钢铁研究学报(英文版)
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2019 Vol. 26 No. 12
Published: 2019-12-25
1257
Zheng-wei Yu, Li-xin Qian, Hong-ming Long, Yi-fan Wang, Qing-min Meng, Tie-jun Chun
Determination method of high-temperature characteristics of iron-ore sintering based on n(Fe
2
O
3
)/n(CaO)
The high-temperature characteristics of iron ores play important roles in optimizing ore proportion of sintering, which are tested by using iron-ore fines and analytical reagent CaO as raw materials. Two calculation methods of CaO addition amount based on binary basicity (basicity method) and n(Fe
2
O
3
)/n(CaO) (mole ratio method), respectively, were employed to evaluate the liquid phase fluidity (LPF) and the capability of calcium ferrite formation (CCFF) of iron ores. The results show that the rule of LPF of iron ores under the mole ratio method is different from that with basicity method. The LPF measured by basicity method has a linear positive correlation with the SiO
2
content, and there is no linear relationship between LPF and Al
2
O
3
content or mass loss on ignition, which are inconsistent with the results of the previous study. And the results of CCFF with low SiO
2
content (< 3 wt.%) or high SiO
2
content (> 7 wt.%) based on basicity method cannot reflect the true CCFF. The mole ratio method could successfully solve this problem by reducing the effect of CaO addition amount changes caused by SiO
2
content of iron ores.
2019 Vol. 26 (12): 1257-1264 [
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1265
Tian-xiong Wang, Cheng-yi Ding, Xue-wei Lv, Sen-wei Xuan, Gang Li
Reduction kinetics of MgO-doped calcium ferrites under CO–N
2
atmosphere
The effect of magnesia on calcium ferrite (CaO
.
Fe
2
O
3
) reduction by CO was examined by isothermal thermogravimetry. Samples of calcium ferrite added with 0, 2, 4, and 8 wt.% magnesia (abbreviated as CF, CF2M, CF4M, and CF8M) were prepared. Phase composition was analyzed by X-ray diffraction, and the results indicated that CF2M and CF4M are reduced to lower reduction degree and with lower apparent activation energy than CF; and CF8M with more MgO
.
Fe
2
O
3
is reduced to a lower degree and with more difficulty compared with CF. Reduction rate analysis revealed that CF, CF2M, CF4M, and CF8M reductions are all typical two-step reactions with the order of CF → CWF (CaO
.
FeO
.
Fe
2
O
3
) → Fe. The apparent reduction activation energies of CF, CF2M, CF4M, and CF8M are 46.89, 37.30, 17.30, and 29.20 kJ/mol, respectively. Sharp analysis depicted that CF2M, CF4M, and CF8M reductions are all described by 2D Avrami–Erofeev (A–E) equation (A
2
) in the whole process, while CF reduction is first expressed by A
2
and then by 3D A–E equation (A
3
). Different from shrinking core model, a new kinetic model for powdery samples reduction was proposed to illustrate the relationship among reduction rates, reduction routes, and model functions.
2019 Vol. 26 (12): 1265-1272 [
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1273
Jiang-yong He, Chong Zou, Jun-xue Zhao, Cheng Ma, Xiao-rui Zhang
Effects of microstructural evolutions of pyrolysis char and pulverized coal on kinetic parameters during combustion
Pyrolysis chars have potential as fuels for pulverized coal injection (PCI); however, their proper and efficient utilization requires evaluation of char combustion kinetics. The combustion characteristics of two chars (F-char and M-char) and two pulverized coals (H-PCI and P-PCI) were analyzed herein using thermogravimetric analysis–mass spectrometry. The apparent activation energy (E
a
) of the sample under non-isothermal combustion conditions was obtained using the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods, and the reaction mechanism for the fuels was established using the Malek method. Additionally, changes in the microscopic pore structure and carbon chemical structure of the fuels at different stages of combustion were characterized using N
2
adsorption and X-ray diffraction to analyze the relationship between microstructural evolution and E
a
. The results suggested that E
a
of the sample first rapidly decreased and then became stabilized during combustion. Compared with pulverized coals, the two chars presented more developed micro-scopic pore structure, less-ordered carbon chemical structure and lower E
a
during reaction. During combustion, the stacking height of the aromatic layer first decreased and then increased, whereas the specific surface area first increased and then decreased. The volatile content significantly influenced E
a
only during the initial stage of combustion. During the middle stage, E
a
was controlled more by the microscopic pore structure and the carbon chemical structure, and those influences disappeared in the later stage. The transition point of the structures affecting E
a
occurred at a combustion rate between 52.9% and 72.0%. In general, the microscopic pore structure and the carbon chemical structure influenced kinetic parameters more than the volatile content.
2019 Vol. 26 (12): 1273-1284 [
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1285
Zhi-yuan Chen, Ying-xia Qu, Christiaan Zeilstra, Jan Van Der Stel, Jilt Sietsma, Yong-xiang Yang
Prediction of density and volume variation of hematite ore particles during in-flight melting and reduction
HIsarna is a promising ironmaking technology to reduce CO
2
emission. Information of phase transformation is essential for reaction analysis of the cyclone reactor of the HIsarna process. In addition, data of density and volume of the ore particles are necessary for estimation of the residence time of the particles in the cyclone reactor. Phase transformation of iron ore particles was experimentally studied in a drop-tube furnace under simulated cyclone conditions and compared with thermodynamic calculation. During the pre-reduction process inside the reactor, the mineralogy of iron ore particles transforms sequentially from hematite to sub-oxides. The density changes of the particles during the melting and reduction can be predicted based on the phase composition and temperature. Therefore, density models in the studies were evaluated with reported experimental data of slag. As a result, a more reliable density model was developed to calculate the density of the formed slag containing mainly FeO–Fe
2
O
3
. The density and volume of the partially reduced ore particles or melt droplets were estimated based on this model. The results show that the density of the ore particles decreases by 15.1% at most along the progressive reduction process. Furthermore, the model results also indicate that heating, melting and reduction of the ore could lead to 6.63%–9.37% swelling of the particles, which is mostly contributed by thermal expansion. It would result in corresponding variation in velocity of the ore particles or melt droplets during the flight inside the reactor.
2019 Vol. 26 (12): 1285-1294 [
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1295
Jing Gu, Li Wang, De-hong Xia, Feng Zhang, Zhao-dong Qi, Wen-qing Ao
Experimental study and industrial demonstration on utilization of Fe, Ti and V from vanadium-bearing titanomagnetite ore sands
In order to achieve highly efficient utilization of three valuable elements Fe, Ti and V simultaneously from vanadium-bearing titanomagnetite ore sands, an improved carbothermic reduction method was proposed and verified in both laboratory scale and industrial test-bed scale. The method combined the process of direct reduction and the process of further reduction and separation. Particularly, pulverized coal injection was introduced. In experimental tests, the effects of parameters such as carbon content in briquette, reduction duration and reduction temperature on the contents of metallic Fe and FeO as well as Fe metallization rate were analyzed. Experimental results indicated that Fe metallization rate in the carbon-containing briquette could reach 75.83%. In the industrial test-bed tests, the effects of carbon content in briquette, reduction duration and reduction temperature were also investigated, respectively. In addition, processes with and without pulverized coal injection were tested. The comparative analysis indicated that the content of TiO
2
in titaniferous slag was increased by applying pulverized coal injection, and it can reach 82.5 wt.%. Meanwhile, the energy performance analysis showed that the equivalent electricity consumption of the test-bed dropped significantly to 2071 kWh per ton of slag, about 26.0% less than that of traditional method. Moreover, the investment payback of the test-bed is 3.4 years. Both experiments and industrial test-bed tests demonstrated that the proposed method has the advantages of highly efficient utilization, high energy efficiency as well as good economic performance.
2019 Vol. 26 (12): 1295-1303 [
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1304
Wang-jun Peng, Guang-xin Wu, Yi Cheng, Jie-yu Zhang
Interface reaction of high-strength low-alloy steel with Al–43.4Zn–1.6Si (wt.%) metallic coating
The microstructure, elemental distribution, phase composition, and thickness of intermetallic layers between high-strength low-alloy steel (H420)/mild carbon steel (DC51) and Al–43.4Zn–1.6Si (wt.%) (galvalume, GL) alloy were comparatively investigated. The experimental results reveal that the interfacial reaction layer was composed of Fe
2
Al
5
, Fe
4
Al
13
, and Al
8
Fe
2
Si intermetallic compounds. Moreover, the growth curves of the Fe
2
Al
5
and Fe
4
Al
13
intermetallic layers fit the parabolic law well, and the total thickness of the intermetallic layers of H420 + GL was almost the same as that of DC51 + GL. However, the thickness of the Fe
2
Al
5
layer in H420 + GL was thinner than that in DC51 + GL. In addition, first-principle calculations were performed to explore the effect of Mn on the growth of the Fe
2
Al
5
intermetallic phase, and the results indicate that Mn substitution in Fe
2
Al
5
removes electronic charge from the Al atoms, thus decreasing the thickness of the Fe
2
Al
5
interface layer.
2019 Vol. 26 (12): 1304-1314 [
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1315
Zhao-liang Li, Kui Xiao, Chao-fang Dong, Xue-qun Cheng, Wei Xue, Wei Yu
Atmospheric corrosion behavior of low-alloy steels in a tropical marine environment
The corrosion behavior of carbon steels and weathering steels was investigated in a tropical marine environment. And both exhibited similar corrosion weight-loss behavior in tropical marine environments. Corrosion weight loss (W) as a function of exposure time (t) can be calculated using the power function, W = At
n
. The values of the initial corrosion rate, A, and corrosion tendency, n, can be easily obtained by taking the logarithm of the power equation. However, the corrosion rust-layer structure of the two materials was quite different. The rust layer of carbon steel presents a single-layer structure. Meanwhile, the rust layer of weathering steel exhibits a single-layer structure after exposure for about 24 months and then gradually evolves into a double-layer structure. The main corrosion products of the steels are β-FeOOH, γ-FeOOH, and Fe
3
O
4
in the initial stage of exposure. In the rust layers, α-FeOOH appeared after 12 months of exposure.
2019 Vol. 26 (12): 1315-1328 [
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1329
Xiao-hui Wang, Jian Kang, Yun-jie Li, Guo Yuan, R.D.K. Misra, Guo-dong Wang
Effect of deformation parameters in unrecrystallization range on microstructural characteristics in Al-bearing hot-rolled TRIP steel
The scanning electron microscope, transmission electron microscope, optical microscope, X-ray diffraction and hardness tests were used to investigate the effect of deformation parameters in unrecrystallization range on microstructural characteristics in Al-bearing hot-rolled transformation-induced plasticity steel. The thermomechanical-controlled processing was carried out with thermomechanical simulation machine, and the samples were compressed to compression strains of 0, 0.15, 0.25 and 0.35 at compression temperatures of 850, 900 and 950 °C. The results showed that the volume fraction of polygonal ferrite increased with the increasing compression strain, while the volume fraction of retained austenite reached the maximum value at compression strain of 0.25. The volume fraction of polygonal ferrite decreased with the increasing compression temperature, whereas the volume fraction of retained austenite possessed the maximum value at compression temperature of 850 °C. Some granular retained austenite was present in uncompressed samples, and some pearlite appeared at large compression strain, while the hardness of the samples exhibited the similar variation tendency to the volume fraction of retained austenite.
2019 Vol. 26 (12): 1329-1339 [
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1340
Bin-zhou Li, Chang-sheng Li, Xin Jin, Jian Zhang
Effect of M–A constituents formed in thermo-mechanical controlled process on toughness of 20CrNi2MoV steel
The effect of martensite–austenite (M–A) constituents formed in thermo-mechanical controlled process on impact toughness of 20CrNi2MoV steel was investigated. The variation in fraction, size and morphology of M–A constituent and its effect on toughness under different cooling rates were carried out. The result shows that there was no significant change in the fraction of M–A constituent under different cooling rates, but the distribution and size of M–A constituent were greatly influenced by cooling rate, which consequently influenced toughness. The amount of large blocky M–A constituents decreased from 4.7% to 1.7%, while that of elongated M–A constituents increased from 3.8% to 8.6% with the coolingrate increasing from 7 to 26 °C/s, and the corresponding impact energy decreased from 132 to 84 J. The deterioration of impact toughness could be related to the increase in the elongated M–A constituents. The elongated M–A constituents existing along the prior austenite grain boundaries in samples of 26 °C/s could easily lead to the formation of cleavage crack, which then results in the lower crack initiation energy than that of low cooling rate samples.
2019 Vol. 26 (12): 1340-1349 [
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1350
Mohammed Ali, David Porter, Jukka Komi, Mamdouh Eissa, Hoda El Faramawy, Taha Mattar
Effect of cooling rate and composition on microstructure and mechanical properties of ultrahigh-strength steels
The influence of cooling rate on the microstructure and mechanical properties of two new ultrahigh-strength steels (UHSSs) with different levels of C, Cr and Ni has been evaluated for the as-cooled and untempered condition. One UHSS had higher contents of C and Cr, while the other one had a higher Ni content. On the basis of dilatation curves, microstructures, macrohardness and microhardness, continuous cooling transformation diagrams were constructed as a guide to heat treatment possibilities. Cooling rates (CRs) of 60, 1 and 0.01 °C/s were selected for more detailed investigations. Microstructural characterization was made by laser scanning confocal microscopy, field emission scanning electron microscopy combined with electron backscatter diffraction, electron probe microanalysis and X-ray diffraction. Mechanical properties were characterized using macrohardness, tensile and Charpy V-notch impact tests. UHSS with the higher C and Cr contents showed lower transformation temperatures and slower bainite formation kinetics than that with the higher Ni content. Higher cooling rates led to lower volume fractions and carbon contents of retained austenite together with finer prior austenite grain size, as well as effective final grain size and lath size. These changes were accompanied by higher yield and tensile strengths. The best combinations of strength and toughness were obtained with martensitic microstructures and by avoiding the formation of granular bainite accompanied by proeutectoid carbides at low CR. For the cooling rates studied, UHSS with the higher C and Cr contents showed the higher hardness and strength but at the cost of toughness.
2019 Vol. 26 (12): 1350-1365 [
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1366
Yen-chun Chen, Chien-ping Ju, Jiin-huey Chern Lin
Effects of solution treatment and cold rolling on structure and tensile properties of hot-rolled Ti–7.5Mo alloy
The effects of solution treatment (ST) and cold rolling (CR) on structure and tensile properties of a heavily hot-rolled (HR) Ti–7.5Mo alloy were investigated. Experimental results indicated that, after HR with a one-pass 65% reduction in thickness, the pores in as-received samples substantially disappeared, the misorientation angle distribution became broader, and grain texture shifted toward <10-10>. Post-HR ST produced an orthorhombic α''-phase with fine needle-type morphology and caused misorientation to narrow down to 55°–65° with substantially random texture; post-ST CR caused misorientation shift toward high-angle side and texture toward <10-10> and <2-1-10>. With an increase in reduction in thickness,
α'
(102) intensity increased at the expense of two adjacent (112)/(022) α''-peaks. All X-ray diffraction, metallography and electron backscattered diffraction on scanning electron microscope results indicated that pre-ST HR did not affect the formation of the desired low-modulus α''-phase when the alloy was subsequently solution-treated. From a practical point of view, the most optimal tensile properties may be found in the sample solution-treated at 900 °C for 30 min and cold-rolled by a 20% reduction in thickness, which demonstrated a yield strength of 924 MPa, an ultimate tensile strength of 933 MPa, a tensile modulus of 73 GPa, and an elongation of 26%.
2019 Vol. 26 (12): 1366-1375 [
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1376
Zheng-wei Gu, Lei Jia, Xin Li, Li-juan Zhu, Hong Xu, Ge Yu
Stretch bending defect control of L-section SUS301L stainless-steel components with variable contour curvatures
The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated. The causes of defects such as wrinkling, section distortion, and poor contour accuracy were analysed, and the corresponding control methods were proposed. The simulation results demonstrated that wrinkling in the small-arc segment could be eliminated by setting the die clearance and adjusting the elongation reasonably. Owing to the sidewall shrinkage of the profile in the process of stretch bending, the die groove depth was correspondingly reduced. Each section of the profile was effectively supported by the bottom of the die groove, and the section distortion could be controlled. Springback was the main reason for the poor contour accuracy, which could be compensated by modifying the die surface based on the springback value. Using the above defect control methods, forming experiments were performed on a new type of stretch bending die with variable die clearance and groove depth developed in this work. Finally, high-quality components were obtained, which verified the efficacy of the defect control methods.
2019 Vol. 26 (12): 1376-1384 [
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钢铁研究学报(英文版)
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