贝氏体碳化物是贝氏体组织的重要组成部分，本文目的是阐明下贝氏体碳化物的来源。为此，本文做了三件事：1. 做了三组实验，结果表明：下贝氏体碳化物是在贝氏体a/g界面的奥氏体一侧析出， 向奥氏体中生长，也在亚单元之间析出。在形态上，碳化物可跨越a/g或a/a界面；2.再做了另一组实验，说明在表观现象上是下贝氏体碳化物主要存在于铁素体内部，而实质上是析出自于a/g界面的奥氏体一侧。在整个相变过程中铁素体与碳化物的长大呈相互竞争机制，铁素体的长大速度远高于碳化物，二者长大的结果是铁素体将碳化物包围，导致碳化物似乎是由铁素体中析出的假象；3.对实验结果用热力学及台阶理论做了分析，在实验证据及理论分析的基础上提出了下贝氏体碳化物的析出及长大模型。 以上工作，明确了下贝氏体碳化物是由富碳残余奥氏体中析出而不是由碳过饱和的铁素体中析出。其实质是确定新形成的贝氏体铁素体中是否过饱和碳，这直接涉及贝氏体相变机制的类型。
The carbides of lower bainite is main constituent of bainite structure. The purpose of this paper is to clarify that where the lower bainitic carbides come from. Therefore ,three things have been completed in this paper:1. By using three group of experiment,the results indicate that the lower bainitic carbides can nucleate in the g side of a/g interface or between two bainitic ferrite sub-units and grow towards austenite. The carbides can exist across the interface of a/g or a/a.2. The results of another experiment indicate that the essence of phenomenon that lower bainitic carbides exist inside the ferrite is lower bainitic carbides precipitate from the g side at a/g interface. The carbides grow competitively with the ferrite,during the whole transformation process. Meanwhile the growing rate of ferrite is higher than that of carbides. As a result, the carbides are surrounded by ferrite which may give us a false concept that the lower bainitic carbides are precipitated from bainitic ferrite.3. The nucleation and growth model of lower bainitic carbides is proprosed on the basic of thermodynamics and the ledge-wise growth theory. From what has been mentioned above,it is suggested that lower bainitic carbides precipitate from carbon-enriched retained austenite rather than supersaturated ferrite. The essential of this paper is to identify whether existing the carbon-supersaturated bainitic ferrite , which directly concerning the mechanism of bainitic transformation.
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