X3CrNiMoNbN23-17 Material 1.3974, X2CrNiMnMoNNb23-17-6-3, SEW 390. Forged rings, flanges, discs, shafts and bars, melted and forged at one works.

Buyers meet this steel under at least four names, which is where purchase orders go wrong. The table separates standard designations from mill trade names, and flags the cross-references that published sources describe only as similar.

Limits below are those published for 1.3974 to SEW 390. Niobium stabilises the steel so that chromium carbides do not form along grain boundaries during welding. Nitrogen does the strengthening work that nickel and molybdenum cannot do without upsetting the austenite balance.

Balance iron. Einsal additionally lists tungsten 0.10 to 0.30 percent, and Remystahl narrows the chromium minimum to 21.5 percent. Product analysis tolerances apply as given in SEW 390.

Against the two grades it is confused with

1.3964 and XM-19 figures as published by Deutsche Edelstahlwerke and voestalpine Specialty Metals. The practical point: 1.3974 carries the most nickel and the most nitrogen of the three. It is the grade specified when seawater service and a guaranteed permeability limit appear on the same drawing.

Suppliers publish two different strength bands for this material because they describe different product forms and section sizes. Both are given here rather than averaged, so you can match whichever your specification quotes.

Physical data as published by Einsal and the Applus+ materials portal for material 1.3974. Figures are informative. Acceptance values for heavy forged sections are agreed in the order documents and verified on prolongations or sacrificial test rings.

Welding

Carbon is capped at 0.03 percent and niobium is present as a stabiliser, so chromium carbide precipitation along grain boundaries is suppressed. Applus+ states that 1.3974 keeps its resistance to intercrystalline corrosion in the welded condition, which is the reason fabricators choose it over leaner austenitics for welded seawater assemblies. Use a nitrogen-bearing filler of matching or higher alloy content, keep heat input down, and avoid holding the weld zone in the intermediate temperature range.

Machining

Sources disagree, so plan for the harder case. Applus+ describes the cutting properties of 1.3974 as good. Nicromal states the opposite, that the high manganese and nitrogen make the material difficult to machine. Deutsche Edelstahlwerke takes the same view of the sister grade 1.3964 and publishes a working guideline for coated carbide tooling of 6 mm depth of cut at 0.5 mm/rev and 110 m/min, easing to 1 mm at 0.2 mm/rev and 150 m/min. Nitrogen-strengthened austenitics work-harden quickly, so rigid setups, sharp tools, positive rake and a cut that stays under the hardened layer are what keep the job predictable.

Hot working

The Deutsche Edelstahlwerke schedule for 1.3964 is a soak at 950 to 1150 C, forging between 900 and 1100 C, then rapid cooling in air or water to stop unwanted phases forming. We use a comparable window for 1.3974 and confirm it against the customer specification before the first heat. The caution is real for this family. Brandis, Heimann and Schmidtmann published on the influence of nitrogen on precipitation in X3CrNiMoNbN23-17 in TEW-Technische Berichte in 1976, and sigma phase in high-chromium austenitics remains a standard topic in the metallurgical literature. Cooling slowly through the intermediate range after annealing costs toughness and intercrystalline corrosion resistance at the same time.

Every item is forged from steel melted in our own furnaces. Nothing is cast, nothing is welded up from sections, and no billet of unknown origin enters the shop, so the certificate traces back to a melt number rather than to a purchase.

Why the melt shop matters for a 0.5 percent nitrogen steel

Holding nitrogen between 0.30 and 0.50 percent is a melting problem before it is a forging problem. Our shop runs 30 t and 60 t vacuum oxygen decarburisation units for stainless and duplex work, and two protective-atmosphere electroslag furnaces of 3 t and 6 t that exist precisely for clean and nitrogen-alloyed grades. A forge that buys billet inherits whatever nitrogen the billet supplier achieved. Here the aim point is set for the part the steel will become.

Delivery condition

As-forged with machining allowance, proof-machined for volumetric inspection, or finish-machined to drawing. Solution annealing and quenching are carried out in the 14 on-site heat treatment furnaces, the largest taking work up to 8,000 x 2,000 x 2,000 mm, with two 15 m well-type furnaces for long parts that have to be quenched vertically. Minimum order is 10 kg with no minimum piece count. Normal lead time is 20 to 60 days.

The works holds CCS, BV, DNV, LR and NK approvals and runs its own laboratory. Because the steel is melted here, chemistry is checked at the furnace instead of being copied from someone else's certificate.

Three tests that buyers of this grade often require are placed with an accredited third-party laboratory and reported alongside the mill certificate: intergranular corrosion to ASTM A262 or ASTM G28, pitting resistance to ASTM G48, and impact testing below -60 C. Magnetic permeability verification on the finished part is arranged on request, which is worth specifying whenever the drawing carries a permeability limit rather than just the grade name.

Certification is issued to EN 10204 3.1 as standard, or to EN 10204 3.2 witnessed by BV, DNV, LR, SGS, TUV or your own inspector. Heat treatment charts, NDT reports, dimensional reports and PMI records accompany the certificate.

These are the fields named by the European mills and distributors that publish data for 1.3974, not a general list of things stainless steel does.

• Shipbuilding and naval engineering. The dominant use, and the reason for the submarine steel nickname. Specified where low magnetic signature sits alongside seawater exposure.
• Seawater and offshore equipment. Resistant in seawater to about 60 C and against stress corrosion cracking, with pitting resistance cited by Nicromal and Remystahl.
• Electrical engineering. Non-magnetizable parts in and around electrical machines, where a permeability below 1.01 keeps eddy currents and field distortion out of the design.
• Mechanical and plant engineering. High-strength corrosion-resistant structural and rotating parts up to the 400 C application limit.
• Defence, chemical process, aerospace, medical and hydrogen equipment. Categories listed by Einsal against this material.

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