I have rusted steel of some sort that I am trying to machine a hole on using flat end HSS in a circular arc. It's only a few mm deep.

One flat end turned melting red and was already burned out just trying to drill the initial hole on the material. The settings were around 300 RPM, approx 12 mm (half inch) flat end, and a very modest 15 mm / minute feed rate and modest cooling by hand. On a Bridgeport clone...

I have previously had significant trouble working with similar material - I thought it would behave like butter which it did when sawing it. What gives?