segment or it may be bonded to an intermediate segment that is positioned between the base and penetrator segments although cemented carbide is the preferred material for the penetrator in this application for its high abrasion resistance its toughness is less than that of the alloy steel of the base making is more notch sensitive in order to take advantage of this type of material the corners and edges of the penetrator are rounded as a means of reducing its notch sensitivity the applicants have also found that when the surface asperities are reduced for example by polishing the surfaces of the penetrator the transverse fracture resistance of the penetrator is increased making it more resistant to crack propagation when experiencing the bending and accelerations during field use as mentioned above additional improvement in the performance of the penetrator 39 s wear resistance may be achieved by varying the composition of the substrate material and by using multiple grades of substrate material fig4 is a further embodiment of the penetrator segment of the present invention it features a unitary substrate body 40 composed of a cemented carbide preferably tungsten carbide its conical working surface 41 is coated with a material having even greater hardness and abrasion resistance than the substrate material such materials include polycrystalline diamond cubic boron nitride and a binderless carbide material as discussed above when these materials are bonded to the substrate they present a penetrator that exhibits the toughness of the substrate and abrasion resistance.