Effects of initial microstructure and shock method on the shock-induced transformation strengthening of carbon steels

On Investigating the Shock History of Ataxites

“…This can be done even in the case of a meteorite in which careful metallographic examination has failed to detect any traces of the epsilon-iron transformation. The X-ray techniques have been highly successful in establishing the previously unknown shock histories of a number of octahedrites and hexahedrites, but they apparently are not applicable to the fine-grained two phase microstructure of the ataxites (Jain and Lipschutz, 1970).Curiously, photomicrographs of ataxites published by Perry (1944) show no visible evidence of the epsilon-iron transformation structure, yet there seems to be little reason for believing that none of the meteorites in this classhas been shock-loaded above 130 kb.Recent work on carbon steels (Koepke, et al, 1971) indicates that higher shock loads are required to produce the epsilon-iron transformation in steels having large proportions of a second phase, cementite, in the microstructure than is the case when the proportion of the second phase is small. This suggests that the presence of large amounts of fine-grained taenite may have suppressed the epsilon-iron transformation in the surrounding kamacite in shocked ataxites -a possible explanation for the lack of visible transformation structure in Perry's photomicrographs.…”

“…Recent work on carbon steels (Koepke, et al, 1971) indicates that higher shock loads are required to produce the epsilon-iron transformation in steels having large proportions of a second phase, cementite, in the microstructure than is the case when the proportion of the second phase is small. This suggests that the presence of large amounts of fine-grained taenite may have suppressed the epsilon-iron transformation in the surrounding kamacite in shocked ataxites -a possible explanation for the lack of visible transformation structure in Perry's photomicrographs.…”