Factors Affecting the Oxidation of Forgings

There are many factors affecting the oxidation of forgings, such as:

(1) Chemical composition of forgings. The carbon content in steel is more than 0.3%. With the increase of carbon content in steel, the oxide scale will decrease. This is because when the carbon content of steel is high, reductive gas CO is produced during the oxidation of steel surface, which weakens the oxidation of oxidative gas on steel surface. When steel contains alloying elements such as Cr, Ni, Al and Mo, these alloying elements will form a dense oxide film on the surface of steel, which can protect the secondary surface of steel from being further oxidized. Because the expansion coefficient of the oxide film of these alloying elements is close to that of steel and the melting point is high, they will firmly adhere to the surface of steel during heating, thus preventing the continuous oxidation of steel. When the content of Al and Cr in steel is more than 13%-20%, there is almost no oxidation.

(2) Gas composition. The composition of furnace gas in flame furnace is composed of oxidizing gas (O 2, CO 2, H 2, SO2, etc.), reducing gas (CO, H 2) and neutral gas (N2). The nature of furnace gas is generally oxidizing, which results in the formation of oxide scale on steel. If the nature of the furnace gas is neutral and reductive, there is almost no oxide scale.

(3) Heating temperature. With the increase of heating temperature, the oxidation process accelerates and the oxide scale becomes thicker. Generally, the oxidation rate is very slow when the heating temperature is below 600 C. When the temperature rises above 900 C, the oxidation process increases rapidly.

(4) Heating time. The oxidation amount is proportional to the heating time. The longer the heating time of forgings, the more serious the oxidation degree of forgings, and the thicker the oxide scale formed.