[r9etb]

reason that phosphorous is eliminated by modern metallurgical process is that it causes the iron to be exceedingly brittle, thus rendering it unsuitable for use as a structural material or say a cannon barrel.

And that, sir, is why you're such a fine wizard.

Of course, had our ancient Indian metalmen been more patient, and added the charcoal somewhat later in the process, they'd have gotten steel....

[tet68]

Keep in mind that this is not a casting but a forging
weighing 6.5 tons.
The skill level is amazing, I have had an interest in the
Pillar for over thirty years as a blacksmith.

[nightdriver]

"Of course, had our ancient Indian metalmen been more patient, and added the charcoal somewhat later in the process, they'd have gotten steel...."

That probably should read "removed the charcoal."

Cast iron is about 3 1/2% carbon, high carbon steel is about 1% carbon, mild steel is 0.2% carbon or less.

The iron pillar has longevity in spite of the high amount of phosphorus in the iron because it is loaded in compression instead of tension where the brittleness will show up.