Stainless steel or brass?

[Éric Bouvéron]

Hi,
On the material list, screws and bolts may be made of stainless steel or brass.
It seems that there are many kinds of stainless steel, and I wonder which one is more appropriate.
Also, what is the better choice, between bras and stainless steel?
Thanks for your answers,
Éric

[Björn]

stainless steel 316 is preferable above all

[kim whitmyre]

A third: Silicon Bronze...Here is a piece from an old wooden boat builder, Jay Greer:

"While stainless can suffer pocket corrosion in anaerobic use, It can be used where it will recieve oxygen. Mast & Deck fittings as well as hull use above the waterline. However, I really prefer bronze fastenings and hardware such as chain plates and mast tangs. Phospore Bronze plate is much much easier to form and cut than stainless and it does not need to be passivated. Stainless seems to have a nasty habit of developing pocket corrosion and cracking, even when in a fully oxygenated environment. So, I find bronze, tobin bronze, silicone bronze, phosphor bronze and manganese bronze to be more trouble free and in the long run more economic to use than stainless. If can be drilled, filed, polished, rivited, silver solderd and formed in the home shop on on the job site with simple tools. Where as stainless often requires a specialized shop to form and work it.
So far as silicone screws breaking down, the installer would do well to dip the threads in hot bee's wax or epoxy prior to instalation. Wet epoxy just as the screws are driven will lube and incase the threads in a protective barrier that will resist electric action and screw sweat that can start rot. Epoxy is messy so I prefer to pre dip my fastenings in bee's wax that does a better job of protecting the fastenings and is antifungicidal.
JG"

[Robert Hughes]

In England you can get fasteners in two grades of stainless.  A2 grade, otherwise known as 304 or 18/8 is ok for domestic use but not suitable for contact with salt water.  What you need is A4 grade, also referred to as 316.  Screws in A4 cost about twice as much as A2 here, but it's not something I'd try to cut corners on.  I got some old A2 washers mixed up with my A4 stock and a few of them used in the cockpit turned red rusty.

Be very careful with "brass".  I now try not to use ordinary brass screws in boats.  The problem is that the different electrical potentials of the copper and zinc in the mix cause preferential corrosion of the zinc, much as a zinc anode corrodes away to protect other metal components in a boat.  The result is that the zinc in brass dissolves and you're left with a spongy copper component with almost no strength.  I had this happen to a gate valve on a seacock which I had thought was bronze, but was actually brass.  Luckily we were tied up to a dock in the USVI when it snapped off in my hand, not mid-ocean...

Brass screws are ok if they are completely protected from salt water and dampness, or where their strength is irrelevant once the epoxy is set, but take care.

Bronze is another matter, it's probably the best material for fastenings in a boat.  As Kim said, it doesn't suffer from crevice corrosion or the multitude of other problems nearly as badly as stainless steel, and is easier to work.  I don't know about other countries, but here in the UK bronze screws are even more expensive than A4 stainless.

The other thing to watch is that terminology on this subject is very confusing.  There are many different types of bronzes and brasses, which are very confusing (eg terms like "naval brass", which I think is more like a bronze).  There are plenty of articles about this on the internet.

For practical purposes, for what you are doing, I'd go for 316 (A4) stainless screws and bolts, as Bjorn suggested.  If nails are needed, bronze "gripfast" ring nails are quite economical.  If you are fitting seacocks use bolts of the same material they are made from.

Enjoy!

Rob

[Éric Bouvéron]

Thank you very much for all your answers. So A4 it will be.

I can add something I found about different A4 -316 Stainless steel, there are three sub-divisions.

(A2 and) A4 grades come in three property classes: 50 (soft) , 70 (cold-worked) & 80 (high-strength)

Thank you again,

Éric

Source:

http://www.graphskill.com/2011/03/21/grades-of-stainless-steel-a2-a...