Meaning
Thermal process used to convert residual high temperature phases into harder martensite in tool steels. Effective retained austenite cryogenic treatment involves cooling the metal to temperatures below negative 150 degrees Celsius after the initial quenching. This transition increases the dimensional stability and wear resistance of the die.
It is effective for steels used in high precision stamping.
Phasal Transformation
Standard quenching often leaves a small percentage of austenite trapped in the microstructure. Retained austenite cryogenic treatment provides the energy necessary to complete the shift to a more stable form. The new martensite is harder and requires a subsequent tempering stage to manage brittleness.
Dimensional Stability
Unconverted phases can transform slowly over time during use, causing the tool to warp. By using retained austenite cryogenic treatment the manufacturer ensures the die maintains its exact shape through millions of cycles. Precision is necessary for the tight tolerances of 21700 and 4680 battery cans.
Wear Improvement
Harder surfaces resist the abrasive action of the workpiece and the lubricant. Increased hardness resulting from retained austenite cryogenic treatment extends the life of the tool. Fine carbides also precipitate during the process, further enhancing the resistance to surface degradation.
This leads to fewer tool changes and more consistent part quality over long production runs. Liquid nitrogen is the most common medium for reaching the required temperatures. Slow cooling and warming rates prevent the formation of thermal shock cracks in the tool steel.
The entire cycle takes several hours to ensure the core of the metal reaches the target temperature.
