VDM® Alloy 36

Alternative and trade names
Pernifer 36, Invar® 36, VDM® Alloy 36
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Description

1.3912 (Ni36) is a binary iron-nickel alloy with a particularly low heat expansion coefficient, whereby the levels of carbon and manganese as well as freedom of impurities are significant. It is ferromagnetic at temperatures below the Curie temperature and non-magnetic at temperatures above. Cold forming also reduces the heat expansion. Artificial aging with gradual heat treatment stabilizes the expansion coefficients in a selected temperature range. It is characterised by the following features and properties:


  • Extremely low expansion coefficient between -250°C (-418°F) and +200°C (392°F)
  • Good ductility and toughness.
  • Good fatigue and mechanical properties at cryogenic temperature
  • Equivalent Materials

    Properties

    General

    Density ρ

    8.1 g/cm³ at 20 °C

    Mechanical

    Elastic modulus E

    133 GPa at -250 °C

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    Elongation A

    40 % 0

    Typical mechanical properties

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    Tensile strength Rm

    520 MPa 0

    Typical mechanical properties

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    Yield strength Rp0.2 Rp0.2

    310 MPa 0

    Typical mechanical properties

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    Thermal

    Coefficient of thermal expansion α

    1.3E-6 - 2.2E-6 1/K at -250 °C

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    Melting point Tm

    1430 °C

    Specific heat capacity cp

    440 J/(kg·K) at -60 °C

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    Thermal conductivity λ

    2 W/(m·K) at -250 °C

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    Electrical

    Electrical resistivity ρel

    4.9E-7 Ω·m at -180 °C

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    Magnetic

    Curie temperature Tc

    230 °C

    Chemical properties

    Element

    Weight %

    Comment

    Fe

    -

    Balance

    Ni

    35 - 37 %

    Mn

    0.6 %

    max.

    Co

    0.5 %

    max.

    Si

    0.4 %

    max.

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    Technological properties

    Application areas

    Sulphuric acid production plant, sulphuric acid heat recovery and distribution systems, nitric-hydrofluoric acid pickling plant, seawater systems, plate or tubular heat exchangers using brackish or seawater as coolant, bleaching plant for chemical pulp.

    Cold Forming

    For cold forming, the workpiece should be in the annealed condition. VDM® Alloy 36 has a similar work hardening rate to austenitic stainless steels. This should be taken into account when selecting forming equipment and planning forming processes. Intermediate annealing is necessary for major cold forming work. Under certain circumstances, a cold-formed microstructure is advantageous because it can reduce the heat expansion coefficient slightly. However, this condition is not stable, in particular when used at high temperatures.

    Corrosion properties

    Pernifer 36 is corrosion resistant in dry atmospheres at room temperature. Under unfavourable conditions, i.e., in humid or moist atmospheres, corrosion can occur in the form of rust.

    General machinability

    VDM® Alloy 36 is preferably processed in the annealed condition. The machined characteristics of VDM® Alloy 36 are similar to those of austenitic stainless steels. Thanks to its high ductility, the chips resulting during machining tend to be string-like and tough, and can therefore result in fast wear to the cutting tool edge guides. The tool should be engaged at all times. A relatively low cutting speed should be used with a feed speed that is not too high. An adequate chip depth is important in order to cut below a previously formed work-hardened zone. This prevents excessive heat development and minimizes its impact on the material's expansion characteristics. Tools made of high speed steel (HSS) or carbide should be used. The cutting edges must be kept sharp. Generally, two types of lubricant are used when machining VDM® Alloy 36: Sulfochloride oils due to their ability to prevent fretting, and emulsions due to their higher cooling capacity. For most machining steps, sulfochloride cutting oils are required.

    Heat Treatment

    The annealing should be performed at temperatures of 820 to 900°C (1,580-1,652°F), followed by air cooling. Compared with air cooling, water cooling following annealing results in a lower heat expansion coefficient. However, the resulting microstructure is not stable. Following cold forming of less than 10%, the annealing temperature should not exceed 860°C (1,580°F). Stress relief annealing is performed at temperatures of approx. 700 °C (1,292°F). The lowest heat expansion values at 100°C (212°F) are achieved in 3 steps with heat treatment: 1) Approx. 30 minutes of annealing at 830°C (1,526°F) with subsequent water quenching, 2) Heating to 300°C (572°F): maintaining the temperature for 1 hour: air cooling, 3) Re-heating to 100 °C (212°F): maintaining the temperature for 30 minutes; furnace cooling to room temperature for 48 hours. The material must be placed in a furnace that has been heated up to the maximum annealing temperature before any heat treatment. For strips and wires as the product form, the heat treatment can be performed in a continuous furnace at a speed and temperature that is adapted to the geometry. The cleanliness requirements listed under "Heating" must be observed.

    Hot forming

    VDM® Alloy 36 can be hot-formed in a temperature range between 1,050 and 800°C (1,950-1,472°F) with subsequent rapid cooling down in water or air. For heating up, workpieces should be placed in a furnace which has been heated up to the maximum hot forming temperature of 1,050°C (1,922°F). The workpiece should be retained in the furnace for around 60 minutes per 100 mm of thickness once the furnace has reached its temperature again. Deformation must take place immediately, whereby reheating is required should the temperature reach the lower limit. Heat treatment after hot forming is recommended in order to achieve optimal properties.

    Other

    In the soft annealed condition, VDM® Alloy 36 has a cubic face-centered crystal structure.

    Welding

    It must be ensured that work is carried out using targeted heat application and low heat input. The stringer bead technique is recommended. The interpass temperature should not exceed 120°C (248°F). In principle, checking of welding parameters is necessary.

    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.