1095, W1, W2, Hitachi Yellow (Shigami): These steels are all similar, essentially 1.00% C and iron, with the minimum of manganese for hardenability and (hopefully) trace impurity. W2 has .2% vanadium added for grain refinement. These steels can be heat treated very hard, and respond very well to various thermal cycles because they are very simple. They have low wear resistance compared to many other steels, only surpassing steels used by forgers for high toughness like 5160 or 1075. Toughness is moderate and edge stability is very high.
Hitachi White (Shirogami) steel: Similar to 1095 and W1 but with even more carbon (1.45%), this steel gets very hard and has a moderate amount of small iron carbides. Higher wear resistance than 1095 or W1 but does not have great wear resistance. Has fairly poor toughness but very good edge stability.
Hitachi Blue (Aogami) #1 and #2: The major downfall of simple carbon steels is their comparatively low wear resistance because of the lower hardness of iron carbide. These steels have high tungsten to form the much harder tungsten carbides for wear resistance. They still have good edge stability because the tungsten carbides are still easily broken up in forging. Blue #1 and #2 have greater wear resistance than any of the previous steels as well as still having good toughness and edge stability. When two steels have the same carbide size and volume but the one steel has harder carbides, the steels will have similar toughness and edge stability but the one with harder carbides will have greater wear resistance. These harder carbides do make the steel somewhat more difficult to sharpen. Blue #1 and #2 are good general purpose steels because they have greater wear resistance than most other simple carbon steels while still having the high edge stability and toughness of most carbon steels. Blue #1 and #2 have less carbon, tungsten, and extra alloy than Blue Super, though in varying amounts, Blue #1 is more wear resistant and less tough than Blue #2.
Hitachi Blue (Aogami) Super: White steel modified with some alloy for greater hardenability and high tungsten for harder carbides. The highest in wear resistance of any of the simple carbon steels generally used in kitchen knives, and also the lowest in toughness. Does have good edge stability because the carbides are little bigger than those in other steels, but is a little bit lower because they are a little bit larger and in a greater volume. Still has much better edge stability than large carbide stainless steels. This steel has one of the highest combinations of wear resistance and edge stability, properties that are generally opposed to each other, which means it is suitable for a variety of cutting tasks or types of knives. Its main disadvantages are low toughness and of course no corrosion resistance.
