Supra 444/4521
EN 1.4521, ASTM TYPE 444 / UNS S44400

General characteristics

Supra 444/4521 is a stabilized, nickel-free, molybdenum alloyed 18% chromium ferritic stainless steel. Supra 444/4521 can be used in many highly corrosive environments and is has good weldability and high temperature properties. Thanks to ferritic microstructure it has resistance to chloride-induced stress corrosion cracking.



Typical applications

  • Hot water tanks
  • Drinking water pipes


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Cold rolled coil and sheet2B, 2D, 2E, Bright annealed0,30-3,60≤ 1560
Hot rolled coil and plateMechanically descale3,61-4,20≤ 1500
Chemical composition

The chemical composition may vary slightly between different product standards. The required standard will be fully met as specified on the order.

The typical chemical composition for this grade is given in the table below, together with composition limits given for the product according to different standards. The required standard will be fully met as specified on the order.

The chemical composition is given as % by mass.

TypicalSupra 444/45210.0218.02.0Ti Nb
ASTM A240/A240MTYPE 444 / UNS S44400<0.025<117.5-19.5<11.75-2.50<0.035Si:<1 P:<0.040 S:<0.030 Ti
EN 10088-21.4521<0.025<117.0-20.01.80-2.50<0.030Si:<1 P:<0.040 S:<0.015 Ti Nb
Mechanical properties

The mechanical properties of the available products are given in the table below.


StandardGradeRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)Supra 444/45213503705255080HRB
Product type: Hot rolled coil and sheet
Typical (thickness 4 mm)Supra 444/45213804204503285
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)Supra 444/452136040054026

1)Elongation according to EN standard:
A80 for thickness below 3 mm.
A for thickness = 3 mm.
Elongation according to ASTM standard A2” or A50.


Corrosion resistance

Supra 444/4521 has very good corrosion resistance in solutions of many halogen-free organic and inorganic compounds over a wide temperature and concentration range. It can withstand many sufficiently diluted organic and mineral acids depending on the temperature and concentration of the solution. Supra 444/4521 may suffer from uniform corrosion in strong organic and mineral acids, as well as in hot concentrated alkaline solutions. More detailed information on the corrosion properties of Supra 444/4521 can be found in Outokumpu’s Corrosion Tables published in the Outokumpu Corrosion Handbook and on

In aqueous solutions containing halogenides, e.g. chlorides or bromides, pitting and crevice corrosion may occur depending on the halogenide concentration, temperature, pH-value, concentration of oxidizing compounds, and crevice geometry, if applicable. The presence of corrosion-inhibiting or accelerating compounds like e.g. transition metal ions or organic compounds may influence the corrosion behavior of Supra 444/4521. Due to its ferritic crystal structure, Supra 444/4521 is not prone to chloride-induced stress corrosion cracking.

Supra 444/4521 can be used for indoor and outdoor applications in rural areas and urban environments where chloride contamination is low. The best material performance is reached usually with the help of adequate design, correct post-weld treatment, and regular cleaning during use (if applicable).


Due to its titanium and niobium content, the risk of sensitization to intergranular corrosion is strongly reduced when compared to non-stabilized ferritic grades. Supra 444/4521 can be used in the temperature range in which chromium carbides would precipitate in non-stabilized ferritic grades. Its maximum service temperature in dry air is 850 °C. The presence of other corrosive compounds in the hot environment, like water or sulphur compounds may reduce the maximum service temperature significantly.

For more information on corrosion resistance, please refer to the Outokumpu Corrosion Handbook or contact the our experts.

Pitting corrosion resistanceCrevice corrosion resistance

PRE Pitting Resistant Equivalent calculated using the formula: PRE = %Cr + 3.3 x %Mo + 16 x %N
CPT Corrosion Pitting Temperature as measured in the Avesta Cell (ASTM G 150), in a 1M NaCl solution (35,000 ppm or mg/l chloride ions).
CCT Critical Crevice Corrosion Temperature is the critical crevice corrosion temperature which is obtained by laboratory tests according to ASTM G 48 Method F


Physical properties

Data according to EN 10088


DensityModulus of elasticityThermal exp. at 100 °CThermal conductivityThermal capacityElectrical resistanceMagnetizable



Supra 444/4521 can be formed using typical forming processes such as folding, bending, and drawing. It has higher minimum proof strength than a standard austenitic stainless steel like Core 304/4301 in combination with lower work hardening behavior. Due to the stabilization, the R-value is higher compared to non-stabilized ferritic stainless steels. These characteristics mean excellent deep-drawability.


Supra 444/4521 is relatively easy to machine. Compared to austenitic grades, it has lower tendency to form edges, which gives a larger machining window. Since the machinability is comparable to that of low-alloyed carbon steels, the same recommendations regarding choice of tool, cutting speed, and cutting feed apply.


Supra 444/4521 has good weldability and can be welded with common fusion and resistance welding methods. Conventional welding methods like MMA, MIG, MAG, TIG, SAW, LBW, or RSW, except gas welding, are applicable. Austenitic 19 12 3 L (316L) or 23 12 2 L (309MoL) filler metals can be used.

Low interstitial levels and added stabilizer have made enormous improvements to the welding characteristics of ferritic grades. Heat input should be minimized to reduce the grain growth in the HAZ. Dual-stabilization (Ti+Nb) of Supra 444/4521 improves autogenously welded joints by refining the grain structure in the weld metal. Stabilization prevents chromium carbide precipitation, which could otherwise lead to sensitization embrittlement. Consequently, the stabilized grades are practically immune to intergranular corrosion in the as-welded condition.

Shielding gases should be Ar/He based, mixed with a maximum of 2% oxygen to improve the arc stability. Hydrogen and nitrogen additions are forbidden.

More detailed information concerning welding procedures can be obtained from the Outokumpu Welding Handbook, available from our sales offices.


Standards & approvals

The most commonly used international product standards are given in the table below.


ASTM A240/A240MTYPE 444 / UNS S44400
EN 10088-21.4521