Site-specific quasi in situ investigation of primary static recrystallization in a low carbon steel

Abstract

Low-alloyed steels with body-centered cubic crystal structure are a material class that is widely used for sheet metal forming applications. When having an adequate crystallographic texture and grain morphology, their mechanical behavior is characterized by an isotropic in-plane flow behavior in combination with a low yield strength. The decisive processing steps for obtaining these beneficial mechanical properties are cold rolling and subsequent annealing. While for the former the number of passes, the deformation rates, and the total thickness reduction are the main processing parameters, the latter is described mainly by the heating rate and the holding temperature and time. Primary static recrystallization during annealing subsequent to the cold rolling process alters mainly two aspects of the material state: It firstly replaces the elongated and heavily deformed grains of the cold rolled microstructure by small, globular grains with low dislocation density and secondly it changes the crystallographic texture insofar as it typically diminishes the α-and strengthens the γ-fiber texture components. In the present work, the recrystallization behavior of a commercial non-alloyed low carbon steel is studied. A quasi in situ setup that enables site-specific characterization is employed to gain a local picture of the nucleation and recrystallization process. From the Kernel Average Misorientation (KAM) values of the deformation structure, the tendency to be consumed by new grains can be predicted. Crystallographic analysis shows that the most deformed regions have either a γ-fiber orientation or belong to heavily fragmented shear band regions. New grains nucleate especially in such highly deformed regions and inherit often the orientation from the deformation microstructure.

Disparity in recrystallization of α- & γ-fibers and its impact on Cube texture formation in non-oriented electrical steel

“…Here, a cubic pixel shape was used in MTEX, similar to the HKL system, where the misorientation data of each pixel was calculated relative to its 8 neighbouring pixels. Care was taken to minimize surface removal during polishing between EBSD scans 30,31 . During the analysis, consistent change in GND density was found across texture components between scans lending credibility to the results.…”

Recrystallisation kinetics and yield-strength adjustment after annealing of cold-rolled microalloyed steel

“…Each thermogram showed two exothermic events, which were confirmed by the first derivative of the DSC curve. The exothermic peaks, whose onset and final temperatures are outlined by continuous lines, are in a temperature range corresponding to ferrite recrystallisation of cold-rolled steel with similar characteristics to the steel under study [10,24,25]. The smooth peaks pointed by arrows in Figure 4 were considered recovery events.…”

Coupled experimental-computational analysis of primary static recrystallization in low carbon steel

“…The simulations are based on a quasi in situ SEM/EBSD annealing experiment of a 65% cold-rolled DC04 low carbon steel [41]. In this experiment, a region perpendicular to the normal direction (ND) of the sheet with size approximately 700×700 μm was repeatedly probed to track the recrystallization process.…”

“…Following [46,47], was used here, wherein b is the magnitude of the Burgers vector, Δ the step size, and Ω the KAM value in radians. Recovery of the dislocation density was assumed to be negligible in the considered body-centered cubic (bcc) material [41] during the growth of new grains. Hence, the dislocation in the deformed microstructure remained constant throughout the simulation.…”