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I finally have some time for knife making and one of the things I've been working on is making more hearth steel. I want to get enough for a tanto, which has been somewhat of a challenge because of a persistent problem with carbon distribution in the initial pucks, more on that later.



On the suggestion of J. Arthur Loose, I got a used HVAC blower (an Amatek Windjammer) to replace the shop vac I was using. Definitely a fan (:D), it's quiet and powerful and the setup wasn't too bad. With a DIY three prong plug and a 0-10V DC power supply it was ready to go and offers very precise control over the air supply. On the right are the materials for one of the melts. This one was an assortment of drops, a mix of high and low carbon steel. I did two other runs with wrought iron nails from the Globe Elevator. I have read a few accounts of these containing phosphorous and hindering carbon uptake, but I was able to get some high carbon steel from them.



This is an attempt to show what I was talking about with carbon distribution. This is the puck from the shop scraps after I flattened it, quenched it, and then started breaking it up with a sledge hammer. These is a very clear demarcation between high carbon steel (the top, note the clean break) and the bottom (the bent piece resting on the anvil). The break test results also match how the material sparks. This is something I have noticed across all of the melts I've done; the top side is very high carbon and almost free of voids while the bottom side is more porous and much lower in carbon (with a few pockets of high carbon). I'm not quite sure what to make of this and would love to hear anyone's thoughts on it, but I have been able to work with it.



This shows all of my viable material so far sorter by carbon content. The left is all or mostly low carbon, the middle is medium carbon or a mix of high and low carbon, and the right is very high carbon.



Since this will be made into a Japanese style blade if it turns out, I decided to take the Japanese approach to consolidation. This is all of my best material, every piece consistently sparking with more branches than a test piece of W1. I would have loved to have a handle or a larger paddle, but that wasn't really possible given the quantity of material I was working with.



Here it is in the forge, along with one of the wrought iron nail pucks. For the first few heats it looked like it was going to be a resounding failure, but somehow it all came together. On the right is the billet after two folds. Since I hope to make this into a tanto, this will get a tone more folds, maybe 8-10 more. I will also likely have to add material from as I go or maybe make one or two smaller bars and weld them all together. If worse comes to worse, I can consolidate more of the low and medium carbon stuff and make some kind of composite. The 12" sunobi may also be too ambitious of a goal which I might have to reevaluate, but I guess we'll see.


Thanks for looking, and again, any insights on the carbon distribution (lots on the top and very little on the bottom) would be greatly appreciated!

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Have you checked my thread a ways down?


The likely reason why you are experiencing low carbon at the bottom and really high at the top, is because you really need the lower chamber to be hotter initially. Perhaps a longer pre-heat before the first injection of material. When the furnace isn't hot enough, the iron doesn't stay molten for long and could freeze up before it reaches the maximum bottom, which also leaves decreases carbon uptake since most of it is from the atmosphere when it is molten. This eventually builds up and the last of the material to be melted is very close to the hottest zone (tuyure blast) thus stays molten or very close to much longer with a lot of CO. 


I also feel like there may be too much scale on your plates for tsumiwakashi. Try to steam blast scale away prior to, or even vinegar soak to remove scale. The inclusions are already present in your initial consolidation and will probably follow you through the folding process. This materials doesn't quite behave like bloomery or tamahagane in which those materials still have enough slag in the beginning to allow easier mending of cracks and delays like that. I have followed many Japanese swordsmiths and this is one of the lessons I have seen shared. Plus, I've had it happen to me.


I personally only use a small air matress blower for this. If you are using a standard 12"^3 furnace, it's all you need. Too much and you increase your chances of making a puddle of cast iron.

Edited by Daniel Cauble
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Thank you for the advice Daniel! I read through that thread (and watched a number of your YouTube videos) when I first decided to try this last year, but it’s probably worth revisiting. It would make sense that the bottom of the fire isn’t hot enough. When I upgraded my blower I noticed the steel came to rest lower, but not quite to the bottom. I’ll try running the furnace longer on startup. Do you think angling the tuyere down more could help with that as well? It’s currently only a few degrees below horizontal. 


As for the scale, that may be the case. I’m going to clean up my billet with a grinder to check the welds. It actually looks fairly solid other than a few unruly pieces. I think I also made my plates a little too thick; even the very high carbon pieces required a lot of force to break. I have one of the nail billets mostly flattened out, I’ll try steam blasting for the scale before I break it up.

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Awesome work sir! This is always sitting in the on-deck circle for me to try again. If I may ask, which Amatek Windjammer did you get?

Daniels suggestion is intriguing. 

On 5/30/2021 at 7:35 AM, Daniel Cauble said:

a small air matress blower for this

I have a small battery powered one that doesn't have any real use anymore.

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  • 2 months later...

@Joshua States sorry for the late reply on this, if you’re still interested it is one of the 116630 line. I don’t know how much the specific capacity matters, I’ve so far never used it much over 50% of the max control voltage. The output also happens to be an excellent fit in the ID if 3/4” pipe,

forming an adequate seal with no fittings or tape. 

In other news, I seem to have overcome the “two tone” carbon content problem I’ve had. Adding more angle of depression and upping the blower speed meant the bottom of the furnace was hotter. So I can remember, I used a control voltage of 6.2 V, YMMV. 


It may be a bit hard to see here, but it’s running hotter than before especially lower down. I didn’t time each charge, but it was faster than last time. 


The top then bottom. Lots of shiny bits! Most spots spark like W1 or more.  The feed stock was 900 g of Globe Elevator nails. It seems some have had trouble with phosphorus inhibiting carbon uptake in these, but I think I've

gotten lucky with my batch because all of my melts with them have yielded at least some very high carbon portions. That’s nice because I still have 20 lbs of them. 


Some more close ups. I’m excited to forge this, but I have a good bit of custom work accumulated during a recent vacation as my first priority. I have a project for this, but I think it needs at least one more puck. My W2 test blade came out to 354 g, but I need 10-12 folds as well. I started the soft metal work months ago but have been stalling out on the steel. It’s nice to start getting some more consistent high carbon stuff!  

Also, @Daniel Cauble you were right about the scale on my wafers. I started to have problems with folding that billet and thanks to your warning saved a lot of time by not chasing them too far. The average carbon content of that stack was maybe 0.6% which is not quite what I need  especially with all the loss from slowly forging it out by hand and alone. 

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  • 1 month later...

Back at it again. I did two runs of 900g this afternoon. One at 6.2V and one at 5.4V (those numbers are mostly for me). I got excellent carbon content but poor consolidation. 


Running the furnace quite energetically as I’ve found that higher temperatures have given me better steel. 


These are all the pieces I pulled out hot. The biggest one is almost but not quite all of the first run while the second split between the second two. Everything but one or two pieces sparks like crazy, I’m pretty excited to start working this stuff! 


These are the stragglers I dug out of the furnace after it cooled off a bit. The super globular one looks like it could almost be cast iron though I haven’t spark tested it. 


A cool shot showing the glass formed from the slag in the nails (the greenish beads spread throughout the steel). Everything I pulled out was sizzling which may have been some combination of liquid slag and steel. Also, the pucks were sitting notably lower in the furnace. 

I hope to start working this stuff soon, I may finally have enough for what I want to do. Also, if anyone has ideas about why my higher carbon pucks have poorer consolidation I would be very interested to hear it. 

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Yesterday I was able to get in some time consolidating this most recent melt and some odds and ends. 


This is a little stack of all more of the high C pieces collected from my worse earlier pucks. 


This is all of the material from my last run flattened out. Minus the cast iron and a few small/low quality bits, it totaled about 1100 g at this stage. 


This is where all of my “bars” are at this point. That billet from earlier I though was failed got a bit nicer after four more folds and is now at six folds. The big crusty one has a large piece almost cracked off so it will take some love. The three fold stack (from the first picture in this post) is consolidating quite nicely and still sparks like crazy. 



The ugly edges of the six fold bar. This one never had great C content and has lost some of what it had, so it will likely become the core steel for a blade. I may actually have enough here for a knife! We’ll see at fold 10-12 though. 


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  • 4 weeks later...

Thanks, Joshua! This project is definitely more marathon than sprint. It takes quite a bit to amass a big bar if this stuff! Luckily, I think I’m really getting the hearth operation down. 


It saves a ton of charcoal to do consecutive burns, but things overheated a bit with the second run and made what looks cast iron (left to right is the order of the runs). Run 1 (5.0 V) created poorly consolidated high carbon steel, run 2 (4.5 V) created cast iron I believe, and run 3 (3.5 V) made well consolidated steel with perhaps less carbon than round 1. I hope to start consolidating tomorrow. 

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