Identifying high P iron/sourcing modern high P feedstock?

[Aiden CC]

I have been experimenting with pattern welding using hearth steel, but I’ve been finding that I don’t quite get the contrast I might want using just low and high carbon material, so I want to start playing with phosphorus iron. I have a variety of different old iron sources I want to try and use and my first question is about trying to identify high P iron, ideally without sending it off to a lab (though if that ends up being the case, I may do that). 
 

I have heard that nails from the Globe Elevator may be high in phosphorus and it seems like there might be some evidence for that. The nails break when struck in a vise with no notch and generally have very little ductility. Would that be how phosphorus induced cold shortness might manifest in wrought iron? The material also does not seem to take up carbon well in a hearth, as the pucks start out sparking/hardening well and then lose it after a few folds. I have tons of pieces of hearth material that have behaved this way, is there some “in-shop” test I could use on material like this?

 

Another thought I’ve had is trying to get a source of feedstock with a known phosphorus content. Are there any common modern alloys that might work for this? All I’ve been able to find is ferrophosphorus, which seems like one of those things that you need to buy 5 tons of, and phosphorus calibration standards which don’t have a listed price, but I imagine would be incredibly expensive. 
 

Any thought here would be appreciated, if I have to send some pieces out for testing, so be it, but I figured it would be good to check here first!

[Jerrod Miller]

Phosphoric acid is the main ingredient of many rust converters.  Perhaps it can be used in the hearth charges as a P source?  

[Alan Longmire]

Globe Elevator iron is indeed high-P, and that cold-shortness carries over when carburized.  As you noticed (and I know you know, this is to help folks new to the concept!), when P-levels get over about 0.3% it prevents carbon uptake over around 0.3% as well.  The added hardness P adds counterbalances the lower C, especially if cold-forged to work harden the material.

 

The reason you don't see modern iron alloys containing phosphorus is because it's a generally bad thing for modern purposes.  It makes cast iron too brittle to use at all, and nobody wants mild steel that won't bend...  

 

There are a few methods of making high-P bloom from low-P ore.  I don't think it can be done in a hearth, though.  Maybe if you lined the floor of the hearth with bone dust? That'd smell great, but you're working on rawhide cow tails, so smell obviously isn't an issue... 

[Alan Longmire]

I totally forgot to mention how to tell if your salvaged wrought iron is high-P:  It etches darker than low-P, but the real test is hot-cutting and forging.  If you get halfway through the bar and it snaps off and shoots across the shop, it's high-P.  If you're forging it and let it get the least bit into the orange-red range and it just falls off the end of the bar, it's high-P. If you're welding it and it falls apart like frozen cottage cheese at a full white heat, it's high-P and may have some sulfur as well.

 

It wasn't popular for good reason.   

[Matt Walker]

1 hour ago, Alan Longmire said:

It wasn't popular for good reason.   

Alan, I may have more of those black painted bars if Y'all can use them.

[Alan Longmire]

Oh, we can use them!  I can take a couple, you can sell them at the hammer-in this fall.

[Matt Walker]

I'll see if I can find them. 

[Aiden CC]

I made a quick coupon from Globe Elevator nail material (thin) and anchor chain (thick) and etched it:

 

The first is after the etch and the second after a quick polish. Interestingly, the material looks less affected right out of the ferric chloride, but then remained “frosty” while the wrought got back some luster. Very good contrast, although this also was basically just welded and then cooled off, so was without time for diffusion to ruin the contrast. 
 

The nails snap when bent cold, but I was able to cut through a few with a hot cut and didn’t have any fracture on me. That being said, they are also quite small, so the hot cut doesn’t need to stretch them as much before it gets all the way through. 
 

Also, I decided to take a look at the Fe-P phase diagram and noticed that once the solubility limit is met, addition P forms iron phosphide. I looked around and found a 3 lb bottle for sale which I picked up to try sprinkling into hearth melts. It looks like it is what’s used to add P to iron and steel those few situations where you might want to, so I figured I would give it a shot. 

[Matt Walker]

Found them! 18 pieces Apx. 3' long. 

My local archaeologist friend tells me the area these came from was a few miles from a place called today Valley Forge. Maybe he will give more details about why high P wrought was known to be produced there.

Edited March 8 by Matt Walker

[Alan Longmire]

Gotta be on the road today, but the short answer is geology.  Carter County, TN led the country in iron production from ca. 1810-1830.  The deposits of ore between the Iron Mountains and Holston Mountain, in Stony Creek and Shady Valley, are excellent low-P, low-Mn brown ores.  The ores from the south side of the Iron Mountains, in Valley Forge and up the Watauga to the NC line, are high-P red ores and sit atop large Mn deposits. When you get onto the Roan massif (big granite intrusive mountain) you get magnetite from metamorphosed red ores.  The big furnace at Valley Forge thus produced high-P iron.  Not a problem for blacksmiths of the time, they knew how to deal with it.  After about 1850, though, the demand for cast iron for rail car wheels ended the demand for the high-P stuff because it was too brittle for that purpose.  By the 1880s all the small furnaces were gone.

[Matt Walker]

Thanks Alan, It's pretty nice to know someone who has this kind of knowledge. 

[Will Robertson]

On 3/7/2023 at 3:12 PM, Aiden CC said:

I have been experimenting with pattern welding using hearth steel, but I’ve been finding that I don’t quite get the contrast I might want using just low and high carbon material, so I want to start playing with phosphorus iron. I have a variety of different old iron sources I want to try and use and my first question is about trying to identify high P iron, ideally without sending it off to a lab (though if that ends up being the case, I may do that). 
 

I have heard that nails from the Globe Elevator may be high in phosphorus and it seems like there might be some evidence for that. The nails break when struck in a vise with no notch and generally have very little ductility. Would that be how phosphorus induced cold shortness might manifest in wrought iron? The material also does not seem to take up carbon well in a hearth, as the pucks start out sparking/hardening well and then lose it after a few folds. I have tons of pieces of hearth material that have behaved this way, is there some “in-shop” test I could use on material like this?

 

Another thought I’ve had is trying to get a source of feedstock with a known phosphorus content. Are there any common modern alloys that might work for this? All I’ve been able to find is ferrophosphorus, which seems like one of those things that you need to buy 5 tons of, and phosphorus calibration standards which don’t have a listed price, but I imagine would be incredibly expensive. 
 

Any thought here would be appreciated, if I have to send some pieces out for testing, so be it, but I figured it would be good to check here first!

I typed a fairly long reply, hit Submit and something glitched and lost it - let me know if you'd like more info. and I can re-type it!

[Aiden CC]

6 hours ago, Will Robertson said:

I typed a fairly long reply, hit Submit and something glitched and lost it - let me know if you'd like more info. and I can re-type it!

If you don’t mind typing it again, I would be happy to hear your take on this. From some forum posts and a review of literature about old swords,  I’m getting the sense that this might be a complicated journey so anything helps. 

[Aiden CC]

I decided to do a test with some of my small amount of high P iron, alternating with medium carbon hearth steel. Interestingly, the steel etched lighter. Looking at metallography of old pattern welded swords, it seems like the phosphorus regions etch light when viewed with optical microscopy and the steel/plain iron is darker. I found the opposite to be the case, as has been noted on this forum a few times; I used four layers of high P material and three layers of hearth steel in this bar, so you can tell which is which:

 

It’s also fairly visible with just a 220 grit finish, and it has a much better contrast than my previous iron and hearth steel combinations after etching. I didn’t have any issues working the material, we’ll see how well it twists soon.