Hole grating in the exhaust ???

Hey guys, so have (had) in my exhaust hole grating. Pretty tough the material, whatever it might be, stainless steel probably. Drilling holes had in the beginning 4 or 4.5 he diameters. Then, because the sense behind lattice in the exhaust did not open up to me, first drilled on 5, then on 6 and then with a seperate step cut through the bridges and have only a small edge stand. Had the material presented to me less unruly, but with dremel and corund attachment I WANT to the rest of the back, but in vain. Someone have an idea what to look for in the exhaust ? Just optical thing maybe ?? Or an idea what to do with the rest. Does a tungsten carbide cutter help there perhaps ? Mfg