Stress relieve 17-4PH 2

[stillcrazy]

We're bringing in forged rings of 17-4 that are at condition 1150. After two rough machining operations, we stress relieve them at 1135-1165 for 2 hours. I'm not sure if this is doing anything useful except paying for my heat treaters new boat. Anybody got a suggestion?

 

[metengr]

We're bringing in forged rings of 17-4 that are at condition 1150. After two rough machining operations, we stress relieve them at 1135-1165 for 2 hours.

Why? Visit here for some background information on this material;

http://www.aksteel.com/markets_products/stainless.asp

 

[stillcrazy]

metengr,
I think what happened here was that the powers to be believed that machining stresses were present after the rough operations. That may or may not be true. However, a short soak like the one described seems tantamount to tickling a rhino with a feather. Does it really do what they want it to do?

 

[metengr]

stillcrazy;
There is a reason to my madness. I provided the web site above so that you could review the information bulletin for 17-4 PH. This material is a precipitation hardening grade of stainless steel and is quite sensitive to heat treatment and any subsequent heat applied to this material will affect mechanical properties. Please review the technical bulletin from AK Steel.

 

[jferguson]

stillcrazy; I don't mean to butt in here...but if you look at Figure 1, pp.9 of the 17-4 PH Data Bulletin referenced above, you see the curve for H1150 is relatively flat. This tells me that exposure to high temperatures for short times (heat from machining) doesn't appreciably affect the strength. Unless 17-4 responds well to work hardening, I don't think you need to do a post machining stress relieve. We buy 17-4 DH 1150 for NACE and machine it every day with no post machine stress relieve. We have never had any problems. The best thing to do if in doubt is to machine a piece with known mechanical properties, then send it out for testing (without stress relief) and see if the properties change. jferguson

 

[redpicker]

stillcrazy,

You ask, "Does it really do what they want it to do?". I'm assuming "what they want it to do" is the relief of residual stresses.

It would all depend on the prior processing. A stress relief operation will lower the residual stresses, if present, and, yes, a two hour stress relief at 1135-1165 F (which is 1150 +/- 15F) for two hours would be effective at relieving stresses. I doubt such an operation would adversely affect the mechanical properties of the material. Of course, if the residual stress level was low to begin with, the benifit would be small.

Could you "get away" with eliminating the SR operation? Perhaps, particularly if the forged ring was properly solution treated and aged after forging and no straightening or cold working was performed. A lot would depend on the dimensional requirements of your finished part and the cost of re-processing and or scrapping if re-processing is not applicable. But, since the cost of SR is relatively low, it is viewed as cheap insurance. It can also eliminate the machinists' most common excuse ("the material moved") for missing tight dimensions.

If you wanted to save money on processing, perhaps you could bring the rings in as Condition A (solution treated), and age them after rough machining, with what would amount to the exact same treatment as your SR treatment. I don't know what specifications you are working to, however, so this might require additional mechanical testing.

rp

 

[EdStainless]

Is your machining symmetrical? Do you see distortion?
If No and yes then you may actually be seeing the effect of hte first heat treatment not being done uniformly.
I don't see any real problem with a re-age as a stress relief, but I would prefer to see it done right the first time.

 

[BTIGUY]

stillcrazy,
For 17-4 stainless why not apply sub-harmonic stress relief if you are interested in machine stability? I recently talked with one of my aerospace customers who said that they are using sub-harmonic stress relief on various high strength materials including 17-4 stainless and they are very happy with their results. The main reason why they SR is for machine stability. They send parts into deep space so they want them to be as precise as humanly possible.

BTIGuy

http://www.Meta-Lax.com

 

[unclesyd]

A very precision 17/4 part without any specific stress relief.

A large part of our critical components are made from the PH alloys, 17/4 H1125 or 455. These components are 8' x 10" x 1" thk rectangular spinneretts with up to 1000 0.0090 dia, holes that are very precisely located in several different patterns. These small holes intersect a 60 degree cone at the end of a 3/32" drilled hole from the back side of said part. The periphery of this component has 48 1/2" counterbored holes for mounting. The counterbore breaks the edge of the part with an arc of 12.5 degrees.
This particular component is used in cyclic service @ 600F for 20 days cooled to RT then 8 hrs in cleaning oven up to 900F and then cleaned and sent to inspection and repair. The inspection is visual and the repair is manual. The key to the this process is that the inspection machine has is keyed to one of the 3/32" counterbores. This one hole allows the machine to locate all the small dia holes on the face automatically. The holes are inspected at 100X with the reticle being on the C/L of the hole within 0.00005". After inspection and repair the component is held at 525F-550F for up to 10 days and then is put into service at the afore mentioned temperature and the cycle is repeated. These components will undergo around 30 cycles during it's service life. The end of life is determined by physical damage to the face that is impractical to repair.