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

Conferencia; IBEROMAT XIII 14 SAM - CONAMET XIII Simposio Materia; 2014

The work hardening in steels is typically originated by a combination of the evolution of the crystal orientation distribution (geometrical hardening) and thesubstructure 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 duringdeformation, small homogeneous samples extracted close to necking areas were investigated using Electron Back Scatter Diffraction (EBSD). The value of theapparent density of GND can be estimated by evaluating the dislocation tensor. GND averages over different distances of the grain boundary reveals that, foruniaxial 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 of1mm 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 factoron ideal orientations {001}<110>, {112}<110>, {111}<110>, {111}<112>, {554}<225> and grain size are discussed.