Vacuum heat treatment of precision die

How to prevent heat treatment deformation of precision die

As we all know, during the vacuum heat treatment, especially in the process of vacuum quenching, due to the temperature difference caused by the different heating and cooling speed of each part of the die cross section, as well as the unequal time of the structure transformation, the volume expansion and contraction of each part of the die cross section are uneven, and the structure transformation is uneven, thus causing the “structure stress” and the temperature difference inside and outside the die Thermal stress. When the internal stress exceeds the yield limit of the die, the deformation of the die will be caused.

In consideration of material selection and heat treatment, SIMUWU vacuum heat treatment furnace plant selects T10A Steel to manufacture complex dies with large difference in section size and small deformation after quenching, and the hardness is required to be 56-60hrc. After heat treatment, the hardness of the die meets the technical requirements, but the die has large deformation and can not be used, resulting in die scrap. After heat treatment, the hardness and deformation of the die meet the requirements. Die heat treatment deformation is one of the main defects in the process of die treatment. For some precision and complex dies, the deformation of heat treatment is discarded.

The forged die steel should be heat treated to obtain the sorbite structure with uniform, fine and dispersive carbide distribution, so as to reduce the deformation of the precision and complex die after heat treatment. Die steel with small carbide segregation shall be selected as far as possible, and the steel with poor material produced by small steel works shall be selected instead of being cheap. The die steel with severe carbide segregation should be forged reasonably to break the carbide crystal block, reduce the grade of uneven distribution of carbide and eliminate the anisotropy of properties. For the large size die or the die that can not be forged, the solution double refining treatment can be used to refine, distribute the carbides evenly and round the edges and corners, so as to reduce the deformation of the die during heat treatment.

The reason of mould ellipse is the existence of non-uniform carbide distributed in a certain direction in the mould steel. The expansion coefficient of carbide is about 30% smaller than the matrix structure of steel. When heated, it prevents the expansion of mould inner hole, when cooled, it prevents the shrinkage of mould inner hole, causes the non-uniform deformation of mould inner hole, and makes the round hole of mould appear ellipse. Generally speaking, Cr12MoV steel is a micro deformed steel and should not have large deformation.