shallow widths and depths are key to hard milling and high speed milling in general it seems. but you need to maintain a certain level, or youll have problems. if you dont have 5000rpm+, your probably not going to have much luck with hard steel.
tool life i dont really have a personal comment on... havent worn out a tool yet as i dont do alot of machining in hard steel right now. i did kill the variable flute bit outright though in some soft o-1 jogging into the piece by accident. before that it was doing great! haha. supposedly tool life vs removal rate isnt much if any worse than going slow - plus you save on coolant.
ive been using the kenametal calculator, which will give you optimized feed rates based on radial depth. the sandvik one does the same, but its meant for their own indexable tooling only so the actual speed recomendations might not apply.
geof on this forum has a video of his haas cutting 1018 at ~600sfm with a 1/2" carbide end mil about 3/4" deep. it was a trocoidal pass with i think .025" radial depth.
there was an article on mmsonline with some starting point guidelines for hard materials.
http://www.mmsonline.com/articles/ha...e-numbers.aspx
basically between hrc 45 and 60 it recomends 400 to 600sfm as a starting reference which seems to be near where i landed.
frank at maritool recomended a slower sfm(200) but even more agressive feed for the tool i was using to improve tool life though he was specifically talking about 58hrc 4340HT which may behave differently than the vise steel or tool steels.
heres a video of the bit i was using - 4140 steel, 450sfm, .45" depth, about 50% stepover, 55ipm. he states the tool life as well in the comments.
YouTube - Double Ended Variable Flute
the strategy with the harder materials is to simply go shallower width or height, but faster.