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dynamic and Static recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel

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Journal of Iron and Steel Research(International) 2014年第2期21卷 233-239页

作者： Qing-yun SHA Da-hang LI Gui-yan LI Technology Center Angang Steel Company Limited

The dynamic recrystallization （DRX） and static recrystallization （SRX） behaviour of coarse-grained aus- tenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1 150 ℃ at a strain rate of 0. 1- 5 s 1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine- grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained aus- tenite is mainly retarded by coarse grain size and Nb in solution during rough rolling.

关键词： coarse-grained austenite dynamic recrystallization static recrystallization critical strain time for 50%softening

Effect of circumferential strain rate on dynamic recrystallization and texture of Mg-13Gd-4Y-2Zn-0.5Zr alloy during rotary backward extrusion

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Journal of Magnesium and Alloys 2020年第4期8卷 1228-1237页

作者： Yingze Meng Jianmin Yu Guanshi Zhang Yaojin Wu Zhimin Zhang Zheng Shi College of Mechanical and Electrical Engineering North University of ChinaTaiyuan 030051China College of Materials Science and Engineering North University of Chinaxueyuan road 3TaiyuanShanxiTaiyuan 030051China

Gleeble-3500 thermal simulator was applied to realize the rotary backward extrusion forming of Mg-13Gd-4Y-2Zn-0.5Zr(wt%)alloy at different circumferential strain rate from 0.009 s^(-1)to 0.027 s^(-1)at 400℃and the dynamic recrystallization mechanism and texture evolution were studied.The results show that the grain size of the alloy was obviously refined after rotary backward extrusion.As the circumferenlial strain rate increased,the dynamic recrystallization fraction gradually increased causing the grain size decreased and the distribution of microstructure became more uniform.At the same time,the texture of{0001},{10-10},{11-20}was weakened and the grain orientation distribution became more random.With the increase of circumferential strain rate,the discontinuous dynamic recrystallization mechanism became dominant,which promoted the weakening of texture and grain refinement of the alloy.

关键词： Mg-Gd-Y-Zn-Zr alloy Rotary backward extrusion dynamic recrystallization Texture

Effects of dynamic recrystallization and strain-induced dynamic precipitation on the corrosion behavior of partially recrystallized Mg-9Al-lZn alloys

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Journal of Magnesium and Alloys 2020年第4期8卷 1016-1037页

作者： Yenny Cubides Dexin Zhao Lucas Nash Digvijay Yadav Kelvin Xie Ibrahim Karaman Homero Castaneda Department of Materials Science and Engineering Texas A&M University575 Ross StreetCollege StationTX 77840USA Department of Engineering Technology and Industrial Distribution 106 Ross StreetCollege StationTX 77843USA National Corrosion and Materials Reliability Laboratory 1041 RELLIS PkwyBryanTX 77807USA

The corrosion susceptibility of recrystallized and un-recrystallized grains in equal channel angular pressed(ECAPed)Mg-9Al-lZn(AZ91)alloys immersed in chloride containing media was investigated through immersion testing and an electrochemical microcell technique coupledwith high resolution techniques such as scanning Kelvin probe force microscopy(SKPFM),transmission electron microscopy(TEM),andelectron backscatter diffraction(EBSD).During ECAP,dynamic recrystallization(DRX)and strain-induced dynamic precipitation(SIDP)simultaneously occurred,resulting in a bimodal grain structure of original elongated coarse grains and newly formed equiaxed fine grainswith a large volume fraction ofβ-Mg17Al12 precipitates.Corrosion preferentially initiates and propagates in the DRXed grains,owing tothe greater microchemistry difference between theβ-Mg17Al12 precipitates formed at the DRXed grain boundaries and the adjacentα-Mgmatrix,which induces a strong microgalvanic coupling between these phases.Additionally,the weaker basal texture of the DRXed grainsalso makes these grains more susceptible to electrochemical reactions than the highly textured un-DRXed grains.The influence of dynamicrecrystallization and dynamic precipitation was also studied in ECAPed alloys with differenl levels of deformation strain through corrosion andelectrochemical techniques.Increasing the strain level led to a more uniform corrosion with a shallow penetration depth,lower corrosion ratevalues,and higher protective ability of the oxide film.Furthermore,higher levels of strain resulted in greater hardness values of the ECAPedalloys.The superior corrosion resistance and strength of the ECAPed alloys with increasing strain level was attributed to the combination ofsmaller DRXed grain size,higher DRX ratio,and higher volume fraction of uniformly distributed fineβ-Mg17Al12 precipitates.c 2020 Published by Elsevier B.V.on behalf of Chongqing University.

关键词： Magnesium alloy Bimodal grain structure dynamic recrystallization dynamic precipitation Severe plastic deformation Microgalvanic coupling

Microstructure investigation of dynamic recrystallization in hard machining:From thermodynamic irreversibility perspective

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Frontiers of Mechanical Engineering 2021年第2期16卷 315-330页

作者： Binxun LI Xinzhi ZHANG Song ZHANG Key Laboratory of High Efficiency and Clean Mechanical Manufacture of Ministry of Education School of Mechanical EngineeringShandong UniversityJinan 250061China Key National Demonstration Center for Experimental Mechanical Engineering Education Shandong UniversityJinan 250061China China Unicom(Shandong)Industrial Internet Co. Ltd.Jinan 250001China

The drastically changed thermal,mechanical,and chemical energies within the machined surface layer during hard machining tend to initiate microstructural alteration.In this paper,attention is paid to the introduction of thermodynamic potential to unravel the mechanism of microstructure evolution.First,the thermodynamic potential-based model expressed by the Helmholtz free energy was proposed for predicting the microstructure changes of serrated chip and the machined surface layer.Second,the proposed model was implemented into a validated finite element simulation model for cutting operation as a user-defined subroutine.In addition,the predicted irreversible thermodynamic state change in the deformation zones associated with grain size,which was reduced to less than 1 mm from the initial size of 1.5 mm on the machined surface,was provided for an in-depth explanation.The good consistency between the simulated results and experimental data validated the efficacy of the developed model.This research helps to provide further insight into the microstructure alteration during metal cutting.

关键词： thermodynamic irreversibility Helmholtz free energy microstructure evolution dynamic recrystallization hard milling

Effect of Niobium and Titanium on dynamic recrystallization Behavior of Low Carbon Steels

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Journal of Iron and Steel Research(International) 2008年第3期15卷 31-36页

作者： MA Li-qiang LIU Zhen-yu JIAO Si-hai YUAN Xiang-qian WU Di Shenyang Metrology Testing Institution Shenyang 110179 Liaoning China State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China Institute of Research and Development Baosteel Co Shanghai 201900 China

Using a Gleeble 3800 thermo-mechanical simulator, the effect of niobium and titanium on the dynamic recrystallization （DRX） behavior of low carbon steels was investigated. Isothermal single compression tests were performed in the temperature range of 850 to 1 150 ℃ at constant strain rates of 0.1 to 5 s-1. The experimental results showed that the addition of niobium and titanium to the low carbon steels significantly increased both the peak stress and steady state stress. The activation energy of deformation Qd was larger than the activation energy associated with the steady state stress Qss. Furthermore, the difference between Qd and Qss became significant because of the addition of niobium and titanium. DRX is effectively retarded because of solute dragging and dynamic precipitate pinning of niobium and titanium, resulting in higher values of the peak strain and steady state strain. Finally, the influence of niobium and titanium on the DRX kinetics and steady state grain size was determined.

关键词： peak strain activation energy dynamic recrystallization

STUDY OF dynamic recrystallization OF LOW CARBON STEEL IN THIN SLAB CONTINUOUS ROLLING PROCESS

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Acta Metallurgica Sinica(English Letters) 2006年第4期19卷 265-270页

作者： X.K. Liang X.J. Sun Q.Y. Liu H. Dong State Key Laboratory of Advanced Steel Processes and Products Central Iron and Steel Research Institute Beijing 100081 China

Combined with the technological characteristics of thin slab continuous rolling process （TSCR）, dynamic recrystallization of an extremely coarse austenite of low carbon steel is studied by Thermecmaster-Z hot simulator. By the analysis of true stress-strain curves and the observation of microstructures at different deformation stages, the critical stress and critical strain are determined under different deformation conditions. The effect of Z parameter on dynamic recrystallization of coarse austenite is studied. The microstructure evolution in real production is also discussed.

关键词： TSCR （thin slab continuous rolling process） coarse austenite dynamic recrystallization

Texture evolution induced by twinning and dynamic recrystallization in dilute Mg-1Sn-1Zn-1Al alloy during hot compression

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Journal of Magnesium and Alloys 2020年第3期8卷 899-909页

作者： Meijuan Hao Weili Cheng Lifei Wang Ehsan Mostaed Liping Bian Hongxia Wang Xiaofeng Niu School of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan 030024China Shanxi Key Laboratory of Advanced Magnesium-Based Materials Taiyuan University of TechnologyTaiyuan 030024China Department of Materials Science and Engineering Michigan Technological UniversityHoughtonMI 49931USA

Texture evolution of an extruded dilute Mg-1Sn-1Zn-1Al alloy was thoroughly investigated based on the twinning and dynamic recrystallization(DRX)behavior via hot compression at a strain rate of 10 s^(-1)and temperature of 225℃.It was found that the types and intensities of the texture are strongly dependent on the fraction of twins and DRX modes as well as regions where sub-grain boundaries(sub-GBs)are intensively accumulated.At the initial stage of deformation,the formation of compression direction(CD)-tilted basal texture was mainly determined by the occurrence of{101^(-)2}extension twins.As the strain increases,the variation in the texture intensity was greatly dominated by the DRX modes but the type of main texture remained unchanged.These findings are of great importance for texture modification of wrought Mg-Sn-based alloys during post-deformation.

关键词： Mg-1Sn-1Zn-1Al Hot deformation Twinning dynamic recrystallization Texture

Predicting Critical Conditions and Stress-Strain Curves for dynamic recrystallization in SPHC Steel

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Journal of Iron and Steel Research(International) 2010年第7期17卷 51-57页

作者： WU Lai-zhi LI Xue-song CHEN Jun ZHANG Hong-bing CUI Zhen-shan Department of Plasticity Technology Shanghai Jiaotong University Shanghai 200030 China

The hot compression tests on an SPHC steel were carried out in the temperature range of 900-1150 ℃ and strain rate range of 0.1-10 s-1,in which the maximum true strain is 0.8.The activation energy of test steel was calculated,to be 299.4 kJ/mol.The critical stresses and strains for initiation of dynamic recrystallization were determined based on changes of the work hardening rate（θ）as a function of the flow stress（σ）or strain（ε）,respectively.The dependence of the peak strain（εp）,the peak stress（σp）,and the steady state stress（σs）were determined based on the Zener-Hollomen parameter.The mathematical models of the flow stress evolution were established in the hardening and dynamic recovery region and dynamic recrystallization region,respectively.The average error between experimental curves and predicted ones was around 3.26%.

关键词： flow stress dynamic recrystallization critical stress critical strain SPHC steel

Constitutive Modeling and dynamic recrystallization Mechanisms of an Ultralow-carbon Microalloyed Steel During Hot Compression Tests

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Journal of Wuhan University of Technology(Materials Science) 2020年第5期35卷 946-957页

作者：李宁 HUANG Yao HAN Renheng BAO Ziming ZHU Yanqing ZHANG Hexin 赵成志 Key Laboratory of Superlight Materials and Surface Technology Ministry of EducationCollege of Materials Science and Chemical EngineeringHarbin Engineering UniversityHarbin 150001China

The hot deformation behavior of an ultralow-carbon microalloyed steel was investigated using an MMS-200 thermal simulation test machine in a temperature range of 1073-1373 K and strain rate range of 0.01-10 s-1.The results show that the flow stress decreases with increasing deformation temperature or decreasing strain rate.The strain-compensated constitutive model based on the Arrhenius equation for this steel was established using the true stress-strain data obtained from a hot compression test.Furthermore,a new constitutive model based on the Z-parameter was proposed for this steel.The predictive ability of two constitutive models was compared with statistical measures.The results indicate the new constitutive model based on the Z-parameter can more accurately predict the flow stress of an ultralow-carbon microalloyed steel during hot deformation.The dynamic recrystallization(DRX)nucleation mechanism at different deformation temperatures was observed and analyzed by transmission electron microscopy(TEM),and strain-induced grain boundary migration was observed at 1373 K/0.01 s^-1.

关键词： ultra-low carbon microalloyed steel hot deformation behavior constitutive modeling dynamic recrystallization