Abstract
The transformation temperatures A_r3 and A_r1 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 A_r1), respectively by the A_c3 temperature (for A_r3). When calculating the A_c3 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.

Key words
hypoeutectoid steel, carbon equivalent, dilatometer test, cooling rate, decomposition of austenite, transformation temperature

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