An excellent air hardening tool steel used by handmade knife makers and by speciality makers like Bark River as well. First maker I know of using it was Harry Morseth in the early 1930s. Performs best at about 60-61 Rc (see hardness). For many years my favorite as well as Ron Lake's. It contains about 1% Carbon, 1% Molybdenum, and 5% Chromium.