Alloy 20 (Carpenter 20Cb-3, UNS N08020)
The sulfuric-acid alloy — 3.5 % copper and 2.5 % molybdenum in a stabilised 35 % nickel base — for acid plants, pickling lines and pharmaceutical process equipment.
What Alloy 20 is.
Alloy 20 is an iron-nickel-chromium alloy with additions of copper, molybdenum and niobium developed for sulfuric acid service. The copper gives resistance to hot sulfuric acid across most concentrations, molybdenum adds chloride pitting resistance, and niobium stabilisation keeps it weldable without intergranular attack. It also resists phosphoric and nitric acids and chloride stress-corrosion cracking better than the 300-series stainless steels.
ASTM B473 covers the bar. We machine Alloy 20 studs, bolts, nuts and components from certified B473 bar.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Nickel | Ni | 32.00 | 38.00 |
| Chromium | Cr | 19.00 | 21.00 |
| Copper | Cu | 3.00 | 4.00 |
| Molybdenum | Mo | 2.00 | 3.00 |
| Niobium + tantalum | Nb+Ta | 8 × C | 1.00 |
| Manganese | Mn | — | 2.00 |
| Silicon | Si | — | 1.00 |
| Carbon | C | — | 0.07 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.035 |
| Iron | Fe | balance | — |
Values per ASTM B473-07(2018) Table 1 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Condition and size | Tensile strength, min (ksi) | Yield strength, min (ksi) | Elongation, min (%) | Reduction of area, min (%) |
|---|---|---|---|---|
| Annealed, hot or cold finished — all sizes | 80 | 35 | 30 | 50 |
| Annealed, strain hardened — up to 2 in. | 90 | 60 | 15 | 40 |
Values per ASTM B473-07(2018) Table 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Specifications that apply.
How Alloy 20 ships from Houston.
- Full-thread studs and stud bolts
- Hex and heavy hex bolts
- Socket head cap screws
- Hex nuts in the same alloy
- Threaded rod
- Machined components from certified bar
Alloy 20 fasteners we make.
Every item is manufactured to your drawing or standard in Alloy 20, imperial or metric, with an EN 10204 3.1 certificate.
What is Alloy 20?
Alloy 20 sits between the austenitic stainless steels and the nickel alloys. Its 35 percent nickel puts it beyond the range where chloride stress-corrosion cracking is a problem, its copper addition is specific to sulfuric acid, and niobium stabilisation lets it be welded and used in the as-welded condition. It is the standard material for sulfuric acid service between the concentrations that 316 and the nickel-molybdenum alloys handle, and B473 gives it 80 ksi tensile and 35 ksi yield in the annealed bar.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or alloy marking 20 with heat number and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
AL-6XN (UNS N08367)
The 6 % Mo super austenitic in nickel-alloy classification — PREN about 43 at minimum chemistry (typically about 45) for seawater, brine and chlorinated water — with 95 ksi tensile in the annealed bar.
ASTM B574 rod · ASTM F468 / F467 fastenersHastelloy C-276 (UNS N10276)
The universal chemical-process alloy — resists oxidising and reducing acids, wet chlorine and sour gas — and the F468 fastener grade Ni 276.
ASTM A193 / ASME SA-193ASTM A193 Grade B8M Class 1 (316 Stainless)
316 stainless bolting with molybdenum for chloride and pitting resistance — offshore, marine, chemical and coastal plant fasteners.