Incomplete transformation of upper bainite in Nb bearing low carbon steels
Incomplete transformation of upper bainite in Nb bearing low carbon steels
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DOI：
10.1179/026708309x12512744
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发表时间：
2010-04
影响因子：
1.8
通讯作者：
T. Furuhara;T. Yamaguchi;G. Miyamoto;T. Maki
中科院分区：
文献类型：
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作者：
T. Furuhara;T. Yamaguchi;G. Miyamoto;T. Maki
Nb含量为0.03mass %的Fe-（0.15或0.05）C-0.2Si-1.5Mn（mass%）合金的贝氏体相变动力学及显微组织贝氏体转变发生在873 K以下。在853 K时，相变迅速进行，形成贝氏体铁素体而无碳化物析出，但在一定时间内出现相变停滞，在相邻的贝氏体铁素体之间留下未相变的奥氏体膜。另一方面，无Nb合金在转变完成之前不显示这种停滞。通过进一步保持，添加Nb的合金中的转变通过在奥氏体膜中形成无位错铁素体与铁素体沉淀的混合物而重新开始。相比之下，贝氏体相变伴随着贝氏体析出发生在无Nb和添加Nb的合金在773 K，导致在转变动力学没有差异。提出不完全相变是由于Nb的偏聚抑制了贝氏体铁素体和奥氏体相间的铁素体形核。
Kinetics and microstructure of bainite transformation in Fe–(0·15 or 0·05)C–0·2Si–1·5Mn (mass%) alloys with Nb addition of 0·03 mass%. Bainite transformation occurs at temperatures below 873 K. At 853 K, transformation rapidly proceeds by formation of bainitic ferrite without carbide precipitation, but transformation stasis appears for a certain period in the Nb added alloys leaving untransformed austenite film between neighbouring bainitic ferrites. On the other band, the Nb free alloys do not show such a stasis until the transformation is completed. By further holding, the transformation in the Nb added alloy restarts by forming the mixture of dislocation free ferrite with cementite precipitation in the austenite films. In contrast, bainite transformation accompanying cementite precipitation occurs in both Nb free and Nb added alloys at 773 K, resulting in no difference in transformation kinetics. It is proposed that the incomplete transformation is caused by suppression of ferrite nucleation at interphase boundaries between pre-existing bainitic ferrite and austenite due to Nb segregation.