Solid-state phase transformations in the γ-loop of the binary Fe-P system were studied using differential scanning calorimetry (DSC) and high-temperature laser scanning confocal microscopy (HT-LSCM). In total, eight alloys with varying P content from 0.026 to 0.48 mass pct. P were investigated in the temperature range of 800 °C to 1450 °C. The first part of the present work deals with the critical evaluation of the approach to couple DSC experiments and HT-LSCM observations in order to characterize bcc/fcc phase equilibria in Fe-based γ-loops. The phase transformation temperatures of a selected alloy with 0.394%P were analyzed by DSC and HT-LSCM and compared with results of the well-established techniques of dilatometry and high-temperature X-ray diffraction (HT-XRD). Then, the overall phase boundaries of the γ-loop were reconstructed by HT-LSCM and DSC data and the phase diagram was compared with thermodynamic assessments from literature. Finally, the quantitative phase fractions of fcc and bcc at 0.394%P were analyzed by Rietveld refinement at temperatures of 1050 °C, 1100 °C and 1150 °C using in-situ HT-XRD. Although the phase boundaries of the γ-loop and phase transformation temperatures have been reproduced accurately by recently published thermodynamic optimizations, larger deviations between HT-XRD measurements and the calculations were identified for the phase fraction prediction. The present work clearly demonstrates that coupling DSC and HT-LSCM is a powerful tool to characterize γ-loops in steel for future research work.
Bibliographische NotizFunding Information:
The authors gratefully acknowledge the financial support under the scope of the COMET program within the K2 Center Integrated Computational Material, Process and Product Engineering (IC-MPPE) (Project No. 859480). This program is supported by the Austrian Federal Ministries for Climate Action, Environment, Energy, Mobility, Innovation and Technology (BMK) and for Digital and Economic Affairs (BMDW), represented by the Austrian research funding association (FFG), and the federal states of Styria, Upper Austria and Tyrol.
© 2021 The Author(s)