Hobson data sheet
BUMAX Grades and Properties Data Sheet: Composition, Strength and Corrosion
A four-page data sheet from BUMAX, distributed by Hobson, comparing every BUMAX stainless fastener grade. It covers chemical composition and PRE, mechanical properties, behaviour at high and low temperatures, physical properties, a corrosion resistance chart and preload guidance.
What this covers
- Grade descriptions
- Chemical composition and PRE
- Mechanical properties
- Low and high temperatures
- Physical properties
- Corrosion resistance
- Preload and tightening
Applies to Threaded Rod (Allthread), Hex Bolts & Set Screws, Machine Screw, Hex Flange Nut, Hex Nut, All-Metal Prevailing Torque Nut, Socket Head Cap Screw, Socket Countersunk Screw, Flat Washer and Mudguard / Penny Washer.
Key things to remember
The essentials from this document in plain words. Check the full document before you rely on a figure.
- Pitting resistance (PRE) by grade: BUMAX 88 and 109 27, Nitro 35, SA 43, LDX 26, DX 36, SDX 42, HDX 49, Ultra 25. A higher PRE means better pitting corrosion resistance.
- BUMAX 88 (M3 to M36): 800 MPa minimum tensile, 640 MPa minimum yield. BUMAX 109: 1,000 MPa tensile, with 900 MPa yield from M3 to M12 and 800 MPa above M12.
- The Duplex grades LDX, DX and SDX come in class 88, 109 and 129 up to M42 (HDX up to M8); class 129 is 1,200 MPa tensile and 1,080 MPa yield. BUMAX Ultra reaches class 169 (1,600 MPa) up to M16. The table values are typical and can vary with size and design.
- Corrosion chart, BUMAX 88 and 109: no corrosion expected in severe urban or mild marine conditions, a possible risk in severe marine (salt water) conditions, and not suitable in hydrochloric acid at 1% and above at 50°C.
- Hyper Duplex (HDX) shows no corrosion in every condition in the chart. Super Duplex (SDX) only fails in 3% hydrochloric acid at 50°C.
- Magnetic permeability: the austenitic grades (88, 109, Nitro, SA, HE, HEP) read 1.001 to 1.007, close to non-magnetic; the Duplex grades read 100 and Ultra 1000.
- Yield strength drops at high temperature; HE and HEP are the grades built for heat. The sheet gives no torque figures: BUMAX recommendations target a preload of about 65 to 70% of yield load with a friction coefficient of 0.14 to 0.16, which the sheet says needs a burr-free surface and high quality lubrication.
Who it helps: Engineers and buyers comparing stainless fastener grades for strength, corrosion, temperature or magnetic requirements.
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