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High-temperature Tensile Behavior in Coarse-grained and Fine-grained Nb-containing 25Cr-20Ni Austenitic Stainless Steel

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Acta Metallurgica Sinica(English Letters) 2020年第11期33卷 1455-1465页

作者： Guodong Hu Pei Wan Dianzhong Li yiyi Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences72 Wenhua Road.Shenyang 110016China School of Materials Science and Engineering Universityof Science and Technology of China72 Wenhua RoadShenyang 110016China Centre of Excellence for Advanced Materials Dongguan 523808China Songshan Lake Laboratory for Materials Science Dongguan 523808China

In this study,tensile behavior of Nb-containing 25Cr-20Ni austenitic stainless steels composed of coarse or fine grains has been investigated at temperatures ranging from room temperature to 900℃.Results show that the tensile strength of fine-grained specimens decreases faster than that of coarse-grained specimens,as the test temperature increases from 600℃ to 800℃.The rapidly decreasing tensile strength is attributed to the enhanced dynamic recovery and recrystallization,because additional slip systems are activated,and cross-slipping is accelerated during deformation in fine-grained *** tensile testing at 700-900℃,sigma phases are formed concurrently with dynamic recrystallization in fine-grained *** precipitation of sigma phases is induced by simultaneous recrystallization as the diffusion of alloying elements is accelerated during the recrystallization ***,the minimum ductility is observed in coarse-grained specimens at 800℃,which is caused by the formation of M23C6 precipitates at the grain boundaries.

关键词： Austenitic stainless steels High-temperature tensile properties Grain size Precipitates

En-route headway-based bus reliability with real-time data at network scale

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Transportation Safety and Environment 2020年第3期2卷 236-245页

作者： yiyi Li Huadong Tan Hunan Communications Research Institute 472 Furong North RoadChangsha410074China Hunan Provincial Communications Planning Survey&Design Institute598 Moon Island RoadChangsha410200China

Bus reliability has long attracted attention and been extensively studied to enhance service ***,existing research generally evaluates bus reliability of specific routes or *** this end,this study explores en-route bus reliability with real-time data at network *** on data of bus automatic vehicle location and smart card usage in Ningbo,China,this study calculates headway-based reliability with the difference between actual and scheduled headway at each *** demonstrate the trend of stop-level reliability along a bus route,reliability is graded and visualized on a map with ridership at each stop,which is then weighted with passenger-boarding ***-level reliability is then quantified and mapped,where unreliable service basically concentrates in or extends through the centre *** respect to network-level reliability,temporal changes are demonstrated with ridership on weekdays and at the *** is observed that on weekdays,the reliability trend is similar to that of ridership,implying a causal relationship between bus travel-time variation and bus waiting-time at ***,a reliability comparison between weekdays in December and October shows the necessity of evaluating periodically and around important events to avoid negative riding experiences that discourage public transport *** research provides insights for bus agencies to systematically evaluate service reliability both spatially and temporarily,in order to identify and prioritize the routes and stops where the scope for reliability improvement and the expected benefit are greatest.

关键词： bus reliability real-time data at network scale multi-level evaluation visualization

Survey of visual sentiment prediction for social media analysis

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Frontiers of Computer Science 2016年第4期10卷 602-611页

作者： Rongrong JI Donglin CAO yiyi ZHOU Fuhai CHEN Cognitive Science Department Xiamen University Xiamen 361005 China Fujian Key Laboratory of the Brain-like Intelligent Systems Xiamen 361005 China

Recent years have witnessed a rapid spread of multi-modality microblogs like Twitter and Sina Weibo composed of image, text and emoticon. Visual sentiment prediction of such microblog based social media has recently attracted ever-increasing research focus with broad application prospect. In this paper, we give a systematic review of the recent advances and cutting-edge techniques for visual senti- ment analysis. To this end, in this paper we review the most recent works in this topic, in which detailed comparison as well as experimental evaluation are given over the cuttingedge methods. We further reveal and discuss the future trends and potential directions for visual sentiment prediction.

关键词： visual sentiment analysis sentiment predication human emotion

Effects of rare earth on microstructure and impact toughness of low alloy Cr-Mo-V steels for hydrogenation reactor vessels

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Journal of Materials Science & Technology 2020年第10期42卷 1-14页

作者： Zhonghua Jiang Pei Wang Dianzhong Li yiyi Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Materials Science and Engineering University of Science and Technology of China72 Wenhua Road.Shenyang 110016China

The effects of rare earth(RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite(GB) composed primarily of bainitic ferrite and martensite and/or austenite(M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700℃ for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature(DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.

关键词： Low alloy Cr-Mo-V steel Rare earth Microstructure Impact toughness Granular bainite Martensite-austenite constituents

Research progress on low dielectric constant modification of cellulose insulating paper for power transformers

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Frontiers of Chemical Science and Engineering 2023年第8期17卷 991-1009页

作者： Wenchang Wei Haiqiang Chen Junwei Zha yiyi Zhang Guangxi Power Transmission and Distribution Network Lightning Protection Engineering Techndogy Research Center Guangxi UniversityNanning 530004China School of Chemistry and Biological Engineering University of Science and Technology BeijingBeijing 100083China Beijing Advanced Innovation Center for Materials Genome Engineering University of Science and Technology BeijingBeijing 100083China

Because of the increase in the transmission voltage levels,the demand for insulation reliability of power transformers has increasingly become *** insulating paper is the main insulating component of power *** improve the insulation level of ultrahigh voltage transformers and reduce their weight and size,reducing the dielectric constant of oil-immersed cellulose insulating paper is highly *** is used to produce power-transformer insulating papers owing to its excellent electrical properties,renewability,biodegradability and *** dielectric constant of a cellulose insulating paper can be effectively reduced by chemical or physical *** study presents an overview of the foreign and domestic research status of the use of modification technology to reduce the dielectric constant of cellulose insulating *** the mentioned methods are analyzed in this ***,some recommendations for future modified cellulose insulating paper research and applications are *** paper can provide a reference for further research on low dielectric constant cellulose insulating paper in the future.

关键词： low dielectric constant chemical and physical modification cellulose insulating paper transformer nanomaterials

Effects of Filler Metal Composition on Inclusions and Inclusion Defects for ER NiCrFe-7 Weldments

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Journal of Materials Science & Technology 2013年第5期29卷 458-466页

作者： Wenlin Mo Shanping Lu Dianzhong Li yiyi Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

The effects of filler metal （FM） composition on inclusions and inclusion defects for ER NiCrFe-7 weldments have been investigated and analyzed. Results show that as Al, Ti content in FM increases from 0.14 wt% Al, 0.30 wt% Ti to 0.42 wt% Al, 0.92 wt% Ti, the Al, Ti reduction will increase during welding. Inclusion defects （point-like defects named by welding workers） are prone to form in the high Al, Ti content weldments. Inclusion defects with Mg, Ca, Al, and Ti as major metallic elements have been found on the surface and interior of the weldments, as Al, Ti content in FM is over 0.29 wt% Al, 0.62 wt% Ti. Less -ri content in FM cannot prevent ductility-dip-cracking （DDC） through producing enough intragranular precipitates and lessening intergranular M23C6 precipitates. Nb can be used to replace Ti to reduce the sensitivity of the DDC in the NiCrFe-7 alloy weldments.

关键词： Filler metal composition ER NiCrFe-7 Inclusions Inclusion defects Ductility-dip-cracking

Principles Giving High Penetration under the Double Shielded TIG Process

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Journal of Materials Science & Technology 2014年第2期30卷 172-178页

作者： Dongjie Li Shanping Lu Dianzhong Li yiyi Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

A new welding method named double shielded tungsten inert gas （TIG） has been developed to improve the TIG weld penetration. The main principles to increase the weld depth have been discussed. Results show that the critical oxygen content in the weld pool is around 100 × 10 -6 as the temperature coefficient of surface tension changes from negative to positive. The tracer test using pure silver shows that the direction of Marangoni convection changes as the oxygen content increases in the weld pool. The effect of arc constriction on the weld depth has been evaluated on a water-cooled copper plate, and the result indicates that the torch of double shielded can give a more powerful arc. Heavy oxide on the pool surface has undesirable impacts on the increasing of weld depth as the oxygen excessively accumulates in weld pool. It is possible to form chromium oxide in the weld process, while the iron oxide may form as the weld surface exposes to the air after the shielded gas moving away.

关键词： Marangoni convection Penetration Tungsten inert gas (TIG) Arc Oxide

Phase field modeling of dendrite growth

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Acta Metallurgica Sinica(English Letters) 2009年第3期22卷 197-201页

作者： Yutuo ZHANG Chengzhi WANG Dianzhong LI yiyi LI Shenyang Ligong University Shenyang 110168 China Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China

Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites during solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms. When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.

关键词： Phase field modeling Dendrite growth Al-Si alloy Isothermal solidification

Effect of aging treatment on the microstructures and mechanical properties evolution of 25Cr-20Ni austenitic stainless steel weldments with different Nb contents

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Journal of Materials Science & Technology 2019年第4期35卷 520-529页

作者： Xu Zhang Dianzhong Li yiyi Li Shanping Lu Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of Sciences School of Materials Science and Engineering University of Science and Technology of China Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700~?C.M_(23)C_6,Nb(C,N),α-Cr phase and Nb-nitride phase(Z phase)were observed in the microstructures of the aged weld *** results showed that theα-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to~ 700?C for 500 h and the element Nb accelerated the precipitation of theα-Cr phase *** density of theα-Cr phase decreased with the increase of the distance away from the primary Nb(C,N).Additionally,theα-Cr phase showed a crystallographic relationship with the austenitic matrix,■.It was observed that the Z phase precipitated in the periphery of the Nb(C,N)and may replace the Nb(C,N)after long term exposure to high *** transformation of the Nb(C,N)into Z phase suggested that the Z phase had a higher stability than the Nb(C,N)par^ticles at 700?C for long term *** tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging ***,the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.

关键词： 25Cr-20Ni steel Weld metal Nb Aging treatment α-Cr phase Mechanical property