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Influence of initial microstructure and grain size on transformation of bainite to austenite in large size forgings

Journal of Iron and Steel Research(International) 2018年第5期25卷 554-562页

作者： Emna Ben Fredj Hadi Ghasemi Nanesa Mohammad Jahazi Jean-benoit morin Department of Mechanical Engineering Ecole deTechnologie Superieure Montreal QC H3C 1K3 Canada Finkl Steel-Sorel St-Joseph-de-Sorel QC J3R 3M8 Canada

The kinetics of austenite formation in the surface and center regions of a 40 t forged ingot of a high-strength medium- carbon low-alloy steel was studied using high-resolution dilatometry. The starting microstructures from the surface or center regions had different proportions of bainite and residual austenite as well as different prior austenite grain sizes. Two heating rates representing the actual heating rates in the surface （5℃ s -1） and center regions （0.5℃ s -1） of large size forged blocks were utilized. Dilatometric curves revealed only one transformation step of austenite formation at both heating rates independent of grain size or proportion of phases. Optical microscopy, field emission gun scanning electron microscopy and X-ray diffraction were used to study microstructure evolution and confirm the results obtained by dilatometry. The kinetic parameters for austenite formation were determined from the dilatometry data by Johnson-Mehl- Avrami-Kolmogorov （JMAK） equation. The JMAK coefficients were determined for each condition of the investigated steels. The calculations indicated that the nucleation and growth of austenite in the surface region were accelerated more than 10,000 times due to a significantly smaller average prior austenite grain size, stability of initial retained austenite, and accumulation of coarse carbides at the surface. The results were discussed in the framework of classical nucleation and growth theories using the kinetic parameters for austenite formation.

关键词： Large size ingot Medium-carbon low-alloy steel Initial microstructure Grain size Austenite formation

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Production, Application, and Field Performance of Abietiv^(TM),the Balsam Fir Sawfly Nucleopolyhedrovirus

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中国病毒学 2007年第2期22卷 163-172页

作者： Christopher J. Lucarotti benoit morin Robert I.Graham Renée Lapointe Natural Resources Canada Canadian Forest Service-Atlantic Forestry Centre PO Box 4000FrederictonNew Brunswick E3B 5P7Canada Population Ecology Group Faculty of Forestry and Environmental Management University of New Brunswick Fredericton New Brunswick E3B 6C2 Canada Natural Resources Canada Canadian Forest Service-Atlantic Forestry Centre PO Box 4000FrederictonNew Brunswick E3B 5P7Canada Population Ecology Group Faculty of Forestry and Environmental Management University of New Brunswick Fredericton New Brunswick E3B 6C2 Canada Sylvar Technologies Inc.P.O.Box 636 Stn.AFrederictonNew Brunswick E3B 5A6Canada

Beginning in the early 1990s, the balsam fir sawfly (Neodiprion abietis) became a significant defoliating insect of precommercially thinned balsam fir (Abies balsamea (L.) Mill.) stands in western Newfoundland, Canada. In 1997, a nucleopolyhedrovirus (NeabNPV) was isolated from the balsam fir sawfly and, as no control measures were then available, NeabNPV was developed for the biological control of balsam fir sawfly. In order to register NeabNPV for operational use under the Canadian Pest Control Products Act, research was carried out in a number of areas including NeabNPV field efficacy, non-target organism toxicology, balsam fir sawfly ecology and impact on balsam fir trees, and NeabNPV genome sequencing and analysis. As part of the field efficacy trials, approximately 22 500 hectares of balsam fir sawfly-infested forest were aerially treated with NeabNPV between 2000 and 2005. NeabNPV was found to be safe, efficacious, and economical for the suppression of balsam fir sawfly outbreak populations. Conditional registration for the NeabNPV-based product, Abietiv?, was received from the Pest Management Regulatory Agency (Health Canada) in April 2006. In July 2006, Abietiv was applied by spray airplanes to 15 000 ha of balsam fir sawfly-infested forest in western Newfoundland in an operational control program.

关键词：生产应用香油锯蝇

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