钢铁研究学报(英文版)
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2019年 26卷 7期
刊出日期：2019-07-25
659
Yan-he Jia, Li-xin Tang, Zhe George Zhang, Xiao-feng Chen
MMPP/M/C queue with congestion-based staffing policy and applications in operations of steel industry
A queueing model of the Markov-modulated Poisson process (MMPP) with thresholds was investigated. The customer arrival with various arrival rates in the model was viewed as the MMPP. In contrast to the Poisson’s arrival process, the MMPP can better describe the situation that the arrival rate changes with changing conditions; therefore, the model fits better with reality. The threshold conversion was added to the model based on the general MMPP/M/C model. When the number of customers in the system exceeds a threshold, all servers work to serve; when the number of customers in the system is less than another threshold, some servers are shut down. This is the congestion-based staffing policy with two thresholds. Specifically, the problems in the slab stocking stage of slab production at the Iron and Steel Complex in China were analysed. In the slab production process, because the rate of the upstream steelmaking is not constant, the rate of slab reaching the slab yard is uncertain. The crane service is used to store slabs in a warehouse. Because the slab arrival rate varies, different numbers of cranes in service need to be optimized for cost control. Thus, MMPP was used to describe slab arrival with varied arrival rates. Therefore, an MMPP/M/C queue with thresholds was used to analyse and solve the practical problems, and the optimal number of service cranes was obtained to minimize the cost of slab stocking.
2019 Vol. 26 (7): 659-668 [
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669
Heng Zhou, Qin-fu Hou, Ming-yin Kou, Shun Yao, Sheng-li Wu
Discrete element method study of solid descending and residence properties in COREX shaft furnace with center gas supply device
Solid descending and residence properties in COREX shaft furnace with a center gas supply device (CGSD) were studied using the discrete element method. Solid flow pattern, residence time distribution, and local solid residence time (SRT) were analyzed. Moreover, the effects of the rotation speed of screws, the radius, and height of CGSD were investigated. The results show that the solid flow is dominantly a plug flow in the shaft furnace with the CGSD. In the upper region of the shaft furnace for gas–solid reduction, uniform distribution of local SRT is observed, which is preferable to match the even gas distribution expected due to the CGSD and slots. For different rotation speeds of the screws, the distribution of solid flow patterns is similar. The averaged residence time, dispersed plug volume fraction, and dead volume fraction decrease with increasing the rotation speed of the screws. The radius of the CGSD affects the solid residence in the shaft furnace. Local SRT above the CGSD increases with the increase in the radius of CGSD, possibly leading to the formation of more agglomerates. Hence, the radius of CGSD should be chosen carefully. The height of CGSD has a minor effect on solid residence in the shaft furnace.
2019 Vol. 26 (7): 669-678 [
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679
Chuan-ping Liu, Bin-jie Li, Li Wang, Shao-wu Yin, Li-ge Tong
Numerical simulation of impact and solidification of melting dust on spherical bead surface and experimental validation
The impact and solidification processes of single melting tin dust at the micron scale on a spherical bead were numerically studied with hot flue gas flow. The geometrical evolution of dust impacting on hot bead and spreading without solidification involved initial spreading, retraction and oscillation, and stabilizing. The increased impact angle was found to reduce maximum spread area, weaken retraction and oscillation, and raise steady spread area. Dust impacting on cold bead completely solidified after liquid spreading and solidification without retraction and oscillation. Increased impact angle raised solidification sliding distance, whereas it reduced solidification spread area. Then, the effects of bead temperature, dust inlet velocity and size on the sliding and spreading of dust were studied, and the results indicated that increasing bead temperature, dust inlet velocity and size could raise solidification sliding distance and solidification spread area. With the dusts continually impacting on the bed, a dust layer forms at the front of bead, being different from that of solid dust, which becomes thick firstly, and then spreads from bead front to sides.
2019 Vol. 26 (7): 679-690 [
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691
Dong-hui Liu, Jun-hua Li, Yue Peng, Jian-liang Zhang, Guang-wei Wang, Xun Xue
Comprehensive evaluation of sintering basic characteristics of iron ore based on grey relational analysis
Sintering basic characteristics of fourteen iron ores were comprehensively evaluated using micro-sinter and grey relational analysis methods. The results show that magnetite has a low assimilability, high bonding phase strength, and high crystal strength. Hematite presents a good assimilability, while limonite exhibits a strong assimilability, but the bonding phase strength and crystal strength of these two kinds of iron ores are comparatively low. Great difference in liquid flowability exists for the same kind of iron ores. When the assimilation temperature of the sinter mixture is too high, limonite can be added; when the bonding phase strength or crystal strength of the sinter mixture is too low, magnetite can be added. The liquid fluidity of the sinter mixture can be adjusted according to the ratios of corresponding iron ores. Grey relational analysis is an effective method to evaluate the comprehensive sintering characteristics of iron ores, which can provide theoretical basis for the purchasing department of the steel enterprises.
2019 Vol. 26 (7): 691-696 [
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697
Xiao-qiang Yan, Jie-bin Qi, Xin-xin Wang
An active method suppressing rolling mill vibration: disturbance estimation and compensation algorithm
The rolling mill vibration not only seriously causes the strip thickness heterogeneity, but also damages the rolling mill equipment and its electrical components. Existing vibration suppression methods are passive and mainly tune mechanical, hydraulic, electrical and rolling process parameters. A new active vibration suppression method was thus proposed using the disturbance estimation and compensation algorithm. Firstly, the hydraulic–mechanical coupling model of the rolling mill vibration was established, and an active vibration suppressor was designed based on the extended state observer. Then, through the numerical simulation, it is found that the vibration energy is reduced by 35.3% using the vibration suppressor, and the vibration suppressor is valid when the vibration frequency is lower than 60 Hz. Finally, the vibration suppressor was applied to the in-site manufacturing, and the expected vibration suppression was obtained. The method makes the produced steel strip have more uniform thickness and further significantly increases the finished product ratio.
2019 Vol. 26 (7): 697-703 [
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704
Yan-mo Li, Yong-chang Liu, Li-ming Yu, Chen-xi Liu, Chong Li, Yuan Huang, Hui-jun Li, Zong-qing Ma
Effect of deformation twinning on high-temperature performance of cold-rolled S31042 steel
Influence of deformation twinning on high-temperature instantaneous performance of cold-rolled S31042 steel was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, and high-temperature tensile test. An increasing number of deformation twins have formed as the cold rolling reduction degree increases during the cold rolling process. During the tensile process at 700 °C, M
23
C
6
particles generated along the deformation twin boundaries, and NbCrN nanoparticles dispersedly precipitated throughout the austenite grains. For the high-temperature tensile sample subjected to cold reduction for 80%, it is observed from the fractured cross section that numerous deformation twin boundaries were decorated by discontinuous M
23
C
6
particles. Therefore, austenite grains were divided into several independent zones by the deformation twins, and the grains were refined. Due to the grain refinement strengthening and precipitation strengthening, the high-temperature temporal strength of the 80% cold-rolled sample was significantly improved, and simultaneously, this sample exhibited favorable high-temperature elongation.
2019 Vol. 26 (7): 704-711 [
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712
Jin-gang Bai, Yi-shi Cui, Jian Wang, Nan Dong, Muhammad Saqlain Qurashi, Hai-rui Wei, Yong-chao Yang, Pei-de Han
Effect of compression deformation on precipitation phase behavior of B-containing S31254 super austenitic stainless steel
Effects of compression deformation on the sigma-phase precipitation behavior of B-containing S31254 stainless steel after solution treatment were studied using the Gleeble compression test. The cold and hot processing characteristics of B-containing S31254 stainless steel were evaluated, and the results show that the speed of compression deformation increased the precipitation rate of the sigma phase, and the location of precipitation extended from the austenite grain boundary to the original hot rolling deformation area. During cold deformation at room temperature, the precipitation rate increased when the deformation reached at 40%. Deformation at 950 °C affected precipitation more obviously. At 1074 °C, when the deformation reached 20%, the precipitated phases started increasing, and above this deformation range, precipitation began decreasing. Also, at 1074 °C, the deformation accelerated the precipitation of sigma phase; but with deformation, there was a change in critical temperature for the sigma-phase excursion. The precipitation position of the sigma phase is strongly related to the area of the original hot rolling deformation. With an increase in the deformation amount, precipitates in this region appeared as coarse-grained, skeletal, and network-like features.
2019 Vol. 26 (7): 712-719 [
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720
Peng-cheng Liu, Jian-chun Cao, Shu-biao Yin, Yin-hui Yang, Peng Gao
Effect of Zr on undissolved phases and carbide precipitation in Ti microalloyed low-carbon steel
The undissolved phases and carbide precipitation in Ti and Ti–Zr microalloyed low-carbon steels were investigated by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. At 1225 °C, the replacement of Ti by Zr formed Zr2CS and (Zr, Ti)N (the Ti/Zr atomic ratio is 0.11) and reduced the consumption of Ti. At 925 °C, it was identified that TiC phases were precipitated at first and Zr was incorporated into the TiC lattice in the subsequent precipitation process, which promoted the precipitation of titanium carbide. The calculation of the interaction coefficient between Ti, C, N and Zr showed that Zr reduced the activity of Ti and C and increased the activity of N in the iron matrix. Therefore, with the addition of Zr, the solubility of Ti was increased, and the consumption of Ti was reduced at high temperature in Ti microalloyed low-carbon steel. The thermodynamic calculation of carbide precipitation transformation showed that the replacement of Ti by Zr increased the nucleation driving force and the nucleation rate of titanium carbide, while the critical core size and the critical nuclear energy were reduced. As the holding time was extended, the Zr/Ti atomic ratio increased and the size of the precipitates also increased. When the Zr/Ti atomic ratio reached a certain level, the size of the precipitates did not increase with further increase in atomic ratio. When the Zr/Ti atomic ratio in (Ti, Zr)C was 0.05–0.17, (Ti, Zr)C was the most stable carbide and the easiest to nucleate at 925 °C. There was more of the (Ti, Zr)C phase than TiC at 925 °C after 50 and 100 s, and the time to complete the coarsening behavior of (Ti, Zr)C was shorter than that of TiC.
2019 Vol. 26 (7): 720-732 [
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733
Xin-ping Xiao, Gen-hao Shi, Shu-ming Zhang, Yu-wei Gao, Qing-feng Wang, ...
Effect of increased nitrogen content on continuous cooling transition of γ→α in hot-deformed low-C Mo–V–Ti steels
The two-stage controlled rolling and cooling at 0.5–50 °C/s of low-carbon Mo–V–Ti steels with the increasing nitrogen content from 0.0032 to 0.0081 and 0.0123 wt.% were simulated through a Gleeble 3500 system. The continuous cooling transition (CCT) of γ→α in each steel was estimated via microstructure characterization and CCT diagram. The results indicated that CCT diagram for each steel was divided into three regions of γ-ferrite, γ-pearlite and γ-bainite, and the increasing N content elevated all the starting temperatures for γ→α. Consequently, the polygonal ferrite (PF) and pearlite formed in each steel cooled at 1 °C/s and, however, the increasing N content led to slightly coarser ferrite grain and pearlite colony. With the increased cooling rate to 10 and 30 °C/s, a mixed microstructure of acicular ferrite (AF), granular bainite (GB) and lath bainite (LB) formed in 32N steel and in contrast, the mixture of PF+AF+GB in 81N and 123N steels. The increasing N content promoted (Ti,V)(C,N) precipitation, enhanced the intragranular PF/AF nucleation, increased martensite/austenite constituent and depressed LB. In addition, the mechanisms dominating the effect of increasing N on this CCT of γ→α were discussed.
2019 Vol. 26 (7): 733-742 [
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743
Xiao-dong Li, Jin Liu, Yan-yan Zhu, Xu Cheng, Dong Liu, Ji-kui Zhang
Solid-state phase transformation of TC11 titanium during unstable thermal cycling in laser melting deposition process
Thermal cycling during laser additive manufacturing (LAM) process causes the appearance of bright and dark patterns on the etched surface of TC11 alloy components. The formation mechanisms of these patterns and the solid-state transformation relating to LAM process are systematically investigated with the predication of temperature fields using the finite element software ABAQUS. The results indicate that by increasing numbers of subsequent thermal cycles, the peak temperatures for every cycle decrease. When the peak temperatures are above T
β
(1010 °C in TC11 alloy), no pattern is observed, and an ultrafine basket-weave α+β microstructure (darkly contrast) shows up in alloy with gradually increased number of α colony (decrease of peak temperatures). A special bimodal microstructure with 'fork-like' α lamellar appears in layer when the peak temperatures of thermal cycles firstly falls into α+β two-phase region. And this special bimodal microstructure gives a brightly contrast and only appears at the region when the peak temperatures are below 970 °C, leaving the rest region with a dark contrast. With the continuing increase of thermal cycles in the α+β two-phase region, α lamellar gradually coarsens. After five times thermal cycles in the α+β two-phase region, no further changes of microstructure are observed, the morphology of α lamellar in dark and bright regions are almost the same but with different amount of α phase.
2019 Vol. 26 (7): 743-750 [
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751
Xiao-wei Zhai, Jin-feng Du, Lin-ping Li, Chao Zhou, Zheng Zhang
Creep behavior and damage evolution of T92/Super304H dissimilar weld joints
Creep tests of T92/Super304H joints were performed at 923 K under the stress of 85–165 MPa. Microstructure evolution was characterized by light microscopy, scanning electron microcopy and transmission electron microscopy to probe the relationship between creep performance deterioration and microstructure evolution. Results showed that for all the creep tests, failure occurred at fine-grained heat-affected zone of T92, and the joints have lower creep strength than the base metal T92. However, as the stress increased from 85 to 165 MPa, the creep fracture changed from a mixed mode, i.e., intergranular fracture in the center part and transgranular fracture in the edge part to total transgranular fracture. The longer the creep life, the greater is the proportion of the intergranular fracture. The M
23
C
6
coarsened and the Laves phase precipitated along grain boundaries during long-term creep. Vacancies nucleate and propagate at the interface between coarse M
23
C
6
, Laves phase and matrix. Finally, cracks forming along grain boundaries are responsible for intergranular fracture.
2019 Vol. 26 (7): 751-760 [
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761
Jun-hui Li, Hong-hong Wang, Qiang Luo, Li Li, Chao Sun, R.D.K. Misra
Correlation between microstructure and impact toughness of weld heat-affected zone in 5 wt.% manganese steels
The microstructure in welding heat-affected zones of 5 wt.% manganese steels was studied, and its effect on impact toughness was analyzed. The simulated coarse-grained heat-affected zone (CGHAZ) had the lowest impact toughness of ~39 J at - 40 °C because of coarse-grained structure and least volume fraction of retained austenite (RA) of 1.2 vol.%. The impact toughness of simulated intercritical heat-affected zone (ICHAZ) and fine-grained heat-affected zone (FGHAZ) were ~165 and ~45 J, respectively, at - 40 °C. The effective grain size of simulated FGHAZ was smaller than that of the simulated ICHAZ. Furthermore, microstructural investigation revealed that the simulated FGHAZ and ICHAZ had similarity in volume fraction and stability of RA. However, tempered martensite was present in ICHAZ and absent in FGHAZ. It is proposed that the presence of tempered martensite contributed to good impact toughness in simulated ICHAZ.
2019 Vol. 26 (7): 761-770 [
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771
Hui-ning Zhang, Qiu-yan Wu, Zhen-ying Hu, Hui Li, Hui-hui Xiong, An-jun Xu
First-principles study on stability, electronic, and mechanical properties of La–C and Ce–C binary compounds
The phase stability and electronic and mechanical properties of rare earth (RE) carbides (La
2
C
3
, LaC
2
, Ce
2
C
3
, CeC
2
, and CeC) were investigated using first-principles calculations based on density functional theory. The calculated equilibrium lattice constants and cell volume agree well with available experimental data. The cohesive energy and formation enthalpy of these carbides show that they are thermodynamically and mechanically stable except LaC. The strong covalent bonding exists in these compounds, and the covalent bonds are mainly determined to be RE–C and C–C bonds. The hardness of RE
x
C
y
compounds is less than 10 GPa, and the bulk modulus, shear modulus, and Young’s modulus of Ce
2
C
3
are the largest. The values of B/G (ratio of bulk modulus to shear modulus) and Poisson’s ratio indicate that all the compounds have good ductility, and the ductility of CeC is larger than others. The Debye temperature of Ce
2
C
3
is 429.67 K, which is the highest in those of experimental compounds.
2019 Vol. 26 (7): 771-778 [
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