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nhschneider · 20-10-2012, 13:47

While touring the deck of another cruiser's boat, we stopped and chatted about his anchor and chain. I mentioned that I had intended to get my Hi-Test chain re-galvanized when we were in New Zealand but it hadn't happened. "Don't do that," the know-it-all cruiser whose boat we were aboard said, "Re-galvanizing Hi-Test chain can make it brittle." I hadn't heard that before but I logged it into my memory.

Later, after thinking about his admonition, I decided that he's full of crap. After all, the chain had been galvanized when it was new - didn't that make it brittle? Would re-galvanizing make it more brittle? On top of that, Hi-Test chain is already somewhat hardened - my limited knowledge of metallurgy has always had hardness and being brittle as pretty similar categories. Besides, the galvanizing process itself isn't all that intense that it should have an effect on the chain's hardness, right?

Any opinions on who is right?

perchance · 20-10-2012, 13:53

To make the chain brittle it would have to be heated to red heat and quenched. The temperature to melt zinc for hot dipping would not approach anywhere near that.

**estarzinger** · 20-10-2012, 14:03

Quote:

Originally Posted by nhschneider

While touring the deck of another cruiser's boat, we stopped and chatted about his anchor and chain. I mentioned that I had intended to get my Hi-Test chain re-galvanized when we were in New Zealand but it hadn't happened. "Don't do that," the know-it-all cruiser whose boat we were aboard said, "Re-galvanizing Hi-Test chain can make it brittle."

Re-galvanizing will not impact G4 chain in any meaningful way (because it's not heat treated), but it 'may' reduce the strength of G7 chain (because it is heat treated). Tests have indicated that regalvanizing G7 chain reduces its strength by about 10%.

G4 is what is commonly called high test. G7 is relatively unusual.

Andrew Troup · 20-10-2012, 14:16

There are other ways to embrittle metal than heat treating in the way perchance specifies.

Hydrogen embrittlement is one example, which afflicts high tensile steels, and hydrogen can indeed be absorbed into the microstructure during the pickling process which precedes hot-dipping (pickle is generally Hydrogen Chloride)

I am not an expert, but it occurs to me that there are others which could conceivably apply.

I'm thinking particularly of strain aging, which applies to high tensile metals which have accumulated appreciable plastic strain, aka cold working.

It happens naturally but very slowly at ambient temperatures, but can be drastically accelerated even at the relatively modest molten zinc temperatures.

(I guess it wouldn't feel that modest if you fell in the tank)

I don't have any interest in or enthusiasm for high test chain on boats, so I'm not particularly up on regalvanising it, so I won't pile into the discussion other than to briefly say this:

A new chain will not be prone to strain aging unless it's badly made: this cannot be said for an old chain, with multiple cycles exploiting the high tensile strength (and if you don't exploit it, why bother with it?). Briefly: regalv under such circumstances is not attractive, IMO

As for pickling: check with your galvaniser. They should know that high tensile steel should NOT be pickled, but must instead by mechanically cleaned, eg grit blasting. This will add cost, and is not realistically likely to be sufficiently thorough for best adhesion in the case of short-link chain, given that the links mask each other so comprehensively.

Andrew Troup · 20-10-2012, 14:17

Evans

It seems to me possible that your Bruce failed due to embrittlement. Do you happen to remember if it was pickled?

(Alternatively I suppose it's conceivable there was some cold work - was the shank ever bent and restraightened?)

ON EDIT:
For those unaware: Bruce anchors were cast from high-tensile steel, so there should be virtually NO cold work when they are galvanised the first time.

In comparison, CQR parts, which were impact forged, would presumably have a degree of cold-work (I could be wrong here - during the forging process, you'd think the material would be cooling, but in fact the hammer blows and the resulting plastic flow do reheat the metal to a considerable degree, so maybe it never got below the cold-work transition zone?)

If there was appreciable cold-work, I'm not sure how they would have dealt with this: perhaps they had careful process controls to ensure the anchors did not spend too long at elevated temps ... and possibly it's not a problem for the first few regalvs

It's worth thinking about, though, for those who have bent a shank on any anchor where high tensile materials are used. (Score one for the hitherto much-pitied Rocna owners!)

If you are going to straighten, it might pay to seek some knowledgeable metallurgist to devise a regime, involving heating to a specified temperature which is a compromise between drawing the temper (making it softer) and inducing cold-work (with the risk of strain aging, especially if you continue regalvanising)

**estarzinger** · 20-10-2012, 14:42

Quote:

Originally Posted by Andrew Troup

Evans

It seems to me possible that your Bruce failed due to embrittlement. Do you happen to remember if it was pickled?

Don't know; interesting question.

(Alternatively I suppose it's conceivable there was some cold work - was the shank ever bent and restraightened?)

No it was never bent and straightened

.......

JonJo · 20-10-2012, 19:26

[QUOTE=Andrew Troup;

It's worth thinking about, though, for those who have bent a shank on any anchor where high tensile materials are used. (Score one for the hitherto much-pitied Rocna owners!)

Surely that's contradictory? I thought the owners were to be pitied because they were not high tensile?

Has anyone bent the shank of a 'genuine' Rocna, Supreme or Excel (or any anchor made with a min 690 MPa shank).

Bisalloy (makers of a whole spectrum of high tensile steels) only recommend galvanising those steels of less than (nominally) 800 MPa - anything with higher tensile strength should not be galvanised because the heat of galvanising reduces or destroys the tensile properties. They also seem to suggest sand blasting, not pickling, for reasons already outlined (though some galvanisers pickle any and everything).

**roverhi** · 20-10-2012, 20:37

There was a tri with a too light CQR that would drag intermittently. Seemed to be no rhyme or reason for it dragging. Someone finally noticed the shank had a significant bend which made bottom penetration laying on one side problematic.

Andrew Troup · 20-10-2012, 23:21

Quote:

Originally Posted by JonJo

Surely that's contradictory? I thought the owners were to be pitied because they were not high tensile?

.

Well yes, everyone did. My semi whimsical point was this:

That pity might change to envy in the hypothetical situation where the Hi Tensile shanks break after regalving, whereas theirs don't

lostsheep · 20-10-2012, 23:51

Hhhmmm...
Kinda off topic, but chain related,
In the trucking industry we use grade 70 transport chain, either 5/16 or 3/8". While not galvanized, how does T70 compare to the chain used for anchoring?

JonJo · 21-10-2012, 03:23

Quote:

Originally Posted by Andrew Troup

That pity might change to envy in the hypothetical situation where the Hi Tensile shanks break after regalving, whereas theirs don't

Too clever for me! Nonetheless - 'envy and 'those' anchors' in one thread. This is a real turnaround. I'm impressed, congratulations. Sorry you had need to explain.

Jonathan

**bstreep** · 22-10-2012, 15:59

After having our chain re-galvanized a couple of months ago, that's not a process I'd repeat.

It's so hard to get it all well coated, and then you have to deal with links that have "drips" on them, that get hung up in the gypsy. It's take a few runs to get relatively smooth - but it DID prompt an R & R and rebed of our windlass. Probably needed to be done anyway, but still. I think I'd have been better off investing it in a new chain.