Strength comparison
BUMAX delivers the strength of high-tensile carbon fasteners while retaining the corrosion resistance of stainless steel.
| Class | Rp0.2 yield | Rm tensile | Material |
|---|---|---|---|
| A2-70 / A4-70 (ISO 3506) | 450 MPa | 700 MPa | stainless |
| A4-80 (ISO 3506) | 600 MPa | 800 MPa | stainless |
| Carbon steel 8.8 | 640 MPa | 800 MPa | carbon |
| Carbon steel 10.9 | 900 MPa | 1000 MPa | carbon |
| BUMAX 88 | 640 MPa | 800 MPa | stainless |
| BUMAX 109 | 900 MPa | 1000 MPa | stainless |
ISO 3506 and carbon-steel values are standard minimums. BUMAX 109 matches carbon class 10.9 on strength while remaining fully stainless; the duplex BUMAX DX 129 corresponds to class 12.9.
Hydrogen embrittlement
High-strength coated carbon bolts (10.9 and above) can absorb hydrogen during pickling and plating, leading to brittle fracture under tensile stress — sometimes weeks after installation, without warning. Austenitic stainless grades are not susceptible to this. BUMAX therefore offers a direct high-strength alternative without the hydrogen-embrittlement risk of coated carbon fasteners.
Corrosion resistance
Classic A4 (AISI 316) resists general corrosion in chloride environments, but at elevated temperature and under tensile stress it becomes susceptible to stress corrosion cracking. BUMAX duplex (DX) and super-duplex (SDX) grades are considerably more resistant thanks to their two-phase structure — suitable for seawater, offshore and chemical installations.
Traceability (EN 10204)
Every BUMAX production batch is tested on the finished product (not only on the raw bar). A common mistake in the field is to present a 3.1 certificate issued by the steel mill for the raw material as if it certified the finished fastener. BUMAX provides:
- EN 10204 3.1 — certificate issued by the manufacturer, based on tests on the finished product;
- EN 10204 3.2 — certified jointly by the manufacturer and an independent inspection body (usually a requirement in nuclear, defence and marine applications).