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Grain growth while forging wrought?


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I've just started forging wrought again, after having only made one sax including it. As my forge is running hot enough again due to good charcoal, I thought I'd try and start on a late iron age sword blade. But after just a few hours work, I noticed that the stuff is crumbling away. I don't mean delamination (that's happening too despite the heat, but that's a different beast to tackle). I'm assuming that because I'm forging it so hot all the time, the grain grows really quickly to the point the iron starts to crumble. While forging modern steels, I frequently let it cool down to red or below, so it automatically gets some recrystalisation rounds in the process and I only normalize after the forging is completed. But as the wrought continuously stays above orange, I suppose grain growth is a major issue forging wrought. What's the common process to prevent this, in terms of normalizings during the forging? And how would they have tackled this in ancient times, before the whole crystalisation process was known? Keeping in mind that for just one heat, it takes easily 10 minutes in the forge. So compared to modern forges the iron spends a lot more time at heat to forge out a blade. I'm trying to get into the mindset of how they were able to do this kind of work without any modern metalurgical knowledge, and yet actually produced tons of fine work rather then crumbled scraps of iron. Any thoughts?

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I am not the one, who has big forging skills or experiences, but with wrought, i go this way

1. I reforge the material on welding temp, only as a stack

2. after that i go forging the shape on lower temperatures

 

it worked for me

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I've never noticed problems of grain growth while forging non hardenable steel. I have done some heavy forging on a 2kg mild steel horn (40x40mm thick stock), with very long soaking time, and breaking didn't happened.

I had some wrought iron crumbling pretty easily some years ago, but I think it was dued most from impurities than from anything else. When iron has too much sulphur, hot shortness happens. I suppose that, as general rule, high temperature is not bad for wrough iron, while too low can produce fractures.

I hope that someone with more experience than me corrects me if I'm wrong.

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I think Giuseppe is right. Too much sulphur OR phosphorus, let alone both, makes wrought iron crumbly. I always forge it at very high temperatures, and while delamination does happen I don't often find a piece with the crumblies. I think you need to find a different source of iron.

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some wrought is good (lovly in fact) and a lot is really crap ! I have had quite a bit crumble and I believe it is high phospherous .

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Thanks! I'll just try different pieces then. I've got a lot of bars from different sources, so there should be some better ones. It makes me wonder though how this one was originally forged. If I look before the area that I forged down, not a single crack. But everything I deformed, it's riddled with cracks allover.

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That is an interesting question. How was it formed to begin with if it crumbles when forged? What is the shape of the bar? (Flat, square, round?)

 

I have a bit of high quality WI anchor chain that I'm gradually breaking down by hand. It's been in and out of the forge many times now and hammered on a LOT at low forge welding temperatures all the way down to red with no signs of separating or crumbling so far. I'm afraid that's the extent of my experience with wrought iron however.

 

Out of curiosity, what is your planned construction of the sax? All of wrought iron or a wrought iron body with a carburized WI edge welded on? I realize a knife made all of wrought iron it wouldn't harden but many ancient knives (and swords for that matter) don't appear to have been made of hardenable steel or even if they were hardenable many don't seem to have been hardened which I find interesting.

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That is an interesting question. How was it formed to begin with if it crumbles when forged? What is the shape of the bar? (Flat, square, round?)
Sorta octagonal (as in forged a bit more round from square).

 

I have a bit of high quality WI anchor chain that I'm gradually breaking down by hand. It's been in and out of the forge many times now and hammered on a LOT at low forge welding temperatures all the way down to red with no signs of separating or crumbling so far. I'm afraid that's the extent of my experience with wrought iron however.

 

Out of curiosity, what is your planned construction of the sax? All of wrought iron or a wrought iron body with a carburized WI edge welded on?
The sax I made before, and has a steel edge. With this piece I'm trying to make an iron age sword blade.

 

I realize a knife made all of wrought iron it wouldn't harden but many ancient knives (and swords for that matter) don't appear to have been made of hardenable steel or even if they were hardenable many don't seem to have been hardened which I find interesting.
Iron age blades were workhardened. That does harden/stiffen them up quite a bit, though naturally no way near quench-hardened steel. I believe they didn't do any quench hardening, as they hadn't mastered tempering yet. Interestingly, even Theophilus in around 1100AD describes tempering

as drying by the fire, without any reference to temper color. That might have been just because he wasn't an iron smith though, so he didn't know all the details (most of his work describes non-ferrous metalworking).

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I don't have a lot to add, save to say that I, like you, have worked some wrought iron that seemed to so poorly consolidated and full of impurities that it made me wonder how it came to be forged in the first place. One can spend time re-consolidating (re-welding) such material, but it will never be good iron. In my experience it is better to put the piece of iron in question into that special corner where you put things that you don't want to throw away, but know you will never use.

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In my experience it is better to put the piece of iron in question into that special corner where you put things that you don't want to throw away, but know you will never use.
Yeah, the non cracked areas are still good enough for stock removal. Though I don't do stock removal, so they'll land outside on the rustpile:) I started on another piece last weekend. This one only cracked in specific areas, so it looked like it's composed of good and bad layers. On some locations there were cracks just in one layer, which may be cracks that were already there before they were welded together. Oh well, I keep working through the pile, and hopefully I'll come across some good pieces.
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Yeah, the non cracked areas are still good enough for stock removal. Though I don't do stock removal, so they'll land outside on the rustpile:) I started on another piece last weekend. This one only cracked in specific areas, so it looked like it's composed of good and bad layers. On some locations there were cracks just in one layer, which may be cracks that were already there before they were welded together. Oh well, I keep working through the pile, and hopefully I'll come across some good pieces.

 

To paraphrase Forrest Gump; "Life is like a box of wrought iron".

Erm... on second thoughts, maybe not.

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I have some wrought that is one step up from wagon tire material, fairly grainy and non-homogenized but not as rough as the wagon iron I’ve seen. It sparks pure iron, no bursts to be seen. It took me forever to figure out how it likes to be forged, since it is even more temper-mental than the usual wrought and cracks or crumbles across the grain at almost any heat, including cold. <_< But it turns out the stuff behaves nicely if you work it at a high yellow/white heat, and also is very malleable at a dull red to black heat. ^_^

Bright red/orange/low yellow and it is cottage cheese, and a cold 90 degree bend in thin sections will snap the piece in two... but with the high and the low heats functional, you can work it pretty well into what ever you want.

Most wrought that I have run across, you can just avoid the orange heat range and be okay. ;)

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IIRC, I was forging the two bars pretty much only at yellow/white, so it didn't seem to like that either. I can try the non-forged areas, and do a check making sure I only forge at those temperatures. Considering that they frequently did use phosphorous wrought in the iron age, if it's that it should be forgeable somehow.

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  • 4 weeks later...

Is that skunky wrought of yours the same I have? Or some other source?

 

I made that mini-hawk from a piece, got it up to "slag dripping out of the metal" white hot, and it finished very clean, no cracks, no splits.

 

 

I would actually like to get my hands on some high P wrought iron someday.

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The stuff you have measured out like this:

C = 0.01

Mn = 0.06

P = 0.188

S = 0.031

Si = 0.33

Ni = 0.04

Cu = 0.03

Al = 0.07

Phosporus is a bit high, but under 0.2 is generally okay, even in steel, and in line with historic non-P iron. I just started looking at the artifact #s to see if my high-P wrought can be used like the historic P-iron, the first couple measurements I've found are in the 0.4-0.6% range for the hi-P, 0.2% and under for the regular.

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  • 3 weeks later...

Don't throw the crumbley stuff away. It is still neat to grind through the layers to achieve pattern. Won't do you much good under a hammer, but you can get most of it to have a sweet bold pattern.

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