中碳和高碳钢中束状马氏体的形成机理

Formation Mechanism of Packet Martensite in Medium and High Carbon Steels

用光学显微镜和扫描电镜观测了 12种中碳和高碳钢淬火组织形态 ,证明了中碳和高碳钢在高温淬火后形成的束状组织不是板条马氏体 ,而是片状马氏体。从晶体学角度探讨了片状马氏体相互平行、呈束状生成的原因。通过改变奥氏体的均匀切变方向和马氏体片晶所平行的奥氏体方向 (即双改变 ) ,来实现邻接马氏体片之间保持孪晶关系 ,以降低形核功和核长大功。马氏体相变的孪晶界面束状机制是细片马氏体相变的普遍方式 ,即在同一惯习面上 ,通过在已形成晶核的旁边生成具有孪晶关系的新晶核 ,以降低界面能和应变能 ,导致形成束状薄片马氏体。

The as-quenched microstructures of twelve commercial steels were observed using optical microscope and scanning electron microscope. It is found that the packet martensite formed in medium and high carbon steels quenched from high temperature is not lath martensite, but rather fine plate martensite. The formation mechanism of the packet martensite was explored in detail from martensite crystallography. Remaining the twin relationship between the adjacent martensitic plates may significantly lower the free energy barrier of martensite nucleation and growth, which may be realized through changing the direction of homogeneous shear of austenite and the austenitic direction, which is parallel with martensite platelet (i.e. double alteration). The packet mechanism of twin boundary proposed is a common fashion of transformation of fine plate martensite, that is to say, a new nucleus with twin relationship will form at two sides of the old nucleus along the same habit plane for diminishing remarkably the boundary energy and the volume strain energy, then forming packet plate martensite.