Zirconium's distinguishing feature is that it resists acids and alkalis alike. Most corrosion-resistant metals are good on one side of the pH scale — tantalum is outstanding in acid and destroyed by caustic; most stainless and nickel alloys struggle in reducing acid. Zirconium handles hydrochloric acid at every concentration to 225 °C, nitric acid to 260 °C, sulfuric acid to 75% at ambient, caustic soda to 50%, and essentially all the organic acids. It is also 19% lighter than stainless steel, conducts heat over 30% better and expands about a third as much, which is why it dominates aggressive-duty heat exchangers. The five ASTM B551 grades divide on two axes: alloy addition (none, tin, or niobium) and oxygen content, which controls strength and formability. Exotic Alloy manufactures zirconium fasteners from material certified to ASTM B550 and B551.
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Hydrofluoric acid and trace fluoride. HF attacks zirconium at any concentration, even at room temperature. As with tantalum the real hazard is trace contamination rather than deliberate HF: ATI's data show 90% nitric acid, a duty zirconium normally handles at under 1 mpy, jumping to over 50 mpy with just 200 ppm of HF present. Oxidising chloride salts are the second exclusion and the one that catches people out — ferric chloride and cupric chloride attack zirconium at over 50 mpy at all concentrations from room temperature to boiling. Aqua regia attacks it. So does sulfuric acid above roughly 70%, where the transition is sharp and temperature-sensitive, and phosphoric acid above about 55% hot.
The wet-versus-dry chlorine behaviour is the inverse of titanium's, and the two are routinely confused. Zirconium handles dry chlorine gas at under 5 mpy but is destroyed by wet chlorine — chlorine gas with more than 0.13% water, or chlorine-saturated water — at over 50 mpy. Titanium is exactly the opposite: it needs moisture to maintain its oxide and reacts violently with dry chlorine. Substituting one for the other in chlorine service on the assumption that both are "corrosion-resistant reactive metals" is a serious error.
Stress-corrosion cracking can occur where the corrosion rate looks perfectly safe, and a tightened fastener supplies exactly the sustained tensile stress SCC needs. Watch ferric and cupric chloride; concentrated nitric acid above about 70%, where ATI's own data record SCC observed while the general rate stays under 1 mpy; methanol-halide mixtures; and hydrochloric acid carrying ferric chloride, where 100 ppm FeCl₃ in 10% HCl produced SCC at a general rate still below 1 mpy. A corrosion-rate chart alone is not sufficient to qualify zirconium for a duty, and residual stress from forming and welding should be removed by a stress-relief anneal at 565 °C.
Hydrogen embrittlement, galvanic coupling and galling. Zirconium absorbs hydrogen and precipitates brittle hydride platelets, and it does not need to be corroding to do so — it only needs to be cathodic. A zirconium bolt clamping a carbon steel or stainless flange in acid is precisely that configuration. Use electrical isolation with non-conducting gaskets, sleeves and washers, anodic protection, or an oxidising addition to the stream. Zirconium also galls like titanium, so every threaded joint needs an anti-seize or dry-film lubricant, a thickened oxide film produced by heat treatment, or a nut in a dissimilar material.
Zirconium fines are pyrophoric. Turnings, grinding dust and powder ignite readily in air, sometimes spontaneously, and burn at very high temperature. A zirconium fire must not be fought with water, which decomposes and feeds it, nor with CO₂ or halogenated agents — only a Class D agent. Exotic Alloy machines and grinds zirconium under heavy flood coolant with swarf collected wet and stored separately. The bulk metal in a finished fastener presents no fire risk at all; the hazard is entirely in the fines generated making it.
No ASTM fastener specification exists for zirconium, and product-form availability is not uniform across the grades. F468 and F467 cover copper, nickel, aluminium and titanium alloys — not zirconium. Fasteners are made from material certified to B550 (bar and wire), B551 (strip, sheet and plate), B523 (tube), B658 (pipe) or B493 (forgings), with thread conformance to the applicable ASME or ISO standard. Critically, B550 covers only R60702, R60704 and R60705 — R60700 and R60706 are flat-product grades only — and only R60702 and R60705 are ASME code-listed. Tell us the service and we will confirm form availability before you commit a drawing to a grade.
Three things govern zirconium fabrication. It machines like austenitic stainless — gummy, work hardening ahead of the tool, prone to gall and smear — so sharp positive-rake tooling, rigid setups, slower speeds with a positive feed and heavy flood coolant are all necessary. Wrought zirconium is strongly anisotropic, because the alpha phase is hexagonal close-packed with only one predominant slip system: strength, elongation, bend ductility and even thermal expansion vary with direction, so forming and test orientation must be specified rather than assumed. And ductility rises sharply with temperature — elongation in Zr 702 goes from about 29% at room temperature to 49% at 204 °C while yield strength more than halves — so warm forming around 200 °C transforms what is achievable on severe work. Threads are rolled rather than cut wherever section permits.
All values are ASTM B551/B551M Table 1 and Table 3 requirements for annealed strip, sheet and plate.
| Grade | Addition | O max | Tensile | Yield | Elong. min | Bend Radius | Forms & ASME |
|---|---|---|---|---|---|---|---|
| R60700 | None — low oxygen | 0.10% | 380 MPa max | 305 MPa max | 20% | 5T | B551 only; not ASME |
| R60702 | None — unalloyed | 0.16% | 380 MPa min | 205 MPa min | 16% | 5T | All forms; ASME listed |
| R60704 | 1.0–2.0% Sn | 0.18% | 415 MPa min | 240 MPa min | 14% | 5T | Bar & flat; not ASME |
| R60705 | 2.0–3.0% Nb | 0.18% | 550 MPa min | 380 MPa min | 16% | 3T | All forms; ASME listed |
| R60706 | 2.0–3.0% Nb | 0.16% | 510 MPa min | 345 MPa min | 14% | 2.5T | B551 only; not ASME |
Note the strength column carefully. R60700 is the only grade in ASTM B551 specified by maximum tensile and yield rather than minimum — the standard sets no lower bound on its strength at all. You buy R60700 to guarantee the metal is soft, for deep drawing, spinning and clad-plate bonding; the other four are specified as minimums in the normal way. Note also that R60706 has the tightest bend radius in the standard at 2.5T but a lower minimum elongation than R60705 (14% against 16%) — the two formability measures do not move together, and it is the bend test that distinguishes that grade. All five permit up to 4.5% hafnium, which occurs with zirconium in nature and does not significantly affect physical, mechanical or corrosion properties; zirconium content is specified as a combined Zr + Hf minimum. None of these is a nuclear grade — reactor service requires hafnium removed to around 0.010% under separate specifications, because hafnium's thermal neutron absorption cross-section is roughly 600 times zirconium's.
We are committed to delivering zero-defect zirconium fasteners. All products undergo rigorous testing including PMI (Positive Material Identification), interstitial analysis for hydrogen, oxygen, nitrogen and carbon against the ASTM limits, bend testing to the grade's specified radius, dimensional inspection and material traceability with EN 10204 3.1 certification. Oxide film enhancement and stress-relief treatment to 565 °C are available at order stage.
Exotic Alloy exports zirconium fasteners and machined components to chemical processing, acetic acid, urea, pulp and paper bleaching, pharmaceutical and heat exchanger clients worldwide. Our dedicated logistics team ensures secure export packaging and timely deliveries by sea and air freight with full customs documentation support.