Study on High‐Temperature Oxidation Kinetics and Layered Oxidation Behavior of X70 Pipeline Steel

This study systematically investigates the effects of heating rate and temperature on the high‐temperature oxidation behavior of industrial X70 pipeline steel in the range from 700 to 1000 °C. Thermogravimetric experiments were conducted to simulate the heating and holding processes during hot rolling, combined with characterization techniques such as SEM, EDS, and EBSD. The non‐isothermal and isothermal high‐temperature oxidation behavior of industrial‐grade X70 pipeline steel was systematically investigated in the hot‐rolling heating range from 700 to 1000 °C. The results show that increasing the heating rate can induce a significant oxidation hysteresis effect, delaying the onset temperature of intense oxidation from 805 °C (10 °C/min) to 850 °C (50 °C/min). The apparent oxidation activation energies during the heating and isothermal stages were calculated to be 140.327 and 12 256.04 J/mol, respectively. A layered evolution characteristic was identified, with Fe ₂ O ₃ , Fe ₃ O ₄ , and FeO arranged sequentially from the outermost layer inward, along with Si–Cr alloy oxides enriched at the interface. For the first time, a coherent cogrowth mechanism was quantitatively revealed between the persistent strong {001} texture in the Fe ₃ O ₄ layer and the {111} plane texture in the FeO layer that intensifies with increasing temperature. This study provides a theoretical foundation for optimizing the heating process and controlling oxide scale defects in the hot rolling of X70 pipeline steel.