Intro to Carbon Steel Knives
Carbon steel, also called plain carbon steel, is a metal alloy, a combination of two elements, iron and carbon, where other elements are present in quantities too small to affect the properties. The only other alloying elements allowed in plain-carbon steel are manganese (1.65% max), silicon (0.60% max), and copper (0.60% max).[1] Steel with a low carbon content has the same properties as iron, soft but easily formed. As carbon content rises the metal becomes harder and stronger but less ductile and more difficult to weld. Higher carbon content lowers steel's melting point and its temperature resistance in general.
As a general rule of thumb, high carbon steel is harder than stainless steel and will stay sharp for a longer period of time. The downside of having steel that is so hard is that when the knife eventually loses its sharp edge, it will be more difficult to re-sharpen. Hunters are particularly fond of high-carbon steel for their field knives because they need a knife that will keep its edge while skinning large animals. Re-sharpening a dull knife while the animal that you just killed is decomposing can be very tedious and frustrating. What many hunters fail to remember is that the high carbon content in their knife makes it much more prone to rust. Moisture is the main cause of rust on most hunting knives. This moisture can come from blood, rain, or water that is used to clean the blade. Always remember to thoroughly dry the blade of your knife (high carbon or stainless) after use if it comes into contact with any moisture. Storing your hunting knife in its sheath (knife holder) for long periods of time can also cause the blade to rust as moisture tends to develop inside of the sheath and sits on the blade which causes corrosion. I recommend that you do not store your knife in its sheath unless you are in the field or need it to be there.
Stainless steel knives tend to be more expensive than high carbon knives due to the fact that more work goes into making the knife stainless or "rust proof". Many hunters are mislead by the word "stainless" and believe that their stainless steel hunting knife will not rust under any condition! This belief is false and many hunters are upset to find rust spots and corrosion on their favorite hunting or outdoor knives after only several uses. I recommend that you use the same caution and maintenance procedures with a stainless knife as you would with a high carbon knife in terms of rust prevention. Stainless steel is softer than high carbon steel and accordingly can be sharpened much easier.
It is a good idea to keep a light coat of non-detergent based oil on your high carbon steel knife when it is not being used.
Properties of performance steels
What is it we're looking for in a steel, anyway? Well, what we are looking
for is strength, toughness, wear resistance, and edge holding. Sometimes,
we're also looking for stain resistance.
Wear resistance - : Just like it sounds, wear resistance is the ability to withstand abrasion. Generally speaking, the amount, type, and distribution of carbides within the steel is what determines wear resistance.
Strength: The ability to take a load without permanently deforming. For many types of jobs, strength is extremely important. Any time something hard is being cut, or there's lateral stress put on the edge, strength becomes a critical factor. In steels, strength is directly correlated with hardness -- the harder the steel, the stronger it is. Note that with the Rockwell test used to measure hardness in a steel, it is the hardness of the steel matrix being measured, not the carbides. This, it's possible for a softer, weaker steel (measuring low on the Rockwell scale) to have more wear resistance than a harder steel. S60V, even at 56 Rc, still has more and harder carbides than ATS-34 at 60 Rc, and thus the S60V is more wear resistant, while the ATS-34 would be stronger.
Toughness: The ability to take an impact without damage, by which we mean, chipping, cracking, etc. Toughness is obviously important in jobs such as chopping, but it's also important any time the blade hits harder impurities in a material being cut (e.g., cardboard, which often has embedded impurities).
The knifemaker will be making a tradeoff of strength versus toughness. Generally speaking, within the hardness range that the steel performs well at, as hardness increases, strength also increases, but toughness decreases. This is not always strictly true, but as a rule of thumb is generally accurate. In addition, it is possible for different heat treat formulas to leave the steel at the same hardness, but with properties such as toughness, wear resistance, and stain resistance significantly differing.
Stain resistance(rust resistance): The ability to withstand rust (oxidation). Obviously, this property can be helpful in corrosive environments, such as salt water. In addition, some types of materials are acidic (e.g., some types of foods), and micro-oxidation can lead to edge loss at the very tip of the edge, over a small amount of time. In "stainless" cutlery steels, stain resistance is most affected by free chromium -- that is, chromium that is not tied up in carbides. So, the more chromium tied up in carbides, the less free chromium there is, which means more wear resistance but less stain resistance.
Edge holding: The ability of a blade to hold an edge. Many people make the mistake of thinking wear resistance and edge holding are the same thing. Most assuredly, it is not; or rather, it usually is not. Edge holding is job-specific. That is, edge holding is a function of wear resistance, strength, and toughness. But different jobs require different properties for edge holding. For example, cutting through cardboard (which often has hard embedded impurities), toughness becomes extremely important, because micro-chipping is often the reason for edge degradation. Whittling very hard wood, strength becomes very important for edge-holding, because the primary reason for edge degradation is edge rolling and impaction. Wear resistance becomes more important for edge holding when very abrasive materials, such as carpet, are being cut.
There are other properties that significantly effect how a steel performs:
Ability to take an edge: Some steels just seem to take a much sharper edge than other steels, even if sharpened the exact same way. Finer-grained steels just seem to get scary sharp much more easily than coarse-grained steels, and this can definitely effect performance. Adding a bit of vanadium is an easy way to get a fine-grained steels. In addition, an objective of the forging process is to end up with a finer-grained steel. So both steel choice, and the way that steel is handled, can effect cutting performance.
Manufacturing process: Cleaner, purer steels perform better than dirtier, impure steels. The cleaner steel will often be stronger and tougher, having less inclusions. High quality processes used to manufacture performance steel include the Argon/Oxygen/Decarburization (AOD) process, and for even purer steel, the Vacuum Induction Melting/Vacuum Arc Remelting (VIM/VAR) process, often referred to as double vacuum melting or vacuum re-melting.