The presence of non-metallic inclusions (NMI) such as sulphides and oxides may be detrimental to the control of the steel casting process and product quality. The need for their identification and characterization is, therefore, urgent. This study uses time-gated Raman spectroscopy for the characterization of synthetic duplex oxide-sulphide phases that contain CaS and the oxide phases of Al₂O₃, CA, C12A7, C3A, and MgO·Al₂O₃ (MA). Binary phase samples of CaS–MA, C3A–CaS, C12A7–CaS, Al₂O₃–CaS, and MA–CaS were prepared with varying phase contents. The relative intensities of the Raman peaks were used to estimate the samples’ phase content. For a quantitative estimation, linear regression calibration models were used to evaluate the change in phase content in the samples. The most suitable Raman peak ratios had mean absolute error (MAE) values ranging from 3 to 7 wt. % for the external validation error, and coefficients of determination (R²) values between 0.94 and 0.98. This study demonstrated the use of Raman spectroscopy for the characterization of the calcium sulphide, magnesium aluminate spinel, Al₂O₃, and calcium aluminate phases of CA, C3A, and C12A7 in a duplex oxide-sulphide system, and it offers potential for inclusion characterization in steel.

Steel quality and properties can be affected by the formation of complex inclusions, including Ti-based inclusions such as TiN and Ti₂O₃ and oxides like Al₂O₃ and MgO·Al₂O₃ (MA). This study assessed the prospective use of Raman spectroscopy to characterize synthetic binary inclusion samples of TiN–Al₂O₃, TiN–MA, Ti₂O₃–MA, and Ti₂O₃–Al₂O₃ with varying phase fractions. The relative intensities of the Raman peaks were used for qualitative evaluation and linear regression calibration models were used for the quantitative prediction of individual phases. The model performance was evaluated with root mean square error of cross-validation (RMSECV) and root mean square error of prediction (RMSEP). For the raw Raman spectra data, R² values were between 0.48–0.98, the RMSECV values varied between 3.26–14.60 wt%, and the RMSEP ranged between 2.98–15.01 wt% for estimating the phases. The SNV Raman spectra data had estimated R² values within 0.94–0.99 and RMSECV and RMSEP values ranged between 2.50–3.26 wt% and 2.80–9.01 wt%, respectively, showing improved model performance. The study shows that the specific phases of TiN, Al₂O₃, MA, and Ti₂O₃ in synthetic inclusion mixtures of TiN–(Al₂O₃ or MA) and Ti₂O₃–(Al₂O₃ or MA) could be characterized by the Raman spectroscopy.

In aluminum‐killed calcium‐treated steels, the characterization of multiphase oxides found in the CaO–MgO–Al₂O₃ system is essential for the study of inclusion formation, modification, and the control process. Herein, Raman spectroscopy is used as a characterization technique for the multiphase mixtures of MgO·Al₂O₃ spinel and calcium aluminate phases of C12A7, C3A, and CA. Multiphase samples of C12A7–CA–MA and C12A7–C3A–MA are synthesized from MgO·Al₂O₃ spinel and calcium aluminates with varying phase content. The relative intensity of the Raman peaks is qualitatively used for the most primary phases present in the sample. Regression models are also identified for predicting the phase composition. Prediction model identification is conducted using the successive projection algorithm (SPA) for feature selection and the partial least squares regression (PLS) model as a regressor. The identified prediction models show a reasonably good prediction performance. Herein, the time‐gated Raman spectroscopy technique to characterize the multiphase mixture of magnesium aluminate spinel and calcium aluminate phases of CA, C12A7, C3A is used, and the potential application for inclusion characterization is demonstrated.

The introduction of hydrogen is considered pivotal in replacing natural gas in reheating furnaces and decarbonizing the steel industry. Substituting natural gas with hydrogen as fuel will change the composition of the furnace atmosphere and may influence the scale formed on the steel surface. The study examines oxide scale formation rates of two low‐carbon steels by simulating combustion atmospheres representing five fuels: natural gas (100% CH₄), hydrogen (100% H₂), and three CH₄–H₂ fuel blends (75% CH₄%–25% H₂, 50% CH₄%–50% H₂%, and 25% CH₄%–75% H₂) with varying free oxygen contents. Thermogravimetric analysis and characterization techniques are used to investigate oxidation behavior and the formation of oxide phases. The amount of scale formed for a fuel blend from 100% CH₄ to 100% H₂ shows moderate scale growth and no noticeable evolution changes in oxide phases compared with natural gas in simulated reheating conditions. Higher concentrations of free oxygen exhibit an increase in the oxide scale formed on the steel surface. Metallographic analysis shows that an atmosphere corresponding to 100% H₂ has an increased oxide scale thickness compared with 100% CH₄. Iron oxide phases, mainly magnetite and wustite, are identified in the samples using various characterization techniques.