Deep cryogenic treatment of hard alloy with liquid nitrogen

Deep cryogenic treatment of hard alloy with liquid nitrogen

Process Introduction:

After heat treatment and quenching, stay at room temperature: After quenching, it is necessary to uniformly cool the inside and outside of the ring to room temperature before cold treatment, otherwise it is easy to crack. After cooling to room temperature, immediately cold treat (generally not more than 30 minutes), otherwise the transformation from austenite to martensite will be stopped.

Temperature of liquid nitrogen cryogenic chamber: The temperature for cold treatment is mainly based on the martensitic transformation termination temperature Mf of the steel, and the influence of cold treatment on mechanical properties and processability factors should also be considered. For GCr15 steel, -70 ℃ is selected for cold treatment; When there are limitations on the precision requirements of the ring or equipment, the cold treatment temperature can be selected as -40 to -70 ℃; Ultra precision bearings can undergo cold treatment between -70 ℃ and -80 ℃. The supercooling temperature affects the impact fatigue and contact life of bearings.

Liquid nitrogen cryogenic chamber: Although the transformation of a large amount of martensite is completed between cooling to a certain temperature and tilting, a certain insulation time is required to ensure that the surface and core of a batch of rings reach the cold treatment temperature uniformly, usually 1-1.5 hours.

Tempering after liquid nitrogen cryogenic treatment: After the ring is cold treated, it is placed in air and the temperature slowly rises to room temperature before tempering is carried out in a timely manner. The temperature rise should not be too fast, otherwise it is easy to crack; Timely tempering, otherwise the large residual stress inside the ring will cause cracking, generally not exceeding 2 hours.

-Function:

Improve the hardness and strength of the workpiece

Ensure the dimensional accuracy of the workpiece

Improve the wear resistance of workpieces

Improve the impact toughness of workpieces

Improve the distribution of internal stress in workpieces and enhance fatigue strength

Improve the corrosion resistance of workpieces

Liquid Nitrogen Cryogenic Box - Industry Applications

During the cryogenic treatment process, a large amount of residual austenite transforms into martensite, especially supersaturated metastable martensite, which reduces supersaturation and precipitates ultrafine carbides with a size of only 20-60A and maintains a coherent relationship with the matrix during the process from -196 ℃ to room temperature. This can reduce lattice distortion and micro stress in martensite, while fine dispersed carbides can hinder dislocation movement during material plastic deformation, thereby strengthening the matrix structure. At the same time, due to the precipitation of ultrafine carbide particles evenly distributed on the martensitic matrix, the catalytic effect of grain boundaries is weakened. The refinement of the matrix structure not only reduces the degree of impurity element segregation at grain boundaries, but also plays a role in grain boundary strengthening, thereby improving the performance of high-speed steel, significantly increasing hardness, impact toughness, and wear resistance. If the hardness of the mold is high, its wear resistance is also good. For example, increasing the hardness from 60HRC to 62-63HRC increases the wear resistance of the mold by 30% -40%.

It can be seen that the relative wear resistance of the mold increases by 40% after cryogenic treatment. After extending the cryogenic treatment time, the relative wear resistance increases without much change in hardness.

Give an example to illustrate:

(1) Convex mold: High speed steel convex molds from automobile factories can only be used 100000 times without deep cooling treatment. However, by using liquid nitrogen for deep cooling treatment at -196 ℃ for 4 hours and then tempering at 400 ℃, the service life is increased to 1.3 million times.

(2) Stamping die: The production and use results show that the output is more than doubled after cryogenic treatment.

(3) Silicon steel sheet cold stamping die: In order to reduce the brittleness and internal stress of the mold after deep cold treatment, deep cold treatment is combined with medium temperature tempering to improve the mold's resistance to damage and other comprehensive properties. The grinding life of the mold is increased by more than three times and stabilized at 50000 to 70000 strokes.

Precision measuring tools that have undergone cryogenic or ultra cryogenic treatment have significantly improved dimensional stability and wear resistance.