I've heard this over and over again: "High Carbon steel is easier to sharpen than SS"
WHY??
Doesn't it really depend on edge geometry and Rockwell hardness?
Personally I think that although there
might be truth to this statement, it really depends on too many variables for it to be considered a general truth. In my opinion an individual's sharpening skills and equipment have much more to do with the "ease" of sharpening than anything else.
Carbon steels are generally used on big "chopper" knives and are run at lower hardnesses--by and large they tend to roll rather than chip. Other times carbon steels are used in knife applications where thinness and slicing ability are the most desireable attributes--when run at HRC values of 62+ they can chip just as readily as other, less tough, stainless steels. In general, carbon steels are tougher and less likely to chip than stainless steels.
If you do a search of the forums you will find a lot of posts with people complaining that they can't get their ESEE (or insert other reputable, high quality knife manufacturer) sharp, despite the knife being made of carbon steel. In many cases, their sharpening skill is fairly rudimentary, and they aren't taking into account the obtuse bevels than are put on their knives. In some other cases you might run into posts with people talking about how easy their Spyderco (or insert other reputable, high quality knife manufacturer) is to sharpen despite being made out of a high quality stainless steel, yet once again this is their first time sharpening a knife with properly acute bevels for the angles that they are sharpening at.
Like parbajtor said, diamond stones seem to ignore the differences between steels--if you have trouble sharpening with your current system(s) you might want to take a look at giving diamond stones a try.
After all of that above, I will say that I have noticed a difference in ease of sharpenability between some steels. High alloy (especially vanadium) content steels seem to take longer to sharpen (e.g. they require more strokes on the stone to get the same effect) than lower alloy steels (which most carbon steels are). On the other hand, I've sharpened some stainless steels (like Buck's 420HC, and the 420J that some knife companies use) that seemed like hard plastic in comparison to higher end stainless steels.
Just because a steel is stainless doesn't necessarily mean it isn't a high carbon steel--in fact many of the high quality stainless steels have
higher carbon contents than "high carbon" non-stainless steels. All "high carbon" means is that the steel has a greater than 0.50% carbon content. With traditional smelting techniques (which the great majority of carbon steels use) carbon content can't really go much above 1.50%. In comparison some of the really crazy high alloy steels (made with powder/particle metallurgy techniques) have contents 2-4 times higher than a "high carbon" low alloy carbon steel. ZDP-189, for example, has a 3.00% carbon content.
