Keywords: furnace, Nitriding Furnace, Nitriding, Nitriding Layer, Mesh, Ripple, Herringbone, Heat Treatment, Needle, Liquid Ammonia, Ammonia Gas, Ammonia Decomposition, Decarburization, Heating,

Nitriding furnace mold nitriding layer appears reticulate, corrugated, needle or herringbone defects causes and preventive measures

    Nitriding furnace mold nitriding surface layer appearing reticulate and corrugated, needle or fishbone nitrides and thick white brittle layer will lead to mold toughness reduction, brittleness increase, impact resistance weakened, fatigue spalling, wear resistance is reduced, greatly reducing the service life of the mold.

    1, nitriding furnace mold nitriding layer appears net-like, corrugated, needle or fishbone defects:

    (1) Some heat treatment manufacturers unilaterally emphasize the improvement of labor productivity, in the development of process documents and the actual operation of the nitriding furnace nitriding temperature is too high heating and cooling cooling speed is too fast; temperature control instrument malfunction, the actual temperature of the furnace than the instrument indication temperature is high. If the temperature is too high, the nitrides in the diffusion layer will gather and grow up, the dispersion will decrease, and a high nitrogen phase will be formed on the grain boundary of the reticular or corrugated organization.

    (2) Nitriding furnace mold preparation heat treatment quenching heating temperature is too high, mold matrix grain is too large.

    (3) The water content of liquid ammonia is high, and the ammonia gas passed into the gas nitriding furnace contains water.

    (4) Nitriding furnace mold design and manufacture is unreasonable, there are sharp corners and edges.

    (5) The ammonia decomposition rate in the gas nitriding furnace is too low, i.e. the nitrogen potential is too high.

    (6) Preparatory heat treatment, quenching and heating is not carried out in a protective atmosphere, the mold surface decarburization is serious, nitriding in the nitriding is very easy to appear needle, fishbone nitride.

    2、Nitriding furnace mold nitriding layer appears net-like, corrugated, needle or fishbone defects in the preventive measures:

    (1) correctly formulate the nitriding furnace mold nitriding treatment process, nitriding temperature selection in the 500 ~ 580 ℃, generally do not exceed 580 ℃, and regularly calibrate the temperature control instrumentation, warming and heating speed should not be too fast.

    (2) nitriding furnace mold preparatory heat treatment quenching heating temperature should not be too high, so as not to mold material internal organization of martensite grain is too large; heating should be carried out in a protective atmosphere, to avoid oxidation decarburization of the mold; tempered parts should be in the machining of decarburization layer removed.

    (3) Ammonia should be passed through the drying device and then passed into the nitriding furnace, and the desiccant should be replaced regularly.

    (4) Nitriding furnace mold design and manufacture should try to avoid sharp corners and sharp edges.

    (5) Strictly control the ammonia decomposition rate in the nitriding furnace, and should not make the nitrogen potential in the furnace too high.

    (6) has produced reticulate and corrugated nitrides in the mold can be about 540 ℃ nitriding furnace for 10 ~ 15h diffusion treatment, in order to effectively eliminate the mold nitriding layer of reticulate and corrugated nitrides.

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