Clevis pin fails double shear....Is rework possible?

[MCFcorp]

I have a lot of clevis pins that failed double shear test. I am trying to determine if they can be reworked to an acceptable condition. The part is MS20392-12C117. It is a 1" diameter by 3.6" effective length pin, cad plated to AMS-QQ-P-416 Type II, Class 2.

Here are the details as the lot sits today;
1. Material 4130
2. Heat treated to 26.5-32 HRC iaw AMS-H-6875A
3. Double shear to be 116,260 lbs min.
4. Independent lab machined specimens to 7/8 dia to fit their fixture. The double shear requirement for 7/8 is 88,840 lbs.
5. 13 samples ranged from 85,544 lbs - 89,118 lbs. only 1 sample was conforming
6. Heat treating facility certified parts to 30-32 HRC
7. My hardness verification shows 24 - 28 HRC w/ 50% of the samples non-conforming.

The question is...
Can these parts be reprocessed to achieve the required properties?

I think I should be about to anneal or normalize the parts as defined in AMS-H-6875 then reprocess through austenitizing, quenchin, and tempering.

What is the correct process...Anneal or Normalize?

Thanks in advance for any insight

 

[MCFcorp]

I have received my test results for the microstructure.

The lab tested 3 samples. They used a 3% nital etchant and 100X-400X magnification.

A cross section was mounted, polished and etched. The examination reveals that all three structures are uniform structures of ferrite and some tempered martensite. There are some inclusions in the material, but not necessarily enough to reduce strength or to reduce load carrying capacity. The hardness values obtained are in the mid 20's (25,27,27) on a HRC scale.

 

[CoryPad]

The microstructure results show that the material is not uniform tempered martensite, which is what you need. Rework is possible, as described previously in this thread. You need to verify final dimensions - oxidation and deoxidation will occur, and distortion may occur, so you need to understand how that affects your final part.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[TVP]

oxidation and deoxidation will occur

this should have appeared as "oxidation and decarburization will occur..."

 

[dbooker630]

Was the noted ferrite at the grain boundaries or was it 'blocky' in appearance? Any other transformation products noted? This would give us an indication of whether there was insufficient soak time or slack quench.

 

[CoryPad]

Actually, I meant that if the parts are re-austenitized, they will oxidize. Then, they likely will be deoxidized by some means (blasting, machining, etc.). This, coupled with any machining needed to address straightness, might mean the parts don't meet the tight diameter tolerance. Of course, decarburization may occur, and if that needs to be removed, then that is yet another consideration.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[jsokal]

If desired, you can minimize oxidation/decarb on re-hardening by performing a copper plate all over to protect the parts. Something around 0.0005" thick should suffice.

John