9%Cr heat resistant steels: Alloy design, microstructure evolution and creep response at 650 °C

► 9Cr alloys with varying Ti and C contents were designed, produced and crept at 650 °C. ► Sub-grain and precipitate distribution and evolution investigated by STEM-HAADF. ► Correlations between microstructure evolution and mechanical properties were studied. ► Coarsening of sub-grain size was larger for Ti-containing 9Cr alloys. ► 9Cr alloy with low C and no Ti showed the highest creep strength of all studied alloys.