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I think you have hit the nail on the head there :chapeau

Precisely, the skill is with the smith and not the metal. The traditional Japanese smiths are without question probably the best in the world. Their Tamahagane steel however is not.

The "extensive...

I'm no razor making expert but I'd have to agree with jimmyHAD, barring full wedges I think a 65HRC hollow ground blade would just chip/break.

There must be a reason why manufacturers don't temper...