One of the most exotic alloying elements is cobalt, which is known to increase hardness and strength, as well as intensifying the effects of other elements in a particular steel formulation. Typically, N690 is hardened to a factor of Rockwell 58-60. Obviously, the key here is the addition of cobalt in the steel matrix. The cobalt allows the creation of a very uniform structure within the steel.
When used in blade steel, this provides a fine and consistent edge, enhancing edge retention and sharpening receptivity.