[wrenchnride247]

I have not done this to a 901 flange, but deal with machining hardened parts often at work. Carbide bits would be a better option. You are correct in using slow RPM's to drill. One problem you are facing is that the bit is only using the outer most part to drill since the hole is close to the size it neeeds to be to install the insert, which wears the flutes out in short order. It may take several bits to do it. Then the fun part will be getting the tap to work without sticking and snapping off even with all the cutting fluid you can pour on it. All you can do is go "slow and steady".