"maybe at 60 RC a knife has high strength and pretty low toughness... but at 58 RC the strength is slightly compromised, while toughness is now way better."
yes, that is how the 3 properties are related (mostly). The following are also true:
As hardness and/or strength increases - toughness decreases As toughness increases - hardness/strength decreases
It is not true however that as hardness increases so does strength - glass, ceramic and diamonds are all harder than steel - not necessarily stronger.
