Si对铸态高碳铬轴承钢中渗碳体类型转变的影响机理

Mechanism of Si on the Cementite Type Transformation in As-cast High Carbon Chromium Bearing Steel

利用真空感应炉制备了四种不同Si(质量分数/%:0.29、0.42、0.71、1.50)的铸态高碳铬轴承钢,并采取非水溶液电解法萃取钢中碳化物。通过扫描电镜观察钢中碳化物的二维和三维形貌,采用X-射线衍射仪(XRD)对不同Si含量下碳化物的类型进行探究,并结合热力学和第一性原理计算明确Si含量影响渗碳体类型的本质机理。研究结果表明,不同Si含量的高碳铬轴承钢中都存在两种类型的碳化物,分别是片层状渗碳体((Fe_(1-X)Mn_(X))_(3)C)和晶界碳化物M23C6。随着w[Si]从0.29%增加到1.50%,M23C6晶界碳化物由连续粗大的棒状结构变为断续细小的点状结构,说明Si含量的增加对晶界碳化物的析出具有抑制效果。而Si含量的增加,降低了Mn在(Fe_(1-X)Mn_(X))_(3)C渗碳体中的占比,渗碳体类型的转变趋势为Fe_(1.8)Mn_(1.2)C向Fe_(3)Mn0C转变。可能的原因是,渗碳体生成析出过程,Si原子被外排到渗碳体周围形成富Si微区,阻碍基体中的Mn原子向渗碳体扩散,降低了Mn在基体中的活度以及扩散迁移能力,从而降低了Mn在渗碳体中的相对含量。

Four as-cast high carbon chromium bearing steels with different Si contents(0.29%、0.42%、0.71%and1.50%)were prepared using a vacuum induction furnace,the carbides in the steel were extracted by nonaqueous solution electrolysis method.The two-dimensional and three-dimensional morphology of carbides in steel was observed through scanning electron microscopy.the types of carbides at different Si contents were investigated by X-ray diffractometer,the essential mechanism of influence of Si content on cementite type was determined by thermodynamics and first principles calculation.The research results indicate that there are two types of carbides in as-cast high carbon chromium bearing steel with different Si contents,namely layer cementite(Fe_(1-X)Mn_(X))_(3)C and grain boundary carbides M_(23)C_6.With the increase of Si content(0.29%-1.50%),the M_(23)C_6 grain boundary carbides change from a continuous coarse rod-shaped structure to a discontinuous fine point like structure,which indicate that the increase of Si content has an inhibitory effect on the precipitation of grain boundary carbides.In addition,the increase in Si content reduces the proportion of Mn in(Fe_(1-X)Mn_(X))_(3)C cementite,and the transformation trend of cementite type is from Fe_(1.8)Mn_(1.2)C to Fe_3Mn_0C.The possible reason is that during the precipitation process of cementite formation,Si atoms are discharged into area around cementite to form a Si rich micro zone,which hinders the diffusion of Mn atoms from the matrix to the cementite,reduces the activity and diffusion migration ability of Mn in the matrix.Thus,the relative content of Mn in the cementite is reduced.