Transformation kinetics of austenite during cooling is influenced by several factors as chemical content or thermomechanical parameters (temperature, dwell time, deformation, strain rate, cooling rate) and initial structure state, consequently initial austenite grain size. The aim of this article was just to assess the effect of initial structure state (casted, deformed, purposely extremely coarsened) on transformation kinetics of austenite during cooling of steel C10, which was moreover deformed uniaxial compression. This comparison was done on the basis of the construction of three transformation diagrams type DCCT (deformation continuously cooling temperature) for different initial structure state of hypoeutectoid steel C10. DCCT diagrams were constructed on the basis of combination dilatometric tests with an influence previous deformation, metallographic analyses, and measurements of Brinell hardness. For the execution of the experiment, the new optical dilatometric module of the plastometer Gleeble 3800 was used. The experiment demonstrated, that in the case of hypoeutectoid and low alloyed steels and in the case of slowly cooling rate (under 10°C/s) area of ferrite and pearlite formation were not dramatically shifted influence different initial grain size. In the case of higher cooling rate are already evident temperature shifts in areas of ferrite and pearlite. The obtained results show that the finer grain size shifted temperature border area of formation of ferrite and pearlite upward towards higher temperatures. Moreover, in the case of purposely extremely coarsened structure, metallographic analyses showed the formation of acicular ferrite after cooling of cooling rate 35 °C/s.Keywords: Initial structure, Transformation kinetics, Transformation diagrams, Steel C10
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