Despite the widespread use of laser heat treatment, a fundamental understanding of austenite formation kinetics at high heating rates remains a challenge. This gap is addressed by developing a novel model that uniquely accounts for the initial pearlite colony size and interlamellar spacing as critical input parameters. The model's predictions are validated against experimental observations, where the spatial variation of hardness reveals a distinct two-zone microstructure: a fully austenitized region and a partially transformed intercritical layer. The results show that the relative size of these zones is directly controlled by the initial microstructure. This research provides a crucial insight that austenite formation under rapid heating conditions occurs with negligible superheating, which is essential for optimizing laser processing parameters to achieve a desired microstructure.

This work investigates the formation of the recrystallisation microstructure and texture of various single-phase ferrite low-carbon steels that were rolled at different temperatures and of which the deformation microstructure was characterized by high resolution electron backscatter diffraction (EBSD). Three cases are considered: (i) cold-rolled interstitial-free (IF) steel, warm-rolled IF steel at 550 °C and warm rolled Fe-Si steel at 900 °C (below the austenitization temperature due to Si). It is well-known that the deformation texture after flat rolling of single-ferrite low carbon steels exhibits the characteristic α/γ-fiber texture, i.e. <110>//Rolling Direction (RD) and <111>//Normal Direction (ND), irrespective of the rolling temperature, as long as there is no concurrent phase transformation. However, different recrystallisation textures appear as a function of the rolling temperature. Generally speaking, the γ-fiber recrystallisation texture is obtained after cold rolling, whereas the θ-fiber components ( <100>//ND) intensify at the expense of the γ-fiber orientations with increasing rolling temperature. Although these phenomena are well-known, the reasons for this behavior in terms of preferential orientation selection remain as yet unclear. In the present paper, recrystallisation microstructures and textures are simulated with a full-field cellular-automaton (CA) description, whereby recrystallisation from its incipient stage is considered as a process of sub-grain coarsening controlled by the well-known physical laws of driving force and kinetics. The simulations integrate in one single model the various conditions that give rise to the observed temperature dependence of the evolving static recrystallisation texture and microstructure. The different rolling temperatures will give rise to different initial microstructures at the onset of recrystallisation with noticeable variations in short-range orientation gradients in γ and θ-fiber orientations, respectively. The mere application of local grain-boundary migration laws on the topology of the deformation structure, without imposing any specific nucleation selection criterion, will properly balance the dominance of γ-fiber grains after cold-rolling and θ-fiber orientations after warm rolling. Finally, the well-known nucleation of Goss orientations ({110}<001>) in shear bands occurring in γ-fiber grains is also simulated in this single conceptual framework.

This study investigates the sub-structure of IF steel in three conditions: cold rolled, statically recovered, and warm rolled. After both cold and warm rolling, the steel exhibits the typical 〈110〉//RD and 〈111〉//ND fiber textures. Considering the short-range misorientation gradient ∆θ/∆x to assess locally stored energy variations, it was observed that 〈111〉//ND grains exhibit significantly higher gradients than 〈001〉//ND grains in all conditions. In the statically recovered conditions, the ∆θ/∆x values are significantly reduced compared to the cold rolled condition, but these values are significantly higher than those of the dynamically recovered after warm rolling. The strongly reduced orientation gradients in the 〈111〉//ND grains after warm rolling may reduce the nucleation potency of these orientations in the ensuing recrystallization. This study enhances our knowledge of deformation microstructure as a function of rolling temperature and is relevant in explaining reported differences in annealing textures during static recrystallization after cold vs warm rolling.