Improvement of High Temperature Strength and Toughness of 12mass%Cr-15mass%Mn Austenitic Steels Developed as a Heat Resisting Material

For the development of a high Mn-Cr austenitic steel as one of the heat resisting materials, the present authors have investigated the high temperature strength, toughness and mirostructural phase instability of 12%Cr-15%Mn steels. High content of carbon (0.1 to 0.2 mass%C) formed the large amount of coarse precipitates of the type M23C6 carbide on grain boundaries and within grains after a long-term aging. These precipitates caused the intergranular and/or quasi-cleavage fracture and deteriorated the toughness. It was clarified that, for the improvement of the toughess, the lowering of carbon content to 0.02mass%C was necessary. The toughness and high temperature strength of the 12% Cr-15%Mn steels were compared and discussed with those of the ordinary SUS316 steel. Creep-rupture strength of the present materials was also compared with that of the TENELON which had been developed by Brady et al (US steel) as a high Mn austenitic heat resisting steel. The creep-rupture strength of the 12%Cr-15%Mn steel was superior to those of the type 316 steel and the TENELON.