Ferrobronze?

Yesterday I poured some stainless steel and ran short, so I melted some mild steel and added like 30-40% copper.

It seems to have made a beautiful ferrobronze alloy. Only, is that a thing? Wikipedia does not have anything like this listed under ferro-alloys.

By question is, any metallurgists out there, what do I have? Is it a decent alloy (seems like it)? Do you think it will be stainless? I know that the definition of "Stainless steel" specifies a minimum chromium content, but will it act like stainless with sufficient copper?

Here's what I was making - it was going to be 2 pours (copper then stainless) but became 3 copper, stainless then ferrobronze. Just messing around trying new things and learning.

This reminds me of a puzzle from a few years ago. A client had asked me to re-do portions of patina on a full size cast bronze dog. It was a seated dog on an octagonal base - attached by steel (badly rusted) bolts that projected from the underside of the dog through the base mount.

The entire piece was ferromagnetic. You can see a rare earth magnet stuck on several areas in the photos. At first I suspected there was steel armature inside the casting but not so; the whole piece was uniformly magnetic.

I drilled a small area to sample and dissolved some turnings in HNO3. It drilled and filed and behaved like ordinary Cu/Sn bronze - dissolved as expected in the acid.

Aside from reacting some of the dilute sol. w/ NH4OH and getting the expected tetraamino blue - thats as far as I investigated. The piece is probably Italian from ~ turn of the century.

I'd never heard of "magnetic" bronze before. There was nothing unusual about the natural patina on unexposed areas but some areas on the exposed surface did appear "rust" stained.

Would love to hear from others about this mystery alloy.

Quote: Originally posted by MeshPL

The problem is, this are the impurities like copper or carbon, that speed up the corrosion of iron. What you just did is you put a ton of copper, which will happily act as a cathode during electrochemical oxidation of iron. Copper by itself is not stainless, it forms patina, which, unlike rust, is relatively non-porous and adherent, so that copper can be used in more demanding condition, than mild steel, but still oxidises. Iron forms a mess of hydrated oxides, which flake off and allow further oxidation. However chromium used in stainless steel forms a thin layer of Cr2O3, which is thin, adherent and remarkably inert. I guess you need to test whether your alloy is corrosion resistant or not, but I wouldn't expect any degree of stainlessness, just a layer of stable oxide, at most. [Edited on 24-4-2016 by MeshPL]

Quote: Originally posted by MeshPL

Nice metalworking, btw. Also, when testing usethe whole ingot made of one alloy, because any piece of other alloy attached will influence results acting as anode or cathode. A quick way to test is to cover the piece with thin layer of salt solution. Iron oxidises that way nearly instantly, although the oxide layer produced is relatively thin. [Edited on 24-4-2016 by MeshPL]

Thank you kindly! Attached is a image of same the pattern all poured in one shot with “ferrobronze”. I love how the coloring; where I want it more yellow/copper to come out I just had to buff it a little more with a wire brush.

Just been messing around with sand - will get back to investment casting here real soon.

And thanks - I started accelerated weathering on it - I got it wet and salty. Will do that a few times a day.

Quote: Originally posted by Fulmen

There are copper alloys with small percentages of iron, and steels with small amounts of copper. But I can't find anything on Cu/Fe-alloys in this range except for master alloys, so it doesn't appear to have any special or useful properties that can't be achieved with simpler or cheaper alloys.

I might be able to argue that point. If this alloy's inertness performs similar (or even superior) to stainless steel or bronze, then it might be possible (and more readily available) to make it for less than what I would have to pay for stainless steel or bronze ingots to be delivered here.

Where I live, there is an abundance of mild steel, aluminum and copper scrap (in that order). There isn't much (if any) tin, bronze or an appreciable amount of stainless steel at the dump pile.

So if I can mix some copper with mild steel to make something beautiful (that might even take a patina) and perform similarly to bronze, I think that is amazing! Not to mention that ~30% copper in my tests is a lot less copper than is typically in bronze, so it should cost less per pound even paying for raw materials.

In small quantities, bronze and stainless ingots can be insanely expensive per pound. Mild steel and copper - not so much.

Quote: Originally posted by argyrium

This reminds me of a puzzle from a few years ago. A client had asked me to re-do portions of patina on a full size cast bronze dog. It was a seated dog on an octagonal base - attached by steel (badly rusted) bolts that projected from the underside of the dog through the base mount. The entire piece was ferromagnetic. You can see a rare earth magnet stuck on several areas in the photos. At first I suspected there was steel armature inside the casting but not so; the whole piece was uniformly magnetic. I drilled a small area to sample and dissolved some turnings in HNO3. It drilled and filed and behaved like ordinary Cu/Sn bronze - dissolved as expected in the acid. Aside from reacting some of the dilute sol. w/ NH4OH and getting the expected tetraamino blue - thats as far as I investigated. The piece is probably Italian from ~ turn of the century. I'd never heard of "magnetic" bronze before. There was nothing unusual about the natural patina on unexposed areas but some areas on the exposed surface did appear "rust" stained. Would love to hear from others about this mystery alloy.