drilling out exhaust bolt holes

[2000Blazer4x4]

I broke off both studs that were welded to the intermediate pipe while trying to remove the y-pipe during my tranny swap. (they were PB blaster treated for a couple days and torched but still broke) Now I am trying to drill out new holes to reasseble the exhaust but it is taking FOREVER!! I am using a 120V, 5.5A, 3000rpm hammer drill with colbalt drill bits. I can't remember from my engineering materials class how much harder colbalt is compared to steel, but I assume quite a bit since these are metal cutting bits. So what I need to know is:
What is a quick, easy way to drill through about a 1/2" of steel?

[s106banger]

do you have oxy/acl torch. i heated them red hot, glowing red. took a punch and they punched right out. there not welded in there pressed, or atleast there were on my truck. i to tried to drill it, why to slow. i dropped the whole cat and did both sides for the future.

[2000Blazer4x4]

no oxy torch

[JollyRojer]

carbide man, gotta go to the carbide always it will make that metal feel like its fckn cheese.