Evolution of secondary phases 12% Cr steel during quenching and tempering

Secondary phase evolution in the 12 wt.% Cr steel austenitized at 1100 and 1330°C and subsequently tempered at 750°C was investigated. To describe the microstructures and identify the secondary phases, methods of light microscopy and transmission electron microscopy including electron diffraction and microanalysis were used. It was found that oil quenching from 1100°C leads to formation of autotempered martensite containing intragranular (Fe4Cr)3C and MN particles. After oil quenching from 1330°C the microstructure consists of martensite, δ-ferrite, intragranular MN particles, and M23C6 particles precipitating at the γ/δ interfaces. In microstructures of tempered states Cr-rich M23C6, Ti-rich MN, and V-rich MC particles were found. It was shown that quenching temperature and/or appearance of δ-ferrite in the microstructure do not significantly affect the evolution of secondary phases during tempering.