Duplex stainless steel casting is an investment casting process with duplex stainless steel as the material. Duplex stainless steels are called "duplex" because they have a two-phase microstructure consisting of ferritic and austenitic stainless steel grains. The picture shows the yellow austenite phase as "islands" surrounded by the blue ferrite phase. When duplex stainless steel melts, it solidifies from the liquid phase to a fully ferritic structure. As the material cools to room temperature, about half of the ferrite grains transform into austenite grains ("islands"). The result is a microstructure of approximately 50% austenite and 50% ferrite.
Duplex stainless steel castings
Duplex 2205 stainless steel is a nitrogen-enhanced duplex stainless steel used in stainless steel casting processes for applications requiring high strength and excellent corrosion resistance. It is designed to increase resistance to stress corrosion cracking, pitting and crevice corrosion. The corrosion resistance of duplex 2205 is almost twice that of other austenitic stainless steels.
Features of Duplex Stainless Steel Castings
Strength: Duplex stainless steel castings are approximately twice as strong as regular austenitic or ferritic stainless steel castings.
Toughness and ductility: The toughness and ductility of duplex stainless steel castings are significantly better than those of ferritic stainless steel castings; however, they do not reach the good values of austenitic stainless steel castings.
Corrosion Resistance: As with all stainless steels, corrosion resistance depends primarily on the composition of the stainless steel casting. For chloride pitting and crevice corrosion resistance, their chromium, molybdenum and nitrogen content is paramount. Duplex stainless steel casting grades offer a range of corrosion resistance similar to the range of austenitic stainless steel castings, i.e. from Type 304 or 316 to 6% molybdenum stainless steel castings.
Resistance to Stress Corrosion Cracking: Duplex stainless steels exhibit very good resistance to stress corrosion cracking, a property they "inherit" from the ferrite side. For standard austenitic castings, such as 304 and 316 stainless steel castings, stress corrosion cracking can be a problem under certain conditions (chlorides, humidity, high temperature).
Cost: Duplex stainless steel castings have lower nickel and molybdenum content than austenitic castings with similar corrosion resistance. Due to the lower alloy content, the cost of duplex stainless steels is lower, especially if the alloy surcharge is higher. Also, due to the higher yield strength of duplex stainless steels compared to austenitic stainless steels, it is often possible to reduce their section thicknesses. This combination results in significant cost and weight savings compared to austenitic stainless steel solutions.
