Supra 316plus
EN 1.4420, ASTM UNS S31655

General characteristics

With its high chromium content, Supra 316plus content delivers high strength, good formability, and excellent weldability, making it ideal for use in a variety of applications, including heat exchangers, water treatment, and piping, as well as in architectural applications such as indoor and outdoor facades.

Supra 316plus is an austenitic CrNiMo stainless steel with 21 wt.-% chromium and relatively low nickel and molybdenum content. Due to its high nitrogen content, it has increased mechanical strength and shows a high degree of work hardening on mechanical deformation. Due to its high chromium content, Supra 316plus offers similar or better corrosion resistance than austenitic CrNiMo standard grades in many corrosive environments.

Supra 316plus is used in applications where increased corrosion resistance and a combination of high mechanical strength and good formability are needed. Due to its tendency to work hardening, Supra 316plus can absorb an increased amount of energy during deformation. It can be delivered in the temper rolled condition with different strength levels.

Typical applications

  • Process and transport tanks
  • Water treatment and pipes
  • Heat exchangers
  • Architectural applications


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Black hot band1U3,50-10,001000-1550
Cold rolled coil2B, 2G, 2K0,70-5,0050-1550
Cold rolled sheet2B, 2G, 2K0,70-5,00400-1550
Hot rolled coil, pickled1D, 1E2,30-8,5050-1550
Chemical composition


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.

Typical 0.0220.
ASTM A240 ≤0.030≤2.0019.5-21.58.0-9.50.50-1.500.14-0.25
EN 10028-7 ≤0.030≤2.0019.5-21.58.0-9.50.50-1.500.14-0.25
Mechanical properties


The mechanical properties of the available products in the soft annealed condition at room temperature are given in the table below. Moderate strengths can be reached at elevated temperatures (~550 °C/1022 °F). Temperatures for excessive scaling are close to 850 °C/1562 °F. This grade, along with other austenitic corrosion-resistant steels, exhibits very high ductility and high elongation to fracture. It is not susceptible to brittle fracture in the solution annealed condition.

StandardRp0.2Rp1.0RmElongationImpact strengthRockwellHBHV
Product type: Cold rolled coil and sheet
Typical (thickness 1 mm)38070045
ASTM A240 ≥ 310 ≥ 635 ≤ 100HRB ≤ 241
EN 10028-7 ≥ 350 ≥ 380650-850 ≥ 35
Product type: Hot rolled coil and sheet
Typical (thickness 4 mm)39040071045
ASTM A240 ≥ 310 ≥ 635 ≤ 241
EN 10028-7 ≥ 350 ≥ 380650-850 ≥ 35
Product type: Hot rolled quarto plate
ASTM A240 ≥ 310 ≥ 635 ≤ 100HRB ≤ 241

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 316plus has excellent corrosion resistance in solutions of many halogen-free organic and inorganic compounds over a wide temperature and concentration range. It can withstand many organic and diluted mineral acids depending on the temperature and concentration of the solution. Supra 316plus may suffer from uniform corrosion in strong mineral acids and hot strong alkaline solutions.

In aqueous solutions containing halogenides, e.g. chlorides or bromides, pitting and crevice corrosion may occur depending on halogenide concentration, temperature, pH-value, concentration of oxidizing compounds, and crevice geometry, if applicable. Due to its high chromium and nitrogen content, the pitting and crevice corrosion resistance of Supra 316plus is on the same level or even better than the corrosion resistance of the austenitic CrNiMo standard grades 4401 and 4404 despite its lower molybdenum content. The presence of corrosion-inhibiting or accelerating compounds like transition metal ions or organic compounds may influence the corrosion behavior of Supra 316plus.

Supra 316plus is prone to chloride-induced stress corrosion cracking at temperatures over about 50 °C depending on the applied stress and the chloride concentration in the environment. Prior cold deformation of the structure under load increases the risk of stress corrosion cracking.

Supra 316plus can be used for indoor and outdoor applications in urban and moderately corrosive industrial environments. In environments where chloride contamination may be high, for instance in coastal areas, pitting and staining is possible. The best material performance is reached usually with the help of adequate design, correct post-weld treatment and regular cleaning during use (if applicable).

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

The crystal structure is austenitic, and therefore the material is non-ferromagnetic in the soft annealed condition. The Md30 temperature is lower than 110° C, which makes this material very stable against martensite transformation.


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

Supra 316plus can be formed using typical forming processes like folding, bending, drawing, etc.

Higher strength values typically correspond to higher springback after forming.

Supra 316plus has remarkably higher proof strength than the standard austenitic stainless steel grade 316L / 1.4404 in combination with the same degree of work hardening.

Due to the design of the composition, the Erichsen Index and LDR (Limiting Drawing Ratio) match those of well-known austenitic stainless steels like 1.4307 or 1.4404.
These characteristics mean good deep drawability and excellent stretch-forming capabilities.



Supra 316plus has excellent weldability and is suitable for the full range of conventional welding methods (like MMA, MIG, MAG, TIG, SAW, LBW, or RSW), except gas welding. To ensure that the weld metal properties (e.g. strength, corrosion resistance) are equivalent to those of the parent metal, matching or slightly over-alloyed fillers should preferably be used. Austenitic 19 12 3 L (316L) filler metals can be used to get matching corrosion resistance and 22 09 NL type duplex welding consumables to get matching strength. Shielding gases should be Ar/He based or contain up to 3% nitrogen to minimize nitrogen drop. Typical heat input values for austenitic grades can be utilized. The high nitrogen content tends to restrict grain growth during the thermal cycle. Welds are not sensitized when normal welding procedures are followed.

Generally, post-weld heat treatment is not required. In special cases with high risks of stress corrosion cracking or fatigue, stress relief treatment may be considered. 

In order to fully restore the corrosion resistance of the weld seam, the weld discoloration should be removed by pickling and passivation.

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

Standards & approvals

Supra 316plus is a trademark of Outokumpu and its ASTM designation is UNS S31655 and EN number 1.4420*.
The grade is included in ASTM tube and pipe standards A249-15, A269-15, A358-15, A554-15 and A312-15.
Work is in progress for EN and ASME standardization.
Polarit Material Specification is available for this grade and it is applied when EN 1.4420 is wanted to be certified prior to EN standardization.
*Designation according to Stahl Eisen Liste (Register of European Steels)


ASTM A240/A240MUNS S31655
EN 10028-7, PED 2014/68/EU1.4420