Q: I’m working on a project that is using Titanium bolts for our equipment and we are considering a few different sizes and grade bolts; we are considering Gr.2, Gr.5, Gr.7 and Gr.12. What would you typically specify as the maximum tensile allowable (i.e. 2/3*yield) and the maximum shear allowable (i.e. 0.4*yield)? If so, could you please provide information on the yield strength and allowables for the various grade bolts at 100°C and 235°C?
A: First off regarding the grades, the biggest determination in the grade of Titanium you need is the corrosive environment and the strength.
- From a corrosion point of view, Titanium grade 2 and 5 screws would be on the lower end of the corrosion resistance, improving with Grade 12 and Grade 7 being the best as it has an addition of palladium.
- From a strength point of view Titanium grade 5 bolts would be the strongest followed by Grade 12 and weakest being TI2 / TI7.
- From a cost point of view, Titanium grade 2 bolts are the most economical followed by Gr5, 12 and 7. I don’t know the exact ratios of the materials but TI5 is generally 30% more expensive than Gr2. Grade 7 will be at least 2x Grade 2. Not sure about 12 as its not that common for fasteners.
- Regarding the mechanical properties, I have attached a chart from the ASTM B348 spec (Ignore the yellow highlight). This will give you the room temperature properties. Also for the strength at temperature I have attached a brochure that will show the strength vs temperature of each allow (starting on page 16). From these charts you could calculate the maximum mechanical properties at temperature.Hope this helps.