The effects of alloying elements on the peritectic range of Fe–C–Mn–Si steels

The peritectic reactions, liquid + δ-(ferrite) → γ(austenite) and the related casting problems during fast manufacturing process remain a big challenge for the compositional design and commercial production of high-quality Fe–C–Mn–Si steels. The precise prediction of the peritectic range of composition in steel is important in order to avoid the failure of casting and rolling; however, the effects of alloying elements on the peritectic range are unclear not only due to the large compositional space in alloyed steels but also its occurrence at high-temperature ranges, > 1400 °C. A combination of experimental measurements and thermodynamic modeling was employed to study the effects of alloying elements on the peritectic range for the wide composition ranges of Fe–C–Mn–Si steels. The phase transformation sequences and temperatures of two model Fe–C–Mn–Si steels were evaluated by differential scanning calorimetry (DSC) and in-situ confocal laser scanning microscope (HT-CLSM) and compared with thermodynamic calculation with TCFE9 database. The total number of 1680 phase diagrams is calculated by varying Mn from 0.3 wt% to 3.0 wt%, Si 0.05 wt% to 2.95 wt% and with and without a 0.02 wt% Ti addition. Using linear regression analyses for the calculations, we have predicted the correlation between peritectic ranges and the compositional space of Fe–C–Mn–Si steels. These results are effectively represented by contour plots and linear regression equations to predict the future outcomes of casting practice with their testing accuracy. It is also revealed that the peritectic ranges are influenced by complex elemental interactions, rather than the single-element effects of Mn, Si or Ti. The composition design of widely-applied Fe–C–Mn–Si steels is subject to a strict manufacturing restriction due to peritectic reaction and the related casting problems. This boundary condition is the topic of the current study.