Crack propagation in Fe-12Mn at 77K

1. Crystallography of crack propagation in steelJohn W. Morris, University of California-Berkeley, DMR 1006160 Research in this project concerns the nature of brittle fracture in high strength martensitic steel, and how the low-temperature transition to brittle fracture is controlled by the microstructure. The microstructure of the best martensitic steels consists of nano-sized laths of dislocated martensite that are gathered into “blocks” and subsequently into “packets” in a hierarchical pattern. Modern electron backscatter diffraction (EBSD) clearly reveals that pattern, as in the nano-lath microstructure of Fe-12Mn steel shown at right. Combining EBSD with scanning electron microscopy shows the crystallographic path of a crack, as at right. This crack follows a crystallographic “packet boundary”, and blunts when its continuation would require penetration into a packet. Crack propagation in Fe-12Mn at 77K Please insert an image (.JPEG)or group of images here. If you need more space, you may reduce the adjacent textbox. Please use lettering that is clearly visible (i.e. not too small). You could also insert chemical or mathematical formulas, molecular models, etc. Visually appealing images that can be appreciated by non-experts are most desirable, but feel free to use whatever is appropriate. Please include a very brief caption for the figures.

2. Crystallography of crack propagation in steelJohn W. Morris, University of California-Berkeley, DMR 1006160 The most important of the high-strength steels now used or proposed for low-temperature, arctic or cryogenic service are lath martensitic. There is a growing need for price- and energy-efficient versions of these alloys that have superior properties. These advances will be made by exploiting the microstructural mechanisms that control low-temperature strength and toughness. Extensive research on the microstructure and toughness of lath martensitic steels has produced a mechanistic picture of the brittle transition that is widely accepted and is increasingly driving steel metallurgy. The present research exploits new and probative research tools that let us map the complex crystallographic relations in lath martensites; the microstructure-property relations that were previously so difficult to visualize can now be probed directly.