Papers by Author: Debashish Bhattacharjee

Abstract: 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.

Abstract: In this study, severe plastic deformation (SPD) of Ti-bearing interstitial-free steel was carried out by multi-axial forging (MAF) technique. The grain refinement achieved was comparable to that by other SPD techniques. A considerable heterogeneity was observed in the microstructure and texture. Texture of multi-axially forged steels has been evaluated and reported for the first time. The material exhibited a six-fold increase in the yield strength after four cycles of MAF.

Abstract: 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.

Abstract: A simple and reliable method has been proposed for determining fracture toughness of thin sheets. The principle of the method considers that critical crack opening displacement (c) corresponds to a specific amount of load drop during fracture toughness tests. The suggested technique yields c value for an interstitial free (IF) steel as 2.04 mm in excellent correspondence with an indirect estimate of 1.97 mm from the popular energy extrapolation technique. The magnitude of c for IF steel sheets is found to decrease with decreasing thickness in agreement with the expected variation of this criterion with specimen thickness in gross yielding fracture mechanics (GYFM) regime.