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2013 Vol. 48 No. 6
Published: 2013-06-15
Technical Reviews
Steelmaking
Metal Forming
Materials
Environmental Protection and Energy
Technical Reviews
1
WANG Yi-de,TANG Di,DANG Ning
Characteristics and Development Trend of Foreign Special Steel Industry
Hot!
The development general situation of the special steel industry abroad was introduced, and the production mode and industry characteristics of industrial developed countries at present stage were analyzed. Through the reorganization and integration in the past decades, reasonable production scale and clear market positioning has formed in developed countries, they preferred to focus on the production of high quality and high value-added professional products, resulting in a number of advanced special steel enterprises, improved the international competitiveness and market share. In addition, the development trend of processing technology and some development direction of special steel products worth noticing was also introduced.
2013 Vol. 48 (6): 1-6 [
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Raw Materials and Ironmaking
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PAN Wen,,WU Keng,ZHAO Yong,,ZHAO Zhi-xing,MIN Dong Joon
Effect of Alkali Metal on Gas-Solid Reduction of Iron Oxide
Fe2O3 and Fe2O3 doped with Na2O from 1.0 to 5.0 mass percent compacts were isothermally reduced at various temperatures from 1073 to 1273K with CO/CO2 mixed gas in a vertical resistance furnace. To determine the effect of Na2O on the reduction of Fe2O3 compacts, mass loss due to oxygen removal was continuously recorded from which the reduction rate and rate constant was obtained. The morphology change was also observed by SEM. The results show that Na2O retards the reduction of Fe2O3 compacts. Morphological examination of reduced compacts and the binary phase diagram of FeO-Na2O show liquid phase formation during the reduction, which decreases the rate of reduction. Porosity and volumetric expansion of reduced compacts were investigated, which shows that the volume and porosity of reduced Fe2O3-Na2O compacts are both decreased with higher Na2O content due to the existence of liquid phase.
2013 Vol. 48 (6): 7-14 [
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15
FENG Shuai,L Qing,LIU Xiao-jie,BI Si-you,LIU Ran,DU Lin-sen
Effect of Adding CaO on Combustion Mechanism of Pulverized Coal Injection in BF
Hot!
CaO is a kind of pulverized coal combustion improver which is suited for the blast furnace. It is adsorbing volatile, making fixed carbon overheat at local regions and increasing carbon activity, in this way, pulverized coal can take fire at lower temperature by DTA and TG curves analysis. Collecting unburned coal through simulating combustion conditions of blast furnace, analyzing XRD, IR spectrum and SEM, the microcrystalline parameters of unburned coal increased, the height and diameter of aromatic slices will increase 0.0024nm and 0.0362nm respectively as CaO joined.The absorption peak of unburned coal powder adding CaO is more obviously than raw coal in 1500cm-1 and 3400cm-1. The particles size of unburned coal powder reduced 2.67μm by adding CaO, the morphological appearance become irregular.
2013 Vol. 48 (6): 15-19 [
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ZHANG Dai-lin,HONG Ying,ZHENG Ming-dong,WANG Pei-zhen
Experimental Study of Petroleum Coke Added Into Coal Blending
In order to develop resource of new coking coals and improve coke quality, the influence of petroleum coke added into coal blending on coke quality was studied in the 5kg coke oven test. The results show that a certain proportion of petroleum coke added into coal blending with good caking quality was able to promote and improve the coke anisotropy to a certain extent, and the value of OTI would be improved. With ratio of the petroleum coke instead of lean coal was enlarged to a certain degree, the coke CRI could be decreased gradually; coke thermal properties could be improved by adding into smaller particle size of petroleum coke, but the larger particle size was not conducive to improve the coke CSR.
2013 Vol. 48 (6): 20-24 [
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YAN Cai-ju,CHENG Xiang-li,GAO Jian-jun,ZHOU Yu-sheng
Effect of High Oxygen Enrichment PCI on BF Iron-Making
By analyzing the role of coke and the variety of process parameters when high oxygen enrichment PCI was adopted, under the proper condition of oxygen enrichment, PCI, blast temperature, charging system, the matching relationship between charging system and blast system, the following results can be achieved, such as improving the combustion rate of pulverized coal, maintaining high tuyere temperature, reducing bosh gas and enhancing productivity. When coke rate and coal rate is half to half in high oxygen enrichment PCI, quantity of coke can meet direct reduction and carburization requirement. Low reactivity and high abrasion resistance coke is necessary in order to play a skeletal role.
2013 Vol. 48 (6): 25-28 [
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Steelmaking
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ZHEN Xin-gang,ZHU Zhi-yuan,YANG Jian-ping,WANG Yu-long,LIU Yang,ZHAO Xin-yu
Formation Mechanism of the Transverse Cracks in Ultra-Thick Slabs for Shouqin
Factors influencing transverse cracks such as the thickness of slabs, the carbon and niobium content in liquid steel, the casting speed, the dynamics model and the technology of 3D sprays, were investigated. The results show that, because of the defects in the dynamic secondary cooling model, for the ultra-thick slabs with low casting speed, by the minimum water restrictions of the secondary cooling zone, and under the comprehensive action of the straightening force and the thermal stress, if the total strain of shell is more than its critical strain, the transverse cracks finally forms along the grain boundary, located at the vibrating mark trough distance slab corner 150-500mm.
2013 Vol. 48 (6): 29-33 [
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34
LIU Zhuang-zhuang，WU Wei，GUO Xian-li，MENG Hua-dong，ZHAO Jun-pu
SiO2-TiO2-CaO-MgO-FeO-MnO Slag System and Thermodynamic Model of Ti-Si Equilibrium in Titanium Removing Process
In order to decrease titanium content in hot metal, a method of removing titanium in hot metal using sinter or pellet has been invented. An activity model of titanium in SiO2-TiO2-CaO-MgO-FeO-MnO slag system was built using software Matlab basing on the coexistence theory. The calculation result shows that the activity of TiO2 will decrease with the increase of MgO, FeO and MnO mole fraction and the increase of basicity. At the same time, it also grows up when the TiO2 mole fraction increases. Final titanium content in titanium removal process is proportional to the silicon content in hot metal. The proportional coefficient can be affected by temperature, metal content and the activities of SiO2 and TiO2 in slag. The calculated results meet with the experimental and industrial data.
2013 Vol. 48 (6): 34-39 [
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Metal Forming
40
WANG Min-ting,LI Xue-tong,RAO Wei-qiang,DU Feng-shan
Numerical Simulation on Microstructure and Properties of Hot Rolled Seamless Tube in Cooling Process
Hot!
To realize controlled cooling of seamless tube between sizing and straightening in the production process of automatic plug mill, the laws of microstructural and mechanical properties change of rolled No.20 tube during the cooling process were investigated using numerical simulation method under the different cooling conditions. Firstly, after the cooling curves of steel probe in the different cooling mediums were measured, the relationship of heat transfer coefficient of probe and work piece’s temperature was obtained by programming and solution using the basic principle of inverse heat conduction method. And a predict system of temperature, phase transformation and mechanical properties in the cooling process of tube was established using finite difference method. The cooled phase and properties of tube were analyzed in the different cooling processes. Finally, the air cooling experiment of tubes was carried out and the temperatures at different time of cooling and mechanical properties of tubes were measured. The simulated results are in good agreement with the measured data. These works lay a foundation of controlled cooling of seamless tube.
2013 Vol. 48 (6): 40-44 [
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BAI Zhen-hua,SI Hong-xin,ZHOU Qing-tian,HE Gao,,LI Peng-cheng,LI Zhong
Prediction and Prevention of “Heart-Shaped Coil” Defect on Cold Rolling Coil
For the “heart-shaped coil” defect on the coil discharge and cooling process of cold rolling coil, fully combined with inner sleeve equipment and related technology characteristics in coiling process of cold rolling thin strip, the reasons of the “heart-shaped coil” were detailed analyzed. The new concept of coil instability factor was firstly introduced to represent the occurrence probability “heart-shaped coil”. From the view of statistics, the judgment condition of “heart-shaped coil” defect was given; a set of “heart-shaped coil” prediction technology was put forward. The practical “heart-shaped coil” management technology based on the equipment parameter optimization choice was developed, including “cold rolled steel coil ‘heart-shaped coil’ defect prediction and sleeve choose software”. The occurrence rate of the “heart-shaped coil” defect was decreased in cold rolled steel coil discharge volume and cooling process.
2013 Vol. 48 (6): 45-49 [
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DING Bo,DING Mei-liang,GUAN Jian-hui,MAO Yong-ming
Analysis and Countermeasure for Descaling Indivisibility of Oxide Scale
The reason that oxide scale of continuous casting slab cannot be incompletely removed was analyzed by SEM. The results show that the inner layer of oxide scale of continuous casting slab for Q235B, Q345B and SPA-H embeds in steel matrix in the form of cuneiform. The oxide scale embedded in steel matrix is mainly Fe2SiO4. With increasing silicon, the content of Fe2SiO4 in the matrix increases, leading to the increment of adhesion force between inner layer oxide scale and steel matrix, which is the fundamental reason for the incomplete remove of oxide scale of continuous casting slab. Therefore, the methods to remove the oxide scale of continuous casting slab were proposed. On the one hand, the temperature of continuous casting slab should be elevated to above 1173℃ by optimization of the heating process, on the other hand, in order to increase the effect of high-pressure water descaling, high-pressure water descaling system parameters can be optimized.
2013 Vol. 48 (6): 50-53 [
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Materials
54
WU Min,LIAN Xiao-jie,ZENG Li,LI Guo-ping
Investigation on Hot Workability of As-Cast S32750 Super Duplex Stainless Steel
In order to investigate the hot deformation behavior and microstructure evolution of as-cast S32750 super duplex stainless steel, high temperature tensile tests and compression tests were carried out at different temperatures(900-1200℃) and strain rates(0.1-25s-1) by Gleeble-3800 thermo-mechanical simulator. High temperature tensile tests show that S32750 has good ductility from 1000℃ to 1200℃. The flow behavior of S32750 was investigated by high temperature compression tests. The flow curves of low temperatures and slow strain rates exhibit a particularly yield-point-elongation-like effect, which is different from single phase stainless steel. The flow curves of high strain rates or high temperatures and slow strain rates were characterized by recrystallization. The microstructure evolution shows that dynamic recrystallization (DRX) can occur in both ferrite and austenite phases, and DRX in ferrite is prior to austenite. By increasing temperature and decreasing strain rate, DRX can be enhanced. Based on this，the hot deformation equation is set up, the apparent stress exponent is 3.99, and the apparent activation energy(Q) is 393.75kJ/mo1. Its softening mechanism varies with Zener-Hollomon parameter (abbreviated Z) in the above mentioned deformation conditions, and with increasing Z parameter, the peak stress of hot deformation increases．
2013 Vol. 48 (6): 54-60 [
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CAO Chong,ZOU Rong,WU Guang-yao,CHEN Wei
Investigation of Cross Section Microstructure of the Steel Bar With Micro Alloying Controlled Rolling and Controlled Cooling Technique
Hot!
The cross section microstructure of the steel bar with micro alloying controlled rolling and controlled cooling technique as well as the reasons of different compositions to the microstructures were investigated. It is found that the segregation of elements (P,Si and Mn et al.) distributes like stripping which results in the such stripping microstructure for steel 20MnSi and 20MnSiV during rolling. The 20MnSiNb steel can not be recrystallized below 1050℃ for the pinning by Nb and its compound containing C and N elements. The proeutectoid ferrite is formed homogemously in grain boundaries of deformation austenite and interior of deformation zone, then, the pearlite belt is separated out in grain boundaries of deformation austenite (between the grain boundaries proeutectoid ferrite and austenite). The bainite strip is generated in the grain of deformation austenite during last cooling stage. The proper order precipitation of the microstructure of the samples shows as follow: grain boundaries of deformed austenite and deformed band of deformed austenite, segregation of elements, grain boundaries of recrystallization austenite.
2013 Vol. 48 (6): 61-66 [
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MIAO Hua-jun,WANG Yan,ZENG Li,LI Yang
Behavior of TiN in the Electric Slag Remelting Process of Ni-22Cr-12Co Nickel-Based Superalloy
By metallographic analysis, scanning electron microscopy, energy spectrum analysis, combined with thermodynamic and kinetic calculation methods, the behavior of titanium-nitride in the electric slag remelting process of Ni-22Cr-12Co nickel-based superalloy were investigated. The results show that: under our experimental conditions, inclusions in the vacuum ingot and esr ingot is TiN which have the core of Al2O3; in the electric slag remelting process, the calculation time of dissolution of TiN is 1.17s; electric slag remelting process have little effect on the removal of the TiN inclusions, calculated TiN precipitated size of about 5μm, is slightly smaller than the experimental values.
2013 Vol. 48 (6): 67-69 [
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LI Xiu-cheng,SONG Xin,SHANG Cheng-jia,MIAO Cheng-liang,ZHANG Guo-dong
C-Mn-Cr-Nb Low-Alloy Steel and Its Hydrogen Induced Cracking-Resistent Performance
Hot!
The evolution of mechanical properties and microstructures of a low-alloy steel containing low C, low Mn, high Cr and high Nb were studied after thermo mechanical control process and tempering process after the rolling, respectively.Moreover, resist-hydrogen induced cracking (HIC) tests were carried out on the tested steels. The results show that the mechanical properties of tempered steels are improved comparing with of rolled steel. After tempered at 600℃ for 1h, its yield strength is increased 100MPa, and tensile strength is increased 50MPa, but the toughness almost has no reduction. The type of microstructures after tempering process is similar with of rolling condition, which is still mainly composed of acicular ferrite, and a small amount of quasi-polygonal ferrite. However, M/A constituent gradually reduces with the increasing of tempering temperature. The results of the HIC test indicate that all the tested steels can meet the requirements of standards, and the resist-HIC performance is improved after the tempering treatment.
2013 Vol. 48 (6): 70-74 [
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L Jia-shun,,LI Feng,YANG Hong-gang,KANG Yong-lin
Experiments Investigation on Microstructure of Galvanized Zn-Al-Mg Coated Steel Sheet
The facts of galvanizing parameters on microstructure of hot-dipped Zn-Al-Mg coated steel sheet were investigated. The surface and cross sectional microstructure of Zn-Al-Mg coating and the chemical composition and the morphology of alloy layer were analyzed by SEM and EDX. The element distribution in the depth direction of coating was analyzed by GDS. The element distribution in coating was analyzed by EPMA. The phase composition of coating were analyzed by XRD. The elements’ content in coating was explored by XPS. It is proved that the distributions of elements are asymmetry in the depth direction in coating, and zinc and magnesium is enriched in coating surface. Coating structure takes on multiphase commix, MgZn2 and pure zinc binary eutectic are the main phase and at the same time there are some zinc-rich nubby phase and a filmy alloy layer.
2013 Vol. 48 (6): 75-79 [
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PAN Xin,ZHANG Yu,LI Xiao-bao,BAO Bing-hui
Effect of Heat Input on Microstructure and Impact Property of HAZ of Offshore Steel Plate EQ47
Gleeble simulation and multi-pass gas metal arc welding (GMAW) method were employed to investigate the effect of heat input on microstructure and impact property of heat affect zone (HAZ) of EQ47. Coarse grained HAZ (CGHAZ) simulation results show that: with t8/5≤6s(17kJ/cm) the CGHAZ composed of a lath martensite (LM) microstructure shows an impact toughness >200J at -40℃; with t8/5 13s(25kJ/cm), formation of upper bainite (UB) are found and the impact toughness decreased to 100J at -40℃; with increasing t8/5 to 20s(30kJ/cm), coarsening of UB occurred, which results in deterioration of impact toughness to <30J at -40℃. Inter-critically CGHAZ (ICCGHAZ) simulation results show that: formation of M-A constituents along the grain boundary deteriorated impact property, and ICCGHAZ impact toughness at -40℃ decreased from 100J at t8/5 of 6s to 37J and 21J at t8/5 of 13s and 20s, respectively. GMAW results show that the impact property of CGHAZ decreased from 134-215J to 39-95J with increased heat input from 17 to 25kJ/cm, which correspond well with simulation results. It is found from both simulation and GMAW results that, the welding heat input should be controlled ≤17kJ/cm to achieve satisfactory HAZ impact toughness.
2013 Vol. 48 (6): 80-84 [
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Environmental Protection and Energy
85
PANG Jian-ming,GUO Pei-min,ZHAO Pei
Research and Development of Efficient Utilization Technology of Ilmenite
Hot!
The reduction of ilmenite was more difficult than the common iron ore in thermodynamic aspect. The dynamic study shows that the reduction rate could be accelerated when ilmenite powder is refined further. The best reduction temperature of ilmenite by powdered carbon should be 900-1100℃. Carburization is favorable for ferrite grain growth. The more carburization is, the better ferrite grain growth is. The outfield has played a noticeable role in ferrite grain growth, which could provide the best condition for the separation between titanium slag and iron. The iron nugget formed by ferrite grain growth and high titanium slag could be obtained by simple magnetic separation. With low reaction temperature and elimination of the electric smelting process, this technology is a new method for an efficient utilization of resources and energy. The efficient utilization technology of ilmenite has the advantages of high efficiency, low-energy consumption, low investment and low cost.
2013 Vol. 48 (6): 85-89 [
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