Effects of Al and Mn on the formation and properties of nanostructured pearlite in high-carbon steels

• A fully pearlitic microstructure with an interlamellar spacing of 82 nm was obtained.
• The nanoscaled pearlitic microstructure is responsible for the high tensile strength of 1685 MPa and elongation of 11.6%.
• The increase of Al content can refine the pearlite.
• The decrease of Mn content can refine the pearlite.

This study investigated the effects of different Al and Mn contents on the formation and properties of pearlitic microstructure in high-carbon steels treated through slack quenching after hot deformation. The microstructure, tensile plastic deformation behavior, and alloying elements partitioning between ferrite and cementite were analyzed using scanning electron microscopy, transmission electron microscopy, and atom-probe tomography. A fully pearlitic microstructure with an interlamellar spacing of 82 nm was obtained at a cooling rate of 120 °C/min in the steel. The nanostructured pearlite was responsible for the high tensile strength of 1685 MPa and the elongation of 11.6%. Microstructure observation verified that with increasing Al content and decreasing Mn content, the interlamellar spacing of the pearlite was remarkably decreased, due to the increased the free energy change during the transformation of austenite to pearlite, and the nucleation density of the pearlite colonies was also increased, because of the increased the A1 temperature and the increased degree of undercooling. Al and Si partitioned to the ferrite phase, whereas Mn and Cr presented high concentrations in the cementite phase. The redistribution of the alloying elements decelerated the pearlite growth.

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