My Cnc mills aluminium very well I think although I have not mastered finishes yet.

I tried to create a small pocket in Mild steel the other day, with a single flute 6mm endmill. Spindle at 9,000rpm , feedrate 90 mm/pm and depth of cut 0.2mm. Don't know what happened, but it ended up snapping the endmill and making a mess. This is all obviously done wrong.
It was only a practice, but please can someone tell me what rates I should be using for cutting slots in 2.5mm mild steel ? This is not something I am going to be doing very often.