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microstructural evolution of Mg9AlZnY alloy with vibration in lost foam casting during semi-solid isothermal heat treatment

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中国有色金属学会会刊：英文版 2010年第S3期20卷 768-773页

作者：赵忠樊自田蒋文明董选普 State Key Laboratory of Material Processing and Die & Mould Technology Huazhong University of Science and Technology

The nearly equiaxed grains of Mg9AlZnY alloy were obtained by vibrating solidification in lost foam casting(LFC) and the microstructure of Mg9AlZnY alloy was analyzed.On this basis,the morphology and size of α-Mg grains fabricated by semi-solid isothermal heat treatment(SSIT) at 530 ℃ and 570 ℃ holding different time were studied.The results show that the main constituent phases of Mg9AlZnY alloy are α-Mg,β-Mg17Al12 and Al2Y,and the Y can greatly refine α-Mg grains.The distribution of α-Mg grains equivalent diameters between 20 and 100 μm is up to 87%,and the average roundness of α-Mg grains reaches 1.37 in the specimen obtained at 570 ℃ and holding time 60 min.According to the analysis of solidification kinetics and thermodynamic,binary eutectic with low melting point melts firstly on SSIT process.As the liquid fraction increases with the solute diffusibility,both of the shape and size of α-Mg grains change ceaselessly.When the liquid fraction reaches equilibrium,the α-Mg grains are gradually spheroidized under the interfacial tension,and then the α-Mg grains begin to combine and grow.Evolution of α-Mg dendritic grains on SSIT process is obviously different from that of equiaxed grains.

关键词： lost foam casting(LFC) semi-solid isothermal heat treatment(SSIT) microstructural evolution magnesium alloy

microstructural EVOLUTION DURING COMBUSTION SYNTHESIS OF TiC-Fe CERMET

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中国有色金属学会会刊：英文版 1999年第2期9卷 82-87页

作者： Quncheng, Fan Huifen, Chai Zhihao, Jin Xi'an Jiaotong Univ Xi'an China

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关键词： microstructural evolutionTiCFe cermetcombustion synthesis

microstructural features and precipitation behavior of Ti,Nb and V microalloyed steel during isothermal processing

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Journal of Iron and Steel Research(International) 2019年第1期26卷 102-111页

作者： Qi Zhou Zhuang Li Zhan-shan Wei Di Wu Jin-yu Li Zhen-yao Shao School of Environment and Chenlical Engineering Shenyang Ligong UniversityShenyang 110159LiaoningChina College of Materials Science and Engineering Shenyang Aerospace UniversityShenyang 110136LiaoningChina State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110004LiaoningChina

Thermal simulations of Ti,Nb and V microalloyed steel were conducled using a thermomechanical simulator,and the microstructural evolution and the precipitation behavior during isothermal processing were analyzed.The results show that with increasing holding time,the microstructural constituents change from the martensite and bainitic ferrites to granular bainite and polygonal ferrite.The maximum hardness is obtained for the specimen after isothermal holding for 5s due to the martensite strengthening effect.The hardness of the specimen decreases after isothermal holding for 10s,because the strengthening contribution of fine dispersed precipitates becomes weaker.The hardness values of the specimens increase and then remain high after isothermal holding for 60 and 600s.This is attributed to the contribution of the interphase precipitation hardening to the hardness of the studied steel.The precipitates in the specimen are coarsened after isothermal holding for 3600s,even though the coarsening is not remarkable.These precipitates are fee(Ti.Nb)(N.C)particles and belong to the MX-type precipitates.The beneficial effects of precipitation strengthening are lost.The hardness decreases to a minimum hardness value due to the presence of large amounts of polygonal ferrite after isothermal holding for 3600s.Relatively coarse precipitates are the primary origin of the hardness decrease.

关键词： Microalloyed steel Isothermal holding time microstructural constituent Precipitation Hardness

microstructural evolution of a steam-turbine rotor subjected to a water-quenching process: numerical simulation and experimental verification

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Advances in Manufacturing 2019年第1期7卷 84-104页

作者： Chuan Wu Qing-Ling Meng National-Local Joint Engineering Laboratory of Intelligent Manufacturing Oriented Automobile Die & Mould College of Mechanical Engineering Tianjin University of Technology and Education Tianjin 300222 People's Republic of China College of Civil Engineering Tianjin University Tianjin 300072 People's Republic of China

Cr-Ni-Mo-V steam-turbine rotors have been widely used as key components in power plants. In this study, a coupled thermomechano-metallurgical model was proposed to simulate the phase transformation and transformation-induced plasticity (TRIP) of a 30Cr2Ni4MoV steam-turbine rotor during a water-quenching process, which was solved using a user defined material mechanical behavior (UMAT) subroutine in ABAQUS. The thermal dilation, heat generation from plastic work, transformation latent heat, phase transformation kinetics, and TRIP were considered in the model. The thermomechanical portion of the model was used to predict the evolution of temperature, strain, and residual stress in the rotor. The phase transformation that occurred during the quenching process was considered. Constitutive models of phase transformations (austenite to pearlite, austenite to bainite, and austenite to martensite) and TRIP were developed. Experimental data were adopted and compared with the predicted results to verify the accuracy of the model. This demonstrates that the model is reliable and accurate. Then, the model was utilized to predict the temperature variation, dimensional change, minimum austenitization time, residual stress, TRIP, and volume fractions of each phase. It is concluded that this model can be a useful computational tool in the design of heat-treatment routines of steam-turbine rotors.

关键词： Thermomechano-metallurgical model user defined material mechanical behavior (UMAT) subroutine microstructural evolution Transformation-induced plasticity (TRIP)- Residual stress

microstructural evolution during reheating of A356 machining chips at semisolid state

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矿物冶金与材料学报：英文版 2017年第8期24卷 891-900页

作者： Fang Wang Wen-qiang Zhang Wen-long Xiao Hiroshi Yamagata Chao-li Ma Key Laboratory of Aerospace Advanced Materials and Performance of the Ministry of Education School of Materials Science and Engineering Beihang University Center for Advanced Die Engineering and Technology Gifu University

The microstructural evolution of A356 machining chips in the semisolid state was studied at different temperatures and holding times. The results showed that the elongated α-Al grains first recrystallized in the semisolid state and then became globular with a high shape factor(SF). Both the temperature and the holding time clearly affected the grain size and SF. When the heating temperature or holding time was increased, the grain size and SF gradually increased and finally became stable. Moreover, the Vickers hardness of primary α-Al grains gradually decreased with increasing heating temperature. The optimal slurry for semisolid processing, with a good combination of grain size and SF, was obtained when the chips were held at 600℃ for 15 min. The semisolid slurry of A356 chips exhibited a lower coarsening rate of α-Al grains than those produced by most of the conventional semisolid processes. The coarsening coefficient was determined to be 436 μm^3·s^(-1) on the basis of the linear Lifshitz–Slyozov–Wagner(LSW) relationship.

关键词： semisolid slurry aluminum chips microstructural evolution grain coarsening microhardness

microstructural evolution and performance of carbon fiber-toughened ZrB_2 ceramics with SiC or ZrSi_2 additive

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Journal of Advanced Ceramics 2018年第4期7卷 343-351页

作者： Kaixuan GUI Fangyu LIU Gang WANG Zhongjia HUANG Ping HU School of Materials Science and Engineering Anhui Polytechnic University National Key Laboratory of Science and Technology on Advanced Composites in Special Environments Harbin Institute of Technology

ZrB_2–SiC/ZrSi_2 ceramics containing 30 vol% carbon fiber(Cf) additive were fabricated by hot pressing at low temperature(1500 ℃) using submicron ZrB_2 powders, and their microstructural evolution and performance were investigated. The addition of SiC or ZrSi_2 significantly reduced the onset sintering temperature and enhanced the densification of ZrB_2. ZrB_2–ZrSi_2–Cf showed poor performance owing to the serious fiber degradation, while the fiber degradation was effectively inhibited in ZrB_2–SiC–Cf resulting in high fracture toughness, substantial fiber pull-out, and non-brittle fracture mode for such material. The critical thermal shock temperature difference of ZrB_2–SiC–Cf was up to 741 ℃, significantly higher than those of ZrB_2–SiC/ZrSi_2 and ZrB_2–ZrSi_2–Cf. Moreover, this composite displayed a good oxidation resistance at 1500 ℃ in air.

关键词： carbon fibers microstructural evolution hot pressing thermal shock resistance oxidation

Post-mortem microstructural Study of Aluminous Refractory Brick Used in Channels of Blast Furnaces

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China's Refractories 2023年第1期32卷 40-43页

作者： Ana Valéria de Sousa COSTA Belmira Benedita de LIMA-KUHN Antonio Renato BIGANSOLLI Department of Chemical Engineering Technology InstituteFederal Rural University of Rio de JaneiroSeropédica 23851-970Brazil

Aluminous refractory materials with high alumina contents are widely used in the steel industry,and the higher the alumina content,the higher the working temperature.Properties such as high refractoriness and thermal shock resistance lead these refractory materials to be used as channel linings of blast furnaces,where they are exposed to the attack by slag,molten steel,working cycles and sudden temperature changes between 25℃(room temperature)and 1520℃(the temperature of molten pig iron).In this work,microstructural changes in post-mortem aluminous refractory bricks were investigated by apparent porosity,X-ray diffraction analysis(XRD),Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy,and X-ray dispersion energy spectrometry(SEM/EDS).The results showed an increase in the apparent porosity and the bulk density and the presence of the phases mullite,sillimanite,alumina,and quartz in the post-mortem brick.Calcium and magnesium were not detected in the microstructure of the post-mortem brick,indicating that slags did not corrode these refractory materials.Therefore,the microstructural changes that occurred in the post-mortem bricks must be due to thermal cycling.In the X-ray diffraction(XRD)test,mullite,sillimanite,quartz,andα-alumina phases were identified.These results indicate that the aluminous refractory was obtained from sillimanite.In infrared spectroscopy(FTIR)it was possible to identify the vibration bands referring to the Si-O and Al-O bonds.The increase in the porosity is a result of cracks caused by work cycles at high temperatures and the temperature gradient to which the refractory was subjected during use.Through the micrograph it was possible to identify the presence of acicular mullite.The absence of magnesium and calcium in the microanalysis results by energy dispersed X-ray spectrometry(EDS)indicates that there was no infiltration by slag or liquid iron.These results indicate that the microstructural changes that occurred in the post-mortem aluminous refractory were of a th

关键词： aluminous refractories steel industry microstructural blast furnace

Effect of melting temperature on microstructural evolutions, behavior and corrosion morphology of Hadfield austenitic manganese steel in the casting process

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International Journal of Minerals,Metallurgy and Materials 2018年第12期25卷 1431-1438页

作者： Masoud Sabzi Sadegh Moeini Far Saeid Mersagh Dezfuli Young Researchers and Elite Club Dezful Branch Islamic Azad University Department of Mechanical Engineering Islamic Azad University Department of Materials Science and Engineering Islamic Azad University

In this study, the effect of melting temperature on the microstructural evolutions, behavior, and corrosion morphology of Hadfield steel in the casting process is investigated. The mold was prepared by the sodium silicate/CO_2 method, using a blind riser, and then the desired molten steel was obtained using a coreless induction furnace. The casting was performed at melting temperatures of 1350, 1400, 1450, and 1500°C, and the cast blocks were immediately quenched in water. Optical microscopy was used to analyze the microstructure, and scanning electron microscopy(SEM) and X-ray diffractrometry(XRD) were used to analyze the corrosion morphology and phase formation in the microstructure, respectively. The corrosion behavior of the samples was analyzed using a potentiodynamic polarization test and electrochemical impedance spectroscopy(EIS) in 3.5 wt% NaCl. The optical microscopy observations and XRD patterns show that the increase in melting temperature led to a decrease of carbides and an increase in the austenite grain size in the Hadfield steel microstructure. The corrosion tests results show that with increasing melting temperature in the casting process, Hadfield steel shows a higher corrosion resistance. The SEM images of the corrosion morphologies show that the reduction of melting temperature in the Hadfield steel casting process induced micro-galvanic corrosion conditions.

关键词： Hadfield steel casting process melting temperature microstructural evolutions corrosion behavior corrosion morphology

Kinetics and microstructural modeling of isothermal austenite-to-ferrite transformation in Fe-C-Mn-Si steels

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Journal of Materials Science & Technology 2019年第8期35卷 1753-1766页

作者： S.J.Song W.K.Che J.B.Zhang L.K.Huang S.Y.Duan F.Liu State Key Laboratory of Solidification Processing Northwestern Polytechnical University

During the multi-stage processing of advanced high-strength steels, the austenite-to-ferrite transformation, generally as a precursor of the formation of other non-equilibrium or metastable structures, has a severe effect on the subsequent phase transformations. Herein, a more flexible kinetic and microstructural predictive modeling for the key austenite-to-ferrite transformation of Fe-C-Mn-Si steels was developed,in combination with the classical nucleation theory, the general mixed-mode growth model based on Gibbs energy balance, the microstructural path method and the kinetic framework for grain boundary nucleation. Adopting a bounded, extended matrix space corresponding to a single ferrite grain, both softimpingement and hard-impingement can be naturally included in the current modeling. Accordingly, this model outputs the ferrite volume fraction, the austenite/ferrite interface area per unit volume, and the average grain size of ferrite, which will serve as the input parameters for modeling the subsequent bainite or martensite transformations. Applying the model, this work successfully predicts the experiment measurement of the isothermal austenite-to-ferrite transformation in Fe-0.17 C-0.91 Mn-1.03 Si(wt%) steel at different temperatures and explains why the final-state average grain size of ferrite has a maximum at the moderate annealing temperature. Effectiveness and advantages of the present model are discussed arising from kinetics and thermodynamics accompanied with nucleation, growth and impingement.

关键词： Isothermal austenite-ferrite transformation Kinetics Thermodynamics microstructural modeling Low-alloy steel