Grade 7 exists for one reason, and it is a good one. In a tight, oxygen-starved crevice — under a gasket, inside a threaded joint, beneath a deposit — commercially pure titanium cannot repassivate and will eventually suffer crevice attack in hot chloride service above roughly 70 to 80°C. The 0.12 to 0.25% palladium addition changes the cathodic behaviour of the surface so that repassivation occurs even under those conditions, which extends useful service into hot brines, wet-process acid plant and reducing acid chloride environments where Grade 2 would fail.
Because a bolted joint is by its nature a collection of crevices, this benefit matters more for fasteners than for almost any other product form. Grade 7 is mechanically identical to Grade 2 — same 345 MPa minimum tensile, same 20% elongation — so specifying it costs nothing in strength or formability; the premium is purely the palladium. Where the cost of palladium is the obstacle, Grade 12 delivers much of the same crevice benefit through molybdenum and nickel instead, and is stronger into the bargain.
Three absolute exclusions. Titanium must not be used in dry chlorine, with which it reacts violently; it must not be used with red fuming nitric acid; and it is rapidly attacked by hydrofluoric acid at any concentration. Fine titanium swarf and grinding dust are also a genuine fire hazard and must be handled wet and stored separately. These limits apply to every grade on this page, including the palladium and molybdenum-nickel modified grades — the alloying additions improve crevice and reducing-acid performance, they do not change these exclusions.
Titanium galls, and for a threaded fastener this is the single most important practical fact about the material. Titanium’s protective oxide is thin and the metal beneath it is adhesive, so a titanium thread run against another titanium thread will cold-weld and seize — often badly enough that the fastener has to be cut off. Every titanium bolted joint needs one of three mitigations: an anti-seize compound or dry-film lubricant such as molybdenum disulphide on the thread; a plated or coated thread, commonly silver or a solid-film lubricant; or a nut in a dissimilar material rather than titanium. Exotic Alloy supplies titanium fasteners with a lubricant or coating specified at order stage, and will advise on the combination if you tell us the mating material.
Titanium is galvanically noble, which makes it a hazard to what it is bolted into. It sits close to the passive stainless steels and the nickel alloys on the galvanic series and well above carbon steel, aluminium, zinc and magnesium. A titanium fastener in an aluminium or carbon steel structure will not itself corrode, but it will drive accelerated corrosion of the structure around it, and the small-anode-large-cathode geometry of a bolted joint is the worst case. Where titanium fasteners are used in a less noble assembly, an insulating washer and sleeve or a barrier coating on the mating faces should be specified.
Note on section size: the ASTM B348 tensile requirements apply to longitudinal sections up to 76 mm (3 in.) thick with a maximum area of 64.5 cm² (10 in.²). Mechanical properties for larger sections are negotiated between manufacturer and purchaser, so for large-diameter bolting the acceptance values must be agreed on the order rather than assumed from the table.
