I like your guess it's Titanium with a coating. Titanium Nitride is the extra hard layer often added to HSS tools like milling cutters and twist drills – TiN. Only a few molecules thick, but the layer multiplies the tool's life.

Your sooper-dooper HSS might be the very best available, but even so it's not in the same league as TiN. Even worse, HSS loses hardness when overheated, which is easily done by rubbing the cutting edge on a surface harder than the tool. As titanium compunds the problems by hardening at red heat, I suspect you're right – you have a Hardened Titanium roller. The description fits this failure mode :

1. HSS blunted after failing to penetrate a very hard surface.
2. Blunt HSS rubs and overheats, thus losing its hardness.
3. Temperature rises to red-heat due to friction, but not enough heat &/or surface exposed to ignite the swarf. Metal removed from work and cutter more by melting rather than cutting. Not good!

Even though it too has limitations, Carbide is much better than HSS against hard surfaces. Carbide has more chance of breaking through a TiN layer than HSS. Also carbide is much less likely to lose its edge when it gets hot than HSS – even at bright red heat. However, flood cooling is advised for a tough job like this. It would protect the tool and, assuming it is Titanium, stop the work hardening due to heat. I don't think machining small quantities of Titanium is a major fire hazard, but flood cooling would fix that risk too. (Titanium experts might know different!)

Often worth scarifying the hard skin found on cast-iron with a grinder. Once the surface is broken up, HSS works well. Might be worth trying the same on your roller – could be a lot softer inside.

Times change – I bet LBSC never had to machine Titanium!

Dave