Abstract
Heat treatment experiments of heavy rail steel samples are performed with varied total calcium (T.Ca) in the steel to investigate the transformation of inclusions. Before heat treatment, original inclusions in the heavy rail steel are homogeneous Al2O3–SiO2–CaO–MgO with little CaS. After soaking for 60 min at 1473 K, the precipitation of the CaS outer layer and MgO·Al2O3 core is clearly observed. The transformation ratio of CaO to CaS in inclusions increases with T.Ca in the steel under current steel compositions. When the T.Ca content in the steel increases from 3 to 9 ppm, the CaS content of inclusions increases by 5.31–16.14%, while the CaO content of inclusions varies in an opposite way by 5.40–14.01%. In addition, the content of Al2O3 in inclusions increases by 1.73–6.33%, the SiO2 content decreases by approximately 6%, while the content of MgO changes little. Thermodynamic calculation performed by FactSage 7.0 verifies the transformation of inclusions from CaO–SiO2 to CaS–Al2O3 in the solid heavy rail steel during heat treatment. A kinetic model is developed to predict the evolution of inclusions in the heavy rail steel during the heat treatment process.
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