The effect of Cr content on intragranular κ-carbide precipitation in Fe-Mn-Al-(Cr)-C low-density steels: A multiscale investigation

Abstract

The effect of Cr content on intragranular κ-carbide precipitation behaviors in Fe-Mn-Al-Cr-C low-density steels was investigated by X-ray diffraction (XRD), scanning (SEM) and (high-resolution) scanning transmission electron microscopy ((HR)STEM), atom probe tomography (APT), thermodynamic and first-principles calculations. We found that the volume fraction of κ-carbides in near-rapidly solidified samples was decreased with increasing Cr content. The increased Cr content also significantly slowed down the growth rate of κ-carbides during isothermal aging treatment (600 °C/9 h). Thermodynamic calculations showed that the increased Cr content decreased the precipitation temperature of κ-carbides and narrowed the temperature range of κ-carbide formation. The impurity of Cr atoms in κ-carbide structure increased its interfacial energy and elastic strain energy for nucleation, thereby significantly increasing the critical energy for the κ-carbide formation in γ-austenite. Simultaneously, the results of APT and first-principles calculation indicated that the impurity of Cr atoms in the κ-carbide structure preferred to occupy the Al sites, which increased the formation energy of κ-carbides making the κ-carbide formation difficult. In addition, the increased interfacial energy between the κ-carbides and γ-austenite, the improved solubility of Al and C in the γ-austenite and the decreased diffusion coefficient of C in γ-austenite caused by increasing Cr content resulted in a slower growth rate of the κ-carbides. • Effect of Cr addition on intragranular κ-carbides is investigated at multiscale. • Cr addition suppresses formation and reduces growth of κ-carbides. • Cr impurity prefers to substitute Al site increasing formation energy of κ-carbides. • Interfacial and strain energies between κ-carbides/γ-austenite are increased by Cr. • Cr addition affects solubility and diffusion rates of Al and C in γ-austenite.