鱼眼区断口呈现表面粗糙度最低的状态，该处的疲劳裂纹扩展痕迹几乎没有，说明疲劳裂纹在该阶段经历了大量的疲劳周次，在存在疲劳压应力的条件下，疲劳裂纹上下表面反复挤压磨损，使得裂纹面变得光滑，在鱼眼区的内部，紧靠夹杂物的部分存在一个致密且表面粗糙度高于鱼眼区的部分，该区域为被称为细晶粒区（FGA）。

The fracture in the fisheye area shows the lowest surface roughness, and there is almost no trace of fatigue crack growth, indicating that the fatigue crack has experienced a large number of fatigue cycles at this stage. Under the condition of fatigue compressive stress, the upper and lower surfaces of the fatigue crack are repeatedly squeezed and worn, making the crack surface smooth. In the inner part of the fisheye area, there is a dense part close to the inclusion, and the surface roughness is higher than that in the fisheye area, This area is called fine grain area (FGA).