Ultrafine Structure and High Strength in Cold-Rolled Martensite

Publication: Research - peer-reviewJournal article – Annual report year: 2012

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Structural refinement by cold rolling (10 to 80 pct reductions) of interstitial free (IF) steel containing Mn and B has been investigated from samples with different initial structures: (a) lath martensite, (b) coarse ferrite (grain size 150 mu m), and (c) fine ferrite (22 mu m). Unalloyed IF steel with a coarse grain size (120 mu m) has also included based on a previous study. Deformation microstructures and structural parameters have been analyzed by transmission electron microscopy and electron backscatter diffraction, and mechanical properties have been characterized by hardness and tensile testing. At low to medium strains, lath martensite transforms into a cell block structure composed of cell block boundaries and cell boundaries with only a negligible change in strength. At medium to large strains, cell block structures in all samples refine with increasing strain and the hardening rate is constant (stage IV). A strong effect of the initial structure is observed on both the structural refinement and the strength increase. This effect is largest in lath martensite and smallest in unalloyed ferrite. No saturation in structural refinement and strength is observed. The discussion covers the transformation of lath martensite into a cell block structure at low to medium strains where the driving force is suggested to be a decrease in the dislocation line energy. Medium to large strain-hardening mechanisms are discussed together with structure-strength relationships assuming additive stress contributions from dislocations, boundaries, and elements in solid solution. Good agreement is found between flow stress predictions and stress values observed experimentally both in the initial undeformed martensite and in deformed samples.
Original languageEnglish
JournalMetallurgical and Materials Transactions A - Physical Metallurgy and Materials Science
Publication date2012
Volume43A
Journal number10
Pages3517-3531
ISSN1073-5623
DOIs
StatePublished

Conference

ConferenceFall 2011 Materials Science and Technology Meeting
CityColumbus, OH
Period16/10/1120/10/11

Bibliographical note

© ASM International

CitationsWeb of Science® Times Cited: 0

Keywords

  • MATERIALS, METALLURGY, LOW-CARBON STEEL, LATH MARTENSITE, NANOSTRUCTURED METALS, MECHANICAL-PROPERTIES, DISLOCATION DENSITY, DEFORMED METALS, LARGE STRAINS, ALLOY-STEELS, GRAIN-SIZE, FE-C
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