Nuestros investigadores

Zaloa Arechabaleta Guenechea

Publicaciones científicas más recientes (desde 2010)

Autores: Pereda, Beatriz; López, Beatriz;
ISSN 1059-9495  Vol. 24  Nº 3  2015  págs. 1279 - 1293
Double-hit torsion tests were performed in order to study the effect of high Al levels (up to 2 wt.%) and Nb microalloying (up to 0.07 wt.%) on the static softening kinetics of 0.2%C-2%Mn steels. The addition of 1%Al leads to a delay in the softening kinetics due to solute-drag effect, equivalent to that exerted by 0.027%Nb. For the 2%Al steels, at temperatures below 1000 degrees C, gamma -> alpha phase transformation occurs after deformation, resulting in a larger retardation of the softening kinetics. At temperatures higher than 1000 degrees C, Nb in solid solution also contributes to the retardation of the static softening kinetics, and at lower temperatures NbC strain-induced precipitation leads to incomplete softening for the 1%Al steel, and to a complex interaction between softening, phase transformation, and NbC strain-induced precipitation for the 2%Al-Nb steels. The effect of Al on the static softening kinetics was quantified and introduced in a model developed in previous works for the prediction of the austenite microstructural evolution. In order to validate the results of the model, multipass torsion tests were carried out at conditions representative of hot strip and plate rolling mills. Model predictions show reasonable agreement with the results obtained at different deformation conditions.
Autores: Pereda, Beatriz; López, Beatriz;
ISSN 0921-5093  Vol. 600  2014  págs. 37 - 46
The effect of Nb (up to 0.07 wt%) and high Al content (up to 2 wt%) on the multipass deformation behaviour of steels with 0.2% C and 2% Mn was studied with the aid of hot torsion simulations. From the tests, the critical Non-Recrystallisation (T-nr), Recrystallisation Limit and Stop Temperatures (RLT and RST) and the ferrite phase transformation start temperature (A(r3)) were determined. It was observed that an increase in Al content from 1% to 2% or a microalloying addition of 0.03% Nb to 1% Al steel both led to a significant increase in the recrystallisation critical temperatures, which is greater than 100 degrees C in the case of the T-nr However, the value of the T-nr was not affected when 0.03% or 0.07% Nb was added to the 2% Al steel. Specimens quenched after several deformation passes were examined by optical and TEM means in order to study the interaction between static recrystallisation, strain-induced precipitation and gamma ->alpha phase transformation, and determine the mechanisms leading to strain accumulation in the steels investigated. The results suggest that for the 1% Al steels, the Al and Nb solute drag effect is the main mechanism leading to the increase in the critical recrystallisation temperatures, while for the 2% Al steels the occurrence of gamma ->alpha phase transformation at temperatures close to the T-nr is the main mechanism involved in softening retardation, with a limited contribution of Nb. However, gamma ->alpha phase transformation taking place at temperatures close to the T-nr resulted in a loss of hot ductility, which can limit the industrial applicability of the 2% Al steels. (c) 2014 Elsevier B.V. All rights reserved.
Autores: Pereda, Beatriz; López, Beatriz;
ISSN 1073-5623  Vol. 45A  Nº 2  2014  págs. 934 - 947
The effect of Al addition on the static softening behavior of C-Mn steels was investigated. Double-hit torsion tests were performed at different deformation temperatures ranging from 1198 K to 1338 K (925 degrees C to 1065 degrees C) with pass strains of epsilon = 0.2 and 0.35. It was found that solute Al produced a significant delay on the static softening kinetics. Additionally, at the lowest temperatures [1198 K to 1238 K (925 degrees C to 965 degrees C)] and highest Al level (2 wt pct), austenite to ferrite phase transformation was found to be concurrent with softening, leading this to higher softening retardation. The softening kinetics of the steels investigated were analyzed using a physically based model which couples recovery and recrystallization mechanisms. The main parameters of the model were identified for the present alloys. An expression for the grain boundary mobility of the base C-Mn steel was derived and the retarding effect of Al in solid solution on the static recrystallization kinetics was introduced in the model. Reasonable agreement was obtained between model and experimental results for a variety of deformation conditions. (C) The Minerals, Metals & Materials Society and ASM International 2013