Stainless steels are steel alloys that contain a large amount (+12%) of chromium. Chromium prevents the steel from rusting but significantly degrades edge holding capabilities of the steel. All steels are composed of grains of the various alloying elements, the relatively large size of chromium results in a blade that will quickly dull and be very difficult to re-sharpen.
52100 steel forms a blade composed of very small grains, enabling it to take a much finer edge, hold it longer, and then re-sharpen very quickly. In addition, the fine grain structure of 52100 makes it tougher than many other steels used in knives. The weakest points of any steel structure are the bonds between the grains, a finer grain structure means that stress it spread across many more of these bonds than in steels containing larger alloying elements such as chromium.