We will now take a look at the sword blade steels, and how they differ. It is very important to get a steel that meets your needs. For example, if you want a display sword, then a steel that rusts is not ideal – you want something low maintenance. Likewise, if you want a combat sword and can take the time to oil it properly, then you want something that is very tough and can spring back into shape. It is time to learn more about the correct steel for your needs.
Blade Steel: Heat Treatment
Heat Treatment: Heating and cooling a material in a controlled manner for the specific purpose of altering its properties.
TIP: The steel’s heat treatment is critical for the quality of the blade.
Blade steel starts out relatively soft and requires heat treatment after it is shaped to achieve its true potential. Assuming you selected the correct steel quality, a proper heat treatment is more important than the steel itself. It is not about making the cutting edge hard, it is about making the whole blade the optimal balance between hardness and resilience. Just keep in mind there is a trade off that varies steel-by-steel. Too soft and it will not be able to cut combat targets. It will also dent easily, which is more annoying than life-threatening. Too hard and the blade will rapidly nick or break, possibly in a catastrophic fashion.
Once you move into the weapons grade steels a certain percentage of blades crack during tempering. Some of these fractures are so tiny they make it through several rounds of inspection (including inspection prior to purchase by the client). One famous maker of expensive Western knives (a single knife generally costs more than a pair of BJD) uses a fluorescent dye and black light to make it easier to inspect, but that process is too expensive for martial arts equipment. If you receive a new blade and see a scratch that appears on both sides of the blade, even if it is only a few millimeters long, that is a hairline fracture that makes the blade unsafe to use. Return it immediately. While having to return brand new swords is definitely annoying, remember this is a high class problem you are unlikely to experience with a wall hanger.
If you differentially heat treat a blade so the spine side is softer than the cutting edge side to absorb impact, you can get away with a far harder cutting edge. Various methods of accomplishing this can create a beautiful wavy line on carbon steels though a knife tempered to maximize aesthetics will probably be too soft for use. This is really overkill for Butterfly Swords, which are relatively thick and squat. Modern BJD are hardened uniformly.
A lot of factors go into deciding the most appropriate cutting edge hardness for a specific sword. We will leave it at that.
The heat treatment is the area where most Butterfly Swords fail miserably. Our high-end forge associate, Iron Man Steel, uses a third-party specialist for weapons requiring uniform heat treatment.
Blade Steels: Carbon, Stainless, and Others
We give our opinions on the most appropriate steels, grinds and construction for Butterfly Swords used for various degrees of contact, including weapon vs. weapon training, because it needs to be said. Be advised here and throughout this article that we never recommend any sword for weapon vs. weapon training because all weapons fail at some point (with potential catastrophic effects) and even if the weapons perform as intended such training can result in injury or death. The odds of sword failure are greater in steel on steel contact. Never train using steel against steel!
Blade Steel: Type of steel the blade is made from.
The most appropriate steel for the blade depends on how the swords will be used. From a purchaser’s standpoint the relevant factors are the intended use, tolerance for performing maintenance chores, and budget. All weapons-grade steels, including weapons-grade stainless steels, rust. Weapons-grade stainless is low maintenance, not no maintenance. Basically you have to prioritize and decide what your true needs are.
If you are doing contact work – weapon vs. weapon or cutting exercises – the best options are in the carbon steel family. Carbon steels require intensive maintenance. You need to clean the blade after touching the steel or training with the weapon, and keep the steel coated with sword oil when it is not in use. That means you must also strip the oil prior to each training session. Several top custom knife makers believe it is better to coat carbon steel blades with non-acidic Renaissance© wax instead of oil. Oil captures dust particles that can facilitate corrosion. Do not leave the blade dirty or unprotected, not even overnight. Very few martial artists are willing to put in the time and effort required to maintain carbon steel. Many knife collectors prefer the high carbon steels for their resilience and feel it is well worth the extra effort.
Medium carbon steels have 0.30% to 0.59% carbon content. High carbon steels have 0.60% to 0.99% carbon. Steels with 0.55% to 0.59% carbon tend to be ideal for “beater” swords.
“Spring steel” is highly elastic, high yield strength steel that returns to its original shape after significant bending or twisting. A number of carbon steels can be processed in this manner. EWC’s testing showed American Iron and Steel Institute (“AISI”) 9260 “Spring Steel” augmented with hammer forging was outstanding for beater use. The hammering realigns the grain of the steel resulting in improved strength characteristics. Hammering can be accomplished with an old fashioned hammer and anvil or using a mechanically assisted “power hammer.”
TIP: Avoid recycled “Spring Steel.” Just think about it.
AISI 1075 and 1095, with 0.75% and 0.95% carbon respectively (the last two digits are the carbon), can produce superior blades for actual combat but they are no longer appropriate “to beat on.” These high carbon steels need to be properly heat treated and water quenched to get their additional benefits. There is no sense upgrading to 1075 or 1095 without the water quench. Water quenching results in a higher rate of blades cracking than oil quenching so it is seldom used.
Some of the mass production Butterfly Swords use a medium or high carbon steel because ordinary carbon steels are cheap. Good quality raw carbon steel for a pair of 12” blade BJD of adequate thickness is only about $30 at retail from a reputable U.S. knife supply house. The odds are minuscule of a manufacturer actually paying for heat treatment sufficient to create a true weapon if they do not advertise the steel type. It might even be low carbon steel.
D2 Tool Steel is a carbon steel used to make dies that cut other steel and hence a “tool steel.” Many experts regard it as the top carbon steel for knife blades. EWC was the first to make BJD out of D-2. Testing by EWC and experience have proven that properly heat treated high quality D-2 has an outstanding combination of characteristics for Butterfly Swords capable of hard use. It is tough, has excellent wear resistance, takes a fine edge and holds it. Let’s talk resilience.
There is an impressive video out there of Iron Man Steel’s third-generation Forge Master, K. Ali, bending back one of EWC’s German Böhler D-2 Butterfly Knife blades and it springing back to shape. In the same video he lightly chops a piece of shop equipment and cuts into it without nicking his blade. (Do not do this yourself!) There is some relevant flexibility in the composition of steel that qualifies as D-2 so it is critical to only purchase from a reputable steel maker.
D-2 is so corrosion resistant for carbon steel that it is known as “semi-stainless.” Its maintenance needs are closer to those of weapons-grade stainless steel rather than ordinary carbon steel. Aaron purposefully (as a test) has neither oiled nor waxed his personal pair of EWC Flagship line BJD. He just wipes off finger oil with his tee shirt and has seen no corrosion. Acidic fingerprints will etch into D-2 steel so we suggest a more thorough cleansing regime than Aaron’s. There are some trade-offs.
Raw D-2 blade steel costs almost three times the price of ordinary carbon steel. It is very hard to work with when making blades and production costs as well as time increase significantly. Using D-2 added about six months to EWC’s 2012 Christmas production run which, admittedly, was a hefty sized project. D-2 is a grainy steel that looks odd when mirror polished and is therefore generally best left with a satin finish. Because D-2 is so tough, it takes a diamond or sapphire hone and far more time to sharpen. Finally, and we recognize that many of you will not regard this as a problem, it tends to damage other weapons it is used against.
If you are just doing forms practice or open air demonstrations, stainless steels are a better choice since they are more stain resistant than carbon steels and, consequently, require less intensive maintenance. The weapons-grade stainless steels have more carbon than wall hanger grades and so are more susceptible to corrosion. Aaron once left an EWC Flagship Line BJD immersed in water for several weeks. The handles expanded/swelled but the weapons grade German Böhler 440C stainless steel blade was fine. On the other hand, we know of a case where the acid from a pregnant woman’s touch stained high quality 440C stainless steel. Do not touch your steel unless you must.
If you keep stainless coated with a non-acidic wax, clean lightly after each use. First remove the physical debris from the blade. Consider gentle tapping, rinsing and/or a soft toothbrush; do not rub debris because it causes scratching. A damp cloth with a non-abrasive, non-acidic detergent (check out dish washing liquids) is usually fine for cleaning stainless steel but you need to rinse well and dry immediately with a soft cloth. Do not use soap to clean weapons grade stainless or carbon steel blades as soap has a caustic etching quality that may produce immediate tarnish lines. Dry completely when done. Strip the wax and clean seriously on a periodic basis.
Stainless steels are more brittle than carbon steels and very inappropriate for a long narrow sword like a Jian but fine for most Butterfly Swords. Butterfly Swords are really just big knives and these days used mostly for non-contact practice.
Most modern Butterfly Swords are made of low quality stainless steel. The advertising seldom identifies the precise blade steel. Would it surprise you to learn that a famous design Butterfly Sword advertised as “combat steel” is actually a stainless steel of a type unknown to the importer rather than medium or high carbon steel? Anyway, the less carbon (other elements also impact this but carbon is the primary one for the affordable steels), the softer and easier for manufacturing.
If an advertisement just says “Stainless Steel” then it is almost always inexpensive AISI 420 stainless, which is very soft and often referred to as “Butter Steel.” Chances are the heat treatment is sub-par, but even with the right heat treatment this low end steel is incapable of producing a cutting edge hard enough for combat. The good news is that lower grade stainless steels tend to have high chromium content and are very rust resistant. Some blades are advertised as “surgical grade stainless steel.” While there is no specific definition, surgical instruments require steel that is corrosion resistant, easy to clean and sterilize, unlikely to leak carbon molecules into the wound, and need only hold an edge for a short period of time.
TIP: “Surgical Steel” Butterfly Swords are probably made of Butter Steel!
There are two notable higher grades of stainless steel in the 420 series. Quality Japanese AISI 420J2 with carbon on the high end of the permissible classification range can theoretically be heat treated to the bottom of the historical weapons-grade range, which has a lower threshold than what we can achieve and prefer today. It will not hold a cutting edge and so cannot serve as a real weapon. You see it a lot on inexpensive knives sold online to individuals who do not use them.
Expertly heat treated quality 420J2 is the lowest grade stainless steel suitable for Butterfly Swords, this is justifiable based on negligible maintenance requirements. It should be used only for non-contact training but, to be frank, is harder than wood so usually ok for the occasional light work against Wing Chun long poles. We do not trust very many forges to get this steel right (ethics and expertise being the issues). Moving up the quality chain, AISI 420HC can easily be hardened into a real weapon. The next step is the AISI 440 series.
A lot of knife snobs regard the 440 series (and the 420 series) as lousy steel. While there are many steel makers with product we would not trust, odds are these disillusioned individuals experienced a knife that simply had poor heat treatment.
TIP: If an advertisement lists 440 steel and the 440 is not followed by a letter A through C you should get a very bad feeling.
AISA 440A is a weapons grade stainless steel commonly seen on entry level Western-style knives. The characteristics of 420HC are arguably more attractive. Randall Made Knives is the most respected name in the Western style knife industry. Their waiting list usually runs about five-years. They smith their stainless steel blades from AISI 440B or AISI 440C so you know that a good quality, professionally heat treated 440B is weapons-grade.
EWC and Modell Design were the first to use AISI 440C stainless steel on non-custom Butterfly Swords. It is a weapons grade tool steel that was adapted by the custom knife making industry. Its extraordinary balance of martial capability with corrosion resistance set the standard for weapons grade knife steels. It takes a sharp edge and is easy to re-sharpen. The top U.S. custom knife maker does most of his military work in 440C (bead blasted for a non-reflective finish), it is favored by several U.S. makers of custom Butterfly Swords, and we have excellent experience using German Böhler 440C on BJD. As with D-2, the precise mix of components for good quality stainless steels permits some relevant variations so it is once again critical to purchase from a reputable source. The Germans really know their steel and Hitachi also makes good 440C.
TIP: Always ask, “Who made the steel?”
We have tested our 440C BJD hollow grind blunts chopping trees and wood poles and, while we do not recommend contact for hollow grind, we experienced no problems against wood. We have also done some truly abusive and destructive testing. Nothing any rational person should repeat including: sword on sword, and sword against granite (granite is a tough customer). We would not hesitate to use one of our 440C models that is sharp in a life-or-death situation.
Quality AISI 440C stainless steel (just the raw steel, not the labor) is slightly more expensive than D-2. It is roughly three times the cost of ordinary carbon steel.
Many U.S. custom knife makers now use the new “super steels,” such as ATS-34, S90V, and third-generation powder metallurgy steel Elmax. These new steels are tweaks on and compared to 440C. They usually trade off corrosion resistance in return for different factors such as better edge holding capability or lateral stress resistance. A friend left an ATS-34 Western knife in his car trunk for about a week and it rusted. That’s part of the turn off of trade off. The raw steel cost of the latest super steel can top five times that of ordinary carbon steel and after a few years it is out of style.
“Wootz steel is a steel characterized by a pattern of bands or sheets of micro carbides within a tempered marten-site or pearlite matrix,” states Wikepedia. It was also called “Damascus Steel.” The technique for making authentic Wootz steel was lost, though some individuals claim to have rediscovered it.
The so-called “Damascus Steel” you see advertised on eBay and available on some Butterfly swords is not Wootz, rather it is a series of thin layers of steel, often different kinds, forged together. Originally in China even cheap Butterfly Swords were made of laminated steel at the village smith to compensate for low steel quality — the blades were more resilient just like modern plywood.
EBay knife “Damascus” lamellar steel is mostly made from two contrasting high carbon steels composed to form decorative patterns rather than optimize resilience. It is usually too soft for a true weapon.
While you can find weapons grade lamellar on a number of quality Japanese and Chinese style long swords, weapons grade modern mono-steels are as good as or better than most modern “Damascus.” There are only a handful of sources offering weapons grade lamellar on Butterfly Swords. Because stainless steel is tougher to forge than high carbon steel, weapons grade stainless lamellar is exceedingly rare.
This video is Parts 2 and 3 of 10 on Choosing Butterfly Swords by Jeffrey Modell. There is also a bonus video of Hammer Tests vs various swords. This video goes along with the blog article, but does not follow the exact same order of topics. We apologize that the AUDIO is OUT OF SYNC. This is the way the camera filmed the footage, so there is little we can do about it (simple aligning will not work). We hope you get some benefit, regardless:
Still haven’t had enough? Check out the next section about Blade Sharpness, Edges, Grinds, Tapers, Ricassos, Choils, & Fullers.
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