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What should be done if the mold looks good but is not practical, with insufficient or uneven hardness?

发布时间：

2025-05-02

LITAI Technology News: The hardness of mold heat treatment is a very important mechanical performance index. Unqualified hardness is a very serious defect. After mold heat treatment, insufficient hardness or uneven hardness will reduce the wear resistance and fatigue strength of the mold and other properties, causing the mold to fail prematurely and seriously reducing the service life of the mold.

1. Causes of occurrence
(1) The cross-section of the mold is large and the steel has poor hardenability. For instance, if a large mold selects a steel type with low hardenability.
(2) The original microstructure of the die steel has severe carbide segregation or coarse structure, and there are graphite carbon and carbide segregation and aggregation in the steel.
(3) The forging process of the mold was incorrect, and no proper spheroidizing annealing was carried out after forging, resulting in poor spheroidizing structure of the mold steel.
(4) The decarburization layer formed during annealing or quenching heating was not completely removed from the surface of the mold.
(5) The quenching temperature of the mold is too high, resulting in excessive residual austenite after quenching; or the quenching temperature is too low and the heating holding time is insufficient, causing incomplete phase transformation of the mold steel.
(6) The cooling rate after quenching heating of the mold is too slow, the temperature and time of step quenching and isothermal quenching are too high or too long, and the quenching cooling medium is improperly selected.
(7) Insufficient water content in the alkaline bath, or excessive impurities in the quenching cooling medium, or aging of the quenching cooling medium.
(8) When the mold is taken out of the quenching cooling medium after quenching, its temperature is too high and the cooling is insufficient.
(9) Insufficient tempering and excessively high tempering temperature, etc.
2. Countermeasures
(1) The correct selection of mold steel grades is crucial. For large molds, high-alloy mold steels with high hardenability should be chosen.
(2) Strengthen the inspection of raw materials to ensure they meet the standards. For the substandard raw material steel, carry out reasonable forging and spheroidizing annealing treatment to ensure a good microstructure. Carbon tool steel should not be annealed repeatedly to prevent graphitization.
(3) Strictly implement the forging process and spheroidizing annealing process to ensure a good microstructure after preliminary heat treatment.
Before heat treatment, rust spots and oxide scale on the surface of the mold should be thoroughly removed. Attention should be paid to protection during heating. Vacuum heating quenching or protective atmosphere heating quenching should be adopted as much as possible. When salt bath heating is used, good deoxidation treatment should be carried out.
(5) Correctly formulate the quenching heating process parameters for the mold to ensure complete phase transformation, and cool it at a cooling rate greater than the critical cooling rate for rapid cooling to obtain a qualified metallographic structure.
(6) Correctly select the quenching cooling medium and cooling method, and strictly control the classificationand isothermal temperature and time.

Note： The term "classification" seems to be a technical term and might be a typo or a specific term in the context. If
(7) The moisture content in the alkaline bath must be strictly controlled. For the quenching cooling medium that has been in use for a long time, regular filtration and periodic replacement should be carried out, and it should be kept clean. The quenching cooling characteristic curve should be regularly tested.
For large-sized molds, appropriately extend the time of immersion in the quenching cooling medium to prevent the mold's temperature from being too high when it comes out of the quenching cooling medium.
After quenching, the mold should be tempered in a timely and sufficient manner, and the tempering temperature should be prevented from being too high.
For molds with high hardness requirements, deep cryogenic treatment (such as -110 to -196℃) can be adopted.
(11) Perform surface strengthening treatment.
Having been deeply involved in the industry for many years, LITAI is well aware that improving the utilization rate of materials is an urgent need for all forging factories. In 2022, LITAI launched four brand-new business service scopes, among which the research and development of new environmentally friendly materials is included, aiming to help enterprises solve problems such as mold material selection and hardness. LITAI strictly controls the mold material selection for forging enterprises from the very beginning and adheres to the concept of green and sustainable development. It innovates green and environmentally friendly mold release agents, optimizes the environment of each forging workshop, ensures the physical and mental health of workers, and makes due contributions to improving the production efficiency and high-efficiency expansion of forging enterprises!