The weather gods have shown pity on us and granted a brief window of dry weather, just enough time for me to gutter the new roof…..and explore a new rabbit hole. With the drainage under control, it's time for me to shift gears a bit and take on something that I've been wanting to try for years; making steel.
Why would anyone want to make their own steel when so many excellent carbon steel alloys are widely available? Is homemade steel better in some way then what is already out there? In a word….
So then, why put time and effort into working with such a ridiculously crude and outdated a material? After all, this is essentially a backdoor production method that hasn't seen the light of day in nearly 300 years. I could go on about the mystical alchemy inherent in the transformation of iron to steel, the connection to ironworkers ages past etc, and while that is certainly true, the short answer is that it's just plain cool. Come on now….who wouldn't want to make their own steel?
In the Japanese swordsmithing tradition, the blacksmith can select a variety of different steels and re-melt them into a more easily worked form. This blacksmith made steel is called Oroshigane, and while I am not especially interested in making swords, I AM interested in their steel. Broken blades that shatter during the quench, old cast iron teapots, even the steely crumbles that accumulate in the bottom of the forge, all of this can be combined and blended to create a steel with the specific qualities desired. Call it extreme up-cycling.
It's all about the carbon
Steel, at its heart, is a simple compound of elemental iron and carbon. The amount of carbon added to the iron is very small, but it's impact can be huge. Take iron and add only 0.2-0.3% of carbon and the result is mild steel, the most common structural steel in use. Kitchen appliances, “wrought iron” furniture, the list goes on and on, but most of what we see on a daily basis is made of iron that has been made tougher by a miniscule addition of carbon. Add 0.4-0.6% carbon and you start getting a steel that can be made harder and therefore suitable for more extreme duties. Car axles and shafts, hammer heads, nails, lawnmower blades, wrenches….generally medium carbon steel.
The sweet spot for carbon steel, at least for cutting edges, is around 0.8-1% carbon. Knife steel, Western woodworking plane blades and chisels, old car springs and such fall into this group. Steel with more than 1% is more of a rare animal, but Japanese woodworking tools (planes and chisels) generally use this very high carbon steel, likewise taps and dies, and some metal working files.
At the higher end of the carbon steel spectrum, steel with carbon in excess of 0.8% makes the material more difficult to work. Forging is physically harder as the material just doesn't like to move, even at a high forging temperature. Forge welding becomes more difficult too, particularly when joining wrought iron to steel as my favorite tools do. Without delving into the metallurgy, any carbon in excess of 0.8% has the potential to cause trouble, unless the smith really knows what they are doing.
Add 1.2%-2%% carbon and steel turns into a tricksy thing, and can exhibit a range of traits not normally associated with traditional carbon steel; superplasticity, extreme toughness, impact resistance and high elasticity…...all the while maintaining a very high degree of hardness. Again, this assumes that the blacksmith is highly skilled. Some of the tool steels used in laminated kanna blades use this UHCS (Ultra high carbon steel is the term) for the cutting edge, laminated to antique wrought iron.
A carbon content upwards of 2% is termed cast iron, and while cast iron is a wonderful thing for pots and pans or engine parts, it's of no direct use in hand forging. As the carbon content of iron rises, the melting temperature falls (a trait that will come into play shortly), so having a very high carbon content allows iron to more easily become fully molten, then be poured into a mold….cast into a usefully shaped component.
So, why all all of this blather about carbon content? At, or near melting temperature, iron is able to either take on (or lose) carbon, and that's what the oroshigane melting furnace is for.
This small shaft furnace heats the iron to a partially molten state as it descends towards the bottom of the column. Wood charcoal acts as both the fuel source and adds the carbon component, all brought to a furious heat by an air source that increases the rate of combustion. The concept is a simple one but, as they say, God is in the details. Shaft volume, air volume and pressure, carbon content of the starting materials, even the size and type of charcoal is important.
Of most importance perhaps, is the height above the floor where the air blast enters the column. The temperature of the furnace is highest proximal to the air inlet, so if your furnace floor is at a level with the air inlet (Tuyere is the term), the molten metal will be getting the full force of the air blast. This will actually burn out carbon, so if you are trying to lower the carbon content of cast iron to a more forgeable level, that's where you want to be. If your aim is to raise the carbon content to make some cutlery steel, you want the iron to be able to fall through the heat zone and collect underneath the air inlet, where it sits and absorbs more carbon, eventually resulting in...cast iron.
I'm just getting going with this, both the steel making and the long winded particulars. If you are truly interested in this field of inquiry, there are a few places to go, materials to read. Here's the shortlist …...
Jesus Hernandez wrote up his experiences forging a blade out of steel made in a so-called “Aristotle” furnace. The swordsmith’s oroshigane furnace I made is nearly identical to this, and it was in reading this forum thread that I first became really interested in making my own steel.
— BROKEN RECORD WARNING—
This thread is a perfect example of how information is disappearing daily from the web. If you find something of interest, document it well, because the original information might be gone before you know it. To view this post in its entirety with all of the important images, you need to go Wayback……the Wayback machine will take you there. Donate if you can.
A new way to make steel
Bladesmiths forum is one of my favorite resources for edgy inspiration. They have a whole topic section devoted to smelting ore and making steel, tons of information here….
Daniel Cauble has had some laudable success in making his own oroshigane, really inspiring work, beautiful steel.
But my main source? The Japanese swordsmith Sumihira gifted us with actual particulars and details of how he raises and lowers carbon content in his work. It is from his writings that I got the measurements for my little furnace. Gold!
The forging process, beginning with making the oroshigane (Google translates oroshigane as “wholesaling”, but you can figure it out….mostly).
Lowering the carbon content of cast iron = sageba = ”lowering place”
It's a start. More to come….