From the Sabatier web site:
"All the SABATIER Diamant knives are made of what could be called “stainless” steel, the X50CrMoV15 (European standard 10088-2, which has no simple equivalence in the United States). This type of steel is very often used in the field of kitchen cutlery and provides a good compromise between the knife's cutting performance and corrosion resistance. Carbon steel knives are reputed to cut better than stainless steel knives and they are easier to sharpen than stainless steel knives. However, carbon steel knives require very meticulous care because they can rust very quickly. A stainless steel knife is far easier to look after and far more hygienic than a carbon steel knife. It is true that it does not rust."