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目的：分析导辊贯穿裂纹萌发和扩展的机理。方法采用扫描电镜和能谱等手段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,运用数值模拟分析裂纹扩展过程中的应力情况,分析Cr12 MoV导辊中贯穿裂纹的萌发原因和扩展机理。结果元素偏析是Cr12 MoV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1327HV,其周围产生大量微裂纹,并相互连接形成网状而分割机体,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；沿裂纹扩展方向,应力先急剧减小,然后呈抛物线型,在导辊径向厚度达最大时存在一个极大值,在导辊上下表面应力最小。结论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。

ABSTRACT:Objective To analyze the germination and expansion mechanism for penetrating cracks in guide roller. Methods The microscopic images and chemical composition of cracks origin and propagation area of penetrating cracks were analyzed by a-dopting the scanning electron microscope and energy spectrum, the types and hardness of the internal carbides in the cracked guide roller were studied using a combination of the X-ray diffract meter and Vickers hardness tester, the stress condition during crack propagation was analyzed using numerical simulation, and the crack origin causes and propagation mechanism of the penetrating cracks in the Cr12MoV guide roller were analyzed. Results The results showed that elements segregation was the main reason for the initiation of penetrating cracks in the Cr12MoV guide roller. As the two elements in near surface, oxygen and chromium, were significantly higher than those at the crack propagation region, the guide roller could be easily separated under the action of internal stress, leading to formation of cracks in the near surface, which further formed cracks origin. The eutectic carbide of high hardness was the main cause for the crack propagation in Cr12MoV guide roller. The eutectic carbide was mainly (Fe,Cr)7C3 type of block-y-shaped particle, with a hardness of 1327HV, which produced quantities of micro-cracks around. Those micro-cracks were inter-connected, formed a mesh, divided the body, and then formed the penetrating cracks under the action of external force. Extended finite element method ( XFEM) was used to simulate the penetrating cracks and analyze the crack propagation stress. It was found that the stress of the crack-tip was the maximum, the stress curve showed a sharp decrease at first, then a parabolic and reached the vertex of parabolic when the radial thickness of guide roller reached its maximum. The stress of the top and bottom surface of guide roller was the minimum. Conclusion The results showed that the alloy elements and eutectic carbides in the guide roller had a great influence on the crack initiation and propagation, and the crack propagation stress field was directly related to the initial crack position and the size of the guide roller.