VDM® Alloy 926

Alternative and trade names
Cronifer 1925 hMo, Incoloy 926, VDM® Alloy 926
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Description

1.4529 (X1NiCrMoCuN25-20-7) is an austenitic, special stainless steel that was developed by VDM Metals on the basis of the many times proven VDM® Alloy 904 L (1.4539). Due to its 6.5 % higher molybdenum concentration, VDM® Alloy 926 has a generally improved corrosion resistance and resistance against pitting corrosion and crevice corrosion compared to VDM® Alloy 904 L. This also has a positive effect on the resistance against stress corrosion that is induced by pitting corrosion. It is characterized by the following features and properties:


  • Very good resistance against chloride-induced stress corrosion
  • Increased resistance against stress corrosion in comparison to other austenitic stainless steels
  • Excellent general corrosion resistance when in contact with oxidizing and reducing media
  • Higher strength than VDM® Alloy 904 L (1.4539)
  • Low propensity to form inter-metallic phases
  • Approval for pressure vessels in the temperature range from -196 to 400°C
  • Approval from building supervisory authorities for components and joining elements made of stainless steels, Deutsches Institut für Bautechnik [German Centre of Competence for Construction], September ’98
  • Equivalent Materials

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    Properties

    General

    Density

    ρ

    8.1 g/cm³ at 23 °C

    Mechanical

    Elastic modulus

    E

    193 GPa at 20 °C

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    Elongation A50

    A50

    35 % at 23 °C

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    Typical mechanical properties for sheet, plate, strip, rod and bar

    Impact strength, Charpy notched

    Ivnot

    1250 kJ/m² at -196 °C

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    Tensile strength

    Rm

    650 MPa at 23 °C

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    Typical mechanical property for sheet, plate, strip, rod and bar

    Yield strength Rp0.2

    Rp0.2

    300 MPa at 20 °C

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    Yield strength Rp1.0

    Rp1.0

    340 MPa at 20 °C

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    Typical mechanical properties

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    Thermal

    Coefficient of thermal expansion

    α

    1.5E-5 1/K at 100 °C

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    Melting point

    Tm

    1320 - 1390 °C

    Specific heat capacity

    cp

    415 J/(kg·K) at 20 °C

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    Thermal conductivity

    λ

    12 W/(m·K) at 20 °C

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    Electrical

    Electrical resistivity

    ρel

    9.6E-7 Ω·m at 20 °C

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    Magnetic

    Relative magnetic permeability

    μrel

    1 [-] at 23 °C

    Chemical properties

    Element

    Weight %

    Comment

    Fe

    -

    Balance

    Ni

    24 - 26 %

    Cr

    20 - 21 %

    Mo

    6 - 7 %

    Mn

    1 %

    max.

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    Technological properties

    Application areas

    Cronifer 1925 hMo is a polyvalent material which finds application in a wide range of industries: fire fighting systems, seawater filtration systems and process, hydraulic and reinjection piping systems in the offshore industry, bleaching plants in cellulose pulp production, polished rods for corrosive oil wells, flexible pipe systems for the offshore industry, tubing and couplings, wire lines and flowline systems in sour gas production. In sour gas environment the alloy is listed in NACE Standard MR0175 (Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment) as acceptable up to Level V in the annealed or cold-worked condition at a hardness level of 35 HRC max., components for flue-gas desulphurization plants, such as dampers and stacks, evaporators, heat exchangers, filters and mixers used in the manufacture of phosphoric acid, sulphuric acid distribution systems and coolers, concentration and crystallization of salts by evaporation, condensers and piping systems in power stations using polluted cooling waters, containers for transportation of aggressive chemicals, production of organic derivatives with acid chloride catalysts, reverse-osmosis desalination plant. Cronifer 1925 hMo is approved for pressure vessels by VdTÜV from -196 to 400 °C, and by ASME.

    Cold Forming

    The workpieces should be in the annealed condition for cold forming. Due to its high molybdenum concentration, VDM® Alloy 926 has a higher work hardening rate than other austenitic stainless steels. This must be taken into account for the design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing is necessary for major cold forming work. For cold forming above 15%, a final solution annealing must be conducted.

    Corrosion properties

    VDM® Alloy 926 is an austenitic, special stainless steel with largely the same chemical composition as VDM® Alloy 904 L, while the nitrogen content was raised to 0.2 % and the molybdenum concentration to about 6.5 %. At the same time, the resistance against stress crack corrosion induced by pitting corrosion is improved. The nitrogen concentration raised to rounded 0.2 % improve the austenite stability and lowers the propensity to form inter-metallic phases. VDM® Alloy 926 is a good pick for media such as diluted sulfuric and phosphorus acids that are contaminated with chlorides, and also for salt concentrations and crystallizations against which the material proves a higher resistance against wear and tear. Due to its good corrosion resistance in seawater, VDM® Alloy 926 is also used for facilities on offshore platforms. The optimal corrosion behavior is only given if the material is used in clean, passivated condition.

    General machinability

    VDM® Alloy 926 is preferably processed in annealed condition. Since the alloy is prone to work hardening, a low cutting speed should be selected with a feed speed that is not too high and the cutting tool should stay engaged at all times. An adequate chip depth is important in order to cut below the previously formed work-hardened zone. An optimal heat dissipation by using large quantities of suitable, preferably aqueous, cold forming lubricants has considerable influence on a stable machining process.

    Heat Treatment

    Solution annealing should take place at temperatures between 1,150 to -1,200°C (2,102 to -2,192°F) and preferably at 1,180°C (2,156°F). The retention time during annealing depends on the semi-finished product thickness. The retention time starts with material temperature equalization; longer times are generally considerably less critical than retention times that are too short. Cooling down should be accelerated with water to achieve optimum properties. Fast air cooling can also be carried out at thicknesses of less than approx. 1.5 mm. The material must be placed in a furnace that has been heated up to the maximum annealing temperature before any heat treatment. For strips as the product form, the heat treatment can be performed in a continuous furnace at a speed and temperature that is adapted to the strip thickness.

    Hot forming

    VDM® Alloy 926 can be hot-formed in a temperature range between 1,200 and 900°C (2,192 and 1,652°F) with subsequent rapid cooling down in water or air. For heating up, workpieces should be placed in a furnace that is already heated up to 1,200 °C (2,192°F). Heat treatment after hot forming is recommended for achieving optimal corrosion behavior.

    Other

    VDM® Alloy 926 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. In principle, checking of welding parameters is necessary and it is therefore required to observe the section energy that is suitable for the material.

    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.