Machining Hardened 17-4 Rings

Brett W · Nov 18, 2021

I was ask to quote, (and pretty sure I am going to turn down) a job today. Part is a 2.25in ring .170 thick, with 16UN thread on the OD, 1.650 ID. This is some sort of retaining nut for inside a tube/bore/etc.

Customer ask for 17-4 heat treated to HR1025 and passivated. So I get to looking at the part and in my mind making this involves the following steps:

Rough machine each ring (20), leaving .050 or more material oversize.
Send out of heat treat
Receive Taco chips back and possibly surface grind flat both sides
Grind ID back to shape to use as a reference for OD threading and finishing operations
Then clamp in fixture and use Mill to thread mill threads into perimeter of said ring.

As I have been told HR1025 is about 40Rc? Being that it is stainless, it will be brutal on tooling if trying to finish machine threads in a single point fashion, assuming I could get it straight enough after heat treat to actually thread within tolerance.

Option 2 rough cut threads and have them finish ground?

Obviously I am out of my depth here on this project, but looking to learn at least the process, not necessarily to do the job.

TeachMePlease · Nov 18, 2021

I think 1025 is only a little less machineable than 17-4 H900.... If I could only cut one material for the rest of my life, it'd probably be 17-4 H900. It's 38-45 HRC, but doesn't machine like it. Quality carbide tooling has no problem with it. I dunno about the thickness though, never done anything that large/thin out of H900...

Booze Daily · Nov 18, 2021

I’ve machined lots of 17-4 that got heat treated by the customer. Parts were made to print with no post HT machining required.

Kingbob · Nov 18, 2021

we buy in this already heat treated, it's really not that bad.

plastikdreams · Nov 18, 2021

17-4 pretty much doesn't move after heat treating. I've made many net parts then heat treated with flatness and parallelism unaffected.

mhajicek · Nov 18, 2021

I prefer to machine 17-4 in the hard. Very stable, good tool life, good surface finish. It threadmills well too. Just order your material pre-hardened, cut the part, passivate, and ship it.

EmGo · Nov 18, 2021

plastikdreams said:
17-4 pretty much doesn't move after heat treating. I've made many net parts then heat treated with flatness and parallelism unaffected.

I would probably either do them hard or rough, then finish hard ... 17-4 doesn't usually distort much but if this happens to be the one time it does, you're screwed.

As I get older I get to be more of a coward ... and the stuff machines fine hard, even threads. 40 is not that hard, for carbide.

Brett W · Nov 18, 2021

Why would I need to passivate if it wasn't oxidized due to the heat treating process? I was under the impression passivation was to fix heat staining on parts?

EmGo · Nov 18, 2021

Brett W said:
Why would I need to passivate if it wasn't oxidized due to the heat treating process?

Because it says so on the print. You'll go crazy if you try to second-guess why customers do things.

Dave G. · Nov 18, 2021

Brett W said:
Why would I need to passivate if it wasn't oxidized due to the heat treating process? I was under the impression passivation was to fix heat staining on parts?

Passivation is to remove any surface iron contamination from machining and handling. A smear of iron on the surface can cause breakdown of the passive film and result in pitting.

plastikdreams · Nov 18, 2021

H1025 is 35 Rc, even turning it hard will be easy. I'd take the job and get paid well for it.

MaxPrairie · Nov 18, 2021

17-4 machines really well in the 1150 1025 and 900 conditions. I think you would be kicking yourself next time you machine the material and see how crisp the chips are and the surface finish you get. Passivation takes away free iron on the surface. The part will be noticeably more shiny after the process. You could do op 1 and leave a couple on the backside to grind to final thickness. I would quote it if it were me. You could stack parts on the grinder to, it grinds pretty nice as well.

MrSteve · Nov 18, 2021

Brett W said:
Why would I need to passivate if it wasn't oxidized due to the heat treating process? I was under the impression passivation was to fix heat staining on parts?

Passivation removes any free iron from the surface and slightly increases the surface chromium concentration improving corrosion resistance.

Archer120x · Nov 18, 2021

I enjoy h1025-h1075 17-4. It finishes so nice.

dian · Nov 19, 2021

as ph 17-4 is martensitic it doenst workharden during machining like an austenitic type would.

Mtndew · Nov 19, 2021

1)Saw the raw stock into 10" chunks
2)Send to HT
3)Part them off in your cnc lathe
4)Make big monies.

stephen thomas · Nov 19, 2021

As said above, depending on the type products you make, 17-4 is a dream material. in pretty much any condition. Also magnetic, so easy to grind. Barely distorts in HT if at all, etc.

You should no-quote so someone with a big number on it can look like a hero.

Course OTOH it is definitely not 12L14.

smt

plastikdreams · Nov 19, 2021

It's pretty much like machining tool steel.

Brett W · Nov 19, 2021

I think I will order some hardened 17-4 From Mcmaster and do a test with it to see if I am comfortable going down the road.

plastikdreams · Nov 19, 2021

dian said:
as ph 17-4 is martensitic it doenst workharden during machining like an austenitic type would.

It's not the work hardening of the part per se but what happens is you get a worn tool which causes a built up edge and the material quickly clogs the flutes or cutting insert and boom goes the tool.

Machining Hardened 17-4 Rings

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