I have a world setting that contains a variety of underwater species, some crustacean, some cephalopodic, and other varieties. Different species are adapted to different depths, and a few are amphibious. Part of their culture is tied to the ability to metalwork. Not a big part but its an important one.
There have been a fair number of posts on similar topics on this site and I've checked over most of them. I'm aware of the concepts of electroplating and electroforming, and obviously I could just leave it up to the amphibians, but frankly I'd rather not. I know cold forging is also feasible, but limited, and that certain metals have properties that protect them from corrosion, such as aluminum and to some degree copper. These are all things that could fit for many forms of common metal craft, but my merfolk need to be somewhat better than common.
First I thought of thermite just because it burns underwater, and could bring heat to the process. But then I found it leaves metal residue. I did some research and found there has been some effort to forge weapons and such by burning thermite into a mold. Backyard scientist on youtube has a video on it. The world is set in a kind of a steampunk industrial revolution that has a different flavor depending on the race. I've been having a hard time with the merfolk's flavor, I don't want to resort to some made up material or fuel, but they need to be good metalworkers.
Specifically, they're chain makers. They use hooks and chains to attack any ship that dare sail their waters, capsizing or tearing them apart. But also, their capitol is something of a world wonder, a buoyant city held down by massive chains, designed so that species of all depths can coexist to a degree. so their chains need to be strong. I'm hoping this leads to a solution for many peoples concerns of underwater forging. I know only select metals can be used to make thermite. However among them are components for corrosion resistant stainless steel. Such as iron (obviously), chromium, and manganese. Lead and copper are on the list too, although I know at least copper is particularly volatile.
So my questions are this (sorry for the long lead up):
Assuming the species has access to electricity in some form (as discussed in other threads) am I correct in thinking thermite forging underwater is plausible
Is thermite metallurgy remotely plausible? (I.E. mixing the oxide powders and melting them together.)
How necessary is it to worry about protecting from corrosion if most of the metalwork never leaves the water, at least not the stuff that has to last.
EDIT: With bioelectricity I would think ll they would need is magnesium at that point to act as a fuse. Since both substances can burn underwater. I also didn't mention manipulators such as hands or tentacles, which would naturally have to occur in a race capable of working metal.
Also as it has been addressed below, despite researching most of the rest of the details, I had the oversight of failing to research if the requisite metals were naturally occurring. That being said, I figure the ability to do this would be something of a cultural goal, a way to make metal in a "pure" way from their perspective. I know its not as practical, but wanted to know if its possible, even if it has to be with considerable effort. However I also believe this has been answered as a wildly impractical potentiality. Which has satisfied my questioning