303 SS Vs 17-4 1

[WGP1]

We're looking at switching to 17-4 SS in place of 303 SS. What are the pros and cons. Material compatibility, machining, surface finish and cost?

Thanks.

 

[NickE]

cost will be higher than the straight 300 grade, will likely machine worse, surface finish can be better, you may need to heat treat to get a good strength in the 17-4.

Why are you changing from the common 303 (austenitic with added sulfur and phos to aid machining) to the rarer 17-4 (semi austenitic precipitation hardening grade)?

nick

 

[WGP1]

Thanks for your response,

We're currently pressing a 303 SS insert into a 303 SS body, of course we're seeing galling. We thought using a deferent grade of SS would work better.

Wayne

 

[israelkk]

This will not help, 17-4 will gall with 303. Basically all stainless steel combinations such as 303, 410, 420, 416, 17-4, 15-5 will gall with each other when you pressfit one to the other. Sometimes it will not gall but when you least expect it, it will gall. We had some manufacturing batches were there was no gall but in the next batch 50% of assemblys had gall. So we had to change one of the mated parts to plated low carbon steel.

You can try Nitronic alloys such as Nitronic 60 or Carpenter NO gall alloys.

 

[WGP1]

Our machinist suggested 304, 316L or 309 because it's harder than 303. If we plate the insert, would the plating flake off during insertion?

 

[israelkk]

304, 316L or 309 are not harder than 303 they are more difficult to machine. 303 is a free cutting version of 302, 304 with added Sulphur or Selenium that improve chip removing.

All 18-8 stainless steels can be purchased in the annealed, 1/4 hard, 1/2 hard. 3/4 hard and hard condition which is achieved by cold work but it will not avoid galling.

See the other post for the gold plating suggestion.

 

[WGP1]

israelkk
I just tried liquid nitrogen, .0001 shrinkage. I like your suggestion for Nitronic alloys, is it hard to machine, costly, hard to find?

 

[israelkk]

I think it is about 40% less machinable.

http://www.hpalloy.com/FTP/Alloys/Nitronic60/Nitronic60brochure.pdf

 

[engamopar]

Age hardening parts made from 17-4ph (solution annealed - AMS 5643). Need: H900 (Rc 40-47). Aging is per AMS 2759/C.
(900degF @ 1hr; +15 min. /-0.00 min). 15 minutes into the soak, power goes out for 10-15 min. When power returns operator cooks parts for additional 45 minutes. Operator's rationale: TOTAL soak is 60 minutes, (though not continuous. The result is that parts exhibit Rc42, right where they should be. Need to pass shear test also. Assuming they shear correctly, are they good, or must they be re-solution annealed and harened all over again? I.e. Are there any delayed maladies that might surface "down the road" though
the parts may test properly today?

 

[lgearhart]

If they pass the shear test, I'd buy them off within a documented engineering review system. Time at temperature is what controls the precipitation reaction, and since you haven't exceeded 900F, and in 10-15 minutes the furnace may not have cooled too much, I'd believe the parts to be acceptable.

 

[EdStainless]

Let's back up for a sec.
You are pressing stainless into stainless.
Why? What purpose does the insert serve? Why isn't this monlithic?

Presuming that you need an insert, why can't you shrink fit this? If you heat the part with the hole you can get a lot of gowth, room temp to 400F the CTE is 9.6ppm/F. If you cool the insert to LN temps you will get shrinkage of 7.5ppm/F.
If this is a 1" insert, by heating and cooling you will open up 0.006" clearance, if the hole and insert were the identical size to start with.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

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