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Old 23-04-2021, 05:47   #1
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Won't bend or rust. What metal do I need?

I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?
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Old 23-04-2021, 06:00   #2
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Re: Won't bend or rust. What metal do I need?

Not all steels are made equal. And unfortunately, commonly available stainless steel such a 304 (A2) and 316 are normally on the weaker side when it comes to tensile strength. ... High tensile steel bolts can withstand high tensile forces such as that which the engine block bolts will be facing during operation.10 June 2020
https://www.boat-renovation.com/high...s-steel-bolts/


Are stainless steel bolts stronger than steel?
Stainless steel is an alloy of low carbon steel and chromium for enhanced corrosion characteristics. ... Therefore, when compared to regular steel, the stainless alloys used in bolts are slightly stronger than an un-hardened (grade 2) steel but significantly weaker than hardened steel fasteners.

Is high tensile steel rust proof?The many benefits of high tensile steel

High tensile steel is also known for its resistance to atmospheric corrosion, the degradation inflicted to materials through exposure to air and air-borne pollutants.17 July 2019


https://www.shapecut.com.au/blog/wha...orth-the-cost/









https://www.boatdesign.net/threads/lifting-keel.839/
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Old 23-04-2021, 06:16   #3
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Re: Won't bend or rust. What metal do I need?

You can get CNC cut titanium and titanium bolts for a reasonable price these days.
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Old 23-04-2021, 06:35   #4
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Re: Won't bend or rust. What metal do I need?

Quote:
Originally Posted by Paul L View Post
You can get CNC cut titanium and titanium bolts for a reasonable price these days.

Paul
I don't know much about the relative strengths of different metals but I just googled

Titanium Bolts VS Steel Bolts

The tensile strength of the most common titanium alloy grade 5 can reach a minimum of 895mpa, so the strength of titanium bolts is much higher than that of stainless steel bolts. For ordinary pure titanium, such as grade 2, the tensile strength is lower than that of stainless steel bolts.

Apparently it depends on the grade of titanium?

Time for bed!
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Old 23-04-2021, 07:35   #5
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Re: Won't bend or rust. What metal do I need?

Thanks all for your help so far. I just need to clarify that tensile strength is not the issue. Apart from corrosion resistance, the essential ingredient is the ability to withstand a bending force. That may be the same as hardness. I believe it is not possible to harden 304 or 316, or to put it another way, you can have hard or anticorrosive, but if you want both, it's a bit of a stretch, and that is where we're at!
Grade 8 steel fits the hardness bill but not the corrosion issue.
Titanium may be on the right track and I'll follow that up.
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Old 23-04-2021, 08:59   #6
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Re: Won't bend or rust. What metal do I need?

Another candidate may be monel.

https://www.atlrod.com/monel-fasteners/
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Old 23-04-2021, 09:00   #7
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Re: Won't bend or rust. What metal do I need?

Bending is depending on tensile strength. To a large amount at least. For fixing hydraulic rams, special polished stainless steel bolts are used. No idea about the material, but any good hydraulic shop should be able to tell you.

Normally the bolt would be set in a kind of fork, with little play, so very little bending can occur, they shear right off insteadYou will find that lite small bolts can take a lot off load if the system is designed correctly.
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Old 23-04-2021, 09:01   #8
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Re: Won't bend or rust. What metal do I need?

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Originally Posted by coopec43 View Post
Paul
I don't know much about the relative strengths of different metals but I just googled

Titanium Bolts VS Steel Bolts

The tensile strength of the most common titanium alloy grade 5 can reach a minimum of 895mpa, so the strength of titanium bolts is much higher than that of stainless steel bolts. For ordinary pure titanium, such as grade 2, the tensile strength is lower than that of stainless steel bolts.

Apparently it depends on the grade of titanium?

Time for bed!
Grade 5
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Old 23-04-2021, 09:05   #9
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Re: Won't bend or rust. What metal do I need?

Have you considered using Grade8 hardened, high tensile steel bolts, but ordering say 6 of them, and have a periodic maintenance schedule? Generously coat them with grease before installing, and then check them, say every 4 to 6 months?
The hardened Grade8 bolts I have experience with on land exposed to road de-icing salt have far higher corrosion resistance than Grade2.
If bending is a problem, a 12x150 bolt (I understand approx 1/2 inch x 6 inch)
seems a little small in cross-section. Can you drill out and re-tap the holes to get a heavier bolt (say 5/8 or even 3/4 inch) to hold that hydraulic cylinder?
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Old 23-04-2021, 09:06   #10
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pirate Re: Won't bend or rust. What metal do I need?

Is tungsten corrosion resistant?
This is why tungsten is now being used in making rock-climbing spikes and golf clubs. Titanium wins the war in corrosion resistance, though. It has more resistance to corrosion in marine and acid rain environments. It doesn't suffer from pitting corrosion, crevice corrosion or stress corrosion cracking.
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Old 23-04-2021, 09:10   #11
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Re: Won't bend or rust. What metal do I need?

Quote:
Originally Posted by Markb250 View Post
I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?
The bolts that hold large outboard engines to a transom might be suitable with a little investigation.

I would be tempted to ask the lads on Boatmad:


https://www.boatmad.com/forum/
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Old 23-04-2021, 09:22   #12
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Re: Won't bend or rust. What metal do I need?

If the one you are replacing is suspect, can you arrange things so as to use a thicker bolt?
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Old 23-04-2021, 09:55   #13
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Re: Won't bend or rust. What metal do I need?

I'm dumb as a rock. A sketch of the application might help. There are grades of stainless other than 300 and 400 series.
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Old 23-04-2021, 10:19   #14
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Re: Won't bend or rust. What metal do I need?

I used to build subs for the Navy. Standard exterior bolt material was Monel, if that wasn't strong enough we used K-Monel (K-500) and if that wasn't strong enough we used Titanium.


Titanium has come way down in price and when I needed a fork for my hydraulic ram I found one in Ti that was cheaper than any SS fork! below is the company I bought my TI fork from..

Allied Titanium - Affordable Titanium Now
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Old 23-04-2021, 10:21   #15
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Re: Won't bend or rust. What metal do I need?

Quote:
Originally Posted by Markb250 View Post
I need to replace a 150 x 12 bolt that secures the hydraulic ram for the centreboard, to the centreboard case. Not permanently submerged but exposed to the sea. My understanding and experience is that 304 0r 316 SS is too ductile for this. The bending force is considerable.
What and where is the bolt that I seek?
Steel (Including SS also) is one of the best against "bending force" and combines high strength with that. The modulus of elasticity is high. You want something with a high Modulus. (resistance to bending prior to permanent deformation) Most steels are very much the same rating for Modulus. Not much is higher other than cast iron a touch higher. Modulus is different than tensile strength. Although it stays about the same whether heat treated or not. More of a ratio.
Compare the GREEN numbers on the chart. Higher is better.
Steels (29)
Stainless steel (26)
Monel is tough and corrosion resistant, it gets close to steel. (26)
Inconel would be great, but expensive. (31)
Titanium isn't even in the ballpark at (15-17).
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