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Improvement of Surface Ridging Resistance of an Ultra-purified Ferritic Stainless Steel by Optimizing Hot Rolling Condition

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Acta Metallurgica Sinica(English Letters) 2016年第6期29卷 561-567页

作者： Chi zhang li-wen zhang Zhen-Yu liu School of Materials Science and Engineering Dalian University of Technology State Key Lab of Rolling Technologies and Automation Northeastern University

The effects of the finisher entry temperatures（FETs） on the surface ridging behavior for an ultra-purified21%Cr ferritic stainless steel have been investigated. The results indicate that decreasing the FET facilitates the formation of in-grain shear bands in the hot rolled slab. The in-grain shear bands supplied recrystallization nucleation sites in grains during subsequent annealing through coalescence of subgrains, which is beneficial to refine the microstructures and intensify the {111}//ND textures. This effect will evolve to the final cold rolled and annealed sheet. The micro-texture analysis indicates that the formation of grain colony in the final sheet is weakened by decreasing the FET. Then, the surface ridging resistance of FSS is enhanced due to the optimizing of micro-texture distribution.

关键词： Ferritic steels Surface ridging Micro-texture Electron backscattered diffraction(EBSD)

Estimating Restricted Common Structural Changes for Panel Data

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Acta Mathematicae Applicatae Sinica 2019年第4期35卷 893-908页

作者： li-wen zhang Zhong-yi ZHU School of Statistics and Management Shanghai University of Finance and Economics Shanghai 200444 China Department of Statistics School of Management Fudan University Shanghai 200433 China

We consider estimating multiple structural changes occurring at unknown common dates in a panel data regression model with restrictions imposed on the coefficients. We establish the consistency and rate of convergence of the structural change estimates and the asymptotic distribution of the parameter *** is shown that the efficiency of the parameter estimators is increased using the restrictions. An efficient dynamic algorithm is proposed to obtain the break date estimates and the parameter estimates. In addition, we propose a testing procedure for the existence of the change points with the restrictions and derive the asymptotic distribution under the null hypothesis of the test statistics. Simulation studies are presented to investigate the performance of the proposed method in finite samples.

关键词： common structural changes panel data consistency

Integral-inequality approach to delay-dependent robust H-infinity control for uncertain neutral systems

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控制理论与应用（英文版） 2008年第2期6卷 208-214页

作者： wen＇an zhang li YU Department of Automation Zhejiang University of Technology Hangzhou Zhejiang 310032 China

This paper focuses on the design problem of a memoryless state feedback robust H-infinity controller for a class of uncertain neutral systems. By using a newly established integral inequality, a new delay-dependent bounded real lemma for such systems is derived without involving a fixed model transformation. Furthermore, new delay-dependent sufficient conditions for the existence of robust H-infinity controllers are presented in terms of nonlinear matrix inequalities. A design procedure involving an iterative algorithm is also proposed to design such controllers. Numerical examples are given to demonstrate the less conservatism of the proposed method.

关键词： Neutral systems Uncertain systems Delay-dependent criteria H-infinity control Integral-inequality

Numerical simulation on recrystallization behavior and microstructure evolution during hot continuous rolling process of 38CrMoAl steel rod

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Journal of Iron and Steel Research International 2022年第10期29卷 1633-1645页

作者： Fei li li-wen zhang Chi zhang Kang-jie Song Pei-gang Mao School of Materials Science and Engineering Dalian University of TechnologyDalian116024LiaoningChina

The control of microstructure during hot rolling process of steel is of great importance and will affect the properties of the steel *** to the production line,a three-dimensional multi-field coupled finite element model of 24-pass continuous hot rolling process of 38CrMoAl steel rod is established using the finite element software *** on the recrystallization kinetics model and the grain growth model,a subroutine written in Fortran is introduced to calculate the recrystallization behavior and microstructure evolution of 38CrMoAl steel during the entire rolling *** distribution and evolution of variables such as strain,temperature and recrystallization fractions during the rolling process are *** temperature variations and grain sizes at both the center and surface of the tested steel are compared with the experimental *** it is found that the simulation results are in good agreement with the experimental ones,confirming the reliability of the established model.

关键词： 38CrMoAl steel Recrystallization Microstructure evolution Hot rolling process Numerical simulation

Applications of molten salt and progress of molten salt electrolysis in secondary metal resource recovery

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International Journal of Minerals,Metallurgy and Materials 2020年第12期27卷 1599-1617页

作者： Xiao-li Ming Feng li-wen zhang Zuo-ren Nie College of Materials Science and Engineering Key Laboratory of Advanced Functional MaterialsEducation Ministry of ChinaBeijing University of TechnologyBeijing 100124China National Engineering Laboratory for Industrial Big-data Application Technology Beijing University of TechnologyBeijing 100124China

Molten salt is an excellent medium for chemical reaction,energy transfer,and *** salt innovative technologies should be developed to recover metals from secondary resources and reserve metals from primary natural *** these technologies,molten salt electrolysis is an economic and environment-friendly method to extract metals from waste *** the perspective of molten salt characteristics,the application of molten salts in chemistry,electrochemistry,energy,and thermal storage should be comprehensively *** review discusses further directions for the research and development of molten salt electrolysis and their use for metal recovery from various metal wastes,such as magnet scrap,nuclear waste,and cemented carbide *** is placed on the development of various electrolysis methods for different metal containing wastes,overcoming some problems in electrolytes,electrodes,and electrolytic *** focus is given to future development directions for current associated processing obstacles.

关键词： molten salt application molten salt electrochemistry resource recycling cemented carbide scrap

On Ekeland's Variational Principle for Set-Valued Mappings

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Acta Mathematicae Applicatae Sinica 2007年第1期23卷 141-148页

作者： Sheng-jie li wen-yan zhang College of Mathematics and Science Chongqing University Chongqing 400044 China

In this paper, we derive a general vector Ekeland variational principle for set-valued mappings, which has a dosed relation to εk^0 -efficient points of set-valued optimization problems. The main result presented in ... 详细信息

关键词： Vector Ekeland variational principle nonlinear scalarization function metric space set-valued mapping

Testing for Change Points in Partially linear Models

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Acta Mathematicae Applicatae Sinica 2015年第4期31卷 879-892页

作者： li-wen zhang Zhong-yi ZHU School of Economics Shanghai University Department of Statistics School of ManagementFudan University

In this paper we provide a method to test the existence of the change points in the nonparametric regression function of partially linear models with conditional heteroscedastic variance. We propose the test statistic and establish its asymptotic properties under some regular conditions. Some simulation studies are given to investigate the performance of the proposed method in finite samples. Finally, the proposed method is applied to a real data for illustration.

关键词： change point partially linear model heteroscedastic variance local linear regression bandwidthselection

3D Crystal Plasticity Finite Element Modeling of the Tensile Deformation of Polycrystalline Ferritic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2017年第1期30卷 79-88页

作者： Chi zhang li-wen zhang wen-Fei Shen Ying-Nan Xia Yu-Tan Yan School of Materials Science and Engineering Dalian University of TechnologyDalian 116024China

A mesoscale model of plastic deformation of ferritic stainless steels （FSSs） is formulated by combining a crystal plasticity finite element model with 3D cellular automaton algorithm. The actual grain orientations of FSS cold rolling and annealing sheet have been detected by electron backscatter diffraction and selected to be assigned to the polycrystal model. The simulation results have been validated by comparing the calculated true stress-strain response with the experimental one. For the lack of considering the interactions of dislocations with impurities, there are no upper and lower yield points in the simulation stress-strain curves. However, the calculated yield strength and the stress-strain response after yielding agree well with the real material. The local stress and strain fields show inhomogeneous at mesoscale. The plastic deformations of the grains with typical orientations have been characterized. The analysis reveals that the grains with fiber texture show higher thickness reduction ratio as compared to others. The deformation behaviors of the grains in polycrystal are not only related to the orientations but also to the interactions from adjacent grains.

关键词： Ferritic steels Crystallographic orientation Polycrystal plasticity modeling Cellular automaton

Synthesis and luminescence properties of Eu^(3+),Sm^(3+) doped(Y_xGd_(1-x))_2O_3:Si^(4+),Mg^(2+) long-lasting phosphor

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International Journal of Minerals,Metallurgy and Materials 2010年第3期17卷 347-352页

作者： Yan liu Shi-xiang liu Ming-wen Wang wen-jun li Ting zhang Xia zhang School of Applied Science University of Science and Technology Beijing Beijing 100083 China

A novel red long-lasting phosphor, （YxGd1-x）2O3：Eu3＋, Sm3＋, Si4＋, Mg2＋, was synthesized by the co-precipitation method using oxalate precipitation as the precursor. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, integrated thermal analyzer （TG）, and photoluminescence spectra （PL） as well as the ST-900PM weak light photometer were used to study the synthesis conditions, morphology, luminescence properties, and the decay time of the phosphor. The XRD results show that the products synthesized at 1400~C for 4 h have good crystallization without any detectable impurity phases. Based on the PL spectra, the optimal conditions are as the following. The molar ratios of Y3＋ to Gd3＋ and Eu3＋ to Sm3＋ are 2：8 and 3：1, respectively, and the contents of Mg2＋ and SiO2 are 5mol% and 3mol%, respectively. The decay time monitored by the ST-900PM weak light photometer is 7200 s, increasing 44% and 100%, respectively, compared with the Eu3＋ and Sm3＋ single-doped phosphors. The results indicate that the energy transfer is from Sm3＋ to Eu3＋ ion, and Sm3＋ is a good sensitizer to Eu3＋.

关键词： long lasting phosphor luminescence energy transfer