Influence of thermal exposure on the interfacial microstructure of Stellite 6 coated 9-12-Cr steels for steam turbine applications

摘要

9-12% Cr steels are widely used in turbine parts in steam power plants because of their good mechanical properties and corrosion resistance at elevated temperatures. However, parts like valve seats and spindles are prone to oxidation, particle erosion or wear. This requires the application of protective coatings with adequate mechanical properties, wear and spalling resistance. Cobalt based coatings like Stellite 6 are applied for service temperatures up to 550℃, but steam temperatures of up to 700℃ are planned for future power plants in order to decrease the CO_2 exhaustion. In this work, the interfacial microstructure of Stellite 6 coated 12% Cr steel before and after long term annealing at elevated temperatures (up to 650℃ and 10000 h) was characterized. The experimental results were compared with the results of additional thermodynamic simulations. It could be shown that a thin (～20 μm), hard and brittle interlayer forms during annealing.