Causes and preventive measures of mold heat treatment quenching cracks
There are many equipments in the heat treatment plant. The furnaces are probably box furnaces, pit furnaces, and box furnaces are used a lot. Many heat treatments can be processed here, such as annealing, normalizing and quenching heating process, tempering and other common heat treatments. Shanghai Xinyan will share with you the causes and preventive measures of mold heat treatment quenching cracks.
Causes:
1) There is serious network carbide segregation in the mold material.
2) There is mechanical processing or cold plastic deformation stress in the mold.
3) Improper mold heat treatment operation (heating or cooling too fast, improper selection of quenching cooling medium, too low cooling temperature, too long cooling time, etc.).
4) The mold has complex shape, uneven thickness, sharp corners and threaded holes, etc., which makes the thermal stress and organizational stress too large.
5) The mold quenching heating temperature is too high to cause overheating or overburning.
6) The mold is not tempered in time after quenching or the tempering insulation time is insufficient.
7) When the mold is repaired and quenched, it is heated and quenched again without intermediate annealing.
8) The grinding process of the mold is improper after heat treatment.
9) When the mold is electrospark machined after heat treatment, high tensile stress and micro cracks exist in the hardened layer.
Preventive measures:
1) Strictly control the intrinsic quality of mold raw materials
2) Improve the forging and spheroidizing annealing process, eliminate network, band and chain carbides, and improve the uniformity of spheroidized structure.
3) After mechanical processing or cold plastic deformation, the mold should be subjected to stress relief annealing (>600℃) before heating and quenching.
4) For molds with complex shapes, asbestos should be used to plug threaded holes, wrap dangerous sections and thin walls, and use graded quenching or isothermal quenching.
5) Annealing or high-temperature tempering is required when repairing or refurbishing the mold.
6) The mold should be preheated during quenching heating, precooled during cooling, and a suitable quenching medium should be selected.
7) The quenching heating temperature and time should be strictly controlled to prevent overheating and overburning of the mold.
8) The mold should be tempered in time after quenching, and the insulation time should be sufficient. High-alloy complex molds should be tempered 2-3 times.
9) Choose the correct grinding process and suitable grinding wheel.
10) Improve the mold EDM process and perform stress relief tempering.