| The microstructural change and penetraion phenomenon of the 0.25% C-Mn-Mo-B steel plate were studied by impacting the blunt. type cylindrical steel rod with high velocity. The projectiles were accelerated to the range of 500m/sec-700m/sec, and the impact velocity was measured by means of light screen. The perforated hole diameter was increased as the hardness of the steel plate was decreased. This corelation of hole diameter and hardness was not related to the penetration resistance : the penetration resistance showed maximum value around HRC33, and then decreased due to the adiabatic shear band farmed in accordance with increased hardness. The average width of adiabatic shear bands was 5-25㎛, and the microhardness of the band, 780-890HV, was much higher than that of matrix, 320-435HV. The microstructure of adiabatic shear band was found to be untempered martensite with high dislocation density and very fine grains. |
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