Letter 41094

Chrome Plate and Shot Peen on PH Steels [North Carolina] 

June 13, 2006

I am designing a couple of linear actuators for the aerospace industry with PH steel rods. I will be requiring chrome plate on each for improved wear resistance. My shotpeening experience is paltry, so I want to make sure I am stipulating requirements correctly/appropriately. The materials and heat treats for each rod are as follows:

Rod #1: PH13-8Mo, H1000 (43-47 HRC)
Rod #2: 15-5PH, H1025 (34-42 HRC)

For each, I envision the following process:

1. After grinding OD, stress relieve at 375F for 3 hours

2. Shotpeen per AMS-S-13165 [link is to info about spec at TechStreet] using ceramic bead, .006-.010A (PH13-8Mo) .012-.016A (15-5PH), 100% coverage required.

3. Chrome plate per AMS-QQ-C-320 [link is to info about spec at TechStreet], Class 2, Type I, .003-.006 inch thick.

4. Hydrogen Embrittlement Relieve at 375F for 8 hours (13-8) 3 hours (15-5) (per AMS-QQ-C-320)

5. Final grind

6. Stress Relieve at 375F for 1 hour.

Question #1
Do any of the stress relief bakes have an adverse effect on the shotpeen (i.e. roll back the residual stress)? I believe that 375F is a safe temperature for PH steels, but I want to be sure.

Question #2
I plan to call out AMS-QQ-C-320 because it appears to have more specific processing information than AMS-2406 [link is to info about spec at TechStreet]. What is the most popular or most widely used of the two? Is there any reason to use one instead of the other, or is it just another case of DoD specs overlapping with SAE?

Thanks for all your help!

Michael Boland
Aerospace Industry - Clemmons, NC, USA

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