In-situ measurement of phase transformation kinetics in austempered ductile iron
In-situ measurement of phase transformation kinetics in austempered ductile iron
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DOI：
10.1016/j.matchar.2013.09.005
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发表时间：
2013-11
影响因子：
4.7
通讯作者：
L. Meier;M. Hofmann;P. Saal;W. Volk;H. Hoffmann
中科院分区：
文献类型：
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作者：
L. Meier;M. Hofmann;P. Saal;W. Volk;H. Hoffmann
对含0.42%Mn和0.72%Cu的奥贝球铁（ADI）在镜面炉中进行了热处理，并用中子衍射原位研究了ADI的相变。热处理包括在920 °C下的奥氏体化和分别在400 °C、350 °C和300 °C下的等温奥氏体化。由于铁素体片晶的生长，奥氏体含量在所有温度下在前15-20 min内迅速降低，并在35 min（400 ℃）至80 min（300 ℃）后达到稳定平台。通过晶格参数的变化监测和表征的残余奥氏体的碳含量增加至1.6 wt.%这是由新形成的铁素体的再分布引起的。在较高的等温淬火温度下，碳向奥氏体的再分配几乎与相变平行发生，而在300 °C时，碳向奥氏体的再分配明显滞后。此外，中子数据揭示了等温淬火过程中奥氏体峰的不对称性，这归因于连续相变。它暂时导致两个部分的奥氏体，初始低碳和富集高碳的修改。
Austempered ductile iron (ADI) alloyed with 0.42% Mn and 0.72% Cu was heat treated in a mirror furnace and the phase transitions were studied in-situ by neutron diffraction. The heat treatment consisted of austenitisation at 920 °C and isothermal austempering at 400 °C, 350 °C and 300 °C, respectively. Due to the growth of ferrite platelets, the austenite content decreases rapidly at all temperatures within the first 15–20 min and reaches a stable plateau after 35 min (400 °C) to 80 min (300 °C).The carbon content of the residual austenite, which was monitored and characterised by the change of the lattice parameter, increases up to 1.6 wt.% caused by redistribution from the newly formed ferrite. While at higher austempering temperatures this takes place almost parallel to the phase transformation, at 300 °C the redistribution of carbon to austenite lags behind considerably.Furthermore the neutron data revealed an austenite peak asymmetry during austempering which is attributed to successive phase transformation. It results temporarily in two fractions of austenite, an initial low-carbon and an enriched high-carbon modification.