17-4 Forging Metallurgy
17-4 Forging Metallurgy
(OP)
Hi All,
I'm tasked with specifying a hollow cylinder to be made out of 17-4 PH (H900 heat treatment) and to be used in a high pressure and wear application. The O.D. will be 12" and it will be in excess of 100" long. I can't go into too much more detail but I'm hoping for some insight into the metallurgy I should call out. I do not have much experience with metallurgy other than what I've tried to learn on my own so any general info would be great.
If I call out a forging, will the recystallization during the solution anneal at 1900 F 'cancel out' the effect on grain structure of the forging, or is there some HWRR that would maintain a finer grain structure post treatment? I imagine this depends on the duration of the soak at 1900 and I.D. of the cylinder.
I've read some literature to indicate that finer grain structure will lead to better wear characteristics (I know it depends on what's wearing on what). This is something I would like to achieve. Would a minimum of HWRR of 4:1 enable finer grains than if it were say, spun-cast? Also I'm thinking that calling out 'open-die forging' will be specific enough?
Thank you for any help.
I'm tasked with specifying a hollow cylinder to be made out of 17-4 PH (H900 heat treatment) and to be used in a high pressure and wear application. The O.D. will be 12" and it will be in excess of 100" long. I can't go into too much more detail but I'm hoping for some insight into the metallurgy I should call out. I do not have much experience with metallurgy other than what I've tried to learn on my own so any general info would be great.
If I call out a forging, will the recystallization during the solution anneal at 1900 F 'cancel out' the effect on grain structure of the forging, or is there some HWRR that would maintain a finer grain structure post treatment? I imagine this depends on the duration of the soak at 1900 and I.D. of the cylinder.
I've read some literature to indicate that finer grain structure will lead to better wear characteristics (I know it depends on what's wearing on what). This is something I would like to achieve. Would a minimum of HWRR of 4:1 enable finer grains than if it were say, spun-cast? Also I'm thinking that calling out 'open-die forging' will be specific enough?
Thank you for any help.





RE: 17-4 Forging Metallurgy
If you anneal and then age, then re-anneal and re-age you will reduce the grain size.
This will increase the toughness and only very slightly reduce the strength.
You could make this part from cnetrif cast hollow that was then forged.
Are you looking at any surface treatments?
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 Forging Metallurgy
I'm not looking at any surface treatments currently. We actually have had these made in the past by another vendor which used their proprietary coating on the I.D., but which cracked due to pressure cycling and differences in modulus, strength, etc. They've made all of our subsequent cylinders out of just 17-4 PH, H900.
Some additional background. We've recently begun using a cylinder that has had heavy particulation due to wear of the I.D. I managed to track down that it was a spin-casting (quenched), and displays a mottled appearance that returns with use despite repeated attempts at polishing.
The other cylinders we've used w/out issue were 17-4 forgings (no surface treatment), but were made so long ago that the specific work history of them is lost (one annealing/aging as far as I know)...so I'm trying to understand what conditions might enable me to recover their performance characteristics in terms of wear.
RE: 17-4 Forging Metallurgy
http://www.jorgensenforge.com/pdfs/JFCbrochure.pdf
RE: 17-4 Forging Metallurgy
RE: 17-4 Forging Metallurgy
A second option is to move to 15-5PH, which is a more stable version of 17-4. It is easier to get good uniform properties in heavy sections. I believe that 15-5 is also available as re-melted material (AOD-ESR).
And don't let someone use the casting chemistry, require the wrought product chem that is listed in the AMS specifications.
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 Forging Metallurgy
As ED noted, both 15-5 and 17-4 are available as arc + ESR melted.
RE: 17-4 Forging Metallurgy
RE: 17-4 Forging Metallurgy
b.t.w. ESR is not under vacuum. vacuum melted (say VIM) 17-4 is not common, while VIM 15-5PH is popular.
RE: 17-4 Forging Metallurgy
Perhaps 15-5 can be a sell for you since it is really just a modified 17-4, the documentation even says that.
In 15-5 I believed that we used Si 0.20-0.50, but we also had a bunch of other restrictions.
Such as S 0.002% max, and S+P+N+O+0.1Nb <0.060% and Nb was 5xC, 0.15min, 0.30max.
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 Forging Metallurgy
RE: 17-4 Forging Metallurgy
Ed Stainless has provided a strong argument for making Your part from 15-5PH VAR ILO 17-4PH... especially since there is the high purity version is readily available [AMS5659].
CAUTION. The H900 or 925 Conditions are prohibited for use in aerospace structural parts MF 15-5PH or 17-4PH, due to low toughness and being prone too SCC failure. See MIL-STD-1587 Table I Restricted materials.
NOTE. I have used 15-5PH [AMS5659] at H900 Condition for bushes and small press-fit parts; and also used 15-5PH [AMS5659] at H925 Condition for small'ish structural and mechanical parts, that are then stress-relieved after all machining... and then shot peened [all surfaces]... and then coated with plating's [must be embrittlement relief baked] or bake-on SFL.
NOTE. IF these parts were used in moderate/low service temperature [LT 500F] and relatively benign corrosion environment, then I'd tend to lean towards PH13-8Mo AMS5934 [extra high toughness], H1025 or H1000 Condition, for best possible long-term service at the stress level You imply [~=H900 for 17-4 & 15-5].
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: 17-4 Forging Metallurgy
It is important to make sure the hot working is performed with the material at a high enough temperature to prevent cold laps, seams, etc in the forged material. It is also necessary to machine off at least 1/8" from any hot worked surface of the forging to remove contaminated material. It would also help to take a look at the recommendations in a heat treat process spec like AMS 2759/3.
RE: 17-4 Forging Metallurgy
We have extruded cast parts (turning them into forgings) and only had success when we took 3/8" off of the OD and >0.500" out of the ID.
There are people out there that will centri cast from clean melt billets, and do it with Ar shield gas.
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 Forging Metallurgy
I'm also unsure as to what specifications to go by, have seen many. ASTM A564, ASTM 705, AMS5643, AMS 5604, UNS S17400, ASTM A693, ASTM 484, ASTM 479, ASTM A788, AMS5659. Also do you guys have any recommendations for void testing?
This is not for an aerospace application, but will be subject to pressure fluctuation, relatively low operating temperature. Calcs have been done by engineers before me to show that the nominal dimensions with 17-4 at H900 would be sufficient from a strength/fatigue perspective. I just don't know what specifics in the forging process would be to call out for optimizing the microstructure and other mechanical properties would be. If I can stay with 17-4 or 15-5 that's probably best.
RE: 17-4 Forging Metallurgy
In aerospace, the problem with 17-4PH/15-5PH H900 temper is primarily SCC [stress corrosion cracking] related. SCC is aggravated by multiple factors that cannot always be easily predicted.
OK, OK, OK... Avoiding a forging parting plane, using cylinder hand-forging techniques, should eliminate worst source of SCC initiation and make for a beneficial circumferential/axial grain-flow.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: 17-4 Forging Metallurgy
RE: 17-4 Forging Metallurgy
You could look at having these hot extruded.
When this is done you have the same structure as a hot forged part.
There are a few press around that could push this part.
I would do this with remelted 15-5PH or 13-8PH, and I would prefer the 13-8.
An extrusion would require modest stock removal from the ID, perhaps 0.150" (0.075" off of the wall).
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P.E. Metallurgy, Plymouth Tube
RE: 17-4 Forging Metallurgy
Specifying a minimum HWRR helps ensure the finished forging material is sound and has the grain characteristics desired. You did not mention what the forged cylinder's wall thickness is. But based on the 12" OD, 100" length, and limited availability of large diameter wrought bar in the alloy required, I think you will need to start with a forged preform made from smaller diameter bar stock. Remember that this mandrel hammer forging process only reduces the material OD as it increases length, with the ID surface being constrained by the mandrel. Unless your cylinder forging has a very thick wall, it should not be too difficult to achieve a 3:1 or 4:1 HWRR from hammer forging over a mandrel.
RE: 17-4 Forging Metallurgy
RE: 17-4 Forging Metallurgy
I'm sure there are several US forging houses with automated equipment that can mandrel forge your flanged thick-wall cylinder shape. Since you mentioned fatigue life is a concern with your cylinder, mandrel hammer forging is definitely the way to go. This process is used to forge cannon barrels. Here is a good video of the process. Note the spiral pattern on the material surface produced by the hammer strikes.
The extra cost (maybe $3/lb) for vacuum melt quality raw material might also be worthwhile for a couple reasons. The cleaner material should help with fatigue performance. If your company offers a warranty for this product, the better reliability provided by vacuum melt quality material can be helpful. Depending on how stringent your NDI acceptance criteria is for the finish machined cylinder, using vacuum melt quality material can minimize part rejections. For example, there are 5 grades of acceptance criteria for mag particle inspection listed in AMS 2442 table 1, grades A,1,2,3 & 4, with grade A being the most stringent and grade 4 being the least stringent. The subsurface indication limits for grade 3 are based on what would be typical for an air melt quality steel produced to AMS 2301 cleanliness requirements, and grade 1 limits are based on what would be typical for a vacuum melt quality steel produced to AMS 2300 cleanliness requirements. So if you were to specify grade 2 (or better) acceptance limits for mag particle inspection of a cylinder made from air melt quality material, there is a good chance it may not pass. It can be very expensive to scrap a part that you have significant amounts of money and time invested in.
Good luck with your project.
RE: 17-4 Forging Metallurgy