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Modelling of dynamic recrystallization kinetics of 300M steel at high strain rates during hot deformation

Science China(Technological Sciences) 2019年第9期62卷 1534-1544页

作者： GUO Peng DENG Lei WANG XinYun LI JianJun State Key Laboratory of Materials Processing and Die & Mould Technology Huazhong University of Science and Technology

The flow curves of 300M steel exhibit a transition from stress peak presence to stress peak absence as the strain rate increases. It is difficult to establish dynamic recrystallization(DRX) kinetics models suitable for strain rates where there are no stress peaks in the flow curves using the existing Avrami equation, and the optimal processing parameters for forging can be scarcely *** this study, the high-temperature flow and DRX behavior of 300M steel are investigated by performing isothermal compression tests at temperatures between 1173–1423K with strain rates between 0.001–50 s-1. Distinct stress peaks can be found in the flow curves at low strain rates, and the average grain size decreases with the increase in the strain rate at the same temperature. The DRX mechanism is a discontinuous DRX, and the grain boundary migration plays an important role in the DRX process. In contrast, no stress peak is observed in the flow curves at high strain rates, and the average grain size no longer decreases with the strain rate increase at the same temperature. The DRX mechanism in this case is a continuous DRX. The demarcated strain rate is calculated based on the characteristics of the obtained flow curves and grain sizes. The recrystallization volume fraction model and prediction grain size model at high strain rates are established. In combination with the existing DRX kinetics models at low strain rates, the processing parameters can be optimized to produce components with excellent mechanical properties.

关键词： 300M steel flow curves demarcated strain rate dynamic recrystallization grain size

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Dispersion of the Bacterium Xylella fastidiosa in Portugal

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Journal of Agricultural Science and Technology(A) 2022年第1期12卷 35-41页

作者： Carla Carvalho-Luis JoséManuel Rodrigues Luís M.Martins DVPF-Norte Institute for Nature Conservationand ForestsI.P.Vila Real 5000Portugal Department of Forest Management and Valorisation Institute for Nature Conservation and ForestsI.P.1069LisboaPortugal Centre for the Research and Technology of Agro Environmental and Biological Sciences(CITAB) University of Trás-os-Montes and Alto DouroVila Real 5000-801Portugal

After the first detection of the gram-negative bacterium,Xylella fastidiosa multiplex in Portugal,in January 2019,a“demarcated Area”was delimited and an“Action Plan”to control the pathogen has been *** is considered one of the greatest threats to plant health worldwide and leads to loss of forests vitality and *** current study was developed till June 2020,with the objective to understand the dimension of the issue worldwide and in Portugal,analyzing the state-of-the-art on the biology,dispersion,symptoms,control and risks associated with this bacterium(Research Phase).In the Prospecting Phase,we collected 5 branches with 5-8 leaves,from the four quadrants of the tree,wrapping and labeling them-so 2,261 samples were collected and sent to the laboratory for *** was possible to determine that the two initial outbreaks were not an isolated case,as 107 additional outbreaks were detected in other places,revealing a much more worrying panorama,requiring further analysis on the real impact of this bacterial strain on the natural *** the end of this study the demarcated area covered about 62,000 *** most affected species was lavender with 30%of positive outbreaks,followed by gorse with 22%,and rosemary with 11%.Spread of Phillaenus spumarius and *** indicates that insect vector and transport links appear to be dispersal facilitators together with Douro *** eradication is unfeasible to achieve in the coming years,containment will be the most appropriate strategy.

关键词： Phytopathogen forest plant health xylem-limited bacteria Xylella fastidiosa multiplex biotic stressors demarcated Area

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