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Does wrought iron rust?

Posted: Tue Sep 20, 2011 7:25 pm
by Eve
Hi
I'm hoping somebody will be able to help me with this query.
Over the weekend I was doing a surgery display and when asked if the instruments were original came out with my usual line about how rare original instruments from medieval and early modern are due to them being iron and therefore prone to rusting.
An engineer in the audience said that the finest quality wrought iron wouldn't rust as it has very little carbon in it and it's the carbon content that makes iron rust. He further said that that's why they built bridges out of it, I assumed they were painted to stop rust.
Can any metal expert help me with this.

Steve

Re: Does wrought iron rust?

Posted: Tue Sep 20, 2011 8:08 pm
by chrisanson
Eve wrote:Hi
I'm hoping somebody will be able to help me with this query.
Over the weekend I was doing a surgery display and when asked if the instruments were original came out with my usual line about how rare original instruments from medieval and early modern are due to them being iron and therefore prone to rusting.
An engineer in the audience said that the finest quality wrought iron wouldn't rust as it has very little carbon in it and it's the carbon content that makes iron rust. He further said that that's why they built bridges out of it, I assumed they were painted to stop rust.
Can any metal expert help me with this.

Steve

bit of a plank that bloke

Re: Does wrought iron rust?

Posted: Tue Sep 20, 2011 8:13 pm
by Malvoisin
Rust or iron oxide is a formed by a reaction between the iron and oxygen in contact with water or moisture. Nothing to do with the carbon content at all as far as I know.

Also Wrought iron tools? I think most cutting/ surgical tools would have at least a hardend steel edge, (to enable durable sharpening) wrought iron being relatively soft, but that would still corrode away in the right conditions.

did he show you his engineering degree? No? They never do do they. :^)

Re: Does wrought iron rust?

Posted: Tue Sep 20, 2011 8:30 pm
by The Iron Dwarf
wrought iron rusts but not as easily as steel does

Re: Does wrought iron rust?

Posted: Sat Sep 24, 2011 10:36 pm
by Chris T
Modern mild steel is about the worst for rust: some applications (such as tractors) which are going to be very weather exposed specifically use iron plate to cut down on this.

In general the irons or other steels are less rust prone to various degrees. Leaving a heat finish also helps somewhat with rust protection.

Re: Does wrought iron rust?

Posted: Sat Oct 29, 2011 5:46 pm
by Gockee
About 10 years ago I talked to the iron founder at Blist's Hill, the only place in the world that still makes wraught iron rather than mild steel. He still works in genuine wraught iron rather than steel stock. He told me that wraught iron rusts, but only on the surface. Once there is a continous layer of surface oxidisation, unless that layer is penetrated or exposed, it wont rust any further, unlike today's mild steels.

Re: Does wrought iron rust?

Posted: Sat Oct 29, 2011 8:15 pm
by The Iron Dwarf
last lot of wrought Iron we bought was made in IIRC Sweden, we had about 3 tonnes of it made for a job, took a while to get it imported so I dont think Blist's Hill is the only place

Re: Does wrought iron rust?

Posted: Sat Oct 29, 2011 11:57 pm
by uksimes
I have a couple of wrought iron ornaments in my back garden.

Yes, they do rust - slowly

Re: Does wrought iron rust?

Posted: Tue Nov 08, 2011 3:40 pm
by guthrie
Yes, it does rust, but slowly. Apart from the lack of carbon, it probably lost sulphur and other dodgy elements which helps.
Recall though that your average piece of medieval iron would hardly be left on a shelf to rust slowly, but might end up in a bog with corrosive acidic environments, or in a river where the electrochemistry would eat it up, or be picked up and used by a passer by as a tool, or used for several generations until the sharpening and re-sharpening had worn the tool down to uselessness and it would get dumped somewhere or re-purposed into something else.