10XX series Carbon Steels are a general "Plain Carbon Steel". Knife blades are generally produced from Carbon Steel in the range between 1045 to 1095. 1095 probably the most popular and 1050 often used for sword blades. The higher the number the more carbon content. The more carbon the harder the blade. 1090 Carbon Steel would not be my first choice for a diving knife but it is easy to sharpen and holds an edge. Corrosion would be an issue so regular cleaning and oil treatment would help.