Magnetic stainless snap shackle

dgadee

dgadee

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Was in organising the repair to a sail cover today and saw a Gibb snap shackle at a good price. Bought it. Put it down on the table where a magnet used to get a mouse line was lying and it catapulted towards the magnet. I presume the shackle is not stainless. Is it a fake Gibb?
 
Just tested my Gibb, the hook is magntetic, the mechanism is not (if that helps).

Different grades of stainless have different levels of magnetism as you no doubt know.

Edit, just realised you asked about Gibb snap shackle and I was talking about Gibb safety clip on safety line / tether.
 
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There are a couple of possibilities. 300 series SS is not normally magnetic but it is not hardenable (= strengthenable) by heat treatment. Components in this material that are strengthened are cold stamped to work harden them but this is not applicable to everything.

Thus many stronger items are made from 400 series SS that may have as much chromium as 300 series but no nickel, which means they are ferritic, rather than fully austenitic. Their corrosion resistance in seawater is almost as good as that of 300 series and they can be heat treated. Alternatively there are several exotic alloys, duplex SS and 17/4PH, that are heat treatable, have excellent corrosion resistance and are magnetic.

When statements are made about 304 SS being partly magnetic it is due to small amounts of retained ferrite. Drillings and turnings of this alloy are often quite strongly magnetic but a good quality 316 will not be.
 
vyv_cox said:
There are a couple of possibilities. 300 series SS is not normally magnetic but it is not hardenable (= strengthenable) by heat treatment. Components in this material that are strengthened are cold stamped to work harden them but this is not applicable to everything.

Thus many stronger items are made from 400 series SS that may have as much chromium as 300 series but no nickel, which means they are ferritic, rather than fully austenitic. Their corrosion resistance in seawater is almost as good as that of 300 series and they can be heat treated. Alternatively there are several exotic alloys, duplex SS and 17/4PH, that are heat treatable, have excellent corrosion resistance and are magnetic.

When statements are made about 304 SS being partly magnetic it is due to small amounts of retained ferrite. Drillings and turnings of this alloy are often quite strongly magnetic but a good quality 316 will not be.
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Thanks - I will leave it in salt water and observe what happens ...
 
vyv_cox said:
When statements are made about 304 SS being partly magnetic it is due to small amounts of retained ferrite. Drillings and turnings of this alloy are often quite strongly magnetic but a good quality 316 will not be.
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Ah, yes but the waste material from plasma cutting 316 will be highly magnetic
 
After a few days in salt water, there was a brownish tinge to the water but I can't see any corrosion on the snap shackle itself apart from a very light deposit which could be easily wipef off. Could it be a martensic stainless steel (17-4 PH say)?

I bought it because it was a bargain - £7.99.
 
dgadee said:
After a few days in salt water, there was a brownish tinge to the water but I can't see any corrosion on the snap shackle itself apart from a very light deposit which could be easily wipef off. Could it be a martensic stainless steel (17-4 PH say)?

I bought it because it was a bargain - £7.99.
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At that price almost certainly 400 series ferritic. Duplex and 17/4PH would be x5 that price. Check Wichard stuff for guidelines. Should be perfectly OK - you are not using it underwater are you?
 
Curiosity got the better of me do I Googled Gibbs Snap Shackle and they say they are made from 17-4 and as I have a lump of it to hand I can confirm it's magnetic. As for the price all I can say is its a lot easier to work with than Duplex and ftom a machinist view easier than 316 even though it's tougher ( which is often the case with machining). I do appreciate the Shackle is more likely to be formed however.
Not sure if that will help or not. ..:ambivalence:
 
colhel said:
Curiosity got the better of me do I Googled Gibbs Snap Shackle and they say they are made from 17-4 and as I have a lump of it to hand I can confirm it's magnetic. As for the price all I can say is its a lot easier to work with than Duplex and ftom a machinist view easier than 316 even though it's tougher ( which is often the case with machining). I do appreciate the Shackle is more likely to be formed however.
Not sure if that will help or not. ..:ambivalence:
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Is your 17/4 in the annealed or precipitation hardened condition? Solution treatment, which gives it its strength, is a two or three stage heat treatment process that needs to be quite carefully controlled. It is for that reason that finished items like shackles are so expensive.

It is magnetic because at only 4% nickel it is not fully austenitic and there is a significant ferrite content.
 
vyv_cox said:
At that price almost certainly 400 series ferritic. Duplex and 17/4PH would be x5 that price. Check Wichard stuff for guidelines. Should be perfectly OK - you are not using it underwater are you?
Click to expand...

There was only one of that kind there (lots of non-Gibb at higher prices) and it looked as though they didn't know what it really was so it may be a better bargain than I first imagined. No - plan to use it on a spinnaker sheet.
 
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