Marine Grade Hadrware That Can be used

[RPMX1k]

My Question to the group is what do you know about Metalurgy and Hardware Grades to be used for Marine Applications ?

We all know Stainless Steel is Used But are there any Other Grades Exceptable or better ? Stainless is Great But the Shear Stength is Lousy..and For Marine Engines This may not be Good because of Expansion / Contraction....

Grade 8 has a High Tensile Stength but does it Hold Up in water ?
or is Stainless The only One ? I also Heard Grade 9 Might be acceptable..anyone else Hear of this ?

 

[tashasdaddy]

Re: Marine Grade Hadrware That Can be used

if you could get by with something cheaper than stainless, it would be on all motors and boats.

 

[dingbat]

Re: Marine Grade Hadrware That Can be used

"Stainless" is nothing more than a generic term for a large group of iron carbon alloys which contain at least 10% Chromium. A stainless alloy that is suitable for use in one application may or may not be suitable for the next.

Generally speaking you don't want to use stainless in any type of application involving high heat, thermal cycling or in combination with heat and dissimilar metals as it becomes very reactive and unstable.

I've got a few years of metallurgy behind me. What exactly are you trying to do?

 

[PhatboyC]

Re: Marine Grade Hadrware That Can be used

"Stainless" is nothing more than a generic term for a large group of iron carbon alloys which contain at least 10% Chromium.

Even when it's grade 316 SS ? I thought it had to adhere to specific qualifications?

 

[Scaaty]

Re: Marine Grade Hadrware That Can be used

Hate to bust a bubble here, buts its "nickle" that does the trick, not Chromium..big diff (if my old febble machinist brain remembers..I can pull up all metal contents later if asked...in my shop though..

 

[dingbat]

Re: Marine Grade Hadrware That Can be used

Hate to bust a bubble here, buts its "nickle" that does the trick, not Chromium..big diff (if my old febble machinist brain remembers..I can pull up all metal contents later if asked...in my shop though..

I would suggest you read up on Ferritic and Martensitic stainless and get back to us on your nickel argument. Ferritic and Martensitic stainless contains very little to no nickel at all.

Stainless is “stainless” because of the passivation layer of chromium oxide (Cr2O3) when exposed to oxygen. Without chromium you don't have Cr2O3 and without Cr2O3 you don't have stainless.

 

[dingbat]

Re: Marine Grade Hadrware That Can be used

Even when it's grade 316 SS ? I thought it had to adhere to specific qualifications?

Yes, 316 has to conform to strict a alloy composition but your now talking about a specific grade of "stainless",not stainless in general

People get confused about stainless because in their mind if it's stainless, it's stainless. They don't understand that the term ?stainless? is inclusive of a lot of different alloys with varying compositions and varying degrees of corrosion resistance.

 

[tommays]

Re: Marine Grade Hadrware That Can be used

Well for example i believe some outboards have done better with chrome plated bolts VS SS in some parts of the motor because of the reaction between the Alu and SS


18-8 SS bolts are a pretty good trade off in some uses


SS also does poor in some underwater uses because of crevice crack corrosion



Tommays

 

[pgdignan]

Re: Marine Grade Hadrware That Can be used

Not a metallurgist but, as has been said a few times, the stainless grade is probably the most important thing to consider. Grade 304 stainless is total junk it'll rust like crazy. Grade 16 stainless is pretty good and there's a brand name stainless (nicopress I think) that's absolutely remarkable in it's ability to resist corrosion. You also have silica bronze fasteners to consider, they're supposed to be pretty good.

 

[j_martin]

Re: Marine Grade Hadrware That Can be used

In critical applications, for instance the single bolt that controls the steering on my XR4, I go with name brand (like cat) grade 8, lots of marine grease, and systematic inspection.

In aluminum engine (hot n cold) assembly, use grade 5 and grease, like a liberal coating of anti-seize. Grade 8 is a waste because you can't utilize the full strength of it anyway. Also, the harder the bolt, the more succeptible it will be to corrosion-stress cracking.

For wet applications, like transom bolts, I go with a good grade of stainless coarse thread, and lube to prevent spalling of the threads.

hope it helps
john

 

[Chris1956]

Re: Marine Grade Hadrware That Can be used

Just to refocus on the thread, Chrome plated Brass and silicon bronze are suitable for marine use as are several grades of stainless steel. Zamak and galvanized steel are suitable for freshwater applications. Aluminum screws, bolts and fittings are suitable for salt or freshwater, if they posess enough strength.

IMHO, SS is used mostly for appearance. For example, cleats could easily be made of bronze or Chrome plated Brass, and hold up just fine in saltwater. Years ago before Stainless Steel was widely available, brass and bronze ruled the seas.