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2012 Vol. 47 No. 8
Published: 2012-08-15
Technical Reviews
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technology Exchange
Technical Reviews
1
ZHANG Xin-xin1,ZHANG An-qiang1,FENG Yan-hui1,LIU Jian1,ZHANG Chang-qing2,YU Zhen-dong2
Energy Consumption Analysis and Technologies of Waste Heat Utilization for Coke Oven
Though coking industry is highly energy-consuming and heavily air-pollutant, it has tremendous potential of energy saving and emission reduction. Based on the material balance and heat balance calculation, thermal efficiency of coke oven was calculated and energy consumption of coke oven was analyzed. To make full use of waste heat of coke ovens, such technologies as coke dry quenching (CDQ) , waste heat recovery of raw gas and coal moisture controlling (CMC) via recovered heat of flue gas should be adopted. It is expected to save energy, improve environment, enhance economic returns, and improve the coke oven production.
2012 Vol. 47 (8): 1-4 [
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Raw Materials and Ironmaking
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CAO Ming-ming1,ZHANG Jian-liang1,XING Xiang-dong1,WANG Chun-long1,BAI Ya-nan1,WEN Yong-cai2
Reduction Mechanism of Vanadium Titano-Magnetite Carbon Composite Pellets
On basis of RHF (rotary hearth furnace) technology, the macro morphology and inner microstructure was investigated under the conditions of different carbon ratio, different roasting temperature and different roasting time. The results show that: with increase in reduction temperature, Ti in the pellets is firstly centralized distribution, and then uniformed distribution, finally centralized distribution; Fe element is gradually separated, Ti and Mg distribution is almost the same, and the V forms almost consistent with Ti. The porosity of pellet is decreased with increase in reduction temperature through observation and analysis by SEM, which can to some degree have effect on reduction process. If the reduction time is controlled about 20 to 40 minutes, Fe and Ti, V can be separated, however Mg and Ti are immiscible together. No matter what proportions of carbon condition, pellets exist metallic iron and (Fe,Mg)Ti2O5. Titanium black stone will limit increase in the metallization rate, and when the w(C)/w(O) is up to 13, the new phase of TiC0.2N0.8 appears in pellet.
2012 Vol. 47 (8): 5-12 [
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13
ZHANG Shu-hui,MU Hong-wang,SUN Yan-qin,L Qing
Desulphurization Dynamics Mechanism of Blast Furnace Slag With Medium Titanium and High Alumina Content
On the basis of the compositions of blast furnace (BF) slag at field, the desulphurization dynamics process was researched for BF slag with medium titanium and high alumina content, which was fabricated from pure chemical agents. The dynamics parameters of desulphurization were obtained. Results show that the sulfur content in liquid iron (w(［S］)) decreases with the elongation of desulphurization reaction time when the temperature is constant. Under the experimental conditions, the desulphurization process of BF slag with medium titanium and high alumina content belongs to second-order reaction, the restricted step of which is sulfur diffusion in the fused slag. The mass transfer coefficient (βS) rises with increasing the reaction, and the diffusion activation energy(ED) of sulfur element in fused slag is 127.03kJ/mol.
2012 Vol. 47 (8): 13-16 [
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17
LI Shuo,ZHU Zi-zong,X Jun,SONG Nan
Optimization and Modification of Semi-Coke Blending for Conventional Cokemaking
The test of modifying semi-coke and blending for cokemaking were carried out in 40kg coke oven for enlarging the application of semi-coke in coking industry. Experimental results show that: the value of caking index (G), maximum thickness of colloidal layer (y), Audibert-Arnu dilatation (b）, plastic range and maximum fluidity of blended coal decrease with the increase of semi-coke. However, it would be improved significantly with the addition of ZBS modifying additive. The best improvement can be achieved when 0.10% of ZBS is mixed with the semi-coke. The quality of the resulted coke was very close to the index of the coke with original coking coal and the production requirements can be met.
2012 Vol. 47 (8): 17-21 [
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Steelmaking
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WANG Lin-song1,YANG Mao-lin2,ZHENG Jia-liang3,GAO Chang-yi2,REN Zheng-de4
Effect of Trace Elements in Hot Metal on Steelmaking Process
V-Ti-tracing-elements hot metal, which was different from common hot metal and high V-Ti hot metal, was produced using low proportion iron ore involving V-Ti element. In order to know the effect of these trace elements on converter steelmaking process, the phase compositions and melting characters of V-Ti slag were analyzed and the steelmaking process in converter was simulated by high frequency induction furnace. The results show that: 1) carbon flame temperature of general hot metal is 1370-1400℃, carbon flame temperature of Shuigang hot metal is 1400-1430℃ which is 30℃ higher than that of general hot metal; 2) at a small rate of blowing oxygen, Ti,Si,Mn and C in melt can be oxidized one by one; 3) foaming and foam storage capacity of TiO2-bearing slag is larger than that of slag without TiO2, active CO bubbles in slag exacerbate slag foaming; 4) in prior and mid period of converter steelmaking, super high FeO content, relatively low alkalinity and C-FeO reaction in slag and foam storage capacity of TiO2-bearing slag are main reasons for the slopping.
2012 Vol. 47 (8): 22-26 [
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27
CHANG E1,WANG Li-jiang2
Influencing Factors on Solidification Microstructure of Ferritic Stainless Steel
Columnar crystals in ferritic stainless steel formed during solidification were harmful to steel formablity, so it was important to avoid columnar crystal forming and promote equiaxed crystal forming for ferritic stainless steel. The solidification microstructure under cast test and continuous cast test conditions was analyzed. The results show EMS benefits equiaxed crystal forming and cooling intensity plays an obvious role to columnar crystals forming under both mould cast test and continuous cast test. C and N contents have also effect on 430 solidification structure under cast test. Under the conditions of strong temperature gradient during continuous casting, effect of C and N content on solidification microstructure will be decreased. However, if liquid steel was stirred during continuous casting, C and N contents still play an obvious role on 430 solidification microstructure.
2012 Vol. 47 (8): 27-30 [
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31
YI Jian1,2，LI Wei-gang1,2，ZHU Jun2，DU Bin1,2
Optimization Method for Tundish Plan Under New Technique Condition of Steelmaking-Continuous Casting
The new improved technique of steelmaking-continuous casting brought about the changes from fixed furnace counts to a fixed time for evaluation mode of tundish lifetime and a corresponding optimization model for tundish plan was constructed. The effects of steel grade, casting width and draw-speed to casting time were taken into account in the model. And then, an optimization method combining heuristic algorithm and DNA evolutionary algorithm was proposed to solve the model. Three heuristic algorithms were designed and detailed steps of DNA evolution process were given based on heuristic algorithm. By simulating on the real production data, the result shows that the proposed optimization method may improve the utilization rate of tundish and is effective.
2012 Vol. 47 (8): 31-35 [
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Metal Forming
36
WU Di1,LI Zhuang2,L Wei3
Controlled Rolling and Cooling of Ultra-High Strength Ferrite-Bainite Dual Phase Steel
Controlled rolling and cooling of ultra-high strength ferrite-bainite dual phase steel in the different conditions were conducted by a laboratory hot rolling mill. Effect of various processing parameters on the microstructure and mechanical properties of the steel was investigated. The results show that ultra-high strength dual phase steel with ferrite-bainite microstructure can be obtained by applying controlled rolling and cooling. The tensile strength values are nearly the same in all cases and always exceed 1000MPa, yield ratio varies from 0.54 to 0.62 and the total elongation varies from 13% to 17% for the specimens which are cooled at different cooling rates after various finish rolling temperatures. The ferrite grains are refined with decreasing finish rolling temperature and accelerating cooling, and the amount of bainite increases with decreasing finish cooling temperature. Tensile strength, total elongation and the product of tensile strength and total elongation for the specimen, which is finished rolling at 800℃ and subsequent laminar cooling to 560℃ and then air cooling to room temperature, reach maximum values (1130MPa, 16% and 18080MPa%, respectively). This is attributed to the ferrite-grain refinement, strengthening of granular bainite, carbide free bainite and a small amount of twinning martensite. The presence of retained austenite improves the ductility of the steel. Multiphase microstructures contain ferrite and bainite as main phase with a small amount of retained austenite and martensite, contribute to enhance mechanical properties of tested steel.
2012 Vol. 47 (8): 36-42 [
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43
Analysis and Control of Strip Wedge in 2250 Conventional Continuous Hot Rolling
This study focused on the product section wedge of one wide strip conventional hot continuous rolling in China. Through finite element method, it established static simulation model, calculated the quantitative effect of work piece deviation and incoming wedge inherit on strip section wedge value at the outlet of hot continuous mill, and validated the calculation result with the practical production data. The author optimized alignment accuracy and opening gap margin of finish vertical rolling and side guide to enhance the alignment during the course of rolling, and also used rough rolling strong side guide, optimized rough rolling roller contour and advanced manual leveling control to improve the incoming wedge of rough rolling; consequently it reduced the 3rd grade shape products rate, that was caused by wedge in the hot continuous mill, from 47% to 10%.
2012 Vol. 47 (8): 43-47 [
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48
YANG Ying,HOU Hua-xing,ZHANG Zhe
Effects of Intermediate Billet Cooling on Surface Microstructure and Property of Q345A Steel Heavy Plate
The effects of intermediate billet cooling on surface microstructure and property of Q345A steel heavy plate were investigated by the methods of thermal and numerical simulation, mechanical property testing and metallographic examination. The results show that the ultrafine ferrite microstructure with average grain size of 1μm can be obtained on 2mm surface layer while a little pearlite phase disperses in it. The matrix microstructure consists of massive ferrite and pearlite which is similar to that of the sample manufactured by the conventional TMCP. The matrix mechanical property, low temperature toughness will not be decreased by intermediate billet cooling. And the hardness on surface is a little more center of steel. Compared new TMCP (with intermediate billet cooling) with conventional TMCP, the steel has excellent crack arrest property.
2012 Vol. 47 (8): 48-51 [
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Materials
52
ZHOU Si-yuan1,2，ZHENG Wen-jie2，SONG Zhi-gang2，ZHANG Li-bo1，FENG Han2
Effect of Carbon Content on Microstructure, Mechanical Properties of 690 Alloy Steel and Analysis of Strengthening Mechanisms
The effect of carbon content on the microstructure and mechanical properties of 690 alloy steel was investigated. The results are as follows: in the range of 0.011%-0.033%, with the increase of carbon content, topography of precipitate on grain boundary of the desensitization 690 alloy gradually transforms into bulky scattered particles from tiny semi-continuous particles; the content of Cr-rich M23C6 which are the main precipitates increases from 0181% to 0.541%; the grain size of the desensitization 690 alloy steel decreases from 23μm to 10 μm; the tensile strength increases from 702.5MPa to 810MPa and the yield strength increases from 300MPa to 402.5MPa at room temperature. The main strengthening mechanisms of 690 alloy steel are fine grained strengthening and the second phase strengthening.
2012 Vol. 47 (8): 52-56 [
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ZHAO Jie1,2，XU Hai-feng1,2,SHI Jie2，LI Jian1，PU Jian1，CAO Wen-quan2
Effect of Grain Refinement Strengthening and Dislocation Strengthening on Strength of Medium Manganese Martensitic Steels
Effect of carbon and manganese content on the mechanical properties and microstructure characteristics of the medium manganese steels quenched in oil, such as dislocation density, volume fraction of retained austenite and grain size were investigated. Microstructures of the medium manganese steels were observed by SEM/EBSD, TEM and XRD techniques and tensile test was conducted at room temperature to examine their mechanical properties. Strengthening mechanisms operating in martensitic steel and the effects of carbon content on the strengthening contributions of the grain refinement and dislocation were discussed. It is found that increasing the carbon content increases the dislocation density, volume of retained austenite and the percent of high angel grain boundaries, but decreases the size of packet and block. This in turn increases the yield strength and tensile strength. Increasing manganese content increases the dislocation density and tensile strength. Dislocation strengthening and grain refinement strengthening are the main strengthening mechanisms operating in as-quenched martensitic steels. According to the strengthening calculation, it is proposed that the microstructure unit controlling the strength of martensite steels is the pre-austenite grain size for the yield strength but the lath size for the tensile strength.
2012 Vol. 47 (8): 57-61 [
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GAO Jian-zhong1,GUO Bin1,2,XU Jin-qiao2,GUO Ai-min1,2,WANG Qing-feng1
Static Recrystallization Behavior of Deformed Austenite in X120 Pipeline Steel
Static recrystallization behavior of microlloyed pipeline steel with Nb was investigated by two-pass uniaxial hot compression tests performed on Gleeble-3500 thermo-mechanical simulator. The static recrystallization fraction under different deformed temperatures was estimated by means of compensating. The results show that the effect of deformation temperature and inter-pass time on static recrystallization behavior is significant. The activation energy of static recrystallization of the X120 pipeline steel is 401.56 kJ/mol. The precipitation-time-temperature curve of the X120 pipeline steel is also obtained.
2012 Vol. 47 (8): 62-64 [
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SU Cheng1,2,DONG Fang2
High Temperature Plasticity of Micro-Alloyed Q345B in Slab Continuous Casting Process
The high temperature plasticity of micro-alloyed Q345B structural steel containing V, Ti and Nb was investigated. The tensile test was carried out by Gleeble-1500D thermal simulation testing machine, and fracture strength and reduction of area with temperature was analyzed under the condition of strain rate 1.5×10－3s-1 and deformation temperature 700-1300℃(Δt=100℃). The results show that Q345B structural steel exists two brittle zones, the first temperature area (Ⅰ) of brittless is solidification temperature about 1300℃, the third temperature area (Ⅲ) of brittless is 850-740℃. Through observation of fracture morphology and microstructure by scanning electron microscopy and optical microscopy, the cause of fracture was cleared to provide the theoretical guidance for the actual continuous casting process.
2012 Vol. 47 (8): 65-69 [
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Environmental Protection and Energy
70
JIA Jun-rong1，AI Li-qun2
Reduction Dephosphorization Behavior of Steelmaking Slag in Microwave Heating Field
The steelmaking slag dephosphorization experiments were carried out by microwave heating and carbon thermal reduction methods. The experiment results indicate that different steelmaking slags have good property in microwave heating field, with preferable dephosphorization results and dephosphorization rate that reach to the range of 51.35% to 81.16%. Considering the significant effects of reductor and temperature by which dephosphorization rate is affected, the appropriate range of carbon equivalent is 3 to 4 times. In order to determine the optimum process parameters, all factors which affect dephosphorization rate would be taken into account.
2012 Vol. 47 (8): 70-73 [
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ZHANG Fu-ming1，HU Zu-rui1，CHENG Shu-sen2
High Temperature Air Combustion of Dome Combustion Hot Blast Stove
NOx is the major technical barrier to increase hot blast temperature and prolong campaign life of hot blast stove at present. In order to restrain the amount of NOx formation during combustion process in the hot blast stove, the generation mechanism of NOx production was investigated, and NOx generation rate and amount in hot blast stove was calculated by means of thermodynamic generation model. A new dome combustion stove was developed based on high temperature air combustion (HTAC) technology. A comparison on the combustion process and characteristic of conventional hot blast stove and HTAC hot blast stove was performed by application of CFD simulation model. Temperature and concentration field distribution, flame shape and NOx concentration distribution of two kinds of stove was calculated. The result shows quite symmetrical HTAC stove temperature field distribution. Under the same dome temperature, NOx generation is 80×10-6 only, reduced by approx 76% in comparison with conventional stove. HTAC hot blast stove can get higher temperature and decrease NOx emission efficiently, as well as realize long campaign life of hot blast stove and energy-saving and emission reduction.
2012 Vol. 47 (8): 74-80 [
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Technology Exchange
81
Wilhelm Burgmann1,Jean Davené2
Cost Structure of Vacuum Degassing Treatment for Melt
The cost for the conversion of steel in secondary steelmaking including a ladle furnace and various vacuum treatment processes have been investigated for a large heat range and comparing two commonly used vacuum pump systems. Dry operating mechanical vacuum pumps offer substantial savings over the whole melt mass range up to 360 t. Such savings differ for the various processes and depend upon the availability of energy, in whatsoever form, as well as upon the plant productivity. The shortening of treatment cycle time by a rapid pump down limits the melt overheating and thus leads to savings in production cost, increased productivity and quality improvement.
2012 Vol. 47 (8): 81-88 [
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