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Thermodynamics of Bainitic Formation in Carbon-depleted Region in Fe-C Alloys

Xiaolei WU , Xiangkang MENG , Xiyan ZHANG , Yanqing YANG and Mokuang KANG(Dept. of Materials Science and Technology , 401 , Northwestern Polytech. University , Xi'an , 710072 , China)

材料科学技术(英文)

Thermodynamic analysis for the formation of bainitic ferrite in carbon -depleted region has been conducted. The results show that the driving force of bainitic formation increases with depleting of carbon in parent austenite and with decreasing the transformation temperature. The critical driving force (absolute value) at the Bs temperature is 600-1 200 J / mol, which increases as the mean carbon content of Fe-C alloys increases. The freshly-formed bainitic ferrite has partial supersaturation of carbon, which increases smoothly with decreasing the transformation temperature Therefore, the displacive formation of bainitic ferrite in carbon-depleted region is thermodynamically feasible in the whole temperature range of bainitic reaction.

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Study of Carbon-poor Regions of Austenite during Bainitic Incubation Period by SAM

Xiaolei WU , Husheng JIA , Xiyan ZHANG and Mokuang KANG(Dept. of Materials Science & Engineering , Northwestern Polytechnical University , Xi'an , 710072 , China)(To whom correspondence should be addressed)

材料科学技术(英文)

The variation of carbon composition in undercooled austenite during bainitic incubation period has been investigated in 40CrMnSiMoVA by scanning auger microprobe (SAM). The results show that the outstanding diffusion and redistribution of carbon occur in isothermally reacted specimens. This leads to the formation of carbon-poor regions (CPR) near austenite grain boundaries and in austenite grains. The carbon content in CPR exceeds the equilibrium carbon composition of ferrite. Furthermore, it is indicated that the existence of CPR is thermodynamically possible.

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Effect of Notches and Environment on Cyclic Life of Alumina

Fenghui WANG , Minxu LU , Jianfeng WE and Xiulin ZHENG (Northwestern Polytechnical University , Xi'an , 710072 , China)

材料科学技术(英文)

Four-point bending cyclic fatigue testing has been performed for alumina specimens with two kinds of notch radius in corrosive environments. Cyclic life is found to be dependent on notch radius and environments, the tests also show that the fatigue notch factor Kf is roughly equal to the theoretical notch factor Kt, the fatigue strength and fatigue limit σc are reduced in environment in the sequence: formamide-room air-distilled water

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