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(DIF), DIF量随形变温度 降低而提高; 在低于750 ℃形变时, DIF量远高于平衡 态铁素体含量54%. DIF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. 在低于A1 (719 ℃)等温处理时, 高于Ad3点形变试样中, 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 for a medium carbon steel, the deformation induced ferrite (DIF) appeared when deformed temperatures lower than A d3 (786 ℃). The volume fraction of DIF increases with decreasing deformation temperature, especially when deformed temperatures lower than 750 ℃ the volume fraction of DIF increases significantly, which is far beyond the equilibrium ferrite fraction of 54%. With the increase of DIF, more and more carbon atoms were rejected into the boundaries of ferrite and interfaces of ferrite/untransformed austenite. During isothermal holding below A1 (719 ℃) temperature just after deformation, supercooled austenite would decompose to different structures in three different ways: when the deformation temperature is higher than Ad3, conventional ferrite-lamellar pearlite structure was obtained; when the deformation temperature is lower than Ad3 whereas higher than Ar3 (645 ℃), retained austenite transformed to ferrite-lamellar or degenerated pearlite-grain boundary cementite; when the deformation temperature decreased to just above Ad3, a microstructure different from lamellar pearlite was obtained, which consisted of fine cementite particle and ferrite.
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