Ferritic-martensitic steel subjected to equal channel angular extrusion

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Title: Ferritic-martensitic steel subjected to equal channel angular extrusion
Author: Foley, David Christopher
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 .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2537
Date: 2009-05-15

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Ferritic-martensitic steel subjected to equal channel angular extrusion. Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2537 .

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