Grade 2 titanium is an unalloyed, commercially pure grade of titanium. In watches it is the pure alternative to the Grade 5 alloy. It is more hypoallergenic, and its natural colour gives a case a slightly warmer, more industrial look. Citizen has used it more often than Grade 5 since its X-8 Chronometer.
How does it differ from Grade 5?
Grade 5 is an alloy. It contains a significant amount of aluminium and was designed to be easier to machine for aerospace use. Grade 2 is unalloyed. Pure titanium is harder to finish to a high standard than Grade 5. One reason given for choosing it despite this is that pure titanium is more hypoallergenic. The difference also shows on the wrist. The natural colour of pure titanium gives a Grade 2 watch a more industrial look and a slightly warmer tone.
What are its properties?
Grade 2 is stronger than Grade 1, yet it can still be formed cold and fabricated reliably. Heat treatment cannot harden it. Working it cold, by contrast, makes it stronger. Like all titanium, it is light and strong, but an untreated surface scratches easily. Making parts from it needs care. Its shavings and dust can ignite, so there is a real fire risk. Outside watchmaking, the same metal goes into chemical plant equipment, heat exchangers, condensers and desalination equipment.
Where it comes from
Citizen’s X-8 Chronometer of 1970 is described as the first titanium watch ever made. Its case was made of titanium that was 99.6% pure, so very little else was in the metal. Since the X-8, Citizen has used pure Grade 2 titanium more often than the Grade 5 alloy, even though pure titanium is harder to finish well.
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