VDM® Alloy 600

Thermocouple sheathing in aggressive atmospheres, vinyl chloride monomer production (resistance to chlorine, hydrogen chloride, oxidation and carburization), conversion of uranium oxide to hexafluoride (resistance to attack by hydrogen fluoride, production and use of caustic alkalis, particularly in the presence of sulphur compounds), production of titanium dioxide by the chlorine route, production of organic and inorganic chlorinated and fluorinated compounds (resistance to attack by chlorine and fluorine), nuclear reactor components, heat treatment furnace retorts, furnace belts and components, particularly with carburizing or nitriding atmospheres, catalyst regenerators in petrochemical production.

The workpieces should be in the annealed condition for cold forming. VDM® Alloy 600 has a significantly higher work hardening rate than 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 of >15%, a final solution annealing must be conducted.

Nicrofer 7216 is resistant to a wide range of corrosive media. Due to the chromium content the alloy possesses better corrosion resistance than Nickel 99.2 (alloy 200) and LC-Nickel 99.2 (alloy 201) under oxidizing conditions. At the same time, the high nickel content results in good corrosion resistance under reducing conditions and in alkaline solutions and leads to virtual immunity to chloride-ion stress-corrosion cracking. Nicrofer 7216 shows moderate resistance to mineral acids and good resistance to acetic, formic, stearic and other organic acids. Excellent resistance is shown in high purity water, as used in the primary and secondary circuits of some nuclear reactors. Nicrofer 7216 is particularly resistant to attack by dry chlorine or hydrogen chloride, even at temperatures up to 650 °C. At high temperatures in air the soft-annealed and solution annealed alloy shows good resistance to oxide scaling and has high strength. The alloy also resists ammonia bearing atmospheres, as well as nitrogen and carburizing gases. Under alternating oxidizing and reducing conditions the alloy may suffer from selective oxidation (green rot).

VDM® Alloy 600 is preferably processed in annealed condition. Since the alloy is prone to work hardening, a low cutting speed should be used 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.

Soft annealing of VDM® Alloy 600 should take place in the temperature range between 920 and 1,000°C (1,688 and 1,832°F). 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 below approx. 3 mm. 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. In each heat treatment, the aforementioned cleanliness requirements must be observed.

VDM® Alloy 600 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 the target value. Heat treatment after hot forming is recommended in order to achieve optimal properties.

VDM® Alloy 600 has a cubic face-centered crystal structure.

VDM® Alloy 600 can be welded using the customary and conventional arc techniques such as TIG or MIG impulse technology. The material should be in its annealed condition for welding. A low heat input and fast heat removal must be ensured. The maximum interpass temperature should be between 100 and 150°C (212 and 302°F). Usually neither pre-heating nor a subsequent heat treatment is necessary.