中碳钢形变及冷却过程中的组织演变

The Microstructure Evolution of Medium Carbon Steel During Hot Deformation and Controlled Cooling

热模拟单向压缩下,中碳钢形变温度低于Ad3(786℃)点时,析出形变诱导铁素体(D IF),D IF量随形变温度降低而提高;在低于750℃形变时,D IF量远高于平衡态铁素体含量54%。D IF析出时碳原子高度富集在铁素体晶界和铁素体/奥氏体界面。形变后在低于A1(719℃)温度等温或控冷过程中,过冷奥氏体将发生不同类型的转变:高于Ad3形变试样中,奥氏体转变为铁素体+片层状珠光体;低于Ad3点但高于Ar3(645℃)点形变时,未转变奥氏体转变为铁素体+片层状珠光体+晶界渗碳体;稍高于Ar3点形变时,将获得铁素体+弥散渗碳体的球化组织。

During uniaxial hot compression the deformation induced ferrite （DIF） is precipitated in medium carbon steel when deformation temperature is under Ad3 （786℃）. The volume fraction of DIF increases with the decrease of deformation temperature. When the deformation temperature is below 750℃ the volume fraction of DIF increases significantly, reaching a level 54% higher than the equilibrium ferrite fraction. With the increase of DIF, more and more carbon atoms are concentrated at the ferrite boundaries and ferrite / austenite interfaces. When the isothermal holding temperature is below A1 （719℃） just after deformation, the supercooled austenite would decompose into three different structures, if the de, formation temperature is above Ad3, austenite would transform into ferrite-lamellar pearlite; if the deformation temperature is below Ad3 but higher than Ar3 （645℃）, the retained austenite would transform into ferrite-lamellar pearlite-boundary cementite; if the deformation temperature is slightly higher than Ar3, a spheroidal structure of ferrite-dispersed cementite will be obtained.