A modern bladesmith rooted in the old traditions

Forging steel

Tamahagane is the Japanese word used to describe the best quality steel coming from the Shimane prefecture tatara. Orishigane is the word used to describe the steel or the process used in the smith’s forge to carburize low carbon steel or iron to turn it into steel with high enough carbon content to be usable to make a sword. In this page you will see one of the processes I used to manipulate steel made in the Aristotle furnace which is for all purposes an oroshigane process and turn that steel into a beautiful blade. The final product is, in my opinion, indistinguishable from the Japanese traditional blade steel.

 

The steel used in this process was provided by Skip Williams. At the end of a run in the small Aristotle furnace, an ingot of steel is recovered. The size of this ingot is very easy to manipulate for most bladesmiths operating a small gas forge.

My first step was to make a rudimentary assessment of the quality of the steel. Without resorting to the expensive chemical analysis, a simple spark-test can give an idea of the carbon content. The Japanese also sort the steel by means of assessing the looks of the fracture of a thin (1/4 inch) section of the steel. To carry out that particular test, the steel is first brought up to a welding heat and gently compacted into a thin plate. That plate is brought up to “austenizing” temperature and rapidly quenched in water to harden it, if it is harden-able. The plate is then hit with a hammer. High carbon steel breaks cleanly and shatters. Iron would not show a clean fracture, the plate would remain attached by strands of metal.

Skip sent two ingots of steel to me. The spark test suggested high carbon content for both pieces. The fracture test of one of the two ingots was limited to a few surviving chunks of steel from the ingot, as it crumbled to pieces during the flattening process. In my experience, this may happen as a result of too high carbon content. The second ingot flattened out nicely.

The looks of the fracture on the remnants of the ingot that crumbled showed strands of malleable iron mixed with layers of nicely grained steel. The ingot that forged flat without crumbling showed a fracture of consistent grain that snapped easily in two. That was suggestive of a nicely homogeneous composition in that particular ingot.

At the end of the flattening and sorting process, I had about six pieces of material measuring about 2 x 2 inches square and ¼ inch thick. Following the Japanese model with a Western twist, I stacked up the pieces of steel alternating one from one ingot and the next from the other. I sprinkled borax on the stack and brought it up to a welding temperature in the forge. I feel like I am outlining a cooking recipe for a TV show, the ingredients and the temperature range being different, but I digress. At any rate, the billet welded nicely, and on the second heat I drew it out to start shaping it into a bar. It was a rather rough looking bar in the beginning, as you can see in the pictures. The forging scale from one side of the bar was cleaned up with a grinder in order to move to the next process, which consists of folding the bar onto itself to refine the steel. In this way, the Japanese were able to take chunks of variable carbon content and turn them into a solid bar of quite homogeneous composition.

After five folds or about 200 layers, the steel bar was behaving as a solid piece of steel. It was easily welded onto itself and showed no tendency to develop any cracks. I decided to draw out the bar to a ¼ thickness in preparation for forging a blade. But I kept looking at the bar, now measuring about 14 inches in length and it was begging to be worked on just a little bit more. I split the bar in four segments, re-stacked and re-welded. I looked at the bar one more time. Then I looked at the forge, nice and hot at welding temperature. I put the bar back in the forge and did an additional two folds. With some quick math and I calculated I was at about 3000 layers. That seemed just about right. Time to call it a day, and the next day I would forge that bar into a tanto.

It is quite obvious from my writings that I favor the Japanese way of making blades and I did not want to stray. For the next step I chose to do a differential hardening by using clay during the thermal treatment of the blade. I was not really sure what to expect here. I knew that I had enough carbon in the blade for it to harden, based on the sparks produced during the rough grinding. I did not know if the steel was a simple steel (iron + carbon and little or insignificant amounts of alloying minerals) or not. A simple low-hardenability steel is best for showing a hamon. The hamon is the demarcation between the martensite and the pearlite crystalline structures in the steel. It was going to be a surprise. I quenched the blade on 8/8/2008 at 8:08 PM for an added magical factor. The blade hardened nicely and achieved a Rockwell score of between 55 and 60 at the edge after tempering. I have simple graduated files to test for hardness and the scale jumps in 5s from 40 to 65. So I can’t be very accurate in this reading. I would say it was closer to 60. You can see the file scratches on the picture the next morning.

The next step was to polish the blade. I used the grinder to remove the scale and put an edge on the blade. Then I moved on to sandpaper, starting at 220 grit and progressing on to 2000 grit. The hamon was already visible at 220 grit. I had a nice grin on my face. Seeing the hamon at that stage almost instantly heals all the pains of having to go through the polishing stages. As the hamon becomes more visible each time you advance on the grit, it makes it more stimulating to continue polishing.

For the final stages of polishing, a fine paste polishing compound is used to bring out the hamon details. I completed the blade by making a poplar wood sheath (shirasaya) with a detail made of bloodwood, a copper habaki fitting, a bamboo peg (mekugi) and a light coat of oil. I hope you enjoyed reading this as much as I enjoyed making this blade. I want to thank Skip for providing the steel and for his efforts to bring the steel-making process to a level where many more can participate.