Effect of Nb and Ti addition on activation energy for austenite hot deformation

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Abstract

Constitutive equations are employed in several algorithms to predict load during hot working. The peak stress (σ p ) can be correlated to the temperature and strain rate at which the metal was deformed using the known expression: Z = A(sinh(ασ p )) n , where, Z is the Zener-Hollomon parameter, given by Z=ϵ exp( Qdef /RT). The activation energy for hot deformation, Q def , magnifies the dependence of the stress on temperature in an exponential way requiring accurate measurement of this quantity. Empirical expressions published in the literature can be used to evaluate Q def . Unfortunately, these equations were derived for alloys with relatively high contents of C and N and when applied to the case of IF austenite, they yield unreasonable values. This is so because IF steels have, simultaneously, very low C and N contents and substantial amounts of microalloying elements leading to over prediction of values of Q def . This paper investigates, therefore, how the chemical composition of IF alloys can influence the values of the activation energy for hot deformation allowing suitable predictions to be made. Measurements of Q def were carried out for IF steels containing Ti and a combination of Ti-Nb additions. Predicted and measured values of Q def were compared to those calculated from published equations and a corrected expression was derived in order to better fit the experimental results here presented.

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Lino, R., Guadanini, L. G. L., Silva, L. B., Neto, J. G. C., & Barbosa, R. (2019). Effect of Nb and Ti addition on activation energy for austenite hot deformation. Journal of Materials Research and Technology, 8(1), 180–188. https://doi.org/10.1016/j.jmrt.2017.11.002

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