Hardness is a very important indicator for mold use, which directly affects the wear resistance and fatigue strength of the mold.

After heat treatment of the mold, often encounter low hardness, uneven hardness and other problems, briefly analyze the causes and develop appropriate measures.

1. Reason.

(1) mold cross-section is large, the steel hardenability is poor, for example, large mold selection of low hardenability steel.

(2) The original organization of the die steel carbide elimination is serious or rough organization, and there are serious non-metallic inclusions in the steel.

(3) The forging process in the die is incorrect, and the spheroidization annealing treatment after forging is improper, resulting in poor spheroidization organization of the die steel.

(4) The decarburized layer formed during the annealing or hardening heating process is not removed from the mold surface.

(5) mold quenching temperature is too high, the amount of residual austenite after quenching is too much; or quenching temperature is too low, the heating and holding time is not enough, so that the phase change of mold steel is not complete.

(6) After the mold tempering and heating, the cooling speed is too slow, the indexing and isothermal temperature is too high, or the time is too long, and the cooling medium is not selected correctly.

(7) too many impurities in the quenching fluid or quenching fluid aging.

(8) Insufficient cooling after mold hardening.

(9) Insufficient release, untimely release, and incorrect release temperature.

2. Appropriate measures.

(1) Correctly choose the type of mold steel, for large molds, high alloy mold steel with high hardenability should be used, you can consult the technical department of Jinhua State.

(2) Strengthen the inspection of raw materials before use to ensure that the raw materials meet the standards. Reasonable forging and spheroidizing annealing of steel with poor raw materials to ensure good organization.

(3) Strictly observe the forging process and spheroidizing and annealing process to ensure that the preparatory heat treatment is well organized.

(4) heat treatment before the surface of the mold should be thoroughly removed from the rust and oxide spots, heating attention to protection, plating solution should be quenched by vacuum heating or protective atmosphere heating quenching.

(5) The correct development of mold quenching heating process parameters to ensure adequate phase change, to obtain the appropriate metallurgical organization.

(6) the correct choice of quenching cooling medium and cooling mode, strict control of indexing, isothermal temperature and time.

(7) long-term use of quenching and cooling media should be regularly filtered and replaced to keep clean, and regularly check its quenching and cooling performance.

(8) For large size molds, appropriately increase the immersion time in the quenching solution to prevent the quenching solution temperature from being too high.

(9) After the mold hardening, it should be thoroughly tempered in time, and the tempering temperature should not be too high.

(10) The mold with high hardness requirements can be deep-cooled (such as -110 ~ -196℃).

(11) Surface strengthening treatment is performed.