Influence of Furnace Pressure on the Growth Characteristic of Oxide Film on Piercing Plug Steel

Different oxidation processes are carried out by using 20Cr2Ni4 piercing plug steel to study the influence of furnace pressure on the growth characteristic of oxide film in high‐temperature C 2 H 5 OH–H 2 O atmosphere. The results show that oxide film under different processes shows clearly two layers. The inner film is porous with the main constituents of FeO and Fe 3 O 4 while the outer film is dense with large bubbles. The elemental Ni aggregates as a dot‐like substance in the inner oxide, where the enrichment of Cr lags behind the frontier boundary of Ni distribution. It is found that the thickness of the oxide film shows a parabolic relationship with product of the square root of oxidation time and furnace pressure. High furnace pressure can keep the pressure balance of the bubbles to swell to sufficient size, but may cause cracking during the relief process of pressure.