2.4856 (NiCr22Mo9Nb) Grade 1 is a nickel-chromium-molybdenum-niobium alloy with excellent resistance to a variety of corrosive. In the soft annealed condition (annealed at 950 to 1,050°C) the alloy is used for wet corrosion applications and is approved by TÜV for pressure vessels in a temperature range from -196 to 450°C and shows the following features and properties:
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8.47 g/cm³ at 23 °C
Coefficient of thermal expansionα
1.251E-5 1/K at 100 °C
1290 - 1350 °C
Specific heat capacitycp
496 J/(kg·K) at 100 °C
12.4 W/(m·K) at 100 °C
1.25E-6 Ω·m at 20 °C
Relative magnetic permeabilityμrel
1 [-] at 23 °C
58 - 71 %
21 - 23 %
8 - 10 %
3.2 - 3.8 %
Equipment for the production of super phosphoric acid;Plants for the treatment of radioactive waste;Production pipe systems and linings of risers in oil production;Offshore industry and seawater exposed equipment;Sea water piping in shipbuilding;Stress corrosion cracking resistant compensators;Furnace linings;Components in the oil and gas extraction;Superheater tubes in waste incineration plants
Cold working should be carried out on annealed material. VDM® Alloy 625 has a higher work hardening rate than austenitic stainless steels. This must be taken into account during design and selection of forming tools and equipment and during the planning of the forming processes. Intermediate annealing may be necessary at high degrees of cold working deformation. After cold working with more than 15% of deformation the material should be soft annealed.
Optimum corrosion resistance can only be obtained if the material is in the correct metallurgical condition and possesses a clean structure. Under these circumstances VDM® Alloy 625 (grade 1) has excellent corrosion resistance to a variety of corrosive media. Excellent resistance to pitting and crevice corrosion in chloride-containing media. Virtual immunity to chloride-induced stress corrosion cracking. High resistance to corrosion attack by mineral acids such as nitric, phosphoric, sulfuric, and hydrochloric acid, as well as by concentrated alkalis and organic acids, both under oxidizing as reducing conditions. Very good resistance in seawater and brackish water, even at elevated temperatures. High resistance to intergranular corrosion after welding and heat treatment and high resistance to erosion corrosion.
VDM® Alloy 625 should be machined in the annealed condition. As the alloy is prone to work-hardening, low cutting speeds and appropriate feed rates should be used and the tool should be engaged at all times. Sufficient chip depths are important to get below the work-hardened surface layer. The optimum dissipation of heat through the use of large amounts of appropriate, preferably water containing cooling lubricants is crucial for a stable machining process.
The soft annealing is carried out at temperatures of 950 to 1,050°C (1,742 to 1,922°F) preferably at temperature of 980°C (1,796°F). Workpieces of less than 3 mm (0.12 in) thickness can be cooled down using air nozzles. The workpiece has to be put into the pre-heated furnace. The furnace should be heated up to the maximum annealing temperature. The cleanliness requirements listed under ‘Heating’ must be complied with.
VDM® Alloy 625 may be hot worked in the temperature range 1,150 to 900°C (2,100 to 1,650°F) with subsequent rapid cooling down in water or by using air. The workpieces should be placed in the furnace heated to hot working temperature in order to heat up. Once the hot working temperature has been reached again, a retention time of 60 minutes for each 100 mm (4 in) of workpiece thickness is recommended. Afterwards, workpieces should be removed immediately and formed during the stated temperature window. If the material temperature falls to 950°C (1,742°F), the workpiece must be reheated. Heat treatment after hot working is recommended in order to achieve optimum microstructure and corrosion resistance.
VDM® Alloy 625 has a face-centered cubic lattice.
VDM® Alloy 625 can be joined by all conventional welding processes. These include GTAW (TIG), TIG hot wire, plasma arc, GMAW (MIG/MAG) and MAG-Tandem, submerged arc welding and SMAW (MMA). For welding, VDM® Alloy 625 should be in the soft or solution annealed condition and be free from scale, grease and markings. Pulsed arc welding is the preferred technique. For the MAG process the use of a multi-component shielding gas (Ar + He + H2 + CO2) is recommended. When welding roots, sufficient protection of the root needs to be ensured with pure argon (Ar 4.6) so that the welding seam is free of oxides after welding. Root backing is also recommended for the first intermediate pass following the initial root pass and in some cases even for the second pass, depending on the weld set-up. Any discoloration/heat tint should be removed preferably by brushing with a stainless steel wire brush while the weld metal is still hot.
This material data has been provided by VDM Metals.