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Blister Steel: Containment Failure


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Inspired by Jim Austin's excellent "Forging Traditional, Laminated Knives (Saxes) with Shear Steel Edges" class, I tried to make some blister steel over the weekend. For my wolf's tooth experiments, I had been working on refining the wrought iron (following a technique also suggested by Jim!). I took four of the wrought iron strips and sealed them in a tube with charcoal powder. I had a few options for heating: electric kiln and my forge welding forge. I opted for the latter so that I could still use the welder while waiting for the wrought iron to carburize. Unfortunately, I had a hard time dialing down the forge and here is the result:

 

containment failure.jpg

 

I call this containment failure!

 

It happened after about an hour and was mostly due to the forge being too small and the burner via reflecting of the wall hitting the container on one side especially hard. It might be possible to wedge a kiln shelf in there next time.

 

However, even the hour was enough to make the wrought iron spark like medium carbon steel.

 

Niels.

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Might have to drop the temps a bit perhaps. Most of my blistering has been done around 1800 f or so and it has worked fine, and easier on the containers if you use mild steel. 4 hours on wrought stock or mild steel gets me into the the 1.0% range.

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that's not really a failure, then. Good job. It is just less-than-optimal success! Interesting process, and something that is quite enticing. I have so much trouble forging wrought out in my press, because the dies suck the heat out so fast that it always cracks (almost). I need to get some thin plates carefully made so I can try it. An inserted edge or a butt-weld edge would look cool as all get out on a seax.

 

thanks for posting in such detail.

 

You could coat the mild steel container in Brownells anti-scale compound, and then put it in your kiln. It would survive a long time like that.

 

kc

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Live and learn my friend.

My first time doing this method, I put a nice 14in. bloom iron seax in a clay tube, with the charcoal.
I did the heat in a charcoal fueled hearth, I built of firebrick. I had two tuyeres gently blowing air. It got way to hot, cracked the clay, and melted all but about 2 in. of the blade. Like gone.
The 2 in. piece was very well carburized. I knew it would work.
I have a bunch of this to do in the near future. I will try to document it all.

Best of luck next run.

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Slightly tangental... I used presses alot in the past, built a bunch, when welding with them I got into the habit of heating up a big square chunk of steel I got scrap, probably 3x4 by 5 long I think, and clamped them between the dies and let it sit there while heating up the billets or what have you. The preheat on the dies helped ALOT with welding and stuff.

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  • 4 weeks later...

Here is the next attempt. 3:30 hours at 1900F; just charcoal.

iron.jpg

I found the pattering interesting; sparks at around 1045?

 

The next experiment is with 15% calcium carbonate but I had no time to look at it yet.

 

Niels.

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Niels,

Did you refine this wrought iron...or are the welding layers, due to your work? There has been some discussion here regarding the diffusion rate of carbon in steels high in Phosphrous ( it may be related ) . It is very likely the ramp up of the metal ( to temperature ) took at least an hour.

 

Did you by any chance grind away a high carbon layer?

 

Jan

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The first two experiments were with the unrefined wrought iron which I suspect to have high Phosphorous. This experiment is with one refining step; 4 layers, 2 pieces per layer; each layer rotate 90 degrees against each other.

 

IMG_8092.jpg

 

15% calcium carbonate. 1900 at 4 hours. Still sparks pretty low :-(

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I had this problem too as my forge gets can get too hot and melt the steel where the burner enters the forge. I put a thin wash of satinite on the container and it helped considerably.

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Having watched Ric Furrer turn some wrought into cast once by accident (heckle heckle, with nothing but love), I've purposely used a thin container for making blister. I figure if a 1/8" wall tube puicks up enough carbon to start burning out, I'd rather have it fail, than over-cook my steel. I can always re-pack and cook my material longer, but once you ruin it by over-carburization it's harder to feel good about trying to recycle it into something useful. Consider it a safety valve.

 

I think it's important to consider, too, that this is a time and temperature balance. It's nice to be able to put a can in the forge and get something useful out 4 hours later, but I think I recall it being described in Sheffield, when they were making shear steel, that their blistering ovens would run for a week or so, at lower temperature. Obviously it's more costly in fuel, but running low and slow would give you far more control over your product, something industrial-scale production should be concerned with. Flirting with welding and melting temperatures doesn't do anything great for the steel, just saves us backyard guys some time.

Edited by Christopher Price
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Exactly right. Clay boxes of highly refined wrought iron strips, filled with powdered charcoal from various sources (often animal), held in ovens at around 1400-1500 degrees F for five days or so, was the traditional way to make blister steel. They wanted full migration of as much carbon as they could get without going over around 1% (even though they had no idea what was actually happening), which they then stacked and wedled into shear steel, so called because it was made by "shearing" the blister steel. Do that twice and it's double-shear steel. Do that three times and you have "treble" steel, a name you sometimes see on top-quality tools and blades from the mid-19th century.

 

Then again, if you put your blister steel in a sealed crucible and melt it, allowing the slag to float up and cool the steel into a puck in said sealed crucible, you have the Huntsman process for making cast steel. You see the "cast steel" name well into the first half of the 20th century.

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Careful not to have inbedded charcoal when melting that blister steel Alan.

 

I have a class running next week where we will do blister steel, shear steel, bloomery smelting and a Huntsman run from the blister steel.

Only class of its kind I think.

 

http://www.doorcountyforgeworks.com/European_steel_making_week.html

 

Ric

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  • 2 weeks later...

It's a little bit less than 1/4in thick. I either need to use more time or improve my charcoal mixture with more ingredients to generate more carbon monoxide. Commercial pack carburizing compounds often contain barium carbonate which is toxic. So far, I have only been using calcium carbonate but I read that sodium and potassium carbonates can also be used.

 

Niels.

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I used Charcoal, sea salt, ash, in my mix on the Germanic sword. The carbon went clear through the 5mm blade, where the heat was greatest.
I went for 5 hours, or so, with a wind blown wood fire, contained in my smelting stack.
The knife I made from the broken tip, is pure high carbon. It's been a bitch to polish, it's so hard.

I used about 10% salt, and 10% ash, all other was hardwood charcoal fines, ground pretty fine.
It worked pretty well, on the home made iron.
I have about 10 more blades of low carbon/ plain iron bloom to carburize this way. I plan to have them nearly to final, heat treating shape, when doing this process.

Niels, does your nice electric heat treating kiln get hot enough for this? That is what I would use, if I had one. Controlled temp, and not likley to melt your containment.

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The first two experiments were with the unrefined wrought iron which I suspect to have high Phosphorous. This experiment is with one refining step; 4 layers, 2 pieces per layer; each layer rotate 90 degrees against each other.

 

attachicon.gifIMG_8092.jpg

 

15% calcium carbonate. 1900 at 4 hours. Still sparks pretty low :-(

 

Niels.. these bars don't seem 'blistered' to me. Maybe not enough soak time to get desired spark??

 

Also.. maybe you've seen some of my posts on this.. but I've been carburizing wrought iron at very low temps in my woodstove in the winter. I was not taking it to full 'blister steel'.. but I was getting good penetration in a very laid-back, easy-on-containers, easy-on-fuel kind of way. And more like it was traditionally made.. over a longer period.

Edited by Scott A. Roush
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That's awfully thick for carburising IMO, to get much penetration in stock like that you'll have to increase the soak significantly.
I usually work in the 1/16 to 1/8 range, with thicker material it's a much different approach and is an all-day affair, 16-20 hours, bit I have not done that in years.

It's a little bit less than 1/4in thick. I either need to use more time or improve my charcoal mixture with more ingredients to generate more carbon monoxide. Commercial pack carburizing compounds often contain barium carbonate which is toxic. So far, I have only been using calcium carbonate but I read that sodium and potassium carbonates can also be used.



Niels.

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We used stock that thick in Ric's class.. but the end result was visibly blistered after a few hours at welding type heats. The refined product in the end was good hardenable steel....

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  • 5 months later...

I have found leather scraps , horse poo and charcoal all work well , and claying the outside of the box is a must in a hot forge.

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