The ballistic properties of tool steel as a potential improvised armour plate

The ballistic behaviour of a 0.95 weight per cent carbon tool steel against 7.62 mm ball and armour piercing bullets was investigated in the unwelded and welded condition. Gross cracking occurred at plate hardnesses of 510 H V and greater. The mode of perforation for tool steel of hardness 380 HV, which was petalling for 5 mm thick plates and ductile hole formation, followed by discing, for 10 mm thick plates, was similar to that of conventional armour plates of comparable hardness. The ballistic limit increased more with plate hardness for the deforming ball projectile than for the non-deforming armour piercing round. For the latter the ballistic limit was similar to that for rolled homogeneous armour of similar hardness. All welded assemblies suffered from heat affected zones with hardnesses greater than 500 HV, and for the thinner plates, there was hydrogen-induced cold cracking which split the plate before ballistic testing could be completed. Thus an improvised armour could be made from a commercial tool steel, provided the hardness was kept to 380 HV and below and that there were no welds in the assembly. Better improvised armours could be created from other commercial low alloy steel plate of lower carbon content, heat treated to 380 HV, where the welding would be more easily carried out. Welding would be best performed using austenitic electrodes and pre-heating of the plate, with a double V-butt weld configuration to reduce macroscopic distortion. (C) 1997 Elsevier Science Ltd.