Strengthening and toughening optimizations of novel G115 martensitic steel: Utilizing secondary normalizing process

Novel G115 martensitic steel (G115 steel) with excellent creep properties, oxidation resistance and low manufacturing cost, has been widely used for ultra-super critical (USC) power plants. Microstructural evolutions were characterized using multiple methods, and their effects on mechanical properties of G115 steel after secondary normalizing process at different temperature (1000 °C, 1050 °C and 1100 °C) were also investigated. The results show that the average width of martensitic lath decreases with increasing secondary normalizing temperature, which is inversely proportional to the dislocation density. The volume fraction of M23C6 precipitates increases with increasing secondary normalizing temperature. The maximum yield strength of G115 steel is achieved after hot-rolling, which is mainly derived from martensitic laths strengthening and dislocations strengthening. Compared to single normalizing treatment, the yield strength, the elongation, and the impact toughness of G115 steel can be improved after secondary normalizing treatment.