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How to deal with overburning and oxidative decarburization in box furnace heating

Time:2022-11-29
  During the heating process of the mold with a box type protection, oxidation and decarburization easily occur, which depletes the metal elements on the surface of the workpiece, which not only affects the surface quality, but also reduces the mechanical properties and corrosion resistance of the metal. The convex and concave molds of the mold generally need to be quenched. After quenching, they are slightly ground before assembly. If the mold is severely oxidized and decarburized during heating, the oxidized and decarburized layer cannot be completely eliminated during assembly, which will affect the use of accessories. If you want to avoid overburning and oxidative decarburization, you must first understand how overburning and oxidative decarburization are formed.

    Overburning phenomenon: The so-called overburning refers to the phenomenon that the heating temperature of the industrial electric furnace is too high, which causes the austenite grains to be coarse, and the grain boundaries are partially oxidized or melted, resulting in the weakening of the grain boundaries. The performance of steel will seriously deteriorate after overburning and even cracks will form during quenching. The overburning structure of the tube furnace cannot be recovered and must be scrapped. In the actual operation process, we must avoid overburning.
    Decarburization phenomenon: The situation of decarburization is generally that when the industrial electric furnace heats the steel, the carbon on the surface reacts with the oxygen, hydrogen, carbon dioxide and water vapor in the medium, which reduces the carbon concentration on the surface, which is the so-called decarburization After decarburization steel is quenched, not only the surface hardness and fatigue strength will be greatly reduced, but also its wear resistance will be weakened, and the residual tensile stress formed on the surface will easily form a network of cracks on the surface.

    Oxidation phenomenon: Oxidation usually occurs when iron and alloys on the surface of the steel react with elements such as oxygen, carbon dioxide, and water vapor in the medium to form an oxide film when heated in a box-type electric furnace, which is called oxidation. For such problems, the surface coating of the workpiece is generally used, the stainless steel foil packaging is used for sealing and heating, and the heating of the salt bath furnace is used to prevent the oxidation and decarburization of the workpiece. Ordinary workpieces will be oxidized when they are above 570 degrees. After oxidation, not only the dimensional accuracy and surface brightness will be extremely deteriorated, but also the hardenability of steel parts with poor hardenability will be prone to quenching soft spots. occur.

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