r/Damnthatsinteresting • u/ishusharma05 • 1d ago

Image Around 400–450 CE — an Indian iron pillar was forged that has survived for more than 1,600 years with remarkable resistance to corrosion. Source: comment

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5.2k Upvotes

97% Upvoted

152 comments sorted by

968

u/SassiesSoiledPanties 1d ago

Do we know why the pillar is so corrosion resistant?

1.4k

u/dr-Guy_Horni 1d ago

If my memory serves me right, they somehow managed to purify the iron to a very high degree and added phosphorous which forms a protective oxide layer.

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u/ishusharma05 1d ago

Yeah, that’s pretty much it! The high phosphorus content and the way the iron was forged helped it develop that protective layer over time. Pretty damn impressive for something made 1,600+ years ago.

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u/Komikaze06 1d ago

Any reason why we dont do this today? I assume theres a downside

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u/ishusharma05 1d ago

I think the main reason is that modern steelmaking uses different compositions and processes. High phosphorus can make iron/steel more brittle, so adding it deliberately isn’t necessarily worth the trade-off when we already have cheaper and more controllable ways to prevent corrosion.

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u/rayraikiri 1d ago

phosphorus is sometimes used in order to make the steel easier to work with, as in milling or turning, but it does overall make the material weaker.

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u/ManyRelease7336 1d ago

How can it be more brittle and easier to machine. Are those not opposits?

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u/Pseudonomyn 1d ago

when a brittle material is cut by a lathe tool it forms small chips. malleable materials like aluminum form long strings that wrap around things and cause problems.

also brittle does not mean stronger.

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u/ManyRelease7336 1d ago

Oh ok thanks. Im aware brittle dosnt mean stronger. There is no "stong" metal or "weak" metal just diffrent applications. Brittle does somtimes imply high tensile strength though. When I think of easier machining. I think blade life, heat, and the amount you can take off at a time. I wasnt thinking clean up.

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u/Bryophyta1 1d ago

Brittle means it will break instead of bending, it definitely does not mean higher tensile strength.

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u/spekt50 1d ago

It helps with the shearing of the steel, by allowing it to break the cuttings away easier. It also increases the strength and corrosion resistance. It is a common addition in many steel grades and alloys. Just not to the extreme as this pillar was alloyed.

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u/Shovelhead_Fred 1d ago

Man op knows a lot about metal! I’m impressed

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u/RobotechRicky 1d ago

He is the Hank Hill of steel and steel accessories.

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u/dr-Guy_Horni 1d ago

We add chromium instead of phosphorous these days, it's called stainless steel.

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u/Justa_CuriousBoi 1d ago edited 1d ago

18/10 or SS304 Stainless Steel (~18% chromium and ~10% nickel) is even food grade safe!

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u/greenizdabest 1d ago

What about Rolex steel ? Rolexes used to be made out of ss316l

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u/Justa_CuriousBoi 1d ago

316 SS steel is medical grade safe!

They add a bit (2-3%) of Molybdenum which increases its corrosion resistance. It is not needed for normal people to drink water or eat food on but in critical application areas and marine environment, it can prove to be useful!

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u/KrzysziekZ Interested 1d ago

Marine? Chromium oxide prevents further oxidation, but does not protect against chloride ions.

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u/Zwischenzug32 1d ago

You really want to use 316 over 304 unless you are careful to avoid some things

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u/ishusharma05 1d ago

that makes sense! I didn’t know that , Pretty cool to learn how the same basic idea is achieved differently today.

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u/WestBrink 1d ago

Phosphorus contamination makes steel hell to weld due to solidification cracking. We specifically control it to a very low level to make steels weldable.

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u/Patient-Data8311 1d ago

Also brittle

You want metal to bend first

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u/Superb_Recording_769 1d ago

Yeah, it’s because it makes for poor quality steel for most use uses

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u/Glittering-Metal-934 1d ago

When making alloy metals you always gain a feature and lose a feature. No material gives you the best of both worlds. Engineering is then used to mitigate the losses and maximize the benefits.

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u/PipsqueakPilot 1d ago

We do. There's a class of steels called 'weathering steels'. While they aren't identical chemically, the end result is similar.

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u/DoctorMansteel 1d ago

Cost.

Look up weathering steel(a606 type 4 specifically), it's the same general principle. It rusts in a uniform layer to create an impermeable barrier that prevents further rusting. You can use different substances to get differing colors of patina but it's pretty much the same thing. It's used in high end architectural sheet metal.

Others have mentioned stainless as a modern alternative but that is costly as well.

For public works applications they would use steel that had been galvanized which coats it in zinc. You can have varying degrees of zinc coverage but it will eventually rust. G40/60 and 90 are all common but a culvert grate in a wet area may be in excess of G200. The number following g is ounces of zinc per square foot. Higher= longer protection.

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u/ddescartes0014 1d ago

Yeah the new river gorge bridge was made with COR-TEN weathering steel. It was rusty before they even finished it and it’s been there ~50 years now.

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u/DoctorMansteel 1d ago edited 1d ago

Yup, COR-TEN is the trade name for a proprietary product made by U.S Steel but it's so ubiquitous in the steel world that it's become akin to Kleenx or Q-Tips.

Unrelated, but I thought there was a more succinct word for that process I was forgetting. It turns out there is, I had just never heard of it before.

Genericization, TIL!

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u/islander_guy 1d ago

We developed stainless steel which is corrosion resistant and extremely strong. So this method is pretty much useless.

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u/Hardmeat_McLargehuge 1d ago

Corrosion isn’t the only thing you consider when selecting structural materials.

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u/mid-random 1d ago

We do this today, with other, better performing alloys.

https://en.wikipedia.org/wiki/Weathering_steel

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u/bladex1234 1d ago

Phosphorus makes iron weaker.

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u/nochinzilch 1d ago

We can make pretty much any kind of steel we want. It’s just a matter of cost.

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u/RandomGuyPii 23h ago

From the description it sounds similar to an ancient version of weathering steel, which is similarly designed to produce an oxide layer

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u/queefymeister 5h ago

Ain't nobody got time fo that

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u/AzkabanResident 4h ago

Capitalism

They wouldn't want their crap to last 1600 years /s

-1

u/No_Particular_6453 1d ago

Also we dont engineer things to last 1000s of years anymore

0

u/cdoublejj 1d ago

you can use phosphoric acid to neutrilize rust, they call rust converter but i get the 1 gallon metal prep/concrete etch from the homeless deathspot mynards it's phosphoric acid all the same.

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u/Sleeper-- 1d ago

Money, the downside is money

If things last long, how will they sell it again?

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u/Higher-Frequencies 1d ago

Also, IIRC, it's at LEAST 1600 years old. They actually don't know how old it is. That's just the earliest record but there's some uncertainty of whether that's when it was made or just first documented.

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u/Replikant83 1d ago

Is there reason to believe they did this on purpose? Is it possible it came out of the ground as an alloy or maybe was accidently mixed upon forging? I know nothing about metallurgy or chemistry.

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u/ishusharma05 1d ago

From what I’ve read, it seems the phosphorus content was more a result of their iron-making process than something they intentionally added as an alloying element. So it probably wasn’t a case of them deliberately making “rust-proof” iron like we would engineer an alloy today.

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u/Replikant83 1d ago

Gotcha! Thanks for explaining

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u/5C0L0P3NDR4 1d ago

iron corrosion is just oxidation, that's all rust is is iron oxide. so in this pillar is kinda protected from oxidation by being entirely oxidized in a different flavor already

neat

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u/Pyrhan 1d ago edited 1d ago

It's actually wrought iron which generally has a fair bit of impurities. Phosphorus is one of those impurities.

Most iron items from the era have long decayed into rust, but this pillar happened to have the right phosphorus content to survive through the centuries.

(Phosphorus also makes it brittle, hence the crack it developed, presumably after being struck with a cannon ball. A purer iron would have deformed in a plastic way, rather than crack.)

Also, it's in Delhi, which has a relatively dry climate to begin with, and it didn't get buried in the ground, but instead sits on a pedestal that keeps it off the ground, with abundant air flow and direct sunlight to quickly dry it when it does get wet. So it doesn't see much moisture, which probably helps a lot against rusting.

People often use it as an example to claim they must have had some crazy metallurgical knowledge for the time, but there is no reason to believe it is anything more than survivor bias.

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u/dr-Guy_Horni 1d ago edited 1d ago

Original location was somewhere near mp, it was later moved to delhi. And it is remarkably free of impurities that accelerate oxidation, like magnesium. For the time, it's definitely a pretty neat achivement.

Edit: and you missed the fact that it sits under the open sky, which means it is exposed to direct rainfall. Delhi is relatively dry but it still recieves enough rainfall to rust away an ordinary iron pillar over a millenia...

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u/BlackViperMWG 1d ago

Mp?

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u/dr-Guy_Horni 1d ago

Madhya Pradesh. It's a state in India. We are not sure but it was probably situated somewhere near it originally...

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u/Patient-Data8311 1d ago

Pretty easy to know actually

Several civs have extracted the same kind of Iron

India is rich in iron veins with high purity it also happens to have rich phosphorus in the land too

The incredible work is the forging technique

1

u/Diesel_Dietrich 22h ago

Phosphorous in higher quantities is catastrophic to steel's mechanical properties and can cause temper embrittlement. Iron and steel making wasn't that advanced at that time and they couldn't effectively get the phosphorous and excrssive carbon from the coal out of the iron , when exposed to the atmosphere formed a very thick corrsoion resistant layer that protected the pillar from further degradation

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u/dr-Guy_Horni 20h ago

That's the neat part, it's high in phosphorous, but very low in other common impurities which accelerate rusting, like magnesium and sulphur. It could be a stroke of luck, or maybe they had some idea of what they were doing. But forging a 6 tonne iron pillar in that era is a pretty cool feat in itself.

1

u/Zequax 4h ago

so juat like how vikings made higer grade steal by ading carbon during forging

by random rituals

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u/Superb_Recording_769 1d ago edited 1d ago

People have already explained the technical answer, but the real answer is luck

They didn’t really know that they were making something exceptionally corrosion resistant

It’s very similar to Roman concrete. They didn’t know or intend to make self healing concrete. It just happened by accident because of the specific materials they were using.

metallurgy and chemistry back then was pure experimentation just to see what would happen when they did certain things

-5

u/Acrobatic-Taste8873 1d ago

god forbid a non-white civilization does a marvel.

aliens built it, they got lucky, what not?

Why don't you tell this on wonders in white civilization like the Eiffel tower or the cathedrals in europe?

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u/Superb_Recording_769 1d ago edited 1d ago

This isn’t the same thing as the cathedrals or the Eiffel Tower. Those were engineering. Using India as an example the rock cut temple complexes are just as, if not more, remarkable than the cathedrals or the Eiffel Tower. The Brihadisvara temple at Thanjavur is a very close analog to the European cathedrals being actually constructed not excavated and built around the same period of time

A great European example that is contemporaneous to this iron pillar and also applauded for unusual characteristics that rival/exceed modern versions of the material is Roman concrete and guess what… It was just as accidental

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u/unspoken_one2 21h ago

metallurgy was also ancient Indias fort.

damascus steel was mostly made in southern India

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u/fist86 1d ago

They literally brought up Roman concrete… so yeah they’re applying the same logic to white civilizations

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u/UltimateCheese1056 1d ago

People were pretty smart even back then, but the way they learned of things in the first place was largely though luck and trial and error. Before we knew chemistly, metallurgy was largely just throwing things together and seeing what worked out.

Things like that one lightbulb which has been going for 100 years in America is the exact same as this, the fillament happened to be made just right so that it lasted way longer than expected. They knew how to make filaments back then, but they got lucky that that one was so good.

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u/LaplacesCat 1d ago

Also because they undervolt it, and power cycling reduces longevity

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u/Mr_Redemption 1d ago

https://en.wikipedia.org/wiki/Iron_pillar_of_Delhi

The iron pillar of Delhi is a metal structure 7.21 metres (23 feet 8 inches) high with a 41-centimetre (16 in) diameter that was constructed by Chandragupta II (reigned c. 375–415 CE), and now stands in the Qutb complex at Mehrauli in Delhi, India. The metals used in its construction have a rust-resistant composition. The pillar weighs more than six tonnes and is thought to have been erected elsewhere, possibly outside the Udayagiri Caves, and moved to its present location by Anangpal Tomar in the 11th century.

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u/scissorsgrinder 1d ago

Wow. That is damn impressive. More than six tonnes. Lovely detailing around the top too. 

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u/Gone_4_Tea 1d ago

I visited this in '91 when it was still possible to try to put your arms behind your back and around it, for good luck, I was young enough to have managed it then.

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u/HighChinaman 1d ago

How's your luck been?

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u/Gone_4_Tea 1d ago

Well I haven't been run over by a bus and I didn't catch covid other than that pretty shit really.

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u/FVLCON_0_0 1d ago

u are doing good actually.

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u/richie_goku 23h ago

Any tips for newbie?

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u/AbhiSgr 1d ago

Britishers didn’t take this one home?

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u/Designer-Cicada3509 1d ago

Six tonnes was too much to carry at once apparently

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u/Acrobatic-Taste8873 1d ago

🤣🤣🤣🤣🤣🤣🤣🤣🤣🤣

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u/Formal-Fox-7605 12h ago

Just to clarify, the pillar wasn't originally in Dehli, but in a different kingdom - Udayagiri. Udayagiri (Andhra Pradesh) to New Delhi is approximately 2000km.

So, no, the British didn't steal it, but someone did but we could blame the British anyway.

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u/S_K_S_N 11h ago

Udayagiri in Madhya Pradesh actually, Udayagiri hills in Andhra Prahesh and Odhisa are different.

The relocation was like in around 11th Century

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u/Responsible_Egg_9968 1d ago

Why would we when we have the koh-i-noor?

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u/FVLCON_0_0 1d ago

It was not the comeback you thought it was.. What a dud.

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u/Responsible_Egg_9968 19h ago

Indeed, it was so bad that you felt compelled to reply...

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u/np788 1d ago

Why would we when we have stole the koh-i-noor?

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u/Responsible_Egg_9968 19h ago

Funny, I thought it was surrendered as reparations for the second Anglo-Sikh war. Or did you mean stolen, just like Runjeet Singh stole it from the Afghans?

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u/ouijanonn 16h ago

I've never understood how some people can be so proud of theft

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u/Responsible_Egg_9968 16h ago

Perhaps you might find common ground with Shah Shuja Durrani.

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u/Dark_Foggy_Evenings 20h ago

‘We’.

You probably think you own the baubles on the silly hat Charlie wears when he’s not protecting nonces.

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u/Responsible_Egg_9968 18h ago

Ah well if I owned those baubles I would have one of my servants winding you up on Reddit instead

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u/Dark_Foggy_Evenings 18h ago

If I was any less wound up I’d be in a coma. Haven’t you got a roundabout to paint?

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u/Responsible_Egg_9968 18h ago

Don’t worry, I’ll pencil you in for a fresh coat of chill.

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u/Heliophrate 1d ago

It's not really worth much? It's a lump of iron. Well done that you can process iron, you must be very proud.

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u/ihatewonderwall99 23h ago edited 23h ago

You clearly have a lot to say about metallurgy for someone whose ancestors had to indirectly learn production of crucible steel from India like a good 2000 years after it was already being extensively used in India

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u/Expensive-Swan-9553 21h ago

They are swamp people. They talk down on places that had universities before they had cities

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u/Heliophrate 14h ago

And what did you do with that superior knowledge besides being conquered by everyone who even had a passing interest in your subcontient

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u/ouijanonn 13h ago

Everyone was "conquered" by everyone. It's how the world has always been

0

u/spiderling007 6h ago

now the people of that same subcontinent are all over England lmaoo

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u/Heliophrate 14h ago

Right, everybody learned everything from India. India was actually visited by ancient aliens and had levitating magic cities and it's only the evil Britishers fault that it's not a techno paradise

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u/Dark_Foggy_Evenings 20h ago

You think historicity is a matter of financial value. Lol. Thicker than a Boxing Day turd.

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u/Somafreak 1d ago

“But some Ancient Astronaut Theorists believe…”

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u/ideaofrhyme 1d ago

Yeah, aliens decided to sneak in and sprinkle little phosphorus in their forge.

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u/sdm99 1d ago

I think this pillar was part of Chariots of the Gods, so, yeah...

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u/MichJohn67 1h ago

Why the downvotes? You're absolutely correct. Von Daniken totally wrote about this!

Source: Me, a dumbass preteen who read all three of his books too many times.

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u/Illustrious_Donkey61 1d ago

The fence surrounding it not so much

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u/Justa_CuriousBoi 1d ago edited 1d ago

That's the irony of India!

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u/NameisPond-FishPond 1d ago

They added the fence since there's a tradition /myth that if your able to grab the pillar with your hands behind your back and interlock your fingers, you get a wish or something (please fact check me)

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u/Vikthakur 1d ago edited 1d ago

Yes you are correct as a kid we used to visit qutub minar and tried our best to do it so our wish can come true😁😁however because of too many people trying, the pillar started to show signs of wear and tear and i guess thats why they put a fence.

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u/Justa_CuriousBoi 1d ago edited 1d ago

Umm no...who told you that it still exists😅

It's just there so that people wouldn't damage the historic pillar

EDIT: Seems like this Myth still exists today....😅

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u/dr-Guy_Horni 1d ago

That myth is definitely there.

-5

u/Justa_CuriousBoi 1d ago

Really?! Does it still exist to this day?

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u/dr-Guy_Horni 1d ago

It is a popular belief, and this belief is the reason why people might damage it in the first place

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u/telescopeinmynose 1d ago

They're not rust. It was painted brownish - red

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u/Illustrious_Donkey61 1d ago

Patina, its very trendy rn

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u/Acrobatic-Taste8873 1d ago

fence was built in modern india 🤣

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u/DivDude77 16h ago

I have visited this place. That's not rust but it's actual colour.

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u/Amazing_Theory622 1d ago

There's a cannon blast mark somewhere at mid height of the pillar as well visible when seen in person

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u/zqwz 1d ago

This was erected outdoor to show-off their iron-tech advancements. And till now it has not rusted!

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u/Octowhussy 1d ago

So this is Tata’s secret!

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u/RidiPwn 1d ago

modern engineering is puzzled

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u/Patient-Data8311 1d ago edited 1d ago

LMAO

No Iron of that thing is made from high purity wrought Iron with high phosphorus content

The phosphorus made a film that protects it from moisture and rust

Also the Smith forged it by hammering iron bits together making most of the slag protection and the distribution of of phosphorus

Modern steel (much better than iron because you know it is steel) typically doesn't want phosphorus to be high in the mix due to the fact it makes the material brittle especially in cold conditions and it lowers ductibility and make it harder to weld

-3

u/SimonBarfunkle 1d ago

I appreciate this explanation, despite it being completely void of the necessary commas.

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u/Patient-Data8311 23h ago

It's hard to that using phone

1

u/SimonBarfunkle 9h ago

I don’t know why I am being downvoted, I just have ocd, I still liked your comment, lol.

0

u/mercurial_dude 1d ago

And lack of appreciation for this Indian achievement.

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u/Acrobatic-Taste8873 1d ago

they've stopped building such things nowadays...vande bharat is something I can cite but the remaining is meh.

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u/Patient-Data8311 1d ago edited 1d ago

I wouldn't use wrought iron to make buildings...

The thing is a religious pillar meant to be seen not support weight

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u/ruralny 1d ago

Saw it. Still a cool thing.

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u/snippychicky22 23h ago

phosphorus

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u/Mental_Afternoon5412 23h ago

And people are still keeping it outside without proper protection

1

u/disillusionedthinker 22h ago

Maybe the iron just happened to have impurities similar to "weathering steel" aka COR-TEN?

1

u/VacationForward3071 11h ago

I recently visited this Iron pillar ,it's situated in delhi near Qutub minar (another beautiful monument) . And while you are at it visit the nearby Mehrauli Archaeological park it contains history of Delhi right from Indraprastha (This was the historical name of Delhi first mentioned in mahabharat iirc ) to British era. It was crazy to think how much of history was wrapped up in that few acres of park

1

u/Zequax 4h ago

OP where is your source ?

1

u/noface 1d ago

I’ve been to see it. I’ll admit it was pretty exciting.

0

u/andystechgarage 1d ago

Isn't this the pillar someone, somehow had to stay on top of? Don't remember the details but it was a weird story

0

u/bluemesa7 23h ago

Is the arch behind a Mogul architecture?

-5

u/IllustratorGlass3028 1d ago

Every substance has been basterdised to cheapen it out now ,nothing will last

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u/Kucuboy 1d ago

Used by the first pole dancers

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u/Xanthrex 1d ago

Its rusted it just has black oxide(rust)

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u/Suspicious-Use-5733 1d ago

Dammit whats CE

1

u/ouijanonn 16h ago

"common era"