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Low-alloy steel 16Mo3 is often used for tubes and other components of the pressure system of a boiler operating at elevated temperature (up to 530 °C). Long-term exposure of low-alloy steel components at elevated temperatures inevitably result in some kind of structural degradation; for example, creep cavitation, carbide coarsening and/or spheroidization, and, less commonly, also graphitization. Graphitization can be detected mainly in carbon steels, but also in 16Mo3 steel where the ferritic matrix is strengthened by Mo in the solid solution. The absence of strong carbide forming elements (typically Cr, V, Nb) is the principal reason why these steels are susceptible to cementite decomposition and graphitization much more than the other creep resistant steels.The paper describes microstructure and material properties of superheater 16Mo3 tube, in which graphite was found after 70.000 hours of exposure at 445 °C. The actual material properties were compared to another tube of the same material delivered in the as-received state. The comparison was based on evaluation and testing of mechanical strength, fracture properties and microstructure. Creep resistance of the steel was studied using small punch creep tests (SPCT).
Keywords: 16Mo3 steel, superheater tubes, graphite, microstructure© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.