“…[8,9] Diverse oxides with different valence states and structures of FeO, Fe 3 O 4 , and Fe 2 O 3 can form a double-layer structured film on steel during oxidation process. [10][11][12][13][14][15] The FeO in the inner oxide film is prone to softening at high temperatures, providing good lubrication during high-temperature pipe piercing, [16] while the outer film with the main composition of Fe 2 O 3 is brittle and easily peels off. [8,17] In order to improve the quality of the oxide film, Zheng [18] developed a novel two-stage oxidation process for preparation of the piercing plug with the first oxidation stage mainly to promote the rapid growth of the oxide film, and then followed by the second reduction stage to improve the structure of the oxide film to not easy to scale off.…”