I prepared these remarks for another audience, but I thought they might be relevant here as well.
I would like to introduce you to my favorite steel Mr. O-1, and his wife in my damascus Mrs. L-6.
I will briefly introduce some of the common alloying elements of steel as well.
In my research early in my damascus making was looking for some suitable steels to make good damascus out of. I started out with 1095 and 15n20, a popular mix, but I thought there might be a better mix. There are many factors necessary to produce a good damascus mix, just as there are many factors of personality necessary to produce a good marriage. In order to produce steel only two ingredients are necessary Iron and Carbon. Each additional element produces certian traits, like personality traits in us. Not only is each element important the quantity is also important. Carbon in quantities around one percent are best for our purposes, over 1.5% and the steel becomes cast iron, lowering the melting point. Carbon around 1% is very good for slicing cutters that require a very strong abrasion resistant edge, but it is not the best for blades made to do heavy cleaving or chopping. Less than .6% and there in not enough carbon to produce enough carbides to give enough wear resistance and hardness for knives. Manganese is commonly added to all modern steels, it helps smooth pouring of the steel when it is molten, in higher quantities it assists in hardening and it is the element most responsible for the dark coloring of the steel in damascus.The main reason for manganese in almost all modern steels is to combat the effects of sulfur, by forming manganese sulfide, a more stable compound that does not liquefy in the grain boundaries. Chromium is a popular alloying element, and in quantities over 13% is responsible for the stainless properties, due to the high concentration of microscopic chromium oxides on the surface of the steel. In lower quantities it produces chromium carbides, which can be benificial in small quantities, however in large quantities they can clump into huge clusters and make sharpening difficult. They have a tendency to break out of the edge rather than being worn down in the sharpening process. Carbide clustering can be controlled by using powder metallurgy or by lowering the carbon content in the steel, thus disallowing the formation of excess carbides. Tungsten (wolfram) is another carbide former, producing fine and very hard carbides, in small quantities it aids in wear resistance as all the carbide formers do, in large quanties it is used in steels used to cut other steels, especially hardened steels. Molybdenum is another carbide former, though not as hard as tungsten, is a common alloying element, especially in the high alloy stainless steels. In non-stainless steels it is added to hot-work steels, those steels which may encounter some heat during use, like drill bits. It gives the steel a much higher tempering temperature, so that heat encountered in use will not affect the hardness of the steel. Silicon gives the steel additional toughness, and has no effect on hardness. Nickel also gives the steel toughness, it also gives the steel acid and etchant resistance, which allows for the contrasting effect in damascus. In higher quantities in collusion with chromium it can produce stainless effect in steel without much carbon and without being hardened. The 300 series of stainless steels used in stainless countertops and food pans.
This has been a general overview of some of the common alloying elements, just to give some basic idea of what certian elements in steel do. I am not a trained metallurgist, however I have made a serious study of the subject. One important fact is that very small amounts of alloys can have a noticeble effects, as little as .05%.
O-1 stats (typical)
C .90%
Mn 1.25%
Si .30%
Cr .50%
W .50%
Fe balance
L-6 stats (typical)
C .75%
Mn .70%
Si.25%
Cr .80%
Ni 1.5%
Mo .30%
O-1 is an oil hardening tool steel with deep hardening qualities with little size change in hardening, with a fine grain structure. These characteristics make it an excellent steel for many purposes, including knives. The small amount of tungsten makes a significant difference in the cutting ability and wear rsistance of this steel. Fully hardened it can reach 65rc.
L-6 is a tough, high-strength oil hardening tool steel suitable for high stress jobs, like saw blades and longer knives.
Fully hardened it can also reach 65rc.
Alloying in steel is always given in a range, so that minor variations can occur; as a result the heat treatment temperatures are also given in a range. One of the things that make these two steels such a perfect match is that those heat treat ranges overlap. This is of critical importance for the high preformance of the finished damascus. This overlap is the reason that only a very few steels can be compatable for damascus, and the reason why 3 steel combinations are impractical.
For these reasons I believe that properly heat treated the O-1 and L-6 damascus is the best combination available for knives. This damascus mix is not for beginners, requiring more skill to work properly than mixes such as 1095/15n20, and more precision with temperatures, but I believe that the extra efoort is worth it in the finished product.
Thanks,
Del
I would also like to give credit to Kevin Cashen, who proof read this and added some additional comments to make this information more complete, and who has helped me with my understanding of metallurgy over the years.
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The only other damascus mix I have used extensively is 1095/15n20 and somewhat less I have used 1084/15n20 and this is an excellent mix to start making damascus mix and many makers use 1084/15n20 sucessfully and feel no need to move beyond. These steels rely heavily on iron carbide for the hardness and iron carbide is not the hardest of the carbides. Some of the elements I listed above and others are strong carbide formers, which means they like carbon even more than iron does and most if not all of them produce harder carbides than iron carbide. This is where the O-1/L-6 mix has the potential to outshine any steel that relies only on iron carbides for hardness. The O-1 has both chromium and tungsten, one of the carbide formers that produce very hard carbides. L-6 has chromium and molybdenum; another strong carbide former. Though the amounts of carbide formers are moderate, I believe that they have a signifcant effect on the edge holding potential of the final mix. One result of having much harder carbides present in the steel matrix is that they are much harder to wear away, thus increasing the overall wear resistanc of the steel. Wear resistance equates to longer edge life, although when taken to an extreme can cause problems sharpening. Many characteristics in steel are a compromise and wear resistance is one of these when wear resistance is low the steel is easy to sharpen, and when it is high the steel stays sharp for a long time, but can be all but impossible to sharpen.( Note: the previous statement is a generalization and could be misinterpreted if taken out of context.)
I have only listed 2 possible mixes for carbon steel damascus and there are many steels available, so why so few available for making damascus? In carbon steel there are 3 broad categories to choose from, the first is the water quenching steels like 1084,1095,w-1,w-2 and 15n20. The second is the oil-quenching steels like O-1,L-6,52100,5160 and others. The third category is the air-quenching steels like D-2,S-7and A-2. There are many others in all three categories, the ones I have listed come to mind easily and are there only to serve as examples. One of the limiting factors in selecting steel for damascus is locating a steel with enough nickel to resist etching. These steels are not common and limit the number of combinations possible. There are only 3 steels available with enough carbon to make it worthwhile to use in high performance damascus, and those are 15n20, and 8670 both water quenching steels, and L-6 an oil quenching steel. There are no suitable steels with enough nickel to use in the air quenching steel category. To make high performance damascus these steels must be paired with another steel with a compatable heat treat. This severely limits the combinations possible. There are a few other steels that contain nickel, like 203e and 4340, but not enough carbon to make a good high performance damascus, carbon diffusion lowers the overall carbon content of the steel mix. Stainless damascus in another creature and I will cover that in a later post.
