Ti-99.7, or ASTM Grade 3, is the third step up the commercially pure titanium ladder, sitting between the widely used Grade 2 and the highest-strength CP option, Grade 4. It remains fully unalloyed — no deliberate alloying additions — but its allowable oxygen content is raised further than Grade 2's, and higher interstitial oxygen is what drives its higher strength. That's the defining trade-off across the whole CP series: as the permitted oxygen and iron content climbs from Grade 1 through Grade 4, tensile strength rises step by step while ductility and cold formability ease off slightly at each stage.

Grade 3 is chosen specifically for applications that need more strength than Grade 2 can offer but don't require — or can't justify the cost and machining difficulty of — an alloyed titanium grade like Ti-6Al-4V. It sees use in aerospace ducting, cryogenic vessels, and marine and chemical-processing components where a higher strength-to-weight ratio matters. Like every CP grade, it retains titanium's hallmark corrosion resistance, protected by the same thin, self-healing oxide layer that makes unalloyed titanium so effective in seawater and aggressive chemical environments.

Grade 3 is subject to the same underlying machining challenges as every titanium grade. Poor thermal conductivity keeps cutting heat trapped at the tool tip rather than carrying it away in the chip, so tool temperatures rise quickly even at cutting speeds that would barely warm up a steel job. Once hot, titanium becomes chemically reactive with common tool materials, encouraging adhesion, galling, and edge chipping instead of a clean shear.

Its low modulus of elasticity lets the workpiece and thin features deflect under cutting force more than steel would, so rigidity in workholding and tooling is essential to avoid chatter and dimensional drift. Titanium also work-hardens readily anywhere a tool rubs rather than cuts cleanly, which makes maintaining a steady, sufficient feed rate more important than nursing the tool with a lighter cut — a light feed just glazes the surface and shortens tool life on the next pass.

Because Grade 3 carries higher oxygen content and correspondingly higher strength than Grades 1 and 2, it machines slightly harder than those lower grades, calling for somewhat reduced cutting speeds — but it's still noticeably easier to cut than any alpha-beta or beta titanium alloy, since it's single-phase and unalloyed. Sharp, positive-rake tooling, adequate feed, rigid setups, and generous coolant remain the keys to good tool life and finish.