Stainless grading

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goldscoter14

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Hi,

I know that 316 or A4 is the preffered choice for stainless for marine use because of its resistance to corrosion, with A2 a poor relation . I've been forcing myself to abide by this despite endless fights with my pocket over the last while. I however have recently come upon a relatively cheap supply of grade 440C stainless and grade 17-4 stainless. They are normally used in making drill bits and similar industrial stuff as they can be hardened easily, but I was wondering if anyone knew how they stand up in a salty environment corrosion wise? would I just be fooling myself thinking I'm saving money, or do they last?

anyone with any experience of this or any thoughts?

thanks in advance
Danny
 
Get a peice of each and chuck it in a bucket of salty water give it a few months, and see how it copes.
I would stick with 316, even it will corrode, especially where it has been ground or sanded with the incorrect abrasives, or drilled with steel and cobalt drills.
 
I have no knowledge of materials, but ferreting around with Altavista came up with this site giving a tremendous amount of data on all kinds and types of metals used in the aircraft industry.

metals specs and info

Any use ?
 
As far as I remember, Martenistic stainless steel, such as 440c, is very hard but only moderately corrosion resistant. It's also magnetic which helps identify it. Austenitic stainless steel contains nickel and is not as hard, but considerably more corrosion resitant - your 316 for example. So, non-magnetic austenitic s/steel is good for we boaties, the other is good for tool makers.
 
Neither will be much use - they are both Martinsitic grades and will corrode to hell in a marine environment. ~ I am sure some pseudo, or wannabee, metallurgists will come along and say they are OK and that they have used then without any problem but personally I would not use them in a marine environment (or any even mildly corrosive environment for that matter). - Your boat - your call. /forums/images/graemlins/grin.gif
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"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>
 
I have to pose the question ~ why do you want to know this?

You say you've come across a supply of s/s ~ have you got access to or do you own a workshop where you could make up any s/s bits you need for a boat?

OR do you do the same as the rest of us and head down to the local swindlery and buy what we need!

Peter.
 
[ QUOTE ]
Neither will be much use - they are both Martinsitic grades and will corrode to hell in a marine environment.

[/ QUOTE ]Yep, true. Actually 304 (or A2) isn't all that bad on the deck: it gets a bit brownish and needs polishing from time to time. It is less subject to crevice corrosion than 316 (A4).
 
I think you're right js48. Its the market price of nickel that makes A4 so much more expensive.

to answer The Boatman, no I don't have a workshop. Like most I have been getting my stuff from local swindlers and licensed thieves. However a friend of mine is working in a factory that made drill bits and its closing down and all the stock is getting sold off for pennies. It was occupying my mind as I bought a length of 20mm threaded stainless bar at 35euros/m recently and will prob have to get more in the near future. Same with screws, bolts etc

I reckon you're all right. I'm going to stay away from it, tempting as it may seem to be. these boat things are expensive though!!!
 
[ QUOTE ]
I think you're right js48. Its the market price of nickel that makes A4 so much more expensive.



[/ QUOTE ]

Not really - its the cost of the molybdenum which makes 316 much more expensive than 304, and its the molybdenum that gives better salt water corrosion resistance.
 
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