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Old 19-02-2014, 09:30   #16
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Re: Duplex steel for deck fittings?

Plate, bar stock and tubing are readily available and cost for the amount needed for your applications should not be that much more than 316. 2205 is used in offshore oil and gas a lot. Good choice.
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Old 19-02-2014, 11:58   #17
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Re: Duplex steel for deck fittings?

Regards the weldability of duplex, information from the industry states that weldability is good and that all common processes are useable. Please see the attached. If you search you will find many more with similar data. It is very important to use the right weld filler alloy. The article I've linked has a chart for the correct fillers for a range of different metals. Duplex can be stick welded, TIGed of MIGed. It is important that the welder understand the importance of controlling heat in the parts. Other than that welding stainless is not difficult. The need to control heat in the parts is common to all stainlesses.

http://www.avestawelding.com/3756.epibrw
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Old 19-02-2014, 15:35   #18
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Re: Duplex steel for deck fittings?

Hey Saltyhog,

Regards cold working 2205, it can be cold worked, but to a lesser degree than softer metals like 316. For comparison: 316 has an elongation at break of 50% to 60%. That means that a bar of 316 will stretch from 50 to 60% of its length before breaking. It's soft. 2205 has an elongation at break of 35%. It is harder. Glass has an elongation at break of about zero. You can't cold work glass. You can cold work 2205, but not as much as 316. Looking at the elongation numbers, you could say that 2205 can be cold worked about 1/2 as much as 316.

Regards, Paul
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Old 19-02-2014, 16:28   #19
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Re: Duplex steel for deck fittings?

Thank You all for a great input
I appreciate it a lot
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Old 20-02-2014, 07:12   #20
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Re: Duplex steel for deck fittings?

Thanks to all. A lot of excellent information here. I'm now thinking that 2205 may have a problem with the bends necessary for my chainplates. The plates will be either 3/8" or 1/2" thick flat bar stock with some having as much as a 30 degree bend. I'm not a mechanical engineer, so I'm not really equipped to determine if it's a problem. Perhaps I'm better off staying with 316 here. I hope I didn't derail the OP's question too far off his specific question.
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Old 20-02-2014, 09:02   #21
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Re: Duplex steel for deck fittings?

Quote:
Originally Posted by Saltyhog View Post
I hope I didn't derail the OP's question too far off his specific question.
I think that we keep this thread going, not to
answer my first question, but just to gain and put together as much as possible info regarding use of duplex and superduplex stainless steel for the fittings. It is even more interesting than I presumed.


Regards to all

Tomasz
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Old 21-02-2014, 01:56   #22
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Re: Duplex steel for deck fittings?

For welding, in some respects 2205 is even easier than 300 series austenitic stainless (eg 316L). The weld metal itself is highly resistant to hot cracking, so the heat input does not need to be carefully limited on that account.

However you do have to pay careful attention to the heat affected zone adjacent to the weld, the primary consideration being to minimise the *total* time it spends at red heat. (To avert carbide precipitation, which grades like 316L are designed to avoid)

This means that multiple weld runs should be avoided if possible, and so should amateur welding. Weld prep should generally be machined to a carefully chosen profile with a uniform land or gap to prevent burnthrough, not offhand ground.

Preheating is inadvisable, and if multipass welding is unavoidable, the maximum temperature of the base metal between passes should be limited to 150deg C (100 deg C for superduplex)


As far as machining, it's a lot tougher than 316. Maybe as much as forty percent. It's right up there with some of the exotic nickel alloys.

The swarf in particular can be a problem, especially when turning, if you don't have a really rigid machine (even by industrial standards) with *lots* of horsepower, so you can jack up the feed rate enough to break the curly swarf up into chips. Otherwise the swarf is so gnarly and strong that it can loop over (say) a toolpost clamping screw, and wrench the toolpost out of whack (DAMHIKT) or even cause damage to the lathe.

I believe this is primarily because in duplex grades the sulphur content is kept exceptionally low for metallurgical reasons, whereas in other grades its inclusion helps promote the swarf breaking into chips.

Drilling is not too bad: it's not as prone to work-hardening as 300 series which is why the latter can be difficult to drill for the unwary. Slow going, though.

If you have lots of holes it's worth investing in an "armour piercing" drill, certainly you want at least cobalt HSS rather than conventional HSS.

Unlike 316, I wouldn't want to try drilling it with a hand drill ...

Cold Forming/bending: you'll need a stronger machine to form 2205 than 303 or 304 or 316. As a rule of thumb, the machine would need about as much tonnage for 2205 of a given thickness as for 316 of double that thickness. Which in turn is already a significantly heavier machine than for mild steel.

Because of the reduced elongation before break mentioned in an earlier post, you also need to increase the minimum bend radii in comparison with 3xx stainless. Maybe by 30% or so. And you'll need to allow for more springback (which means for the purposes of illustration you might have to bend it through maybe 100 degrees to end up with a 90 degree bend, in the situation when the same bend in 316 would require say 95 degrees. In practice the amount is determined by trial and error, but the tooling may not have enough angular clearance, if it's not intended for such springy material)

It is less sensitive to the relative direction of rolling grain with respect to fold lines than most other rolled plate.

It makes pretty nice castings, and you can often buy up offcuts of large engineering rounds (round bar, short ends of maybe 100mm or 150 diameter) at a surprisingly affordable rate which you can supply to the foundry as raw material. Naturally you need to pick a foundry who are experienced with casting this grade.


If my genuine Bruce anchor ever gets irretrievably jammed I've made an accurate 3D CAD model (trickiest shape I've ever dealt with! I should have 3D scanned it, but I hate backing down) and I'd get a pattern CNC machined, or even possibly a sand mould 3D printed, and cast a replacement in 2205.

That's because the bow of my boat, including the anchor launching and retrieval, is designed around that anchor. And the original anchor is cast from a very strong, tough grade of manganese steel - I think 2205 would be an eminently suitable replacement.

(Incidentally, I do not personally consider 316 suitable for an anchor used for other than overnight stays, from a corrosion resistance standpoint. I think it's an unfortunate innovation of recent times, along with 316 anchor chain.)
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Old 21-02-2014, 02:16   #23
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Re: Duplex steel for deck fittings?

Andrew, thanks for that informative post. Lots of factors that I didn't have a handle on.

Forming it must be a bugger! Glad that my chainplates are simple flat stock with a few holes therein.

Cheers,

Jim
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Old 21-02-2014, 02:25   #24
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Re: Duplex steel for deck fittings?

Sandvik has stock & the electrodes.
I have never come across anything other than 316 (G4) for deck fittings though.
I am currently fabricating a bow roller, with 2205 sched. tube to mount my forestay tang atop.
The tube is 7.5mm wall 73mm ID. Nearly twice as stiff as 316.
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Old 21-02-2014, 13:03   #25
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Re: Duplex steel for deck fittings?

Quote:
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Sandvik has stock & the electrodes.
I have never come across anything other than 316 (G4) for deck fittings though.
I am currently fabricating a bow roller, with 2205 sched. tube to mount my forestay tang atop.
The tube is 7.5mm wall 73mm ID. Nearly twice as stiff as 316.
By stiff, do you mean, strong?

To an engineer, they are separate -- and to a degree independent -- characteristics, and the inherent stiffness of all steels, stainless or not, strong or weak, is much the same.

Some very famous engineers have occasionally demonstrated by their design choices that they have temporarily forgotten this, and almost all "practical" metalworkers and even self-trained, often brilliant designers and machinebuilders I know simply fail to believe it, (although it's very easy to prove, they are typically not interested) so it seems to me anyone else sharing this very popular misconception is in excellent company.
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Old 21-02-2014, 15:14   #26
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Re: Duplex steel for deck fittings?

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Originally Posted by Andrew Troup View Post
By stiff, do you mean, strong?

To an engineer, they are separate -- and to a degree independent -- characteristics, and the inherent stiffness of all steels, stainless or not, strong or weak, is much the same.
As always, the master of specifity. Thanks Andrew for keeping me honest.
I meant strong...said stiff . Which is as you have pointed out.
Although I have been thinking stiffness as in wall thickness. Stiffness being proportional to cube of the thickness? Thats why I upped to 7.5mm wall.
I like the simplicity of my solution but its a clumsy, indirect way of transferring the load to the stem via a tube on its side. Usinng bending resistance.
I am wondering about headstay tension and mast pump.
I really dont want to make it a triangle but that would solve it.

Apologies for the hijack Dblwhisky.
Heres a bit of 2205 data off my heat sheet. (My peice of 2205)
SAF2205 0.2% yield = 573Mpa
UTS = 766Mpa

vanilla 316L .2%yield= 170Mpa
UTS =485 Mpa
As 316L is generally not specifically tested "vanilla 316L" may, in fact, be higher in your case, as the figure I gave is an average.
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Old 21-02-2014, 15:25   #27
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Re: Duplex steel for deck fittings?

Quote:
Originally Posted by lateral View Post
Apologies for the hijack Dblwhisky.
No need for any apologies
I got my original question answered, so let keep this thread for all matters duplex and superduplex related (as in title of the thread and even broader)
For me it is more and more fascinating
Thank You all!
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Old 21-02-2014, 15:33   #28
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Re: Duplex steel for deck fittings?

Then there is SAF2207 & 2707. But, hold onto your wallet.
2205 is a similar price to 316L owing to 2207 & 2707 & high demand for 316L.
(I was told)
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Old 22-02-2014, 03:10   #29
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Re: Duplex steel for deck fittings?

I guess, lateral, another factor is that in terms of composition, 2205 (in comparison with 316) increases chromium at the expense of nickel

It seems from a quick check that the latter is currently about three times the price of the former, at least in the raw feedstock form used for steelmaking.

The extra strength and pitting resistance of duplex stainless is the result of smart microstructure design, rather than indicative of the 'brute force' superabundance of expensive alloying constituents.

Duplex stainless has always been misunderestimated (a useful GWB coinage, arguably the useful GWB coinage!)
and I guess that's why the tonnage demand has historically been less than the merits of the material would suggest.

(I guess being a #@$ to machine didn't help, either...)
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Old 26-02-2014, 15:39   #30
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Re: Duplex steel for deck fittings?

For the experts here: I'm replacing my chainplates. I can use bar stock and I've found a source of 2205 in a size I can use. However, they only have it in "sheared and edged". Alternatively, they have 316L in rolled flat bar. My limited understanding is that rolled would be better in this application, but I'm not sure if that is still true of 2205? Also, is hot rolled better than cold rolled in this application? Would it make a difference with respect to how I make the bends in the chainplates? Would I need to have them annealed after bending? I'm probably over-thinking this, but it's interesting and all new information to this electrical engineer who admits to sleeping through his strength of materials class in college.
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