Japanese Style Blade Forging
Intro: Japanese Style Blade Forging
So, before we start, I'd like to try and answer a quick question that a lot of people have: Why is forging better than stock removal?
For those of you that don't know, stock removal is a way of creating a knife that involves removing material from a piece of steel until a knife shape is revealed. Forging is the process of creating a knife where the steel is heated then moved by repeated hammering, until it is in the shape of a knife.
So why forge when you can use stock removal?
1) Steel waste: Stock removal requires lots of cutting and grinding. All the steel that is removed ends up becoming waste material, and is thrown away. With forging, I can often make a blade using ~70% the steel that would be needed for stock removal. This lowers costs, and is just in general less wasteful
2) Shape of the blade: One of the biggest differences I see between stock removal blades and forged blades is the distal taper. Distal taper is basically a smooth taper from the the thick part of the blade to the thin tip. It is very difficult to put in an accurate distal taper with a grinder. Most stock removal blades end up being the same thickness along the entire spine then suddenly decrease in thickness at the tip. Forged blades can have a smooth distal taper easily forged in, which increases the blade's balance and cutting ability.
3) Larger blades: Stock removal is great for making small blades, but what happens if you ever want to make something big? Stock removal simply doesn't scale up as well as forging does.
4) Tools and money: A good belt grinder can easily cost in excess of $1500. Most beginning knife makers can't afford this. Although a forge may seem inaccessible, they are actually rather easy to build and can be built cheaply. I built my forge for a little under $200 dollars, and still ended up with enough material to potentially build a second one
5) Forging is fun!: Forging is actually really fun and interesting to do! I have nothing against people who use stock removal methods, but I think you should at least try forging once. You may find that you really enjoy it!
Also, a quick note. This is Japanese STYLED forging. Traditionally, Japanese blades were made by forge welding a type of raw steel together called tamahagane. This process, however, is currently well outside the resources I have at my disposal. Basically, this instructable will cover the basic hammer, beveling, and shaping techniques used to create Japanese blades, but instead will use modern steel as the blade material.
Sorry for the long winded introduction, now onto the forging!
For those of you that don't know, stock removal is a way of creating a knife that involves removing material from a piece of steel until a knife shape is revealed. Forging is the process of creating a knife where the steel is heated then moved by repeated hammering, until it is in the shape of a knife.
So why forge when you can use stock removal?
1) Steel waste: Stock removal requires lots of cutting and grinding. All the steel that is removed ends up becoming waste material, and is thrown away. With forging, I can often make a blade using ~70% the steel that would be needed for stock removal. This lowers costs, and is just in general less wasteful
2) Shape of the blade: One of the biggest differences I see between stock removal blades and forged blades is the distal taper. Distal taper is basically a smooth taper from the the thick part of the blade to the thin tip. It is very difficult to put in an accurate distal taper with a grinder. Most stock removal blades end up being the same thickness along the entire spine then suddenly decrease in thickness at the tip. Forged blades can have a smooth distal taper easily forged in, which increases the blade's balance and cutting ability.
3) Larger blades: Stock removal is great for making small blades, but what happens if you ever want to make something big? Stock removal simply doesn't scale up as well as forging does.
4) Tools and money: A good belt grinder can easily cost in excess of $1500. Most beginning knife makers can't afford this. Although a forge may seem inaccessible, they are actually rather easy to build and can be built cheaply. I built my forge for a little under $200 dollars, and still ended up with enough material to potentially build a second one
5) Forging is fun!: Forging is actually really fun and interesting to do! I have nothing against people who use stock removal methods, but I think you should at least try forging once. You may find that you really enjoy it!
Also, a quick note. This is Japanese STYLED forging. Traditionally, Japanese blades were made by forge welding a type of raw steel together called tamahagane. This process, however, is currently well outside the resources I have at my disposal. Basically, this instructable will cover the basic hammer, beveling, and shaping techniques used to create Japanese blades, but instead will use modern steel as the blade material.
Sorry for the long winded introduction, now onto the forging!
STEP 1: Materials and Tools
I will be forging an ~9 inch long tanto. The thickness is ~1/8 inch (this is unusually thin for a tanto, but thinner material is easier to work. I recommend this thickness for beginners). If you want to make a larger blade, you will have to scale up the size of the material appropriately.
Materials and tools:
*7"×1/8"×5/4" piece of shallow hardening steel (1070, 1095, w1, w2, etc). I used 1095 for this one
*Hacksaw
*Some form of anvil
*Square hammer, ~3 lbs
*Cross peen hammer, ~2-3 lbs. Not required, but very helpful.
*Tongs
*Spray bottle with water. More on this later
*Bucket of water. (for cooling tongs and emergencies)
*Forge of some sort
*Vice
*File
*Safety equipment (gloves, apron, safety goggles, etc)
Materials and tools:
*7"×1/8"×5/4" piece of shallow hardening steel (1070, 1095, w1, w2, etc). I used 1095 for this one
*Hacksaw
*Some form of anvil
*Square hammer, ~3 lbs
*Cross peen hammer, ~2-3 lbs. Not required, but very helpful.
*Tongs
*Spray bottle with water. More on this later
*Bucket of water. (for cooling tongs and emergencies)
*Forge of some sort
*Vice
*File
*Safety equipment (gloves, apron, safety goggles, etc)
STEP 2: Cutting and Prepping Material
This part is pretty simple. Mark an approximately 7" length of steel. If you want a larger or smaller blade, mark a length that is ~70-80% less than your desired final length. During forging, the material will be stretched quite a bit, and your blade will grow by a pretty large margin. The thicker the material is when it starts, the more it will stretch.
When you have marked your steel, clamp it in a vice and cut along the marking with a hacksaw. After it is cut, I file off the burrs and slightly round the edges. This is just a personal preference and isn't required. I find that it helps prevent inclusions from being forged in later.
When you have marked your steel, clamp it in a vice and cut along the marking with a hacksaw. After it is cut, I file off the burrs and slightly round the edges. This is just a personal preference and isn't required. I find that it helps prevent inclusions from being forged in later.
STEP 3: Sunobe: Part 1, the Nakago
To start the form of the blade you have to forge the sunobe. Sunobe is basically the process of creating all the necessary tapers and drawing certain portions out. Sunobe is done on both the nagasa (blade and tip portion of a knife) and the nakago (tang portion), but I always start with the nakago.
Quick note: I have numbered the pictures for convenience and will be referring to the numbers often in my explanations.
To begin, start your forge up. You will also need your tongs, anvil, hammers, and water out. Once the forge is up to heat, place the metal in the forge, nakago first. While you are waiting, take your spray bottle and put a layer of water on the face of your anvil, like in picture 9. This may seem counter intuitive, but it is a technique called water forging. The steam that is created when the blade touches the anvil will blow off excess scale and oxidation, saving you work in the long run. Now wait for the metal to heat. You will know the metal is fully heated when its color becomes the same as the surrounding forge. At this point, the metal should be around 2000°-2100° F, which looks to me like a bright lemon color. Too hot, and your metal will be sparking and oxidizing rapidly. Too cold, and you won't get very much time to work the metal and it won't move very much.
Once the metal is up to heat, grab the side that is facing towards you with the tongs. Set the metal so the edge (not the face) is resting on the anvil, like in picture 6. Begin to hammer in the direction and placement that the arrows designate in picture 6. Make sure you are working both sides of the metal evenly, by turning the blade 180° every few hammer strikes. Once your metal dulls to a dark red, put it back in the forge. The idea here is to slightly round and taper the very end of the nakago. It should begin to look like picture 7.
Once you've got your nakago looking similiar to picture 7, pull out your cross peen hammer. Again, place the metal so the edge rests on the anvil. begin to hammer with the cross peen perpendicular to the edge of the nakago. Make sure to work both sides evenly. This should put some tiny bumpy waves in the nakago, like in picture 8. Take your flat hammer and begin to hammer the waves flat. This will cause the nakago to stretch lengthwise, a process called "drawing out". Keep alternating with a cross peen and flat hammer until you've got the nakago slightly shorter than what you want. Make sure you are replenishing the water on your anvil in between heats.
Once your nakago looks somewhat similar to picture 10, you can hammer in the machi. The machi are the two slight divots at the very base of the tang that the habaki will eventually rest on. I have arrows pointing to them in picture 11. To hammer in the machi, simply place where you want the machi to be on the edge of the anvil and tap directly above it, then repeat for the opposite side. This process is shown in picture 13.
At this point, the nakago is around 3 inches long and tapered slightly, as seen in picture 14. However, you can see in picture 12 that all the hammering has caused the nakago to thicken. This is where a distal taper, or tapering of thickness comes in. Having a distal taper in the nakago is essential for it to be able to have a habaki and tsuka (mountings) put on later. To do this, start by resting the face of the metal on the anvil. Take the flat hammer, and start lightly tapping near the base of the nakago. Gradually move your hammer down the nakago, and gradually increase the strength with which you strike the steel. In picture 15, the blue dots represent where my hammer is striking, and the size of the dots represent the force behind the strike. Keep repeating this, making sure to work both faces evenly. In 16, you can see the start of a taper develop. In 17, the taper has become more defined and the machi are now the thickest part of the nakago. 18 shows how Smooth the metal should look (no large dents), and in 19 the taper is complete. This has caused the metal to stretch quite a bit, and my nakago is now just under 4", as shown in 20.
You now should be ready to move onto forging the sunobe in the nagasa.
Quick note: I have numbered the pictures for convenience and will be referring to the numbers often in my explanations.
To begin, start your forge up. You will also need your tongs, anvil, hammers, and water out. Once the forge is up to heat, place the metal in the forge, nakago first. While you are waiting, take your spray bottle and put a layer of water on the face of your anvil, like in picture 9. This may seem counter intuitive, but it is a technique called water forging. The steam that is created when the blade touches the anvil will blow off excess scale and oxidation, saving you work in the long run. Now wait for the metal to heat. You will know the metal is fully heated when its color becomes the same as the surrounding forge. At this point, the metal should be around 2000°-2100° F, which looks to me like a bright lemon color. Too hot, and your metal will be sparking and oxidizing rapidly. Too cold, and you won't get very much time to work the metal and it won't move very much.
Once the metal is up to heat, grab the side that is facing towards you with the tongs. Set the metal so the edge (not the face) is resting on the anvil, like in picture 6. Begin to hammer in the direction and placement that the arrows designate in picture 6. Make sure you are working both sides of the metal evenly, by turning the blade 180° every few hammer strikes. Once your metal dulls to a dark red, put it back in the forge. The idea here is to slightly round and taper the very end of the nakago. It should begin to look like picture 7.
Once you've got your nakago looking similiar to picture 7, pull out your cross peen hammer. Again, place the metal so the edge rests on the anvil. begin to hammer with the cross peen perpendicular to the edge of the nakago. Make sure to work both sides evenly. This should put some tiny bumpy waves in the nakago, like in picture 8. Take your flat hammer and begin to hammer the waves flat. This will cause the nakago to stretch lengthwise, a process called "drawing out". Keep alternating with a cross peen and flat hammer until you've got the nakago slightly shorter than what you want. Make sure you are replenishing the water on your anvil in between heats.
Once your nakago looks somewhat similar to picture 10, you can hammer in the machi. The machi are the two slight divots at the very base of the tang that the habaki will eventually rest on. I have arrows pointing to them in picture 11. To hammer in the machi, simply place where you want the machi to be on the edge of the anvil and tap directly above it, then repeat for the opposite side. This process is shown in picture 13.
At this point, the nakago is around 3 inches long and tapered slightly, as seen in picture 14. However, you can see in picture 12 that all the hammering has caused the nakago to thicken. This is where a distal taper, or tapering of thickness comes in. Having a distal taper in the nakago is essential for it to be able to have a habaki and tsuka (mountings) put on later. To do this, start by resting the face of the metal on the anvil. Take the flat hammer, and start lightly tapping near the base of the nakago. Gradually move your hammer down the nakago, and gradually increase the strength with which you strike the steel. In picture 15, the blue dots represent where my hammer is striking, and the size of the dots represent the force behind the strike. Keep repeating this, making sure to work both faces evenly. In 16, you can see the start of a taper develop. In 17, the taper has become more defined and the machi are now the thickest part of the nakago. 18 shows how Smooth the metal should look (no large dents), and in 19 the taper is complete. This has caused the metal to stretch quite a bit, and my nakago is now just under 4", as shown in 20.
You now should be ready to move onto forging the sunobe in the nagasa.
STEP 4: Sunobe: Part 2, the Nagasa
The sunobe for the nagasa mainly consists of forming the basic shape of the kissaki (tip of knife) and forging in a distal taper down the blade.
To start, flip the knife around and use the tongs to grab it by the nakago. Place it tip first in the forge, with the nakago facing you. Make sure that you keep your anvil face wet.
Once the metal comes to heat, pull it out by the nakago and place the metal so the edge is on the anvil. Then, very similarly to how the nakago was started, start to round off the very tip, striking according to the arrows in picture 3. Here's where the process starts to differ. Instead of stopping when the tip is rounded, continue hammering the tip until it is pointed and a centered triangular shape. pictures 4-8 show the formation of the point in the tip heat by heat.
In picture 9, you'll notice that the tip has now become very thick. So to correct this I hammer a distal taper into the tip and down the blade. In picture 10, the dots show the position of my hammer strikes for the distal taper, and the size of the dots corresponds to the force behind the strike. It is very important that you work both sides evenly. During this process, the tip may become rounded off. Hammer it back into a sharp tip like in picture 12 if this happens.
Once you've got the sharp triangular tip and a distal taper, move on to the next step.
To start, flip the knife around and use the tongs to grab it by the nakago. Place it tip first in the forge, with the nakago facing you. Make sure that you keep your anvil face wet.
Once the metal comes to heat, pull it out by the nakago and place the metal so the edge is on the anvil. Then, very similarly to how the nakago was started, start to round off the very tip, striking according to the arrows in picture 3. Here's where the process starts to differ. Instead of stopping when the tip is rounded, continue hammering the tip until it is pointed and a centered triangular shape. pictures 4-8 show the formation of the point in the tip heat by heat.
In picture 9, you'll notice that the tip has now become very thick. So to correct this I hammer a distal taper into the tip and down the blade. In picture 10, the dots show the position of my hammer strikes for the distal taper, and the size of the dots corresponds to the force behind the strike. It is very important that you work both sides evenly. During this process, the tip may become rounded off. Hammer it back into a sharp tip like in picture 12 if this happens.
Once you've got the sharp triangular tip and a distal taper, move on to the next step.
STEP 5: Beveling the Nagasa
To bevel the nagasa, set the face of the blade on the anvil. Choose a side that will become your edge. Beginning at the tip, strike according to the blue dots in picture 1. Your tip should start to naturally curve backwards towards the spine. The thicker the material, the more curved it will become during beveling. The metal that I was using was too thin for the tip to curve into place with beveling alone, so I set the spine of the blade on the anvil and begin to lightly tap the tip into place. Picture 2 shows where I struck the metal in order to get a flat spine. Once the spine is straight, you can begin to move down and bevel the rest of the nagasa. Picture 4 shows where to strike along the blade. Make sure to work both faces of the blade evenly, or your edge won't be perfectly aligned in the end. Also, you should still be wetting the face of your anvil to blow off the scale that your knife has accumulated. When you bevel the blade, it may curve backwards during the process. If this happens, set the spine of the blade on the anvil face again and lightly tap the edge in order to straighten the blade. pictures 5 and 6 illustrate this. Once the entire edge has been brought to a little under the thickness of a dime, the beveling is basically complete. Sight down the length of your blade to check if it's straight. Correct any slight warps in the straightness of the blade, then move onto the next step.
STEP 6: Beveling the Nakago
For this style of blade, the Nakago must also be beveled. Picture 1 shows where I strike the blade with my hammer to get a bevel. Make sure to work both faces evenly. The Nakago may curl slightly upwards during this process, whether you leave that in or not is up to personal preference. I personally like to have the Nakago curl upwards very slightly, so I left it in.
Once the Nakago hs been fully beveled, sight down the blade to see if it is straight. At this point, I usually heat the blade up, take it to the mini vice anvil, and just lightly tap up and down the whole length of the blade, on both sides. The purpose of this is to smooth the surface and promote blade straightness and edge alignment.
Once the Nakago hs been fully beveled, sight down the blade to see if it is straight. At this point, I usually heat the blade up, take it to the mini vice anvil, and just lightly tap up and down the whole length of the blade, on both sides. The purpose of this is to smooth the surface and promote blade straightness and edge alignment.
STEP 7: Finished
At this point, the blade should very closely resemble what you want the final shape of your blade to be. From this point on the rest of the shaping will be done with a sander and files.
Anyway, I hope you enjoyed and maybe learned something new! Forging is such a vast topic that there's no way I could have covered every single thing about it in a single instructable. So feel free to ask me questions or for clarification on any parts in the instructable. You can either post it in the comments or even shoot me an email at yozakuraforge@gmail.com
As for future instructables, here's what I have planned:
*Hamon and Heat Treatment of Japanese Blades
*Blade Polishing and Sharpening
*Water Casting Copper + Japanese Tsuba (Sword Guard)
*Handmade Chisels
Please tell me which of these you'd like to see next, and I'd love to hear other suggestions for instructables that I don't have in the list.
Thanks for reading!
Anyway, I hope you enjoyed and maybe learned something new! Forging is such a vast topic that there's no way I could have covered every single thing about it in a single instructable. So feel free to ask me questions or for clarification on any parts in the instructable. You can either post it in the comments or even shoot me an email at yozakuraforge@gmail.com
As for future instructables, here's what I have planned:
*Hamon and Heat Treatment of Japanese Blades
*Blade Polishing and Sharpening
*Water Casting Copper + Japanese Tsuba (Sword Guard)
*Handmade Chisels
Please tell me which of these you'd like to see next, and I'd love to hear other suggestions for instructables that I don't have in the list.
Thanks for reading!
40 Comments
m1kbee 7 years ago
Xexos 7 years ago
The reason they fold and laminate the steel is because the tamahagane (steel created from the tatara) does not have a uniform composition at all. Folding the tamahagane helps to make the steel have the same alloying composition throughout all the steel. Since modern steels are 99.9% uniform throughout, it would be completely pointless to fold them (except as a practice excercise, haha)
Thanks for the read! :)
MichaelW317 6 years ago
MichaelW317 6 years ago
folding is like making bread to get an even consistency, the more its folded the less definition in the hada pattern in the steel if you go to far it would be hard to see any grain
tytower 7 years ago
Err don't think so ! My understanding is it was done to impregnate the carbon from the flames on the outside of the steel into the center of the steel making a stronger carbon steel. It was common to fold it 100 times or more
Xexos 7 years ago
So the reason for folding IS to create uniform composition throughout the steel, basically they are making a pseudo mono-steel
bennypollok 7 years ago
Doesn't folding the steel also "layer" it, not only making it of uniform composition, but also more flexible and less prone to breaking? For example, instead of having one large stick, having many small sticks tied together then smaking them both against the same hard surface to see which one breaks first? (not that I'd expect to be smacking a sword against a tree or anything)
Wouldn't that, in a sense, make it stronger? (or less "weak")
Xexos 7 years ago
So this is actually a question that has a couple different viewpoints currently. In theory, this COULD actually strengthen the blade, in exactly the same manner as you described. However, in my personal opinion, the difference would probably be very negligible. With diffusion welded steel, you can also run into a strength problem called delamination. When diffusion welded steel is put under considerable stress (stress that no well-used blade would ever normally come into contact with), it has a tendency to "peel" apart between the welded layers.
In the end, the most important process (with relation to strength) is lamination and differential hardening. Lamination is the process where a soft core is inserted and welded into a U-shaped piece of higher carbon metal. The high carbon becomes the edge, and the soft core rests in the spine and absorbs shock. Differential hardening is the process where the spine of the blade is coated with clay, then the blade is quenched. The edge fully transforms into martensite (hard molecular form of steel) whereas the spine retains pearlite and ferrite within its structure (softer molecular forms of steel) thus increasing its shock absorption properties.
In direct answer to your question, I personally think a properly welded billet of steel and a billet of mono steel would probably perform almost identically in stress tests (although I'd give the mono steel a slight edge). I'd love to see some scientific testing on the subject, but, as far as I know, none have ever been recorded. :/
Hope this helps!
bennypollok 7 years ago
Xexos 7 years ago
jpfalt 7 years ago
Actually, you don't need the tatara. If your forge runs hot enough to forge, it is likely hot enough to hammer weld. A coal forge is definitely hot enough, charcoal works and a properly contained propane forge is also plenty hot. What's important is that as you add carbon to iron, the melting temperature of the metal decreases until you get up to about 4% carbon. Also, as the surface of the steel oxidizes, the resulting iron oxide also melts at a lower temperature and squirts out of the joint when it is hammered. In practice, you add a minimum of .75% carbon and a maximum of 1.2%, or the steel will not harden without spontaneously cracking as it cools.
To do the weld, you clean the iron, flux it and heat it until the surface of the iron looks a little wet and runny. the color should be orange, going to yellow hot. At this temperature, the iron can still be handled with the tongs and has plenty of strength to stay in one piece. If sparks come off the iron while in the forge, it is too hot, and you are burning the carbon out of the surface of the steel. Then you hammer.
Xexos 7 years ago
jpfalt 7 years ago
A few minor corrections:
The starting material for a Japanese traditional knife was smelted iron and had almost no carbon in it. It is roughly the same material as wrought iron or pig iron directly smelted from ore. Carbon had to be added from charcoal to develop a steel alloy. If you add silicon and carbon, you get cast iron.
The Japanese used a mixture of finely ground pumice and either willow or hoof charcoal during the folding process. The pumice melts to glass at forging temperature and flows as a liquid flux to prevent the iron surface from oxidizing. The charcoal of willow or hoof is nearly pure carbon and ash free and goes into the iron surface to make the carbon steel.
The folding of the steel did two things. The carbon on the surface of the iron and the low carbon iron underneath stretch out into thinner layers. As you add more folds, the layers thin further and the carbon from the charcoal dissolves and diffuses in the iron to make a more uniform steel composition. The thinning and folding also makes defect size in the original iron smaller. The defect size is limited to the thickness of a single layer of iron in the fold. If there was a defect in the original iron and there was no folding, the defect is a significant location where the tool can break. With 8 folds, the defect is stretched out and thinned to be 1/256 th the thickness of the knife and is much less likely to cause a break.
The end result is something with the hardness of the steel and the toughness of the original iron. You can chop a red brick in two without damaging the edge of the blade.
I worked several years with a metallurgist who studied these blades and have made a few forge welded blades myself.
As a point of interest, the Scandinavians made similar forge welds, but used sea salt instead of pumice as the flux. You can get enough heat with a charcoal forge to do welding, but an atmosphere controlled forge makes it easier. Most of mine were done using a coal fired forge.
Xexos 7 years ago
However, I have to disagree when you say that the starting material for a japanese blade had little to no carbon in it. First of all, saying that a material with almost no carbon in it is roughly the same as pig iron or cast iron is just simply wrong. Pig iron and cast iron both have incredibly large amounts of carbon in them - sometimes between 2-4%. Secondly, the steel that comes from the tatara may begin as iron ore, but its carbon content is significantly increased even before it is welded and folded. That is why the tamahagane must stay in the tatara for days at a time - to allow the carbon time to diffuse from the charcoal into the molten iron. That is also why the tamahagane is broken into shards before welding, it allows the smiths to check the crystallized grain structure to find roughly how much carbon the steel contains (usually .4-.9%). Thirdly, although the smiths did use a carbon based flux, very little of this added to the overall carbon content of the steel. In fact, smiths had to work quickly to weld and fold the metal, because having steel heated to 2400° repeatedly can actually cause the steel to LOSE carbon content over time. The glass like pumice flux will hardly diffuse into steel when the metal is below melting point. The flux never actually gets folded into the steel, it is actually blown out in a shower of molten sparks during the strike of a hammer. When the flux is evacuated from the steel, the oxidation free, very hot surfaces of the steel meant to be welded are allowed to contact each other, this fusing into a solid piece.
jpfalt 7 years ago
You are right that cast iron has high carbon content. Cast iron is an alloy of iron, carbon and silicon. The silicon causes the carbon to precipitate out in flakes as the cast iron solidifies. If you look at the microstructure it shows areas of low carbon iron, areas of structure called cementitie which have some carbon and zones of nearly pure carbon. If you cut cast iron and rub it, you get carbon rubbing off almost like a pencil mark.
However, new refined iron from iron ore, referred to as pig iron has almost no carbon and has very little if any alloying materials present. It is also very difficult to forge as it is hot short and tends to crumble if the temperature is not just right. When finished the Japanese knife blade has somewhere between .85 to 1.15% carbon. This classifies as a W-1 grade of high carbon tool steel. The carbon is added in the form of the willow or hoof charcoal. If you look at the microstructure of the material, you see layers of low carbon iron and layers of high carbon steel with grain structures of mixed bainite and martensite. The martensite is very hard, but brittle and looks like a pile of sewing needles in the microstructure. The bainite is very tough and of medium hardness with a mixed up looking structure. Because of the very thin layers, a fracture in the martensite arrests and stops as soon as it reaches the adjacent iron layer. The quench on the blade is into 98 degree brine. Occasionally the Japanese Katana was quenched by being plunged into a prisoner. The Romans preferred fresh urine from red haired boys. Can you believe that the Roman government taxed urine as an industrial and commercial commodity?
To make pig iron forgeable, the refiner goes through a process called puddling, where pure iron is mechanically mixed with slag as it cools. The mixed iron and slag is then hammered or rolled. The result is wrought iron. The slag inclusions make the wrought iron forgeable over a larger temperature range. The downside is that if forged too hot, the wrought iron delaminates at the slag inclusions and can fall apart on the anvil as you hammer it like strands of string in a rope. Traditional wrought iron develops an appearance of wood grain as it corrodes, due to the films of slag stretched through the material during forging. I have two Japanese hammers that have wrought iron cores with high carbon tool steel faces hammer welded to the ends or the wrought iron core. It's neat stuff.
Xexos 7 years ago
Saying that pig iron has no carbon is false. Here's a link for the quote, and this data is backed up by multiple other sources.
https://en.m.wikipedia.org/wiki/Pig_iron
"When the satetsu (iron ore) is smelted in the tatara, the resulting steel has a high carbon content - up to 2 or 3 percent. However, to make a functional and practical sword, steel with .6-.7 percent is ideal. Thus, the the swordsmith's first task upon receiving the tamahagane from the tatara is to refine the steel and reduce the carbon content to this level.
The goals of the Smith are to make the steel more homogeneous, to produce a uniform carbon content, and to remove impurities in the steel. This is accomplished by hammering out the tamahagane into a thin plate, then breaking the plate into small pieces about an inch (2-4 cm) in size. These pieces are then stacked, heated, and hammered out into a billet. The billet is then repeatedly folded over onto itself.
Throughout the process of hammering and folding the steel, the Smith reduces the carbon content by about .2% with each fold. The steel is repeatedly folded until it reaches the appropriate carbon content of .6-.7 percent. The smith can judge the carbon content of the steel by its behavior during the folding and forging process."
This is a direct quote from Yoshindo Yoshihara's book, The Art of the Japanese Sword. For those of you that don't know who Yoshindo is, he's the number one ranked bladesmith in Japan. General consensus is that he is also the best bladesmith in the world, and he is by far the foremost authority on traditional blade processes, including the making of tamahagane.
In the paragraphs I quoted, he touches on two main points:
1) Iron Ore that is smelted in the tatara into tamahagane comes out of the tatara with a significant amount of carbon in it. Keep in mind that this is BEFORE the metal has been forge welded and folded at all. Saying that katana begin with a metal that contains almost no carbon is not true
2) Yoshindo says that, during folding, one of the goals is to REDUCE the carbon content in the steel - not increase it! (and yes, he does use hooves and charcoal as a flux) Saying that the goal of forge welding with a carbon rich flux is to increase the steel's carbon content is also not true.
jpfalt 7 years ago
You are right and I have learned something. Pig iron per your sources is high carbon and the forging and folding process appears to serve the purpose of decarburizing the surface layer of the steel. The carbon in the flux appears to be intended to avoid too much decarburization. Interesting and good work.
Xexos 7 years ago
Sorry if I seemed rude, I just was trying to avoid having conflicting information on the comments thread. For beginners just trying to learn new stuff, it can be very confusing to see two different sets of information. I remember when I was first learning to weld up billets in the forge, I was told some incorrect information, and ended up ruining a pretty big batch of steel.
I appreciate your ability to have a civil conversation, it's not often that you see that on the Internet, haha. :)
MichaelW317 6 years ago
which is a hyperutectide steel made in a tatara furnace which is anything up to 2% carbon as hard as a modern file the smith then picks the best to make the skin steel with he heats it and hammers it into thin sheets then gets the plates red hot and drops them in water then each one is broken into smaller bits and stacked on a plate of the same steel with a handle when he has enough for whatever blade he is making he wraps it in paper and ties it up ready for into the forge for welding heat is reached when sparklers rise from the forge then begins the welding process,
the folding will loose carbon with every reheat so to help in between each he dumps the hot tamahagane in a slurry of iron clay and straw before re heating it folded around 12-14 times giving thousands of layers, when finished it will be around 6 to 7% carbon ready to be made into a blade,
can you tell me why wrapped in paper why in clay and straw
MichaelW317 6 years ago