图为EA4T钢低温疲劳断口形貌，EA4T钢室温时出现颈缩，随着温度的降低，裂纹扩展区占比逐渐增加，与疲劳寿命趋势一致。图 (e)-(g)给出了-20℃试样裂纹起裂区、裂纹扩展区和瞬断区微观形貌，与0.05V钢相同，疲劳断口为单点起裂，扩展区呈解理状，瞬断区呈韧窝状。

The figure shows the low-temperature fatigue fracture morphology of EA4T steel. Necking occurs in EA4T steel at room temperature. With the decrease of temperature, the proportion of crack growth zone increases gradually, which is consistent with the trend of fatigue life. Figure (e)-(g) shows the micromorphology of the crack initiation zone, crack propagation zone and transient fracture zone of the sample at -20℃, which is the same as that of the steel at 0.05V. The fatigue fracture is a single point of initiation, and the propagation zone is like cleavage, while the transient fracture zone is like dimple.