HAP40 is an extremely hard (often HRC65) powder semi-stainless steel by Hitachi Metals in Japan. It holds an edge for an extremely long time and will develop a patina with use. It has enough chromium content to ward off rust spots if left wet for short periods, but best to be kept dry after use. It can be tricky to sharpen without a coarse stone of around 500 grit to get the burr moving.

Store it in a dry environment using magnetic strips, knife rolls, or sayas. Avoid hitting hard or frozen objects and twisting the blade while cutting. These knives are not dishwasher safe. Clean with hot water and a soft cloth, and dry immediately after use to prevent rust spots on the high carbon steel. For more information please read the blog below.