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2017 Vol. 52 No. 12
Published: 2017-12-15
1
ZHANG Jian-liang，，JIAO Ke-xin，，LIU Zheng-jian，，YANG Tian-jun，
Comprehensive regulation technology for hearth protective layer of blast furnace longevity
A stable protective layer forming in brick heating surface of blast furnace hearth， which avoided direct contact by seperating molten iron with brick， was a necessary condition to keep the longevity of hearth and delay the corrosion of brick. In order to study the essence of blast furnace hearth longevity. Firstly， class system of blast furnace hearth protective layer was established through blast furnace damage surveys and dissection research， and also by analyzing hearth protective layer phase composition and microstructure. Protective layer was classified as iron-rich layer， slag-rich layer， graphite-rich layer and titanium-rich layer according to the formation mechanism of protective layer. Secondly， the technical design of comprehensive regulation of the blast furnace hearth protective layer was formulated. And it was also proposed that reasonable control of the hearth refractories heating surface temperature and hot metal composition was the key to form hearth protective layer. The strength of the formation ability of hearth protective layer decreased from titanium-rich layer and graphite-rich layer toiron-rich layer.At last， it was clear that the measures of design， control of hot metal and production oprations should be taken to promote the formatin of graphite-rich layer during blast furnace production.
2017 Vol. 52 (12): 1-7 [
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8
XU Wen-xuan，CHENG Shu-sen，NIU Qun，ZHAO Guo-lei，CHEN Yan-bo
Effects of charging patterns of bell-less top blast furnace with two parallel hoppers on burden distribution of stock surface
In order to investigate the influence of charging patterns on the burden distribution of the stock surface in blast furnace with two parallel hoppers， the full model of bell-less top system with two parallel hoppers in actual 5 500 m3 blast furnace was established， and the motions of burden materials in the cases of the ore （A）-ore （B）-coke charging pattern and the ore-coke charging pattern were calculated by Discrete Element Method， respectively. The effects of charging patterns on the burden distribution of the stock surface were comparative and analyzed. The results show that the burden distribution of the stock surface is different in two different charging patterns， because the burden falling trajectory is not coincident while the ore-A and ore-B are charged into the stock surface. In the radial direction of the stock surface， the influence of charging patterns on the ore volume distribution and the ore/coke ratio distribution of the stock surface is negligible. In the circumferential direction of the stock surface， the standard deviation of the ore volume distribution of the stock surface in the ore-ore-coke charging pattern and the ore-coke charging pattern is 0.133 and 0.147， respectively， and the standard deviation of the ore/coke ratio distribution of the stock surface in the ore-ore-coke charging pattern and the ore-coke charging pattern is 0.074 and 0.086， respectively. The ore volume distribution and the ore/coke ratio distribution of the stock surface is more uniform in the ore-ore-coke charging pattern.
2017 Vol. 52 (12): 8-15 [
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16
ZHAO Hai-quan， ，QI Yuan-hong，SHI Yong-lin，FENG Huan-lin，NA Xian-zhao
Mechanism and experimental for dephosphorizion and chromium conservation of chromium containing melted iron
To solve the problem on the iron utlizion limition as high P，calculation and industry test on dephosphorization and chromium conservation of iron with Cr and Ni was studied，so as stainless steel dust could be recycled by the process of shaft furnace. But the liquid iron smelted by this process had the problem of high phosphorus content， which then led to the use of liquid iron restricted. For realizing dephosphorization and chromium conservation of liquid iron， through calculation， including thermodynamic conditions of the reduction of chrome， nickel and iron oxide and the critical oxygen potentials of phosphorus， chromium and carbon oxidized， three measures were put forward. The measures were using CaO alkaline slag series， controlling oxygen potential and tapping temperature. On the basis of the theoretical calculation， experimental study about dephosphorization and chromium conservation of chromium-nickel containing liquid iron which was smelted by shaft furnace， was carried out in industry. 35 t of chromium-nickel containing liquid iron was smelted in experiment. The results show that when the slag basicity is 1.15， the content of FeO in slag is controlled at about 5%， the tapping temperature is controlld within 1 673-1 684 K， dephosphorization rate could be reached to more than 36%， content of phosphorus in molten iron could be dropped to 0.023%， and Cr yield is over 88%. Experiment indicates that the purpose of dephosphorization and chromium conservation could be achieved by using the measures studied， and the problem of high phosphorus content in liquid iron containing chromium and nickel could be solved.
2017 Vol. 52 (12): 16-20 [
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21
LIU Wei，YANG Shu-feng，LI Jing-she，LI Ji-kang，ZHANG Shuo
Modification of sulphide inclusions in 20CrMnTi steel by calcium-magnesium treatment
The resulphurized 20CrMnTi steel is with good machinability， but the mechanical property is poor. Ca-Mg duplex treatment can reduce the harm of sulphide in this steel. The effect of Ca-Mg duplex treatment with different proportions on resulfurized 20CrMnTi steel was studied through high temperature experiment and SEM-EDS analysis. The results show that the duplex treatment can modify the II type sulfide inclusion from strip and chain shapes to spherical shape or wrap on oxide inclusion core. The average aspect ratio and diameter decrease dominantly after treatment. During the duplex treatment， Ca mainly reacts with S in steel， which strengthens the spheroidization of sulfide inclusion， and Mg mainly reacts with O in steel， which generates diffusing oxide core of small size. The inclusion types are MnS-CaS-MgO（-Al2O3-CaO）after treatment.If adding superfluous Mg， MgS will show up insulfide inclusion and if adding superfluous Ca， CaO will show up in oxide inclusion. The Mg in the treatment strengthens the modification effect of Ca， which means that less Ca is needed to reach the same modification， and duplex treatment is better than Ca treatment.
2017 Vol. 52 (12): 21-27 [
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28
QIN Jie，，QI Jian-ling，LIU Gong-guo，LI Zhan-jun
Reduction mechanism of SiO2 and counter measures of over-reduction
In order to solve technical problems and improve production efficiency， works have been carried out in time. In the smelting process of V-Ti metallized pellets with EAF， SiO2 can be over reducted easily， which will lead to a series of problems， such as unsmooth smelting process in EAF， difficult vanadium recovering from the hot metal， etc. In order to solve these problems， the effects of reactants， smelting temperature and smelting time on SiO2 reduction were studied. Then countermeasures were proposed， including binder optimization， control of deoxidizer adding amount， reduction of reaction temperature and smelting time. With these countermeasures， the technical indicators were improved obviously in the sixth campaign of the furnace. The accepted ratio of hot metal composition is above 85%，[w(V)]and[w(Si)]in vanadium-bearing hot metal are not less than 0.35% and not more than 0.5%， respectively.
2017 Vol. 52 (12): 28-35 [
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36
LI Mao-yin，YANG Shu-feng，LI Jing-she，GAO Wei，GU Yu，CHEN Zheng-yang
Optimization for internal quality in wide and heavy die billets by soft reduction
To eliminate the central segregation and porosities in wide and heavy billets of plastic die steel 1.231 1 （450 mm× 2 180 mm），the pin-shooting experiments combined with mathematical simulation by the software of ProCAST have been carried out to measure slab shells’ thickness as well as intuitively display the process of slab solidification and heat transmission. The position of soft reduction facilities were determined according to the center solid fraction of slab in different positions which were directly exported by ProCAST. Then the study of soft reduction was arranged and the industrial experiments were carried out systematically on position，amounts and ratio of soft reduction. The results showed that the position and rate of reduction is significant to macroscopic quality. The internal porosities were effectively eliminated after the position of soft reduction was moved from[fs＝0.30～0.70]to[fs＝0.50～0.85.]The degree of segregation especially the width was reduced remarkably after the reduction rate was raised from 0.8 to 1.4 mm/m .
2017 Vol. 52 (12): 36-41 [
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42
ZHAO Cheng-lin，，TANG Fu-ping，ZHU Xiao-lei，，LIAO Xiang-wei，，CHEN Dong
Experiment on distribution characteristics of surface inclusions in IF steel continuous casting billet
Inclusions are important factors that affect the surface quality of IF steel. It is significant to determine the optimum cleaning depth of continuous casting billet in different states when the IF steel continuous casting slab is cleaned on-line flame automatically. The second pouring piece of slab，the steady casting billet and the transfer billet between head and second cans of IF steel was dealed with. A total of 28 analytical samples are equidistance divided along with the width direction of the inner and outer surfaces of the each casting，and the size of each specimen is 29 mm×21 mm×30 mm. The changes of morphology，quantity and maximum size of inclusions under different cleaning depth are studied. The results show that the number of inclusions which is 20-50 μm in the second piece of slab is decreased with the increase of the cleaning capacity，the number of inclusions which is larger than 50 μm is slightly increased，and the number of inclusions which is larger than 20 μm in the steady state and the transfer billet is slightly reduced. When the surface of the slab is not cleaned，the maximum inclusions on the surface of the three slabs are 500，200 and 200 μm respectively. If the critical dimension of the inclusions affecting the surface quality of the steel plate is 100 μm，the second slab cleaning depth should be 4-5 mm，the steady casting billet and the transfer billet should be 2 mm.
2017 Vol. 52 (12): 42-47 [
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48
XIE Hong-biao，WANG De-wei，YU Chao，QI Zi-chen，XIAO Hong
Stainless steel/carbon steel composite plate prepared by hot-roll bonding with pure iron as intermediate material
When stainless steel and carbon steel composites were produced by hot rolling under vacuum，C in carbon steel and Cr in stainless steel are easy to form carbides that reduce the bonding strength during hot rolling. To attempt to solve this problem，pure iron as intermediate material were used to bond stainless steel and carbon steel by hot rolling. The bonding strengths under different reductions were measured，and the microstructure and the distribution of elements of the composites were examined. The results show that when pure iron is used，the pure iron and the carbon steel have a metallurgical bonding. The diffusion of C from the carbon steel to bonding surface can be hindered，it decreases the formation of carbon chromium compounds，and it is beneficial to improve the bonding strength.
2017 Vol. 52 (12): 48-53 [
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54
TIAN Bao-liang，，NIU Pei-feng，
Design and application of electromagnetic heating beam in shape optimization of strip
In the process of strip rolling，aimed at the uneven distribution of the convexity in the axial direction of the work roll，the internal stress distribution is not reasonable in the strip after rolling，which leads to the partial tear of the strip steel. According to the eddy current principle，the electromagnetic heating beam device is designed to adjust dynamically the local perimeter convexity of work roll and reduce the residual stress inside the strip after rolling. The device is effectively integrated with the flatness control system to make the flatness measurement closer to the set value. Through the industrial test and verification，the device can effectively reduce the unreasonable stress distribution inside the strip. The purpose of improving control accuracy and shape quality is achieved to meet the precise shape control requirements of rolling mill.
2017 Vol. 52 (12): 54-60 [
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61
LI Wei-gang，，DENG Ken，ZHAO Yun-tao，LIU Xiang-hua
Self-learning method for rolling model based on continuous surface
The traditional self-learning method of rolling model based on division of layer，resulting in the problems of model self-learning coefficients of adjacent layers are jumping greatly，discontinuous and other issues，the construction mechanism of rolling model based on "mechanism model+feature points+quasi-interpolation+self-adaptive" is proposed，which replacing the original layer concept with multidimensional space continuous surface and upgrading the structure of rolling model. Constructing continuous surfaces characterized by feature points and the continuous function is used to interpolate the self-learning coefficients of each feature point in space to obtain the equation of smooth surface. The multidimensional space are continuous and differentiable adjacent layers，so the model self-learning coefficients can correct to any point in the space，which make a great breakthrough with the precision of the rolling model. The model has been successfully applied to on-line calculation of deformation resistance in a large hot strip mill in China. The practical application shows that the prediction accuracy of deformation resistance and rolling force is improved remarkably after the new method on line，the pre-blockade capacity of strip steel due to oversize thickness reduced by 44% to meet the hot strip rolling strip production requirements.
2017 Vol. 52 (12): 61-66 [
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67
ZHANG Wan-li，WANG Hui，，XU Hai-feng，，YU Feng，XU Da，CAO Wen-quan
Spheroidizing process of ultrahigh carbon steel with 2% aluminum addition
In order to obtain a fully spheroidizing microstructure， the spheroidizing annealing process for ultra-high carbon steel with 2% aluminum addition （UHCS-2Al） was studied based on the mechanism of divorced eutectoid transformation. It is found that the forging microstructure of the ultra-high carbon steel with aluminum addition is composed of the pearlite with different interlamellar spacing and the continuous carbide networks due to the inhomogeneity of the composition. It is difficult to make it completely spheroidization only by using divorced eutectoid transformation process. The thickness of carbide networks is below 1 μm， normalizing below[Acm]temperature can obtain uniform and fine pearlites and eliminate carbide networks. It can also reduce the number of strip shape carbides in normalizing microstructure by increasing the normalizing temperature， which is beneficial to get better spheroidizing microstructure. The complete spheroidizing microstructure for UHCS-2Al consisted of ultrafine ferrite and fine spherical cementite was obtained after normalizing at 900-925 ℃， austenitizing at 830 ℃ and then isothermal treatment for 4 h at 760 ℃.
2017 Vol. 52 (12): 67-74 [
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75
DING Li-juan，SHI Chun-li，，YIN Hong-xia，ZHANG Tao，LI Hui，
Influence of annealing treatment on microstructure and mechanical properties of low-carbon Ni-containing DP steel
A low carbon and Ni-containing DP steel was studied. The CCT curve was analyzed by Gleeble3500 simulation tester，and then different annealing treatment was designed based on this curve. Based on the five factors and four levels of orthogonal test，combing mechanical test and SEM investigation，the influence of annealing treatment on microstructure and mechanical properties of DP steel was analyzed. The results indicate that the[Ac1]and[Ac3]are 712 and 928 ℃ respectively. During the continuous cooling process，the critical cooling rate of transformation of bainite and martensite are 5 and 30 ℃/s respectively. The biggest factors influencing ratio of yield strength and tensile strength is annealing temperature，and annealing time of n value. The heat treatment to gain best properties is to anneal at 840 ℃ for 210 s in the beginning，then cooled to 740 ℃ slowly，finally quenched to 350 ℃ and holding for 240 s.
2017 Vol. 52 (12): 75-79 [
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AN Zhi-guo，MENG Yan-jun， SHI Yuan， LI Jian-chao， SUN Xiao-ran， SUN Yan
Effect of Cu on continuous cooling transformation of medium carbon Si-Mn steel
In order to understand phase transformation of Cu-containing medium carbon Si-Mn steel，the effect of Cu on microstructures and micro-hardness of medium carbon Si-Mn steel at different cooling rates were investigated by a DIL805L thermal dilatometer. The Cu-rich precipitates were analyzed by high resolution transmission electron microscope. The results show that Cu could prolong bainite ncubation period， reduce bainite and martensite starting transformation temperature. During continuous cooling transformation，The Cu-rich particles dispersive precipitate in the ferrite and refine ferrite grain. The micro-hardness of copper bearing medium carbon Si-Mn steel increased with the cooling rate increase when the cooling rate was lower than 21 ℃/s. The content of Cu-rich particles increased with the increase of cooling rate，meanwhile the bainite and martensite also increased. Instead，Cu can lower the micro-hardness of bainite and martensite in the steel when the cooling rate was higher than 21 ℃/s.
2017 Vol. 52 (12): 80-85 [
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86
LI Ji-dong， REN Yong-xiu
Inspection and analysis on flakes defect of ferrite steel
Suspect flakes defects in ferrite steel were analysed by OM and SEM. The results showed that the suspect defects appeared zigzag crack，which is the characteristic of flake crack. According to fracture analysis，at macro fracture of low carbon ferrite steel was distributed silver grey and round spot，which is the characteristic of flake defect，and there was no flakes defect characteristics at macro fracture of ferrite stainless steel. However，the fractographic of suspect flakes of ferrite stainless steel was intergranular fracture and cleavage fracture as the source of inclusions，which two are characteristics of hydrogen fracture. In conclusion，the suspect flakes defects in two ferrite steel were all flakes defect. The morphology features of flakes defect in ferrite stainless steel was different from normal flakes defect such as clouds，rippled wall， clavage feathers，microporosity and so on，and the morphology of flakes defect in different samples of ferrite stainless steel were different. One was intergranular fracture，the other was cleavage fracture as the source of inclusions.
2017 Vol. 52 (12): 86-90 [
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91
RUAN Zhi-yong
Desulfurization and denitration of sintering flue gas based on ammonia and activated carbon process
In order to reduce the emission of SO2 and[NOx]in the iron ore sintering， the desulfurization and denitration of iron ore sintering flue gas based on ammonia-activated carbon process was developed. The results show that more than 70% denitration rate was obtained using activated carbon after SO2 was removed by ammonia process. The denitration mechanism is that the escaping NH3 reacted with C-OH in the surface of activated carbon to produce the N2 and H2O. For the sintering plants using ammonia desulfurization process， more than 99% desulfurization rate and 70% denitration rate were achieved just connecting a single stage activated carbon adsorption tower after the desulfurization spray tower， which could reduce the capital cost and also solve the secondary environmental pollution due to the NH3 escape.
2017 Vol. 52 (12): 91-96 [
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