Arunansu Haldar

Evolution of Crystallographic Texture and Microstructure During Cold Rolling of Twinning-Induced Plasticity (TWIP) Steel: Experiments and Simulations

A systematic investigation of the evolution of deformation microstructure and texture of twinning-induced plasticity (TWIP) steel during cold rolling has been carried out using electron backscatter diffraction and X-ray diffraction, as well as viscoplastic self-consistent simulations. It is found that extensive twinning leads to the formation of the strong Brass {110}〈112〉 and Goss {110}〈001〉 components in TWIP steel even at low strains. At higher reduction, heterogeneous deformation contributes to further strengthening of Brass (Bs) component. The origin and stability of Bs component as well as the impact of the evolution of texture and microstructure on mechanical anisotropy is further explored using viscoplastic self-consistent simulations.

Development of Multiphase Microstructure with Bainite, Martensite, and Retained Austenite in a Co-Containing Steel Through Quenching and Partitioning (Q&P) Treatment

The quenching and partitioning (Q&P) treatment of steel aims to produce a higher fraction of retained austenite by carbon partitioning from supersaturated martensite. Q&P studies done so far, relies on the basic concept of suppression of carbide formation by the addition of Si and/or Al. In the present study Q&P treatment is performed on a steel containing 0.32 C, 1.78 Mn, 0.64 Si, 1.75 Al, and 1.20 Co (all wt pct). A combination of 0.64 Si and 1.75 Al is chosen to suppress the carbide precipitation and therefore, to achieve carbon partitioning after quenching. Addition of Co along with Al is expected to accelerate the bainite transformation during Q&P treatment by increasing the driving force for transformation. The final aim is to develop a multiphase microstructure containing bainite, martensite, and the retained austenite and to study the effect of processing parameters (especially, quenching temperature and homogenization time) on the fraction and stability of retained austenite. A higher fraction of retained austenite (~13 pct) has indeed been achieved by Q&P treatment, compared to that obtained after direct-quenching (2.7 pct) or isothermal bainitic transformation (9.7 pct). Carbon partitioning during martensitic and bainitic transformations increased the stability of retained austenite.

Micromechanics of emergent patterns in plastic flows

Crystalline solids undergo plastic deformation and subsequently flow when subjected to stresses beyond their elastic limit. In nature most crystalline solids exist in polycrystalline form. Simulating plastic flows in polycrystalline solids has wide ranging applications, from material processing to understanding intermittency of earthquake dynamics. Using phase field crystal (PFC) model we show that in sheared polycrystalline solids the atomic displacement field shows spatio-temporal heterogeneity spanning over several orders of length and time scales, similar to that in amorphous solids. The displacement field also exhibits localized quadrupolar patterns, characteristic of two dislocations of the opposite sign approaching each other. This is a signature of crystallinity at microscopic scale. Polycrystals being halfway between single crystals and amorphous solids, in terms of the degree of structural order, descriptions of solid mechanics at two widely different scales, namely continuum plastic flow and discrete dislocation dynamics turns out to be necessary here.

Development of asymmetric rolling for the better control over structure and mechanical properties in IF steel

In the present study, the effects of kinematic and geometric asymmetries in rolling during multi-pass processing of IF steel are examined. The theoretical investigation by final element simulations and experimental investigations by means of electron-backscatter diffraction analysis and tensile tests suggest that asymmetric rolling increases the total imposed strain compared to symmetric rolling, and largely re-distributes the strain components due to additional shear. This enhances the intensity of grain refinement, strengthens and tilts crystallographic orientations, and increases mechanical strength. The effect is highest in the asymmetric rolling with differential roll diameters.

Structure and Mechanical Properties of Asymmetrically Rolled IF Steel Sheet

As-received hot-rolled 5.6 mm thick IF steel sheet was symmetrically/asymmetrically cold rolled at room temperature down to 1.9 mm. The asymmetric rolling was carried out in monotonic (an idle roll is always on the same side of the sheet) and reversal (the sheet was turned 180º around the rolling direction between passes) modes. Microstructure, texture and mechanical properties were analysed. The observed differences in structure and mechanical properties were modest, and therefore further investigation of the effects of other kinds of asymmetry is suggested.

Texture and Microstructural Evolution in Pearlitic Steel During Triaxial Compression

This article presents the deformation behavior of high-strength pearlitic steel deformed by triaxial compression to achieve ultra-fine ferrite grain size with fragmented cementite. The consequent evolution of microstructure and texture has been studied using scanning electron microscopy, electron back-scatter diffraction, and X-ray diffraction. The synergistic effect of diffusion and deformation leads to the uniform dissolution of cementite at higher temperature. At lower temperature, significant grain refinement of ferrite phase occurs by deformation and exhibits a characteristic deformation texture. In contrast, the high-temperature deformed sample shows a weaker texture with cube component for the ferrite phase, indicating the occurrence of recrystallization. The different mechanisms responsible for the refinement of ferrite as well as the fragmentation of cementite and their interaction with each other have been analyzed. Viscoplastic self-consistent simulation was employed to understand deformation texture in the ferrite phase during triaxial compression.

Low carbon high manganese bainitic steel

Abstract The present study concerns the mechanical properties of low carbon (0·05 wt-%) high Mn bainitic steel. The continuous cooling transformation diagram exhibited bainitic transformation without any prior diffusive transformation of austenite even for a cooling rate as low as 0·5°C/s. The bainitic steels have shown continuous elongation behaviour with attractive combination of strength (>1200 MPa) and elongation (>14%). The bainitic microstructure obtained after annealing treatment has yielded excellent combination of strength, uniform elongation, yield ratio and static toughness value.

Effect of short duration tempering on the microstructure and mechanical properties of a continuously annealed dual phase steel

Abstract The effect of short duration tempering on the microstructure and mechanical properties of a continuously annealed dual phase steel was investigated using techniques like electron microscopy, dilatometry and thermodynamic calculations. It was found that a complex interplay of phenomena like tempering of martensite, quench aging of ferrite and recovery of the overall structure was responsible for the change in mechanical properties recorded.

Microstructure and mechanical property of cold rolled low carbon steel after prolonged annealing treatment

Abstract The effects of ferrite–pearlite and ferrite–martensite starting microstructures on ferrite grain sizes and carbide particle sizes after cold rolling and prolonged annealing treatment have been investigated. Ferrite–martensite starting microstructures showed finer grain and particle sizes and improved tensile properties after cold rolling annealing cycle compared to ferrite–pearlite starting microstructures. A ‘fibrous’ martensite morphology developed by intermediate quenching treatment is more beneficial in that respect compared to the ‘blocky’ martensite morphology obtained from the step quenching treatment.

Hot-rolled and continuously cooled bainitic steel with good strength–elongation combination

The current work demonstrates the microstructural evolution and mechanical property evaluation of a newly designed steel composition after hot rolling in laboratory-scale rolling mill, followed by continuous cooling. The steel thus developed has typically about 80% carbide-free bainite; about 20% retained austenite and can deliver ∼1400 MPa ultimate tensile strength along with more than 20% total elongation. The presence of ultra-fine bainite plates (∼100–130 nm thick) with high dislocation density was thought to be responsible for ultra-high strength. Excellent ductility at such strength level could be due to the presence of sufficient amount of retained austenite (∼20%) thermally stable at room temperature but starts transforming to martensite during deformation exhibiting transformation-induced plasticity effect.