I wish I had the metallurgical knowledge of steel that some have. All I can say is that even steels that are the same "hardness" on the Rockwell scale can be very different in ease of sharpening. I found this out the hard way. ATS-34, D2, 154CM, CPM 154, and a few other steels are just hard as heck for me to sharpen on a stone. Even on a belt sander, they heat up fast and take longer to sharpen than 1095. Swamp Rat's SR101 is harder to sharpen than 1095, but man does it ever take an edge. It is still easier for me to sharpen than 154CM. SR77 is fairly easy to sharpen.