1.4521 Open-Die Forgings: X2CrMoTi18-2 / UNS S44400 / AISI 444

Forged bars, seamless rolled rings, discs, blocks, hollow bars and sleeves in 18Cr-2Mo stabilised ferritic stainless steel, made to drawing by Jiangyin Jiangnan Metal Co., Ltd. in Jiangyin, Jiangsu, China.

EN number

1.4521

EN name

X2CrMoTi18-2

UNS

S44400

AISI / ASTM

Type 444

Structure

Ferritic, magnetic

PREN

approx. 24-25

1. Designations and equivalent grades

1.4521 is listed under several national designations. They all cover the same 18Cr-2Mo titanium and niobium stabilised ferritic stainless steel, but the composition limits are not identical, so state the ordering standard on the purchase order.

Equivalences are for guidance. Where a specific product standard such as ASTM A240 Type 444 is mandatory, we forge and certify to that standard.

2. Chemical composition

The limits below are from EN 10088 for X2CrMoTi18-2. Carbon and nitrogen are held low and tied up by titanium and niobium. That stops chromium carbides forming at the grain boundaries, so the steel does not sensitise after welding or after slow cooling.

3. Mechanical properties

Values apply to the annealed condition at room temperature. Test material is taken from prolongations of the same heat and the same heat-treatment batch, and the results go on the EN 10204 3.1 certificate.

Ferritic stainless steels have a ductile-to-brittle transition. If the part will run below about 0 °C, or if impact values matter in a heavy section, tell us before ordering. Section size, forging ratio and test location need to be agreed first.

4. Physical properties

Thermal expansion is lower and thermal conductivity higher than in austenitic 304 and 316. In heat exchangers and water heaters that means less distortion, quicker heat transfer and lower thermal fatigue stress.

5. Corrosion resistance

The 2 % molybdenum puts the pitting resistance equivalent number at roughly PREN 24 to 25 (PREN = %Cr + 3.3 × %Mo + 16 × %N). For localised corrosion that is about the same as austenitic 1.4404 / 316L.

• Chloride stress-corrosion cracking: 1.4521 is highly resistant. This is the main reason it replaces 304 and 316 in hot-water tanks and solar thermal storage.
• Pitting and crevice corrosion: possible in chloride solutions. How much depends on chloride content, temperature, pH, redox potential and crevice geometry. Design, correct post-weld cleaning and periodic cleaning in service all raise the working limit.
• Intergranular corrosion: titanium and niobium tie up carbon and nitrogen, so welds do not sensitise.
• Potable water: accepted for drinking-water contact under the German DVGW and Swiss SVGW schemes. Approval is per product and per producer, so confirm the certificate that applies to your supply.
• Limits: not for reducing acids such as concentrated sulphuric or hydrochloric acid. For seawater and high-chloride duty use a duplex or super-duplex grade, for example A182 F51, A182 F53 or A182 F55.

6. Forged product forms and size range

All forms below are produced on hydraulic open-die presses, with ring rolling for seamless rings. Heat treatment, machining and testing are done in house.

These are normal working ranges rather than absolute limits. Send the drawing to sales@steelforgepieces.com and we will confirm feasibility, forging ratio and machining allowance for your part.

7. Forging and heat treatment

Forging

Billets are heated to 1000-1100 °C. Going higher is avoided because ferritic 18Cr-2Mo steel coarsens quickly at high temperature, and coarse grain costs toughness. Finish forging is completed above about 850 °C, with enough reduction to break down the cast structure. The grain flow then follows the contour of the part, which is what gives a forging its advantage in fatigue and in through-thickness properties over material machined from plate.

Heat treatment

Forgings are annealed at 950-1050 °C and cooled quickly in air or water. Fast cooling through the 350-550 °C range matters, because slow cooling risks 475 °C embrittlement. 1.4521 does not harden on quenching and is supplied in the annealed condition.

Machining, welding and finishing

• Machining: similar to 1.4016 / 430. Chips break more cleanly and work hardening is lower than with austenitic grades. Use rigid set-ups, sharp tooling and plenty of coolant.
• Welding: TIG, MIG and plasma all work, thanks to the titanium and niobium stabilisation. Keep heat input low to limit grain growth in the heat-affected zone. Filler is either matching ferritic or an over-alloyed austenitic such as 316L or 309Mo, depending on what the joint has to do. Thin sections need no preheat. Back-purge to protect the root.
• Post-weld cleaning: pickle and passivate, or at least clean mechanically, to restore the passive film. Skipping this step accounts for a large share of the corrosion problems seen in service.

Testing and inspection

• Heat chemical analysis by spectrometer, product analysis on request
• Tensile, hardness and, where specified, impact testing on prolongations from the heat-treatment batch
• Ultrasonic testing to EN 10228-3 or ASTM A388 acceptance classes, penetrant testing for surface indications
• Dimensional report against the drawing, plus grain size and intergranular corrosion testing to ASTM A763 when required
• Certification: EN 10204 type 3.1 as standard, type 3.2 witnessed by TÜV, SGS, BV, Lloyd's or your own inspector on request

8. Typical applications

• Heat exchangers and condensers: low thermal expansion, good conductivity, resistant to chloride stress-corrosion cracking
• Hot-water tanks, boilers and water heaters: the most common use for the grade
• Solar thermal water heaters: cyclic hot water carrying dissolved chlorides
• Potable-water piping and fittings: DVGW and SVGW applications
• Food, beverage and brewing equipment: hygienic duty with hot cleaning cycles
• Automotive exhaust and EGR parts: condensate corrosion resistance
• Desalination and sugar refinery equipment: chloride-bearing process streams

9. 1.4521 compared with neighbouring grades

1.4521 contains almost no nickel, so its price moves far less with the nickel market than 304 or 316. On large water-heating and heat-exchanger contracts that often settles the choice.

10. Frequently asked questions about 1.4521