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2021 Vol.  56 No.  11
Published: 2021-11-15

Technical Reviews
Raw Material and Ironmaking
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technology Exchange
Technical Reviews
1 LI Xin-chuang
High quality development of China′s steel industry promoted by differentiated management and control
Scientific management and control of crude steel output is important for healthy development of Chinese steel industry. It analyzes growth direction and reasons of crude steel output in detail,investigates significance of management and control of crude steel output,and focus on research about scientific regulation of crude steel output by means of differentiated management and control. China's crude steel production control should adhere to the "two kinds of thinking" of bottom line and overall situation. Under the new development condition that domestic circulation is main body and domestic and international dual circulation are promoted mutually,it is necessary to build consensus and form a joint force,strengthen the market of fair competition,formulate long-term mechanism of scientific management and control,promote combination of effective market and capable government,enhance existing advantages further and advance dynamic balance between supply and demand,in order to promote high quality development of the steel industry.
2021 Vol. 56 (11): 1-9 [Abstract] ( 35 ) [HTML 1KB] [PDF 0KB] ( 25 )
10 ZHANG Jian-liang, JIANG Chun-he, LI Ke-jiang, BI Zhi-sheng
Research situation and prospect of interfacial wetting behavior of iron-coke-slag system in blast furnace
As the blast furnace is currently the world′s largest moving bed metallurgical reactor, maintaining good gas and liquid permeability in the blast furnace is the key to ensuring the stability of the blast furnace. The interior of the blast furnace is divided by the cohesive zone, divided into an upper solid bulk area and a lower solid-liquid coexistence area. The lower solid-liquid coexistence area is an important area that determines the gas permeability and gas flow distribution of the blast furnace. Therefore, a comprehensive study of the reaction of the solid-liquid coexistence zone in the lower part of the blast furnace is the key to clarifying the gas and liquid permeability of the blast furnace. The interaction between the coke bed and liquid iron/slag in the high-temperature zone of the blast furnace is an important factor that determines the iron-coke-slag interaction and gas and liquid permeability of the blast furnace. Adjusting the wettability changes of the liquid iron/slag and coke bed can effectively improve the gas and liquid permeability, which will ultimately affect the production efficiency and stability of the blast furnace. This article first summarizes the interfacial wetting behavior, and then summarizes the effects of liquid iron composition and coke properties on the iron-coke interfacial wetting behavior. Secondly, the effects of temperature, slag composition, and coke′s properties on the wetting behavior of the slag-coke interface are analyzed. The results showed that the current research on the wetting behavior of the slag-iron-coke interface in the blast furnace has been studied from laboratory experiments and basic simulations. It can provide preliminary theoretical guidance for blast furnace operators to understand the wetting behavior of the slag-iron-coke interface in the blast furnace. However, it is still necessary to conduct in-depth research on the changes in wetting behavior that can reflect the actual complex conditions in the blast furnace.
2021 Vol. 56 (11): 10-18 [Abstract] ( 44 ) [HTML 1KB] [PDF 0KB] ( 36 )
Raw Material and Ironmaking
19 ZHAO Kai, WEI Zhi-fang, ZHANG Qiao-rong, ZHANG Yu-zhu, WANG Bin, SHEN Yao-zong
Numerical simulation of charge settlement and heat transfer behavior in oxygen coal combustion melting and separating furnace
The rotary kiln-pre-reduced oxygen coal combustion fusion iron making process uses the fine ore of wide particle size into furnace directly. After the counter current heat transfer and pre reduction of flue gas in the rotary kiln, the charge particles reach the oxygen coal combustion melting and separating furnace through the settling tube. In order to avoid the phenomena of charge particles scouring the furnace wall, wall accumulation and uneven gas-solid heat transfer in the settlement area, realize the coupling control of particle settlement and heat transfer process, minimize the temperature difference between charge and molten pool, ensure the stability of molten pool smelting and achieve good smelting effect. Computational fluid dynamics discrete element method (CFD-DEM) was used to study the effects of gas velocity and charge size on the settling trajectory and heat transfer behavior of charge particles under the action of counter current gas in the upper zone of oxygen coal combustion melting and separating furnace. The numerical simulation results show that the settling velocity of charge particles decreases with the increase of gas flow rate, and the effect of gas on small particle size is particularly obvious. The sedimentation effects of charge particles for each particle size are good when the gas velocity is 1 m/s; the sedimentation effects of charge particles with sizes of 1.0, 1.5 and 2.0 mm are relatively good when the gas velocity is 2 m/s; the charge particles with sizes of 1.5 and 2.0 mm can settle smoothly when the gas velocity is 3 m/s. For the heat transfer behavior of charge particles, the larger the gas velocity is, the smaller size of charge particles is, and the better heat transfer effect of the charge particles is. Considering the heat transfer and settlement behavior of charge, the settlement velocity and heat transfer of charge particles with particle size of about 1.0 mm are good under the action of gas velocity of 1 and 2 m/s.
2021 Vol. 56 (11): 19-29 [Abstract] ( 22 ) [HTML 1KB] [PDF 0KB] ( 21 )
30 WU Qiang, ZHU Zi-zong, WANG Ying-dong, SUN Can, FAN Jin-tao
Production of coke by modifying coal blending with high proportion of gas coal
In the attempt to reduce the proportion of high-quality coking coals (rich coal and coking coal) and increase the proportion of gas coal for low-expense coke-making, coke-making experiments using high-proportion gas coal were conducted in a 2 kg laboratory coke oven in term of raw materials including two types of gas coal, rich coal and coking coal, one kind of lean coal, and original pulverized coal modifier. The experimental results show that coke quality indexes worsened when the contents of high-quality coking coal and gas coal were lower than 50% and greater than 35%, respectively. The coke reactivity index (CRI) is more than 36%, and the coke strength after reaction index (CSR) is less than 50%, which cannot meet the requirements of medium and large blast furnaces. However, under the action of the modifier, when the high-quality coking coal was gradually replaced by gas coal in coke-making, the thermal strength indexes of the modified coke were significantly improved. Although the ratio of gas coal in coal blending was increased to 45% and the ratio of high-quality coking coal was reduced to 40%, the modified coke with CRI less than 30% and CSR more than 58% can still be produced. Combined SEM, XRD and Raman, the analysis results about the difference on the microscopic layer of coke show that adding high-proportion gas coal will increase the amount and size of void in coke and the content of amorphous carbon, and decrease the volume and density of microcrystal units, resulting in the increase of reactivity of coke and the decrease of coke strength after reaction. By adding the modifier, the modified coke′s properties dramatically improved and the distributions of microstructures and components of modified coke with high proportion of gas coal were closed to the level of coke produced with high proportion of high-quality coking coal. Eventually, industrial experiments proved the possibility of adding 45% gas coal to produce high-quality coke under the premise of using the modifier, which is a new method to save high-quality coking coal and reduce the cost of coal blending.
2021 Vol. 56 (11): 30-38 [Abstract] ( 21 ) [HTML 1KB] [PDF 0KB] ( 21 )
39 YU Chun-mei, TENG Hai-peng, LIN Hao, REN Kun, WANG Guang-wei
Coke dissolution characteristics in molten iron of COREX
Iron and steel is the basic industry supporting the development of national economy, but it was also belongs to the resource and energy intensive industry. With the gradual implementation of the national environmental protection policy, it is faced with increasing resources and environmental protection. Due to the disadvantages of high energy consumption and high pollutant discharge, the development of the traditional blast furnace ironmaking process has been greatly restricted, and the non-blast furnace ironmaking process attracts more and more attention. The dissolution characteristic and kinetic behavior of different cokes are investigated in molten iron. The results showed that the process of coke and hot metal contact consumption is dominated by dissolution reaction, because the Gibbs free energy of dissolution reaction occurs when the hot metal contact with carbon atoms is much smaller than that of the formation reaction of Fe3C. The rapid dissolution reaction occurred after coke contacting hot metal. The content of carbon in hot metal increased rapidly, but the increased range decreased rapidly with the high carbon content. After the dissolution reaction time exceeds 120 min, the carbon content in hot metal basically remains constant. The order of the dissolution reaction rate of different coke from high to low was stamp-charging coke, top-charging coke and gas coal coke. The temperature of hot metal had an obvious effect on the dissolution reaction. With the increase of temperature, both the dissolution reaction rate and the amount of carbon in hot metal increased. At last, the average activation energy of stamp-charging was largest, followed by top-charging coke, and that of gas coal coke is the smallest by kinetic analysis.
2021 Vol. 56 (11): 39-46 [Abstract] ( 21 ) [HTML 1KB] [PDF 0KB] ( 25 )
47 LUO Yun-fei, YANG Tao, ZHOU Jiang-hong, CHUN Tie-jun, PEI Yuan-dong, LONG Hong-ming
Effect of steam injection from material surface on output and quality of sinter and CO emissions
With the continuous tightening of the ultra-low emission standard for the pollutants from sintering flue gas in the steel industry, the sintering material surface injection technology has become a new research hotspot due to its potential advantages of energy saving and emission reduction, it is widely considered as a sintering process control technology with certain comprehensive emission reduction effect at present. In order to find out the optimal process system of steam injection on the material surface and to find out the mechanism of the effect of steam injection on the sintering process, in order to realize its industrial application, a sintering raw material of a steel plant was used, the effects of total steam injection rate, injection flow rate and initial injection time on sinter quality and CO emission were studied. The results show that under the condition of 50 kg sinter cup raw material, the best experimental conditions of steam injection on the material surface should be 15 min after 8 min of sintering ignition, 0.02 m3/min of injection flow and 180 g of total injection, the production rate and drum strength increased by 0.60% and 1.94%, the solid energy consumption decreased by 1.15 kg/t, and the CO concentration decreased by 10.91%. The results show that the injection steam can make the carbon in the fuel fully react with other blended minerals, and the effect of high temperature reaction is remarkable, and then the yield and drum strength are improved. At the same time, the suitable addition of steam to the sintering high temperature zone reaction is beneficial to the reaction of H2O with C and O2, and the CO in the reducing atmosphere is converted into CO2, and then the CO emission and the sintering solid energy consumption are reduced. On the whole, under the reasonable injection system, the steam injection can reduce the CO emission and improve the sinter quality.
2021 Vol. 56 (11): 47-54 [Abstract] ( 25 ) [HTML 1KB] [PDF 0KB] ( 19 )
Steelmaking
55 WU Yao-guang, XIAO Bu-qing, ZHU Li-guang, WANG Yan
Current situation analysis and prospect of iron and steel raw material for electric arc furnace steelmaking
As the core technology of short-path steelmaking, electric arc furnace steelmaking (EAF) has the characteristics of high iron recycling rate, low energy consumption and good environmental benefits. Promote the healthy development of EAF steelmaking, which is in line with the requirement of green development of iron and steel to achieve the goal of emission peak and carbon neutrality. EAF has various and flexible raw iron and steel materials for charging than the converter, and which affect directly the process control of EAF smelting. To create a good starting condition for excavating and exerting fully the advantages of EAF, the application, advantages and disadvantages of scrap, hot metal and direct reduced iron (DRI) as the main raw materials were analyzed from their production and storage, process operation, energy consumption, environmental protection and other aspects base of the current situation and characteristics of the main steel raw materials for EAF, and it is as a key point that the characteristics and technical indexes of direct reduction pellets are compared and analyzed, which provided a theoretical basis for exploring and optimizing the structure of raw iron and steel materials of EAF steelmaking. The scrap and direct reduced pellets will turn into the main raw materials of short-path steelmaking in the future considering resource consumption and environmental protection. Combined with the gradual maturation of iron and steel recycling technology and industrial specialization, and the development of more green hydrogen metallurgy technology, the new technologies, including comprehensive recycling technology of scrap, production technology of high-grade clean pellet as well as direct reduction technology of hydrogen shaft furnace, will be the development direction of production technology of iron and steel raw materials charged for EAF. Meanwhile, matching new and high efficient intelligent electric arc furnace smelting technology will be the development direction of short-path steelmaking in the future.
2021 Vol. 56 (11): 55-62 [Abstract] ( 34 ) [HTML 1KB] [PDF 0KB] ( 20 )
63 WANG Lin-zhu, LI Xiang, ZHAO Yu-dong, YANG Shu-feng, LI Jun-qi, CHEN Chao-yi
Effect of order of deoxidant addition on Al-Ti composite inclusions
Parameters such as morphology, composition, size, quantity and distribution of inclusions in steel with different order of Al-Ti deoxidation addition were detected and analyzed by SEM-EDS. Chemical reactions in liquid steel in the deoxidation process were analyzed and the predominance diagram of inclusion was obtained by thermodynamic calculation. The results indicate the order of deoxidant addition had a great influence on the morphology of inclusions. When Ti was added prior to Al, many Al-Ti composite inclusions containing Fe phase with concentration gradient ("hollow”) formed in the liquid steel. The radial length of inclusions increases, and inclusions are more likely to be partial. So this deoxidation method is not conducive to refining and dispersing inclusions. When Al was added prior to Ti, alumina is formed in the steel, which will not be reduced by dissolved titanium, so the inclusion does not contain iron phase inside. The inclusions are mainly Al-Ti-O (-N) inclusions. The size and quantity of inclusions are less than Ti was added prior to Al.The formation and evolution mechanism of inclusions under different Al-Ti deoxidation order and the formation mechanism of Al-Ti composite inclusions with "hollow structure" with concentration gradient was explored and analyzed based on the results of FactSage calculation, chemical reaction analysis, and experimental detection. The effect of the addition order of deoxidizer on the size, number and distribution of inclusions was discussed. It is found that under the deoxygenation mode of adding titanium first and then aluminum, titanium oxides will react with aluminum metal, titanium oxides will gradually change into "hollow" alumina shell, while dissolved aluminum, titanium and oxygen oxidation reaction, forming a concentration gradient of Al2O3-TiOx complex inclusions, and finally titanium oxide completely converted into alumina shell and disappear. With the filling of iron liquid, an aluminum titanium inclusion containing iron phase is formed.
2021 Vol. 56 (11): 63-71 [Abstract] ( 29 ) [HTML 1KB] [PDF 0KB] ( 17 )
72 ZHU Ren-lin, LI Jian-li, SHEN Jia-hao, YU Yue, ZHU Hang-yu
Mineral composition of KR desulfurization slag and precipitation behavior of sulfur-containing phases
KR desulfurization slag is a by-product of the desulfurization pretreatment process about hot metal, in which the mass percent of CaO in the tailings after magnetic separation is more than 50%. It can be used as a slag-making material by recharging to converter steelmaking process to reduce the economic cost of converter steelmaking. However, the sulfur in the KR desulfurization slag (w((S))=1.0%-2.5%) has become an obstacle to the recycling of converter smelting, and its direct use in converter smelting will increase the sulfur content in the steel. Therefore, according to the chemical composition of industrial KR desulfurization slag, the mineral composition and precipitation behavior of sulfur-containing phase in KR desulfurization slag were investigated in the form of synthetic slag. The purpose is to clarify the mineral phase composition of KR desulfurization slag, the precipitation behavior and occurrence state of sulfur in slag, so as to provide theoretical reference for the subsequent effective removal of sulfur in KR desulfurization slag through oxidizing atmosphere. FactSage 8.0 was adopted to simulate the solidification process of CaO-SiO2-CaS-CaF2-based slag, and XRD and SEM-EDS were employed to analyze the mineral composition and microscopic morphology respectively. The thermodynamic calculation results show that the crystallization temperature of CaS is 1 320 ℃, which is lower than that of MeO#1 phase, MeO#2 phase and 2CaO·SiO2phase. The results of surface scanning analysis of slag samples show that a small amount of sulfur in slag did not precipitate to form CaS crystal due to the increase of residual liquid viscosity during the actual solidification, and it exists in the matrix phase in the form of amorphous state. KR desulfurization slag mainly composes of C3S, MeO#1 (based on CaO), MeO#2 (based on MgO), matrix and CaS. The sulfur element mainly precipitates along the boundary of the silicate (C3S) phases.
2021 Vol. 56 (11): 72-77 [Abstract] ( 23 ) [HTML 1KB] [PDF 0KB] ( 20 )
Metal Forming
78 SONG Jun, REN Ting-zhi, WANG Kui-yue, WANG Jun-sheng
Optimization of work roll bending model in unsteady process of tandem cold rolling based on CF-PSO-SVM
Flatness quality is an important technical quality specifications of cold rolled strip. At the same time,work roll bending is one of the most effective control methods to improve the flatness quality of cold rolled strip. The strip flatness control precision of tandem cold mill can reach a high level in the process of high speed and stable rolling,but the effect of shape control is not ideal in the process of unsteady rolling,this has also become a negative factor restricting the quality of cold rolled strip. In order to improve the control precision of flatness in the unsteady process of acceleration and deceleration,the principle of bending force setting in tandem cold rolling was studied,combined with the intelligent algorithms and the actual rolling data samples including the strip thickness at the entry and outlet,the tension between the stands,the rolling speed,the middle roll shifting,the strip width,the roll inclination and the rolling force,a bending force prediction strategy based on the support vector machine theory of which parameters were optimized by the particle swarm optimization algorithm was proposed. The principle of support vector machine (SVM) theory and particle swarm optimization (PSO) algorithm was studied. In order to improve the parameters optimization ability,the concepts of compression factor were introduced in the PSO algorithm. Moreover,the PauTa criterion and five-point three-time smoothing method were used to process the relevant rolling data,and then the performance of the prediction strategies was compared by the evaluation indexes,such as mean square error and mean absolute error. The results show that the proposed algorithm was verified with good predictive performance and excellent generalization ability,at the same time,according to the actual production data sample,the compensation model of bending force gap based on rolling speed and roll elasticity coefficient was regressed,and the validity of the model was verified,the model reduced the load of the flatness control system and improved the flatness control precision in unsteady rolling process,the quality pass rate of the head and tail of the product was increased by 5.1%.
2021 Vol. 56 (11): 78-86 [Abstract] ( 20 ) [HTML 1KB] [PDF 0KB] ( 20 )
87 LIU Xiao, FU Lun, LU Yue-feng, WANG Tao, XIAO Hong
Theory and numerical simulation of minimum rolling thickness for thin strip rolling
With the miniaturization and integration development of the Intelligent manufacturing,electronic communication,and other industries,it is required to improve the product quality of precision rolled strips,especially for the control accuracy of the thickness. Therefore,the theoretical research on the contact deformation zone in the rolling process of the precision strip is of great significance. The Stone rolling force model as the classic model of conventional cold rolling theory of thin strip assumes that the roll maintains a circular profile in the contact deformation zone. And the average unit pressure is obtained by solving the contact arc length with the Hitchcock formula. On this basis,the Stone theory of the minimum rolling thickness is established. In the experiment and actual production,many scholars found that the calculated value of the Stone rolling force is far from the actual value sometimes. This is because there is a neutral zone in the contact deformation zone under some rolling conditions and the assumption of the circular roll shape is no longer applicable. The existence of the neutral zone increases the rolling force prominently,but the extension deformation of strip metal is very little,that is,the rolling difficulty increases,and the rolling efficiency decreases. The finite element method is used to analyze the rolling process of the thin strip with different thicknesses. The variation rules of the profile of the contact deformation zone and the distribution of contact pressure under different reductions are obtained. The smaller the initial thickness of the strip or the greater the single-pass reduction,the larger the proportion of the neutral zone in the contact deformation zone,and the contact pressure distribution tends to parabolic distribution. Based on the Stone rolling force formula,the minimum rolling thickness model of thin strips with rolling efficiency consideration is established. For the ratio of the initial thickness to the Stone minimum rolling thickness,the critical pass reduction can be calculated when the contact deformation zone is without neutral zone according to the rolling process parameters by this model. The range of high-efficiency rolling thickness and the applicable conditions of the Stone rolling force model can be determined based on the critical single-pass reduction,which provides theoretical guidance for the production process of precision thin strip rolling.
2021 Vol. 56 (11): 87-95 [Abstract] ( 28 ) [HTML 1KB] [PDF 0KB] ( 25 )
Materials
96 YAO Hao, ZHANG Li-Feng, REN Qiang, REN Ying, YANG Wen
Effect of cooling rates on transformation of acicular ferrite in a Ti-Zr treated steel
The toughness of the low alloy steel is reduced by the wide use of high heat input welding technology and the addition of Ti and Zr elements can promote the nucleation of acicular ferrite which refine the microstructure and improve the properties of the low alloy steel. To study the transformation mechanism of acicular ferrite in Ti-Zr treated steel,the steel required for the experiment was smelted in a 25 kg vacuum induction furnace,0.04% Ti and 0.014% Zr were added to low alloy steel;the effect of different cooling rates on the transformation of acicular ferrite was observed by high temperature confocal microscope;the inclusion of Ti-Zr treated steel and the nucleation of acicular ferrite on the surface of the inclusions was observed by scanning electron microscope;the microstructure under different cooling rates was observed by optical microscope. Through experiments,it is found that with cooling rate increased from 1 ℃/s to 10 ℃/s,the start transformation temperature of side plate ferrite decreased from 770.2 ℃ to 632.4 ℃,the onset transformation temperature of acicular ferrite decreased from 731.5 ℃ to 612.6 ℃,and the area percent of acicular ferrite increased from 47.91% to 68.04%,the ratio of the area fraction for acicular ferrite to side plate ferrite increased from 1.34 to 3.54,and the ratio of the difference between the start and end transformation temperatures for acicular ferrite to side plate ferrite increased from 0.52 to 0.83. There is a proportional relationship between the ratio of area percent and the ratio of the transition temperature range on acicular ferrite and side plate ferrite. The main inclusions in Zr-treated steel were ZrO2-TiN-MnS and the ZrO2-TiN-MnS inclusion could effectively promote the nucleation of acicular ferrite. The nucleation mechanism is that transformation driving work increased by Mn-depleted zone the and inclusion has a good lattice matching with ferrite that interface energy was reduced.
2021 Vol. 56 (11): 96-103 [Abstract] ( 22 ) [HTML 1KB] [PDF 0KB] ( 25 )
104 ZOU Ying, HAN Yun, LIU Hua-sai, LI Yan, QIU Mu-sheng, WANG Chao-bin
Microstructure, properties and surface quality of hot-rolled galvanized dual phase steel
In order to solve the problem of insufficient corrosion resistance in hot rolled and pickled dual phase steel for automobile,a hot-rolled galvanized ferrite-bainite dual phase steel was developed. The effects of process parameters on microstructure and properties of ferrite-bainite dual phase steel were studied by using scanning electron microscope (SEM),transmission electron microscope (TEM),tensile testing machine,forming testing machine,and so on. Moreover,the surface quality of dual phase steel under the optimal annealing process was evaluated. The results showed that the microstructure of as-hot-rolled steel was mainly composed of ferrite and bainite, and the volume percent of bainite was 13.3%. The bainite decomposed into cementite when soaking at 620-700 ℃,and the volume percent of bainite decreased from 10.1% to 6.6% with the soaking temperature increase from 620 ℃ to 700 ℃. When soaking at 740 ℃ or above,the cementite disappeared and the volume percent of bainite decreased from 17.2% to 10.7% with the increase of soaking temperature from 740 ℃ to 820 ℃. During cooling and galvanizing,nano-sized NbC or (Nb,Ti)C was precipitated in the steel. With the increase of soaking temperature,the yield and tensile strength of the test steel first increased and then decreased,while the total elongation and hole expansion rate first decreased and then increased. The effects of soaking temperature on mechanical properties and hole expansion rate were mainly based on its effects on cementite formation,volume percent of bainite and hardness difference of microstructure. Excellent mechanical properties with yield strength of 520 MPa,tensile strength of 606 MPa and total elongation of 22% were achieved,when soaking at 780 ℃. The local formability of the test steel was also outstanding,with an average hole expansion rate as high as 107%. Besides,the minimum relative bending radius was 0 under transverse and longitudinal bending test with a bending angle of 180°. The platability of the test steel was improved by the combination of pre-oxidation and furnace humidification. The control of small convexity at hot rolling and large skin pass rolling force at pickling and zinc plating finishing was helpful to obtain higher coating thickness uniformity.
2021 Vol. 56 (11): 104-111 [Abstract] ( 25 ) [HTML 1KB] [PDF 0KB] ( 18 )
112 WANG Qing-juan, WANG Qin-ren, DU Zhong-ze, HE Ze-en, DANG Xue, QI Ze-jiang
Hot deformation model and dynamic recrystallization behavior of 40Cr10Si2Mo steel
In order to optimize the hot-rolling production process parameters of the martensitic heat-resistant steel 40Cr10Si2Mo and establish digital design and intelligent system database for wire and bar rolling, the constitutive equation of the strain compensation and the dynamic recrystallization behavior of martensitic heat resistant steel 40Cr10Si2Mo at temperatures ranging from 900 to 1 100 ℃ and stain rates from 0.1 to 20 s-1were studied by single-pass compression tests carried out on Gleeble-3500 thermo-mechanical simulator,which can provide theoretical basis for the plastic deformation behavior and optimizing microstructure of 40Cr10Si2Mo steel. The results show that the stress decreases with the increase of deformation temperature and increases with the increase of strain rate. The effect of temperature and strain rate on thermal deformation resistance (true stress) is mainly determined by the interaction of work hardening, dynamic recovery, recrystallization and other softening mechanisms that occur inside the metal during the plastic deformation process. A constitutive model of Arrhenius was established. The correlation (R2) and the average relative error (AARE) are 0.983 97 and 4.531% respectively between the predicted value of the proposed model and the experimental results. The method of fourth order polynomial fitting and derivation to the σ-ε curves were used to analyse the softening process of 40Cr10Si2Mo steel and the critical conditions of dynamic recrystallization at different deformation conditions. The relationship between the critical condition of dynamic recrystallization and the value of lnZ (Zener-Hollomon parameter) was described. When the lnZ value was less than 63,the critical strain of dynamic recrystallization increased with the increase of the lnZ value. When the lnZ value was greater than 63,the critical strain of dynamic recrystallization did not change significantly with the increase of the lnZ value. Through comparing the microstructure of 40Cr10Si2Mo steel,it was found that the grains swallowed each other and merged, and some of the recrystallized grains did not grow up under the conditions of 1 100 ℃/0.1 s-1,which eventually led to the appearance of mixed crystal structure. However,increasing the strain rate was beneficial to refine the dynamic recrystallization grains.
2021 Vol. 56 (11): 112-121 [Abstract] ( 23 ) [HTML 1KB] [PDF 0KB] ( 16 )
122 XIE Xiao-hui, LIU Yu-long, LI Guang-qiang, CHEN Xin-yuan, ZHU Cheng-yi
Effect of Ce-La alloying treatment on characteristics of inclusions in grain-oriented silicon steels
In order to study the effect of rare earth treatment on the characteristics of inclusions in the grain-oriented silicon steels,the composition,morphology,size and quantity of inclusions were analyzed in the hot-rolled grain-oriented silicon steels after rare earth treatment using FE-SEM/EDS and image analysis software,and the effect mechanism was elucidated. The research results show that the typical inclusions were irregular MnS-AlN composite inclusions and flake or strip AlN inclusions in the rare-earth free samples. The inclusions mainly include spherical or ellipsoidal CeS-LaS,CeS-LaS-AlN,Ce2O2S-La2O2S composite inclusions and AlN inclusions in the rare-earth added samples. Rare earth treatment effectively improves the morphology of inclusions,especially the morphology of large size nitrogen sulfide,and no MnS type inclusions were detected in the steel. Although the number of inclusions increases, and the average size of inclusions larger than 5 μm increased most obviously (0.89 μm) after so much rare-earth added in the steel,the average size of all detected inclusions only increases by 0.40 μm. Due to the excellent desulphurization effect of rare-earth and difference of lattice constant between rare-earth sulfide and AlN,the quantity density and area percent of nitrogen sulfide in steel was reduced. The addition of rare earth reduced the equilibrium product of AlN at the solidification front of the steel, leading to more AlN inclusions precipitating, and AlN appears to grow to a certain extent. Rare earth elements inhibit the precipitation of MnS at the solidification front, which is beneficial to the precipitation of more MnS and AlN used as inhibitors during hot rolling and normalizing process. In the fully deoxidized grain-oriented silicon steels, it is expected to exert the inhibition effect of MnS and AlN and alloying effect of Ce-La by appropriately reducing the content of acid-soluble aluminum in the steel and adjusting the addition amount of rare earth in the steel, and large size inclusions don′t generate. In addition,the micro structure and rolling workability of the steel can be improved by controlling the morphology of inclusions after rare earth elements are added.
2021 Vol. 56 (11): 122-134 [Abstract] ( 19 ) [HTML 1KB] [PDF 0KB] ( 26 )
135 ZHAO Jin-yue, GUO Yong-huan, YAN Bo
Effect of Ce and Nb modification on weld impact properties of DP780 duplex steel
The two-phase performance difference of ferrite and martensite in dual-phase steel,caused the welded joint to soften. When the using temperature was low, the impact energy decreased,caused the material change from a ductile state to a brittle state. In order to research the Ce and Nb addition on the brittleness with low temperature improvement of DP780 weld,used low temperature impact test and tensile test,to study mechanical properties of DP780 weld with different Ce and Nb addition. Used metallographic microscope,SEM and other methods, clarified the changes in weld microstructure and morphology which added different Ce and Nb. The results showed that at -40 ℃,residual austenite appeared in the microstructure without Ce and Nb,the impact energy of the weld was 0.465 J. And a large number of river patterns appeared on the cleavage step surface,which belonged to brittle fracture. As the Ce and Nb mass percents changed,the impact energy of the weld was nonlinear with Ce and Nb addition. When the mass percent of Ce and Nb was 0.35% and 0.15% of the deposited metal,the weld had the best overall performance,the impact energy of the weld reached to 3.9 J. The deposited metal structure had dense grain boundaries,and dimples appeared around the tearing edge,showed mix fracture characteristics. It appeared that add appropriate amount of Ce and Nb,rare earth compounded form in welds,could increase the fracture deformation resistance and energy consumption. Thereby effectively retard the crack propagation,significantly improved the low-temperature impact toughness of DP780,and would not greatly reduce its tensile strength,ensured the welding quality of dual-phase steel. But there was no fixed function relationship between Ce and Nb on weld performance,and the sample size was small,could not be accurate to any addition amount. In the follow-up research,algorithms could be introduce to predict the mechanical properties of DP780 welds,build the model before production,to find the best addition of cerium and niobium,improved safety performance.
2021 Vol. 56 (11): 135-140 [Abstract] ( 15 ) [HTML 1KB] [PDF 0KB] ( 20 )
Environmental Protection and Energy
141 YE Heng-di, LI Qian, WEI Jin-chao, ZHOU Hao-yu, WANG Zhao-cai, SHEN Wei-min
Technology route research of metallurgical and urban solid waste co-processing using steel industrial furnace
Hazard-free and reutilization treatment are still the main directions of solid waste disposal,especially,under the background which achieving "peak carbon dioxide emissions carbon neutral" target,"replacing carbon by waste" is also an important route to reduce carbon emission. However, in current situations, the disposal cost of waste is still high, reutilization of waste is still insufficient, "NOT IN MY BACKYARD" effects is serious. Therefore, the new plot of co-processing metallurgical and urban difficult-to-process solid waste using steel industrial furance, especially sintering and pellitizing process, was presented. A new multi-dimension index system based on material property, energy property, hazardous property, and ecological match law based on best disposal route, should be established. A new co-processing technological route using smelting process, including Fire/Mositure pretreatment method coupling with thermal regulation optimizing, was built. Besides,the conception of reginal intelligent co-processing platform of solid waste based on Big Dipper and Web of Things was shown. The direction guidance and technological reference for co-processing of multi-source solid waste were given.
2021 Vol. 56 (11): 141-147 [Abstract] ( 26 ) [HTML 1KB] [PDF 0KB] ( 23 )
148 CHEN Zhuo, ZHENG Rui-qi, DU Wei-tong, JU Dian-chun, GAO Jian-jun, QI Yuan-hong
Experiment on co-processing of chromium-containing sludge with zinc-bearing dust by carbothermic reduction method
In order to realize the green and circular development of steel industry,the disposal and utilization of zinc-bearing dust and chromium-containing sludge in steel plants should meet the requirements of environmental protection and efficient use of resources. Firstly,taking the zinc-bearing dust and chromium-containing sludge of a steel plant as an example to study the co-processing of carbothermic reduction,the potential reactions occurred in the process and variations of gas-liquid-solid were calculated using the Equilib module of FactSage software. Secondly,the effects of reaction temperature and ratio of zinc-bearing dust and chromium-containing sludge on carbothermic reduction were studied by laboratory experiment for simulating the rotary hearth furnace,and XRD and SEM-EDS methods were used to study the phase composition and morphology of metalized pellets after the reaction. Finally,combined with thermodynamic analysis and experimental results,the reaction mechanism of carbothermic reduction was clarified. The results show that ZnFe2O4and FeCr2O4 can effectively decompose into iron oxide and chromium oxide. As the temperature rising,the iron oxide is reduced to metallic iron and the reduction process follows the law of stepwise reduction. The chromium oxide can be reduced to metallic chromium at a higher temperature compared to iron oxide,and the experimental results are consistent with the thermodynamic calculation trend. When the carbon-containing pellets mixed at a ratio of 1∶4 are roasted at 1 300 ℃ for 60 minutes,the optimum reduction of carbon-containing pellets can be reached. The use of multiple solid waste co-processing methods can not only solve the problem of large amounts of dust accumulation,but also extract valuable metal elements from zinc-bearing dust and chromium-containing sludge to prepare metalized pellets. The method can also provide new ways for the harmless disposal of chromium-containing wastewater,realize comprehensive utilization of resources, and improve the economic benefits of enterprises.
2021 Vol. 56 (11): 148-159 [Abstract] ( 32 ) [HTML 1KB] [PDF 0KB] ( 18 )
Technology Exchange
160 QIAN Sheng, GU Qing, LI Xue-tong, BAI Zhen-hua
Development of comprehensive treatment technology for strip C-shaped warp defect in galvanizing unit
In order to study the serious problem with uneven coating of hot-dip galvanizing strip steel products caused by C-shaped defects, continuous annealing process of hot-dip galvanizing units is optimized, and the comprehensive treatment technology of C-shaped defects of strip are developed. Firstly, the equipment and process characteristics of the continuous annealing process of hot dip galvanizing was considered, the formation mechanism of C-shaped warping was analyzed. The influencing factors such as the state of open burner, the state of the radiation tube, the state of the cooling fan, the gravity of the strip, and the genetic shape of the upstream process section were analyzed, which made the larger temperature difference on the surface of the strip, resulting in the uniform distribution of transverse residual plastic deformation of the strip in its thickness direction. When it exceeded its critical instability condition, C-shaped warping occurred. And then, from the perspective of systematics, the system function of continuous annealing furnace with the influencing factors of C-shaped warping defect was established. The multivariable coupling and complex nonlinear characteristics of continuous annealing furnace were considered, the continuous annealing process was divided into subsystems in the unit of process section, and the minimum warping of each process section was taken as the optimal goal. Based on C-shaped warping prediction model of the strip, the temperature optimization objective function of heating section, the temperature optimization objective function of soaking section and the optimization objective function of cooling fan state in cooling section were established respectively, and the system function was established in the form of the objective functions of each process section superposing. The comprehensive optimization method of process parameters in each process section of continuous annealing process was obtained, and the optimization process was formulated. The key technologies such as temperature optimization setting technology in heating section, temperature optimization setting technology in soaking section and optimization setting technology of cooling fan state in cooling section were formed. Finally, the comprehensive treatment technology was applied to a domestic iron and steel company and good results were achieved. The results show that the maximum warpage of the typical specification strip decreases from 17.0 mm to 5.9 mm, the warping of strip are compared before and after the process parameters optimizating. The production statistics of coating thickness of this type strip show that the average coating thickness on the upper and lower surfaces of the strip is reduced to the range required by the user after the C-shaped warping of the strip is improved.
2021 Vol. 56 (11): 160-168 [Abstract] ( 18 ) [HTML 1KB] [PDF 0KB] ( 26 )
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