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Microstructure, texture and mechanical properties in a low carbon steel after ultrafast heating. AbstractHeating experiments in a wide range of heating rates from 10 to 1200 °C/s and subsequent quenching without isothermal soaking have been carried out on a low carbon steel. The thermal cycles were run on two different cold rolled microstructures, namely ferrite + pearlite and ferrite + martensite. It is shown that the average ferritic grain size, the ferrite grain size distribution, the phase volume fractions and the corresponding mechanical properties (ultimate tensile strength and ductility) after quenching are strongly influenced by the heating rates and the initial microstructure. The ferrite grain size distribution is significantly modified by the heating rate, showing a markedly bimodal distribution after fast annealing. The rise of the heating rate has produced a change in the relative intensities of texture components, favouring those of the cold-deformed structure (RD fibre) over the recrystallization components (ND fibre).

This paper presents an experimental analysis and a numerical simulation of the mechanical behaviour experienced during the tensile test by both cylindrical and strip specimens of different materials for which the classical so-called Bridgman's procedure aimed at predicting the stress distribution at the necking zone cannot be directly applied. A set of experiments has been carried out in order to derive the elastic and hardening parameters that characterize the material response. The simulation of the deformation process during the whole test is performed with a finite element large strain elastoplasticity-based formulation. Finally, the results obtained with the simulation are experimentally validated.

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A B S T R A C T The S-N-P (stress, number of cycles, failure probability) curves for 2024 T3 and 7075 T7351 aluminium alloys were obtained. Previously, surface treatments of degreasing and different types of anodizing were applied to samples, evaluating the influence of these treatments on the fatigue life of the alloys. The determination of the S-N-P curves was done using Maennig's method. Rotary fatigue was used because this technique produces greater stress on the sample surfaces, the zone in which it is important to evaluate fatigue resistance. Both the transition range and the finite life range were evaluated, calculating the 1, 50 and 99% fracture probability. SEM was performed in order to characterize the fracture micromechanism. The conclusions were that Maennig's method is useful to evaluate fatigue life of these materials in a fast and efficient manner. Moreover, surface treatments produce a decrease in the fatigue life of both alloys, associating this effect with the surface damage produced on each sample during the treatment.

There is great interest in the steel industry of incorporating new products that go beyond the properties of existing ones. Among these properties, corrosion resistance is extremely important for countries that, like Chile, have an extensive ocean coastline. In costal zones, the chloride ions in air produce corrosion that reduces the service life of structures. For this reason, it is of utmost importance to study the influence of different alloying elements such as nickel, which lead to improve steel's resistance to marine corrosion. In this context the development of new types of steel is hindered if the evaluation of their corrosion resistance takes very long times. This paper presents a methodology based on accelerated wet-dry cycle corrosion experiences to simulate the behaviour of steel over time in a marine environment. The results of the proposed methodology allow adequate prediction of corrosion thickness in ASTM A242 and A588 steels exposed for years to a specific marine environment.

Abstract:The microstructure and texture evolution of cold-rolled low carbon steel after ultrafast heating and quenching is investigated. Experiments were carried out at heating rates of 150 • C/s and 1500 • C/s. The recrystallization of ferrite is studied by scanning electron microscopy and electron backscattered diffraction techniques. The texture evolution of cold rolled steel during ultrafast heating was studied, making it possible to estimate the precise effect of heating rate on the orientations of newly formed grains. The experimental results showed that the recrystallization of ferrite was not completed before the full transformation of austenite. The noticeable increase in the fraction of recrystallized grains of diameter less than 1 µm, when the heating rate is increased from 150 • C/s to 1500 • C/s suggests that the increase of the heating rate enhances the nucleation of ferrite. The crystallographic orientations in recrystallized ferrite are strongly influenced by the heating rates. The effect of heating rate in the releasing of stored energy, carbon diffusion and spheroidization of cementite might explain some differences in textures observed in recrystallized ferrite.