Often referred to as Yasugi #1 Blue Steel, this is a great knife makers steel. It is hard, rusts more slowly than white steel, is capable of an outstanding mirror finish, and provides a long-lived edge. What more could you want? This is high-performance steel.
Special care must be taken with carbon knives as they are reactive and prone to rust. Make sure to wipe off the blade regularly during use as well as wash and dry it thoroughly when you're done. However, after a nice strong patina has formed on the blade they are less likely to rust. Patina is your friend!