Do you have to machine austenitic duplex stainless steel ??
Use 10-12mm carbide roughing end mill with 4 flute (variable pitch) with straigh cutting edge and the cutting length should be more than 40mm.
Don't use chip breaker. The hardness of your material will break the profile of your chip breaker
If it's the case:
1) Go in the center of pocket (outside the material)
2) Go into the material with helical path (10mm of depth) and diameter of your helical milling is 20mm. The depth of your first helical milling = 10mm
(Vc = 50m/min, fz = 0.03, slope of your helical milling = 1-2°)
3) Remove the material only by shouldering (ae = 1mm, ap = 10mm, Vf = 500mm/min Vc = 50m/min)
4) Repeat this operation four times
Here is a video in order to explain what I mean
Look Z-carb videos
Of course, don't use dry lubrication and the feedrate is lower is your material. Austenitic stainless steel is more difficult to cut.