JOURNAL OF IRON AND STEEL RESEARCH INTERNATIONAL

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	2016 Vol. 23 No. 5
	Published: 2016-05-15

Metallurgy and Metal Working

	409	Shuang-yin CHEN,Xiao-jiao FU,Man-sheng CHU,Xi-zhe LI,Zheng-gen LIU,Jue TANG
		Carbothermic Reduction Mechanism of Vanadium-titanium Magnetite
		To achieve the high-efficiency utilization of vanadium-titanium magnetite (VTM), reduction experiments were conducted to determine the carbothermic reduction mechanism of VTM. Effects of volatile matter, temperature, time, and carbon ratio (molar ratio of fixed carbon in coal to oxygen in iron oxides of VTM) on reduction degree were investigated. Results show that reduction degree increases with increasing volatile matter in coal, temperature, time, and carbon ratio. Phase transformation, microstructure, and reduction path were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and FactSage 6.0. The thermoravimetry-differential scanning calorimetry-quadrupole mass spectrometer method was used for kinetic analysis of the main reduction process. Results indicate that the kinetic mechanism follows the principle of random nucleation and growth (n=4), and the activation energy values at 600-900 and 900-1350 ℃ are 88.7 and 295.5 kJ/mol, respectively.
		2016 Vol. 23 (5): 409-414 [Abstract] ( 461 ) [HTML 0KB] [PDF 0KB] ( 13 )

	415	Xiao-bing LI,Yi MIN,Zhe YU,Cheng-jun LIU,Mao-fa JIANG
		Effect of Mg Addition on Nucleation of Intra-granular Acicular Ferrite in Al-killed Low Carbon Steel
		To verify the formation behaviors and mechanisms of intra-granular acicular ferrite (IAF) grains nucleated by Mg-Al-O in low carbon steel, the steels containing different Mg contents were refined in a vacuum induction furnace. The effect of Mg addition on the formation of IAF structure in Al-killed low carbon steel was investigated by optical microscope (OM) and scanning electron microscope with energy dispersive X-ray spectroscope (SEM-EDX). It reveals that the IAFs are only detected in Mg-added steels, and the volume fraction of IAF increases with the Mg concentration from 8×10-6 to 26×10-6. It shows that not only the MgO-Al2O3-MnS and MgO-Al2O3-P2O5 particles are the effective nucleation sites for IAF, but also the pure MgO·Al2O3 phase can promote the ferrite nucleation. A Mn-depletion zone (MDZ) is characterized adjacent to the MgO-Al2O3-MnS, which is believed to be one of the possible mechanisms to explain the IAF nucleation. The MDZ around the MgO-Al2O3-MnS inclusion would be induced by the MnS precipitation on the inclusion. It seems that the ability of Mg-containing inclusions to induce the nucleation of ferrite might be attributed to a new mechanism, i.e., the P-rich zone formed on a few Mg-Al-O inclusions might be another factor for promoting the IAF formation.
		2016 Vol. 23 (5): 415-421 [Abstract] ( 528 ) [HTML 0KB] [PDF 0KB] ( 19 )

	422	Bo WANG,Xiao-dong WANG,Yuri KOLESNIKOV,San ZHANG,Yan-qing TAN,Xian-zhao NA
		An Experimental Prototype of an Innovative Fluid-driven Electromagnetic Stirring Technique
		A new electromagnetic stirring technique that is driven by hydrodynamic forces was presented. This technique offers the following advantages. First, the stirrer can be immersed in the liquid metal, thereby significantly increasing the penetration depth of the electromagnetic forces and significantly improving the stirring efficiency; thus, this technique is particularly suitable for large-scale liquid metal. Second, under certain conditions, this technique can overcome difficulties that are encountered with traditional stirrers, such as accessing regions that are difficult to reach in working spaces with complex or narrow shapes. This stirrer also has a simpler structure than a traditional stirrer; thus, the design can be easily modified, and no external power supply is required. An experimental prototype was also presented for controlling the fluid flow rate, thereby controlling the electromagnetic force and velocity field of the driven liquid metal. The velocity distribution in a liquid GaInSn alloy under fluid-driven electromagnetic stirring was quantitatively measured using ultrasonic Doppler velocimetry (UDV). The primary results show that a remarkable velocity field has been achieved and that fluid-driven electromagnetic stirring is an effective means of stirring liquid metal. Finally, the potential applications of this technique in industry, along with key challenges, were discussed.
		2016 Vol. 23 (5): 422-427 [Abstract] ( 473 ) [HTML 0KB] [PDF 0KB] ( 22 )

	428	En-xia GAO,Ti-chang SUN,Zhi-guo LIU,Chao GENG,Cheng-yan XU
		Effect of Sodium Sulfate on Direct Reduction of Beach Titanomagnetite for Separation of Iron and Titanium
		The effect of sodium sulfate on direct reduction of beach titanomagnetite, followed by magnetic separation, to separate iron and titanium was investigated. Direct reduced iron (DRI) with a high Fe content, low TiO2 content and low iron recovery was obtained after adding sodium sulfate. When the sodium sulfate dosage was increased from 0 to 10 mass%, the Fe content of the DRI increased from 90.00 mass% to 93.55 mass% and the TiO2 content decreased from 1.27 mass% to 0.70 mass%. The reduction mechanism of sodium sulfate was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). Results revealed that the metallic iron grains in the reduced ore with sodium sulfate were larger than those in the ore without sodium sulfate. Sodium sulfate promoted the migration of iron as well as the accumulation and growth of metallic iron grains by low-melting-point carnegieite and troilite formed in the redox system. Low-melting-point carnegieite decreased the melting point of the system and then promoted liquefaction. Troilite could decrease the surface tension and melting point of metallic iron grains.
		2016 Vol. 23 (5): 428-433 [Abstract] ( 573 ) [HTML 0KB] [PDF 0KB] ( 33 )

	434	Gui-ming YANG,Xiao-hui FAN,Xu-ling CHEN,Xiao-xian HUANG,Zong-ping LI
		Intelligent Control of Grate-kiln-cooler Process of Iron Ore Pellets Using a Combination of Expert System Approach and Takagi-Sugeno Fuzzy Model
		Grate-kiln-cooler has become a major process of producing iron ore pellets in China. Due to the diversity of the raw materials used and the multi-device multi-variable characteristics, this process still encounters with control problem. An attempt was proposed to deal with this issue. The three-device-integrated feature of the process was firstly analyzed to obtain control strategy, and then an intelligent control system using a combination of expert system approach and Takagi-Sugeno (T-S) fuzzy model was developed. Expert system approach was used to diagnose and remedy the abnormal conditions, while T-S fuzzy model was used to stabilize the thermal state. In the construction of T-S fuzzy rules, antecedents were identified by fuzzy c-mean clustering algorithm incorporated with subtractive clustering algorithm, and consequent parameters were identified by recursive least square algorithm. The control system was applied in a Chinese pelletizing plant and the application results demonstrated its effectiveness of stabilizing the thermal states within three devices.
		2016 Vol. 23 (5): 434-441 [Abstract] ( 473 ) [HTML 0KB] [PDF 0KB] ( 9 )

Material

	442	Ye XIA,Xi-nan LUO,Xiao-yan ZHONG,Hui-hua ZHOU,Cun-yu WANG,Jie SHI
		In-situ TEM Observation of Cementite Coarsening Behavior of 5Mn Steel during Tempering
		The cementite formation and coarsening behaviors of 0.2 mass% C-5 mass% Mn steel during tempering at 500 ℃ were investigated by in-situ transmission electron microscope (TEM). In-situ TEM observation showed uniform distribution of cementite particles at the early stage of tempering in the rapidly heated (500 ℃/s) sample. Elemental analysis confirmed that the cementite growth was dominated by Mn diffusion. During the cementite growth, the coarsening behavior of intragranular cementite was significantly controlled by the matrix diffusion, while that of the intergranular cementite was mainly governed by the boundary diffusion. The in-situ TEM observation revealed that the dislocation pipe diffusion of Mn took place during tempering, which accelerated the Mn diffusion between cementite particles. The coarsening rates of individual cementite particles were calculated based on the in-situ TEM observation.
		2016 Vol. 23 (5): 442-446 [Abstract] ( 532 ) [HTML 0KB] [PDF 0KB] ( 29 )

	447	Jian-jun ZHENG,Chang-sheng LI,Shuai HE,Ban CAI,Yan-lei SONG
		Deformation Behavior of Fe-36Ni Steel during Cryogenic (123-173 K) Rolling
		Microstructural evolution and mechanical properties of cryogenic rolled Fe-36Ni steel were investigated. The annealed Fe-36Ni steel was rolled at cryogenic temperature (123-173 K) with 20%-90% rolling reduction in thickness. The deformation process was accompanied by twinning at cryogenic temperature, and the mean thickness of deformation twins was about 200 nm with 20% rolling reduction. When the rolling reduction was above 40%, twinning was suppressed due to the stress concentration in the tested steel. Deformation microstructure of Fe-36Ni steel consisted of both twin boundaries and dislocations by cryogenic rolling (CR), while it only contained dislocations after rolling at room temperature (RT). The tensile strength of Fe-36Ni steel was improved to 930 MPa after 90% reduction at cryogenic temperature, while the tensile strength after 90% reduction at RT was only 760 MPa. More dislocations could be produced as the nucleation sites of recrystallization during CR process.
		2016 Vol. 23 (5): 447-452 [Abstract] ( 558 ) [HTML 0KB] [PDF 0KB] ( 14 )

	453	Hui LI,Yong-feng LIANG,Feng YE
		Evolution of Microstructure and Ordering in Rolling Process of Fe-6.5 mass% Si Alloy
		rolling process; microstructure; ordering; Fe-6.5 mass% Si alloy
		2016 Vol. 23 (5): 453-458 [Abstract] ( 454 ) [HTML 0KB] [PDF 0KB] ( 25 )

	459	Xiao-ping DONG,Yan-rong PANG,Li-ying YANG,Qing WANG,Zhi-yuan LI
		Effect of Spark Plasma Sintering Temperature on Electrochemical Properties of La0.82Mg0.18Ni3.50Co0.15 Alloy
		Electrochemical properties of La0.82Mg0.18Ni3.50Co0.15 alloys synthesized by spark plasma sintering (SPS) were investigated based on the electrochemical measurements, physical parameters and microstructure observation. The sintering behavior of La0.82Mg0.18Ni3.50Co0.15 alloys at the temperatures of 900, 950 and 1000 ℃ is characterized by four stages, i.e., initial slight shrinkage, expansion, abrupt shrinkage and slight expansion. The maximum shrinkage displacement increases with increasing sintering temperature. All of the alloys consist of (La,Mg)2(Ni,Co)7 phase; additionally, temperatures of 900 and 950 ℃ are beneficial to the formation of (La,Mg)(Ni,Co)3 phase, whereas the LaNi5 phase is easy to form in the alloy synthesized by SPS at 1000 ℃. The electrochemical measurements indicate an evident change of the electrochemical performance of the alloys associated with increasing the sintering temperature. The discharge capacity of the alloys first increases and then decreases as sintering temperature rises, whereas their cycle stability clearly grows all the time. Furthermore, the charging-discharging potential difference and discharging efficiency both demonstrate that the electrochemical properties of the alloy electrodes first augment and then decline with increasing sintering temperature.
		2016 Vol. 23 (5): 459-465 [Abstract] ( 492 ) [HTML 0KB] [PDF 0KB] ( 30 )

	466	Ding-qian DONG,,Fei CHEN,Zhen-shan CUI
		Static Recrystallization Behavior of SA508-III Steel during Hot Deformation
		The static recrystallization behavior of SA508-III steel was investigated by isothermal double-hit hot compression tests at the deformation temperature of 950-1250 ℃, the strain rate of 0.01-1 s-1, and the inter-pass time of 1-300 s. The effects of deformation parameters, including forming temperature, strain rate, degree of deformation (pre-strain) and initial austenite grain size, on the softening kinetics were analyzed. Experimental results show that static recrystallization kinetics is strongly dependent on deformation temperature and degree of deformation, while less affected by the strain rate and initial grain size. The kinetics and microstructural evolution equations of static recrystallization for SA508-III steel were developed to predict the softening behavior and the statically recrystallized grain size, respectively. Based on the comparison between the experimental and predicted results, it is found that the established equations can give a reasonable estimate of the static softening behavior for SA508-III steel.
		2016 Vol. 23 (5): 466-474 [Abstract] ( 513 ) [HTML 0KB] [PDF 0KB] ( 20 )

	475	Wei-jun HUI,Cheng-wei SHAO,Yong-jian ZHANG,Si-lian CHEN,Han DONG
		Influence of Vanadium on Fracture Splitting Property of Medium Carbon Steel
		The fracture splitting property of medium carbon steel 37MnSiS microalloyed with V up to 0.45% was investigated by using simulated fracture splitting test, for the development of new crackable medium carbon steel to manufacture high performance connecting rod. Conventional high carbon steel C70S6 was used for comparison. The results show that the volume fraction of both ferrite and V-rich M(C,N) particles increases, and the pearlite interlamellar spacing decreases with increasing V content, which in turn results in gradual increase of strength and decrease of ductility and impact energy. The fracture splitting property of the tested steel could be improved significantly due to the increase of V content mainly through the precipitation hardening mechanism of fine M(C,N) precipitates. The fraction of brittle cleavage fracture in the crack initiation area increases noticeably with increasing V content and full brittle cleavage fracture surface could be obtained when V content was increased to 0.45%. It is concluded that medium carbon steel with V content higher than about 0.28% possesses not only comparable or even higher mechanical properties with those of conventional steel C70S6, but also excellent fracture splitting property, and therefore, is more suitable to fabricate high performance fracture splitting connecting rod.
		2016 Vol. 23 (5): 475-483 [Abstract] ( 564 ) [HTML 0KB] [PDF 0KB] ( 17 )

	484	Hong-xiao CHI,,,Dang-shen MA,Hui-xia XU,Wang-long ZHU,Jian-qing JIANG
		Phase Transformation of a Cold Work Tool Steel during Tempering
		The hardness and microstructure evolution of a 8% Cr cold work tool steel during tempering for 40 h were investigated. Transmission electron microscope examinations showed that M3C carbides precipitated from supersaturated martensite after tempering at 350 ℃. When the tempering temperature was higher than 520 ℃, the M23C6 carbides precipitated to substitute for M3C carbides. After ageing at the temperature of 520 ℃ for 40 h, it was observed that very fine and dense secondary Mo2C precipitates were precipitated. Thus, it can be concluded that the early stage of Mo2C-carbide precipitation is like to be Gunier-Preston (G-P) zone formed by ［Mo-C］ segregation group which is responsible for the secondary hardening peak at 520 ℃. Overageing at 700 ℃ resulted in recovery of martensitic microstructure and precipitation of M23C6 carbides. When ageing at 700 ℃ for more than 20 h, recrystallization occurred, which resulted in a change of the matrix morphology from martensitic plates to equiaxed ferrite. It was noticed that the size of recrystallized grain/subgrain was very fine, which was attributed to the pinning effect of M23C6 precipitates.
		2016 Vol. 23 (5): 484-488 [Abstract] ( 644 ) [HTML 0KB] [PDF 0KB] ( 21 )

	489	Cun-jiang TANG,Shi-long LIU,Cheng-jia SHANG
		Micromechanical Behavior and Failure Mechanism of F/B Multi-phase High Performance Steel
		The deformation and micro-voids formation mechanisms in ferrite/bainite (F/B) multi-phase steel with the volume fraction of bainite less than 50% were studied by numerical simulation and experimental observation. The results show that the micro-strain concentrates at the soft/hard phase (F/B) interface in the multi-phase steel, which should be correlated with the mechanism of incoordinate deformation. During the necking of the steel, the micro-voids initially form around the F/B interface, which also form in ferrite and bainite with the severe strain. The micro-voids in bainite are more dense and finer than those in ferrite. The failure mechanism of bainite is the coalescence of micro-voids, and the failure mechanism of ferrite is the growth and tearing of micro-voids. Due to the different failure mechanisms of ferrite and bainite, a suitable part of soft phase would be beneficial to the capability of anti-failure of F/B multi-phase steel during the ductile fracture.
		2016 Vol. 23 (5): 489-494 [Abstract] ( 475 ) [HTML 0KB] [PDF 0KB] ( 44 )

	495	Biao JU,Hui-bin WU,Di TANG,Ning DANG
		Characterization of (Nb,Ti,Mo)C Precipitates in an Ultrahigh Strength Martensitic Steel
		A study on ultrahigh strength steel plate subjected to novel thermo-mechanical control process was presented. The mechanical properties examination showed that the investigated steel exhibited excellent combination of ultra-high strength (2200 MPa) and toughness (26 J). The microstructure of the experimental steel was observed by scanning electron microscope and transmission electron microscope. Desired martensitic lath with width of about 180-250 nm was obtained. Nanostructured carbide precipitates with sizes of 20-50 nm, which contained Nb, Ti and Mo, were observed in the lath martensitic microstructure, and confirmed to be MC-type carbides with B1 structure by means of selected area electron diffraction. The compositional characteristics revealed by energy dispersive X-ray spectrometer mapping implied that the carbide forming elements Nb, Ti and Mo distributed in the precipitates evenly. Three-dimensional atom probe tomography reconstruction further indicated that Mo incorporated into the precipitates without enrichment in the carbide-matrix interface and probably substituted for Nb and Ti to form the (Nb,Ti,Mo)C carbides.
		2016 Vol. 23 (5): 495-500 [Abstract] ( 503 ) [HTML 0KB] [PDF 0KB] ( 60 )

	501	Lin LU,Long-gang HOU,Hua CUI,Jin-feng HUANG,Yong-an ZHANG,Ji-shan ZHANG
		Hot Deformation Behavior and Processing Map of Spray Formed M3∶2 High Speed Steel
		Hot deformation behavior of a new type of M3∶2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1150 ℃ and strain rate of 0.001-10 s-1. A comprehensive constitutive equation was obtained, which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses, which were calculated by the comprehensive constitutive equation, agreed well with the test data at low strain rates (≤1 s-1). The material constant (α), stress exponent (n) and the hot deformation activation energy (QHW) of the new steel were 0.00615 MPa-1, 4.81 and 546 kJ·mol-1, respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain (T=1050-1150 ℃, =0.01-0.1 s-1) with about 33% peak efficiency of power dissipation (η). Cracks was expected in two domains at either lower temperatures (＜1000 ℃) or low strain rates (0.001 s-1) with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s-1 at all testing temperatures.
		2016 Vol. 23 (5): 501-508 [Abstract] ( 463 ) [HTML 0KB] [PDF 0KB] ( 35 )

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