A4-70 vs BUMAX 88 in Ammonium Nitrate: Stainless Fastener Comparison

Key things to remember

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

• ✓Both are molybdenum-bearing austenitic stainless steels. BUMAX 88 has more molybdenum (typical 2.7% against 2.1%) and less carbon (0.02% against 0.04%).
• ✓Average PRE: BUMAX 88 26.2 (range 24.7 to 28.4), 316 A4-70 23.7 (range 23.1 to 24.7).
• ✓Minimum strength: BUMAX 88 800 MPa tensile and 640 MPa yield; A4-70 700 MPa and 450 MPa. Typical BUMAX 88 values, averaged over more than 4,000 batches: 950 MPa tensile, 856 MPa yield.
• ✓The sheet's preload comparison uses 80% of yield for BUMAX 88 (512 MPa) and 65% for A4-70 (292 MPa).
• ✓Chemical resistance chart (ambient temperature, a general guide only): for ammonium nitrate BUMAX 88 rates A (no effect), 316 and 304 stainless B (minor effect) and 302 C. In sulphuric acid up to 10%, BUMAX 88 rates A and 316 C.
• ✓BUMAX 88 is stated to resist crevice, stress and intergranular corrosion better than 316, and to be up to 8 times better against corrosion in a Sandvik test in 10% sulphuric acid.
• ✓The higher strength can allow a smaller size or fewer fasteners, according to the sheet.

Who it helps: Engineers and maintenance buyers choosing stainless fasteners for fertiliser, mining or chemical sites with ammonium nitrate.