Using torsion tests a improved model has been constructed to predict the static recrystallization kinetics of deformed austenite in low alloy and microalloyed steels. The model quantifies the influence of the most common elements (C, Si, Mn, Mo) in low alloy steels and the typical elements (V, Nb) in microalloyed steels, when they are in solution. Activation energy (Q) is the parameter sensitive to the content and nature of each alloying element, and an expression for Q is shown as a function of the percentage of each one. Nb is the element that contributes most to increasing the value of Q, and thus that which most delays recrystallization kinetics. C is seen to be the only alloying element that contributes to lowering the value of Q, and thus to accelerating recrystallization kinetics. Extrapolation of the expression of Q to pure iron in the austenitic phase gives a value of 148 637 J mol Ϫ1 , which is similar to other values found in the literature for the grain boundary self-diffusion energy of pure Fe g . Static recrystallization kinetics follow Avrami's law and expressions are given for the parameter t 0.5 and the exponent n.KEY WORDS: austenite; static recrystallization; low alloy steels; microalloyed steels.compositions are shown in Table 1. The twenty-six steels include different combinations of C, N and metallic precipitate-forming elements such as V and Nb. Given that the nitrides, carbides or carbonitrides of Nb are less soluble in austenite than those of V, the limit imposed on C and N contents has been that the solubility temperature should not exceed 1 300°C. In this sense, some compositions, such as steel N9, with a very low Nb content and high C content, are not currently standard compositions, but the interest in studying them lies in ascertaining the influence of low Nb contents on recrystallization.Torsion specimens were prepared with a gauge length of 50 and 6 mm diameter. The reheating temperature prior to torsion deformation was different depending on whether the steel was microalloyed with V or with Nb (Table 1), as the solubility temperature of the precipitates depends on their nature and on the precipitate-forming element content. For steels containing vanadium, designated by the letter V, the reheating temperature was 1 230°C for steels V1, V2 and V3 and 1 200°C for the rest, which is sufficient to dissolve vanadium nitrides and carbides. In the case of niobium steels, designated by the letter N, the reheating temperature depended on the C, Nb and N contents, but was always above the solubility temperature of niobium carbonitrides.
17)All the C-Mn/Si steels (C1, C2, C3, M1, M2, S1, S2), C-Mo steels (Mo1, Mo2) and the microalloyed steels V1, V2, V3, N1 and N2 have been studied previously 14,15) in relation with static recrystallization, but their results are taken into account in order to achieve greater universalization of the model proposed in this work.To ensure that the testing temperatures corresponded to the austenitic phase, critical transformation temperatures were measured by d...
