目的 分析导辊贯穿裂纹萌发和扩展机理。方法 采用扫描电镜和能谱分析贯穿裂纹的裂纹源和扩展区域的显微图像和化学成分,结合X射线衍射仪和维氏硬度仪研究裂纹导辊组织中碳化物的种类及硬度；并运用数值模拟分析裂纹扩展过程中的应力情况；以此研究Cr12MoV导辊中贯穿裂纹的萌发原因和扩展机理。结果 研究发现,元素偏析是Cr12MoV导辊贯穿裂纹萌发的主要原因,近表面氧、铬两种元素明显高于裂纹扩展区域,导辊在内应力的作用下分离,在近表面处产生裂缝,形成裂纹源；高硬度共晶碳化物是Cr12MoV导辊裂纹扩展的主要原因,共晶碳化物主要是(Fe,Cr)7C3型块状颗粒,硬度为HV 1327,其周围产生大量微裂纹,并相互连接,形成网状,分割机体,在外力的作用下扩展,形成贯穿裂纹；采用扩展有限元法(XFEM)对贯穿裂纹进行模拟仿真,对裂纹扩展应力进行分析,裂纹尖端应力最大,约为裂纹扩展应力的1.5倍,且沿裂纹扩展方向应力先急剧减小,然后呈抛物线型,在导辊径向厚度刚达最大时应力为抛物线顶点,在导辊上下表面应力最小。结论 结果表明,导辊中合金元素和共晶碳化物对其裂纹的萌发和扩展具有较大影响,裂纹扩展应力场与初始裂纹位置和导辊尺寸直接相关。

Objective To analysis the reason of through cracks germination and Extended of guide roller. Methods By adopting the scanning electron microscope and energy spectrum to analyze the microscopic images and chemical composition of cracks origin and propagation area of through cracks，using a combination of the X-ray diffract meter and Vickers hardness tester to research the types and hardness of the internal carbides, and using numerical simulation to analyze the stress condition during crack propagation, the crack origin causes and propagation mechanism of the through cracks of the Cr12MoV guide roller are analyzed. Results Research shows that elements segregation is the main reason for the through cracks initiation of the Cr12MoV guide roller. As the the two elements in near surface, oxygen and chromium, are significantly higher than the crack propagation region, the guide roller can be easily separated under the action of internal stress, which forms the cracks in the near surface, and becomes cracks origin. The eutectic carbide of high hardness is the main reason for the crack propagation in Cr12MoV guide roller, the eutectic carbide is mainly (Fe, Cr)7C3 type of blocky-shaped particle, the hardness is 1327 HV, which produces quantities of micro-cracks around. Those micro-cracks are interconnected, form a mesh, divide the body, and then form the through cracks under the action of external force. Extended finite element method (XFEM) is carried out on the simulation of through cracks and the analysis of crack propagation stress. The results find out that stress of the crack-tip is the maximum, the stress curve is a sharp decrease at first, then a parabolic and reaches the vertex of parabolic when the radial thickness of guide roller has just reached their maximum. The stress of the top and bottom surface of guide roller is minimal. Conclusion The results show that the alloy elements and eutectic carbides in the guide roller have a great influence on the crack initiation and propagation, and the crack propagation stress field is directly related to the initial crack position and the size of the guide roller.