For heat treatment of steel, all want to control the direction and degree of deformation, but because of the chemical composition and heat treatment technology, quality, geometric shape, design will change the direction and degree of deformation of plastic mold, thus affecting the final size of the mould, so, only by optimizing the heat treatment process to minimize the mold deformation degree.
(1) the deformation caused by residual stress endured strict grinding steel, bending and cutting jobs after the stress is very high, so we must eliminate the stress produced by these assignments and, in the heat treatment deformation happens.
(2) in the process of heat treatment heating fast deformation caused by heat treatment heating speed should be slow enough, so that all parts of the mold temperature is basically consistent.
During fast heating, thin cross section than the thick section expands quickly, it will generate stress in the joint of mold, if the stress is greater than the yield strength of steel, makes the mold deformation. In addition, in the process of quick heating, when thin section first reaches a critical temperature, and began to shrink and thick section is still in the expansion, which will cause deformation.
During the slow heating, synthetic stress below the yield strength moulds, so will not happen deformation. And when quick heating, synthetic stress is greater than the yield strength, so the mould will produce deformation, when the resultant stress exceeds the rupture strength of steel, will lead to mold broken.
In heat treatment, surface mould parts processing oxidation and decarburization and increase carbon effect, will bring serious impact mold service life. Using vacuum as a ideal heating medium, vacuum heat treatment furnace. Die steel has excellent surface state after vacuum heat treatment, the surface oxidation and decarburization, quenching deformation is small. After vacuum quenching, the fracture toughness of steel, die life by 40% ~ 400% higher than that of conventional technique, is even higher.
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