A182 F309S · 309S UNS S30908 · EN 1.4833 · X12CrNi23-13 — open-die forgings, rolled rings, flanges, shafts, discs, sleeves and bars

All three variants share the same chromium and nickel base. Only carbon separates them. Low carbon in 309S buys weldability and resistance to sensitisation. High carbon in 309H buys creep strength at temperature. For comparison, 310S (S31008) steps up to 24.0 to 26.0 % chromium and 19.0 to 22.0 % nickel for duty above the practical ceiling of 309.

Annealed 309S normally tests well clear of these floors. Published typical figures include tensile around 90 ksi and yield around 40 to 45 ksi. A forging is nonetheless bought against the specification minimum, and a heavy section cools more slowly than a test coupon, so we test on sacrificial prolongations representative of the heaviest section unless the enquiry states otherwise.

ASTM A182 Table 3 requires austenitic grades to be solution treated and quenched, with a minimum solution temperature of 1900 F (1040 C). Published practice for 309S places the solution anneal in the approximate range 1040 to 1175 C, held around 30 minutes per inch of section, followed by rapid cooling. Heavy forgings are water quenched; thin or distortion-sensitive geometry may be cooled by accelerated air.

The object is to take chromium carbides back into solution and then pass quickly through the sensitisation range on the way down. Slow cooling through roughly 850 to 450 C re-precipitates carbides at grain boundaries and reduces intergranular corrosion resistance, which is the exact condition the low-carbon analysis exists to avoid. No hardening treatment applies: 309S is non-hardenable, strengthened only by cold work, and essentially non-magnetic in the annealed condition.

309S is selected for oxidation resistance at elevated temperature. In thermal processing that covers annealing boxes and covers, burner grids, muffles and retorts, furnace doors and fans, walking beams and neutral salt pots. In petroleum refining it appears in catalytic recovery systems and recuperators, and the low-carbon variant is the one normally requested where polythionic acid stress corrosion cracking during shutdowns is a concern. Pulp and paper plants use it in digesters, liquor tanks and paper machine hardware; waste treatment uses it in thermal oxidisers. It is also found in food processing equipment and storage, pharmaceutical and biochemical production, power generation and gas compression trains, shipbuilding and general heavy machinery.

Where service temperature or sulphur level exceeds what 309S will tolerate, the usual step up is AISI 330 or a nickel-base grade such as Incoloy 800H and 800HT or Inconel 601. Where the duty is aqueous corrosion rather than heat, A182 F347, 904L or a duplex such as F51 and F53 is normally the better choice. We forge all of them, so the recommendation is not limited by what happens to be in stock.

Melting is carried out in our own steel plant by EAF with LF and VOD refining, in heats up to 60 t, with VIM, VAR and ESR available where cleanliness or segregation control justifies it. Forging is open-die on a 6,300 t press, with ring rolling to 6 m diameter for circular parts, followed by solution treatment and quench, machining to drawing and final inspection. Melting and forging under one roof means one heat number carries through from ladle to certificate.

Ultrasonic testing is carried out to ASTM A388, EN 10228-3 or SEP 1921 at the class nominated on the order. PMI, liquid penetrant, intergranular corrosion testing to ASTM A262, hardness survey and impact testing are available as supplementary requirements. Certificates are issued to EN 10204 3.1, or 3.2 with third-party witness. The works holds CCS, BV, DNV, LR and NK approvals.

Send a drawing, or the finished dimensions and quantity. Outside diameter, inside diameter and height for a ring, or diameter and length for a bar, is enough for us to quote forging weight and price.