下贝氏体中碳化物的析出  

PRECIPITATION OF THE CARBIDES IN LOWER BAINITE

作　　者：方鸿生[1] 冯春[1] 郑燕康[1] 郑秀华[2] 张弛[1] 白秉哲[1] 

机构地区：[1]清华大学材料科学与工程系先进材料教育部重点实验室,北京100084 [2]北京理工大学材料科学与工程学院,北京100081

出　　处：《金属学报》2007年第6期583-588,共6页Acta Metallurgica Sinica

摘　　要：通过3组实验证实了下贝氏体碳化物是在α/γ界面的奥氏体一侧析出,并向奥氏体中生长,同时也在贝氏体亚单元之间析出．在形态上,碳化物存在于铁索体内,也可跨越α/γ或α/α界面;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,碳化物从α/γ界面的γ一侧析出,但铁索体的长大速度远高于碳化物,二者长大的结果是铁索体将碳化物包围,导致碳化物似乎是由铁索体中析出的假象;用热力学及台阶理论对实验结果做了分析,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;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索体中析出,其实质是确定新形成的贝氏体铁素体中是否含有过饱和碳,这直接涉及贝氏体相变机制的类型．By using three groups of experiment, it is shown that the lower bainitic carbides can nucleate in the γ side of α/γ interface or between two bainitic ferrite sub-units and grow towards austenite. Morphologically, the carbides can exist inside the α or pass across the interface of α/γ or α/γ; The carbides grow competitively with the ferrite during the whole transformation process, and the carbides are precipitated from austenite side of the α/γ interface, meanwhile the growing rate of ferrite is higher than that of carbides, as a result, the carbides are surrounded by ferrite, resulting in a false inpression that the lower bainitic carbides are precipitated from bainitic ferrite; The nucleation and growth model of lower bainitic carbides is proprosed on the basics of thermodynamics and the ledge-wise growth theory; It is suggested that the lower bainitic carbides precipitated from carbonenriched retained austenite rather than supersaturated ferrite, which directly concerns the mechanism of bainitic transformation.

关 键 词：下贝氏体 碳化物 析出 贝氏体相变机制 

分 类 号：TG111.5[金属学及工艺—物理冶金]