What Is 1.4466 Stainless Steel?

What Is 1.4466 Stainless Steel?

1.4466 is the EN material number for X2CrNiMoN25-22-2, a nitrogen-strengthened fully austenitic stainless steel also designated UNS S31050. It belongs to the family of urea-grade stainless steels developed for the most demanding sections of urea production plants, where equipment operates in hot ammonium carbamate at high pressure and temperature. The high chromium, nickel and molybdenum contents, together with a deliberate nitrogen addition, give the alloy an outstanding combination of resistance to stress corrosion cracking and general corrosion in this aggressive environment.

Designation and standard references

EN 10088 lists the grade as 1.4466, X2CrNiMoN25-22-2. The American equivalent is UNS S31050, covered by ASTM A240 for plate, sheet and strip and by ASTM A312/ASME SA312 for pipe. The material is sometimes confused with lean duplex 2202 (UNS S32202, EN 1.4062), a duplex grade with a different microstructure and lower alloy content; the two materials are not interchangeable.

Chemical Composition

The table below gives the composition limits for UNS S31050 as listed in ASTM A240, consistent with EN 10088-2 for material 1.4466. Values are maximum percentages unless a range is shown.

Element	C	Mn	P	S	Si	Cr	Ni	Mo	N
1.4466 (S31050)	0.020	2.00	0.025	0.010	0.40	24.0-26.0	21.0-23.0	2.0-2.5	0.10-0.16

Mechanical Properties

Minimum mechanical properties per ASTM A240 are tensile strength 540 MPa (78 ksi), yield strength 260 MPa (38 ksi) and elongation 40%. The nitrogen addition raises the yield strength well above that of conventional 304L while maintaining full austenitic ductility and toughness.

Property	Minimum per ASTM A240
Tensile strength	540 MPa (78 ksi)
Yield strength 0.2% offset	260 MPa (38 ksi)
Elongation in 2 in	40%

Key Characteristics

Excellent resistance to stress corrosion cracking in hot chloride and carbamate media, where standard austenitic grades such as 316L can fail.

High strength in the solution-annealed condition, allowing thinner wall designs in pressure equipment.

Good weldability with matching nitrogen-bearing filler metal; the low carbon content avoids sensitisation.

Applications

The grade is used for urea plant high-pressure equipment: strippers, condensers, scrubbers, high-pressure piping and valves. It is also applied in chemical and petrochemical plants where chloride stress corrosion cracking is a risk, and in heat exchangers handling aggressive process streams.

Heat Treatment and Supply Condition

The material is supplied in the solution-annealed condition, typically annealed at approximately 1050-1150 C followed by rapid cooling, which keeps carbides in solution and restores optimum corrosion resistance.

Frequently Asked Questions

Q1: Is 1.4466 the same as lean duplex 2202?

A1: No. 1.4466 is a fully austenitic grade, UNS S31050. Lean duplex 2202 is UNS S32202 (EN 1.4062), a duplex grade with a ferritic-austenitic microstructure; the two are not interchangeable.

Q2: What is the UNS number for 1.4466?

A2: The UNS designation is S31050, and the EN steel name is X2CrNiMoN25-22-2.

Q3: Why is 1.4466 used in urea plants?

A3: It resists stress corrosion cracking in hot ammonium carbamate, the aggressive process medium of urea synthesis, which causes rapid failure of standard austenitic grades.

Q4: Can 1.4466 replace 316L?

A4: Where chloride or carbamate stress corrosion cracking is a risk, yes, the higher alloy content is justified. It is considerably more expensive than 316L, so the decision should be based on the process environment.

Q5: Is 1.4466 weldable?

A5: Yes. It is welded with matching nitrogen-bearing austenitic filler metal, using low heat input; the low carbon content avoids sensitisation of the heat-affected zone.

Q6: Which standards cover 1.4466?

A6: EN 10088-2 covers the plate and sheet as 1.4466, and ASTM A240 / ASTM A312-ASME SA312 cover the American designations for plate and pipe respectively.