X2CrNiMo18-15-4 Forgings (EN 1.4438 / AISI 317L / UNS S31703)

1. The grade in short

X2CrNiMo18-15-4 sits in the special austenitic group of EN 10088-3. Think of it as a 316L with the molybdenum pushed up to 3 to 4 % and the nickel raised to match, so the structure stays fully austenitic. The X2 prefix marks the extra low carbon ceiling of 0.030 %, which holds back chromium carbide precipitation at the grain boundaries. That matters for forged nozzles, flanges and tube sheets that get welded into a vessel and will never see a post-weld anneal.

Where the grade earns its place is between 316L and the 6 % molybdenum super-austenitics. Buyers come to it when 316L is pitting in service but 904L or F44 would be hard to justify on price. Typical users are pulp and paper bleach plants, sulphuric and phosphoric acid handling, and flue gas desulphurisation.

Solution annealed, the steel is non-magnetic, tough at low temperature, and weldable by all the usual processes. Like every austenitic it work hardens, so we allow for that in machining stock on rough-machined parts.

2. Chemical composition

On nickel: EN 10088-3 gives 13.0 to 16.0 % for bars, rods and semi-finished products. Other published datasheets quote 13.0 to 17.0 %, and the French equivalent Z3CND19-15-04 narrows it to 14.0 to 16.0 %. We aim the heat at the window that satisfies every standard named on the order, and the actual ladle analysis is printed on the certificate.

Where 1.4438 and 317L differ

The two grades are treated as equivalent, but the limits are not the same. Worth checking before anyone orders a dual-stamped forging.

In practice a heat aimed at Cr 18.0 to 19.5 %, Ni 14.0 to 15.0 %, Mo 3.1 to 3.6 % and C below 0.025 % clears EN 1.4438, 317L / S31703 and 317S12 at the same time. That is the target we use when a customer wants the forging stamped to both the European and the American grade.

Pitting resistance

Using PREN = %Cr + 3.3 x %Mo, the EN composition limits give a range of roughly 27 to 33, against about 24 to 28 for 316L on the same calculation. Nitrogen is not deliberately added to this grade, so it is normally left out of the sum. The figure is an index for comparing grades, not a guarantee of service performance; the operating temperature, chloride level and surface condition all decide the outcome.

3. Equivalent grades

European pressure work is usually ordered against EN 10222-5 for stainless steel forgings; in the ASME world the equivalent is ASTM A182 F317L. Both are routine here.

4. Mechanical and physical properties

The figures below are for the solution annealed condition, which is how we ship unless the order says otherwise. Specified minima and typical measured values are kept apart so there is no argument at inspection.

Elevated temperature proof strength and creep data to EN 10088-3 and EN 10028-7 can be sent on request against a specific design temperature. We prefer to quote those from the governing standard edition rather than from a general table.

5. Melting, forging and heat treatment

Hot working runs between about 1150 C and 800 C. Finishing below 800 C risks cracking and leaves residual strain that will not come out without an anneal. After forging the part is solution annealed at 1020 to 1100 C and cooled fast, water quenched on heavy sections, to take the chromium carbides back into solution.

EN 10088-3 does allow the forging heat itself to act as the solution treatment, provided the temperature never falls below the solution annealing minimum, with 1000 C given as the floor for molybdenum-bearing steels. We still run a separate furnace cycle by default, because it is the safer route on pressure parts and it gives a chart to attach to the certificate.

The grade cannot be hardened by heat treatment. Strength comes only from cold work, which we avoid on parts headed for corrosive service.

6. Forged products in X2CrNiMo18-15-4

Everything listed is made to customer drawing, or to a dimensional standard the customer names, in the as-forged, rough-machined or finish-machined condition.

These ranges cover normal open-die and ring rolling work. Check oversize or very heavy single pieces with the sales office before you issue the order.

7. Service areas

8. Inspection and paperwork

Forgings leave with a mill certificate to EN 10204 3.1, or 3.2 witnessed and counter-signed by a third party such as TUV, SGS, BV, DNV or Lloyd's Register. Volumetric examination follows EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class named on the order. Ladle analysis is always reported, product analysis when asked for. Mechanical testing covers tensile, Charpy V and hardness, taken from prolongations that represent the heat treatment lot. Intergranular corrosion testing to ASTM A262 Practice E and positive material identification are available as extras.

Documents normally issued with a shipment: material certificate, heat treatment chart, UT report, dimensional report, NDT operator qualifications, and a declaration of conformity to the ordered standard.

9. Questions we get asked

10. Request a quotation

For a firm price, send the drawing or the rough dimensions, the quantity, the governing standard (EN 10088-3, EN 10222-5, ASTM A182 F317L, or your own specification) and the test and certification scope. Quotations normally come back within one working day, with forged weight, machining allowance, lead time and inspection plan.

Related grades

• A182 F44
• 904L / 1.4539
• A182 F51
• A182 F53
• A182 F55
• Sanicro 28
• AISI 347H
• Incoloy 825

Composition limits are taken from the EN 10088-3 tables for steel 1.4438; comparison values for 317L, 317S12 and Z3CND19-15-04 from published grade datasheets. Figures here are for enquiry and preliminary design. The governing documents for any delivery are the purchase order and the EN 10204 certificate issued with the forging. Page last reviewed 9 October 2026.