stainless steel fasteners really a problem?

[Graflex45]

First, I'm aware of the issues with galling and use quality antisieze on all the stainless fasteners. Second, I'm not using stainless bolts on the body of the tractor in places where its structural and supporting loads, I use good grade 5 or 8 bolts.
I'm using low grade 304 fasteners, nothing expensive or exotic. Some purchased from Amazon before I fiqured Mcmaster carr parts are much better quality screws and in some cases less expensive in quantity.
I think the confusion on how much an issue this is comes from looking at electronegativity charts and seeing the stainless steel entries on it that are very far from carbon steel, when those are specifically passivated stainless. I've used some of these fasteners to bolt together decorative stuff outdoors and after a while they clearly show a bit of reddish patina in the crevices, which only non passivated stainless does. You have to pay for a higher grade of fastener to get actual passivated stainless which might cause a problem if the decks got wet enough that water penetrated under all the fasteners.

[PBIjim]

Passivated stainless has been treated by some process, such as acid immersion. This leaches the ferrous ions from the surface & leaves a skin of pure chromium, which is rather inert chemically and is not prone to rust. If you scuff that surface, the passive skin is ruptured and the protection is gone from that small area, until it is treated again.

Crevice corrosion occurres when oxidation gets past the passive layer and then works it's way down the lattice of ferrous ions in the alloy. This corrosion happens behind the surface where you can't see it. The strength in the alloy comes from the ferrous structure, so once that has been oxidized internally, you will have a structural deficiency. The next time you present a heavy load, the part will break and then you will have a front row seat to seeing how much of the part was compromised internally. The shiny portion at the break is the portion that was still good. There are tests, like magnafluxing, that can spot crevice corrosion in it's early stages. Noticing it with the naked eye is a bit of a trick. Just to complicate it further, if rusting steel is nearby & water carrying that rust drips onto the stainless, you can get rust spots that stick to the outside of the chromium skin. These make it look like the stainless is rusting, but cause no actual damage, as long as the passive surface is still good.

Higher alloys of stainless have greater natural corrosion resistance without the need for surface treatment. Even without surface treatment, lowly 304 still has much better corrosion resistance compared to carbon steels, like grade 5 or 8. This is why carbon steel bolts typically have either zinc or cadmium plating. Bare carbon steel loves to rust

Those electronegativity charts, also known as galvanic charts, or nobility charts, become more important when the two dissimilar metals are in the presence of an electrolyte. Salt water is an excellent electrolyte. Rain water, and common tap water are not nearly as active, but the activity is still not zero. I don't know how active wet grass clippings are.

When using anti seize with stainless, consider the metals that are used in the compound and see where they fall on the nobility scale. Most anti seize is based on nickel and gallium. Some is copper based. I use grease when temperature is not an issue.

I think that the big question is - how have your fasteners been failing? Optimize against the most common risk by choosing the material that is least susceptible to that mode of failure.

To dumb down my response a bit - I would most likely just use 304 until I found an actual real-world reason not to. If I didn't see an actual failure myself, I'd stick with the stainless on the deck.

As an afterthought, adding rubber washers might help with electrical isolation, vibration damping, and covering up scratched paint.

[Graflex45]

I haven't had any fastener failures on new stainless bolts ive installed.
I've been restoring multiple attachments for the tractors I've bought over the last couple years and the struggle of removing fasteners that were completely rusted together made me vow to use stainless bolts so if I have to disassemble them to repair or replace a part down the line they wont be such a chore to clean out threads and unfreeze a bolt.
I've bought and stripped down 3 cub decks (1 more disassembled for parts and sent to the scrapyard), rear tiller and gearbox, latest has been a GE Electrak mower deck that was originally assembled in a very poorly thought out way. It had all the bolts pointing inward were the threads would get covered in grass and grit and could get damaged by debris. The first deck I disassembled and rebuilt I too apart this spring to get it sandblasted and powder coated and the bolts came apart easy just like I hoped.
I use the high quality grey loctite grey antisieze. Its an aluminum and graphite based formula.

[PBIjim]

Originally Posted by Graflex45

I haven't had any fastener failures on new stainless bolts ive installed.

It sounds to me like you have the answer to your original question.

Originally Posted by Graflex45

latest has been a GE Electrak mower deck that was originally assembled in a very poorly thought out way. It had all the bolts pointing inward were the threads would get covered in grass and grit and could get damaged by debris.

Acorn nuts may be an option to consider

[PBIjim]

Originally Posted by Graflex45

Its an aluminum and graphite based formula.

That's interesting. Graphite is basically carbon and that is pretty much all the way at one end of the galvanic scale. Aluminum is just a few elements in from zinc, which is at the other end. I'm surprised to see them together in that mix. The carrier lubricant must be pretty good at keeping the moisture out.

Back in the old days, when EverReady batteries were silver and had a black cat jumping through a red 9 on the label, they were made of carbon and zinc with an electrolyte because those chemicals were so galvaniclly active that they produced usable voltage & current.

[Frank1541]

I think it would take a catastrophic event to cause weaker stainless bolts to break in a place where CC uses Grade 5 bolts. I had just an event a couple of years ago when the gauge wheel on my 54 inch deck broke off while I was mowing. Before I could react I ran over the wheel. It stopped the blades on the deck in an instant. Fortunately there was no major damage. I do wonder what could have happened if the spindles were attached with stainless bolts instead of the Grade 5 that I used.

https://www.onlycubcadets.net/forum/...ad.php?t=57120