Milling 316A at 55 HRC

exkenna · Apr 25, 2018

Well I had some fun today. Milling a Textron bracket, customer tearing up APKT cutters right and left.
They tried every combination of feed and speed they could think of, inserts snapping like crazy.
So I thought, hmm.. 316 shouldn't be THAT bad. But I had a hunch so I asked them to put it on the hardness tester while I went to get a 2" 4-flute feed mill. Came back with cutter and ended up getting a good cut at 215 sfm and 49 IPM at .035 DOC.

The material tested at 55 HRC. I had no idea you could get 300 series to harden like that.
Customer claims that the mil-spec process calls out heating to 1900F and water quench.

Ever heard of such a thing??

X

XD341 · Apr 25, 2018

Nope, I was always under the impression that real 300 series was not heat treatable. That's about the range for 17-4 H900, but that stuff doesn't cut that bad. It's also not austentitic. (sp?)

My first reaction would be to question the nature of the material. It's shinny and bright and maybe resists corrosion but at 55Rc I'd doubt it's 316

The next possibility is that it was a bad hardness test, or wrong scale.

Bobw · Apr 25, 2018

exkenna said:
Well I had some fun today. Milling a Textron bracket, customer tearing up APKT cutters right and left.
They tried every combination of feed and speed they could think of, inserts snapping like crazy.
So I thought, hmm.. 316 shouldn't be THAT bad. But I had a hunch so I asked them to put it on the hardness tester while I went to get a 2" 4-flute feed mill. Came back with cutter and ended up getting a good cut at 215 sfm and 49 IPM at .035 DOC.

The material tested at 55 HRC. I had no idea you could get 300 series to harden like that.
Customer claims that the mil-spec process calls out heating to 1900F and water quench.

Ever heard of such a thing??

X

Yes, you can get 300 series stainless really hard, but not by heat... You can get dowel pins from 304 (18-8)
that are up in the 40's.. Its cold worked, there is NO heat treatment that should ever be able to harden a
300 series stainless.. Softer yes, harder, no.

1900 and quench, and its HARD... Tells me its not a 300 series stainless.... Did they have the right
tip on their hardness tester?

Something stinks.. Here is a possibility, it happened to me once (victim).. Customer saw 3## in the material
spec, so they had castings made from 3##SS.. SUCKED!!!!! Turns out the actual SPEC with letters before it and
all that, was just some garbage cast iron with a tensile strength of about 32ksi.

Kind of like thinking that A286 and A356 are anywhere in the same ball park.

Something definitely is wrong... But it gives me comfort that YOU were able to cut it.

JCarroll · Apr 25, 2018

Yeah,
I have but we heat treated the parts after machining.
How the part enters the water bath is apparently a big deal.

XD341 · Apr 25, 2018

JCarroll said:
Yeah,
I have but we heat treated the parts after machining.
How the part enters the water bath is apparently a big deal.

and these were 304 316 321 or 347 parts? I would be interested in seeing info on that, I have never heard of hardening 300 series, I've seen it annealed but never made harder.

exkenna · Apr 25, 2018

I agree. Something stinks. But you can't file it or knock the burr off with a debur blade.
Had to put it on the belt sander to get the bur off.

XD I agree about 17-4, it cuts better heat treated to 38-42.
I wonder if they got slipped some Inco

JCarroll · Apr 25, 2018

It was in the 80's but the parts were 316 as I recall.
Round parts that had a parabolic OD then a flat moving towards the center for an inch or so.then a radius that decreased the thickness to a 2" diameter spud with a round pocked from one side in the center.
The thickness where the part thinned was 0.090". The "ring" around the OD was an inch thic and the spud in the center was 2" thick and received a pure tungsten core that was pressed in. That's why I remember the job. The part had to be heated enough to allow a huge amount of interference at room temperature but had to drop in when the part was heated.
Anyway, the HT process was called out in some detail and required the parts to be rolled on their edge into the water bath.

Most of the free World saw these in action and there is probably still a video around somewhere.
They were the powered triggers for the goofy laser that was powered by a nuclear explosion.
It was a one use weapon because the building that powered the thing collapsed on itself when the nuclear device detonated.

I made the wave guides for the trigger as well.

robert123 · Apr 26, 2018

1900-2050 and water quenching is the annealing procedure. Did they perform the hardness test on an area they had previously cut? If it was really 316 and they were burning up inserts, the material was likely being work hardened.

azmachining · Apr 26, 2018

Jcarrol, I think your mistaken, they were rolled (cold) to harden.

azmachining · Apr 26, 2018

Could be nitronic.

DMF_TomB · Apr 26, 2018

exkenna said:
Well I had some fun today. Milling a Textron bracket, customer tearing up APKT cutters right and left.
They tried every combination of feed and speed they could think of, inserts snapping like crazy.
So I thought, hmm.. 316 shouldn't be THAT bad. But I had a hunch so I asked them to put it on the hardness tester while I went to get a 2" 4-flute feed mill. Came back with cutter and ended up getting a good cut at 215 sfm and 49 IPM at .035 DOC.

The material tested at 55 HRC. I had no idea you could get 300 series to harden like that.
Customer claims that the mil-spec process calls out heating to 1900F and water quench.

Ever heard of such a thing??

X

.
in general the harder the material the less the depth of cut. not unusual to be taking only .001 or .002 depth milling 65 rockwell stuff. if you take too much you loose the corners.
.
stuff can also be abrasive and full of slag hard spots. bigger hard spots can wipe out 10 sets of carbide inserts within a seconds of hitting it.

JCarroll · Apr 26, 2018

"Did they perform the hardness test on an area they had previously cut? "
Yes and there was a test part for destructive testing purposes.
My primary involvement was due to the fact that I could program the shape.
Thirty five years is a pretty long time when counted in parts.
LOL
I remember distinctly that the parts were as hard as the hobbs of hell, stalling out a MAZAK QSH10.
I ended up moving them to an older M2 Mazak oil field lathe which was a real hassle because the thing had a tape reader on a Fanuc 2000C control.
No BTR or anything.
CAM was in the early days and the guys at Sandia sent me over to a shop on the edge of the Acoma Indian reservation to get the job moving.
The job was a cast iron bitch and I still cringe at 300 series SS in spite of the fact that most of the people I know cutting it - mostly 303 and 304 - day in and day out love the stuff.

Kaszub · Apr 26, 2018

303 best ever to cut
304 not bad
302 can suck
316 sucks most of the time

Dan from Oakland · Apr 26, 2018

Only way I know to get 300 series stainless that hard is to nitride it. But that's a surface hardening process. By any chance was the core soft once you got thru the skin?

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