VDM® Alloy 601

VDM® Alloy 601 has found a wide variety of applications in high temperature areas in furnace construction, the chemical industry, in environmental protection facilities, in the automobile industry and in power plants. Typical application fields include: rays, baskets and fixtures for heat treatment plants, e. g. in carburizing or carbonitriding environments, refractory anchors, strand-annealing and radiant heater tubes, high-velocity gas burners, wire mesh belts in industrial furnaces, isolating inserts in ammonia crackers and catalyst support grids in nitric acid production, high temperature components in automotive parts, e. g. manifolds, glow plug tubes or sensor caps, combustion chambers in solid waste incinerators, tube supports and ash-handling components, components in exhaust gas systems, oxygen preheaters.

Cold working should be carried out on annealed material. VDM® Alloy 601 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 in order to avoid recrystallization to a fine-grained microstructure with low creep resistance during operation. Scaled workpieces can also be cold-worked. The inside bending diameter should be at least 1.5 times the sheet/plate thickness.

According to DIN EN 10095 VDM® Alloy 601 is termed a heat resistant alloy on account of its excellent resistance above 550 °C against hot gases and combustion products, as well as against molten salt, while at the same time exhibiting good mechanical short-time and long-term properties. Even under severe conditions, such as under cyclic heating and cooling, VDM® Alloy 601 retains a tightly adherent oxide layer which is very resistant to spalling. According to DIN EN 10095, the maximum operating temperature in air is 1200 °C, while the loss of weight from scaling is not higher than 1 g/m² h on average. Resistance to carburization is good. VDM® Alloy 601 has also shown good resistance in (carbo) nitriding conditions, if a sufficiently high oxygen partial pressure is present.

VDM® Alloy 601 should be machined in the solution 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. 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.

For any thermal treatment the material should be charged into the furnace at maximum annealing temperature observing the precautions concerning cleanliness mentioned earlier under ‘Heating’. Solution annealing should be carried out in the temperature range 1,100 to 1,200 °C (2,010 to 2,190 °F). Optimum creep strength is achieved by a relatively coarse grained microstructure (≤ 5 according to ASTM E 112 or > 65 µm) using annealing temperatures between 1,140 and 1,160°C (2,084 and 2,120°F). The retention time starts when the annealing temperature is reached. Longer retention times are less critical than too short retention times. 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. In components made of VDM® Alloy 601, stress relaxation cracks may occur during in continuous operation (>100 h) in the temperature range between 600 and 650 °C (1,112 and 1,202°F). The risk of cracking can significantly be reduced through a thermal treatment at 980 °C (1,796°F) for ~3 h. Heating rates are not critical, but should not be too high in order to avoid material distortion.

VDM® Alloy 601 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. The workpieces should be placed in the furnace heated to hot working temperature in order to heat up. Heat treatment after hot working is recommended in order to achieve optimum fabrication properties (cold forming, machinability, weldability) and creep resistance.

VDM® Alloy 601 has a face-centered cubic lattice. The good mechanical properties are determined by the precipitation of carbides below 1150 °C. Below 800 °C, additional γ’ precipitations may occur.

For welding, VDM® Alloy 601 should be in the annealed condition and be free from scale, grease and markings. VDM® Alloy 601 can be welded using the following procedures: GTAW (TIG), GMAW (MIG/MAG), plasma, electron beam welding (EB) and SMAW (MMA).