Reference
Why Titanium Fasteners
What actually changes when a steel or stainless fastener is replaced with Grade 5 titanium.
Material
The Four Reasons
Weight
Titanium has a density of about 4.43 g/cm³ against about 7.85 g/cm³ for steel. Swapping a steel fastener for the same size in Ti-6Al-4V removes roughly 44 percent of the mass of that fastener.
Strength
ASTM Grade 5 is specified with a minimum tensile strength of 895 MPa and a minimum yield strength of 828 MPa, so the strength is in the range of a medium strength alloy steel rather than of aluminium.
Corrosion
Titanium carries a stable oxide film that re-forms as soon as it is damaged in air or water. It resists seawater and chloride environments that pit and crevice corrode common stainless grades.
Non magnetic
Titanium and its alloys are non magnetic, which matters around sensors, imaging equipment and magnetically sensitive instruments.
Comparison
Titanium Against Steel And Stainless
| Property | Ti-6Al-4V Gr.5 | Carbon and alloy steel | Austenitic stainless |
|---|---|---|---|
| Density | About 4.43 g/cm³ | About 7.85 g/cm³ | About 7.9 to 8.0 g/cm³ |
| Minimum tensile strength | 895 MPa per ASTM B348 | Depends on grade and heat treatment | Typically well below Gr.5 titanium in the annealed condition |
| Chloride resistance | Stable passive oxide film | Corrodes without a coating | Prone to pitting and crevice attack |
| Magnetic response | Non magnetic | Magnetic | Largely non magnetic when fully austenitic |
| Galling tendency | High, anti seize needed | Low | High, anti seize needed |
Steel and stainless figures vary by grade and condition, so they are given as ranges and behaviours rather than as single values. Titanium figures are the published values for Ti-6Al-4V and for ASTM B348.
Trade Offs
What Titanium Costs You
A titanium fastener is not a drop in replacement in every respect and it is worth being clear about that before a conversion.
- It galls readily against titanium and against stainless, so an anti seize is not optional if the joint has to be broken again
- A steel torque figure cannot be carried over, so the assembly procedure has to be reworked for the alloy and for the lubricant actually used
- The modulus is about half that of steel at roughly 114 GPa, so for the same clamp load the fastener stretches further, which changes how the joint holds preload
- It is a noble metal, so galvanic pairings with aluminium and magnesium have to be planned rather than discovered
- It costs more per piece than a steel or stainless fastener of the same size
Use Guide
Fitting Titanium Fasteners
Use anti seize on the threads
Titanium galls readily against titanium and against stainless. A dry film or copper free anti seize on the thread and under the head keeps the torque to tension relationship predictable and lets the joint be broken later.
Torque to a titanium figure not a steel figure
Do not carry over a torque value from a steel or stainless fastener of the same size. The friction behaviour is different and the safe clamp load has to be set for the alloy and for the lubricant actually used.
Seat the drive fully before applying load
Push the Torx key or the socket right to the bottom of the recess before turning. A partly seated drive concentrates load on the top edge of the recess.
Watch galvanic pairings
Titanium is a noble metal. Where it is bolted directly to aluminium or magnesium in a wet environment, isolate the joint or accept that the lighter metal will carry the corrosion.
Keep the bearing face clean and flat
A wide flange or saucer face only works if it lands on a flat clean surface. Swarf or paint under the head shifts the clamp load off centre.
FAQ
Frequently Asked Questions
How much lighter is titanium than steel
Is Grade 5 titanium as strong as steel
Why does titanium gall
Can I use the same torque as the steel fastener it replaces
Does titanium rust
Ask Us About Your Application
Send the joint the duty and the environment. We will tell you which grade and which size suits it and quote against that.
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