4.6 Article

Effect of Cold Rolling on the Microstructural Evolution and Mechanical Properties of Fe-25Mn-3Si-3Al-0.3Nb TWIP Steel

Journal

COATINGS
Volume 12, Issue 7, Pages -

Publisher

MDPI
DOI: 10.3390/coatings12070900

Keywords

cold rolling; TWIP steel; Nb-microalloying; twinning; mechanical properties

Funding

  1. Basic Research and Strategic Reserve Technology Research of PetroChina Company Limited [2018Z-03]
  2. Scientific Research and Technology Development Project of PetroChina Company Limited [2017F-19]
  3. Special Support Program for High Level Talents of Shaanxi Province [00439]

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The microstructural evolution, deformation mechanism, and mechanical properties of Fe-25Mn-3Si-3Al-0.3Nb steel in the process of cold rolling were investigated. High-density dislocation structures and strain-induced twins appeared at 30% strain, and their characteristics changed at higher strains. The addition of 0.3 wt.% Nb did not alter the plastic deformation mechanism of the steel. Cold rolling significantly improved the strength and hardness of the steel while reducing its elongation. Micro-pore aggregation fractures were observed on the fracture surface of specimens with different strains.
The microstructural evolution, deformation mechanism and mechanical properties of Fe-25Mn-3Si-3Al-0.3Nb steel in the process of cold rolling were studied by optical microscopy, scanning microscopy, transmission electron microscopy, X-ray diffractometry, tensile testing and microhardness tests. A high-density dislocation structure and a small number of strain-induced twins appeared in the microstructure of the steel at 30% strain. At 50% strain, the strain-induced twins in austenite increased conspicuously, and the lamella thickness of the twins decreased. At 70% strain, the original grains were clearly refined by the micro-shear bands and twinning intersections to form a large number of sub-grains, and some sub-grains were at the nanoscale. The steel still remained a single-phase austenite during cold rolling even if the strain was as high as 70%. The plastic deformation mechanism of the steel was not changed through the addition of 0.3 wt.% Nb, and both dislocation slipping and twinning were still the fundamental plastic deformation mechanisms for the steel. Furthermore, cold rolling led to a drastic rise in the strength and hardness of the steel, but a remarkable decrease in the elongation. The characteristics of micropore aggregation fractures could always be observed on the fracture surface of static tensile specimens with various strains.

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