Meaning
Thermal conditioning processes that subject metallic components to temperatures below minus one hundred and fifty degrees Celsius are used to optimize the microstructure of high-performance tool steels. Cryogenic treatment involves cooling the steel slowly to transform the soft, unstable phase known as retained austenite into the harder, more stable phase called martensite. This deep-freezing process is inserted between the conventional quenching and tempering cycles.
It is not effective on metals that do not undergo a phase transformation during heating and cooling.
Phase Transformation
The low temperature forces the crystal lattice of the steel to undergo a complete structural reorganization. Executing cryogenic treatment ensures that virtually all remaining austenite is converted into martensite, which increases the uniform hardness of the tool steel.
Stress Relief
Slow cooling and warming rates prevent the generation of new thermal gradients within the metal. Performing cryogenic treatment reduces internal residual stresses that arise from the initial quenching process, preventing dimensional distortion during subsequent machining or grinding operations.
Wear Resistance
The precipitation of fine eta-carbides during the deep-freeze cycle enhances the abrasive wear resistance of the tooling. Tooling subjected to cryogenic treatment maintains its sharp cutting edges for a significantly longer duration, which reduces the frequency of sharpening and production downtime.
