硕士论文“钢中贝氏体相变机理的研究”---指导教师：刘宗昌

chg1555

9.8兆的好资料---高清
摘要
奥氏体的中温转变产物贝氏体，从被发现之日起就受到广泛怀疑，而贝氏体相变机制至今还在延续着切变观点和扩散观点近个多世纪的针锋相对的论争。本文应用透射电镜(JEM．2100F)、环境扫描电镜(Quanta-400)、扫描隧道显微镜(Nanofrist．1000型)和光学显微镜(LeiCa)等仪器对20CrMo、35CrMo、45CrNiMoV、S7、60Si2CrV、GCrl8Mo、GCrl5、9Cr3Ni等工业用钢分别进行等温实验和表面浮凸观察实验。对组织形貌观察表明，上贝氏体不止可在界面形核，还可以在晶内激发形核，随着碳含量的增加，组织形貌由片条状逐渐过渡为羽毛状；针状贝氏体束构成下贝氏体组织；通过对铁原子和替换原子扩散系数、贝氏体长大速度的计算和表面浮凸的观察，表明贝氏体相变切变机制和扩散机制与实际不符；并且证明了贝氏体形核和长大过程中，相界面处铁原子和替换原子的非协同热激活跃迁性。同时，实验分析和理论研究，表明贝氏体转变开始于贝氏体铁素体的形核，且在贝氏体铁素体和原奥氏体界面析出形核的贝氏体碳化物通过长大形成的贝氏体亚单元，使得贝氏体形貌多样化。贝氏体铁素体和贝氏体碳化物形核．长大过程中铁原子和替换原子是以原子非协同热激活跃迁方式进行的。贝氏体热激活跃迁机制是相界面处铁原子和替换原子以不同位移矢量跃迁，使贝氏体铁素体／奥氏体(BF／A)和贝氏体碳化物／奥氏体(Bc／A)界面向奥氏体中推移，形成贝氏体，且原子跃迁距离在一个原子间距内。最后，在系统的自组织作用下，贝氏体组成相有序组合，有效配合，最终形成贝氏体组织；并指出表面浮凸只是表面转变必然存在，不能作为某些相变的特征进行研究。本论文也对贝氏体转变的原子热激活跃迁机制提供实验和理论支持。
Abstract
Bainite，the isothermal transformation product of austenite，was widely suspected from the day of discovery．Bainitic transformation mechanism was debated by displace and diffusion points，which has been mOll than half of the century．In the paper,isothermal experimentation and surface relief observation experimentation of 20CrMo steel，35CrMo steel，45CrNiMoV steel，S7 steel，60Si2CrV steel，GCrl8Mo steel，GCrl 5 steel and 9Cr3Ni steel of industrial steels were investigated by ransmission electron microscopy(JEM一2 1 00F)，environmental scanning electron
microscope(Quanta-400)，scanning tunneling microscopy(Nanofrist-1 000)and optical microscopy(LeiCa)and SO on．
111e observation of the morphology showed that the upper bainite moil than Call be nucleated at the boundary and also Call be stimulate—nucleated in the intragranular,the morphology gradually transmitted from the needle—like to feathered by increasing of carbon contents；needle bainite beam formed lower bainite；bainitic transformation
shear mechanism and actual diffusion mechanism were inconsistent supported by the calculation of growth speed of bainite，the replacement of iron atoms and atomic diffusion coemcient，and the observation of surface relief；and non-concerted thermal activation transition of iron atoms of the interface and replacement atoms were proved
in nucleation and growth process of bainite．At the sal'ne time，experimental analysis and theoretical research showed that bainitic transformation occurred at the beginning of nucleation of bainitic ferrite，also bainitic carbide of bainitic ferrite and original austenite interface nucleation formed as bainitic sub-unites by,which made diversely bainite morphology．111e iron atoms and replacement atoms were conducted by atom non-concerted thermal activation transition way in the process of growing and nucleation of bainitic ferrite and bainitie
carbide．The bainitic thermal activation transition mechanism was different displacement vector transition between iron atoms of the interface and replacement atoms，which made the bainitic ferrite／austenite(BF／A)and bainitic carbide／austenite (Be／A)interface lapse to the austenite to formed as bainite，and also the atom transition distance within an atom．Finally,the bainite was formed by the system’S function of self-organization,orderly combination and efficiency cooperation of composition phase of bainite，and also indicated that surface relief was must exist in surface transition,could not be studied as the characteristics of some phase transitions．In the paper,the experiments and theories were presented to support the mechanism of atom thermal activation transition of bainite transformation．