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G115 martensitic steel is anticipated to be one of the preferred candidate materials in ultra-super critical (USC) power plants with steam temperatures above 650°C. Microstructure evolutions and mechanical properties of G115 martensitic steel after applying various heat treatment processes were investigated. The results demonstrate that the main precipitate in G115 martensitic steel after applying various heat treatment processes is M 23 C 6 phase with Cr enrichment. The time required for M 23 C 6 phase precipitation decreases with increasing secondary normalizing temperature and the extension in holding time according to its precipitation-temperature-time (PTT) curves. Volume fraction of M 23 C 6 phase increases with increasing secondary normalizing temperature and holding time, which strengthens the inhibitory effect of precipitates on dislocations recovery and laths growth. Therefore, G115 martensitic steel can obtain the best mechanical properties after applying the highest secondary normalizing temperature and the longest holding time. In the current work, the excellent strength of G115 martensitic steel mainly derives from precipitates strengthening and laths strengthening. • Volume fraction of M 23 C 6 phases increases with increasing secondary normalizing temperature and the extension in holding time. • Dislocations recovery and laths growth are inhibited by M 23 C 6 phases. • The strongest factor increasing G115 steel's yield strength is lath strengthening. [ABSTRACT FROM AUTHOR]

Alumina-forming austenitic (AFA) steel, a promising candidate for use in high-temperature components of ultra-supercritical power plants, has high creep strengths and outstanding high-temperature corrosion resistance. The effects of microstructural evolution on the mechanical properties of Fe-20Ni-14Cr-3Al alumina-forming austenitic (3Al-AFA) steel with micro-cold deformation were investigated by multiple characterization methods, and the micro-cold deformation process was analyzed by conducting compression experiments. Tensile properties and hardness were also examined. The results show that the reduction of deformation has significant influences on the increase in the density of dislocation, the reduction of grain size, and the distribution of precipitates, which play an essential role in the enhancement of mechanical properties. As the reduction of deformation increases, the density of dislocations rises, the fragmentation of grains results in a reduction of grain size, and the distribution of precipitates at the grain boundaries gradually increases, which causes a rise in strength and a decrease in elongation. Since the elastic deformation range expands with an increase in deformation before the strain reaches 5 ​% of the CR0 sample in the compression test, the variation in the average grain aspect ratio between a reduction of 2 ​% and 6 ​% is relatively small. It contributes more to hardness and strength when the grain aspect ratio is high. [ABSTRACT FROM AUTHOR]