Overview

X2CrNiMnMoNNb21-16-5-3 is a nitrogen-strengthened, niobium-stabilised, non-magnetic austenitic chromium-nickel-manganese-molybdenum stainless steel (nominally 21% chromium, 16% nickel, 5% manganese, 3% molybdenum — reflected in the EN designation). This datasheet presents the material within the European standard system.

Its high alloy content gives non-magnetic behaviour (relative permeability about 1.04), high tensile and yield strength, and very good corrosion resistance — particularly in seawater and coastal environments. The low carbon content means that welding does not cause chromium-carbide precipitation, so the steel resists intergranular corrosion even in the as-welded (sensitised) condition. The high manganese and nitrogen stabilise the austenite and provide strength, while molybdenum contributes to pitting and crevice resistance. Note that the high manganese content can reduce pitting resistance somewhat relative to an equivalently-alloyed low-manganese steel.

Typical applications include non-magnetic structural components, shipbuilding and marine hardware, high-strength fasteners and shafting, and equipment for the food-and-beverage and chemical industries (cold nitric and organic acids, chloride-bearing media at moderate concentration).

1. Physical Properties

Values per manufacturer data, solution-annealed condition.

2. Chemical Composition (wt %)

Composition per VdTÜV-Wbl 493 / SEW 390 (W.Nr. 1.3964, X2CrNiMoNNb21-16-5-3).

Nominal: 21Cr-16Ni-5Mn-3Mo-N high-nitrogen austenitic stainless steel. The high nitrogen with manganese gives roughly double the yield strength of standard austenitics while retaining excellent corrosion resistance. The EN composition (Ni 15-17, Mo 3.0-3.5) differs from the US grade.

3. Mechanical Properties

Solution-annealed condition (1020-1050 °C), per VdTÜV-Wbl 493 for W.Nr. 1.3964.

Values per EN/DIN; confirm against the inspection certificate (EN 10204).

4. Corrosion Resistance

Note: the relatively high manganese content can reduce pitting-corrosion resistance compared with an equivalently-alloyed low-manganese steel. Intergranular-corrosion testing per AFNOR NF A05-159 / ISO 3651 / DIN 50914 confirms resistance after welding.

5. Heat Treatment

An austenitic stainless steel; it cannot be hardened by heat treatment. High strength comes from nitrogen and manganese; strength can be raised further by cold work.

Solution Anneal 1020–1050 °C, followed by rapid cooling in air or water, to dissolve secondary phases and give optimum corrosion resistance and the low magnetic permeability.

Because of the low carbon content, welding does not lead to chromium-carbide formation; the alloy resists intergranular corrosion in the as-welded (sensitised) condition. After forging, rapid cooling in air or water is required to avoid undesirable phases.

6. Weldability and Joining

Has good weldability. Owing to the low carbon content, welding does not result in chromium-carbide formation, and the alloy resists intergranular corrosion in the as-welded condition. Where a filler is required, the matching grades W.Nr. 1.3954 or 1.3984 are used. Post-weld heat treatment is normally unnecessary; if required (extensive cold deformation or heavy wall thickness), the solution anneal is applied.

No preheat required. Low carbon content resists weld-zone sensitization; post-weld heat treatment normally unnecessary.

7. Machinability and Fabrication

Owing to its high alloy content, 1.3964 is difficult to machine; coated hard-metal (carbide) tooling is recommended.

Machining Guidelines (solution-annealed, Rm 560–640 N/mm²; coated carbide)

Forming / Forging

8. Applications

9. Available Product Forms and Standards

Nitrogen-strengthened, niobium-stabilised non-magnetic austenitic stainless steel (21Cr-16Ni-5Mn-3Mo). W.Nr. 1.3964 (X2CrNiMnMoNNb21-16-5-3); VdTÜV-Wb 493; SEW 390.

10. Comparison with Related Alloys (EN Symbol System)

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