VDM® Alloy 59

Plant components for organic chemistry processes with media containing chloride, multi-purpose plants in the chemicals industry, plant parts in active substance preparation and the pharmaceuticals industry, scrubber, heat exchangers, flaps, ventilators and agitators for flue gas desulfurization (FGD) in fossil fuel power plants and waste combustion plants, SO₂-washers for ship diesel engines, components for seawater and concentrated brines, equipment and components for geothermal energy and acid gas applications, reactors for acetic acids and acetic anhydrides, reactors for hydrofluoric acid and sulfuric acid coolers.

The workpieces should be in the annealed condition for cold forming. VDM® Alloy 59 has a significantly better work hardening rate than the widely used austenitic stainless steels. 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 for major cold forming work. For cold forming of >15%, a final solution annealing must be conducted.

Due to the extremely low carbon and silica concentrations, VDM® Alloy 59 has no propensity for grain boundary dispersions in hot forming or welding. The alloy can therefore be used in many chemical processes with oxidizing and reducing media. Furthermore, VDM® Alloy 59 is more resilient against chloride ion attack due to its high nickel, chrome and molybdenum concentrations.The corrosion tests described in the relevant standards usually refer to oxidizing conditions under which the VDM® Alloy 59 has proven to be clearly superior over all other Ni-Cr-Mo alloys. But VDM® Alloy 59 is also highly resistant under reducing conditions. Accordingly, its corrosion rate in boiling 10%-sulfuric acid is less than one-third of the attack measured on other introduced Ni-Cr-Mo alloys. With this excellent behavior, the alloy has also become successfully established in the chemical process industry in applications with reducing media.

Machining of VDM® Alloy 59 should take place in an annealed condition. Because of the considerably 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 chip depth 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.

The solution annealing should take place at temperatures between 1,100 and 1,180°C (2,012-2,156°F), preferably at 1,120°C (2,049°F). The retention time commences 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 or air in order to achieve optimum properties. The material must be placed in a furnace that has been heated up to the maximum annealing temperature before any heat treatment. For the product form strip, the heat treatment can be performed in a continuous furnace at a speed that is adapted to the strip thickness and a temperature that differs from the specified temperatures and times. The cleanliness requirements listed under "Heating" must be observed.

VDM® Alloy 59 should be hot-worked in a temperature range between 1,180 and 950°C (2,156-1,742°F) with subsequent rapid cooling down in water or air. For heating up, workpieces should be placed in a furnace which has been heated up to the maximum hot forming temperature. Heat treatment after hot forming is recommended for achieving optimal corrosion behavior.

VDM® Alloy 59 has a cubic, face-centered crystal structure.

VDM® Alloy 59 can be welded using conventional processes with metals of the same type as well as many other metals. This includes TIG, GMAW (MIG/MAG), plasma, electron beam welding and handheld electrical welding. The use of a pulse technique is preferable during shielding gas welding processes. The use of a multi-component shielding gas (Ar+He+H2+CO2) with low CO2 concentrations (<0.12%) is recommended for the MAG process. For welding, VDM® Alloy 59 should be in a solution-annealed condition and free of scale, grease and markings. When welding the root, care should be taken to achieve best quality root protection using pure argon (argon 4.6) so that the welding edge is free of oxides after welding the root. Root protection is also recommended for the first and, in certain cases depending on the welded construction, also for the second intermediate layer weld after root welding. Any heat tint in the intermediate layers must be removed while the welding edge is still hot, preferably by means of a stainless steel brush.