317L / UNS S31703 forgings Seamless rolled rings, forged rings, flanges, shafts, discs, tube sheets, sleeves and bars to ASTM A182 Grade F317L

317L sits between 316L and the 6 percent molybdenum superaustenitics. It is specified when 316L pits in service but a 6Mo grade or a duplex is more alloy than the duty needs.

The grade carries 18 to 20 percent chromium, 11 to 15 percent nickel and 3 to 4 percent molybdenum. Molybdenum is what buys the pitting resistance: in the standard index PREN = Cr + 3.3Mo + 16N, each percent of molybdenum counts three and a third times as much as a percent of chromium. Taking a mid-range analysis of 18.5 Cr, 3.1 Mo and 0.06 N, 317L computes to 29.7 against 24.2 for a typical 316 and 19.0 for 304.

The L suffix is the second half of the specification. Carbon is capped at 0.030 percent, low enough that chromium carbides do not precipitate at the grain boundaries when the steel passes slowly through 427 to 816 C. Welded fabrications therefore resist intergranular attack as welded, with no post-weld solution anneal. Where a component will spend time in that temperature band, 317L is the choice over plain 317.

Values are computed from mid-range typical analyses, not from specification limits. A heat aimed at the top of the 317L range, 20 Cr and 4 Mo, reaches a PREN near 34.8. If your specification sets a minimum PREN, state it on the enquiry so the melt can be aimed accordingly.

Composition range for UNS S31703. Figures given without a range are maximums, in weight percent.

Chemistry is verified on the works optical emission spectrometer and the infrared carbon and sulphur analyser at the furnace, before the heat is teemed, rather than taken from an incoming billet certificate.

Forgings and plate are accepted against different specifications with different minimum values. For forged product the governing document is ASTM A182 Grade F317L.

The typical column is measured data from wrought material, not an acceptance criterion. On a heavy forging the result depends on section size, the reduction ratio achieved under the press and the orientation of the test coupon. Send the section thickness with your enquiry and the works will confirm what is achievable before the order is placed.

Physical properties

317L is a strong performer in reducing and chloride-bearing media and a poor choice in strongly oxidising acid. Knowing both sides prevents a misapplication that a PREN figure alone will not catch.

Related grades forged at this works

• A182 F44, 6Mo
• A182 F51, duplex 2205
• 904L
• A182 F347
• Alloy 20
• Incoloy 825

Melting, forging, ring rolling, heat treatment, machining and testing are all on one site in Zhouzhuang Town. No step is subcontracted.

Melting

317L follows the stainless route: a 25 t electric arc furnace, refining in a 25 t or 50 t ladle furnace, then vacuum oxygen decarburisation in a 30 t or 60 t unit. Vacuum decarburisation is what brings carbon reliably under the 0.030 percent ceiling without stripping chromium, and it is also where nitrogen is controlled if a minimum PREN has been specified. Maximum heat size is 60 tonnes. Electroslag remelting is available on the 3 t and 6 t protective-atmosphere furnaces where a cleanliness or segregation requirement justifies it.

Forging and ring rolling

Hydraulic open-die presses of 6,300 t, 4,000 t and 2,000 t cover heavy cogging through to smaller blanks, with 5 t, 3 t, 2 t, 1 t and 750 kg hammers for drawing out and short runs. Rings are rolled on radial-axial mills of 6 m, 3 m and 1 m, giving outside diameters up to 6,000 mm. Below the ring mill range, down to OD 50 mm, rings are made by the upset and punch route.

Solution annealing

317L is annealed at 1010 to 1121 C, 1850 to 2050 F, and cooled rapidly. Where hot working finishes below the minimum working temperature, a higher solution treatment of 1080 to 1180 C followed by quenching is applied. The grade does not respond to hardening heat treatment; strength rises only through cold work. Fourteen furnaces are available, including three high-temperature car-bottom furnaces and two 15 m well-type furnaces that allow long shafts to be quenched vertically rather than laid down, which keeps distortion out of the part.

Machining

317L work-hardens quickly, so it is cut at low speed with a constant, uninterrupted feed. It is tougher than 304 and throws a long stringy chip, which makes chip breakers worth using. Vertical lathes take work to 5,000 mm swing, horizontal lathes to 14 m between centres, and the deep-hole drilling machine bores to 1,600 mm diameter by 10,000 mm.

Welding

The grade welds by the standard fusion and resistance processes with AWS E317L or ER317L filler. Post-weld heat treatment is not required because of the carbon limit. Oxyacetylene welding should not be used.

Every item is forged from one piece of steel melted on site. No welding, no casting, no purchased billet.

Delivery condition is as-forged with machining allowance, proof-machined for volumetric inspection, or finish-machined to drawing.

The works holds CCS, BV, DNV, LR and NK approvals and runs its own laboratory. EN 10204 3.1 is standard; 3.2 witnessed certification is available on request.

ASTM A262 Practice E is the usual acceptance test for intergranular attack on an L grade and is placed with an accredited outside laboratory, with the report issued alongside the mill certificate. State the requirement at enquiry stage so it is scheduled before shipment rather than added afterwards. Traceability runs from the melt number through forging, heat treatment and machining to despatch.

Minimum order is 10 kg with no minimum piece count. Normal lead time is 20 to 60 days. Sending the six items below in the first email usually gets a price back within two working days.