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

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

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

(OP)
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

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

Did the machining alter the properties?  What makes you think the same thing won't happen again?

Perhaps you should find someone who can do the test without messing with the material.

TTFN

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

(OP)
IRstuff,
Doubtful, I had thought about that but they alter test specimens all the time. It is a fairly common practice in the fastener industry for mechanical testing.

The bottom line is my hardness results are deviating by as much as 30% from those listed on the heat treaters certification.

I am confident it is a process issue at the heat treaters.

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

Have you taken your stuff back to the supplier and witnessed some retesting?  Seems to me that you're arguing that they've essentially lied on their certs, and you should demand that they do a retest with a witness present to demonstrate compliance or not.

If their testing also shows non-compliance, then it's up to them to make it right, whether by reworking or replacement.  Either way, it shouldn't be you doing the reworking.

TTFN

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

(OP)
I am already scheduled to witness them retesting the parts tomorrow. We are pretty much on the same page. It is possible that the samples they pulled in their test were OK but that other parts of the lot were bad.

I just need to have a recovery plan and understand my options when I go there tomorrow.

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

I would also have a representative part sectioned, polished and etched for microstructural analysis. Is the heat treater capable of performing this? There can be several reasons for the discrepancy that are not due to misinformation.

Sampling-is their cert based only on a first or last piece?
Load density-your part did not get to austenitizing temp.
Quench severity-part shows slack quenched (bainitic) structure, quench temp fluctuation?.
Decarburization-was there a furnace issue?.

It helps to know the microstructure so the correct rework recipe can be implemented. Otherwise you're just guessing.

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

(OP)
dbooker630,
That is a excellent suggestion. I just returned from the heat treater. The hardness results from their facility were chaotic to say the least. The oven charts revealed that the tempering was only held for 45 minutes. The temp was 1075 F. The parts took roughly 1/2 hour to come up to temp during tempering.

There was a lot of sanding off of cad plating, dusting off the indentor, wiping off the anvil, wiping off the part, etc. to get acceptable readings. Even then the results were at the low end of the acceptable range. While non of the results reached those specified on their certification.

They cross sectioned a part and checked mid radius and core. Those readings were in the low 20's (21, 22) for both the mid and core. I am reasonably condifent that those are not adequate results. I will have samples sent for microstructure evaluation as you suggest.

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

MCFcorp,

Based on your description of the heat treater's hardness testing I would employ a third party to perform a micro for you.

Water-quenched 4130 1" diameter, typically has a hardness of 26-27 HRC after tempering at 1100F; 31HRC at 1000F. With the short tempering cycle you report the hardness should have been in the low 30's HRC - unless they are quenching in oil.

4130 is typically a water-quenched grade of steel. The micro will tell you if the quench is severe enough.

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

(OP)
they oil quenched at 144 F

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

For the moment I have my doubts about a sufficient quench but I'll wait for your micro results. If you had said 144F polymer I would have less doubt.

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

With oil quenched 4130, I'm not surprised with these results.  You might get marginally acceptable surface hardnesses, but the core hardnesses can be low.  It's not impossible to get good results in oil, but it would require careful fixturing of the parts and a well agitated quench.

This also explains why your test failed.  Machining the 1" diameter to 0.875" removed the hardest part of the pin.

These could be slavaged with a quench and temper operation (normalizing would not help much at this point).  Water quench would be preferred, but if they are using an integral quench furnace, it may not be possible.  If they have to use oil, have them fixture the pins in a vertical position with at least 1/2 radius between parts to insure adequate oil circulation during quench.  The tempering time needs to be sufficient so that all parts see the same soak cycle.

rp

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

Going back to your original question, yes, re-working is possible to obtain higher strength.  A martensitic microstructure is optimal for austenitizing, so just re-heat the parts to 815-870 C (hardness will be maximized by using the higher end of the range), then quench.  dbooker630 and redpicker provided some good information about the various quenchants-- 4130 does not have great hardenability, so quenching into a water-polymer mixture will result in higher hardness.  If this is not a possibility due to risk of distortion/cracking or unavailability, then use the "fastest" oil possible.  If your heat treater does not know what fast or slow oil is, then you need a new heat treater.  Tempering info was also provided previously.

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

While waiting on the microstructure results I would try to reprocess a small batch of pins.
Reprocessing will present a few problems since your parts are Cad plated. This plate will have to be stripped, preferably in a non acid bath.

I would normalized the parts prior to the Austenizing step.

This is almost a necessity if there is a ring or tab on the end of the pin.

I would austenize at 1575F and warm water quench and then temper at 1000F. Myself I would double temper.

After the test batch of pins are HT I would give them a wet PT examination.

 

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

(OP)
The lab still has the 13  samples from the double shear. I ordered microstructure evaluation on 3 of those samples. 2 samples are those that had the lowest load at failure during the double shear, the 3 one is the only sample that passed double shear. I should have results in 2 days.

In the meantime I may have half a dozen samples reprocessed.

What would be the difference between reprocessing as TVP describes vs unclesyd's recommendation to normalize? The clevis pin does have a head.

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

The differences would be cost and homogeneity, with unclesyd's recommendations possibly providing more homogeneity at higher cost.  If your supplier is not doing the current process correctly, then they won't do this proposed one well either.  

Regards,

Cory

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

(OP)
higher cost isn't much of a concern. I have 15K in sellable product stuck in MRB. Making these good parts is the only option.

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

MCForp

Being in this same situation .

This is a long thread all ready.


before doing anything I recommend this
I would recommend a driffrent lab to reverify met lab
     properties. ( holding 2 points on the hardness scale to my experience is hard to hold)It may have been over tempered, or tempered to high.
    In addition 1/8 material removal can make a big diffrence,if I under stood you corectly


#1) what the qty of parts ?

#2) are are parts centerless ground or turned?
    what is the tolerance of the OD?

#3) if you reheat treat these pins there is no doubt in my
    that it can be reworked to achieve the correct properties.

#5) however the question #2 applies, parts will distort
    violating Straightness & or Tolerance requirement.

#6) supplier who did the testing machined the 1.000" pins
    down to 7/8 dia? that is bogus.
    according to my Timken Handbook 4130 hardness will    rapidly drop.

    
    

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

(OP)
mfgenggear,
1. There are approximately 630 pcs in the lot
2. The parts are turned. The tolerance is +0.000/-.002
6. Good point. I will request that they retest using a proper fixture. If they cannot I will call and find another A2LA lab to do the testing.

What section in the Timken Handbook are you refering too?

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

(OP)
TVP,
I appreciate the assistance as well as that help from everyone else who has spoken up in this thread.

I will update with results from microstructure and full size double shear test in a few days.

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

(OP)
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.

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

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

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

Quote (CoryPad):

oxidation and deoxidation will occur

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

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

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.

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

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

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

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

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