Abstract
This paper presents the characterization of austenite to pearlite transformation in rail steels (premium and standard) using dilatometry. The critical transformation temperatures were measured as a cooling rate function and the obtained microstructures were qualitatively and quantitatively characterized. Aiming to study the transformation kinetics, three equations proposed by technical literature were evaluated in order to predict the transformation evolution. Experimental and calculated CCT diagrams were compared. It was concluded once the kinetics of phase transformation in rail steels is well characterized, it can be used as reference to enable suitable heat treatment to obtain pearlitic microstructures for the standard steel as refined as those of premium. The minor prior austenite grain size of the standard steel favoured the pearlite nucleation, however its highest Mn, Nb and Si contents delayed the growth stage. All equations evaluated in order to predict the kinetics of austenite to pearlite transformation under continuous cooling were satisfactory.
Highlights
Most of the production of ore and agricultural products around the world is increasingly being transported by railways across continents
The mechanical properties of pearlitic steels are controlled by the microstructures arising from their thermomechanical processing, especially by characteristics such as previous austenitic grain size, pearlite interlamellar spacing and pearlite colony size[1,2,3,4,5,6,7,8,9,10,11]
According to the AREMA12, these rail steels presenting pearlitic microstructures can be classified into two classes: standard and premium
Summary
Most of the production of ore and agricultural products around the world is increasingly being transported by railways across continents. With the continuous increase of train operation speed and transported axle load, the use of better rail steels and the improvement of welding techniques have been sought with the aim to increase the rail life and to decrease the cost of track maintenance. This actual need has been the driving force for recent developments and for the increasingly number of published studies addressing the improvement and innovation in rail steel manufacturing and welding[1,2,3,4,5,6,7]. The premium rails, with a better designed chemical composition, have more refined
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