碳含量对铬钼钢贝氏体组织形貌的影响  

Effect of Carbon Content on Bainite Microstructure of Chromium-Molybdenum Steels

作　　者：刘宗昌[1] 计云萍[1] 任慧平[1] 李文学[1] 王海燕[1] 

机构地区：[1]内蒙古科技大学材料与冶金学院,内蒙古包头014010

出　　处：《热处理》2008年第4期19-25,共7页Heat Treatment

基　　金：内蒙古自治区高等学校科学研究项目(NJ06073)

摘　　要：取超低碳的高纯钢和12CrMo、20CrMo、35CrMo、9Cr2Mo和GCr15等工业用钢,淬火时发生中温转变,然后应用QUANTA-400型环境扫描电镜观察贝氏体组织形貌的变化。发现,随着碳含量的增加,过冷奥氏体在中温区的转变,由块状相变到低、中碳无碳化物贝氏体转变,演化到高碳羽毛状上贝氏体和竹叶状下贝氏体。表明含碳量对贝氏体形貌产生显著的影响。探讨了影响机制,认为:(1)块状转变与贝氏体相变有亲缘关系。贝氏体相变时由成分涨落形成贫碳区,并且在贫碳区中形核(BF),它与块状转变的γ→α没有本质上的区别,属于非协同型的无扩散相变。依靠原子的热激活跃迁进行界面移动的过程,新相可连续长大。(2)随着碳含量的增加,在贝氏体铁素体片条之间留下富碳的奥氏体薄膜,铁素体片条之间不能融合时,则得到无碳贝氏体;如果BF片条之间的富碳奥氏体中析出碳化物,则形成羽毛状上贝氏体;如果在BF/γ相界面上析出碳化物,将贝氏体片分割成许多细小的亚单元,则得到竹叶状下贝氏体。The microstructure evolution of bainite of ultra-low carbon and high purity steel, 12CrMo, 20CrMo, 35CrMo, 9Cr2Mo and GCrl5 steels ,was studied by QUANTA-400 electronic microscope after their medium temperature phase transformation took place during the quenching. The results show that, with increase of the carbon content, the medium temperature transformation of overcooled austenite in the steels were＇ as follows ： transformation from massive microstructure to low-carbon, medium-carbon and carbon-free bainites, and further to high-carbon feathery upper bainite and bamboo-leaf-shaped lower bainite, which indicated that the carbon content of steel had great effect on the morphology of bainite. In the meantime, the mechanism of the effect of carbon content on the microstructure of bainite was investigated. The main points of view are described as follow ： （ 1 ） There is a affine relationship between massive transformation and bainite transformation. In bainite transformation, carbon-poor area forms by way of composition fluctuation and bainitie ferrites nucleate in carbon-poor austenite. Bainite transforma- tion has no essential difference with γ→α transformation in massive transformation and belongs to incoordinate transformation without diffusion. The interface moves by means of thermal activation transition of atoms and new phase can grow continuously. （2） Carbon-free bainite will come into being when ferrite pieces do not mix together because of carbon-rich austenite film left between bainite ferrite pieces with increment of the carbon content. Feathery upper bainite will form if carbide precipitates from carbon-rich austenite between bainite ferrite pieces. Bamboo-leaf-shaped lower bainite will be obtained if carbide precipitates from phase interface of BF/γ so that bainite ferrites are divided into many fine subunits.

关 键 词：贝氏体 碳化物 亚单元 块状转变 热激活跃迁 整合 

分 类 号：TG142.1[一般工业技术—材料科学与工程]