heh yeah gotta love 420 and 440 stainless steel...
from the Metallury Experts of Highlander (actually it's fairly accurate), if you plan on buying swords (not just katana's) a little chemistry lesson as well
Caution on Marketing Language
Please be careful when shopping with sword smiths. Some use anything from magic and mysticism to all kinds of marketing hype. We've heard every manner of hogwash under the sun.
Some claim they use a particular tool steel because it's used to cut through other steels. Sounds great when you're marketing swords. Others say, "we use spring steel; our steel comes from Mercedes truck springs. If it's good for a two-ton truck, it's good for a sword." Technically this is true. But rather than get brand new 5160, some third world countries actually get them tank springs and try to forge them. Improper heat treatment results in the "memory" of the original shape being retained in the steel, which can further result in microcrystaline fractures. What this means to you is this: research the totality of that smith's smithing process, or you will pay dearly. One smith sells his "live warblades" for $6,000. Word has it that some customers find they crack easily!
And finally, who could resist web pages that have all kinds of metallurgical baloney such as "secret steel" or "steel of the Knights Templar" or "our blades function as one crystal" and "edge packing of the edges" and the occurence of an "electromagnetic hum" that can be "felt" - the appearance of "magic."
Twentieth century metallugy is a science. Most non-swordsmiths buy into anything on a website. A lot of it is inaccurate and misleading.
There is no such thing as an indestructable sword or indestructable sword steel. Even those websites that claim secret recipies and magical properties are reported to us whereupon customers claim anything from cracked blades to foul tempered business owners!
Grades of Steel
Traditional/Original Japanese Steel - Always the best, this contains iron, carbon, silicon and many various trace elements. Approx. 0.6-0.7% carbon. One modern smelter in Japan that was used during World War II provides steel of the following composition: 0.04% molybdenum, 0.05% tungsten, 0.02% titanium, 1.54% copper, 0.11% manganese, and a few other traces, a varying amount of silicon (due to the sand - amount depends on sand/ore ratio in a particular load), between 0.1% and 3% carbon and the balance being iron. The presence of silicon increases structural strength as well as improving flexibility characteristics.
AISI/American 1050/10xx - A good choice! While not identical to medieval Japanese steel, this plain carbon steel is the closest we have today. AISI 10xx steel contains iron, manganese and carbon, thus differing slightly from traditional steel. AISI 1065 maybe closer in carbon content to Traditional than 1050, but 1050 is tougher steel, and compensates somewhat for the lack of silicon in the steel (silicon improves strength and flexibilty). The xx in 10xx indicates the percentage of carbon, where 1050 has .50% carbon, and 1070 has .70% carbon, etc. The higher the carbon content, the harder the steel. The lower the carbon content, the more tough the steel is. Too hard, and the blade can shatter upon impact. Too soft, and it can easily be cut through. Many ask, "Which is the best for swords?" However, it's all in the heat-treating. But generally, you want a low-alloy steel for your sword. The biggest difference between 10xx and traditional Japanese steel tamahagane is the presence of manganese in 10xx but also the lack of silicon.
AISI/American 5160 - a low Chromium (0.7%) alloy tool steel, it also contains 0.2% silicon, and is considered widely to be a superior steel for swords in general, particularly European style swords, because it is so tough. Although this steel contains chromium, there is not enough to make it stainless (More than 13% is required to make steel "stainless". 440C contains 16-18% chromium) or to affect the strength of the steel. This steel has a slightly richer alloy mix than the AISI 10xx series. Some Malaysian manufacturers use this steel, but do a poor job with heat-treatment so the resulting blade is inferior. However, this inferiority is the fault of the sword-maker and not the steel itself! The steel's chromium content is enough to make it extremely difficult to create a hamon (temper line). Also, 5160 is a bit more corrosion resistant than 10xx when it comes to fingerprint oils' acidity. You could touch it without fear of instant rusting, but clean your sword still before resheathing it.
A2 Tool Steel - The "A" of "A2" means "Air Hardening" which means it can be cooled with an air blast ("slow cooling") rather than being quenched in water or oil ("fast cooling") A2 is a chromium tool steel, rated for high toughness and in a knife, very good edge holding potential. The chromium content is not enough to make the steel "stainless" or to weaken the grain boundaries significantly (like 420 and 440 Stainless). Despite its excellent properties, for use in a Japanese style blade, it cannot be clay treated (for differential hardening) in the traditional manner - which gives the katana its superiority, as traditional blades are fast cooled instead, and clay does not work to prevent hardening of the blade's back in cooling A2. Because of this, you generally cannot create a hamon (temper line) with A2. Phill Hartsfield however, uses A2 and is the only smith in the world able to create a temper on this steel with a "secret" process (some have observed from personal experimentation that running an oxy-acetaline torch does the job, but this really compromises the toughness of the edge due to this air-hardening steel's uneven hardening). In short, A2 will make a good sword steel. Swordmaker Tom Maringer uses D2 in his fantasy and Japanese-style swords. We have received reports of various A2 swordblades that have been returned to some smiths, suffering cracks. A lower-alloy high carbon steel may perform better. Generally, the marketing pitch on A2 swords is that "it's a tool steel that cuts through other steels, so it's good for a sword."
D2 Tool Steel - This is a good chrome-vanadium tool steel; it has 12.5% chromium which is not enough to make it stainless, but which in other steels, would be enough to rule it out as a sword steel. However, D2 also has vanadium and tungsten which act as grain refiners and counteract some of the weakening effects of the chrome. Because of the addition of molybdenum and some nickel, it is very tough, very hard (from the tungsten) and holds a good edge (only stellite and maybe 440V come close in terms of edge holding, but 440V is much more brittle, and stellite is a cobalt alloy, not a steel). Unfortunately, like A2 and other high alloy, deep hardening steels, you cannot create a hamon on it. A sword of this material would be incredibly tough. And despite its edge holding characteristics on paper, it is said that it holds a lousy edge and will hold it forever. Like A2, it's an air-hardening steel and is hard to heat treat properly. If you manage, then that's great. L6 may be a better choice for high performance steel (it's not too hamon-friendly either). It is said that D2 may be a little better than high carbon stainless steels.
S-5 Steel - The "S" stands for "shock-resistant" which comes about as a result of its 2% silicon content. This might be better than 1050, but it is more difficult to find, and will most certainly be more expensive than plain carbon steels.
S-7 Steel - Another shock-resistant tool steel, air hardening, which means that unless the smith really knows what he's doing, this finnicky steel is hard to heat treat. Some may use a torch to treat the edge to give it a Japanese style temper line - such a maneuver might be okay with knives, but in swords there is almost always a total loss of control of quality. We've gotten reports of certain "Angelic" swords cracking. The marketing hype is "Shock resistance" so everyone things this steel that "cuts through other steels" must automatically be good for swords. Take into account the totality of the sword smithing process! Inferior heat treating can result in a poor steel. S-7 is getting very alloy-rich for use as a high-performance sword. S-5 might be a better way to go, but it's pricey.
CK55 Krupp Steel - You've seen it advertized in some of Museum Replica's catalogs - which earlier Del Tin swords and blades were forged from. It's the European equivalent of AISI 1055. "C" stands for "Carbon" and "K" for Krupp - the German company that makes it.
50CRV4 - This is a steel with very small amounts of Vandium and Chromium. Chromium in higher quantities lends to a steel's "stainless" properties. However, in 50CRV, there isn't enough to make it "stainless" - and metallurgically brittle. Thus it makes a good spring steel. It contains trace amounts of Silicon and Manganese. The tensile strength of CK55 and CK50 is about 600 N/mm2, while 50CRV4 ranks about 750 N/mm2. (Many thanks to Fulvio Del Tin for this information!)
420, 440A, 440B, 440C, 440V, ATS-34 - Stainless steel. Great for kitchen knives, folding knives, etc. Sword-makers such as Gladius and Marto/Martespa of Spain use it a lot. However, they are unsuitable for swords and swordplay re-enactment, namely because of the weak grain boundaries caused by the presence of the chromium, which is used as a grain enhancer and gives it it's "stainless" properties and mirror finish when polished, but makes it more brittle. Chromium and other alloying elements like Vanadium, tungsten, etc. can make steels stainless, fine grained, heat resistant, etc but really add to the problem because you cannot create a beautiful hamon ("cloud pattern") line with these steels. The ones that appear on replicas are ugly acid or electro-etched sine waves! NOTE: Some rip-off companies only put "440 STAINLESS STEEL" on their products, but neglect to say whether it's 440A, B, or C. Since 440C is the most qualitative of the lot, they just say "440" and lean on the popularity of 440C, which is dishonest.
NEW! CPM420V Stainless Steel - Made by the Crucible Materials Corporation as an upgrade for CPM440V, this high alloy (20 percent) stainless steel was developed originally as a high-wear steel for wear and corrosion resistance (on par with most othe rpopular stainless knife steels). For a knife blade, this steel has good things going for it. It has good edge holding capabilities (you can make a very aggressive edge on blades made of CPM440V), howbeit you'll find some ductility and pliability with this steel. On the downside, it's difficult to get a decent finish on it due to its high alloy content. It's an excellent steel but not a workhorse like D2, 51200 (used for ball bearings), 440C, and 154CM/ATS34 (a modification of 440C). However, knifemakers find CPM440V blades outcut all other steels hands down.
420J2 Stainless Steel - Again, just because it's "100% pure Stainless Steel" doesn't mean it's all that great. 420 Stainless Steel could normally produce a fair wallhanger sword. However, 420J2 has very little carbon content, so the Rockwell hardness won't be higher than 53 Rockwells. Even though many Marto and Martespa products fall into this range - and the spines (not edges) of Japanese swords are in this range - the unfortunate fact that 420J2 swords are so quickly churned out by these rip-off overseas companies that they've been independently rated at a mere 45 Rockwells! That means that a Marto wallhanger could cut through it! So why do these companies use 420J2 for their swords? First off, it's extremely easy to grind - almost like butter. But because they can grind ten swords to shape in the same time it takes to make, say, a Marto, the fact is that their greed for money exceeds the importance to them that their swords cannot hold an edge after going through cardboard a few times! Think of 420J2 as the stainless equivalent of mild steel - with very low carbon content and thus will not harden.
High Carbon Steel / High Carbon Spring Steel - They may use words like "Spring Steel" or "Live Steel" in their sales pitch. Spring Steel is a term that refers to any member of a group of steels that various types of springs are usually made out of (e.g, car springs are commonly made of 5160, but they can also be 1065). "Live Steel" is another euphemism for "plain carbon steel" (i.e., it can refer to any of 1050, 1065, 5160, CK55 or any plain carbon or low alloy steel) used by one mail-order/web company. Because these are not stainless, swords made of these materials do require oiling to prevent rusting. You may want to keep Iberia swords outside of their scabbards to avoid moisture damage and corrosion from chemicals used to treat the leather. Their high carbon spring steel is from the Philippines and comes from automobile springs (typically 5160), and can flex somewhat and return true. The high carbon steel used in Indian swords is similar to 1065. But, watch out! Even though many Indian, Filipino and Malaysian companies use superior steel, they put it through very poor heat-treating, which results in an inferior blade! In terms of "bang for the buck" you're getting an okay sword, but I wouldn't bet my life on an Indian, Filipino or Malaysian blade due to low-quality tempering.
Damascus Steel - Damascus is interesting. The original Damascus was a crucible steel with an extremely high carbon content. When forged into a blade, the carbides in the steel formed into a pattern that was visible on the surface of the steel. This material is also called "Wootz" or "Bulat". What most people think of today when they hear the word "Damascus" is actually pattern-welded damascus. Now this steel is composed of many layers of high and low carbon steel, and when etched, the high and low carbon steels are attacked at different rates by the acid, resulting in a visible pattern. Pattern-welded steels have existed since man began working with iron and steel (the Vikings made many pattern welded blades, however the technique fell into disuse until after the Crusades, when the smiths attempted to re-create the appearance of Wootz blades brought back by the knights by pattern welding steels).
Now, regarding modern (or pattern-welded) damascus in a Japanese-style sword, Atlanta Cutlery probably kinda inspired this ever since they began selling a full tang samurai damascus blade, at the request of many customers. However, this blade was produced by Windlass Steelcraft and was done improperly! It suffers from a condition known as "carbon migration" which means that all the carbon from the high carbon layers has gone into the low carbon layers, and the overall carbon content is now too low and the blade is unhardenable. It is very soft and weak and will not stand a chance against a well-constructed blade.