Drop hammer impact tests were conducted to study crack features and the ductile–brittle transition in sea ice under low-speed impact. Crack images were analyzed using Hessian filtering and Hough transform methods, and a finite element model was created. Material parameters were validated using the crack tip strength factor. Energy dissipation, focusing on kinetic energy, was analyzed to understand energy conversion and crack propagation in sea ice during low-speed impact. The results indicate that the angular distribution of the crack mode exhibits central symmetry, with the peak frequency at each angle approximately 5°. As the initial impact kinetic energy increases, the dynamic response of the sea ice plate transitions from toughness to brittleness; the kinetic energy dissipation increases linearly, while its utilization efficiency declines. The variation in the kinetic energy conversion rate (η) is associated with the mode of ice plate failure. The crack propagation rate follows a normal distribution in relation to changes in time and kinetic energy. The stress wave effect predominates in the fracture formation mode, further elucidating the ductile–brittle transition behavior of sea ice. This research holds significant implications for ice-breaking operations.