Tempering

The continuous process of tempering blade strips

The tempering of blade strips consists of hardening and subsequent one-time tempering. The crystal lattice structure of the blade band is transformed.

In the following, this will be explained briefly and in a very simplified way using the example of martensitic stainless steel.

• Hardening
  Heating and holding for austenitizing the blade strip at approx. 1,100 °C in the hardening furnace. Conversion of ferrite into austenite; contained carbides are partially dissolved, thereby increasing the content of carbon and chromium in the matrix.
  Subsequent quenching to room temperature in the cooling section. Conversion of most of the austenite into martensite.
• Deep-freezing
  of the blade strip in deep-freezing to approx. -80 °C. Further, permanent transformation of austenite into martensite. Depending on the freezing temperature, approx. 15% residual austenite remains in the microstructure.
• Tempering
  at approx. 200 °C without holding time in the tempering furnace. Reduction of brittleness and increase of toughness; achievement of additional hardness. Subsequent cooling to room temperature in the cooling unit.

The continuous process of tempering bimetal saw bands

Bimetal saw bands are composed of two different materials: The carrier band and the tooth cutting edges. While the carrier band should have a high flexibility, the tooth cutting edges must be hard and wear-resistant.

When tempering saw bands, these different properties are achieved by the following process steps:

• Hardening:
  Heating and holding the saw band to hardening temperature in the hardening furnace and subsequent quenching in the cooling section
• Tempering:  
  Multiple heating and holding to tempering temperature in the tempering furnace and subsequent cooling in cooling sections