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Monday, March 31, 2014

Enter Inferno

Each spring, Baltimore Knife and Sword Co hosts their fabled Fire and Brimstone hammer-in. This past year, we made steel in just about every way I can think of (short of blister, shear, and brescian steel). Returning to me roots, albeit short ones, in steel making, the following details two hearth furnaces built over the weekend by two of the best authorities on the subject, Zeb Deming and Mark Green. 

Zeb's furnace was built out of firebrick on a steel tabletop, about as simple as I have ever seen and staggeringly effective. The tuyere he brought has a special fitting on the end that allows you to see through the pipe into the hearth, which is quite a sight (and difficult to capture the molten metal on camera). The air supply is ingeniously fed by a small vacuum and a dimmer switch, affording a good deal of precision. And there is a gate valve (just barely visible on the left side) to release excess flow.

Building the furnace Saturday morning with a bucket of cobb, wire, and brick as the day began to warm was the first part in an exciting weekend of melting and smelting. After leaving behind snow up north, Baltimore was a nice reprieve when the temperature rose above 50.

As with all furnaces, the entry angle and height of the tuyere will play an important part in the qualities of metal produced from the melt. Inside, the pipe enters about 1.5~2 inches from the top of the table, which has been insulated with a cake of ash (if I remember correctly).

Burning handfuls of charcoal throws so many sparks out of the hearth it is like a firework display. At night, the show is even better!

In Zeb's hearth a good amount of steel was made on Saturday. Above, he is running wrought iron from a wagon wheel through, carburizing it into steel. Inside a hearth furnace, there are three general zones, carburizing, decarburizing, and neutral. Lee Sauder, another expert in the field, offers a much better overview than I can, which can be found here- Aristotle's Steel.

Here is a view through the tuyere midway through the day's second melt. In this run, pure iron is being carburized into steel, originating as a 00Fe bar, meaning that the carbon content is <0.01% carbon.

The resulting puck came out solid and easy to work compared to conventional bloom, which is smelted from iron ore amongst other things. Above, Zeb is hammering the carburized pure iron, with the wagon wheel wrought on the right of the stone.

Also run through Zeb's furnace were a collection of forsaken blades of another smith who wanted to recycle them from their either broken or undesired form into hearth steel so he might then forge another knife from them.

Mark Green brought his Evenstad Furnace, which has a few notable differences than Zeb's. It is much shallower and wider, allowing for an easier examination of what is being melted. Control of where the metal enters the charcoal is a little more precise, and longer pieces do not need to be fed end up into the flames.

Into Mark's furnace went a collection of bloom steels from his other smelts, using the different zones to carburize the low carbon steels and decarburize the cast irons. The amount of control and predictability is astonishing.

I missed the first run Mark did on Friday afternoon, coming in at the very tail end. He ran the furnace using a double pair of bellows instead of an air pump, and was just as successful. For the rest of the weekend, however, electricity was used for sake of convenience.

Here, Mark is consolidating decarburized cast iron.

And finally, spark testing one of the day's many hearth melts.

In my continued exposure to the steel making process, and being able to talk with people far more knowledgeable in the subject than myself, I have been able to start experimenting in the processes on my own, and soon I will be using it to make blade steel of my own.

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