EBSD assessment of geometrically necessary dislocations near grain boundaries in AKDQ steel sheets under different mechanical straining

C. SCHWINDT; A ROATTA; NATHALIE BOZZOLO; BOLMARO, RAÚL E.; MARTINA AVALOS; J. W. SIGNORELLI

Santa Fe

Congreso; Congreso Internacional de Metalurgia y Materiales. SAM-CONAMET-IBEROMAT-Materia 2014; 2014

SAM-CONAMET

The work hardening in steels is typically originated by a combination of the evolution of the crystal orientation distribution (geometrical hardening) and the substructure developed during plastic deformation. This work deals with the assessment of the accumulation of Geometrically Necessary Dislocations (GND) near grain boundaries in an AKDQ steel sheets of 0.67 mm thickness deformed under tension-compression and tension-tension conditions. For this purpose, hourglass-type samples were tested with a 40 mm punch and die fixturing. In order to quantify the localization of GNDs due to strain gradients developed during deformation, small homogeneous samples extracted close to necking areas were investigated using Electron Back Scatter Diffraction (EBSD). The value of the apparent density of GND can be estimated by evaluating the dislocation tensor. GND averages over different distances of the grain boundary reveals that, for uniaxial tension (UAT) and plain strain (PS) at failure, the GND localization factor is close to 15% and 20% over the mean value for a threshold distance of 1mm from the grain boundary, respectively. The variation on the localization factor with distance from grain boundary shows a slower change in equibiaxial (EBA) than in UAT and PS samples, in agreement with the high fragmentation observed in most grains after EBA stretching. Correlations of localization factor on ideal orientations {001}, {112}, {111}, {111}, {554} and grain size are discussed.