Texture evolution during strain-induced martensitic phase transformation in 304L stainless steel at a cryogenic temperat
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E austenitic stainless steels have a metastable facecentered-cubic (fcc) (g) structure and, upon cooling below the martensite start temperature (Ms), the martensitic phase transformation occurs. With the aid of plastic strain, the transformation may be induced at temperatures higher than Ms.[1,2,3] The newly formed martensite phases have hexagonal close packed (e) and body-centered cubic (a9) structures.[4,5] The martensitic transformation in transformation-induced plasticity (TRIP) steel has been reported to be grain orientation dependent, meaning that grain families with particular orientations relative to the loading direction are preferred for the transformation.[6] In a previous publication,[7] it has been reported that the fcc grain family with the (200) plane-normal parallel to the compressive loading axis is preferred for the fcc to bcc transformation in 304L stainless steel, and the (200) plane-normal of the newly formed bcc phase is along the loading direction, that is, (200)g//(200)a9. For the fcc to hcp transformation, the transformation occurs by the coalescence of the partial dislocations on the fcc (111) planes. The orientation relationship between the fcc and hcp crystals is (111)g//(0001)e,[8] and it is implied that the fcc grain family with (111) plane-normal parallel to the loading axis is closely associated with the fcc to hcp transformation at 203 K.[7] Therefore, the newly formed martensites (both bcc and hcp phases) should be textured due to the preferential phase transformation during loading, while the ausKAIXIANG TAO, Graduate Research Assistant, is with the Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996. DONALD W. BROWN, Instrument Scientist, is with MST-8, Los Alamos National Laboratory, Los Alamos, NM 87545. SVEN C. VOGEL, Instrument Scientist, is with LANSCE-LC, Los Alamos National Laboratory, Los Alamos, NM 87545. HAHN CHOO, Professor, is with the Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831. Contact e-mail: [email protected] Manuscript submitted May 7, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS A
tenite develops its own texture by the compressive plastic deformation (slip). However, the results mentioned previously are based on the observations of the intensity changes of relevant hkl planes at 690 deg diffraction angles (i.e., only in the directions parallel and perpendicular to the loading direction) measured using the SMARTS diffractometer at Los Alamos Neutron Science Center (LANSCE). In terms of the texture, the SMARTS measurement does not provide enough pole figure coverage. To investigate the texture evolution of both austenite and martensites during the phase transformation and the plastic deformation, the neutron diffraction study was performed using the high pressure preferred orientation (HIPPO) diffractometer at LANSCE. Due to the multidetector capability and the deep penetration of neutrons into the material, the HIPPO diffractometer is an ideal tool for bulk texture measurement
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