Electric arc furnace slag (EAF) has the potential to be re-utilized as an alternative to stone material, however, only if it remains chemically stable on contact with water. The presence of hydraulic phases such as larnite (2CaO SiO2) could cause dangerous elements to be released into the environment, i.e. Ba, V, Cr. Chemical treatment appears to be the only way to guarantee a completely stable structure, especially for long-term applications. This study presents the efficiency of silica addition during the deslagging period. Microstructural characterization of modified slag was performed by SEM and XRD analysis. Elution tests were performed according to the EN 12457-2 standard, with the addition of silica and without, and the obtained results were compared. These results demonstrate the efficiency of the inertization process: the added silica induces the formation of gehlenite, which, even in caustic environments, does not exhibit hydraulic behaviour.

Super Duplex Stainless Steels (SDSSs) are composed of α-ferrite and γ-austenite grains, the simultaneous presence of which forms an optimal microstructure to achieve the best combination of mechanical and corrosion resistance properties. Moreover, international quality standards are strict about the phase fraction ratio. The purpose of this work is the achievement of a better description of the phase ratio evolution taking place during annealing at 1080 • C in the super duplex stainless steels F53-S32750 and F55-S32760. The experimental results show a damped sinusoidal trend in the α/γ phase ratio evolution with the increase of the soaking time of thermal treatment. This can be described by coupling both the competitive coarsening growth regime and the concept of the local equilibrium phase transformations, pointing out a good correspondence with the experimental data. Further, recrystallization phenomena also play a major role. Finally, the additivity character of the observed processes has been proven.

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The demand of green and recycling technology has become, nowadays, a crucial issue for the scientific community. In this work, a preliminary approach for safe and reliable "black slag" use is discussed on chemical and microstructural characterization basis. Different EAF slag types, coming from several steelmaking plants, are analyzed. The characterization is aimed to explain the diffusion, dissolution and releasing mechanisms of the polluting elements that affect the black slags and avoid their recycle as alternative filler materials. Furthermore, the work focuses on the leaching inhibition of these dangerous species in the environment.Experiments involve SEM-EDS and SEM-EBS analysis and elution tests, according to the UNI EN 12457 standard, on high FeO content slag, on slag featured by chromium high content and on slag with low FeO content. The analysis allows to recognize the phases responsible for the polluting elements releasing and to identify the phases to be promoted in order to obtain a safe and inert by-product.

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