One source said there are three kinds of Steel: Spring Steel, Tool Steel, and High-Speed Steel.
Another source said there are many types, including: Mild (Low-Carbon) Steel, Carbon steel, Stainless steel (+chromium), Maraging steel (+nickel), Alloy steel (hard), and Tool steel (harder).
Steel is primarily made of carbon and iron atoms. When steel is heated, it expands, and as it expands, the carbon atoms are displaced from their usual spots in the matrix. If heated steel is allowed to cool slowly, the desired hardening is not achieved, as the carbon atoms return to where they were. But by "quenching," or cooling the steel quickly, you can lock the carbon atoms out of place, which makes steel harder.
Forging requires using simple steels, not high-alloy or complex super-steels, so forged blades cannot achieve the same wear retention as super steels. That is because wear rentention is directly tied to the makeup of the steel, not just the heat treat.
Knife blade steel is evaluated according to four criteria: Hardness, toughness, wear retention, and workability. Hardness is resistance to rolling and bending (a rolled or bent edge is no good), toughness is resistance to chipping or breaking (You don't want a blade to snap in half, or an edge to chip), wear-resistance is how well an edge holds its edge while performing routine cutting chores such as slicing, and workability is how easy the steel allows one to shape it and work it. If it's a royal pain in the neck to grind and smooth, it may not be very practical for knifemaking.
Most modern super-steel prioritize toughness, so the blade won't snap in half. But they sacrifice some hardness in the process. Wear resistance depends largely on steel make-up. Heat treating is a very complex science, especially as more alloys or carbides are added to the steel, because each will cause the steel to respond differently to the heat treating.
Proper heat treating is more important for a good knife blade than the steel one starts out with. A low grade steel, well heat-treated, will outperform a high-grade steel, poorly heat-treated.
Busse Combat's proprietary INFI steel, for example, is put through a 80-hour dry, multi-cycle cryogenic heat treat, even though a "regular" heat treat only takes a couple of hours. Such attention to the heat-treating allows INFI steel to outperform much of its competition It is not uncommon for Busse enthusiasts to chop down trees or wood for two hours and find that the edge on their INFI blade is sharper than when they started! Old Japanese swords were also subjected to laborious heat-treating.
