In the heat treatment of die steel, quenching is a common process. However, due to various reasons, it is inevitable that quenching cracks will sometimes occur, leading to the waste of previous efforts. Analyzing the causes of cracks, and then taking corresponding preventive measures, has significant technical and economic benefits.
(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 heat treatment of the mold (heating or cooling too fast, improper selection of quenching cooling medium, too low cooling temperature, too long cooling time, etc.);
(4) The mold shape is complex, uneven thickness, sharp corners and threaded holes, etc., which cause excessive thermal stress and organizational stress;
(5) The mold quenching heating temperature is too high, resulting in overheating or overburning;
(6) The tempering is not timely after the mold is quenched or the tempering holding time is insufficient;
(7) When the mold is reworked and quenched, it is reheated and quenched without intermediate annealing;
(8) Improper grinding process for mold heat treatment;
(9) During EDM machining after the heat treatment of the mold, there are high tensile stresses and microcracks in the hardened layer.
2. Preventive measures
(1) Strictly control the internal quality of mold raw materials;
(2) Improve the forging and spheroidizing annealing process to eliminate the network, band, and chain carbides, and improve the uniformity of the spheroidizing structure;
(3) After mechanical processing or cold plastic deformation, the mold is subjected to stress relief annealing (>600°C), and then heating and quenching;
(4) For molds with complex shapes, asbestos should be used to block threaded holes, bandage dangerous sections and thin walls, and adopt hierarchical quenching or austempering;
(5) When reworking or refurbishing molds, annealing or high temperature tempering is required;
(6) The mold should be preheated during quenching and heating, and pre-cooling measures should be taken when cooling, and suitable quenching medium should be selected;
(7) The quenching heating temperature and time should be strictly controlled to prevent the mold from overheating and overburning;
(8) After quenching, the mold should be tempered in time, and the holding time should be sufficient, and the high-alloy complex mold should be tempered 2-3 times;
(9) Choose the right grinding process and suitable grinding wheel;
(10) Improve the mold EDM process and carry out stress relief and tempering.
Post time: Nov-16-2021