Deep-freezing of knife steel

Deep-freezing is used if cooling to room temperature does not produce sufficient hardness, and involves cooling down the knife blades to a temperature in the range -20°C to -150°C (-4 to -238°F) before they are tempered. In this guide Sandvik provides hardening programs with -20°C (-4°F) or -70°C (-94°F), respectively.

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The simplest way of deep-freezing the knife blades is to place them in a freezer or immerse them in dry ice. The knife blade is then left to 'thaw' to room temperature, and is then tempered in the usual way.

Deep-freezing increases the hardness by 1–3 HRC, but reduces the toughness slightly. For most applications, hardness between 57 and 58 HRC provides a good balance between edge stability, toughness and grindability.

Effect of deep-freezing on Sandvik 12C27, in which the hardness increases by about 2 HRC.