Core 347/4550
EN 1.4550, ASTM TYPE 347 / UNS S34700, TYPE 347H / UNS S34709

General characteristics

Core 347/4550 is a niobium stabilized alternative Core 321/4541 with improved intergranular corrosion resistance and good mechanical properties at high temperatures. Core 347/4550 is particularly useful in applications with intermittent heating in the range 400–900 °C/750–1650 °F. Core 347/4550 is an austenitic stainless steel that belongs to the standard CrNi stainless steels. Core 347/4550 can be welded in all dimensions without becoming susceptible to intergranular corrosion.

The austenitic CrNi standard grades are the most widely used group of stainless steels. Their well-balanced material properties make them suitable for the fabrication of many products.

Typical applications

  • High temperature gaskets
  • Rocket engine parts
  • Expansion joints
  • Aircraft collector rings
  • Exhaust manifolds
  • Chemical production equipment
  • Flanges and valves


Product forms, available sizes and finishes


Product typeFinishesThicknessWidth
Cold rolled coil and sheet2B0,30-3,00≤ 1250
Hot rolled coil and plateHot rolled white3,00-6,00≤ 1250
Quarto plateHot rolled white5,00-130,00≤ 3200
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.

TypicalCore 347/45500.0517.59.5Nb
ASTM A240/A240MTYPE 347 / UNS S34700<0.08<217.0-19.09.0-13.0Si:<0.75 P:<0.045 S:<0.030 Nb
ASTM A240/A240MTYPE 347H / UNS S347090.04-0.10<217.0-19.09.0-13.0Si:<0.75 P:<0.045 S:<0.030 Nb
EN 10088-21.4550<0.08<217.0-19.09.0-12.0Si:<1 P:<0.045 S:<0.015 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)Core 347/455027530062082HRB82
Product type: Hot rolled coil and sheet
Typical (thickness 4 mm)Core 347/455032036564053
Product type: Hot rolled quarto plate
Typical (thickness 15 mm)Core 347/455026029059545

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

Core 347/4550 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 sufficiently diluted mineral acids depending on the temperature of the solution. Core 347/4550 may suffer from uniform corrosion in strong mineral acids, for instance hot concentrated nitric acid, and hot strong alkaline solutions.

Due to its niobium content, the risk of senzitisation for intergranular corrosion is strongly reduced when compared to other austenitic CrNi standard grades with normal carbon content.

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. The presence of corrosion-inhibiting or accelerating compounds like e.g. transition metal ions or organic compounds may influence the corrosion behavior of Core 347/4550.

Core 347/4550 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.

Due to its niobium stabilization against intergranular corrosion, Core 347/4550 can be used in the temperature range in which chromium carbides would precipitate in other austenitic CrNi standard grades. Its maximum service temperature in dry air is 850°C. The presence of other corrosive compounds in the hot atmosphere, like water or sulfur 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 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

Data according to EN 10088


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

*) Austenitic stainless steel grades may be magnetizable to a certain degree after cold deformation, e.g. in temper rolled condition.


Cold forming

Core 347/4550 can be readily formed and fabricated by the full range of cold forming operations. It can be used in heading, drawing, and bending. Any cold working operations will increase the strength and hardness of the material, and may leave it slightly magnetic. Work hardening is accentuated by the partial transformation of the austenite phase of the material to hard martensite.


Core 347/4550 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. Core 347/4550 has about 50% higher thermal expansion and lower heat conductivity compared to carbon steels. This means that larger deformation and higher shrinkage stresses may result from welding.

In thin sections, autogenous welding may be used. 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. Suitable filler metals are 19 9 Nb or 19 9 L.

Generally, post-weld heat treatment is not required. In special cases where there is high risk 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.

Surface slag particles containing Nb might form with TIG and plasma welding.

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 347 / UNS S34700; TYPE 347H / UNS S34709
EN 10088-21.4550