420 – The 420 steel is on the lower end of the quality spectrum but still perfectly fine for general use applications.  It has a relatively low carbon content (usually less than 0.5%) which makes for a softer blade and as a result will tend to lose it’s edge quicker than higher end steels.   Blades made from 420 steel will rapidly lose their sharp edge over a relatively short time period.  That said, it’s typically tough with high flexibility and extremely stain resistant  but it is not particularly resistant to wear and tear. As you would expect, knives made from this type of steel are generally low priced, mass produced items.

420HC– Generally considered the king of the 420 steels, 420HC is similar to 420 steel but with increased levels of carbon (HC stands for High Carbon) which makes the steel harder.  Still considered a lower-mid range steel but the more competent manufacturers (e.g. Buck) can really bring out the best in this affordable steel using quality heat treatments.  That results in better edge retention and resistance to corrosion.  In fact, this is one of the most corrosion resistant steels out there, despite it’s low cost.  You’ll find it mostly on budget blades (< $50) and multi-tools.

440A – Very much like 420HC but with slightly more carbon which results in enhanced levels of wear resistance and edge retention but suffers from weaker anti-corrosion properties.

440C – Once considered the high-end in US knife steels, 440C is a good all-round steel that has now been overshadowed by many of the newer super-steels on the block.  This is a stainless steel commonly used on many mass-manufactured pocket knives and represents a solid affordable all-round choice.  It’s reasonably tough and wear resistant but it really excels at stain resistance.  Holds an edge better than it’s 400-series counterpart 420HC but at the expense of some corrosion resistance.  The 440C blades can be sharpened relatively easily.  It has the highest levels of carbon and chromium in this group.