The combined effect of chemical composition and cooling rate on transformation temperatures of hypoeutectoid steels

Abstract

The transformation temperatures Ar3 and Ar1 of four unalloyed hypoeutectoid steels with a carbon content of 0.029-0.73 % were determined using dilatometric tests. Unusually high cooling rates of 2 and 8• C s −1 were used intentionally, corresponding to the conditions in the wire rod rolling mills. The developed regression models are phenomenological and allow a simple prediction of transformation temperatures, depending only on the cooling rate and the chemical composition of the steel represented by the carbon equivalent (in the case of Ar1), respectively by the Ac3 temperature (for Ar3). When calculating the Ac3 temperature, it was worth considering its non-linear dependence on carbon content. It has been verified that the derived equations are applicable even at relatively low cooling rates when the austenite decomposes exclusively on ferrite and pearlite.K e y w o r d s : hypoeutectoid steel, carbon equivalent, dilatometer test, cooling rate, decomposition of austenite, transformation temperature

Continuous cooling transformation diagrams of HSLA steel for seamless tubes production

“…The nucleation rate is high; however, the mobility of phase interfaces is severely decelerated by a high density of dislocations in austenite and that is why the final fraction of ferrite decreases. In the case of very large plastic deformation, the high nucleation rate compensates the slow growth of nuclei and the resulting ferrite fraction is approximately the same as in the case of austenite not affected by plastic deformation; however, the ferrite grains are much finer [17,[23][24][25][26][27][28].…”