3" 316 Stainless Sch 40 Burning Up Inserts

1st time posting on here. I machine 3/4" - 24" MIPT threaded transitions and Victaulic Groove Ends for a pipefitting manufacturer on Haas SL-40 lathes. We machine all our fittings from black steel pipe but occasionally use stainless when we get an order.

While barbing the I.D. with a Kennemetal DMNG432RP insert, we can run the carbon steel all day usually on 1 or 2 sides of an insert, but this week we had an order for 3" IPS 316S Sch 40 Threaded Transitions and had to write up a new program for it. Immediately it started tearing up inserts after only 2 or 3 parts a side, going through 4 or 5 whole inserts a shift. No chatter, just ruining inserts.

We're running G71 stock removal for the roughing of the barbs, looking something like this:
G71 S500 P1 Q20 D0.04 I-0.02 K0.005 F0.0085
This is alot like our carbon steel program just slowed down a little. We don't do a whole lot of stainless and aren't 100% on speeds feeds and depths so I was wondering if anyone has any experience in this sort of area. I just feel like we can get more than 3 parts a side and have messed around all week trying to find a sweet spot with no luck.

Maybe we're running too high a spindle speed? Maybe feeding too much or not enough depth? Maybe the weld bead in the pipe is just much more hard than we're used too or not using the right insert ?

Any help or suggestions would be great. Thanks.

speeds to high your going to be around 300sfm insert will last long time. with a d series insert you might have to slow the feed down cause they suck for removing stock.

agreed ,
roughing 250-400
finishing 275-500

start at 250 SFM

What grade of insert are you using? and what coating?

also the 392 SFM is fast for stainless. Heat kills all, even carbide.

id at least drop it back 30% from where you had it for spindle speed. if not 50%