International Journal of Minerals, Metallurgy and Materials

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Application of a water cooling treatment and its effect on coal-based reduction of high-chromium vanadium and titanium iron ore

Song-tao Yang, Mi Zhou, Tao Jiang, Shan-fei Guan, Wei-jun Zhang, Xiang-xin Xue

2016, 23(12): 1353-1359. doi: 10.1007/s12613-016-1358-1

中文摘要(290) PDF(7) SpringerLink

摘要:
A water cooling treatment was applied in the coal-based reduction of high-chromium vanadium and titanium (V–Ti–Cr) iron ore from the Hongge region of Panzhihua, China. Its effects on the metallization ratio (η), S removal ratio (R_S), and P removal ratio (R_P) were studied and analyzed on the basis of chemical composition determined via inductively coupled plasma optical emission spectroscopy. The metallic iron particle size and the element distribution of Fe, V, Cr, and Ti in a reduced briquette after water cooling treatment at 1350°C were determined and observed via scanning electron microscopy. The results show that the water cooling treatment improved the η, R_S, and R_P in the coal-based reduction of V–Ti–Cr iron ore compared to those obtained with a furnace cooling treatment. Meanwhile, the particle size of metallic iron obtained via the water cooling treatment was smaller than that of metallic iron obtained via the furnace cooling treatment; however, the particle size reached 70 μm at 1350°C, which is substantially larger than the minimum particle size required (20 μm) for magnetic separation. Therefore, the water cooling treatment described in this work is a good method for improving the quality of metallic iron in coal-based reduction and it could be applied in the coal-based reduction of V–Ti–Cr iron ore followed by magnetic separation.

Kinetic studies on the reduction of iron ore nuggets by devolatilization of lean-grade coal

Chanchal Biswas, Prithviraj Gupta, Arnab De, Mahua Ghosh Chaudhuri, Rajib Dey

2016, 23(12): 1360-1368. doi: 10.1007/s12613-016-1359-0

中文摘要(413) PDF(5) SpringerLink

摘要:
An isothermal kinetic study of a novel technique for reducing agglomerated iron ore by volatiles released by pyrolysis of lean-grade non-coking coal was carried out at temperature from 1050 to 1200°C for 10–120 min. The reduced samples were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and chemical analysis. A good degree of metallization and reduction was achieved. Gas diffusion through the solid was identified as the reaction-rate-controlling resistance; however, during the initial period, particularly at lower temperatures, resistance to interfacial chemical reaction was also significant, though not dominant. The apparent rate constant was observed to increase marginally with decreasing size of the particles constituting the nuggets. The apparent activation energy of reduction was estimated to be in the range from 49.640 to 51.220 kJ/mol and was not observed to be affected by the particle size. The sulfur and carbon contents in the reduced samples were also determined.

Water model experiments of multiphase mixing in the top-blown smelting process of copper concentrate

Hong-liang Zhao, Pan Yin, Li-feng Zhang, Sen Wang

2016, 23(12): 1369-1376. doi: 10.1007/s12613-016-1360-7

中文摘要(302) PDF(11) SpringerLink

摘要:
We constructed a 1:10 cold water experimental model by geometrically scaling down an Isa smelting furnace. The mixing processes at different liquid heights, lance diameters, lance submersion depths, and gas flow rates were subsequently measured using the conductivity method. A new criterion was proposed to determine the mixing time. On this basis, the quasi-equations of the mixing time as a function of different parameters were established. The parameters of the top-blown smelting process were optimized using high-speed photography. An excessively high gas flow rate or excessively low liquid height would enhance the fluctuation and splashing of liquid in the bath, which is unfavorable for material mixing. Simultaneously increasing the lance diameter and the lance submersion depth would promote the mixing in the bath, thereby improving the smelting efficiency.

Comprehensive recovery of gold and base-metal sulfide minerals from a low-grade refractory ore

Wen-juan Li, Shuang Liu, Yong-sheng Song, Jian-kang Wen, Gui-ying Zhou, Yong Chen

2016, 23(12): 1377-1386. doi: 10.1007/s12613-016-1361-6

中文摘要(235) PDF(2) SpringerLink

摘要:
The comprehensive recovery of small amounts of valuable minerals such as gold and base-metal sulfide minerals from a low-grade refractory ore was investigated. The following treatment strategy was applied to a sample of this ore: gold flotation–gold concentrate leaching–lead and zinc flotation from the gold concentrate leaching residue. Closed-circuit trials of gold flotation yielded a gold concentrate that assayed at 40.23 g·t^-1 Au with a recovery of 86.25%. The gold concentrate leaching rate was 98.76%. Two variants of lead-zinc flotation from the residue—preferential flotation of lead and zinc and bulk flotation of lead and zinc—were tested using the middling processing method. Foam from the reflotation was returned to the lead rougher flotation or lead–zinc bulk flotation, whereas middlings from reflotation were discarded. Sulfur concentrate was a byproduct. The combined strategy of flotation, leaching, and flotation is recommended for the treatment of this kind of ore.

Effects of stress ratio on the temperature-dependent high-cycle fatigue properties of alloy steels

Zhi-yang Lü, Ao-shuang Wan, Jun-jiang Xiong, Kuang Li, Jian-zhong Liu

2016, 23(12): 1387-1396. doi: 10.1007/s12613-016-1362-5

中文摘要(201) PDF(4) SpringerLink

摘要:
This paper addresses the effects of stress ratio on the temperature-dependent high-cycle fatigue (HCF) properties of alloy steels 2CrMo and 9CrCo, which suffer from substantial vibrational loading at small stress amplitude, high stress ratio, and high frequency in the high-temperature environments in which they function as blade and rotor spindle materials in advanced gas or steam turbine engines. Fatigue tests were performed on alloy steels 2CrMo and 9CrCo subjected to constant-amplitude loading at four stress ratios and at four and three temperatures, respectively, to determine their temperature-dependent HCF properties. The interaction mechanisms between high temperature and stress ratio were deduced and compared with each other on the basis of the results of fractographic analysis. A phenomenological model was developed to evaluate the effects of stress ratio on the temperature-dependent HCF properties of alloy steels 2CrMo and 9CrCo. Good correlation was achieved between the predictions and actual experiments, demonstrating the practical and effective use of the proposed method.

Monte Carlo study on abnormal growth of Goss grains in Fe-3%Si steel induced by second-phase particles

Dong-qun Xin, Cheng-xu He, Xue-hai Gong, Hao Wang, Li Meng, Guang Ma, Peng-fei Hou, Wen-kang Zhang

2016, 23(12): 1397-1403. doi: 10.1007/s12613-016-1363-4

中文摘要(297) PDF(3) SpringerLink

摘要:
The selective abnormal growth of Goss grains in magnetic sheets of Fe-3%Si (grade Hi-B) induced by second-phase particles (AlN and MnS) was studied using a modified Monte Carlo Potts model. The starting microstructures for the simulations were generated from electron backscatter diffraction (EBSD) orientation imaging maps of recrystallized samples. In the simulation, second-phase particles were assumed to be randomly distributed in the initial microstructures and the Zener drag effect of particles on Goss grain boundaries was assumed to be selectively invalid because of the unique properties of Goss grain boundaries. The simulation results suggest that normal growth of the matrix grains stagnates because of the pinning effect of particles on their boundaries. During the onset of abnormal grain growth, some Goss grains with concave boundaries in the initial microstructure grow fast abnormally and other Goss grains with convex boundaries shrink and eventually disappear.

Microstructure evolution and thixoforming behavior of 7075 aluminum alloy in the semi-solid state prepared by RAP method

Jin-long Fu, Kai-kun Wang, Xiao-wei Li, Hai-kuan Zhang

2016, 23(12): 1404-1415. doi: 10.1007/s12613-016-1364-3

中文摘要(277) PDF(5) SpringerLink

摘要:
The effects of isothermal treatments on the microstructural evolution and coarsening rate of semi-solid 7075 aluminum alloy produced via the recrystallization and partial remelting (RAP) process were investigated. Samples of 7075 aluminum alloy were subjected to cold extrusion, and semi-solid treatment was carried out for 5–30 min at temperatures ranging from 580 to 605°C. A backward-extrusion experiment was conducted to investigate liquid segregation during the thixoforming process. The results revealed that obvious grain coarsening and spheroidization occurred during prolonged isothermal treatments. In addition, higher soaking temperatures promoted the spheroidization and coarsening process because of the increased liquid fraction and the melting of second phases. Segregation of the liquid phase caused by the difference in fluidity between the liquid and the solid phases was observed in different regions of the thixoformed specimens.

Influence of shielding gas on the mechanical and metallurgical properties of DP-GMA-welded 5083-H321 aluminum alloy

Amin Reza Koushki, Massoud Goodarzi, Moslem Paidar

2016, 23(12): 1416-1426. doi: 10.1007/s12613-016-1365-2

中文摘要(411) PDF(8) SpringerLink

摘要:
In the present research, 6-mm-thick 5083-H321 aluminum alloy was joined by the double-pulsed gas metal arc welding (DP-GMAW) process. The objective was to investigate the influence of the shielding gas composition on the microstructure and properties of GMA welds. A macrostructural study indicated that the addition of nitrogen and oxygen to the argon shielding gas resulted in better weld penetration. Furthermore, the tensile strength and bending strength of the welds were improved when oxygen and nitrogen (at concentrations as high as approximately 0.1vol%) were added to the shielding gas; however, these properties were adversely affected when the oxygen and nitrogen contents were increased further. This behavior was attributed to the formation of excessive brown and black oxide films on the bead surface, the formation of intermetallic compounds in the weld metal, and the formation of thicker oxide layers on the bead surface with increasing nitrogen and oxygen contents in the argon-based shielding gas. Analysis by energy-dispersive X-ray spectroscopy revealed that most of these compounds are nitrides or oxides.

Effect of continuous induction annealing on the microstructure and mechanical properties of copper-clad aluminum flat bars

Xin-hua Liu, Yan-bin Jiang, Hong-jie Zhang, Jian-xin Xie

2016, 23(12): 1427-1436. doi: 10.1007/s12613-016-1366-1

中文摘要(279) PDF(4) SpringerLink

摘要:
Copper-clad aluminum (CCA) flat bars produced by the continuous casting–rolling process were subjected to continuous induction heating annealing (CIHA), and the effects of induction heating temperature and holding time on the microstructure, interface, and mechanical properties of the flat bars were investigated. The results showed that complete recrystallization of the copper sheath occurred under CIHA at 460°C for 5 s, 480°C for 3 s, or 500°C for 1 s and that the average grain size in the copper sheath was approximately 10.0 μm. In the case of specimens subjected to CIHA at 460–500°C for longer than 1 s, complete recrystallization occurred in the aluminum core. In the case of CIHA at 460–500°C for 1–5 s, a continuous interfacial layer with a thickness of 2.5–5.5 μm formed and the thickness mainly increased with increasing annealing temperature. After CIHA, the interfacial layer consisted primarily of a Cu₉Al₄ layer and a CuAl₂ layer; the average interface shear strength of the CCA flat bars treated by CIHA at 460–500°C for 1–5 s was 45–52 MPa. After full softening annealing, the hardness values of the copper sheath and the aluminum core were HV 65 and HV 24, respectively, and the hardness along the cross section of the CCA flat bar was uniform.

Microstructures and properties of Al₂O₃ dispersion-strengthened copper alloys prepared through different methods

Zhi-qiao Yan, Feng Chen, Fu-xing Ye, Dong-ping Zhang, Yi-xiang Cai

2016, 23(12): 1437-1443. doi: 10.1007/s12613-016-1367-0

中文摘要(349) PDF(8) SpringerLink

摘要:
Al₂O₃ dispersion copper alloy powder was prepared by internal oxidation, and three consolidation methods—high-velocity compaction (HVC), hot pressing (HP), and hot extrusion (HE)—were used to prepare Al₂O₃ dispersion-strengthened copper (Cu–Al₂O₃) alloys. The microstructures and properties of these alloys were investigated and compared. The results show that the alloys prepared by the HP and HE methods exhibited the coarsest and finest grain sizes, respectively. The alloy prepared by the HVC method exhibited the lowest relative density (98.3% vs. 99.5% for HP and 100% for HE), which resulted in the lowest electrical conductivity (81% IACS vs. 86% IACS for HP and 87% IACS for HE). However, this alloy also exhibited the highest hardness (77 HRB vs. 69 HRB for HP and 70 HRB for HE), the highest compressive strength (443 MPa vs. 386 MPa for HP and 378 MPa for HE), and the best hardness retention among the investigated alloys. The results illustrate that the alloy prepared by the HVC method exhibits high softening temperature and good mechanical properties at high temperatures, which imply long service life when used as spot-welding electrodes.

Influence of nano-Al₂O₃-reinforced oxide-dispersion-strengthened Cu on the mechanical and tribological properties of Cu-based composites

Xiang Zhao, Lei-chen Guo, Long Zhang, Ting-ting Jia, Cun-guang Chen, Jun-jie Hao, Hui-ping Shao, Zhi-meng Guo, Ji Luo, Jun-bin Sun

2016, 23(12): 1444-1451. doi: 10.1007/s12613-016-1368-z

中文摘要(294) PDF(5) SpringerLink

摘要:
The mechanical and tribological properties of Cu-based powder metallurgy (P/M) friction composites containing 10wt%–50wt% oxide-dispersion-strengthened (ODS) Cu reinforced with nano-Al₂O₃ were investigated. Additionally, the friction and wear behaviors as well as the wear mechanism of the Cu-based composites were characterized by scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS) elemental mapping. The results indicated that the Cu-based friction composite containing 30wt% ODS Cu exhibited the highest hardness and shear strength. The average and instantaneous friction coefficient curves of this sample, when operated in a high-speed train at a speed of 300 km/h, were similar to those of a commercial disc brake pad produced by Knorr-Bremse AG (Germany). Additionally, the lowest linear wear loss of the obtained samples was (0.008 ± 0.001) mm per time per face, which is much lower than that of the Knorr-Bremse pad ((0.01 ± 0.001) mm). The excellent performance of the developed pad is a consequence of the formation of a dense oxide composite layer and its close combination with the pad body.

Effect of niobium alloying level on the oxidation behavior of titanium aluminides at 850°C

Alexandra Banu, Maria Marcu, Simona Petrescu, Nicolae Ionescu, Alexandru Paraschiv

2016, 23(12): 1452-1457. doi: 10.1007/s12613-016-1369-y

中文摘要(252) PDF(3) SpringerLink

摘要:
This work addresses the alloying of titanium aluminides used in aircraft engine applications and automobiles. The oxidation resistance behavior of two titanium aluminides of α₂ + γ(Ti₃Al + TiAl) and orthorhombic Ti₂NbAl, recognized as candidates for high-temperature applications, was investigated by exposure of the alloys for 100 h in air. Thus, oxidation resistance was expressed as the mass gain rate, whereas surface aspects were analyzed using scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy, and the type of oxidation products was analyzed by X-ray diffraction and Raman spectroscopy. The orthorhombic Ti₂NbAl alloy was embrittled, and pores and microcracks were formed as a result of oxygen diffusion through the external oxide layer formed during thermal oxidation for 100 h.

Thermodynamic simulation of the effect of slag chemistry on the corrosion behavior of alumina–chromia refractory

Shi-xian Zhao, Bin-li Cai, Hong-gang Sun, Gang Wang, Hong-xia Li, Xiao-yan Song

2016, 23(12): 1458-1465. doi: 10.1007/s12613-016-1370-5

中文摘要(242) PDF(14) SpringerLink

摘要:
The corrosion behavior of alumina–chromia refractory against two kinds of industrial slags (coal slag and iron smelting slag) at 1550°C was investigated via thermodynamic simulations. In the proposed simulation model, the initial slag first attacks the matrix and surface aggregates and subsequently attacks the inner aggregates. The simulation results indicate that the slag chemistry strongly affects the phase formation and corrosion behavior of the refractory brick. Greater amounts of alumina were dissolved and spinel solid phases formed when the brick interacted with iron smelting slag. These phenomena, as well as the calculated lower viscosity, may lead to much deeper penetration than that exhibited by coal slag and to more severe corrosion compared to that induced by coal slag. The thermodynamic calculations well match the experimental observations, demonstrating the efficiency of the proposed simulation model for evaluating the corrosion behavior of alumina–chromia refractory.

Effect of TiO₂ pigment gradation on the properties of thermal insulation coatings

Lu-wei Shen, Ya-mei Zhang, Pei-gen Zhang, Jin-jie Shi, Zheng-ming Sun

2016, 23(12): 1466-1474. doi: 10.1007/s12613-016-1371-4

中文摘要(403) PDF(9) SpringerLink

摘要:
This study was designed to evaluate the thermal performance and mechanical properties of coatings with different gradations of TiO₂ pigments. The solar reflectance, cooling performance, wash resistance, and film adhesion strength of the coatings were investigated. The influence of TiO₂ powder gradation on the final properties of the coatings was studed. The solar reflectance and the thermal insulation were observed to increase with increasing content of nanosized TiO₂. The mechanical properties of the coatings, such as their wash resistance and film adhesion strength, were observed to increase with increased incorporation of nanosized TiO₂. Such improvements in the properties of the coatings were attributed to the greater specific surface area and lower thermal conductivity of nanosized TiO₂ particles compared to normal TiO₂ particles.

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2016年第23卷第12期

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