A thermodynamic assessment of precipitation, growth, and control of MnS inclusion in U75V heavy rail steel

Thermodynamic analysis of the precipitation behavior, growth kinetic, and control mechanism of MnS inclusion in U75V heavy rail steel was conducted in this study. The results showed that solute element S had a much higher segregation ratio than that of Mn, and MnS would only precipitate in the solid–liquid (two-phase) regions at the late stage during the solidification process at the solid fraction of 0.9518. Increasing the cooling rate had no obvious influence on the precipitation time of MnS inclusion; however, its particle size would be decreased greatly. The results also suggested that increasing the concentration of Mn would lead to an earlier precipitation time of MnS, while it had little effect on the final particle size; as to S, it was found that increasing its concentration could not only make the precipitation time earlier but also make the particle size larger. Adding a certain amount of Ti additive could improve the mechanical properties of U75V heavy rail steel due to the formation of TiO x –MnS or MnS–TiS complex inclusions. The precipitation sequences of Ti3O5 → Ti2O3 → TiO2 → TiO → MnS → TiS for Ti treatment were determined based on the thermodynamic calculation.

Corrosion Behaviors of U75V, U76CrRE Heavy Rail Steel in Simulated Industrial Atmosphere

The corrosion of heavy rail steel is severity in south. Now there are not studies on the corrosion of heavy rail steel in atmosphere. The corrosion of heavy rail steel were studied by periodic infiltration corrosion test and electro-chemical testing technique in simulated industrial atmosphere. The result showed that U76CrRE has apparently more excellent anti-corrosion ability than that of steel U75V. The Cr and Re in U76CrRE enriched in local of base that promotes the rapid generation of α FeOOH and the increase of content. Thus the ability of the rust layer against the corrosive media from entering the layer was improved. Anti-corrosion capacity of heavy railroad steel in industrial atmosphere can be improved significantly by adding Cr and RE alloy.

Model Prediction on the Behavior of Cerium in Heavy Rail Steel

The thermodynamic model which quantificationally described the behavior of cerium in heavy rail steel was proposed. From the model, the effects of cerium on the composition, sequence and transformation condition of inclusions and the content of cerium dissolved in heavy rail steel were studied principally. When the cleanliness of heavy rail steel is low, the sequence of inclusions precipitation in heavy rail steel is Ce2O3, Ce2O2S, Ce2S3 and CeS. With increasing the cleanliness of steel, the sequence of inclusions precipitation is Ce2O2S and CeS. At 1783 K, the necessary condition of Ce2O3 precipitation in heavy rail steel is ao/as≥0.186, for Ce2S3 precipitation is ao/as≤0.394. The content of cerium dissolved in heavy rail steel is mainly affected by Ce2S3 inclusion. With the precipitations of all inclusions being stable, the curve between the dissolved cerium content and cerium addition becomes linear.