Experimental Study of High Temperature Phase Equilibria in the Iron-Rich Part of the Fe-P and Fe-C-P Systems

• DOI: 10.1007/s11661-020-05912-z
• Publication Date: 2020-07-23T22:02:15Z
• Authors: Michael Bernhard; Peter Presoly; Nora Fuchs; Christian Bernhard; Youn-Bae Kang
• Keywords: 1ST-PRINCIPLES; CARBON CONTENT; STEEL; CONCENTRIC SOLIDIFICATION; 0211 other engineering and technologies; 02 engineering and technology; DIAGRAM; SOLUBILITY; 7. Clean energy; THERMODYNAMIC ASSESSMENT; PHOSPHORUS; 0205 materials engineering; CRYSTAL-STRUCTURE; TRANSITION

Abstract During the solidification of steel, phosphorus strongly segregates in the interdendritic liquid phase. In the continuous casting process, even low levels of P may have a detrimental effect on the final product quality. However, phosphorus is partly added up to 0.10 wt pct to improve the mechanical properties of advanced steel grades nowadays, e.g., High-Strength Interstitial-Free (HSIF). To provide new experimental data for the development of thermodynamic databases and solidification models for P alloyed steel grades, phase equilibria in the Fe-P and Fe-C-P key systems were studied up to 1550 °C using differential scanning calorimetry (DSC) and high temperature laser scanning confocal microscopy (HT-LSCM). Special focus was placed on solid/liquid equilibrium temperatures in the Fe-rich part of the binary Fe-P system between 0.025 and 9 wt pct P. In the ternary system, three isoplethal sections with 0.10 mass pct. P, 0.20 mass pct. C and constant mass percent ratio P/C of 2 were investigated. In the latter section, HT-LSCM observations were linked with DSC signals to optically identify present phase stabilities. Particularly at [pct P] < 1, significant differences between performed measurements and calculated phase equilibrium temperatures using thermodynamic assessments from the literature were identified. In all ternary sections, the experiments indicate less influence of P on the hypo-peritectic range compared to the thermodynamic calculations.