BUMAX Duplex Stainless Steel Fasteners: Data Sheet

Key things to remember

The essentials from this document in plain words. Check the full document before you rely on a figure.

• ✓Duplex stainless has a roughly 50/50 mix of ferrite and austenite. That gives high strength, good elongation, strong fatigue resistance and about 25% lower thermal expansion than austenitic stainless.
• ✓Four grades by PRE: Lean Duplex LDX 26 (about the corrosion resistance of A4, used for bridges, wind turbines and storage tanks), Duplex DX 36, Super Duplex SDX 42 and Hyper Duplex HDX 49.
• ✓Strength: class 10.9 (1,000 MPa tensile, 900 MPa yield) in LDX from M8 to M30, and DX and SDX from M3 to M30; class 12.9 (1,200 MPa, 1,080 MPa) on request; HDX class 12.9 from M3 to M8.
• ✓All BUMAX Duplex fasteners are thread rolled. The sheet says machined Duplex fasteners cannot go above class 8.8, and that temperatures above 600°C in hot forging can harm Super and Hyper Duplex.
• ✓Corrosion guide: in saltwater, A4 and LDX show a possible risk while DX, SDX and HDX show no risk. HDX shows no risk in every acid condition listed, including 3% hydrochloric acid at 50°C.
• ✓Fatigue test on M6 x 50 bolts pre-stressed to 400 MPa, stopped at 10 million cycles: BUMAX DX reached the limit in every test up to ±80 MPa, BUMAX 88 up to ±55 MPa, while A4-80 failed at 0.3 to 0.5 million cycles at ±60 MPa.
• ✓Coated with a wax for low friction and less risk of galling. SDX class 10.9 is the regular range; LDX, DX and HDX are made on request (HDX up to M8).

Who it helps: Engineers specifying high strength stainless fasteners for offshore, chemical, pulp and paper or large structural projects.