Originally Posted by
FBinNY
This thread has reached new levels of rediculousness to the point that I don't remember what we're arguing about. Since Cycocommute and I seem to be the main protagonists, I offer a suggestion. We each post a short summary of our theory relating to the cause of the OP's then simply leave it there for others to consider on their own. Keep in mind thatthe goal is to stop arguing and
post positive assertions for folks to consider, rather than attack each other.
I'll start.
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The proximate cause is hydrogen embrittlement resulting from the OP soaking the chain in an acid bath.
The specific mode of failure is stress cracking of the outer plates at the pin holes. Outer plates are stressed by virtue of the force fit over the pins, which press outward creating a tension stress akin to hoop stress. Normally this is OK and the loads factored into the design. However the embrittlement weakened the plates causing cracks to form at the hole (the point highest localized stress) which then propagated outward to the edge.
It's a simple two step process, weaken the plate then let it's own internal stresses take their toll.
In support,
crack formation due to hydrogen embrittlement of steel is a well documented phenomenon, with plenty of scholarly articles available on the net. The type of failure at the pins that I describe is also well documented, and a quick search for
bicycle chain plate cracks will bring up countless images showing radial cracks running outward from the pin at all angles. The holes are the most common location for plate cracks, and you won't find similar cracks on inner plates which are not stressed the same way. Morevover, the all angle aspect is important because it implies a cause other than the normal tension load imposed by the rider. Note also that you'll see the same radial cracks or relatively new chains showing minimal wear, and no markings near the cracks.
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Now it's Cycocommute's turn to post his theory,
Although I have gone on above ad infinitum, I’ll have a go.
First, let’s review what elfmachine said in the original post:
Originally Posted by
elfmachine
Hello. I installed a SunRace CNM84 chain on my bicycle last year and after many months it rusted so much that it got stiff. Pretty strange that it rusted so strongly despite being plated with chrome or nickel. I didn't have time to lubricate it so I rode my bike with an unlubricated chain which became more flexible after a ride. Now removed the chan and placed it into a bath with phosphoric acid with zinc aka rust remover to remove rust before lubricating it with teflon wax. After a while I started hearing popping sounds and after chain inspection I noticed that many links had cracks! Did rust remover somehow cause breakage or cracks developed from riding an unlubricated rusted chain?
The chain was ridden while rusted which freed it up a little. elfmachine
then put it in an acid bath during which elfmachine heard popping noises. The chain was not cleaned and then ridden but popped in the acid bath. elfmachine doesn’t tell us if the chain was inspected for cracks prior to the acid bath but audible noises are not generally associated with the use of naval jelly treatments.
The chain may have been compromised before the acid treatment but observations provided point to the acid treatment
causing the cracking. Not through hydrogen embrittlement but through acid dissolution of the metal at the stress risers of the stamped logo. If the chain had been treated with a nonacidic or even less acidic rust remover, the chain likely would not have cracked.
To be clear, I am not saying that chains can’t crack. Nor am I saying that inner plates can crack. I
am saying that cracking of the outer plates is a rare occurrence. And contrary to what you have stated earlier in the thread, I am also saying that the cracking of the outer plates in this case was caused by placement of the chain in the acid bath
and by the acid in that bath.
Finally, I have never attacked you. I have never questioned your expertise nor your abilities nor your knowledge. You, on the other hand, have not offered me the same courtesy.