Coupled strengthening in a medium manganese lightweight steel with an inhomogeneously grained structure of austenite
- Authors
- Lee, Chan-Young; Jeong, Junyeong; Han, Jeongho; Lee, Seung-Joon; Lee, Sukjin; Lee, Young-Kook
- Issue Date
- Feb-2015
- Publisher
- PERGAMON-ELSEVIER SCIENCE LTD
- Keywords
- Grain size; Mechanical properties; Strain hardening rate; Twinning; TRIP-assisted steel
- Citation
- ACTA MATERIALIA, v.84, pp.1 - 8
- Indexed
- SCIE
SCOPUS
- Journal Title
- ACTA MATERIALIA
- Volume
- 84
- Start Page
- 1
- End Page
- 8
- URI
- https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/157892
- DOI
- 10.1016/j.actamat.2014.10.032
- ISSN
- 1359-6454
- Abstract
- The deformation mechanism of a medium-Mn lightweight steel with an inhomogeneously grained structure of austenite was investigated as a function of annealing temperature. All annealed specimens exhibited three different phases: gamma-austenite, delta-ferrite and alpha'-martensite. Specimens annealed at temperatures below 1000 degrees C exhibited high strain-hardening rates (SHRs) and good combinations of ultimate tensile strength and ductility (similar to 35,000-37,000 MPa%) due to the sequential occurrence of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) during tensile deformation. The SHR-true strain curves of the annealed specimens are divided into four different stages: dynamic recovery of dislocations (stage I), active TRIP (stage II), slow TRIP (stage III) and mechanical twinning (stage IV). However, the specimen annealed at 1000 degrees C did not exhibit stage IV, most likely due to its coarse grain size. Whereas the TRIP occurred in coarse gamma-austenite grains at small tensile strains, the TWIP took place in fine gamma-austenite grains with a size of less than, similar to 10 mu m at large tensile strains. This result indicates that grain refinement induced the transition in deformation mechanism from the TRIP to the TWIP. The inhomogeneously grained structure of gamma-austenite in the annealed specimens consists of coarse grains pre-existing in the hot-rolled state and fine grains newly formed during annealing.
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