Plastic mold heat treatment characteristics

Plastic mold heat treatment characteristics

(1) Heat treatment characteristics of carburized steel plastic mold
1. For plastic molds with high hardness, high wear resistance and high toughness requirements, carburized steel should be used for the manufacture, and carburizing, quenching and low temperature tempering should be used as the final heat treatment.

2. For the requirements of the carburized layer, the thickness of the general carburized layer is 0.8-1.5 mm. When the plastic containing the hard filler is pressed, the thickness of the carburized layer of the mold is required to be 1.3-1.5 mm, and the carburized layer is pressed when the soft plastic is pressed. The thickness is 0.8 to 1.2 mm. The carbon content of the carburized layer is preferably from 0.7% to 1.0%. If carbon and nitrogen are used together, abrasion resistance, corrosion resistance, oxidation resistance, and anti-adhesion are better.

Plastic mold heat treatment

3. The carburizing temperature is generally 900-920 ° C, and the small mold of the complex cavity can take 840 ~ 860 ° C medium temperature carbonitriding. The carburizing holding time is 5~10h, which should be selected according to the requirements of the thickness of the layer. The carburizing process is preferably carried out by using a graded carburizing process, that is, a high temperature stage (900 to 920 ° C) to rapidly infiltrate carbon into the surface of the part; in the middle temperature stage (820 to 840 ° C), the thickness of the carburized layer is mainly increased, so that A uniform and reasonable carbon concentration gradient distribution is established in the carburized layer to facilitate direct quenching.

4. The quenching process after carburizing is different according to the steel type. After carburizing, it can be used separately: reheating quenching; direct quenching after grade carburizing (such as alloy carburizing steel); direct quenching after medium temperature carbonitriding (such as industrial use) Small precision molds for cold extrusion of pure iron or low carbon steel); air-cooled quenching after carburizing (such as large and medium-sized molds made of high-alloy carburized steel).

(2) Heat treatment of hardened steel plastic mold
1. A mold with a relatively complicated shape is heat-treated after roughing, and then finished to ensure minimum deformation during heat treatment. For precision molds, the deformation should be less than 0.05%.

2. The surface of the plastic mold cavity is very strict. Therefore, during the quenching and heating process, it is necessary to ensure that the surface of the cavity is not oxidized, decarburized, not eroded, and not hot. It should be heated in a protective atmosphere furnace or in a salt bath furnace after strict deoxidation. If it is heated by a common box type resistance furnace, it should be coated with a protective agent on the cavity surface, and at the same time, the heating speed should be controlled. The cooling medium controls the cooling rate to avoid deformation, cracking and scrapping during the quenching process. Generally, quenching by hot bath is preferred, and pre-cooling and quenching can also be used.

3. After quenching, it should be tempered in time. The tempering temperature should be higher than the working temperature of the mold. The tempering time should be sufficient. The length depends on the mold material and the section size, but at least 40~60min.

plastic mold
(3) Heat treatment of pre-hardened steel plastic mold
1. Pre-hardened steel is supplied in a pre-hardened state. Generally, no heat treatment is required, but sometimes it is necessary to carry out the forging, and the forged blank must be heat-treated.

2. Pre-heat treatment of pre-hardened steel usually adopts spheroidizing annealing, the purpose is to eliminate the forging stress, obtain a uniform spherical pearlite structure, reduce the hardness, improve the plasticity, and improve the cutting performance or cold extrusion forming property of the mold blank.

3. The pre-hardening treatment of pre-hardened steel is simple, and most of them adopt quenching and tempering treatment, and the tempered sorbite structure is obtained after quenching and tempering. The high temperature tempering temperature range is wide enough to meet the various working hardness requirements of the mold. Since such steels have good hardenability, oil quenching, air cooling or nitrate salt quenching can be used for quenching. Table 3-27 shows the pre-hardening treatment process for some pre-hardened steels for reference.

Plastic mold heat treatment characteristics list
Table 1 Pre-hardening treatment process for part of pre-hardened steel

Heating temperature / °C
cooling method
Tempering temperature / °C
Prehardness hardness HRC
Oil cooling or 160-180 ° C nitrate classification
Oil cooler
Oil or air cooling
Oil-cooled or nitrate-classified
Oil cooler

(4) Heat treatment of age hardening steel plastic mold.
1. The heat treatment process of age hardening steel is divided into two basic processes. First, the solution treatment is carried out, that is, the steel is heated to a high temperature, and various alloying elements are dissolved in the austenite to complete the austenite post-quenching to obtain the martensite structure. The second step is aging treatment, using aging to achieve the final required mechanical properties.

2. Solution treatment heating is generally carried out in a salt bath furnace or a box furnace. The heating time can be taken as follows: 1 min/mm, 2 to 2.5 min/mm, quenching is oil-cooled, and steel having good hardenability can also be air-cooled. If the final forging temperature can be accurately controlled when the blank is forged, the solution hardening can be directly performed after forging.

3. The aging treatment is preferably carried out in a vacuum furnace. If it is carried out in a box furnace, in order to prevent oxidation of the surface of the cavity, the furnace must be filled with a protective atmosphere, or alumina powder, graphite powder, cast iron chips, in the box. Ageing under protective conditions. Packing protection heating should extend the holding time properly, otherwise it will be difficult to achieve the aging effect. Refer to Table 2 for the heat treatment specifications of some age hardening plastic mold steels.

plastic mold

Table 2 Heat treatment specifications for some age hardened steel

Solution treatment process
Aging treatment process
Ageing hardness HRC
800~850°C oil cooling
510 ~ 530 ° C × (6 ~ 8) h
800~850 °C air cooling
510 ~ 530 ° C × (3 ~ 5) h
880 ° C water quenching or air cooling
900 ° C × 2 h oil cooling + 700 ° C × 2 h
510 ° C × 10h
1050 ° C solid solution air cooling

These are plastic mold heat treatment characteristics

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