Originally Posted by trees
Proper speed is the key to nice hole and tool life. You have destroyed the tool by too much speed which generated too much heat which destroyed the temper and the teeth. Been there: done that. Same is true for any cutting tool such as end mills, saw blades and drill bits. Get an old Machinist Handbook and read up on cutting speeds for various tools (size matters) and materials. Save a lot of bucks.
Yup and use plenty of cutting oil to keep the tool cool..