Table of Content

05 October 2012, Volume 28 Issue 5

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专题论述

Review of progress of steelmaking technology in the first decade of the new century and outlook in the “12th fiveyear development” period

2012, 28(5):  1-7.  doi:

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The progress of science and technology in the steelmaking in China in the first decade of the new century has promoted the rapid growth of the steel production in China for sustained 10 years and pushed forward the science and technology level of the whole steelmaking industry of the Country.Six main basic steelmaking technologies have been developed,e.g.the technologies of high efficient and low cost clean steel production,energy saving,pollution control,etc in those ten years period.In the 12th development period the general trend of scientific and technological innovation of steelmaking is still to make all efforts to realize the general goal of green steelmaking,namely high efficient,low consumption,excellent quality and less pollution discharge and energetically accelerate application of optimal clean steel refining process,namely DeS and converter type DeSi and DeP hot metal pretreatment and raise the level of utilization,conversion and reclamation of the energy resource and vigorously develop high efficiency and constant velocity continuous casting equipments and technologies for various steel grades and improve the level of intelligent steelmaking and strengthen research and development of the frontier technology of continuous casting.

生产实践

Low temperature tapping technology for converter of Tangsteel

2012, 28(5):  8-12.  doi:

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On the basis of analysis on the affecting factors namely the tapping temperature and the process temperature drop and by way of adoption of such a series of technical measures as stabilizing the tapping time, perfecting the baking schedule of the alloy materials, full course covering for ladle, improving the turnover rate of the ladle and casting speedily at low temperature,the average tapping temperature of the converter is steadily controlled within the level of 1 635 ℃ below and the tapping time is 2.4 min. The molten steel temperature drop in the full course including tapping, argon blowing at the bottom of the ladle, ladle turnover and slab casting is only 20, 11.1and 25.9 ℃ separately. The inner lining baking temperature of the ladle rises from 820 ℃ to 1 020 ℃. The converter service life reaches approximately 24 000 heats and consumption of lime is reduced greatly.

Optimizing low-nitrogen-steel metallurgy process in combined blowing converter

2012, 28(5):  13-15,1.  doi:

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The present paper analyzed the reasons for the high nitrogen content in the pipeline steel and lownitrogensteel in a 250 t combined blowing converter metallurgy process and introduced the counter measures including adoption of automatic blowing process and decrease of reblowing, increase in the ratio of hot metal, control on the bottom lownitrogen model blowing of converter and prevention against nitrogen pick up during tapping and reduction of the nitrogen content in steel (controlling the average nitrogen content in steel within the limit of 22.13×10-6.

Development and application of carbon-alloy material for steelmaking

2012, 28(5):  16-19.  doi:

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A new carburet material is developed to solve the problem of long smelting time and low carbon rate when the blind coal is used as the carburant and its metallurgical effects are also investigated by industrial experiments. Results show that in comparison with the carburant of the blind coal the newly developed carbon-manganese carburant is featured of high smelting rate, high carbon and manganese yield (the average carbon yield 92.95 % and average manganese yield 93.31 %).By adoption of the new carburant the quality of the liquid steel can be ensured and the tapping temperature lowered and material flow time shortened and thus the cost for steel-making reduced.

Development and application of long life technology of WG-3Y stirrer in KR desulphurization

2012, 28(5):  20-23.  doi:

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In view of the difficulties of improvement in the comprehensive performance of the KR stirrer at home and abroad on the basis of the results of theoretical research and water model test of KR stirring desulphurization a new structure of WG-3Y stirrer is developed. Depending on the water model research a new structure of WG-3Y stirrer used for desulphurization stirring in the 100 t and 200 t hot metal ladle is developed and tested in the industrial scale and now is broadly popularized in the practical use and as the results the kinetic conditions for desulphurization is improved and the technical and economical index of the desulphurization raised as well.

Practice of control on carbon and sulphur content in the pipeline steel

2012, 28(5):  24-27.  doi:

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The present paper analyzes the effect of the converter steelmaking process “KR hot metal desulphurization→topbottom combined blowing of 130 t converter(BOF)→bottom argon blowing at argon station→LF ladle refining→RH vacuum refining→slab continuous casting” on the carbon and sulphur content in the pipeline steel. In light of the characteristics of each technological process such a few control measures as increase in the hot metal temperature, optimization of the refining process and control of the carbon and sulfur content in the initial ladle and the followup one separately have been adopted and as the results the qualification rate of the chemical compositions for the pipeline steel rises to 92.89 %from 80.30%.

Production practice for development of titanium microalloyed high strength steel for automobile body use

2012, 28(5):  28-31.  doi:

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In view of the advantage of rich vanadium titanium resource in Chenggang proceeding from the conception of production of the low cost and high strength steel using titanium micro-alloying technology the 600 MPa steel grade for automobile body use with optimal chemical compositions is finally developed by implementation of a series of technological measures such as strengthening the hot metal desulphurization and pretreatment process, strictly controlling the nitrogen and oxygen content in steel, optimizing the structure of tundish, implementing the CC protective casting technology and rational rolling process and using the necessary check and evaluation means for instance the metalloscope, scanning electron microscope, tensile testing machine, impact testing machine and other means of detection. Results show that the average yield strength of the steel sheets comes up to 566 MPa, and its average tensile strength reaches 655 MPa, with advantages of homogeneous microstructure, better impact toughness and cold bending property. That can completely satisfy requirements of customers.

Research and practice on control of nitrogen contents during VD process

2012, 28(5):  32-34.  doi:

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The process of nitrogen content controlling in VD is studied in this paper and the impact of parameters such as vacuum, bottom blown flux, vacuum processing time etc. and chemical compositions such as sulfur, oxygen and nitrogen in liquid steel on denitrification is analyzed separately. The analysis indicates that such a few processing measures as reduction of the initial nitrogen content, strictly control of the sulfur and oxygen contents during VD process, enhancement in the strength of bottom blowing, extension of the holding time of vacuum pressure are favorable for production of the low nitrogen steel. The reason for increase of nitrogen contents after vacuum break is analyzed and in the end it's pointed out that the nitrogen pick up in the liquid steel can be reduced by appropriately changing the vacuum break operating schedule and readjusting the soft blowing rate.

Analysis and measures for mold narrow taper change

2012, 28(5):  35-37,4.  doi:

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The mold narrow taper change frequently occurs in the mechanical width adjustment mechanism of the mold of the slab continuous caster. The present paper analyzes the origin of the defect and puts up the measures to check it effectively. Since implementation of “up-pull-down-push” method the mold narrow taper changes have been eliminated basically except casually occurrence of 2 mm narrow taper change at the top of the mold in one specific heat and the maximum taper deviation is only 0.2mm. Practice shows that mold taper deviation can be effectively prevented by adoption of the “up-pull-down-push” method.

Research of billet quality and optimization of steel-making process for 70 highcarbon steel in KISC

2012, 28(5):  38-42.  doi:

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To improve quality of product the steelmaking process of 70 highcarbon steel in KISC is optimized and improved and the macrostructure and index of central carbon segregation in the billet are analyzed by sampling. In the meanwhile inclusions in the billet are researched by using large sample electrolysis，scanning electron microscopy and spectroscopy test. The results show that quality of billet is improved significantly after process optimization，defect level of macrostructure for the most 70 high-carbon steel billets is less than 0.5 grade，ratio of equiaxed zone for the billet is more than 40 %；index of central carbon segregation in billet is decreased from 1.06 to 1.03and segregation of chemical compositions is small. The total amount of inclusions in 10 kg large sample electrolysis is reduced from 28.95 mg to 9.78mg and the inclusions are mainly composed of SiO2-Al2O3-CaO and SiO2-MnO-Al2O3with low melting point and good plastic. The drawing break ratio of wire rod in one hundred tons is decreased from 7.5 times to 4.9 times and the drawing performance of wire rod is improved obviously.

试验研究

Study on control technology of slag composition for low-sulfur & low-oxygen steel

2012, 28(5):  43-47.  doi:

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In order to effectively reduce the content of oxygen and sulfur in steel and produce low-sulfur and low-oxygen steel studies on slag have been carried out. Refining slag series CaO-SiO2-Al2O3 is determined to be used in refining the low sulphur and low oxygen steel under the conditions that all the factors concerned such as amount of slag from the converter, the oxidizability of the converter slag and the activity of the oxygen are taken into full consideration and in the meanwhile a schedule for modification of the ladle slag in refining the low sulphur and low oxygen steel is drawn up in connection of the slag modification technology of the converter slag and the chemical composition control technology of the ladle slag in LF refining. The results show that oxygen content in the tube steel blank 27CrMoNbV produced using this technology is not more than 15×10-6and sulfur content is as low as 0.005 %and therefore the aim of production of low sulphur and low oxygen steel is realized.

Inclusion control of oil drilling steel SAE4137

2012, 28(5):  48-51,7.  doi:

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In consideration of inclusion control in smelting drilling steel SAE4137 by convert process, the software Factsage is applied on the deoxidation technology, composition of ladle slag and calcium treatment technology. The tests show that the deoxidation technology is reasonable and the oxygen content of molten steel is not more than 5.0×10-6and 3.2×10 -6 on average. The inclusion of bar is less and like a ball. The effect of calcium treatment is good. The inclusion is transformed in refining process，and the absorbing ability to inclusion of ladle slag is strong. The level of any type of inclusion is not more than grade 1.5. The mechanical performance of SAE4137 bar meets the requirements, and the inclusion control technology does not influence the mechanical performance of bars.

A novel fluoride-free low melting point deep desulphurization slag for LCAK steel

2012, 28(5):  52-55,6.  doi:

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A novel low melting point and fluoridefree CaO-Al2O3-SiO2 based slag system for deep desulphurization of low-carbon aluminum killed (LCAK) steel has been developed on thermodynamics basis. The composition of the basic slag is w(CaO)=57 %～62 %，w(SiO2)=5 %～10 %，w(Al2O3)=29 %～36 %. In the industrial application, the basic slag turned out to be 85 %～95 %, w(MgO)<10 %and w(T.Fe+MnO) <1.5 %. The novel slag system was used for the LF refining of SPAH steel to make the final sulfur content about 20×10-6, when the initial sulfur content was less than 160×10-6.Corresponding desulphurization ratio was higher than 75 %, and hence the slag consumption was reduced from 15 kg/t to 10 kg/t thus the cost is reduced accordingly.

Theoretical calculation for aluminum pick-up of high carbon steel in LF refining process and study on tundish nozzle clogging

2012, 28(5):  56-60.  doi:

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Probability analysis of silicon and carbon in steel and Al2O3 in refining flux reacting on the acid soluble aluminum content
pick-up of the high carbon steel have been researched through thermodynamic calculation during LF refining. LF refining factors related to
influence aluminum content were studied theoretic to determine the better LF refining process. Mechanism and countermeasures of high
carbon steel are summarized to solve nozzle clogging. The theoretical results show that the present LF refining process can eliminate the
tundish nozzle clogging, and the proper LF refining process should be controlled that the basicity of the slag (R≤1.0)and w(Al2O3)≤5 % and refining temperature (t＜1 600 ℃), then aluminum content in the molten steel can be controlled under 3.5×10-6.

Development of soft reduction zone prediction model for medium-thick slab continuous caster

2012, 28(5):  61-64.  doi:

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In this study, a mathematical model with heat transfer and solute diffusion is developed for simulating the solidification process of slab in the
slab casters in the No.4 Continuous Casting Operating Area of the Steelmaking Plant in Angang Steel Co., Ltd. The model can be used to
calculate distribution of solid phase fraction and visualize the inner solidification process of slab. In practical production the calculation
results of the model are used to determine soft reduction zone. The soft reduction with model-predicted parameters can be used for designing
the corresponding continuous casting process for various steel grades and developing new process.

Study on clogging of submerged-entry nozzles during CSP casting high-Al steel in WISCO

2012, 28(5):  65-68.  doi:

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The phenomenon of nozzle clogging in refining the high aluminum steel
（w(AlS)=0.20 %～0.45 %）by “BOF→LF→RH→CC”process route in CSP line in WISCO is investigated and results show that the very important factor causing the nozzle clogging lies in adoption of improper calcium treatment process leading to occurrence of a huge number of high melting point composite inclusions such as CaS and xCaO·yAl2O3in steel. Since optimization of the calcium treatment process the average heats of the
continuous casting rises from the original 3.25heats to 10.86 heats and thus the difficult problem of undesirable castability in refining the high aluminum steel in the CSP line is basically solved.

Simulation and verification of solidification process of stainless steel 316 in the mould during continuous casting

2012, 28(5):  69-73.  doi:

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The effect of δ ferrite content in the high temperature zone on the solidification of the liquid steel in the process of continuous casting is studied by 3dimensional finite element technology. By means of simulating the process of casting the slab of stainless steel 316 the law of effects of δ ferrite content on the variation of the outlet temperature of the solidification shell, corner temperature and shell thickness in the process of solidification is obtained. It is found that the contents of the δ ferrite have great effects on the gradient of temperature along the casting direction，but only have very little effects on the variations of the lateral temperature gradient. By calculating the results it’s determined that the shell in the vicinity of the area 40 mm away from the corner section is the thinnest. In the meanwhile the law of the shell thickness variations at the outlet is investigated systematically and results show that with increase of the δ ferrite content the thickness of the shell at the outlet reduces and the difference of the thickness becomes greater gradually.

Study on cleanliness of SPHC steel by CSP process

2012, 28(5):  74-77.  doi:

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By the methods of metallographic observation, EPMA, and sampleelectrolyzing, the morphologies and composition of nonmetallic inclusions in SPHC steel are investigated. The results show that w(T.O) and w(N) in slab are (28~33)×10-6 and (30~43)×10-6 separately. The average number of inclusions decreases form 8.979 3 mm-2 to 7.344 2 mm-2, the
proportion of less than 10 μm inclusions is 93 %. Under the normal conditions the macroinclusion content of 10 kg liquid steel in
tundish is 6.8and 5.9mg in slab. However as soon as slag entrapment occurs large inclusions will increase rapidly and they may reach as high as 12.3 mg and the 100~280 μm inclusions come up to 26.32 %. The inclusions in the tundish are mainly composed of deoxidized products and deoxidized compound inclusions; the inclusions in the slab mainly consist of compound inclusions; inclusions in the tundish and slab are mainly silicon aluminate compound inclusions and silicate inclusions and magnesium and potassium are also found in the inclusions. It shows that the lining of the tundish is already eroded and slag entrapment occurs in the mold as well.