The relationship between toughness and microstructure in Fe-high Mn binary alloys |
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Authors: | Y Tomota M Strum and J W Morris |
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Affiliation: | (1) Ibaraki University, Faculty of Engineering, Hitachi-Shi, Japan;(2) Department of Materials Science and with the Lawrence Berkeley Laboratory, University of California, 94703 Berkeley, CA |
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Abstract: | The influence of Mn content on the ductile-brittle transition in 16 to 36 wt pct Mn steels was investigated and interpreted
in light of the evolving microstructure. It was found that when hcp ε martensite is present in the as-quenched condition or
forms during deformation, it lowers the toughness. In 25Mn steel, the stress concentrations at e plate intersections result
in the formation of planar void sheets along the {111}γ planes. The deformation-induced α’ martensite in 16 to 20 pct Mn alloys enhances the toughness, but leads to a ductile-to-brittle
transition at low temperatures that is due to the intrusion of an intergranular fracture mode. Binary alloys with greater
than 31 pct Mn also fracture in an intergranular mode at 77 K although the impact energy remains quite high. Auger spectroscopy
of the fracture surfaces shows no evidence of significant impurity segregation, which suggests the importance of slip heterogeneity
in controlling intergranular fracture in these alloys. |
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