If you are running without a constant coolant flow, I recommend running at 25 to 35 SFM with HSS, even with oil. When I ran a mill I ran HSS at 50 SFM with constant coolant on most steels. For dry engine machine work I run HSS dry at much slower speeds on steel and cast iron. Make sure you are feeding hard enough to make a chip which also cools the tool and reduces work hardening; a dull tool will not make a good chip.
