In Situ Study of the Influence of Nickel on the Phase Transformation Kinetics in Austempered Ductile Iron
In Situ Study of the Influence of Nickel on the Phase Transformation Kinetics in Austempered Ductile Iron
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DOI：
10.1007/s11661-015-3261-1
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发表时间：
2016-02
期刊：
影响因子：
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通讯作者：
P. Saal;L. Meier;Xiaohu Li;M. Hofmann;M. Hoelzel;J. N. Wagner;W. Volk
中科院分区：
文献类型：
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作者：
P. Saal;L. Meier;Xiaohu Li;M. Hofmann;M. Hoelzel;J. N. Wagner;W. Volk
用原位中子衍射法测定了三种不同镍含量的等温球铁样品的相组分和奥氏体碳含量。样品在1178 K（905°C）下奥氏体化30分钟，在523 K和723 K（250°C和450°C）温度下用镜面炉等温加热3.5小时。根据他们的情景中子衍射研究，导出了决定I阶段反应结束的平台时间。考虑到高温下的相变加速，选择适当的等温时效时间，随着等温温度的升高，奥氏体含量增加。在等温温度为523 K ~ 723 K（250°C ~ 450°C）时，得到了合适的等温时间。镍含量的增加导致了更高的奥氏体相分数。定量分析了镍对相变的延缓作用。将相分数的平台值和相应的等温回火次数转换成TTT图。奥氏体碳含量的演变在623 K（350℃）等温回火时达到最大值。这可以用温度相关的碳化物沉淀和碳扩散到晶格缺陷来解释。通过初步的APT分析，发现铁素体内部存在细小的碳化物。
Phase fractions and austenite carbon contents in austempered ductile iron samples with three different nickel contents were determined byin situneutron diffraction. The samples were austenitized at 1178 K (905 °C) for 30 minutes and austempered for 3.5 hours at temperatures between 523 K and 723 K (250 °C and 450 °C) using a mirror furnace. Based on thein situneutron diffraction studies, plateau times were derived, which determine the end of stage I reaction. The austenite contents increase for higher austempering temperatures when the austempering times are selected properly, considering the accelerated phase transformation at higher temperature. Appropriate austempering times were derived for austempering temperatures between 523 K and 723 K (250 °C and 450 °C). Increased nickel contents lead to higher austenite phase fractions. Moreover the retarding effect of nickel on the phase transformation was quantified. The plateau values of phase fraction and the according austempering times were converted to TTT diagrams. The evolution of the austenite carbon content shows a maximum at 623 K (350 °C) austempering temperature. This can be explained by temperature-dependent carbide precipitation and carbon diffusion into lattice defects. Fine carbides within the ferrite could be found by preliminary APT analysis.