Javier Aguilar-Carrillo

In recent years, elevated concentrations of arsenic (As) have been detected in the Tertiary detrital aquifer of Madrid. A significant number of areas where waste from old mining operations, rich in metals and metalloids, accumulate may partially explain contamination events by toxic elements. In these environments, colloidal particles can act as nanovectors for the dispersion of As, enhancing its migration and contamination of surrounding soils. This work studies the mobilization of As-rich colloids from a waste zone of an old mining operation in the Community of Madrid. These wastes, mainly composed of arsenopyrite [FeAsS] ([As] = 0.2 g kg-1), are deposited near a natural stream and exposed to environmental conditions. In order to follow the mobility of As-rich colloids, the combined techniques of asymmetric flow field flow fractionation and inductively coupled plasma mass spectrometry (AF4-ICP-MS) are used to obtain the size distribution of the colloidal fraction and associated As, while X-ray absorption spectroscopy (XAS) techniques are utilized for the study of the chemical speciation of As in the solid phase. In addition, geochemical modeling allows prediction of the thermodynamically favored phases in each of the studied areas. The mobilization of colloidal As from mining waste to water and soil located up to 1 km from the source of contamination is described. The essential role of colloidal Fe oxyhydroxides as As mobilizing nanovectors is also highlighted.

In this work, different processing routes were investigated to evaluate the effects of hot rolling temperature, annealing before cold rolling (ABCR), and one- or two-stage cold rolling and annealing schedules to obtain more efficient electrical steels. The correlation between processing variables, microstructure, thickness, and magnetic properties was established from the analysis of 3D surface plots. It was found that the lowest core loss values (3.4 W/kg) were obtained when steel is processed by hot rolling (800 °C), ABCR (880 °C–180 min), first cold rolling (up to 0.25 mm), first annealing (850 °C–10 min), second cold rolling (up to 0.2 mm), and second annealing (850 °C–10 min). The better combination between thickness and grain size leads to the enhancement of the magnetic properties, which affects the way eddy and hysteresis losses contribute to the total core losses.

In the present work, a Cr+Mo+Si low-alloyed low-carbon steel was fabricated at laboratory scale and processed to produce multiphase advanced high-strength steels (AHSS), under thermal cycles similar to those used in a continuous annealing and galvanizing process. Cold-rolled steel samples with a microstructure constituted of pearlite, bainite, and martensite in a matrix ferrite, were subjected to an intercritical annealing (817.5 °C, 15 s) and further isothermal bainitic treatment (IBT) to investigate the effects of time (30 s, 60 s, and 120 s) and temperature (425 °C, 450 °C, and 475 °C) on the resulting microstructure and mechanical properties. Results of an in situ phase transformation analysis show that annealing in the two-phase region leads to a microstructure of ferrite + austenite; the latter transforms, on cooling to IBT, to pro-eutectoid ferrite and bainite, and the austenite-to-bainite transformation advanced during IBT holding. On final cooling to room temperature, austenite transforms to martensite, but a small amount is also retained in the microstructure. Samples with the lowest temperature and largest IBT time resulted in the highest ultimate tensile strength/ductility ratio (1230.6 MPa-16.0%), which allows to classify the steel within the third generation of AHSS. The results were related to the presence of retained austenite with appropriate stability against mechanically induced martensitic transformation.

The present work presents a theoretical and experimental study regarding the microstructure, phase transformations and mechanical properties of advanced high-strength steels (AHSS) of third generation produced by thermal cycles similar than those used in a continuous annealing and galvanizing (CAG) process. The evolution of microstructure and phase transformations were discussed from the behavior of intercritical continuous cooling transformation diagrams calculated with the software JMatPro, and further characterization of the steel by scanning electron microscopy, optical microscopy and dilatometry. Mechanical properties were estimated with a mathematical model obtained as a function of the alloying elements concentrations by multiple linear regression, and then compared to the experimental mechanical properties determined by uniaxial tensile tests. It was found that AHSS of third generation can be obtained by thermal cycles simulating CAG lines through modifications in chemistry of a commercial AISI-1015 steel, having an ultimate tensile strength of UTS = 1020–1080 MPa and an elongation to fracture of Ef = 21.5–25.3%, and microstructures consisting of a mixture of ferrite phase, bainite microconstituent and retained austenite/martensite islands. The determination coefficient obtained by multiple linear regression for UTS and Ef was R² = 0.94 and R² = 0.84, respectively. In addition, the percentage error for UTS and Ef was 2.45–7.87% and 1.18–16.27%, respectively. Therefore, the proposed model can be used with a good approximation for the prediction of mechanical properties of low-alloyed AHSS.