According to the specs at aksteel.com, its just a ferrite free version of 17-4. Use carbide tooling with sharp edges(minimum edge prep) and a quality coolant such as syntillo 9913. Myself, I would use TIN coated endmills rather than TIALN. High speed machining is ideal for this type of material. I have a video on youtube that shows what can be done with 17-4 ss. Good luck.
[nomedia="http://www.youtube.com/watch?v=E3AqIZURMbI"]YouTube - HIGH SPEED MACHINING(REALLY HIGH!!!)[/nomedia]