Cryogenic processing, the deep chilling of tool steel so that the molecular makeup of the metal is brought to cryogenic stillness in order to improve wear characteristics, is not a new technology. In the past, tool makers would bury components in snow banks for weeks or even months to improve their wear resistance. Castings were always left outside in the cold for months or years to age and stabilise.
Today’s dry process is computer controlled, using a prescribed schedule and maintained at -150°C for a particular time before slowly returning the parts to room temperature. Prior to the deep cryogenic step, many tool steels require a preconditioning step consisting of a short temper. After being subjected to the deep freeze, the materials must be tempered to about +150°C. This temperature varies for different materials, and the processing time varies for different material cross sections.
Cryo processing improves performance and increases the life of metalcutting tools, blades, punches, dies, slitters, shears and knives, and increases abrasive wear resistance, raises the tensile strength and decreases brittleness with only one permanent treatment. It creates a denser molecular structure and closes the grains structure, resulting in a larger contact surface area that reduces friction, heat and wear. Cryogenic treatment changes the entire structure, not just the surface. Subsequent refinishing or regrinding operations do not affect the permanent improvements of the processing.
When the cryo treated tool does wear, the degree of wear reportedly is less severe, slower and more uniform. Therefore, less material must be removed to re-sharpen it. Customers have reported a material removal rate of less than half the normal material removed in re-sharpening. Cryo treating reduces the cost of the product by having longer tool life, less scrap, fewer rejections and above all, less costly downtime. Gains between 50% and 500% may occur, depending on the component structure and previous heat-treating. Every application is unique and the benefits for each one is application specific. There is no blanket prediction that can be made or previous results used to guarantee the same results for every operation. Each one has to be tested.
Cryogenics is not a substitute for heat treating. Instead, it simply adds the finishing touch to the heat treating process. It completes the austenite-to-martensite conversion in tool steel.
Another benefit of cryo treating is its ability to make the grain structure more uniform, which ultimately improves dissipation of heat beneficial to the racing industry.
