VDM® Alloy 800

Typical fields of application for VDM® Alloy 800 are: Heating element sheaths, acetic anhydride cracking furnaces VDM® Alloy 800 shall be used in the soft-annealed condition up to 600 °C. The solution annealed version VDM® Alloy 800 H shall be considered for application temperatures above 600 °C.

VDM® Alloy 800 is easily cold-shaped. However, it has a slightly higher work-hardening than carbon steel. This must be taken into account during the design and selection of forming tools and equipment and during the planning of forming processes. Intermediate annealing is necessary during cold working.

VDM® Alloy 800 is resistant to many corrosive media. For wet corrosion, the increased nickel content of this alloy results in good resistance to stress cracking corrosion. The elevated chromium content increases the resistance to pitting and crevice corrosion. The alloy shows good resistance in nitric acid and organic acids, but only limited resistance to sulfuric and hydrochloric acid. Pitting corrosion may occur in halogen-containing acids. The material shows good resistance in oxidizing and reducing saline solutions. It is also resistant in fresh water and steam as well as mixtures of steam, air and carbon dioxide. At elevated temperatures, VDM® Alloy 800 exhibits excellent resistance in oxidizing and carburizing atmospheres as well as in alternating oxidizing and carburizing atmospheres. The resistance to hydrogen, nitrogen and sulfuric gases is good, whereby it is better under oxidizing conditions than under reducing conditions.

Machining of VDM® Alloy 800 should take place in an annealed condition. Because of the elevated tendency toward work hardening in comparison with low-alloy austenitic stainless steels, a low cutting speed and a feed level that is not too high should be selected and the cutting tool should be engaged at all times. An adequate depth of cut is important in order to cut below the previously formed strain-hardened zone. Optimum heat dissipation through the use of large quantities of suitable preferably aqueous lubricants has considerable influence on a stable machining process.

VDM® Alloy 800 is used in the soft-annealed condition in applications whose operating temperatures are below approximately 600°C (1,112°F). The annealing should be performed at temperatures of 920 to 980°C (1688-1796°F), preferably at about 950°C (1,742°F). The retention time commences with material temperature equalization; longer times are generally considerably less critical than retention times that are too short. Cooling should be accelerated with water to achieve optimum corrosion properties. Fast air cooling can also be carried out at thicknesses below approx. 3 mm. The material must be placed in a furnace that has been heated up to the maximum annealing temperature before any heat treatment. For strip products, the heat treatment can be performed in a continuous furnace at a speed and temperature that is adapted to the strip thickness. The cleanliness requirements listed under "Heating" must be observed.

VDM® Alloy 800 can be hot-formed at a temperature range of between 1,200 and 900°C (2,192-1,652°F) with subsequent rapid cooling down in water or in air, whereby the temperature range from 760 to 540 °C (1,400-1,004°F) must be passed through quickly. Hot bending is performed between 1,150 and 1,000°C (2,102-1,832°F). For preheating, the workpieces may be placed in the furnace which has already been preheated to the maximum hot forming temperature. The workpieces should be retained in the furnace for around 60 minutes per 100 mm of thickness once the furnace has reached its temperature again. After this, the workpiece should be removed from the furnace immediately and formed within the temperature interval stated above, whereby reheating is necessary once the temperature reaches 900 °C (1,652°F). Heat treatment after hot-working is recommended for the achievement of optimal corrosion properties and microstructure.

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

Care should be taken that the work is performed with a deliberately chosen, low heat input. The stringer bead technique is recommended. The interpass temperature should not exceed 120°C (248 °F). The welding parameters should be monitored as a matter of principle.