TEM characterization on new 9% Cr advanced steels thermomechanical treated after tempering

Phase transformation on new six reduced activation ferritic/martensitic steels (RAFMs) was investigated to provide the basis for the design and development of advanced steels to maintain adequate strength and creep resistance above 500 °C. The new alloys are designed to increase the amount of fine MX precipitates and reduce coarse M₂₃C₆ carbides through alloy composition refinement and the application of thermomechanical treatments. The microstructural investigations by TEM have shown M₂₃C₆, M₂X, and MX precipitation after tempering at 700 °C/2h with low dislocation recovery, while at 825 °C/2h the martensite developed to subgrain formation and growth. At this stage, only M₂₃C₆ and MX were detected. Preliminary results demonstrate that it is feasible to produce fine MX strengthened particles dispersed in the matrix with further optimization of tempering treatments.