The optimal hardness for a kitchen knife is that of the specific job needed.  If a knife is going to cut only vegetables, a high hardness is desired but if some abuse is required (cutting harder materials/ hitting bones etc) then seeking a lower hardness is wise. Do not forget hardness is only an indicative of how a steel will perform the type of steel and geometry also plays a huge role!

Generally speaking, we could say that:

Harder steels(60+HRC):

• Pros – Holds an edge better, greater edge stability
• Cons – More difficult to hone and sharpen
• Cons – Less tough, prone to chipping/cracking

Softer steels (58-60HRC)

• Pros – Easier to hone and sharpen
• Pros – Tougher, doesn’t chip easily
• Cons – Doesn’t hold the edge for a long time, bad edge stability