Cementite Formation and Carburization Behavior of Hydrogen-Based Direct Reduced Iron in CO-Dominant Atmospheres: Effects of Temperature, Gas Composition, and Time

Abstract The carburization of hydrogen-based direct reduced iron has been experimentally investigated at 600°C, 800°C, and 1000°C using gas mixtures predominantly composed of carbon monoxide (CO), with hydrogen ( $${\mathrm{H}_2}$$ H 2 ) and methane ( $${\mathrm{CH}_4}$$ CH 4 ) as secondary components. The formation of cementite ( $${\mathrm{Fe}_{3}\mathrm{C}}$$ Fe 3 C ) was confirmed by X-ray diffraction and quantified using Mössbauer spectroscopy, while total carbon content was determined by combustion analysis. Statistical analyses, including descriptive statistics and multiple linear regression, were employed to identify experimental outliers, assess sample variability, and quantify the effects of temperature, gas composition, and carburization time on key response variables, including mass change, cementite content, total carbon, and free carbon (soot) fractions. The regression models exhibited adjusted R -squared values exceeding 0.7 for key responses, indicating that temperature and time explain a substantial portion of the observed variance within the tested parameter space, with notable gas–temperature interactions observed at 600°C in CO- $${\mathrm{H}_2}$$ H 2 atmospheres and at 800°C and 1000°C in CO- $${\mathrm{CH}_4}$$ CH 4 atmospheres. Regression analysis further indicated that cementite formation is maximized in CO- $${\mathrm{CH}_4}$$ CH 4 gas mixtures at 800°C. These findings provide mechanistic guidance for optimizing cementite formation in CO-rich industrial atmospheres, with implications for electric arc furnace steelmaking.