当回火时间为15 min时个别韧窝中含有第二相粒子，塑性变形显著，具有较高的冲击韧度。随着回火时间的延长，韧窝所占区域、韧窝尺寸和深度减小，而放射区面积则增大，存在明显的放射区特征，断口整体较平整，塑性变形程度有所下降。

When the tempering time is 15 minutes, individual dimples contain second-phase particles, which have significant plastic deformation and higher impact toughness. With the extension of the tempering time, the area occupied by the dimples, the size and depth of the dimples decrease, while the area of the radiation zone increases. There are obvious characteristics of the radiation zone, the fracture is relatively flat and the degree of plastic deformation decreases.