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2014 Vol. 49 No. 3
Published: 2014-03-15
Technical Reviews
Materials
Environmental Protection and Energy
Technology Exchange
Technical Reviews
1
ZHANG Fu-ming,CAO Chao-zhen,XU Hui
Current Status and Prospects of Gas-Based Shaft Furnace Direct Reduction Technology
The technical characteristics and current status of gas-based shaft furnace direct reduction process have been expounded and the major problems faced by gas-based direct reduction technology development under China’s resource and energy condition have been analyzed. Based on the characteristics of the gas-based shaft furnace direct reduction process, analysis of raw materials and reduction gases of this technology have been undertaken. It has been pointed out that a significant reduction in investment and operating costs of pressurized coal gasification technology and the effective exploitation of unconventional natural gas resource is the main driving force of the future development of gas-based shaft furnace direct reduction technology; meanwhile it is still another important direction of current gas-based shaft furnace development to produce DRI by taking advantage of the excess gas resources of steel plants and natural gas resource in some areas where the natural gas resource is relatively abundant. According to the raw material and energy prices in Tangshan region, the production costs of DRI has been calculated and the technical and economic feasibility has been analyzed under the scale of 0.8Mt/a. The results show that the effect of price fluctuations of raw materials on the DRI costs is significant, and the reducing gas accounts for about 10 %-25 % of DRI total costs. If considering the economic benefits of using DRI instead of scrap in converter, the natural gas price should be lower than 1.8yuan/m3.
2014 Vol. 49 (3): 1-10 [
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Metallurgical Technology
11
WU Kai-ji，CHEN Ling，ZHANG Tao，GUO Min，LU Cun-fang
Experimental on CH4 Reforming Behavior of Coke Oven Gas in Gas-Based Shaft Furnace
Gas-based shaft furnace direct reduction process using coke oven gas，which can produce the high-quality sponge iron，is a good method to extend the industrial chain of the coking industry．On the other hand，it can also promote the development of the EAF process steelmaking with the scrap and sponge iron，which has a great significance to the change of the energy and product structure adjustment in Chinese steel industry．Effects of the operating conditions on CH4 reforming behavior of coke oven gas in gas-based shaft furnace，which include the temperature，H2O and CO2 ratio，and high temperature sponge iron，had been researched by basic experimental study．The results show that increasing temperature is beneficial to CH4 reforming behavior of coke oven gas，the content of effective reducing gas comes up to its highest value (about 80%) at 1000℃．Hot sponge iron greatly catalyze and promote CH4 reforming of coke oven gas，which can improve the ratio of CO2 in reaction to 84.9% and the ratio of H2O in reaction to 100%；the appropriate addition of CO2 should be set 2%-6%, the addition of H2O 4%-10%．
2014 Vol. 49 (3): 11-16 [
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17
LI Yan-long，ZHANG Li-feng，YANG Wen，WANG Lin-shu
Development of Ladle Slag Reducer Using Aluminum Dross
In the current study，ladle slag reducer was made using aluminum dross that contained a low content of metallic aluminum and high percentage of AlN．Laboratory experiments were performed in MgO crucibles under 1600℃ with a 1∶10 dross-steel ratio and a 4∶6∶1 dross-lime-fluorite， the samples were cooled by nature convection after 90 min heat preservation．The results indicate that both AlN and metallic aluminum in the dross could work as reducer to remove the oxygen in BOF slags carried on．Using this kind of aluminum dross，the w(（FetO)) in BOF slag could be decreased from 31.2% to 3.2%，w(［O］) in the steel can be lowered from 480×10-6 and 17×10-6，and w(［S］) in the steel is lowered 190×10-6 and 75×10-6．However，the w(［N］) in the steel is increased from 66×10-6 to 129×10-6．
2014 Vol. 49 (3): 17-23 [
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24
ZHOU Chao-gang ，，LI Jing，，WU He，，CAI Ke-sen，WU Guo-ping，CAO Yu-liang
Study on the Temperature of First Deslagging of Double Slag Dephosphorization in Converter
In order to dephosphorized efficiently at the first deslagging with double slag method in combined converter，the theoretically directed temperature of first deslagging was analyzed and calculated in thermodynamics．In this paper，the new model of temperature controlling of first deslagging was proposed．Through field test，the dephosphorization efficiency was studied at different temperature of first deslagging．The results show that it can make the phosphorus content of semi-steel decreased by 0.034%，dephosphorization rate increased by 28%，the phosphorus partition ratio improved by 28 when the temperature of first deslagging was increased from 1348℃ to 1427℃，and it can also achieve high dephosphorization efficiency of phosphorus content removed under 0.025%，dephosphorization rate more than 79%，the phosphorus partition ratio over 61 at first deslagging of double slag dephosphorization process．
2014 Vol. 49 (3): 24-28 [
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29
ZHU Zheng-hai,,XIAO Li-jun,WANG Qiang,PENG Shi-heng,GAN Yong
Micro-Structural Evolution of E36 Slab During Process of Continuous Casting-Conveying-Heating
Based on study for heat transfer of slab in process of continuous casting-conveying-heating, as for the micro-structural evolution of E36 slab, the effect of different thermal history for micro-structural evolution was investigated to provide the reference for the improvement of interface-technique. Their start rolling microstructure is no significant difference after heating when slab conveyed by different way and then cooled down to the temperature below 625℃. γ-α-γ phase transformation is one of the main factors affecting the start rolling microstructure. The micro-structural evolutions of slab cross section at different positions are not the same. If low charging temperature is adopted, the temperature of central of slab cross section should be below 625℃. Whereas, the temperature of slab corner should be above 805℃.
2014 Vol. 49 (3): 29-35 [
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36
XU Zhi-gang,WANG Xin-hua,ZHOU Li,HUANG Fu-xiang,YIN Yu-qun
Effects of Soft Reduction Parameters on Semi-Macro Segregation in Continuously Cast Slab
The effects of soft reduction parameters, including soft reduction position (fs), soft reduction ratio(RSR) and soft reduction amounts(ASR), on the semi-macro segregation in continuously cast slabs were investigated in present work. The results reveal that centerline segregation is composed of independent semi-macro segregates, which the areal fraction is proportional to the maximum segregation index of carbon. Thus, the key to improving the centerline segregation is to decreasing the area fraction of semi-macro segregates. Soft reduction is an effective measure to reduce the areal fraction of semi-macro segregates. The results of the industrial experiments show that the areal fraction of semi-macro segregates is reduced remarkably as fs>0.75, RSR=1.2mm/m and ASR=4.5mm, consequently, the centerline segregation is improved.
2014 Vol. 49 (3): 36-41 [
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42
YANG Shuang-ping，DU Xin，LIU Jie，WANG Jian
Experimental Research of High-Phosphorus Pig Iron Dephosphorization
With CaO-Fe2O3-CaF2 system slag as dephosphorization，the influencing factors of such for ratio，temperature，addition rate，basicity of slag was studied in laboratory GSL for dephosphorization．As a result，when the w（CaO）/w（Fe2O3）=2.5，the basicity is 2.5，the flux were added in an amount of 12% and addition some flux rate，so that the phosphorus content decreased to 0.47% in temperate conditions of 1450℃．Finally，the best ratio was derived dephosphorization by adjusting the amount of flux．
2014 Vol. 49 (3): 42-45 [
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46
JING Cai-liang,LUO Bo-gang,TIAN Zhi-hong
Study and Practice of High Casting Speed Technology on No.3 Slab Caster of Shougang Jingtang Steel
In order to achieve the casting speed of 2.5m/min on No.3 slab caster of Shougang Jingtang steel group, the mold cooling density, mold flux composition and structure of submerged entry nozzle were optimized based on the current casting parameters. Results of industry practice showed that, the casting speed could be held at 2.3m/min stably after the parameters optimized. The surface oscillation was improved obviously, the average heat flux of broad and narrow face was stable, the mold copper temperature filed was rational, the thickness of liquid flux was suitable and the powder consumption was increased. The casting speed could be increased from these industry practice results.
2014 Vol. 49 (3): 46-50 [
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HAN Hui-quan,HU Jian-ping,WANG Qiang
Effect of Water Flux on Heat Transfer Coefficient for Steel Pipe Cooling
The effect of water flux on cooling degree of steel pipe was investigated by using a pipe-outside jet cooling device and thermal couples welded in pipe for recording the pipe temperature during cooling. The mathematic model between heat transfer coefficient and water flux was established with the aid of finite element analysis. The model was embedded in steel pipe temperature field calculation software. And then calculation accuracy of the software was verified by the engineering practice. The result shows that accuracy of the steel pipe temperature field calculation software containing the mathematic model is up to above 90%.
2014 Vol. 49 (3): 55-58 [
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Materials
59
ZHANG Chuan-guo,YANG Jian-qiang,ZHENG Lei,XIE Shi-qiang
Research of SSCC Test for Weld Seam of X65 UOE Pipe Under Specified Load
The sulfur stress corrosion crack (SSCC) test of weld seam of X65 UOE pipe were studied by using four point bending (FPB) specimen according to the NACE 0177 standards. The strain gauge was used for identifying target strain and loading target stress. The results show that it is efficient to build the relationship among strain, load and stress for four point bending (FPB) specimen by utilizing the method of strain gauge. The target load strain against target load stress can be obtained by the relationship. The loading of 90% actual yield stress were accomplished for the three test specimens by using the method of strain gauge, no crack was observed on the specimen surface after immersion in H2S saturate solution of 720 hours. The test materials show high resistance to the sulfur stress corrosion crack.
2014 Vol. 49 (3): 59-62 [
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63
ZHENG Yang,,LIU Zhong-yi,LI Wei,
Abrasion Characteristic Research of Thin Slab Continue Casting and Rolling Low Alloy Wear-Resistant Steel
30CrMo, 50CrV4 thin slab continue casting and rolling low alloy wear-resistant steel were designed. After quenching and low temperature tempering, the abrasion characteristic was researched by low stress abrasion test, and was compared with 45, 16Mn, Q235 steel. The results show that the relative wear resistance of quenched and tempered 30CrMo, 50CrV4 steel specimens is more than 1.6 times hot rolled Q235 steel. In the low stress abrasion condition, micro cutting mechanism is the main wear mechanism, quenched and tempered thin slab continue casting and rolling low alloy wear-resistant steel has good wear resistance because of its high hardness. The relative wear resistance can be improved significantly when the hardness of the test steel plate is higher than 450HBW. In low stress abrasive wear condition, 30CrMo steel shows the best overall performance taking the microstructure, mechanical properties and wear resistant of the two kinds of thin slab continue casting and rolling low alloy wear-resistant steels into account. 50CrV4 steel also shows good wear resistant and extreme low impact toughness.
2014 Vol. 49 (3): 63-67 [
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68
LIU Shuang，TANG Guang-bo，LI Ji-guang，LI Bin，GAO Han-feng,
Strengthening Mechanism and Precipitation of Complex MC Particles in Ultra-High Strength Steel
Precipitation time temperature curve of a novel ultra-high strength steel, with micro-alloy element of Nb, V, Ti and Mo was tested in austenite region by the stress relaxation method. The results show that the shape of precipitation-time-temperature(PTT) is a “C” curve and the quickest precipitation juncture is about 3.6 s at 940 ℃. Composition, quantity and particle size distribution of the precipitated phase in the hot rolled plate of test steel were investigated by chemical phase analysis and small-angle X-ray scattering method; morphology of the second phase particles in the hot rolled plate was also examined by TEM. The results show that M(C,N), ε-Fe3C compose the precipitated phase in the steel, MC phase particle mainly distributed below 10nm, and all are globose or subglobose; the refinement strengthening increment is about 207.95 MPa and the precipitation strengthening increment of MC phase is about 195.70 MPa.
2014 Vol. 49 (3): 68-73 [
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Environmental Protection and Energy
74
LIU Ran,GAO Fu,WANG Xing-juan,L Qing
Migration Behavior of Boron From Boron-Rich Slag in Carbothermic Reduction Process
Based on thermodynamic analysis, the reduction and volatilization of boron in boron-rich slag were studied using carbothermal reduction method. Predominace diagram for the B-C-O system was presented. Phase composition and microstructure of products were determined by X-ray diffraction (XRD), and scanning electron microscopy. The experimental results show that the mass loss rate of boron in boron-rich slag increases with rising temperature, of which the maximum is 53.702% at 1470℃ for 8h. Boron has stabilized in the form of CaB2O4, affecting the volatilization of boron. The phase of reaction product is complex. Part of the volatilized matter and the volatilized magnesium/silicon form white powder, which deposit at the opening of furnace tube.
2014 Vol. 49 (3): 74-77 [
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78
HU Jing-tao,WEI Jun ,LIU Shan-xi,WEI Guo-zeng ,LI Zhan-qing
Study on Reducing Power Consumption of LF Refining
Based on the theoretical calculation, it is concluded that the power utilization ratio has nothing to do with the temperature rise speed; and the slag thickness should be larger than 50mm when gear 3 is used to refine. When the slag is thinner than 50mm, gear 4 is more effective to save power. Besides, gear 2 and gear 5 are not suggested for the purpose of temperature promotion only. According to real practice and theoretical calculation, it is found that when the bypass blowing is applied, the temperature drop is enhanced with the increase of initial temperature, and the heat dissipation of slag surface is reduced through improving the hit ratio of element adjustment at first time. On the basis of the practical process, the methods of reducing power consumption consisting of shortening the refining time, decreasing the utilization rate of non-turnover ladles and optimizing argon bottom blowing are also suggested, meanwhile compositions and temperatures of molten steel for different steel grades as they get in LF station are determined. According to these methods, the power consumption of LF was reduced by 6.8（kW·h）/t in present study.
2014 Vol. 49 (3): 78-82 [
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Technology Exchange
83
YANG Sen-xiang，HUANG De-sheng，ZENG Jian-hua
Control of Sulfur Content in the Production of Rail Steel
There are more advanced requests on steel cleanness and shape control of non-metallic inclusions for producing rail steel．According to the smelting situations of hot metal with high sulphur content at Panzhihua Steel，technologies for controlling the sulfur content during hot metal pretreatment，converter smelting，and second refining are developed．Technologies in clean steelmaking such as increasing the cleanness of steel，quantity and shape control of non-metallic inclusions are formed．Rail steel at a speed of 350km/h has been produced．As for the high speed rail steel，over 95% of the steel has the w(［S］)≤0.008%，the content of w(T［O］) deceases to below 0.001 5%，and the distribution and shape of inclusions are controlled effectively．
2014 Vol. 49 (3): 83-87 [
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