(1) In the heating process of oxidized steel, especially when heated to high temperature, its surface iron will be oxidized gas in the furnace gas (e.g. 2, CO2, pressure 0, SO2, etc.) occur drastic chemical reactions, so that the surface metal of the steel is oxidized into an oxide skin.
The factors affecting oxidation include furnace gas composition, heating temperature, heating time and chemical composition of steel.
The damage of oxide skin: cause the burning of steel material; Affect the surface quality of forgings; Reduce die life.
Measures to reduce oxidation: try to use rapid heating to shorten the heating time; Different heating stages adopt different air volume in the furnace (i.e. adopt different flame); Ensure complete fuel combustion; When the blank is evenly wet, the small positive pressure should be kept in the furnace to prevent the cold air from being inhaled; The billet is added in protective gas or inert gas and the billet is coated with a protective layer and heated.
(2) When decarbonized steel is heated at high temperature, the carbon in the surface layer and the oxidizing gas in the furnace gas (e.g. 2, COz, HzO, etc.) and some reducing gases (such as H2) occur chemical reactions, resulting in the reduction of carbon content in the surface of the steel material.
Factors affecting decarbonization include furnace gas composition, heating temperature, heating time and chemical composition of steel.
The harm of decarbonization: after decarbonization, it is easy to crack in the forging process, and the surface hardness, strength and wear resistance, fatigue strength are reduced, leading to premature fracture of parts subjected to long-term alternating load. When the thickness of decarbonized layer is larger than the machining allowance, the quality of forging will be affected.
Measures to prevent decarbonization: The measures described above to reduce oxidation can also be used to prevent decarbonization.
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