Precipitation and Assembling Behavior of Alloying Elements of Piercing‐Plug Steel under High‐Temperature C₂H₅OH–H₂O Atmosphere

A tungsten (W) and cobalt (Co) bearing high‐alloy piercing‐plug steel is designed to improve the service life by employing a two‐stage oxidation–reduction surface treatment process under a C 2 H 5 OH–H 2 O atmosphere. Morphology, chemical composition, and phase constituents of the oxide scale are studied by using scanning electron spectroscope, energy‐dispersive X‐ray spectroscopy, and X‐ray diffraction, while the microstructure and hardness distribution of decarbonizing layer are studied with optical microscope and microhardness tester. It is shown that the W alloying element can precipitate at 1020 ºC as WC, WSi 2 , and W 5 Si 3 to strengthen the steel, and the precipitations aggregate and assemble into a cluster in the inner oxide scale as the steel matrix lattice is destroyed by oxidation of ferrum (Fe) atoms. It is found that Me 3 O 4 and FeO phases are present together with Ni and WSi 2 with certain orientation relationship in the inner oxide scale, and both Co and nickel (Ni) exist as elementary substances in the oxide scale and show a cooperative precipitation behavior. It is noted that Co distribution in the outer oxide layer and W clustering with a hardness of 966.7 HV in the inner layer are the main factors for the improved service life of this steel piercing plug.