I used to drill holes in a machine shop years ago.
You need the right drill bits and they need to be sharp, and they will get very dull very quick if you don't use cutting oil to lube the bit.
Carbite tip (colbalt will likely NOT work very well) and cutting oil (not motor oil, get cutting oil) and a slow speed to start followed by moderate speed, that will cut through it. Even if the top was hardened by welding. have an assistant continue to drip cutting oil on it while you drill.