In the following description, I will demonstrate the process that I used for transforming one of these steel ingots into a beautiful blade. The final product is, in my opinion, indistinguishable from the Japanese tamahagane steel. After describing how I made a tanto out of this steel, I will include a description by Skip of the contruction and operation of the furnace. I am very thankful to Skip and Lee for allowing me to participate in this process and for letting me play with the steel and turn the first blade made out of it. I am also thankful to both of them for the work thay have put into developing this method which may probe helpful to many of us here.
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. You can’t limit yourself to carrying out the test on one single spot of the ingot. Several areas need to be sampled, as the steel made in this way tends to be variable in 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 the so-called "austenizing" temperature and rapidly quenched in water. The plate is then hit with a hammer. High carbon steel will break cleanly and shatter. Iron will remained attached by strands of metal that did not harden and are pliable.
Skip sent to me two ingots of steel. 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 or alloying elements causing the steel to be red short. Other variables may also play a role in this “crumbling” of the ingot or bloom, such as grain size. Larger grain size may allow for the steel to increase hardenability thus turning it red short as it is being worked on. The second ingot flattened out nicely without crumbling.
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 after being quenched and hardened in water. 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. At this point of writing up this report, I felt as if I was outlining a cooking recipe for a TV show. Just the ingredients and the temperature range change. At any rate, the billet welded nicely, and on the second heat I drew it out to start shaping it into a bar. It is a rather rough looking bar in the beginning as you can see in the pictures. The forging scale from one side of this 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 that 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 to 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, 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, so I did not want to disappoint. 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 the 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 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 and Lee for providing the steel and for their efforts to bring the steel-making process to a level where many more can participate.
And now for the description and operation of the furnace provided by Skip.
There are three well known traditional ways to make steel, directly in the tatara or bloomery furnace, by pack carburizing soft iron in charcoal, and by the Wootz or crucible process. A few years ago Lee Sauder and I discovered that by melting waste scraps of iron in our bloomery we could make a very nice steel ingot quickly and cheaply. It has taken us a few years to improve upon the initial experiments and now with the assistance of Jesus Hernandez we feel it is time to share what we have learned.
This is everything that you will need to make your own simple steel ingot, a small clay furnace, wood for preheating, several kilograms of charcoal, and a pound or so of scrap iron rods.
The furnace is made of clay, sand, and peat. The stack which measures approximately 12 inches tall and 4-5 inches wide is built by placing the clay around an empty soda bottle or any other suitable form. Connecting an air blower to a clay furnace is always a challenge. I find that it is easiest and most reliable to screw a short metal tube to the base that the furnace will be built upon and then build the furnace right over the air tube. Air is fed into a 2” diameter passage built against the side of the stack that houses the angled blow hole. After the stack and air passage have been built and have had time to harden the blow hole is made by poking a 3/8” rod through the opening at the top of the air passage and then passing it through the wall of the stack.
The bottom of the stack must now be shaped into a bowl by adding a replaceable lining. The lining is a mixture of the material used to build the furnace and an equal volume of charcoal fines. I use only fines that will pass through a window screen. Knead the lining material by hand (15 minutes or more) until it has the consistency of rising dough and then form a bowl in the bottom of the stack. The lowest point of the bowl should be in the center of the stack and 4” below the blow hole.
Go ahead and plug the top of the air passage with a lump of clay and start your preheating fire. It’ll take an hour or two before the furnace will be dry and ready for making steel.
There are only two special tools you’ll want to have on hand. The lower one is just a thin iron rod that you’ll use to probe the temperate of the hot zone in the furnace before you start adding iron.
The upper tool is more important, it is the ingot hook! At the end of a melt the bottom of your furnace will contain a steel ingot in a slag bath. You have to get the ingot out before everything hardens into an immovable mass or it will ruin your furnace.
Preheat the furnace with small wood splits. When you think it is hot enough change over to charcoal broken into ½” pieces or smaller. Adjust the air rate so that you are burning 100 grams of charcoal per minute. The tin can in the top photo is what I’ve been using for a 100 gram measure. After just a few minutes you’ll be able to stick your temperature probe rod into the stack and when you pull it out it will be sparkling hot.
Now it’s time to start making your ingot. Stick your first iron rod into the stack about 2/3 of the way across the stack from the blow hole. The rod will melt and slowly descend. Keep refilling the stack with 100gm measures of charcoal. After the first rod has disappeared into the charcoal stick in the second rod and so forth until you have melted 500gm to 700gm of iron rod. This whole process will only take ten to fifteen minutes. Wait until you think that the last of the iron has melted and then stop adding charcoal. Let the charcoal burn down a few inches and turn off the air supply. With your ingot hook pry the ingot loose from the bottom of the furnace and take it out. And most importantly, stir up the slag and charcoal in the bottom of the furnace before it freezes. The slag can then be spooned out of the furnace and you will be ready for another run.
The product is
Edited by Jesus Hernandez, 10 October 2011 - 06:29 AM.