Specifications

Chemical composition and mechanical properties

Limits as given in the ASTM B specifications for N08020.

Pipe, bar and forging requirements are given in ASTM B464, B729, B473 and B462.

Actual values for each heat are reported on the mill test certificate.

Why Alloy 20

Alloy 20 is a niobium-stabilised nickel-iron-chromium alloy with molybdenum and copper, designed for sulphuric acid. It is chosen for sulphuric acid across a wide range of concentrations, phosphoric and nitric acids, pickling liquors and chloride-bearing water. Compared with 316L, Alloy 20 resists sulphuric acid and chloride stress corrosion cracking far better; compared with 904L it has higher nickel; for hot concentrated or heavily contaminated acids, Hastelloy C276 is used instead.

How we manufacture Alloy 20 bars

We manufacture Alloy 20 round bars from certified billets by hot rolling or forging, followed by annealing. Bright bars are peeled, turned or centreless ground to close tolerance. Every bar is marked with grade and heat number, and ultrasonic testing is carried out on request for bars that will be machined into pressure parts.

Machining Alloy 20

Alloy 20 is tough and work-hardens, similar to other high-nickel austenitic alloys. Use rigid machines, sharp carbide tools with positive rake, low speeds, steady feeds and plenty of coolant, and avoid light finishing cuts that rub rather than cut. Threads for fasteners are preferably rolled. Pump shafts and valve stems are often finish ground for a smooth sealing surface.

Welding and fabrication

Alloy 20 is welded by TIG, MIG and manual arc processes with matching ER320LR filler or suitable nickel-based fillers, on clean joints free of oil, paint, marking crayon, sulphur and lead, using low heat input and controlled interpass temperatures. Heat tint is removed and welds are pickled where corrosion resistance at the weld matters. Fabrication areas should be kept separate from carbon steel, and dedicated tools used to avoid iron contamination.

Testing and ordering

Common supplementary requirements are an intergranular corrosion test to ASTM A262, positive material identification and third-party inspection by the buyer's nominated agency. Please give the grade and specification, product type, size, schedule or class, quantity and any testing or inspection requirement with your enquiry. Each piece is marked with grade, specification, size and heat number, packed in wooden boxes or on pallets, and traceable to its mill test certificate.

Sizes, supply and packing

Bars are supplied in random mill lengths, typically 3 to 6 metres, or cut to the lengths needed for machining, which reduces waste of an expensive alloy. Diameters are offered in metric and imperial sizes; bright bars are held to tolerance classes such as h9 to h11, and black bars to the hot-rolled tolerances of the standard. Bars are bundled or boxed, with bright bars wrapped to protect the surface. For each order we confirm the available diameters and the delivery of any special sizes before quoting.

Certification and traceability

Alloy 20 is often confused with 300-series stainless steels and with other nickel alloys of similar appearance. Every piece carries its grade and heat number, and the mill test certificate reports the full chemistry – including nickel, copper, molybdenum and niobium – and mechanical properties. Positive material identification can be carried out before dispatch on request, and intergranular corrosion testing can be added where the end user specifies it.

Applications and related products

Alloy 20 round bars are used for acid pump shafts and impellers, valve stems and trim, agitator shafts, fasteners, flanges and fittings machined from bar, and pickling-line components. Matching products include Alloy 20 pipes and tubes, Alloy 20 sheets and plates, Alloy 20 flanges and Alloy 20 pipe fittings. Background on the alloy is on the Alloy 20 page. Other bar materials are on the round bars, rods and wires page.