Mould heat treatment is an important way for steel to enhance the hardness performance, which is generally carried out after the mould rough machining. After heat treatment then do finishing machining. But there is a risk during the process. The improper handling will cause the steel cracks easily and scrapped, then what causes plastic mold steel abnormalities:

. The mould material has serious reticular carbide segregation.

. There are mechanical or cold plastic stresses in the mould.

. Improper operation of the mould heat treatment (heating or cooling too fast, improper selection of quenching and cooling medium, cooling temperature is too low, the cooling time is too long, etc.).

. Mould shape complex, uneven thickness, with sharp corners and thin threaded holes, so that thermal stress and tissue stress residue is too much.

. Plastic mould quenching process heating temperature is too high to produce overheating or over burning.

. Mould quenching after tempering is not timely or tempering insulation time is insufficient.

. Mould rework quenching heating, without intermediate annealing and then heating and quenching again.

. Improper grinding process.

. When do EDM after heat treatment, there is a high tensile stress and micro-cracks in the hardening layer.