17-4 SST Fatigue Properties

[Danimal001]

I need to compare H1150 vs H900 in an axially loaded part. The H1150 parts have failed where expected(stress conc.) and I wonder if H900 will fill the bill even though the Ut of H900 indicates severe brittleness. For reference, the machined surface finish is 32 Ra and the stress concentration factor for my radius is about 1.7. I am a bit contrained on geometry...

Any comments or experiences are welcome! Thanx.

 

[israelkk]

What was the failure mode?
What were the calculated stresses at the radius?
If the failure is fatigue what were the mean, minimum and maximum stress?
How many cycles to failure?

 

[TVP]

You can obtain fatigue data on this alloy from MIL-HDBK-5 or DOT/FAA/AR-MMPDS-01. Use the ASSIST website:

http://assist.daps.dla.mil/quicksearch/

 

[Danimal001]

- Fatigue crack propogation
- ~50 ksi
- Max = 32 ksi, Mean = 0 ksi, Min = -32 ksi(compression)
- 2.058M cycles. We need infinite life with corrosion resistance.

Thanks for your input.

 

[NickE]

From my experience with fatigue you'll want the highest UTS that you can get. Especially with fully reversed stresses. You might also (if you can use coil steel) consider
17-7CH900 Ive had certain types of spring elements last very long (>10M cycles).

Depending on if your surfce initiated the crack you might want a smother finish. We generally put a finish ~1.2Ra and ~12.0Rz on our standard parts, although we do have parts that get far better finishes also.

If you dont have any forming to do check out Sandvik Flapper Valve Steels, or Sandvik steel in general. They use special practices to produce very clean steel. go here:

http://www.smt.sandvik.com/

 

[Danimal001]

Thank you for all of your time! This site is the cat's a$$..Where have I been for all these years....

In my haste I forgot to mention that there is an impact load during changeover that I haven't quantified yet. Apologies as this is an important fact. Would this alter the opinion of going to the higher UTS? I see that going from H1150 to H900 reduces the elongation roughly 38%. The counterargument to this is they both have the same modulus and I should get a larger strain value with the higher Uy and Ut....

 

[unclesyd]

Stay away from H900. With a long history with using 17/4 PH and many conversations with the technical people at Armco there has never been a recommendation for using 17/4 in the H900 condition except for a thrust washers and collars. Our internal spec call for using 17/4 H1100/H1125 for all shafting.

You mention corrosion would you come back with the chemical and physical enviroment that the shaft is exposed to.
17/4 does have some problems in certain environments.