Yes, the grandparent is probably misattributing annealing of the cutting tool to hardening of the Titanium. Titanium has a very high melting point and very low

Yes, the grandparent is probably misattributing annealing of the cutting tool to hardening of the Titanium. Titanium has a very high melting point and very low heat conductivity (for a metal). Using a hardened steel tool to cut Titanium too fast without sufficient cooling will heat up the tool hot enough to anneal the tool. It appears the Titanium has become harder, but in fact the steel tool has become less hard. Note, I'm talking about cutting rates that you'll achieve by hand or by conventional CNC machine tools. At very high cutting rates, the chip (discarded metal) carries away significant amounts of heat, and in some cases increasing cutting rate actually reduces tool temperature and prolongs tool life. This was an active area of research in the late 1990s.