cad plating 17-4 ph - Hardness effects 3

[engamopar]

Have: 17-4ph 1/4 dia. pins, Age hardened to HRC40 Min.
Parts subsequently CAD plated type II, CLass2 IAW AMS-QQ-P-416. Hydrogen embrittlement relief carried out for a minimum of only 4 hrs IAW 3.4.1 of NAS1332 ILO 8hrs as spec'd by ...P416. Parts were HRC40 min prior to Age harden.
As returned from plater, HRC now down around 38HRC, now below minimum. Would the hydrogen embrittlement relief cause this? (Carried out at
375+/- 25 deg F. Any thoughts? along these lines - or others?)

 

[israelkk]

Did you actually checked the pins prior to cad plating or you assume/hope the hardness was 40RC Min? I assume that this was the requirement in the drawing but I believe there was also a heat treatment requirements such as H1025. What was the heat treatment of the 17-4PH? Was it H1025 or H1075? if so then 375F for embrittlement relief has no effect. One more fact to take into account is that for a specified heat treatment such as H1015 the hardness can vary up to 10RC. This is why you will never see a hardness specified in MIL-HDBK-5 for precipitation hardening alloys such as 17-4PH or 15-5PH, etc., but only yield and tensile strength. Therefore, the min 40RC requirement has no meaning if a heat treatment is specified.

 

[TVP]

As israelkk noted, heating 17-4PH to 400 F for 4 hours will not reduce the strength if it was properly aged to the H900 condition (900 F, 40 HRC min according to ASTM A 564, etc.). You will need to metallurgically evaluate the pins in order to determine the issue.

 

[mighoser]

Are you measuring the same exact pins? Statistical variation could explain your findings. Are you measuring on a flat surface or concave surface and correcting the value? How thick is the CAD plate? If you were doing microhardness and converting I could see the CAD plate throwing your readings lower. Remove the plating and recheck your hardness.