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Influence of cooling medium and cooling method

    The heat treatment deformation of the mold is often manifested after quenching and cooling. Although this has the influence of the above factors, the influence during the cooling process cannot be ignored.

    1. Causes of deformation

    When the mold is cooled below the Ms point, the steel undergoes phase transformation. In addition to the thermal stress caused by the inconsistent cooling, there is also the structural stress due to the unequal time of the phase transformation. The faster the cooling rate, the more the cooling Uneven, the greater the stress, the greater the deformation of the mold.

    2. Preventive measures

    (1) On the premise of ensuring the hardness of the mold, try to use pre-cooling. For carbon steel and low-alloy mold steel, it can be pre-cooled until the corners and corners are black (720″760ºC). For supercooled austenite in the pearlite transformation zone The more stable steel can be pre-cooled to about 700ºC.

    (2) The use of hierarchical cooling and quenching can significantly reduce the thermal stress and structural stress generated during mold quenching, and is an effective method to reduce some complex mold deformation.

    (3) For some precision and complex molds, austempering can significantly reduce deformation.