通过光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和能谱仪(EDS)等实验方法,研究了三种不同N含量的超低碳贝氏体钢的显微组织和析出相的成分、尺寸、形貌以及分布等特征.结果表明:低氮含量的钢组织为粒状贝氏体,高氮含量的钢组织为粒状贝氏体+少量的针状铁素体.当实验钢中V/N比为3.4时,通过细晶强化和沉淀强化综合作用,可以使材料的屈服强度和抗拉强度分别增加231 MPa和95MPa.与氮含量低的钢相比,高氮含量的钢具有更细小的贝氏体铁素体板条亚结构,且析出相尺寸减小,体积分数增加.基体中存在两种尺寸的纳米级析出相:一种尺寸在10～15nm之间,为V(C,N)析出相,弥散分布在贝氏体板条内部；另一种是含有Cr和V尺寸在10nm以下,具有面心立方结构的(V,Cr) (C,N)复合析出相.%The morphology, size, distribution and chemical composition of precipitates and the micro-structure of the ultra-low carbon bainitic steel with three different nitrogen contents were investigated by optical microscope (OM), scanning electron microscope(SEM) , transmission electron microscope (TEM) and energy disperse spectroscopy (EDS). The results show that the microstructure of the steel with low nitrogen content is granular bainite, while the steel with high nitrogen content is granular bainite as well as some acicular ferrite. When the value of V/N is 3. 4, the yield strength and ultimate strength increase by 231MPa and 95MPa, respectively, which is attributed to precipitation strengthening and fine-grain strengthening. Compared with the low nitrogen steel, the high nitrogen steel can obtain finer bainitic ferrite lathes, the number of precipitates increases and the size decreases. There are two kinds of different sizes of the nanometer-sized precipitate particles in matrix, one of these are vanadium carbonitride, which are the range of particle sizes from 10nm to 15nm and distributed within bainitic ferrite lathes. The other precipitates are smaller than 10nm enriched with Cr and V. It seems that this carbide can maintain the NaCl-type of structure.
展开▼
