VDM® Alloy 800 H

VDM® Alloy 800 H has a wide range of applications in areas of elevated temperatures in furnace construction, in the chemical industry, in environmental protection equipment, in the automotive industry and in power plants. Typical applications include furnace muffles, containers, bins, holders in various heat treatment plants and burner components. Because of its resistance to carburization and nitriding, the alloy is furthermore used in the areas of: steam/ hydrocarbon reformers, ethylene pyrolysis, Equipment for acetic anhydride and ketone production.

Cold working should be carried out on annealed material. VDM® Alloy 800 H 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 10 % deformation the material should be solution annealed.

The high nickel and chromium contents in VDM® Alloy 800 H ensure excellent resistance to oxidation. The alloy is also highly resistant to carburizing, nitriding and oxidation in sulphurous atmospheres. The protective oxide layer is adherent under static and cyclic thermal stress. The material is particularly resistant to carburization if a thin oxide film was formed by pre-oxidation. The resistance to hydrogen embrittlement of VDM® Alloy 800 H is excellent, so that the alloys can be used in the production of hydrogen and steam/hydrocarbon reformers.

VDM® Alloy 800 H should be machined in the solution annealed condition. As the alloys are 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. Due to the high temperature loads on the cutting edge during machining, large amounts of cooling lubricants should be used. Water-based emulsions, as they are also used for construction and stainless steels, are suitable for instance.

Solution heat treatment should be carried out at 1,150°C. Water quenching should be carried out rapidly if the material should be further fabricated after solution annealing. Workpieces of less than 3 mm (0.12 in) thickness can be cooled down using air nozzles. If the solution annealing is the last fabrication step, the material can be cooled down more slowly in order to avoid material distortion. Solution annealed VDM® Alloy 800 H is prone to stress relaxation cracks in the temperature range of 550 and 750°C and should therefore be subjected to stabilizing annealing when a continuous operation (> 100 h) in the mentioned temperature range is intended. The stabilizing annealing temperature depends on the welding material and should be determined with VDM Metals’ Technical Customer Support. If possible, the stabilizing annealing should be carried out when all welding work is completed, because the heat-affected zones of the welds are particularly susceptible to cracking. Heating rates are critical and should not be too high to avoid disortion.

VDM® Alloy 800 H may be hot-worked in the temperature range 1,200 to 900°C (2,192 to 1,650°F) with subsequent rapid cooling down in water or by using air. In particular the temperature range from 760 to 540 °C (1,400 to 1,004°F) must be passed quickly. Hot bending is carried out at 1,150 to 1,000°C (2,102 to 1,832°F). The furnace should be heated up to maximum working temperature (1,200°C/2,192°F) before workpieces are inserted into the preheated furnace. The holding time is about 60 minutes per 100 mm thickness. After the hot forming a solution heat treatment is recommended in order to achieve optimum creep strength.

VDM® Alloy 800 H is an austenitic solid solution alloy which precipitates carbides and γ’ phase during high-temperature ageing.

For welding, VDM® Alloy 800 H should be in the annealed condition and be free from scale, grease and markings. VDM® Alloy 800 H can be welded using the following procedures: GTAW (TIG), GTAW (TIG) hot wire, plasma, SMAW (MMA), GMAW (MIG/MAG) and submerged arc welding.