Short version
Grade 1 and grade 2 is unalloyed titanium and by that too soft for knives. For knifeblades only alloyed titanium is hard enough (and in comparison to steel still quite soft).
Long version
I have no HRC-values for unalloyed titanium, but for titanium-alloys:
"beta titanium" has between 44 and 46 HRC, TiAl6V4 (used eg. for framelock-frames) has about 38 HRC
2 examples for beta-titanium:
1. Beta III (UNS R 58030) Ti-11,5Mo-6Zr-4,5Sn ~ 40 HRC
2. Titan Beta 21S (UNS R 58210) Ti-3Al-0,3Fe-15Mo-28Nb-0,2Si ~ 43,6 HRC
If 0.25% Oxigene is added than you get about 46 HRC.
The advantage of titanium is that it doesn't rust, but it's hard to machine & beta titanium is quite expensive. I would only use it for a divers' knife.
Hope that helps.
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