What Is 1.4565 Stainless Steel? Composition, Properties and Applications

1.4565 is the EN material number of a high-alloy, fully austenitic stainless steel with the steel name X2CrNiMnMoN25-18-6-5, standardized in EN 10088-2 for sheet and strip and covered in the United States by ASTM A240 as UNS S34565. It is a nitrogen-strengthened grade: roughly 25 percent chromium, 17-19 percent nickel, 4-5 percent molybdenum, 5-7 percent manganese and up to 0.60 percent nitrogen combine to produce a fully austenitic structure with yield strength approaching duplex levels and pitting resistance well above that of 316L or 904L.

Because the steel is designed for extreme chloride and acid service, it is a common specification in offshore water handling, flue-gas desulfurization, chemical processing and desalination.

Designation Clarification

1.4565 corresponds to UNS S34565 and the steel name X2CrNiMnMoN25-18-6-5. It is important not to confuse it with UNS N08926 or UNS N08031, which are different austenitic alloys standardized under different material numbers. When ordering, always state the full designation, for example EN 1.4565 or UNS S34565, to avoid substitution errors.

Chemical Composition per EN 10088-2

Element	1.4565, X2CrNiMnMoN25-18-6-5 (wt%)
Carbon, max	0.03
Silicon, max	1.00
Manganese	5.00–7.00
Phosphorus, max	0.030
Sulfur, max	0.015
Chromium	24.0–26.0
Molybdenum	4.0–5.0
Nickel	16.0–19.0
Nitrogen	0.30–0.60

Manganese is deliberately high because it raises the solubility of nitrogen in the austenitic matrix, allowing the steel to carry 0.3-0.6 percent nitrogen without porosity or precipitates. Nitrogen provides solid-solution strengthening and, together with chromium and molybdenum, drives the pitting resistance.

Mechanical Properties, Solution Annealed

Property	Typical value
0.2% proof strength, min (MPa)	420
Tensile strength (MPa)	800–950
Elongation, min (%)	35
Hardness, max (HB)	230
Density (kg/m3)	8000
Modulus of elasticity (GPa)	190

The proof strength of 420 MPa is roughly twice that of annealed 316L, which permits thinner sections for equal load and partially offsets the higher alloy cost.

Corrosion Resistance and PREN

The pitting resistance equivalent number, PREN = Cr + 3.3 x Mo + 16 x N, is the standard screening index for chloride pitting. Using the mid-range composition of 1.4565, 25 + 3.3 x 4.5 + 16 x 0.45, the PREN is about 47, with values above 40 throughout the specification range. In practice the grade resists pitting and crevice corrosion in seawater, brine and other high-chloride media, and tolerates sulfuric and phosphoric acids across wide concentration and temperature ranges. It is fully austenitic and therefore not subject to the ferrite-austenite balance requirements of duplex grades, which simplifies welding procedure qualification.

Fabrication, Welding and Heat Treatment

The grade is supplied solution annealed and water quenched, typically around 1100-1150 C. It is weldable by standard processes with matching or over-alloyed filler metals; nickel-base filler such as UNS N06625 is a common choice to guarantee weld-metal corrosion resistance. Control heat input and interpass temperature to avoid grain growth and phase precipitation, protect both sides of the joint with argon-based shielding, and clean the weld area after welding to restore the passive film. Cold forming follows the practice for high-strength austenitics: allowance must be made for springback and for the higher flow stress.

Typical applications include seawater piping, pumps and valves in offshore platforms and desalination plants; scrubbers, ducting and chimney liners in flue-gas desulfurization systems; reactors, heat exchangers and piping for sulfuric, phosphoric and mixed acid service; and process equipment in the pharmaceutical and fine-chemical industries where strong cleaning agents are used.

FAQ

Is 1.4565 the same as UNS N08926?

No. 1.4565 is X2CrNiMnMoN25-18-6-5, UNS S34565. UNS N08926 is a different austenitic alloy with a different EN material number. The designations must never be treated as interchangeable; confirm the exact UNS or EN number on the order.

What does the designation X2CrNiMnMoN25-18-6-5 mean?

X2 indicates a low-carbon alloy steel, followed by the main alloying elements and their nominal contents: chromium 25, nickel 18, manganese 6 and molybdenum 5 percent, with nitrogen as a deliberate strengthening addition.

How strong is 1.4565 compared with 316L?

The minimum proof strength is about 420 MPa, roughly twice the minimum of annealed 316L, while tensile strength is also higher. This allows weight savings in pressure and structural components.

Can 1.4565 be welded?

Yes, with matching or over-alloyed filler such as UNS N06625, controlled heat input and proper shielding. The fully austenitic structure avoids the ferrite-balance controls that complicate duplex welding.

What is the PREN of 1.4565?

Using mid-range composition, PREN = 25 + 3.3 x 4.5 + 16 x 0.45, about 47. Throughout the EN 10088-2 range the value stays above 40, the common threshold for severe seawater service.

Which industries specify 1.4565?

Offshore oil and gas, desalination, flue-gas desulfurization, chemical processing and pharmaceutical manufacturing, wherever chlorides, acids or aggressive cleaning chemicals are combined with a demand for long service life.