| dc.description.abstract | Modified 9Cr-1Mo ferritic-martensitic steel (T91) has been extensively
investigated as a structural material for GenIV nuclear reactors and Accelerator Driven
Transmutation systems. One attractive characteristic of this steel in these applications is
its superior radiation damage tolerance in comparison to typical austenitic stainless steels
such as 316L. In some GenIV applications, it also has a significantly higher corrosion
resistance. Further improvement of both is necessary if GenIV designs are to become
commercially viable. Other work has shown an improvement in radiation damage
tolerance via cold rolling or sputtering nanoscale multilayered films. Additionally,
corrosion resistance can be improved by homogenizing the microstructure. Further, these
changes can improve the strength of the material. However, there has been no fabrication
of bulk ultra fine grain ferritic-martensitic steel candidates that might offer these avenues
of improvement. This work demonstrates the refinement and homogenization of T91 by
Equal Channel Angular Extrusion (ECAE) and heat treatment. Processing temperature
and strain level were varied to produce multiple levels of refinement. Materials were
characterized by microhardness, tensile testing, x-ray diffraction and transmission
electron microscopy. An ultra-fine, highly misoriented and homogeneous microstructure was achieved
in the material. Refinement was demonstrated both in ferritic and ferritic-martensitic
compositions of the steel. Microhardness increased by as much as 70% and ultimate
tensile strength by 80%. More significantly, tensile strength was improved by 40%
without decreasing ductility. | en |
