Manufacturing of ferritic stainless steels flat bars is an important industrial topic and the steel 1.4512 is one of the most commonly used grades for producing this component. In this paper, the origin of some edge defects occurring during hot rolling of flat bars of this grade is analyzed and thermomechanical and microstructural calculations have been carried out to enhance the quality of the finished products by reducing the jagged borders defect on hot rolled bars. An accurate investigation has been carried out by analyzing the defects on the final product from both the macroscopic and microstructural point of view through the implementation of thermomechanical and metallurgical models in a finite element (FE) MSC Marc commercial code. Coupled metallurgical and damage models have been implemented to investigate the microstructural evolution of ferritic grain size and material damaging. Three levels of prior ferritic grain size (PFGS) and three furnace discharge temperatures have been considered in the thermo-mechanical simulations of the roughing passes. Rheological laws for modeling the evolution of ferritic grain have been modified to describe the specific cases simulated. Results have shown that the defect is caused by processing conditions that trigger an anomalous heating which, in turn, induces an uncontrolled grain growth on the edges. The work-hardened and elongated grains do not recrystallize during hot deformation. Consequently, they tend to squeeze out the surrounding softer and recrystallized matrix towards the edges of the bar where the fractures that characterizes the surface defect occur.

The adoption of the ultrafast heating (UFH) process has gained much attention in the last few years, as the green energy and minimization of CO₂ emissions are the main aspects of contemporary metal science and thermal treatment. The effect of ultrafast heating (UFH) treatment on carbon steels, non-oriented grain (NGO) electrical steels, and ferriticor austenitic stainless steels is reported in this review. The study highlights the effect of ultrarapid annealing on microstructure and textural evolution in relation to microstructural constituents, recrystallization temperatures, and its effect on mechanical properties. A strong influence of the UFH process was reported on grain size, promoting a refinement in terms of both prior austenite and ferrite grain size. Such an effect is more evident in medium–low carbon and NGO steels than that in ferritic/austenitic stainless steels. A comparison between conventional and ultrafast annealing on stainless steels shows a slight effect on the microstructure. On the other hand, an evident increase in uniform elongation was reported due to UFH. Textural evolution analysis shows the effect of UFH on the occurrence of the Goss component (which promotes magnetic properties), and the opposite with the recrystallization g-fiber. The recovery step during annealing plays an important role in determining textural features; the areas of higher energy content are the most suitable for the nucleation of the Goss component. As expected, the slow annealing process promoted equiaxed grains, whereas rapid heating promoted microstructures with elongated grains as a result of the cold deformation.

For spherical silicon nanoparticles produced by laser pyrolysis in a temperature range below the melting point of the bulk phase, the average particle size measured by transmission electron microscopy has been found to be larger than the crystallite size derived from profile fitting of broadened X-ray diffraction peaks. This result, interpreted in terms of aggregation and solidification of particles during the coagulation process, has been explained by a sectional model suitably developed to describe coagulation and aggregation of particles. The model predicts the evolution of the size distribution of both macroscopic polycrystalline particles and of crystallites composing the aggregates. Single crystal particles are supposed to form not only by collisions between liquid particles but also by collisions between a larger solid and a smaller liquid particle coexisting in the system due to capillarity effects which are responsible for the decreasing of the melting point of nanometre-sized particles with respect to the bulk phase. On the other hand, polycrystalline aggregates are supposed to form by collisions between solid particles. The spheroidal shape of particles found in the analysed powders has been explained by observing that the characteristic sintering time was at least one order of magnitude smaller than the characteristic time for coagulation. The good predictive capabilities of the model for the average particle size of both the macroscopic size distribution and that of crystallites have confirmed that the hypothesis of aggregation is able to quantitatively reproduce the experimental findings.

A discrete multi-particle model of Ostwald ripening based on direct pairwise interactions is developed for particles with incoherent interfaces as an alternative to the classical LSW mean field theory. The rate of matter exchange depends on the average surface-to-surface interparticle distance, a characteristic feature of the system which naturally incorporates the effect of volume fraction of second phase. The multi-particle diffusion is described through the definition of an interaction volume containing all the particles involved in the exchange of solute. At small volume fractions this is proportional to the size of the central particle, at higher volume fractions it gradually reduces as a consequence of diffusion screening described on a geometrical basis. The topological noise present in real systems is also included. For volume fractions below about 0.1 the model predicts broad and right-skewed stationary size distributions resembling a lognormal function. Above this value, a transition to sharper, more symmetrical but still right-skewed shapes occurs. An excellent agreement with experiments is obtained for 3D particle size distributions of solid–solid and solid–liquid systems with volume fraction 0.07, 0.30, 0.52 and 0.74. The kinetic constant of the model depends on the cube root of volume fraction up to about 0.1, then increases rapidly with an upward concavity. It is in good agreement with the available literature data on solid–liquid mixtures in the volume fraction range from 0.20 to about 0.75.