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Xiaoli Zhao,Chuanwei Li,Lizhan Han,Jianfeng Gu 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6
Dilatometry is a useful technique to obtain experimental data concerning transformation. In this paper, a dilation conversionalmodel was established to calculate carbides fraction in AISI H13 hot-work tool steel based on the measured length changes. After carbides precipitation, the alloy contents in the matrix changed. In the usual models, the content of carbon atoms afterprecipitation is considered as the only element that affects the lattice constant and the content of the alloy elements suchas Cr, Mo, Mn, V are often ignored. In the model introduced in this paper, the alloying elements (Cr, Mo, Mn, V) changescaused by carbides precipitation are incorporated. The carbides were identified using scanning electron microscope andtransmission electron microscope. The relationship between lattice constant of carbides and temperature are measured byhigh-temperature X-ray diffraction. The results indicate that the carbides observed in all specimens cooled at different ratesare V-rich MC and Cr-rich M23C6,and most of them are V-rich MC, only very few are Cr-rich M23C6. The model includingthe effects of substitutional alloying elements shows a good improvement on carbides fraction predictions. In addition, lowercooling rate advances the carbides precipitation for AISI H13 specimens. The results between experiments and mathematicalmodel agree well.
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Effect of Interstitial Solutes on Precipitation Behavior of 9-12% Chromium Ferritic Steels
Xingang Tao,Chuanwei Li,Lizhan Han,Jianfeng Gu 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.3
Effects of nitrogen and carbon content on precipitation behavior in two 9-12% Cr ferritic heat-resistant steels during isothermal transformation were investigated. Isothermal aging treatments at 700 °C after solution annealing were carried out for the different periods up to over 220 h. Microstructure characterization was performed by many characterization methods, such as physicochemical phase analysis, X-ray diffraction and scanning electron microscope etc. It was found that Cr-rich M2N nitride was formed as the main precipitate in the alloy A with content of 0.15% N and 0.03% C in wt%, together with some Cr-rich M23C6 carbide and Nb-rich MN nitride. Comparatively, the aged alloy B with 0.05% N and 0.11% C, predominantly contains Cr-rich M23C6 carbides. Besides, both alloys showed the similar microstructure evolution process: The precipitates were found to be formed initially along prior austenite grain boundaries, then grew toward interior of grain in the form of cell with the increasing aging time. Meanwhile, the cell growth feature was also discussed based on the experimental observation in well-controlled specimens.
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