Comprehensive Evaluation of Phosphorus Enrichment Capacity for Decarburization Slag at Different Temperatures Based on Industrial Experiments, Mineral Phase Analysis and Ion-Molecule Coexistence Theory

In the present work, the effects of decarburization endpoint temperature on the molten steel dephosphorization and phosphorus enrichment behavior of decarburization slag are studied with New Double slag converter Steelmaking Process (NDSP) industrial experiments under the temperature range of 1602 degrees C-1701 degrees C and the slag basicity of about 3.4. The phosphorus enrichment capacity of decarburization slag has been comprehensively evaluated at different temperatures based on the industrial experiment results, ion-molecule coexistence theory (IMCT) and mineral phase analysis of slag. With increasing the temperature from 1602 degrees C to 1701 degrees C, the dephosphorization ratio in decarburization stage decreases from 90.0 to 75.8 pct, and the phosphorus content in molten steel increases from 0.007 to 0.022 pct. The oxidation capacity of different reaction interfaces is large in the sequence of: slag layer > slag-steel interface > molten steel layer, in which temperature has the greatest influence on the oxidation of decarburization slag. The area fraction in SEM images of (Mg + Fe)O phase that cannot dephosphorize in decarburization slag increases with increasing temperature, which significantly decreases the area fraction in SEM images of P-rich phase and weakens the phosphorus enrichment capacity of decarburization slag. The value of phosphorus enrichment contribution ratio of C2S is about 0.82-0.84. The calcium phosphate in decarburization slag has the greatest contribution to phosphorus distribution ratio and phosphate capacity, which can reach 99.99 pct, in which the contribution ratio of 3CaO ae P2O5 is about 95.81 pct. The prediction model of phosphorus distribution ratio and phosphate capacity based on IMCT and slag oxidizability can accurately predict the phosphorus distribution ratio and phosphate capacity at the endpoint of decarburization stage in NDSP within the average relative error of 2.5 pct. The phosphorus enrichment capacity of decarburization slag in NDSP characterized by industrial experiment results, mineral phase results and IMCT model shows a consistent downward trend with increasing temperature. (C) The Minerals, Metals & Materials Society and ASM International 2022