the converter slag was examined by petrographic microscopy analysis and its stabilization was investigated in 5～10 mm steel slag through a designed digestion device. Results show that f.CaO was surrounded by tricalcium silicate and dicalcium silicate with a grain size of 40 μm. In the hot wet environment injection of vapour and carbon dioxide to the slag is propitious to transformation of f.CaO into calcium hydroxide and calcium carbonate.

Application of sulfur distribution ratio in optimization of LF ladle slag composition

2009, 25(03):  37-41.  doi:

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The sulphur content of the Al2O3-CaO-MgO-SiO2 series of various constituents in the slag and the sulphur distribution ratio under the equilibrium condition are calculated and the effects of change of various constituents in the slag and variation of the hot metal temperature on the sulphur distribution ratio analyzed using the empirical expression derived by Ohta and Suito and the Young et al.’s model. By calculation of the sulphur content in the LF refining slag and the sulphur distribution ratio in a specific Steel-making Plant of Shougang the calculation model is validated and the compositions of the refining slag optimized in a bid to achieve the best desulphurization effect.

Mathematical and physical simulation and application of tundish with gas curtain

2009, 25(03):  42-44,6.  doi:

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According to the structure and the operating parameters of the tundish at No3 Steel Plant of WISCO the effect of the gas curtain technology on the flow of the liquid steel and removal rate of inclusions in the tundish was mathematically and physically simulated and thereupon industrial scale experiments carried out. Experimental results show that that the flowing conditions of the liquid steel can be effectively improved, the average duration of the liquid steel in he tundish prolonged, the volume of the dead zone reduced and the removal rate of the inclusions raised by aaplication of the the gas curtain technology. It is more suitable for the tundish in refining the super clean steel.

Investigation in the behavior of sticking breakout and its propagation in slab continuous casting mould based on the temperature monitoring in plant trial

LIU Yong-zhen;WANG Xu-dong;JIA Qi-zhong;YAO Man

2009, 25(03):  45-48,5.  doi:

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Based on the measured mould temperature data in slab and thin slab continuous casting, the characteristics of temperature variation and distribution in the mould in normal condition are analyzed. According to the measured samples about sticking, the response of the temperature and the process of sticking breakout are investigated, especially focusing on the sticking’s propagation along the height and transverse direction. The results can provide guidance for the breakout prediction under high speed casting and design of thermocouples arrangement.

Water Modeling and Industrial Practice of Inclusion Removal ina Big Round Billet Continuous Casting Tundish

2009, 25(03):  49-52.  doi:

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The effect of two different flow controlled tundishes (U-baffled tundish and Y-baffled tundish) on inclusion removal was studied using water modeling and industrial experiments. Comparing to the U-baffled tundish, the Y-baffled tundish obviously improved inclusion removal. The removal percent of the total oxygen remarkably increased, and more inclusions>50m can be removed while the micro-inclusions observed using 2D optical microscope changed little. Furthermore, the amount of inclusions at the different strands of the Y-baffled tundish is more homogeneous. Using the U-baffled tundish, the nitrogen pickup less occurs in the metallurgical process from tundish to the continuous caster.

Industrial experiment of producing high-strength reinforcement metal with nitrided ferrovanadium

2009, 25(03):  53-56.  doi:

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The results of industrial experiment on producing 4 batches (a total of 159 heats) of high-strength reinforcement metal with nitrided ferrovanadium were introduced. The basic process route is 100 t BOF smelting→ 165 mm×165 mm billet continuous casting→hot continuous rolling(Φ20～32 mm thread steel). In the industrial experiments comparative experiments were aslo carried out using Fe-V and V-N. Results show that ⑴ the composition was controlled stably by alloying with Fe-V-N, ⑵ the yielding rate of the alloyed vanadium was higher using nitrided ferrovanadium (Fe-V-N) than that using Fe-V or V-N, ⑶ The vanadium content in the steel and the addition amount of vanadium obviously affected the mechanical properties of steel. The derived empirical formulas can be used as reference for alloy composition design, ⑷ HRB400 Steel can be produced by alloying with Fe-V-N. There were prospects for reducing alloy consumption and cutting down the alloying cost.

Production of extra low sulfur pipeline steel and analysis of main parameters

2009, 25(03):  57-59.  doi:

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In production of the low sulphur steel by the process route of hot metal pretreatment→BOF→LF→VD→CC the sulfur content can be reduced to 10×10-6 stably and in some heats the sulfur content can be reduced to the extra low level(5×10-6).Based on the industrial experiment the main desulphurization parameters are evaluated using the desulphurization model for refining. The results show that :the theoretical Ls is much bigger than the real Ls and the sulphur distribution ratio will swiftly fall with the rise of the oxygen activity as soon as the oxygen activity in steel arrives at（3～10）×10-6 and in the process of LF refining the theoretical sulphur distribution ratio will increase by 4 to 5 each time when the temperature rises by 10℃.

Solidificatin mode of low Ni-containing austenitic stainless steel and effect of nitrogen

2009, 25(03):  60-63.  doi:

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The effect of N2 content on the initial solidification structure of low Ni-contained austenitic stainless steel was studied by choosing different N2 content slab sample, reheating and melting a partial of the sample in a THERMORESTOR-W type welding simulation machine, and then quickly cooling it down with a specific cooling speed within a set cooling temperature range. The results show that the solidification mode of sample 1 with lower N2 content was different from sample 2 which has higher N2 content, and significant difference of the trend of change in the ferrite and precipitation phase content inside the crystal between them appeared as their cooling speed increased.

Contrast between GCr15 sprayed blank and sprayed powder

2009, 25(03):  64-68.  doi:

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Spray forming is a fast developing and brand new technique for the metal & alloy forming in the recent years. The microstructures of the GCr15 spray formed blank and the GCr15 spray formed powder were examined and analyzed with the metallographic microscope and the scan electronic microscope. Results indicate that the microstructure of the spray formed powder is of the dendrite morphology in powders of different sizes whereas the microstructure of the spray formed precipitated blank appears to be fine equi-axed grains due to atomization crash of the atomization gas. The grain size of the powder is limited in the range from 35 to 80 µm while the grain size of the spray formed blank is ranging from 80 to 120 µm.

设计改造

Reliability analysis of sustainment frame in active segment of steel bloom CC

2009, 25(03):  69-73.  doi:

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For check and examination of the working reliability of the sustaining frame of the cast roller in the movement segment of the bloom continuous caster the load of the sustaining frame was sorted in accordance with the actual working conditions of the sustaining frame in that seegment and the dynamic drawing resistance and the dynamic bulging force of the bloom in the movement segment under the designed working conditions were calculated respectively by means of the finite element numerical analysis software and the dead load of the frame determined by the traditional theoretic method. Taking each calculated load value as the boundary conditon the stress simulation analysis on the sustaining frame of the movement segment was carried out. Results indicate that the original design plan was cast off since it was not reasonable. A scientific check and examination model can be provided for the mechanical analysis and calculation on the sustaining frame in the movement segment of the caster and at the same time the technical support is also provided for a specific iron-making and steel-making plant in safely and timely use of the sustaining frame.

Study on upgrading of second cooling in slab continuous cast

2009, 25(03):  74-77.  doi:

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The present paper elaborates the necessity and feasibility of upgrading the process control and automation system in the slab continuous caster introduced from Voestalpine AG and analyzes the effect of such a few parameters as the drawing speed and the overheat extent on the processs of the slab production by the established secondary cooling dynamic control model in the continuous casting slab solidification heat-transfer process . The deviation value of the tundish temperature and the target temperature are introduced in the secondary cooling water control model as the feedforward control of the flow revision and as the result the adaptability of the secondary cooling water flow to the change of the drawing speed is improved, thus contributing a great deal to the equality and consistency of the surface temperature of the slab as well as to the improvement in the quality of the slab. On the basis of the above mentioned effort development of the secondary cooling control system under the Windows operating system was accomplished and comparison was made beween the running results of the current system and that of small sized Alpha machine running under the off-line condition and they are in good agreement with each other. It shows that the new model can replace the secondary cooling control function of the small sized machine under the Windows operationg system.