Milling of Stainless Steel Casting in HN alloy

[Supra1]

Hi friends,

I have a requirement of milling slots in a Stainless Steel Casting conforming to ASTM A 297 Gr HN.
I have tried using a K20 endmill but it has to be reground repeatedly as it loses its edge.
Can somebody advise me on the cutter to be used?
Thanks.
Supra

 

[musashi99]

Tell me more about the slots you are milling.

 

[Supra1]

Actually I am milling the bore of a roller casting to generate four flat surfaces in the bore so that the roller can be locked on the shaft which has four flats on its diameter.The depth of the flat in the bore of the roller is 60mm.The bore is 150mm and the flats are 80mm in length.

Supra