Residual Retained Austenite Reduction
A targeted sub-zero cooling step after quenching to completely transform remaining unstable retained austenite into martensite. This prevents undesirable dimensional changes during subsequent service.
After quenching, retained austenite remains in the microstructure. It is transformed into martensite during retained austenite transformation by controlled cooling. If you leave the retained austenite in, the part can later undergo dimensional changes and develop internal stresses, which can lead to cracks. The part will also become harder and more brittle than you want. So cool the workpiece quickly and in a controlled manner after quenching, then the transformation sets in cleanly. How deep and how fast you need to cool depends on the material – you have to follow the data sheet.