440 A, B, and C all have identical composition except for Carbon content. A is .65-.75%. B is .75-.95%. C is .95-1.20%.
So C has the best wear resistance, the best HRC potential, and the least toughness. It is not fine blankable.
B is tougher than C but not as tough as A. B should have more wear resistance than A.
420 has .15% Carbon.
420 HC has .46% Carbon. HC stands for High Carbon, which means the Carbon content is high for a 420 series stainless. It can be fine blanked which greatly speeds the production process. It also is a little easier to sharpen than 440C.
In simple steels (without a lot of alloying elements), the low, medium, and high Carbon designations go 1040, 1070, and 1095 where the last two digits describe the Carbon content as .40%, .70%, and .95% respectively. The higher the Carbon, the harder the steel can be made. The lower the hardness, the tougher the steel is. Understand that simple steels are available in many formulations like 1020, 1050, 1080, etc. and that the designation actually represents a range of composition. IE 1080 steel ranges between .75 and .88% in Carbon content.
Simple steels get their wear resistance from their HRC (Hardness Rockwell C scale) which is determined by the crystal structure of the Iron Carbides. Highly alloyed steels get wear resistance from their HRC and their wear resistant inclusions like Chrome Carbide, Vanadium Carbide, Molybdenum Carbide, etc.
This pedant needs a Scotch.