Stainless Steel A4-80 (316) Fasteners | PREN 24–26 for Coastal and Chemical Service
A4-80 is made from austenitic stainless 316 / 316L (16Cr-10Ni-2–3Mo), and the molybdenum gives it clearly better pitting resistance than 304: PREN rises from 18–20 to 24–26, about 35% higher, which in practice moves the corrosion safety envelope by a whole environment class. Coastal, salt-spray, de-icing-salt, chemical and marine projects should go straight to A4-80 — this is why the legacy material table assigns 316 to marine and high-corrosion service. The price is a higher raw-material cost than 304, and the strength remains mid-range; 316 cannot reach class 10.9.
Properties & Specifications
| Property Class | A4-80 per GB/T 3098.6 / ISO 3506 |
| Tensile Strength | 800 MPa (nominal, from the A4-80 class designation) |
| Base Material | Austenitic stainless 316 / 316L, 16Cr-10Ni with 2–3% Mo |
| Pitting Resistance Equivalent (PREN) | ≈ 24 – 26 (about 35% above 304) |
| Corrosion Envelope | Excellent against chlorides: seawater spray, de-icing salt, chemical atmospheres |
| Finish | Solution treated and passivated |
| Strength Ceiling | Cannot reach class 10.9 — use Delta-Tone carbon steel when both are required |
| Relative Cost | High (above 304, above coated carbon steel) |
Material Advantages
The 2–3% molybdenum buys real chloride resistance — a head start 304 cannot recover through surface treatment
A genuine service-life difference at the coast and in plant: 304 pits through in chloride service while 316 moves the margin by a whole environment class
Coating-free, so no coating breach over life and a stable appearance — valued in food, pharmaceutical and marine equipment
Good toughness and low-temperature behaviour, without the delayed-fracture sensitivity of high-strength alloy steel
Available with matching A4 nuts and washers, avoiding the galvanic couple created by mixed materials
Applications
Coastal and island works — guard rails, facades, solar mounts, marine hardware
Shipbuilding and offshore equipment
Chemical and pharmaceutical plant — chlorinated pipe racks, reactor accessories
Swimming pools and water treatment facilities
Road and bridge accessories exposed to de-icing salt
Wash-down zones on food and dairy lines (CIP duty)
Grade Selection
| Class / Grade | Service temperature | Notes |
|---|---|---|
| A4-70 | 同 A4-80 | A lower-strength 316 class listed in the legacy table; confirm against ISO 3506 |
| A4-80 | 含氯水高温工况需按介质评估 | The workhorse 316 class at the 800 MPa level; first choice for coastal and chemical duty |
| A2-70 | 氯离子环境会点蚀 | 304 — the cheaper route inland and indoors; not for the coast |
| 2205 | > 60°C 含氯水环境的升级方案 | Duplex 22Cr-5Ni-3Mo-N, PREN 33–35, special order |
Frequently Asked Questions
304 has no molybdenum and a PREN of about 18–20, so it pits through in chloride service such as seawater, salt spray and de-icing salt. 316 carries 2–3% Mo with PREN around 24–26, roughly 35% better pitting resistance. In engineering terms the two are a whole environment class apart, so coastal work must use 316 — ideally with periodic fresh-water rinsing.
Choose Delta-Tone coated carbon steel. 316 cannot reach class 10.9 (A4-80 tops out around the 800 MPa level), whereas Delta-Tone gives 500–1000 h+ salt spray with no electroplating hydrogen. That is why it is the stated default for corrosion-protected high-strength bolts.
Not recommended. Dissimilar stainless in damp chloride service creates a galvanic couple, and the mismatched class and corrosion envelope create inspection ambiguity. Matching A4 nuts and washers from the same batch is our default for export projects.
Right for coastal works, salt spray, de-icing salt, chemical and marine plant, swimming pools and food-line wash-down zones. Watch the austenitic failure mode: in chlorinated water above 60°C there is still a stress-corrosion cracking risk, so assess by medium concentration and move to duplex 2205 or a nickel alloy, optionally with a coating barrier.
Get Grade Selection & Quotation
Submit your duty parameters (temperature, pressure, media, speed) — engineers reply with grade selection and quotation within 24 hours.