VDM® Alloy 20

Alternative and trade names
Nicrofer® 3620 Nb, VDM® Alloy 20
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Description

2.4660 is a low carbon, niobium stabilized austenitic nickel-iron-chromium alloy with alloying additions of copper and molybdenum which shows the following features and properties:


  • Excellent resistance to sulphuric and phosphoric acids
  • Good resistance to intergranular corrosion
  • Very good resistance to chloride-ion induced stress-corrosion cracking
  • Good resistance to pitting and crevice corrosion
  • Good mechanical properties at both ambient and elevated temperatures, up to approximately 500°C (930 °F)
  • Related Standards

    Equivalent Materials

    This material data has been provided by VDM Metals.

    All metrics apply to room temperature unless otherwise stated. SI units used unless otherwise stated.
    Equivalent standards are similar to one or more standards provided by the supplier. Some equivalent standards may be stricter whereas others may be outside the bounds of the original standard.

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    Properties

    General

    PropertyTemperatureValue

    Density

    23.0 °C

    8.1 g/cm³

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    Mechanical

    PropertyTemperatureValueComment

    Elastic modulus

    20.0 °C

    202 GPa

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    100.0 °C

    198 GPa

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    200.0 °C

    192 GPa

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    300.0 °C

    185 GPa

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    400.0 °C

    179 GPa

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    500.0 °C

    172 GPa

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    600.0 °C

    164 GPa

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    700.0 °C

    157 GPa

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    Elongation A5

    23.0 °C

    30 %

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    for 20 to 300°C

    Hardness, Brinell

    23.0 °C

    217 [-]

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    max.

    Tensile strength

    20.0 °C

    550 MPa

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    100.0 °C

    520 MPa

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    150.0 °C

    505 MPa

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    200.0 °C

    495 MPa

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    250.0 °C

    480 MPa

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    300.0 °C

    470 MPa

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    Yield strength Rp0.2

    20.0 °C

    240 MPa

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    100.0 °C

    210 MPa

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    150.0 °C

    195 MPa

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    200.0 °C

    180 MPa

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    250.0 °C

    170 MPa

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    300.0 °C

    160 MPa

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    Yield strength Rp1.0

    20.0 °C

    280 MPa

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    100.0 °C

    250 MPa

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    150.0 °C

    235 MPa

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    200.0 °C

    220 MPa

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    250.0 °C

    210 MPa

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    300.0 °C

    200 MPa

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    Thermal

    PropertyTemperatureValue

    Coefficient of thermal expansion

    100.0 °C

    1.5E-5 1/K

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    200.0 °C

    1.56E-5 1/K

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    300.0 °C

    1.6E-5 1/K

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    400.0 °C

    1.64E-5 1/K

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    500.0 °C

    1.67E-5 1/K

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    600.0 °C

    1.71E-5 1/K

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    700.0 °C

    1.74E-5 1/K

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    Melting point

    1380 - 1420 °C

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    Specific heat capacity

    20.0 °C

    456 J/(kg·K)

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    100.0 °C

    466 J/(kg·K)

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    200.0 °C

    476 J/(kg·K)

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    300.0 °C

    485 J/(kg·K)

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    400.0 °C

    492 J/(kg·K)

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    500.0 °C

    500 J/(kg·K)

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    600.0 °C

    508 J/(kg·K)

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    700.0 °C

    515 J/(kg·K)

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    Thermal conductivity

    20.0 °C

    11.5 W/(m·K)

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    100.0 °C

    13 W/(m·K)

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    200.0 °C

    14.8 W/(m·K)

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    300.0 °C

    16.5 W/(m·K)

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    400.0 °C

    18.2 W/(m·K)

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    500.0 °C

    19.8 W/(m·K)

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    600.0 °C

    21.5 W/(m·K)

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    700.0 °C

    23 W/(m·K)

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    Electrical

    PropertyTemperatureValue

    Electrical resistivity

    20.0 °C

    1.07E-6 Ω·m

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    100.0 °C

    1.1E-6 Ω·m

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    200.0 °C

    1.13E-6 Ω·m

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    300.0 °C

    1.16E-6 Ω·m

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    400.0 °C

    1.19E-6 Ω·m

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    500.0 °C

    1.21E-6 Ω·m

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    600.0 °C

    1.23E-6 Ω·m

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    700.0 °C

    1.25E-6 Ω·m

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    Magnetic

    PropertyTemperatureValueComment

    Relative magnetic permeability

    23.0 °C

    1 [-]

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    max.

    Chemical properties

    PropertyValueComment

    Carbon

    0.07 %

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    max

    Chromium

    19 - 21 %

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    Copper

    3 - 4 %

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    Iron

    Balance

    Manganese

    2 %

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    max.

    Molybdenum

    2 - 3 %

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    Nickel

    32 - 38 %

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    Niobium

    0.56 - 1 %

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    Nb+Ta

    Phosphorus

    0.05 %

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    max.

    Silicon

    1 %

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    max.

    Sulfur

    0.035 %

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    max.

    Tantalum

    0.56 - 1 %

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    Nb+Ta

    Technological properties

    Property
    Application areas

    Nicrofer 3620 Nb is used in a wide variety of applications up to temperatures of approximately 500°C. Typical applications are: Equipment for the manufacture of sulphuric acid and for processes based on sulphuric acid, extraction columns in the production of amines and the processing of pharmaceuticals, production of plastics and synthetic fibres, equipment for food processing to protect against contamination.

    Cold Forming

    Cold working should be carried out on annealed material. Nicrofer 3620 Nb has a work-hardening rate similar to that of austenitic stainless steel and the forming equipment must be adapted accordingly. When cold working is performed, interstage annealing may become necessary. After cold reductions of more than 15 %, a final stabilising anneal is required before use.

    Corrosion properties

    Nicrofer 3620 Nb has excellent corrosion resistance to sulphuric, phosphoric and organic acids and to aqueous solutions of their salts. Resistance to nitric acid is also good. Due to the controlled chemical composition, the alloy also has excellent resistance to such forms of corrosion as intergranular corrosion and stress corrosion. The molybdenum content ensures good resistance to pitting and crevice corrosion. Optimum corrosion resistance can only be obtained if the material is in the correct metallurgical condition and clean.

    General machinability

    Nicrofer 3620 Nb should be machined in annealed condition. The alloy’s high work-hardening rate should be considered, i.e. only low surface cutting speeds are possible compared with low-alloy standard austenitic stainless steel. Tools should be engaged at all times. Heavy feeds are important in getting below the work-hardened ‘skin’.

    Heat Treatment

    Soft or stabilising annealing should be carried out in the temperature range 920 to 960°C (1690 to 1760°F), preferably at about 950°C (1740°F). Water quenching or rapid air cooling is recommended for thicknesses above about 3 mm (1/8 in.) and is essential for maximum corrosion resistance. Stress-relief annealing may be performed at temperatures up to 540°C (1000 °F). During any heating operation, the precautions outlined earlier regarding cleanliness must be observed.

    Hot forming

    Nicrofer 3620 Nb may be hot-worked in the range 1150 to 900°C (2100 to 1650°F). The final hot-working temperature must not exceed 950°C (1740°F). Cooling should be by water quenching or as fast as possible. Annealing after hot working is required to ensure maximum corrosion resistance and an optimum microstructure. For hot working, the material may be charged into the furnace at maximum working temperature. After soaking for the required time the material should be withdrawn immediately and worked within the specifed range. If the metal temperature falls below the minimum working temperature, it must be reheated.

    Other

    Nicrofer 3620 Nb has a face-centred cubic structure. The balanced chemical composition and optimum annealing temperature promote the formation of niobium carbides and ensure that the corrosion resistance is not impaired by sensitisation.

    Welding

    Nicrofer 3620 Nb can be welded by all the conventional methods. Proven welding processes are: GTAW (TIG), GMAW (MIG), Plasma, PHW, SMAW. Pulsed arc welding is the preferred technique. Prior to welding, material should be in annealed condition, clean and free from scale, grease, marking paints, etc. A zone approximately 25 mm (1 in.) wide on each side of the joint should be ground to bright metal. Sometimes tarnishing can be removed by brushing the joint in the warm condition. Low heat input is necessary. The interpass temperature should not exceed 120 °C (250 °F). Neither pre- nor post-weld heat treatment is required.