No where really,… just that “hardness” itself is ambiguous and three fold. In metallurgy we generally think of hardness as “indentation hardness”, but mainly because it’s a quick, easy, industrially inexpensive test and simplifies things. However, hardness is not that simple and each type can apply to the art of knifemaking,... Steel exhibits all three, and all three are related… to some degree or another.
... Just thinking material, I guess. Something to ponder.