There are a multitude of different types of knife steels on the market and trying to keep them straight can drive you nuts. Here is a fast reference to the most common types of knife steels.
154CM knife steel: This is a high carbon steel with 1.05% carbon. It also contains about 14% chromium. Many people consider 154CM knife steel to be “super steel”, if you find the older stock. 154CM is not a standard grade designation, rather a manufacturers trade name. 154CM steel is similar to 440 C. 154CM steel has fair corrosion resistance and a very good edge holding ability, especially on knives for heavy cutting.
420 knife steel: 420 knife steel has less than ½ % carbon content which makes this a very soft steel. 420 steel does not hold an edge very well. This 420 steel is often used in the production of diving knives as it is very stain resistant. 420 knife steel is also used in the production of inexpensive knives. Other than for the manufacture of diving knives 420 steel is too soft to be used for the blade on a good utility knife.
420HC knife steel: 420HC steel is a higher carbon version of the 420 steel. 420HC steel has .4 to .5% carbon and about 13% chromium. This is a lesser quality steel but when it is properly treated like Buck Knives does it produces a good general purpose knife steel with good corrosion resistance and edge holding ability.
440 knife steel: 440 knife steel is considered stainless steel and has three grades. 440 A has a carbon content of .75%. 440 B has a carbon content of .9% while 440 C has a carbon content of 1.2%. 440 C is the least rust resistant of these three knife steels but it is also considered an excellent steel for stainless steel knives. 440 A knife steel is the most rust resistant. If your knife is marked 440 it is probably 440 A steel. With good heat treatment it is acceptable for everyday use. 440 B steel is better and 440 C steel is the best of the three.
425M knife steel: 425 M is similar to 440 A.
ATS-34 knife steel: Japanese stainless steel that is considered to be the equal of 154CM steel.
AUS knife steel: Like 440 knife steel AUS steel comes in three grades. AUS-6, AUS-8 and AUS-10. This steel is Japanese stainless steel and is comparable to 440 knife steel. AUS -10 is comparable to 440 C. AUS -10 has a little less chromium than 440 C so it should be a little less rust resistant but tougher. AUS knife steel has vanadium that the 440 steel doesn't which improves the wear.
D-2 knife steel: This is sometimes called “semi-stainless”. Is has a chromium content of 12%. There is no hard and fast rule for the amount of chromium required to make knife steel “stainless steel”. The accepted standard in the cutlery industry for steel to be “stainless steel” is 13%, but other reference books cite various numbers including 10%. D-2 knife steel is excellent for holding an edge but may not be as tough as some carbon steel.
H1 Knife Steel: This is relatively new steel from Japan is a breakthrough in corrosion resistance. H1 steel is a PH steel meaning it is a precipitation-hardened steel. It's naturally hard without heat-treating. One of the most common misconceptions is that H1 steel has no Carbon and uses Nitrogen instead. By definition, steel is a commercial iron that contains carbon in any amount up to about 1.7% as an essential ingredient. H1 steel is another "nitrogen added" steel like CPM-S30V, X15Tn and Infi. In "Q-Fog" testing, H-1 did much better than even 440C steel and ranked with Cobalt based materials. There was no rust. Edge testing indicates cutting ability comparable to AUS-6 / AUS-8.
VG-10 Knife Steel: Here is another relatively new knife steel from Japan. The Spyderco Knife Company seems to have been one of the first companies to have brought this steel to the U.S. market. VG-10 is similar to several other high-end stainless steels but has the additional element cobalt, which is supposed to enhance the qualities of some of the other alloying elements. VG-10 steel has good edge retention and corrosion resistance but doesn't measure up in the area of scratch resistance. It has better toughness (ability to withstand lateral stress) than some of the other steels. It has a little less edge retention than the harder and more brittle steels like 154CM but lends itself to things like prying that would be riskier with harder, more brittle steel. So it makes a great corrosion resistant steel for things like a camp knife or hunting knife.
S30V knife steel: This steel was developed primarily for the cutlery industry. S30V knife steel contains very high amounts of carbon and Vanadium. This gives the steel good corrosion resistance and a superior edge holding ability. Some feel that S30V is the best knife steel for blades available today.
Hopefully this knife steel guide will help you select the pocket knife that is just right for what your need and the conditions you will use it in.