The amount of manganese necessary for increasing the hardenability of steel is between 0.9-1.2%, or more, by weight. Not very much really. But for work hardening steels like railroad rail or the others mentioned, it can be as high as 12% or so. Manganese and iron are often found in very close proximity in the ore mines.

Interestingly, the steel analysis project from Josh seemed to indicate very low manganese steels. IMO that is a desirable state as is reduces the chances of the blades being brittle to some degree. The minor alloying elements have very large effects on the outcome. The maker has to account for those in the heat treatment equation.