Formation and Evolution of Nitrides in Fe–Cr–Al Electric Heating Alloy

To investigate the precipitation behavior of nitrides in Fe–Cr–Al electrical heating alloys, this study conducted thermal treatment experiments based on alloy sample. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were employed to analyze the morphology and distribution of nitride inclusions in the as-cast sample (S1), the electrode tip sample after heat treatment (S2), and the central sample (S3). The results showed that the S1 sample contained a significant number of AlN and TiN inclusions, mostly appearing as irregular blocky or near-rhombohedral particles, with sizes concentrated in the range of 2.5–5 μm. In the S2 sample, AlN inclusions had nearly disappeared, and the number of TiN inclusions decreased, although their size remained similar to that in S1. In the S3 sample, only a few fine AlN and TiN inclusions were observed, with minimal change in morphology and size compared to S2. Thermodynamic precipitation calculations indicated that under the experimentally measured nitrogen content, the actual solubility products (logQ) of AlN and TiN were consistently higher than their equilibrium solubility products (logK), demonstrating a strong driving force for precipitation at the solidification front. At lower nitrogen contents, intersections appeared between logQ and logK curves, suggesting that precipitation shifted to occur during solidification, with AlN precipitating at lower temperatures than TiN under the same nitrogen level. Competitive thermodynamic analysis revealed that TiN is more likely to form preferentially over AlN when nitrogen is limited. Growth kinetics calculations showed that TiN inclusions generally had larger radii than AlN under identical conditions, indicating stronger growth capability. Dissolution kinetics results further demonstrated that TiN had a larger residual radius than AlN, suggesting superior thermal stability during high-temperature condition. This study systematically elucidates the precipitation behavior and evolution mechanism of nitride inclusions in Fe–Cr–Al alloys through thermodynamic and kinetic models, providing a theoretical basis for inclusion control and performance optimization.